A multilocus evaluation of ermine (Mustela erminea) across the Holarctic, testing hypotheses of Pleistocene diversification in response to climate change

USGS Publications Warehouse

Dawson, Natalie G.; Hope, Andrew G.; Talbot, Sandra L.; Cook, Joseph A.

2013-01-01

Aim: We examined data for ermine (Mustela erminea) to test two sets of diversification hypotheses concerning the number and location of late Pleistocene refugia, the timing and mode of diversification, and the evolutionary influence of insularization. Location: Temperate and sub-Arctic Northern Hemisphere. Methods: We used up to two mitochondrial and four nuclear loci from 237 specimens for statistical phylogeographical and demographic analyses. Coalescent species-tree estimation used a Bayesian approach for clade divergence based on external mutation rate calibrations. Approximate Bayesian methods were used to assess population size, timing of divergence and gene flow. Results: Limited structure coupled with evidence of population growth across broad regions, including previously ice-covered areas, indicated expansion from multiple centres of differentiation, but high endemism along the North Pacific coast (NPC). A bifurcating model of diversification with recent growth spanning three glacial cycles best explained the empirical data. Main conclusions: A newly identified clade in North America indicated a fourth refugial area for ermine. The shallow coalescence of all extant ermine reflects a recent history of diversification overlying a deeper fossil record. Post-glacial colonization has led to potential contact zones for multiple lineages in north-western North America. A model of diversification of ermine accompanied by recent gene flow was marginally less well supported than a model of divergence of major clades in response to the most recent glacial cycles.

Somma-Vesuvius ground deformation over the last glacial cycle

NASA Astrophysics Data System (ADS)

Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

2013-04-01

Vertical ground movements at Somma-Vesuvius during the last glacial cycle have been inferred from micropalaeontological and petrochemical analyses of rock samples from boreholes drilled at the archaeological sites of Herculaneum and Pompeii as well as on the apron of the volcano and the adjacent Sebeto and Sarno Valleys. Opposing movements occurred during the periods preceding and following the Last Glacial Maximum (LGM). The uplift began 20 ka ago with marine deposits rising several tens of metres up to 25 m a.s.l., recovering previous subsidence which occurred during the Late glacial period, suggesting a strict connection between volcano-tectonic and glacial cycles. Here we present the analysis of deposits predating the LGM, which confirms subsidence of the Campanian Plain where Mt. Somma-Vesuvius is located, shows variable surface loading effects and highlights the volcano-tectonic stages experienced by the volcano. The self-balancing mechanism of the volcanic system, evolving towards an explosive, subaerial activity 60 ka ago, is testified to by a large ground oscillation in phase with sea level change during the last glacial cycle.

Strong and deep Atlantic meridional overturning circulation during the last glacial cycle.

PubMed

Böhm, E; Lippold, J; Gutjahr, M; Frank, M; Blaser, P; Antz, B; Fohlmeister, J; Frank, N; Andersen, M B; Deininger, M

2015-01-01

Extreme, abrupt Northern Hemisphere climate oscillations during the last glacial cycle (140,000 years ago to present) were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic meridional overturning circulation (AMOC), which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage, is still poorly constrained beyond the Last Glacial Maximum. Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima. Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic. Parallel measurements of two independent chemical water tracers (the isotope ratios of (231)Pa/(230)Th and (143)Nd/(144)Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard-Oeschger interstadials (Greenland warm periods).

Climatic and topographic controls on the style and timing of Late Quaternary glaciation throughout Tibet and the Himalaya defined by 10Be cosmogenic radionuclide surface exposure dating

USGS Publications Warehouse

Owen, L.A.; Finkel, R.C.; Barnard, P.L.; Haizhou, Ma; Asahi, K.; Caffee, M.W.; Derbyshire, E.

2005-01-01

Temporal and spatial changes in glacier cover throughout the Late Quaternary in Tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region, and the lack of numerical dating. To help reconstruct the timing and extent of glaciation throughout Tibet and the bordering mountains, we use geomorphic mapping and 10Be cosmogenic radionuclide (CRN) surface dating in study areas in southeastern (Gonga Shan), southern (Karola Pass) and central (Western Nyainqentanggulha Shan and Tanggula Shan) Tibet, and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands. Each of the study regions receives its precipitation mainly during the south Asian summer monsoon when it falls as snow at high altitudes. Gonga Shan receives the most precipitation (>2000 mm a-1) while, near the margins of monsoon influence, the Karola Pass receives moderate amounts of precipitation (500-600 mm a-1) and, in the interior of the plateau, little precipitation falls on the western Nyainqentanggulha Shan (???300 mm a -1) and the Tanggula Shan (400-700 mm a-1). The higher precipitation values for the Tanggula Shan are due to strong orographic effects. In each region, at least three sets of moraines and associated landforms are preserved, providing evidence for multiple glaciations. The 10Be CRN surface exposure dating shows that the formation of moraines in Gonga Shan occurred during the early-mid Holocene, Neoglacial and Little Ice Age, on the Karola Pass during the Lateglacial, Early Holocene and Neoglacial, in the Nyainqentanggulha Shan date during the early part of the last glacial cycle, global Last Glacial Maximum and Lateglacial, and on the Tanggula Shan during the penultimate glacial cycle and the early part of the last glacial cycle. The oldest moraine succession in each of these regions varies from the early Holocene (Gonga Shan), Lateglacial (Karola Pass), early Last Glacial (western Nyainqentanggulha Shan), and penultimate glacial cycle (Tanggula Shan). We believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south Asian monsoon and, in particular, in regional precipitation gradients. In zones of greater aridity, the extent of glaciation has become increasingly restricted throughout the Late Quaternary leading to the preservation of old (???100 ka) glacial landforms. In contrast, in regions that are very strongly influenced by the monsoon (???1600 mm a-1), the preservation potential of pre-Lateglacial moraine successions is generally extremely poor. This is possibly because Lateglacial and Holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations. Furthermore, the intense denudation, mainly by fluvial and mass movement processes, which characterize these wetter environments, results in rapid erosion and re-sedimentation of glacial and associated landforms, which also contributes to their poor preservation potential. ?? 2004 Elsevier Ltd. All rights reserved.

Phylogeography and postglacial recolonization of Europe by Rhinolophus hipposideros: evidence from multiple genetic markers.

PubMed

Dool, Serena E; Puechmaille, Sébastien J; Dietz, Christian; Juste, Javier; Ibáñez, Carlos; Hulva, Pavel; Roué, Stéphane G; Petit, Eric J; Jones, Gareth; Russo, Danilo; Toffoli, Roberto; Viglino, Andrea; Martinoli, Adriano; Rossiter, Stephen J; Teeling, Emma C

2013-08-01

The demographic history of Rhinolophus hipposideros (lesser horseshoe bat) was reconstructed across its European, North African and Middle-Eastern distribution prior to, during and following the most recent glaciations by generating and analysing a multimarker data set. This data set consisted of an X-linked nuclear intron (Bgn; 543 bp), mitochondrial DNA (cytb-tRNA-control region; 1630 bp) and eight variable microsatellite loci for up to 373 individuals from 86 localities. Using this data set of diverse markers, it was possible to determine the species' demography at three temporal stages. Nuclear intron data revealed early colonization into Europe from the east, which pre-dates the Quaternary glaciations. The mtDNA data supported multiple glacial refugia across the Mediterranean, the largest of which were found in the Ibero-Maghreb region and an eastern location (Anatolia/Middle East)-that were used by R. hipposideros during the most recent glacial cycles. Finally, microsatellites provided the most recent information on these species' movements since the Last Glacial Maximum and suggested that lineages that had diverged into glacial refugia, such as in the Ibero-Maghreb region, have remained isolated. These findings should be used to inform future conservation management strategies for R. hipposideros and show the power of using a multimarker data set for phylogeographic studies. © 2013 John Wiley & Sons Ltd.

Holocene glacial fluctuations in southern South America

NASA Astrophysics Data System (ADS)

Reynhout, S.; Sagredo, E. A.; Kaplan, M. R.; Aravena, J. C.; Martini, M. A.; Strelin, J. A.; Schaefer, J. M.

2016-12-01

Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

Friis Hills glacial history: an international collaboration to examine Miocene climate in Antarctica

NASA Astrophysics Data System (ADS)

Halberstadt, A. R. W.; Kowalewski, D. E.

2016-12-01

The Friis Hills, Antarctica (western McMurdo Dry Valleys) contain unique, well-preserved records of Miocene climate. These terrestrial deposits hold geomorphic clues for deciphering the glacial history in a region directly adjacent to the East Antarctic Ice Sheet. Stacked till sheets, interbedded with lake sediments and non-glacial deposits, reveal a complex history of ice flow and erosion throughout multiple glacial-interglacial cycles (Lewis and Ashworth, 2015). Fossiliferous beds containing Nothofagus, diatoms, algal cells, pollen, insects, and mosses provide past climatological constraints. The Friis Hills sustained multiple alpine glaciations as well as full ice-sheet development, recording glacial drainage reorganization and evidence of previous ice configurations that possibly overrode the Transantarctic Mountains (Lewis and Ashworth, 2015) exposing only scattered nunataks (i.e. a portion of Friis Hills). Lack of chronological control has previously hindered efforts to link the Friis Hills glacial history with regional context; a tephra deposit at the base of the glacial drifts currently provides a single age constraint within the drift deposits. To build upon previous studies, an international collaboration between the USAP, Antarctic New Zealand, and the Italian Antarctic community proposes to core a paleo-lake in the center of the Friis Hills in November 2016, thereby acquiring one of the oldest continuous sedimentological records within the McMurdo Dry Valleys. Here we report discoveries from this year's fieldwork, and reconstruct paleoenvironment at the periphery of the East Antarctic Ice Sheet for the mid-early Miocene, a critical time when marine isotopic records indicate dramatic ice fluctuations. Ash within the sediment core stratigraphy will provide a more robust chronology for the region, and will also suggest possible outcrop locations of corresponding ash deposits to pursue while in the field. We anticipate that the Friis Hills stratigraphy will have the necessary chronological control for correlation with offshore marine records from the Ross Embayment, including the ANDRILL project.

The glacial iron cycle from source to export

NASA Astrophysics Data System (ADS)

Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A. J.; Nienow, P. W.; Telling, J.; Bagshaw, E.; Simmons, S. L.

2014-12-01

Nutrient availability limits primary production in large sectors of the world's oceans. Iron is the major limiting nutrient in around one third of the oceanic euphotic zone, most significantly in the Southern Ocean proximal to Antarctica. In these areas the availability of bioavailable iron can influence the amount of primary production, and thus the strength of the biological pump and associated carbon drawdown from the atmosphere. Despite experiencing widespread iron limitation, the Polar oceans are among the most productive on Earth. Due to the extreme cold, remoteness and their perceived "stasis", ice sheets have previously been though of as insignificant in global biogeochemical cycles. However, large marine algal blooms have been observed in iron-limited areas where glacial influence is large, and it is possible that these areas are stimulated by glacial bioavailable iron input. Here we discuss the importance of the Greenland and Antarctic ice sheets in the global iron cycle. Using field collected trace element data, bulk meltwater chemistry and mineralogical analysis, including photomicrographs, EELS and XANES, we present, for the first time, a conceptual model of the glacial iron cycle from source to export. Using this data we discuss the sources of iron in glacial meltwater, transportation and alteration through the glacial system, and subsequent export to downstream environments. Data collected in 2012 and 2013 from two different Greenlandic glacial catchments are shown, with the most detailed breakdown of iron speciation and concentrations in glacial areas yet reported. Furthermore, the first data from Greenlandic icebergs is presented, allowing meltwater-derived and iceberg-derived iron export to be compared, and the influence of both in marine productivity to be estimated. Using our conceptual model and flux estimates from our dataset, glacial iron delivery in both the northern and southern hemisphere is discussed. Finally, we compare our flux estimates to other major iron sources to the polar regions such as aeolian dust, and discuss potential implications of increased melting of the ice sheets on the global iron cycle in the future.

Hydrothermal deposition on the Juan de Fuca Ridge over multiple glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Costa, Kassandra M.; McManus, Jerry F.; Middleton, Jennifer L.; Langmuir, Charles H.; Huybers, Peter J.; Winckler, Gisela; Mukhopadhyay, Sujoy

2017-12-01

Hydrothermal systems play an important role in modern marine chemistry, but little is known about how they may have varied on 100,000 year timescales. Here we present high-resolution records of non-lithogenic metal fluxes within sediment cores covering the last 500,000 years of hydrothermal deposition on the flanks of the Juan de Fuca Ridge. Six adjacent, gridded cores were analyzed by x-ray fluorescence for Fe, Mn, and Cu concentrations, corrected for lithogenic inputs with Ti, and normalized to excess initial 230Th to generate non-lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available. Fe fluxes vary with global sea level over the last two glacial cycles, suggesting higher hydrothermal deposition during interglacial periods. The observed negative relationship between Fe and Mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary Mn over time. Thus, Mn fluxes may not be a reliable indicator for hydrothermal activity in the Juan de Fuca Ridge sediment cores. Cu fluxes show substantial high-frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods. Deglacial hydrothermal peaks on the Juan de Fuca Ridge are consistent with previously published records from the Mid-Atlantic Ridge and the East Pacific Rise. Moreover, on the Juan de Fuca Ridge, the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period.

The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination

NASA Astrophysics Data System (ADS)

Schaefer, Joerg M.; Putnam, Aaron E.; Denton, George H.; Kaplan, Michael R.; Birkel, Sean; Doughty, Alice M.; Kelley, Sam; Barrell, David J. A.; Finkel, Robert C.; Winckler, Gisela; Anderson, Robert F.; Ninneman, Ulysses S.; Barker, Stephen; Schwartz, Roseanne; Andersen, Bjorn G.; Schluechter, Christian

2015-04-01

Glacial maxima and their terminations provide key insights into inter-hemispheric climate dynamics and the coupling of atmosphere, surface and deep ocean, hydrology, and cryosphere, which is fundamental for evaluating the robustness of earth's climate in view of ongoing climate change. The Last Glacial Maximum (LGM, ∼26-19 ka ago) is widely seen as the global cold peak during the last glacial cycle, and its transition to the Holocene interglacial, dubbed 'Termination 1 (T1)', as the most dramatic climate reorganization during this interval. Climate records show that over the last 800 ka, ice ages peaked and terminated on average every 100 ka ('100 ka world'). However, the mechanisms pacing glacial-interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood. Here we show evidence for a full glacial maximum in the Southern Hemisphere 65.1 ± 2.7 ka ago and its 'Unfinished Termination'. Our 10Be chronology combined with a model simulation demonstrates that New Zealand's glaciers reached their maximum position of the last glacial cycle during Marine Isotope Stage-4 (MIS-4). Southern ocean and greenhouse gas records indicate coeval peak glacial conditions, making the case for the Southern Glacial Maximum about halfway through the last glacial cycle and only 15 ka after the last warm period (MIS-5a). We present the hypothesis that subsequently, driven by boreal summer insolation forcing, a termination began but remained unfinished, possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the North Atlantic through Heinrich Stadial 6 to drive a full termination. Yet the Unfinished Termination left behind substantial ice on the northern continents (about 50% of the full LGM ice volume) and after another 45 ka of cooling and ice sheet growth the earth was at inter-hemispheric Last Glacial Maximum configuration, when similar orbital forcing hit maximum-size northern ice sheets and ushered in T1 and thus the ongoing interglacial. This argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the Southern Hemisphere climate could transition from interglacial to full glacial conditions in about 15,000 years, while the Northern Hemisphere and its continental ice-sheets required half a glacial cycle.

Simulation of climate, ice sheets and CO2 evolution during the last four glacial cycles with an Earth system model of intermediate complexity

NASA Astrophysics Data System (ADS)

Ganopolski, Andrey; Brovkin, Victor

2017-11-01

In spite of significant progress in paleoclimate reconstructions and modelling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial-interglacial cycles are still not fully understood - in particular, in relation to CO2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of the co-evolution of climate, ice sheets, and carbon cycle over the last 400 000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO2, global ice volume, and other climate system characteristics in good agreement with paleoclimate reconstructions. These results provide strong support for the idea that long and strongly asymmetric glacial cycles of the late Quaternary represent a direct but strongly nonlinear response of the Northern Hemisphere ice sheets to orbital forcing. This response is strongly amplified and globalised by the carbon cycle feedbacks. Using simulations performed with the model in different configurations, we also analyse the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO2 evolution, especially during glacial terminations, are sensitive to the choice of model parameters. Specifically, we found two major regimes of CO2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO2 concentration occurs at the beginning of the interglacial and CO2 remains almost constant during the interglacial or even declines towards the end, resembling Eemian CO2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO2 concentration continues to rise during the interglacial, similar to the Holocene. We also discuss the potential contribution of the brine rejection mechanism for the CO2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.

Denudation of the continental shelf between Britain and France at the glacial-interglacial timescale.

PubMed

Mellett, Claire L; Hodgson, David M; Plater, Andrew J; Mauz, Barbara; Selby, Ian; Lang, Andreas

2013-12-01

The erosional morphology preserved at the sea bed in the eastern English Channel dominantly records denudation of the continental shelf by fluvial processes over multiple glacial-interglacial sea-level cycles rather than by catastrophic flooding through the Straits of Dover during the mid-Quaternary. Here, through the integration of multibeam bathymetry and shallow sub-bottom 2D seismic reflection profiles calibrated with vibrocore records, the first stratigraphic model of erosion and deposition on the eastern English Channel continental shelf is presented. Published Optical Stimulated Luminescence (OSL) and 14 C ages were used to chronometrically constrain the stratigraphy and allow correlation of the continental shelf record with major climatic/sea-level periods. Five major erosion surfaces overlain by discrete sediment packages have been identified. The continental shelf in the eastern English Channel preserves a record of processes operating from Marine Isotope Stage (MIS) 6 to MIS 1. Planar and channelised erosion surfaces were formed by fluvial incision during lowstands or relative sea-level fall. The depth and lateral extent of incision was partly conditioned by underlying geology (rock type and tectonic structure), climatic conditions and changes in water and sediment discharge coupled to ice sheet dynamics and the drainage configuration of major rivers in Northwest Europe. Evidence for major erosion during or prior to MIS 6 is preserved. Fluvial sediments of MIS 2 age were identified within the Northern Palaeovalley, providing insights into the scale of erosion by normal fluvial regimes. Seismic and sedimentary facies indicate that deposition predominantly occurred during transgression when accommodation was created in palaeovalleys to allow discrete sediment bodies to form. Sediment reworking over multiple sea-level cycles (Saalian-Eemian-early Weichselian) by fluvial, coastal and marine processes created a multi-lateral, multi-storey succession of palaeovalley-fills that are preserved as a strath terrace. The data presented here reveal a composite erosional and depositional record that has undergone a high degree of reworking over multiple sea-level cycles leading to the preferential preservation of sediments associated with the most recent glacial-interglacial period.

Peatlands through the Last Glacial Cycle: Evidence and Model Results

NASA Astrophysics Data System (ADS)

Kleinen, T.; Treat, C. C.; Brovkin, V.

2017-12-01

The spatiotemporal distribution of peatlands prior to the last glacial maxium (LGM) is largely unknown. However, some evidence of non-extant peatlands is available in the form of buried organic-rich sediments. We have undertaken a synthesis of these "buried" peatlands from > 1000 detailed stratigraphic descriptions and combined it with data on extant peatlands to derive a first global synthesis of global peatland extent through the last glacial cycle. We present results of this synthesis in combination with modeling results where we determined peatland extents and carbon stocks from a transient simulation of the last glacial cycle with the CLIMBER2-LPJ model. We show that peat has existed in boreal latitudes at all times since the last interglacial, that evidence for tropical peatlands exists for the last 50,000 yrs, and that the model results in general agree well with the collected evidence of past peatlands, allowing a first estimate of peat carbon stock changes through the last glacial cycle. We discuss data and model limitations, with a focus on requirements for improving model-based peatland estimates.

Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume.

PubMed

Abe-Ouchi, Ayako; Saito, Fuyuki; Kawamura, Kenji; Raymo, Maureen E; Okuno, Jun'ichi; Takahashi, Kunio; Blatter, Heinz

2013-08-08

The growth and reduction of Northern Hemisphere ice sheets over the past million years is dominated by an approximately 100,000-year periodicity and a sawtooth pattern (gradual growth and fast termination). Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles, and statistical tests have demonstrated that the glacial cycles are indeed linked to eccentricity, obliquity and precession cycles. Yet insolation alone cannot explain the strong 100,000-year cycle, suggesting that internal climatic feedbacks may also be at work. Earlier conceptual models, for example, showed that glacial terminations are associated with the build-up of Northern Hemisphere 'excess ice', but the physical mechanisms underpinning the 100,000-year cycle remain unclear. Here we show, using comprehensive climate and ice-sheet models, that insolation and internal feedbacks between the climate, the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity. The responses of equilibrium states of ice sheets to summer insolation show hysteresis, with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet, its mass balance remains mostly positive through several precession cycles, whose amplitudes decrease towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to make the mass balance negative. Therefore, once a large ice sheet is established, a moderate increase in insolation is sufficient to trigger a negative mass balance, leading to an almost complete retreat of the ice sheet within several thousand years. This fast retreat is governed mainly by rapid ablation due to the lowered surface elevation resulting from delayed isostatic rebound, which is the lithosphere-asthenosphere response. Carbon dioxide is involved, but is not determinative, in the evolution of the 100,000-year glacial cycles.

Initial Results from the Deep Drilling of Lake Junin, Perú

NASA Astrophysics Data System (ADS)

Rodbell, D. T.; Abbott, M. B.; Weidhaas, N.; Hatfield, R. G.; Woods, A.; Hillman, A. L.; Tapia, P. M.; Chen, C. Y.; McGee, D.; Stoner, J. S.

2016-12-01

Lake Junín (11.0°S, 76.2°W, 4085 masl) is an intermontane, high-elevation lake in the inner-tropics of the Southern Hemisphere that spans 300 km2. With a maximum water depth of 12m, Lake Junin is dammed at its northern and southern ends by alluvial fans that emanate from glacial valleys in both cordillera. These fans can be traced to moraines that are >250 ka, indicating that the lake is at least this old. During the maximum extent of late Cenozoic glaciation, glaciers reached the lake edge but at no time over the last 1 million years, or more, has Lake Junín been overridden by ice. Lake Junín is thus one of the few lakes in the tropical Andes that predates the maximum extent of glaciation and is in a geomorphic position to record the waxing and waning of alpine glaciers in nearby cordillera. Sediment cores obtained between 1980 and 1996 reveal that sediment deposited during the last glacial cycle ( 30-16 ka) is dominated by glacial flour whereas sediment deposited during the last 16 ka consists predominantly of authigenic calcite (marl) with ostracod carapaces punctuated with intervals of gyttja and peat. In July and August of 2015, piston cores were obtained from three sites in Lake Junin. Multiple overlapping cores from the deepest water site (Site 1) extend to 100 m below lake floor (mblf), and those from two shallow water, paleoglacier-proximal sites (Sites 2 and 3) extend 23 and 51 mblf, respectively. Samples acquired at 8-cm resolution from Site 1 were analyzed for total organic carbon (TOC) and total inorganic carbon [as Ca(Mg)CO3; TIC] by coulometry. Total carbon (TC) was analyzed by combusting 10 mg samples at 1000°C and quantifying the resultant CO2 by coulometry whereas TIC was analyzed by reacting 10 mg samples in 6N H3PO4 and quantifying the resultant CO2 by coulometry; TOC was determined from TOC=TC-TIC. Over the last glacial postglacial cycle (last 30 ka), mean CaCO3 and TOC concentrations in Site 1 cores are higher ( 33% and 7.4%, respectively) than those in shallow water settings ( 9.5% and 4%). Similarly, mean magnetic susceptibility (MS) is lower in Site 1 cores (6.9 SI) than in the most paleoglacier-proximal shallow water site (Site 2, 9.4 SI). Site 1 records 7 glacial and interglacial cycles whereas shallow water locations appear to be dominated by sediment deposited during the last glacial-interglacial cycle.

Insolation-driven 100 kyr glacial cycles and millennial climate change

NASA Astrophysics Data System (ADS)

Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Raymo, M. E.; Okuno, J.; Takahashi, K.; Blatter, H.

2013-12-01

The waxing and waning of Northern Hemisphere ice sheets over the past one million years is dominated by an approximately 100-kyr periodicity and a sawtooth pattern (gradual growth and fast termination). Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles, and statistical tests demonstrated that the glacial cycles are indeed linked to eccentricity, obliquity and precession cycles. However, insolation alone cannot explain the strong 100 kyr cycle which presumably arises through internal climatic feedbacks. Prior work with conceptual models, for example, showed that glacial terminations are associated with the build-up of Northern Hemisphere 'excess ice', but the physical mechanisms of 100-kyr cycle at work remain unclear. Here, using comprehensive climate and ice sheet models, we show that the ~100-kyr periodicity is explained by insolation and internal feedback amongst the climate, ice sheet and lithosphere/asthenosphere system (reference). We found that equilibrium states of ice sheets exhibit hysteresis responses to summer insolation, and that the shape and position of the hysteresis loop play a key role in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that, after its inception, the ice sheet mass balance remains mostly positive or neutral through several precession cycles whose amplitude decreases towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to turn the mass balance to negative. Therefore, once the large ice sheet is established, only a moderate increase in insolation can trigger a negative mass balance, leading to a complete retreat within several thousand years, due to the delayed isostatic rebound. The effect of ocean circulation and millennial scale climate change are not playing the dominant role for determing the 100kyr cycle, but are effective for modifying the speed and geographical pattern of the waxing and waning of the Northern Hemisphere ice sheets and their melt water. (reference of the basic results: Abe-Ouchi et al, 2013, Insolation-driven 100,000 year glacial cycles and hysteresis of ice-sheet volume, Nature, 500, 190-193.)

Ice sheet load cycling and fluid underpressures in the Eastern Michigan Basin, Ontario, Canada

USGS Publications Warehouse

Neuzil, Christopher E.; Provost, Alden M.

2014-01-01

Strong fluid underpressures have been detected in Paleozoic strata in the eastern Michigan Basin, with hydraulic heads reaching ~400 m below land surface (~4 MPa underpressure) and ~200 m below sea level in strata where unusually low permeabilities (~10−20–10−23 m2) were measured in situ. Multiple glaciations, including three with as much as 3 km of ice cover at the site in the last 120 ka, suggest a causal link with the underpressures. We examined this possibility using a one-dimensional groundwater flow model incorporating mechanical loading from both ice weight and lithospheric flexure. Because hydrologic and mechanical changes during glaciation are not well characterized and subsurface properties are imperfectly known, the model was used inversely to estimate flexural loads and loosely constrained permeabilities by matching observed pressures. Acceptable matches were obtained for a surprisingly wide range of scenarios with permeabilities close to measured values and plausible flexural loads. Matches were not obtained when too many parameters were preselected, or when permeabilities were constrained to be significantly larger than measured values. In successful model runs groundwater expulsion under glacial-mechanical loads caused the underpressuring, and flexural loads were important if aquifer and sub-glacial pressures were significantly elevated during glaciation. Simulated fluid pressures in the low-permeability strata fluctuated by 30–40 MPa during glacial cycles but resulted in advective transport of only tens of meters or less. Although other mechanisms cannot be ruled out, we conclude that glacial-mechanical forcing of a water-saturated system can explain the observed underpressures.

Linking glacial melting to Late Quaternary sedimentation in climatically sensitive mountainous catchments of the Mount Chlemos compex, Kalavryta, southern Greece

NASA Astrophysics Data System (ADS)

Pope, Richard; Hughes, Philip

2014-05-01

Compared to the mountainous areas of northern Greece (e.g. Woodward et al., 2008), the influence of deglaciation cycles on sedimentation in mountainous catchments in southern Greece remains poorly understood due to the poor preservation of small moraines and limited opportunities to date glacial and fluvial sediment dynamics fluvial sediments (Pope, unpublished data). Nevertheless, intriguing new insight into links between glacial cycles and sediment transfer/deposition phases in upland catchments have emerged by applying multiple dating techniques to well-preserved multiple generations of moraines and extensive glacio-fluvial fan systems on Mount Chelmos (2355 m a.s.l.). U-series dating of calcites within proximal fan sediments constrain the earliest phase of glacio-fluvial sedimentation to 490 (±21.0)(ka (MIS 12), while OSL dating of fine sands constrains the deposition of extensive medial glacio-fluvial gravels in (valley we walked down through trees) to between 250.99 (±20.67) and 160.82 (±11.08) ka. By comparison, cosmogenic dating of moraine boulders indicates that three generations of well-preserved moraines in the highest cirque areas date to 31-23 ka, 17-16 ka and 12-11.5 ka. OSL dating also provides ages of 18 and 17 (±11.08) for an extensive glacio-fluvial terrace in a major valley draining the southern flanksof Mount Chelmos. The initial Mount Chelmos geochronology suggests that the earliest and middle phases of glacio-fluvial sedimentation are coincident with the Middle Pleistocene glacial stages stages recorded in the Pindus range (Hughes et al, 2006). These include the Skamnellian (MIS 12) and the Vlasian (MIS 6) Stages as well as other cold stage between these (e.g. MIS 8).Evidence of glacio-fluvial outwash in MIS 8 is interesting since evidence for this in the moraine records has remained elusive although is suggested further north in the Balkans (Hughes et al., 2011). The valley moraines and glacio-fluvial terraces (late MIS 2) post-date the local last glacial maximum and are coeval with the later part of the Tymphian stage in the Pindus range. Refs: Hughes, P.D., Woodward, J.C., Gibbard, P.L., Macklin, M.G., Gilmour, M.A. & Smith G.R. (2006) The glacial history of the Pindus Mountains, Greece. Journal of Geology 114, 413-434. Hughes, P.D., Woodward, J.C., van Calsteren, P.C. and Thomas, L.E. (2011) The Glacial History of The Dinaric Alps, Montenegro. Quaternary Science Reviews 30, 3393-3412. Woodward, J.C., Hamlin, R.H.B., Macklin, M.G., Hughes, P.D. & Lewin, J. (2008) Pleistocene catchment dynamics in the Mediterranean: glaciation, fluvial geomorphology and the slackwater sediment record. Geomorphology 101, 44-67.

The Role of Orbital Forcing in the Early-Middle Pleistocene Transition: Continuing the Precession Verses Obliquity Debate

NASA Astrophysics Data System (ADS)

Maslin, M. A.; Brierley, C. M.

2015-12-01

The Early-Middle Pleistocene Transition (EMPT) is the term used to describe the prolongation and intensification of glacial-interglacial climate cycles that initiated after 900,000 years ago. During the transition glacial-interglacial cycles shift from lasting 41,000 years to an average of 100,000 years. The structure of these glacial-interglacial cycles shifts from smooth to more abrupt 'saw-toothed' like transitions. In fact we argue there is shift from a bimodal climate to a tripartite climate system (see Figure). Despite eccentricity having by far the weakest influence on insolation received at the Earth's surface of any of the orbital parameters; it is often assumed to be the primary driver of the post-EMPT 100,000 years climate cycles because of the similarity in duration. The traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity. This 'eccentricity myth' is due to an artefact of spectral analysis which means that the last 8 glacial-interglacial average out at about 100,000 years in length despite ranging from 80,000 to 120,000 years. With the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial-interglacial cycles. Some argue that post-EMPT deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle. We review these current theories and suggest that though phase-locking between orbital forcing and global ice volume may occur and seem to primarily driven by the timing of precession; the chaotic nature of the climate system response means the relationship is not consistent through the last 900,000 years.

Detection and structural identification of dissolved organic matter in Antarctic glacial ice at natural abundance by SPR-W5-WATERGATE 1H NMR spectroscopy.

PubMed

Pautler, Brent G; Simpson, André J; Simpson, Myrna J; Tseng, Li-Hong; Spraul, Manfred; Dubnick, Ashley; Sharp, Martin J; Fitzsimons, Sean J

2011-06-01

Dissolved organic matter (DOM) is ubiquitous in aquatic ecosystems and is derived from various inputs that control its turnover. Glaciers and ice sheets are the second largest water reservoir in the global hydrologic cycle, but little is known about glacial DOM composition or contributions to biogeochemical cycling. Here we employ SPR-W5-WATERGATE (1)H NMR spectroscopy to elucidate and quantify the chemical structures of DOM constituents in Antarctic glacial ice as they exist in their natural state (average DOC of 8 mg/L) without isolation or preconcentration. This Antarctic glacial DOM is predominantly composed of a mixture of small recognizable molecules differing from DOM in marine, lacustrine, and other terrestrial environments. The major constituents detected in three distinct types of glacial ice include lactic and formic acid, free amino acids, and a mixture of simple sugars and amino sugars with concentrations that vary between ice types. The detection of free amino acid and amino sugar monomer components of peptidoglycan within the ice suggests that Antarctic glacial DOM likely originates from in situ microbial activity. As these constituents are normally considered to be biologically labile (fast cycling) in nonglacial environments, accelerated glacier melt and runoff may result in a flux of nutrients into adjacent ecosystems.

U-Th and 10Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia

NASA Astrophysics Data System (ADS)

Cogez, Antoine; Herman, Frédéric; Pelt, Éric; Reuschlé, Thierry; Morvan, Gilles; Darvill, Christopher M.; Norton, Kevin P.; Christl, Marcus; Märki, Lena; Chabaux, François

2018-03-01

The estimation of sediment transfer times remains a challenge to our understanding of sediment budgets and the relationships between erosion and climate. Uranium (U) and thorium (Th) isotope disequilibria offer a means of more robustly constraining sediment transfer times. Here, we present new uranium and thorium disequilibrium data for a series of nested moraines around Lago Buenos Aires in Argentine Patagonia. The glacial chronology for the area is constrained using in situ cosmogenic 10Be analysis of glacial outwash. Sediment transfer times within the periglacial domain were estimated by comparing the deposition ages of moraines to the theoretical age of sediment production, i.e., the comminution age inferred from U disequilibrium data and recoil loss factor estimates. Our data show first that the classical comminution age approach must include weathering processes accounted for by measuring Th disequilibrium. Second, our combined data suggest that the pre-deposition history of the moraine sediments is not negligible, as evidenced by the large disequilibrium of the youngest moraines despite the equilibrium of the corresponding glacial flour. Monte Carlo simulations suggest that weathering was more intense before the deposition of the moraines and that the transfer time of the fine sediments to the moraines was on the order of 100-200 kyr. Long transfer times could result from a combination of long sediment residence times in the proglacial lake (recurrence time of a glacial cycle) and the remobilization of sediments from moraines deposited during previous glacial cycles. 10Be data suggest that some glacial cycles are absent from the preserved moraine record (seemingly every second cycle), supporting a model of reworking moraines and/or fluctuations in the extent of glacial advances. The chronological pattern is consistent with the U-Th disequilibrium data and the 100-200 kyr transfer time. This long transfer time raises the question of the proportion of freshly eroded sediments that escape (or not) the proglacial environments during glacial periods.

Glacial refugia, recolonization patterns and diversification forces in Alpine-endemic Megabunus harvestmen.

PubMed

Wachter, Gregor A; Papadopoulou, Anna; Muster, Christoph; Arthofer, Wolfgang; Knowles, L Lacey; Steiner, Florian M; Schlick-Steiner, Birgit C

2016-06-01

The Pleistocene climatic fluctuations had a huge impact on all life forms, and various hypotheses regarding the survival of organisms during glacial periods have been postulated. In the European Alps, evidence has been found in support of refugia outside the ice shield (massifs de refuge) acting as sources for postglacial recolonization of inner-Alpine areas. In contrast, evidence for survival on nunataks, ice-free areas above the glacier, remains scarce. Here, we combine multivariate genetic analyses with ecological niche models (ENMs) through multiple timescales to elucidate the history of Alpine Megabunus harvestmen throughout the ice ages, a genus that comprises eight high-altitude endemics. ENMs suggest two types of refugia throughout the last glacial maximum, inner-Alpine survival on nunataks for four species and peripheral refugia for further four species. In some geographic regions, the patterns of genetic variation are consistent with long-distance dispersal out of massifs de refuge, repeatedly coupled with geographic parthenogenesis. In other regions, long-term persistence in nunataks may dominate the patterns of genetic divergence. Overall, our results suggest that glacial cycles contributed to allopatric diversification in Alpine Megabunus, both within and at the margins of the ice shield. These findings exemplify the power of ENM projections coupled with genetic analyses to identify hypotheses about the position and the number of glacial refugia and thus to evaluate the role of Pleistocene glaciations in driving species-specific responses of recolonization or persistence that may have contributed to observed patterns of biodiversity. © 2016 John Wiley & Sons Ltd.

Comparing Terrestrial Organic Carbon Cycle Dynamics in Interglacial and Glacial Climates in the South American Tropics

NASA Astrophysics Data System (ADS)

Fornace, K. L.; Galy, V.; Hughen, K. A.

2014-12-01

The application of compound-specific radiocarbon dating to molecular biomarkers has allowed for tracking of specific organic carbon pools as they move through the environment, providing insight into complex processes within the global carbon cycle. Here we use this technique to investigate links between glacial-interglacial climate change and terrestrial organic carbon cycling in the catchments of Cariaco Basin and Lake Titicaca, two tropical South American sites with well-characterized climate histories since the last glacial period. By comparing radiocarbon ages of terrestrial biomarkers (leaf wax compounds) with deposition ages in late glacial and Holocene sediments, we are able to gauge the storage time of these compounds in the catchments in soils, floodplains, etc. before transport to marine or lacustrine sediments. We are also able to probe the effects of temperature and hydrologic change individually by taking advantage of opposite hydrologic trends at the two sites: while both were colder during the last glacial period, precipitation at Titicaca decreased from the last glacial period to the Holocene, but the late glacial was marked by drier conditions at Cariaco. Preliminary data from both sites show a wide range of apparent ages of long-chain n-fatty acids (within error of 0 to >10,000 years older than sediment), with the majority showing ages on the order of several millennia at time of deposition and age generally increasing with chain length. While late glacial leaf waxes appear to be older relative to sediment than those deposited in the Holocene at both sites, at Cariaco we find a ~2-3 times larger glacial-interglacial age difference than at Titicaca. We hypothesize that at Titicaca the competing influences of wetter and colder conditions during the last glacial period, which respectively tend to increase and decrease the rate of organic carbon turnover on land, served to minimize the contrast between glacial and interglacial leaf wax storage time compared to Cariaco where temperature and hydrologic change may have acted in concert on the rate of terrestrial carbon turnover. This study has important implications for understanding the effects of large climate change on terrestrial carbon storage, as well as applications of terrestrial biomarkers for paleoclimate records.

Glacial Ordovician new evidence in the Pakhuis Formation, South Africa : sedimentological investigation and palaeo-environnemental reconstruction

NASA Astrophysics Data System (ADS)

Portier, E.; Buoncristiani, Jf.; Deronzier, Jf.

2009-04-01

During the Late Ordovician (Hirnantian) an ice sheet covered a great part of the Gondwana. In Africa, several studies present the stratigraphy and the complexity of these glacial records. The different glacial landsystems correspond to several glacial cycles, related to rapid ice front oscillations and are grouped into two major ice-sheet advances, separated by a major ice sheet recession. The study was performed on three well outcropping Late Ordovician sections in South Africa. The Ordovician IV is described as the Pakhuis Rm, and is divided into three different lithological members (known as Sneekop, Oskop and Sternbras Mb) that could be related to two major glacial cycles. In the first cycle (pool the two first Mb), facies association indicate continental environment, with : massive sandy tillites with facetted and striated erratics, subaerial outwash plain to glaciolacustrine cross bedded sands and laminated silts. Near Clanwilliam, the outcrops exhibit a high lateral variability in facies and thickness, ranging from a few meters to several tens of meters. The second cycle is dominated by clear marine sedimentation and may be interpreted as a transgressive sequence, quite different from what occurred in North Gondwana. Typical facies define shoreface environment, and periglacial evidence such as dropstones at base are encountered, passing progressively to a clear offshore environment at top of the series, likely Silurian aged, and known as Cederberg fm. Two glacial pavements were also described. The most spectacular one was firstly described by Visser et al. 1974 and should be interpreted as an intra-formational glacial pavement, with striae indicating a flow from East to West. This pavement is overlying a newly discovered glacial floor which exhibits grooves, crescents marks, en echelon fractures, with the same E-W general orientation, and shaped as ‘roches moutonnées', which are typical evidences of glacial erosion on indurated substratum. Reconstructing paleoenvironment suggests a clear structural paleo-topography controlling the erosion and distribution of paelo-valleys, lakes and glacial lobes. The glaciogenic Ordovician deposits constitute a proven oil and gas bearing reservoir on the North Gondwana margin, also known for their sharp and rapid facies changes. Also, such a study provides an excellent opportunity to understand and appraise the complex architecture and geometries of the sands bodies, the structural control of the glacial erosion and infill of this promising play. Visser, 1974 J.N.J. Visser, The Table Mountain Group: a study in the deposition of quartz arenites on a stable shelf, Trans. Geol. Soc. S. Afr. 77 (1974), pp. 229-237.

Mid-latitude trans-Pacific reconstructions and comparisons of coupled glacial/interglacial climate cycles based on soil stratigraphy of cover-beds

NASA Astrophysics Data System (ADS)

Alloway, B. V.; Almond, P. C.; Moreno, P. I.; Sagredo, E.; Kaplan, M. R.; Kubik, P. W.; Tonkin, P. J.

2018-06-01

South Westland, New Zealand, and southern Chile, are two narrow continental corridors effectively confined between the Pacific Ocean in the west and high mountain ranges in the east which impart significant influence over regional climate, vegetation and soils. In both these southern mid-latitude regions, evidence for extensive and repeated glaciations during cold phases of the Quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants. In South Westland, these variably aged glacial landforms are mantled by layered (multisequal) soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment. These cover-bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial/warm and glacial/cold climate during the Quaternary. In this study, we recognise multisequal soils overlying glacial landforms in southern continental Chile but, unlike the spodic (podzolic) soil sequences of South Westland, these are of dominantly volcanigenic (andic) provenance and are very similar to multisequal soils of andic provenance that predominate in, and adjacent to, areas of rhyolitic to andesitic volcanism in North Island, New Zealand. Here we develop a soil-stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental Chile. Based on proxy data from southern Chile, we propose that persistent vegetation cover and high precipitation on the western side of the Andes, during colder-than-present episodes tended to suppress the widespread production of glacially-derived loessial materials despite the pervasive occurrence of glacial and glacio-fluvial deposits that have frequently inundated large tracts of this landscape during the Quaternary. Given the lack of loess cover-beds that have traditionally assisted in the relative dating of glacial episodes prior to the Late Quaternary, surface exposure dating techniques could provide another chronological alternative to address this issue. However, there have been two main obstacles to successfully apply this dating technique in Patagonia. First, minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion, although dating outwash plains is more robust. Second, on the wet western side adjacent to the Andes, persistent vegetation cover during both glacial and post-glacial times, as well as widespread inundation by volcanic mass-flows, appear preventive. We make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted Andean-sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified. As already demonstrated by New Zealand studies, multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the Quaternary. On this basis, similar sequences in northwest Patagonia provide a relatively untapped archive to enable Quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed.

Induced stress changes and associated fracture development as a result of deglaciation on the Zugspitzplatt, SE Germany

NASA Astrophysics Data System (ADS)

Leith, Kerry; Kupp, Jan; Geisenhof, Benedikt; Krautblatter, Michael

2015-04-01

Bedrock stresses in alpine regions result from the combined effects of exhumation, tectonics, topography, inelastic strain (e.g. fault displacement and fracture formation), and external loading. Gravitational loading by glacial ice can significantly affect near-surface stress magnitudes, although the nature of this effect and it's impact on stress distributions and bedrock fracturing is strongly dependent on the stress history of the bedrock landscape. We assess the effects of recent (post-Little Ice Age , ~1850 AD) and future deglaciation on bedrock stresses in the region of the Zugspitzplatt, a glaciated plateau surrounded by 1500 m high bedrock walls in SE Germany. We address this by undertaking a 2-D elasto-plastic finite element method analysis of stress changes and fracture propagation due to repeated glacial - interglacial cycles. Our model is initialised with upper crustal stresses in equilibrium with bedrock strength and regional tectonics, and we then simulate two cycles of major Pleistocene glaciation and deglaciation in order to dissipate stress concentrations and incorporate path-dependent effects of glacial loading on the landscape. We then simulate a final glacial cycle, and remove 1 m of bedrock to approximate glacial erosion across the topography. Finally, ice levels are reduced in accordance with known late-glacial and recent ice retreat, allowing us to compare relative stress changes and predicted patterns of fracture propagation to observed fracture distributions on the Zugspitzplatt. Model results compare favourably to observed fracture patterns, and indicate the plateau is likely to be undergoing N-S extension as a result of deglaciation, with a strong reduction of horizontal stress magnitudes beneath the present-day Schneeferner glacier. As each glacial cycle has a similar effect on the plateau, it is likely that surficial stresses are slightly tensile, and each cycle of deglaciation produces additional sub-vertical tensile fractures, which are then exploited by the karst groundwater system. Here we show how stress histories and brittle deformation in near-surface stress models can provide a better understanding of long-term rock slope evolution and failure as well as karst co-evolution in Alpine Environments.

A Model-based Interpretation of Low-frequency Changes in the Carbon Cycle during the Last 120,000 years and its Implications for the Reconstruction of Atmospheric (delta) 14-C

NASA Technical Reports Server (NTRS)

Koehler, Peter; Muscheler, Raimund; Fischer, Hubertus

2006-01-01

A main caveat in the interpretation of observed changes in atmospheric (Delta)C-l4 during the last 50,000 years is the unknown variability of the carbon cycle, which together with changes in the C-14 production rates determines the C-14 dynamics. A plausible scenario explaining glacial/interglacial dynamics seen in atmospheric CO2 and (delta)C-13 was proposed recently (Kohler et al., 2005a). A similar approach that expands its interpretation to the C-14 cycle is an important step toward a deeper understanding of (Delta)C-14 variability. This approach is based on an ocean/atmosphere/biosphere box model of the global carbon cycle (BICYCLE) to reproduce low-frequency changes in atmospheric CO2 as seen in Antarctic ice cores. The model is forced forward in time by various paleoclimatic records derived from ice and sediment cores. The simulation results of our proposed scenario match a compiled CO2 record from various ice cores during the last 120,000 years with high accuracy (r(sup 2) = 0.89). We analyze scenarios with different C-14 production rates, which are either constant or based on Be-10 measured in Greenland ice cores or the recent high-resolution geomagnetic field reconstruction GLOPIS-75 and compare them with the available (Delta)C-14 data covering the last 50,000 years. Our results suggest that during the last glacial cycle in general less than 110%0o f the increased atmospheric (Delta)C-14 is based on variations in the carbon cycle, while the largest part (5/6) of the variations has to be explained by other factors. Glacial atmospheric (Delta)C-14 larger than 700% cannot not be explained within our framework, neither through carbon cycle-based changes nor through variable C-14 production. Superimposed on these general trends might lie positive anomalies in atmospheric (Delta)C-14 of approx. 50% caused by millennial-scale variability of the northern deep water production during Heinrich events and Dansgaard/Oeschger climate fluctuations. According to our model, the dominant processes that increase glacial (Delta)C-14 are a reduced glacial ocean circulation (+ approx.40%0), a restricted glacial gas exchange between the atmosphere and the surface ocean through sea ice coverage (+ approx. 20%), and the enrichment of dissolved inorganic carbon with C-14 in the surface waters through isotopic fractionation during higher glacial marine export production caused by iron fertilization (+ approx.10%).

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks.

PubMed

Torres, Mark A; Moosdorf, Nils; Hartmann, Jens; Adkins, Jess F; West, A Joshua

2017-08-15

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO 2 , we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO 2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean-atmosphere CO 2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO 2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O 2 Future work on glaciation-weathering-carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

PubMed Central

Torres, Mark A.; Moosdorf, Nils; Hartmann, Jens; Adkins, Jess F.

2017-01-01

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals. PMID:28760954

Numerical simulations of the Cordilleran ice sheet through the last glacial cycle

NASA Astrophysics Data System (ADS)

Seguinot, Julien; Rogozhina, Irina; Stroeven, Arjen P.; Margold, Martin; Kleman, Johan

2016-03-01

After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2-56.9 ka) and 2 (23.2-16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

Extraterrestrial accretion and glacial cycles

NASA Technical Reports Server (NTRS)

Muller, R. A.

1994-01-01

We propose that the approx. 100-k.y. cycle seen in terrestrial glaciation is due to changes in meteor flux that come from changes in the Earth's orbit. This model can explain a 70-k.y. 'anomalous' period in climate data and the apparent discrepancy between present extraterrestrial fluxes and those in oceanic sediments. It can be tested by measuring Ir densities in sediments and ice during glacials and interglacials.

Cyclostratigraphic constraints on the duration of the Datangpo Formation and the onset age of the Nantuo (Marinoan) glaciation in South China

NASA Astrophysics Data System (ADS)

Bao, Xiujuan; Zhang, Shihong; Jiang, Ganqing; Wu, Huaichun; Li, Haiyan; Wang, Xinqiang; An, Zhengze; Yang, Tianshui

2018-02-01

Constructing an accurate timeline is critical for reconstructing the Earth systems through critical transitions in climate, geochemistry, and life. Existing dates constrain synchronous initiation (ca. 717 Ma) and termination (ca. 660 Ma) of the Sturtian glaciation from multiple continents. The termination of the younger Marinoan glaciation is also well dated at ca. 635 Ma, but the onset of this glaciation is only roughly constrained as ≤ ca. 654 Ma (South China) and ≥ ca. 639 Ma (Namibia). To test if the Marinoan glaciation started close to ca. 654 Ma or ca. 639 Ma, we have conducted a cyclostratigraphic study on the Cryogenian non-glacial Datangpo Formation that conformably overlies and underlies Sturtian and Marinoan glacial diamictites, respectively, in a deep-water basin section in South China. A total of 28,765 magnetic susceptibility (MS) measurements from a drillcore of the 292-m-thick, muddy siltstone- and shale-dominated Datangpo Formation are used for cyclostratigraphic analysis. The results reveal significant decameter- to meter-scale sedimentary cycles of 16-12 m, 3.6-3.0 m, 1.0-0.8 m, and 0.6-0.4 m. The ratios of these cycle wavelengths match well with those of the Milankovitch cycles calibrated for the Cryogenian Period. The established astrochronologic time scale suggests that the duration of the Datangpo Formation is about 9.8 million years. Together with the radiometric age of ca. 660 Ma for the termination of the Sturtian glaciation, the cyclostratigraphic data suggest that the Nantuo (Marinoan) glaciation in South China initiated at ca. 650 Ma, which is slightly younger than but consistent with the ca. 654 Ma U-Pb age from the top of the Datangpo Formation in shelf sections. This age, however, is significantly older than the ages obtained from Marinoan-age glacial diamictites in South China (ca. 636 Ma) and Namibia (ca. 639 Ma). Given that most of the shelf sections may have suffered from glacial erosion, obtaining the onset age of the Marinoan glaciation should focus on relatively complete, deep-water successions.

Phylogeography of Quercus variabilis Based on Chloroplast DNA Sequence in East Asia: Multiple Glacial Refugia and Mainland-Migrated Island Populations

PubMed Central

Kang, Hongzhang; Sun, Xiao; Yin, Shan; Du, Hongmei; Yamanaka, Norikazu; Gapare, Washington; Wu, Harry X.; Liu, Chunjiang

2012-01-01

The biogeographical relationships between far-separated populations, in particular, those in the mainland and islands, remain unclear for widespread species in eastern Asia where the current distribution of plants was greatly influenced by the Quaternary climate. Deciduous Oriental oak (Quercus variabilis) is one of the most widely distributed species in eastern Asia. In this study, leaf material of 528 Q. variabilis trees from 50 populations across the whole distribution (Mainland China, Korea Peninsular as well as Japan, Zhoushan and Taiwan Islands) was collected, and three cpDNA intergenic spacer fragments were sequenced using universal primers. A total of 26 haplotypes were detected, and it showed a weak phylogeographical structure in eastern Asia populations at species level, however, in the central-eastern region of Mainland China, the populations had more haplotypes than those in other regions, with a significant phylogeographical structure (N ST = 0.751> G ST = 0.690, P<0.05). Q. variabilis displayed high interpopulation and low intrapopulation genetic diversity across the distribution range. Both unimodal mismatch distribution and significant negative Fu’s FS indicated a demographic expansion of Q. variabilis populations in East Asia. A fossil calibrated phylogenetic tree showed a rapid speciation during Pleistocene, with a population augment occurred in Middle Pleistocene. Both diversity patterns and ecological niche modelling indicated there could be multiple glacial refugia and possible bottleneck or founder effects occurred in the southern Japan. We dated major spatial expansion of Q. variabilis population in eastern Asia to the last glacial cycle(s), a period with sea-level fluctuations and land bridges in East China Sea as possible dispersal corridors. This study showed that geographical heterogeneity combined with climate and sea-level changes have shaped the genetic structure of this wide-ranging tree species in East Asia. PMID:23115642

Role of Marine Biology in Glacial-Interglacial CO2 Cycles

NASA Astrophysics Data System (ADS)

Kohfeld, Karen E.; Le Quéré, Corinne; Harrison, Sandy P.; Anderson, Robert F.

2005-04-01

It has been hypothesized that changes in the marine biological pump caused a major portion of the glacial reduction of atmospheric carbon dioxide by 80 to 100 parts per million through increased iron fertilization of marine plankton, increased ocean nutrient content or utilization, or shifts in dominant plankton types. We analyze sedimentary records of marine productivity at the peak and the middle of the last glacial cycle and show that neither changes in nutrient utilization in the Southern Ocean nor shifts in plankton dominance explain the CO2 drawdown. Iron fertilization and associated mechanisms can be responsible for no more than half the observed drawdown.

Temporal evolution of mechanisms controlling ocean carbon uptake during the last glacial cycle

NASA Astrophysics Data System (ADS)

Kohfeld, Karen E.; Chase, Zanna

2017-08-01

Many mechanisms have been proposed to explain the ∼85-90 ppm decrease in atmospheric carbon dioxide (CO2) during the last glacial cycle, between 127,000 and 18,000 yrs ago. When taken together, these mechanisms can, in some models, account for the full glacial-interglacial CO2 drawdown. Most proxy-based evaluations focus on the peak of the Last Glacial Maximum, 24,000-18,000 yrs ago, and little has been done to determine the sequential timing of processes affecting CO2 during the last glacial cycle. Here we use a new compilation of sea-surface temperature records together with time-sequenced records of carbon and Nd isotopes, and other proxies to determine when the most commonly proposed mechanisms could have been important for CO2 drawdown. We find that the initial major drawdown of 35 ppm 115,000 yrs ago was most likely a result of Antarctic sea ice expansion. Importantly, changes in deep ocean circulation and mixing did not play a major role until at least 30,000 yrs after the first CO2 drawdown. The second phase of CO2 drawdown occurred ∼70,000 yrs ago and was also coincident with the first significant influences of enhanced ocean productivity due to dust. Finally, minimum concentrations of atmospheric CO2 during the Last Glacial Maximum resulted from the combination of physical and biological factors, including the barrier effect of expanded Southern Ocean sea ice, slower ventilation of the deep sea, and ocean biological feedbacks.

Quantitative assessment of glacial fluctuations in the level of Lake Lisan, Dead Sea rift

NASA Astrophysics Data System (ADS)

Rohling, Eelco J.

2013-06-01

A quantitative understanding of climatic variations in the Levant during the last glacial cycle is needed to support archaeologists in assessing the drivers behind hominin migrations and cultural developments in this key region at the intersection between Africa and Europe. It will also foster a better understanding of the region's natural variability as context to projections of modern climate change. Detailed documentation of variations in the level of Lake Lisan - the lake that occupied the Dead Sea rift during the last glacial cycle - provides crucial climatic information for this region. Existing reconstructions suggest that Lake Lisan highstands during cold intervals of the last glacial cycle represent relatively humid conditions in the region, but these interpretations have remained predominantly qualitative. Here, I evaluate realistic ranges of the key climatological parameters that controlled lake level, based on the observed timing and amplitudes of lake-level variability. I infer that a mean precipitation rate over the wider catchment area of about 500 mm y-1, as proposed in the literature, would be consistent with observed lake levels if there was a concomitant 15-50% increase in wind speed during cold glacial stadials. This lends quantitative support to previous inferences of a notable increase in the intensity of Mediterranean (winter) storms during glacial periods, which tracked eastward into the Levant. In contrast to highstands during ‘regular’ stadials, lake level dropped during Heinrich Events. I demonstrate that this likely indicates a further intensification of the winds during those times.

Simulation of Glacial Cycles Before and After the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Ganopolski, A.; Willeit, M.; Calov, R.

2017-12-01

In spite of significant progress achieved in understanding of glacial cycles, the cause of Mid-Pleistocene transition (MPT) is still not fully understood. To study possible mechanisms of the MPT we used the Earth system model of intermediate complexity CLIMBER-2 which incorporates all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, aeolian dust and marine biogeochemistry. We run the model through the entire Quaternary. The only prescribed forcing in these simulations is variations in Earth orbital parameters. In addition we prescribed gradually evolving in time terrestrial sediment cover and global volcanic outgassing. We found that gradual removal of terrestrial sediment from the Northern Hemisphere continent by glacial processes is sufficient to explain transition from 40-ka to 100-ka worlds around 1 million years ago. By starting the model at different times and using the same initial conditions we found that modeling results converge to the same solution which depends only on the orbital forcing and lower boundary conditions. Our results thus strongly suggest that Quaternary glacial cycles are externally forced and nearly deterministic.

Miocene-Oligocene sequence stratigraphy of the Malay Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lovell, R.; Elias, M.R.; Hill, R.E.

1994-07-01

The Malay Basin has experienced extension of the Eocene ( ) through Oligocene, sag in the early Miocene, and compression in the middle Miocene through Pliocene-Pleistocene. The interaction of structurally induced and glacial-eustatic accommodation changes has resulted in complex, interrelated play elements, including multiple reservoirs, diverse nonmarine sources, discontinuous migration pathways, and thin seals. Extensional subbasins were filled with braided streams, associated coastal plain, lacustrine deltas, and thick lake shales (groups M-K). This initial rift fill comprises an overall second order progradational cycle punctuated by 3rd-order cycles. These 3rd-order cycles are capped by thick, source-rich, lacustrine shale packages. The lowermore » Miocene section (groups I and J) consists of progradational to aggradational fluvial to tidally-dominated estuarine sands. Hydrocarbons are generated from interbedded coals and other coal-related lithologies.« less

Quaternary history of sea ice and paleoclimate in the Amerasia Basin, Arctic Ocean, as recorded in the cyclical strata of Northwind Ridge

USGS Publications Warehouse

Phillips, R.L.; Grantz, A.

1997-01-01

The 19 middle-early Pleistocene to Holocene bipartite lithostratigraphic cycles observed in high-resolution piston cores from Northwind Ridge in the Amerasia Basin of the Arctic Ocean, provide a detailed record of alternating glacial and interglacial climatic and oceanographic conditions and of correlative changes in the character and thickness of the sea-ice cover in the Amerasia Basin. Glacial conditions in each cycle are represented by gray pelagic muds that are suboxic, laminated, and essentially lacking in microfossils, macrofossils, trace fossils, and generally in glacial erratics. Interglacial conditions are represented by ochre pelagic muds that are oxic and bioturbated and contain rare to abundant microfossils and abundant glacial erratics. The synglacial laminated gray muds were deposited when the central Amerasia Basin was covered by a floating sheet of sea ice of sufficient thickness and continuity to reduce downwelling solar irradiance and oxygen to levels that precluded photosynthesis, maintenance of a biota, and strong oxidation of the pelagic sediment. Except during the early part of 3 of the 19 synglacial episodes, when it was periodically breached by erratic-bearing glacial icebergs, the floating Arctic Ocean sea-ice sheet was sufficiently thick to block the circulation of icebergs over Northwind Ridge and presumably other areas of the central Arctic Ocean. Interglacial conditions were initiated by abrupt thinning and breakup of the floating sea-ice sheet at the close of glacial time, which permitted surges of glacial erratic-laden ice-bergs to reach Northwind Ridge and the central Arctic Ocean, where they circulated freely and deposited numerous, and relatively thick, erratic clast-rich beds. Breakup of the successive synglacial sea-ice sheets initiated deposition of the interglacial ochre mud units under conditions that allowed sunlight and increased amounts of oxygen to enter the water column, resulting in photosynthesis and biologic productivity, and strong oxidization of the pelagic sediment. The lithostratigraphy of Northwind Ridge suggests that during at least late Pleistocene time, glacial conditions in the Arctic Ocean were initiated abruptly and continued unabated until terminated, also abruptly, by onset of the succeeding interglacial warming. Variations in abundance of glacial erratics within the interglacial units of the late Pleistocene indicate that during at least most interglacial episodes northern North America was glaciated, but with generally diminishing severity, until onset of the succeeding continental glaciation. Magnetostratigraphy suggests that the glacial-interglacial cycles on Northwind Ridge had an average periodicity of approximately 93.5 k.y. during the Brunhes normal and approximately 105 k.y. during the latter part of the Matuyama reverse polarity zone. These average periodicities are close to the 100 k.y. temperature cycles found in North Atlantic deep-water sediments of the Brunhes normal polarity chron, which have been ascribed to forcing by a Milankovitch eccentricity cycle. They are also close, however, to the average interval (101 k.y.) between the aperiodic glacial terminations in the 500 k.y. Pleistocene continental climate record from Devil's Hole, Nevada, which have been ascribed to nonlinear feedbacks within the Earth's atmosphere-ice sheet-ocean system.

Global pulses of organic carbon burial in deep-sea sediments during glacial maxima

PubMed Central

Cartapanis, Olivier; Bianchi, Daniele; Jaccard, Samuel L.; Galbraith, Eric D.

2016-01-01

The burial of organic carbon in marine sediments removes carbon dioxide from the ocean–atmosphere pool, provides energy to the deep biosphere, and on geological timescales drives the oxygenation of the atmosphere. Here we quantify natural variations in the burial of organic carbon in deep-sea sediments over the last glacial cycle. Using a new data compilation of hundreds of sediment cores, we show that the accumulation rate of organic carbon in the deep sea was consistently higher (50%) during glacial maxima than during interglacials. The spatial pattern and temporal progression of the changes suggest that enhanced nutrient supply to parts of the surface ocean contributed to the glacial burial pulses, with likely additional contributions from more efficient transfer of organic matter to the deep sea and better preservation of organic matter due to reduced oxygen exposure. These results demonstrate a pronounced climate sensitivity for this global carbon cycle sink. PMID:26923945

Glacial Cycles Influence Marine Methane Hydrate Formation

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A. E.; Daigle, H.; Oryan, B.

2018-01-01

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sediments with greater organic carbon content deposited during the penultimate glacial cycle ( 120-240 ka). The model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.

Relative role of astronomical forcings and the atmospheric carbon dioxide during the glacial cycles of the last 1.5 million years

NASA Astrophysics Data System (ADS)

Abe-Ouchi, A.; Saito, F.; Chan, W. L.; Kino, K.; Watanabe, Y.; Oishi, R.

2017-12-01

Climate change with wax and wane of large Northern Hemisphere ice sheet occurred in the past 800 thousand years characterized by about 100 thousand year cycle with a large amplitude of sawtooth pattern, following a transition from a period of 40 thousand years cycle with small amplitude of ice sheet change at about 1 million years ago. Although the importance of insolation as the ultimate driver is now appreciated, the mechanism what determines the timing and strength of ice age termination as well as the amplitude of glacial cycles are far from clearly understood. Here we simulate the glacial cycles of the last 1.5 Ma and investigate the origin of 100ka periodicity and the role of astronomical forcing and atmospheric carbon dioxide content using a three dimensional ice sheet model with the input examined by the MIROC 4m GCM. The model is forced by astronomical parameters (Berger, 1978) and atmospheric CO2 change obtained from ice cores (Vostok, EPICA and DomeF), where available. Ice age cycles with a saw-tooth shape 100 ka periodicity are simulated at low CO2 levels, with the major NH ice sheet volume as well as geographical distribution and timing of interglacials successfully simulated. The model shows the interglacials at the right timings even under constant CO2 levels, with few exceptions, e.g. MIS11 around 400 thousand years ago (400 kyr BP). Through sensitivity experiments we examine individual factors determining the glacial termination, such as constant and variable CO2 levels, obliquity, precession and eccentricity.

Spurious Additional Warming Reconstructed From Borehole Temperatures Corrected for the Effect of the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Šafanda, Jan

2018-03-01

Reconstructions of past ground surface temperature changes from temperature logs conducted in several hundred meter deep boreholes have proved to be a valuable independent source of information on climate variations over the last millennium. The reconstruction techniques have been evolving for more than two decades to extract optimally the climate signal of the last millennium contained in the temperature logs of different length performed in sites with different histories of the Last Glacial Cycle. This paper analyzes the method of the Last Glacial Cycle thermal effect removal from such borehole temperature profiles used by Beltrami et al. (2017, https://doi.org/10.1002/2016GL071317) in reconstructing the last 500 year history. I show that the reported results of additional warming in this period reconstructed from the corrected borehole data for North America are an artifact generated by the correction.

Phosphorus in the ocean and marine sediments: similarities between present and past processes

NASA Astrophysics Data System (ADS)

Tamburini, F.

2004-12-01

Because phosphorus (P) is an essential nutrient, geochemical research has focused over the years on understanding the different aspects of the P cycle in the oceans, from the global to microbial scale. In the last 40 years, giant phosphorite deposits were largely studied, and their episodic occurrence in the geological record was alternatively interpreted as the product of shallow water environments, high productivity, low-sedimentation rates, and/or changes in sea level. Although research has focused more recently on the oceanic burial fluxes and residence time of P, there is still a general agreement on the need for more data. Thanks to new analytical techniques, allowing the detection of small quantities of phosphate (on the order of ?mol/g), and to the increased availability of sediment cores, P-bearing sediments have been found everywhere beneath the ocean floor. This finding has changed our understanding of P behavior in the ocean, and is redefining the role of P as an important nutrient, for example, over glacial-interglacial time scales. I will present glacial-interglacial reconstructions of burial and benthic fluxes of P, with the goal of understanding to which extent the P cycle is linked to global processes. The data, averaged to the whole ocean, indicate that burial fluxes of reactive P during glacial times are not considerably lower than during interglacials. This observation could lead to the conclusion that no changes occurred in P cycle on glacial-interglacial timescales and, therefore, that C cycle and climate variations were independent of P cycle. However, when the benthic flux estimates are taken into account, a different picture arises. During low sea level periods, the redistribution of sediments from shallow to deep waters, due to the reduction of the continental margin surface, fostered P regeneration during settling of organic matter. Even if P burial fluxes remain fairly constant, the oceanic phosphate inventory of glacial bottom waters was probably higher. On a different time scale, the shift in P behavior between glacial and interglacial periods could have been promoted by conditions similar to those that led to the formation of phosphorite deposits, which are abundant in the geological past but rare today.

Contrasting scaling properties of interglacial and glacial climates

PubMed Central

Shao, Zhi-Gang; Ditlevsen, Peter D.

2016-01-01

Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard–Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

Evolution of the early Antarctic ice ages

NASA Astrophysics Data System (ADS)

Liebrand, Diederik; de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Ruessink, Gerben; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

2017-04-01

Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ˜110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ˜85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ˜110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (˜28.0 My to ˜26.3 My ago) and across the Oligocene-Miocene Transition (˜23.0 My ago). However, the high-amplitude glacial-interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.

The timing and extent of Quaternary glaciation of Stok, northern Zanskar Range, Transhimalaya, of northern India

NASA Astrophysics Data System (ADS)

Orr, Elizabeth N.; Owen, Lewis A.; Murari, Madhav K.; Saha, Sourav; Caffee, Marc W.

2017-05-01

The glacial history of three tributary valleys (Namlung, Gopal Kangri and Stok Kangri) of the Stok valley, south of the Indus valley in the northern sector of the Zanskar Range, northern India is characterized using geomorphic mapping and cosmogenic 10Be surface exposure dating. The new glacial chronostratigraphy for the Stok valley is the first for the northern Zanskar Range and provides insights into the spatial variability of glaciation in the Himalayan-Tibetan orogen. This framework facilitates the understanding of the nature and the timing of landscape evolution and paleoenvironmental change in the Himalayan-Tibetan orogen. At least four glacial stages are evident within each of the tributary valleys of Gopal Kangri (MG1-MG4, youngest to oldest) and Stok Kangri (MS1-MS4) that feed into the Stok valley. With the exception of the MG4 glacial advance ( 124 ka) in Gopal Kangri, the Stok valley has preserved evidence of glaciations from 50 ka to the present. Equilibrium-line altitudes and glacier reconstructions for the Stok valley and its tributaries demonstrate that glaciations have become progressively less extensive through time. Former glacier extents of the Stok region are comparable in length with glacial advances during the last glacial cycle in eastern Zanskar and in the southern Ladakh Range to the south and north of the Indus valley, respectively. Landscape evolution in the study area has occurred across numerous glacial-interglacial cycles by a combination of glacial and fluvial processes and is similar to that of the Ladakh Range.

The vegetation history of the last glacial-interglacial cycle in eastern New South Wales, Australia

NASA Astrophysics Data System (ADS)

Williams, N. J.; Harle, K. J.; Gale, S. J.; Heijnis, H.

2006-10-01

We present a reconstruction of the vegetation history of the last glacial-interglacial cycle (ca. 75 k cal. yr BP-present) at Redhead Lagoon, an enclosed lake basin in coastal, eastern New South Wales, Australia. The sequence of vegetation change at the site is broadly comparable with the pattern of climatically induced changes observed in many other pollen records in southeast Australia. Open woodland-herbland and woodland-forest communities correspond with glacial and interglacial periods respectively, with an additional change towards a more open understorey vegetation assemblage over the last 40 000 yr. The driest conditions appear to have occurred during the height of the last glacial (some time between 30 and 20 k cal. yr BP). This is consistent with other records from southeast Australia, and provides support for a poleward shift in the subtropical anticyclone belt and, less certainly, for the thesis that the Southern Hemisphere westerlies intensified during this period. In marked contrast to most sites in southeast Australia, Casuarinaceae dominates the pollen record through the height of the last glacial period and into the Holocene. The postglacial climatic amelioration is accompanied by the general reappearance of tree pollen in the record, by the disappearance of several open and disturbed environment indicator taxa, by increases in organic sediment deposition and pollen taxon diversity, and by higher water balances. While climate appears to have been the major control on patterns of vegetation change at this site throughout most of the last glacial-interglacial cycle, changes in depositional environment and hydrology have also played a role. Significantly, substantial increases in the rate and magnitude of many indicators of environmental disturbance since European settlement suggest that humans are now the most important mechanism for environmental change. Copyright

Evolution of surface and deep water conditions in the Antarctic Southern Ocean across the MPT

NASA Astrophysics Data System (ADS)

Hasenfratz, A. P.; Jaccard, S.; Martinez-Garcia, A.; Hodell, D. A.; Vance, D.; Bernasconi, S. M.; Kleiven, H. F.; Haug, G. H.

2016-12-01

The mid-Pleistocene transition (MPT; 1.25-0.7 Myr) marked a fundamental change in the periodicity of the climate cycles, shifting from a 41-kyr to a high-amplitude, asymmetric 100-kyr cycle without any noticeable change in orbital forcing. Hypotheses to explain the MPT involve non-linear responses to orbital forcing, changes in glacial dynamics and internal changes in the carbon cycle. Specifically, a decrease in pCO2 during peak ice age conditions and the associated global cooling has been proposed as one of the possible triggers for the MPT. Previous results have indicated that the Southern Ocean provides a coherent two-part mechanism for the timing and amplitude of the glacial/interglacial pCO2 variations. However, there is still much uncertainty and debate regarding the response of the Antarctic Southern Ocean biogeochemistry to changes invoked for the MPT, and its contribution to the proposed pCO2 variations. Here, we show 1.5 Myr-long records of export production, and planktonic (Neogloboquadrina pachyderma) and benthic (Melonis pompilioides) foraminiferal stable isotopes and trace metals from ODP Site 1094 retrieved from the Atlantic sector of the Antarctic Southern Ocean (53.2°S, 5.1°E, 2807m). While glacial planktonic δ18O increases across the MPT, glacial Mg/Ca-derived SST decrease later, around 700 ka, when glacial atmospheric pCO2 has already dropped. As glacial export production that is crucially related to micronutrients upwelled from the subsurface ocean remains unchanged across the past 1.5 Myr, it seems that cooling of the glacial surface ocean did not significantly alter the stability of the water column. Furthermore, paired measurements of benthic δ18O and Mg/Ca enables the determination of seawater δ18O of the deep ocean, which allows us to estimate changes in the density gradient and the salinity of the deep water.

Glacial cycles influence marine methane hydrate formation

DOE PAGES

Malinverno, A.; Cook, A. E.; Daigle, H.; ...

2018-01-12

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sedimentsmore » with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.« less

Glacial cycles influence marine methane hydrate formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, A.; Cook, A. E.; Daigle, H.

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sedimentsmore » with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.« less

Radiocarbon constraints on the glacial ocean circulation and its impact on atmospheric CO2

NASA Astrophysics Data System (ADS)

Skinner, L. C.; Primeau, F.; Freeman, E.; de La Fuente, M.; Goodwin, P. A.; Gottschalk, J.; Huang, E.; McCave, I. N.; Noble, T. L.; Scrivner, A. E.

2017-07-01

While the ocean's large-scale overturning circulation is thought to have been significantly different under the climatic conditions of the Last Glacial Maximum (LGM), the exact nature of the glacial circulation and its implications for global carbon cycling continue to be debated. Here we use a global array of ocean-atmosphere radiocarbon disequilibrium estimates to demonstrate a ~689+/-53 14C-yr increase in the average residence time of carbon in the deep ocean at the LGM. A predominantly southern-sourced abyssal overturning limb that was more isolated from its shallower northern counterparts is interpreted to have extended from the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the deep ocean of a fast escape route for accumulating respired carbon. While the exact magnitude of the resulting carbon cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency of the biological carbon pump that could have accounted for as much as half of the glacial-interglacial CO2 change.

Impacts of Quaternary History on Critical Zone Structure and Processes: Examples and a Conceptual Model from the Intensively Managed Landscapes Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Anders, Alison M.; Bettis, E. Arthur; Grimley, David A.; Stumpf, Andrew J.; Kumar, Praveen

2018-03-01

The concept of a critical zone (CZ) supporting terrestrial life has fostered groundbreaking interdisciplinary science addressing complex interactions among water, soil, rock, air and life near Earth’s surface. Pioneering work has focused on the CZ in areas with residual soils and steady-state or erosional topography. CZ evolution in these areas is conceptualized as progressive weathering of local bedrock (e.g. in the flow-through reactor model). However, this model is not applicable to areas in which weathering profiles form in transported materials including the formerly glaciated portion of the Central Lowland of North America. We present a new conceptual model of CZ evolution in landscapes impacted by continental glaciation based on investigations at three study sites in the Intensively Managed Landscapes Critical Zone Observatory (IML-CZO) The IML-CZO is devoted to the study of CZ processes in a region characterized by thick surficial deposits resulting from multiple continental glaciations, with bedrock at depths of up to 150 m. Here the physical (glacial ice, loess, developing soil profiles) and biological (microbes, tundra, forest, prairie) components of the CZ vary significantly in time. Moreover, the spatial relationships between mineral components of the CZ record a history of glacial-interglacial cycles and landscape evolution. We present cross-sections from IML-CZO sites to provide specific examples of how environmental change is recorded by the structure of the mineral components of the CZ. We build on these examples to create an idealized model of CZ evolution through a glacial cycle that represents the IML-CZO sites and other areas of low relief that have experienced continental glaciation. In addition, we identify two main characteristics of CZ structure which should be included in a conceptual model of CZ development in the IML-CZO and similar settings: (1) mineral components have diverse origins and transport trajectories including alteration in past CZs, and, (2) variability in climate, ecosystems, and hydrology during glacial-interglacial cycles profoundly influence the CZ composition, creating a legacy retained in its structure. This legacy is important because the current physical CZ structure influences the occurrence and rates of CZ processes, as well as future CZ responses to land use and climate change.

The enigma of the Australian Alps, young landscapes and missing cryogenic features.

NASA Astrophysics Data System (ADS)

Slee, Adrian; Shulmeister, James; Clark, Doug

2014-05-01

Widespread evidence for pre last glacial cycle glaciation of late Quaternary ages has been documented from mid-latitude southern hemisphere mountain environments in New Zealand, southern South America and the Tasmanian Highlands. On mainland Australia however cirque and small valley glaciation in the Australian Alps is limited to OIS 4-3 and the last glacial maximum (OIS 2) (Barrows et al. 2001). This contrasts with the other southern hemisphere glacial records that indicate significantly more extensive glaciations preceding the last glacial cycle. In both the Southern Andes and Tasmania the maximum glaciations occurred prior to 783 kya (Glasser et al. 2008, Colhoun et al. 2010) while in tectonically active New Zealand it is at least clear that the scale of glaciation has been diminishing over the last 3 glacial cycles (Shulmeister et al. 2010). In all these locations early workers argued for extensive ice coverage, but subsequent investigations limited the extent and number of glacial advances before more recent work has locally re-extended the glacial limits and greatly increased the number of glacial advances. Similarly, in the highlands of SE Australia the possibility of more pervasive ice coverage was initially entertained; but since the 1960s and especially the 1980s the general consensus is that the lack of glacial evidence is a result of cold dry conditions prevailing for much of the Quaternary on the Australian Alps (Reeves et al. 2013) Recent work by the authors on the extent of relict periglacial block deposits in Australia have identified these block deposits as far north as 29°30'S on the Great Dividing Range, confirming strong freeze-thaw conditions well into the sub-tropics at moderate (900-1200 m) elevations. Curiously, however, the same mapping work has also highlighted the limited development of block deposits and other freeze-thaw landforms, such as tors, in the highest regions of the Australian Alps, in areas beyond the known limits of glaciation. It is also noteworthy that the periglacial features on mainland SE Australia that have absolute ages relate primarily to the last glacial maximum (Barrows et al. 2004). This again contrasts with Tasmania were the periglacial features are both associated with multiple ice ages and are often polygenetic. This presentation reviews geomorphic evidence from two of the highest regions of SE Australia (Bogong High Plains and the Kosciuszko Massif) to determine the extent and nature of cryogenic landscape features in these areas. It will attempt to resolve questions both about the nature of processes operating in these landscapes and add to the debate about the curious paucity of pre-last glacial landscapes at high elevations in SE Australia. References: Barrows, T.T., Stone, J.O., Fifield, L.K. and Cresswell, R.G., 2001. Late Pleistocene glaciation of the Kosciuszko Massif, Snowy Mountains, Australia. Quaternary Research, 55: 179-189 Barrows, T.T., Stone, J. O. and Fifield. L.K, 2004. Exposure ages for Plestocene periglacial deposits in Australia. Quaternary Science Reviews, Vol. 23 (5-6): 697-708 Colhoun, E.A., Kiernan, K., Barrows, T.T. and Geode, A., 2010, Advances in Quaternary studies in Tasmania. Geological Society, London, Special Publications 346:121-139 Glasser, N.F., Jansson, K.N., Harrison, S. and Klenman, J., 2008. The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S. Quaternary Science Reviews 27 (3-4): 365-390 Reeves, J.M., Barrows, T.T., Cohen, T.J., Kiem, A.S., Bostock, H.C., Fitzsimmons, K.E., Jansen, J.D., Kemp, J., Krause, C., Petherick, L. and Phipps, S.J., Climate variability over the last 35,000 years recorded in marine and terrestrial archives in the Australian region: an OZ-INTIMATE compilation. Quaternary Science Reviews 74: 21-34 Shulmeister, J, Thackray, G.D., Rieser, U, Hyatt, O.M, Rother, H., C.C. Smart, and D.J.A. Evans 2010. The stratigraphy, timing and climatic implications of glacilacustrine deposits in the middle Rakaia Valley, South Island, New Zealand. Quaternary Science Reviews 29:2362-2381.

Reduced plant water status under sub-ambient pCO2 limits plant productivity in the wild progenitors of C3 and C4 cereals

PubMed Central

Cunniff, Jennifer; Charles, Michael; Jones, Glynis; Osborne, Colin P.

2016-01-01

Background and Aims The reduction of plant productivity by low atmospheric CO2 partial pressure (pCO2) during the last glacial period is proposed as a limiting factor for the establishment of agriculture. Supporting this hypothesis, previous work has shown that glacial pCO2 limits biomass in the wild progenitors of C3 and C4 founder crops, in part due to the direct effects of glacial pCO2 on photosynthesis. Here, we investigate the indirect role of pCO2 mediated via water status, hypothesizing that faster soil water depletion at glacial (18 Pa) compared to post-glacial (27 Pa) pCO2, due to greater stomatal conductance, feeds back to limit photosynthesis during drying cycles. Methods We grew four wild progenitors of C3 and C4 crops at glacial and post-glacial pCO2 and investigated physiological changes in gas exchange, canopy transpiration, soil water content and water potential between regular watering events. Growth parameters including leaf area were measured. Key Results Initial transpiration rates were higher at glacial pCO2 due to greater stomatal conductance. However, stomatal conductance declined more rapidly over the soil drying cycle in glacial pCO2 and was associated with decreased intercellular pCO2 and lower photosynthesis. Soil water content was similar between pCO2 levels as larger leaf areas at post-glacial pCO2 offset the slower depletion of water. Instead the feedback could be linked to reduced plant water status. Particularly in the C4 plants, soil–leaf water potential gradients were greater at 18 Pa compared with 27 Pa pCO2, suggesting an increased ratio of leaf evaporative demand to supply. Conclusions Reduced plant water status appeared to cause a negative feedback on stomatal aperture in plants at glacial pCO2, thereby reducing photosynthesis. The effects were stronger in C4 species, providing a mechanism for reduced biomass at 18 Pa. These results have added significance when set against the drier climate of the glacial period. PMID:27578764

Paleodust variability since the Last Glacial Maximum and implications for iron inputs to the ocean

NASA Astrophysics Data System (ADS)

Albani, S.; Mahowald, N. M.; Murphy, L. N.; Raiswell, R.; Moore, J. K.; Anderson, R. F.; McGee, D.; Bradtmiller, L. I.; Delmonte, B.; Hesse, P. P.; Mayewski, P. A.

2016-04-01

Changing climate conditions affect dust emissions and the global dust cycle, which in turn affects climate and biogeochemistry. In this study we use observationally constrained model reconstructions of the global dust cycle since the Last Glacial Maximum, combined with different simplified assumptions of atmospheric and sea ice processing of dust-borne iron, to provide estimates of soluble iron deposition to the oceans. For different climate conditions, we discuss uncertainties in model-based estimates of atmospheric processing and dust deposition to key oceanic regions, highlighting the large degree of uncertainty of this important variable for ocean biogeochemistry and the global carbon cycle. We also show the role of sea ice acting as a time buffer and processing agent, which results in a delayed and pulse-like soluble iron release into the ocean during the melting season, with monthly peaks up to ~17 Gg/month released into the Southern Oceans during the Last Glacial Maximum (LGM).

Tropical/Subtropical Peatland Development and Global CH4 during the Last Glaciation.

PubMed

Xu, Hai; Lan, Jianghu; Sheng, Enguo; Liu, Yong; Liu, Bin; Yu, Keke; Ye, Yuanda; Cheng, Peng; Qiang, Xiaoke; Lu, Fengyan; Wang, Xulong

2016-07-28

Knowledge of peatland development over the tropical/subtropical zone during the last glaciation is critical for understanding the glacial global methane cycle. Here we present a well-dated 'peat deposit-lake sediment' alternate sequence at Tengchong, southwestern China, and discuss the peatland development and its linkage to the global glacial methane cycle. Peat layers were formed during the cold Marine Isotope Stage (MIS)-2 and -4, whereas lake sediments coincided with the relatively warm MIS-3, which is possibly related to the orbital/suborbital variations in both temperature and Asian summer monsoon intensity. The Tengchong peatland formation pattern is broadly synchronous with those over subtropical southern China and other tropical/subtropical areas, but it is clearly in contrast to those over the mid-high Northern Hemisphere. The results of this work suggest that the shifts of peatland development between the tropical/subtropical zone and mid-high Northern Hemisphere may have played important roles in the glacial/interglacial global atmospheric CH4 cycles.

Tropical/Subtropical Peatland Development and Global CH4 during the Last Glaciation

PubMed Central

Xu, Hai; Lan, Jianghu; Sheng, Enguo; Liu, Yong; Liu, Bin; Yu, Keke; Ye, Yuanda; Cheng, Peng; Qiang, Xiaoke; Lu, Fengyan; Wang, Xulong

2016-01-01

Knowledge of peatland development over the tropical/subtropical zone during the last glaciation is critical for understanding the glacial global methane cycle. Here we present a well-dated ‘peat deposit-lake sediment’ alternate sequence at Tengchong, southwestern China, and discuss the peatland development and its linkage to the global glacial methane cycle. Peat layers were formed during the cold Marine Isotope Stage (MIS)-2 and -4, whereas lake sediments coincided with the relatively warm MIS-3, which is possibly related to the orbital/suborbital variations in both temperature and Asian summer monsoon intensity. The Tengchong peatland formation pattern is broadly synchronous with those over subtropical southern China and other tropical/subtropical areas, but it is clearly in contrast to those over the mid-high Northern Hemisphere. The results of this work suggest that the shifts of peatland development between the tropical/subtropical zone and mid-high Northern Hemisphere may have played important roles in the glacial/interglacial global atmospheric CH4 cycles. PMID:27465566

Cosmogenic 10Be and 26Al exposure ages of tors and erratics, Cairngorm Mountains, Scotland: Timescales for the development of a classic landscape of selective linear glacial erosion

USGS Publications Warehouse

Phillips, W.M.; Hall, A.M.; Mottram, R.; Fifield, L.K.; Sugden, D.E.

2006-01-01

The occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre-Quaternary landscapes beneath protective covers of non-erosive dry-based ice. Here, we test for the preservation of pre-Quaternary landscapes with cosmogenic surface exposure dating of tors. Numerous granite tors are present on summit plateaus in the Cairngorm Mountains of Scotland where they were covered by local ice caps many times during the Pleistocene. Cosmogenic 10Be and 26Al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected. Many Cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion, leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides. As the surfaces have been subject to episodic burial by ice, an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data. Exposure ages and weathering characteristics of tors are closely correlated. Glacially modified tors and boulder erratics with slightly weathered surfaces have 10Be exposure ages of about 15 to 43 ka. Nuclide inheritance is present in many of these surfaces. Correction for inheritance indicates that the eastern Cairngorms were deglaciated at 15.6 ?? 0.9 ka. Glacially modified tors with moderate to advanced weathering features have 10Be exposure ages of 19 to 92 ka. These surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine Oxygen Isotope Stage 5 or earlier. Tors lacking evidence of glacial modification and exhibiting advanced weathering have 10Be exposure ages between 52 and 297 ka. Nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events. Maximum erosion rates estimated from 10Be range from 2.8 to 12.0 mm/ka, with an error weighted mean of 4.1 ?? 0.2 mm/ka. Three of these surfaces yield model exposure-plus-burial ages of 295-71+84, 520-141+178, and 626-85+102 ka. A vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long-term emergence rate of 31 ?? 2 mm/ka. These findings show that dry-based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes. Bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous (too old) exposure ages. While many Cairngorm tors have survived multiple glacial cycles, rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre-Quaternary rock surfaces. ?? 2005 Elsevier B.V. All rights reserved.

A continuous record of glacial-interglacial cycles spanning more than 500 kyr from Lake Junín, Perú

NASA Astrophysics Data System (ADS)

Rodbell, D. T.; Abbott, M. B.; McGee, D.; Chen, C. Y.; Stoner, J. S.; Hatfield, R. G.; Tapia, P. M.; Bush, M. B.; Weidhaas, N.; Woods, A.; Valero-Garces, B. L.; Lehmann, S. B.; Bustamante, M. G.; Larsen, D. J.

2017-12-01

Lake Junín (11.0°S, 76.2°W) is a shallow (zmax 12 m), intermontane, high-elevation (4080 masl) lake in the inner-tropics of the Southern Hemisphere that spans 300 km2. It is dammed by coalescing alluvial fans that are >250 ka that emanate from glacial valleys. Lake Junín has not been overrun by glacial ice in several hundred thousand years and is ideally located to receive glacigenic sediment. The Junín basin is underlain by carbonate rocks that have provided a source of Ca and HCO3 ions; precipitation of CaCO3 in the western margin of the lake during the present interglacial period has occurred at 1mm yr-1. An airgun seismic survey revealed a strong reflector at 105 meters depth, which marks the base of the lacustrine section. Drilling focused on three sites. Site 1, located near the depocenter and most distal to glacial sources, yielded a composite sediment thickness of 95m; Site 2, proximal to glacial outwash fans, yielded a composite thickness of 28 m; Site 3, located at an intermediate distance yielded a sediment thickness of 55m. The stratigraphy of Site 1 is marked by 8 glacial/interglacial cycles; the latter are characterized by low bulk density and magnetic susceptibility (MS) and high CaCO3. These units are intercalated with glacigenic sediment that has high density and MS, and low CaCO3. The age model for Site 1 is based on AMS radiocarbon dates on terrestrial macrofossils and dozens of U/Th ages on authigenic CaCO3. Strong and protracted interglacial periods appear to be associated with intervals of reduced variability of solar insolation in the Southern Hemisphere tropics. During these intervals there is strong covariation (r2>0.9) between the δ13C and δ18O of authigenic calcium carbonate, and δ18O values are relatively enriched (-12 to -2‰); examples include interglacial periods correlative with marine isotope stages (MIS) 1, 13, and 15. The magnitude of tropical glaciation appears to have been greater during glacial cycles prior to the LGM ( MIS 2-4) and this is consistent with dated moraine sequences in glacial valleys within the Junin basin, but contrasts with the record of global ice volume. Sediment correlative with the LGM at Site 1 is marked by cycles of grain size variability that may be associated with short term variations in glacier mass balance, ablation rates, and/or subglacial plumbing.

Contrasting scaling properties of interglacial and glacial climates

NASA Astrophysics Data System (ADS)

Ditlevsen, Peter; Shao, Zhi-Gang

2017-04-01

Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H˜0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H˜1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. Ref: Zhi-Gang Shao and Peter Ditlevsen, Nature Comm. 7, 10951, 2016

Regional contributions of ocean iron fertilization to atmospheric CO2 changes during the last glacial termination

NASA Astrophysics Data System (ADS)

Opazo, N. E.; Lambert, F.

2017-12-01

Mineral dust aerosols affect climate directly by changing the radiative balance of the Earth, and indirectly by acting as cloud condensation nuclei and by affecting biogeochemical cycles. The impact on marine biogeochemical cycles is primarily through the supply of micronutrients such as iron to nutrient-limited regions of the oceans. Iron fertilization of High Nutrient Low Chlorophyll (HNLC) regions of the oceans is thought to have significantly affected the carbon cycle on glacial-interglacial scales and contributed about one fourth of the 80-100 ppm lowering of glacial atmospheric CO2 concentrations.In this study, we quantify the effect of global dust fluxes on atmospheric CO2 using the cGENIE model, an Earth System Model of Intermediate Complexity with emphasis on the carbon cycle. Global Holocene and Last Glacial Maximum (LGM) dust flux fields were obtained from both dust model simulations and reconstructions based on observational data. The analysis was performed in two stages. In the first instance, we produced 8 global intermediate dust flux fields between Holocene and LGM and simulated the atmospheric CO2 drawdown due to these 10 dust levels. In the second stage, we only changed dust flux levels in specific HNLC regions to isolate the effect of these ocean basins. We thus quantify the contribution of the South Atlantic, the South Pacific, the North Pacific, and the Central Pacific HNLC regions to the total atmospheric CO2 difference due to iron fertilization of the Earth's oceans.

Precession-paced thermocline water temperature changes in response to upwelling conditions off southern Sumatra over the past 300,000 years

NASA Astrophysics Data System (ADS)

Wang, Xingxing; Jian, Zhimin; Lückge, Andreas; Wang, Yue; Dang, Haowen; Mohtadi, Mahyar

2018-07-01

Modern variations of sea surface temperature (SST) and thermocline water temperature (TWT) off southern Sumatra are responding to local upwelling conditions which are controlled by the Australian-Indonesian winter monsoon. The relationships between SST, TWT and upwelling during the past glacial-interglacial cycles are less clearly understood. In this study, SST and TWT variabilities over the past 300 kyr are reconstructed by using foraminiferal Mg/Ca-paleothermometry in sediment core SO139-74 KL off southern Sumatra (6°32.6‧S, 103°50‧E; 1690 m water depth). Whereas SST shows a clear glacial-interglacial cycle, TWT displays a predominant cycle at the precession band. Generally, the TWT record varies with total organic carbon content, revealing that similar to today, TWT and upwelling intensity off southern Sumatra vary in concert during the past 300 kyr. The lack of glacial-interglacial variability in the TWT suggests a limited role of glacial boundary conditions, such as changing sea level and ice volume, on the upwelling intensity in this region. The vertical gradients of upper water δ18O and temperature at this site also reveal precessional cyclicity. Our model simulation of air-sea interaction further supports the low TWTs during periods of enhanced upwelling and precession minimum.

Climate sensitivity derived from orbital-scale, δ11B-based pCO2 estimates in the early Pleistocene, ~1.5 Ma

NASA Astrophysics Data System (ADS)

Dyez, K. A.; Hoenisch, B.

2015-12-01

Atmospheric CO2 concentrations in the late Pleistocene have been characterized from ancient air bubbles trapped within polar ice sheets. Ice-core records clearly demonstrate the glacial-interglacial relationship between the global carbon cycle and climate, but they are so far limited to the last 800 ky, when glacial cycles occurred approximately every 100-ky. Boron isotope ratios (δ11B) recorded in the tests of fossil planktic foraminifera offer an opportunity to extend the atmospheric pCO2 record into the early Pleistocene, when glacial cycles instead occurred approximately every 41-ky. We present a new high-resolution record of planktic foraminiferal d11B, Mg/Ca (a sea surface temperature proxy) and salinity estimates from the deconvolution of δ18O and Mg/Ca. Combined with reasonable assumptions of ocean alkalinity, these data allow us to estimate pCO2 over three of the 41-ky climate cycles at ~1.5 Ma. Our results confirm the hypothesis that climate and atmospheric pCO2 were coupled beyond ice core records and provide new constraints for studies of long-term CO2 storage and release, regional controls on the early Pleistocene carbon cycle, and estimating climate sensitivity before the mid-Pleistocene transition.

Marked genetic divergence among sky island populations of Sedum lanceolatum (Crassulaceae) in the Rocky Mountains.

PubMed

Dechaine, Eric G; Martin, Andrew P

2005-03-01

Climate change during the Quaternary played an important role in the differentiation and evolution of plants. A prevailing hypothesis is that alpine and arctic species survived glacial periods in refugia at the periphery of glaciers. Though the Rocky Mountains, south of the southernmost extent of continental ice, served as an important glacial refuge, little is known about how climate cycles influenced populations within this region. We inferred the phylogeography of Sedum lanceolatum (Crassulaceae) within the Rocky Mountain refugium to assess how this high-elevation plant responded to glacial cycles. We sequenced 884 base pairs (bp) of cpDNA intergenic spacers (tRNA-L to tRNA-F and tRNA-S to tRNA-G) for 333 individuals from 18 alpine populations. Our highly variable markers allowed us to infer that populations persisted across the latitudinal range throughout the climate cycles, exhibited significant genetic structure, and experienced cycles of range expansion and fragmentation. Genetic differentiation in S. lanceolatum was most likely a product of short-distance elevational migration in response to climate change, low seed dispersal, and vegetative reproduction. To the extent that Sedum is a good model system, paleoclimatic cycles were probably a major factor preserving genetic variation and promoting divergence in high-elevation flora of the Rocky Mountains.

Quaternary Glacial Mapping in Western Wisconsin Using Soil Survey Information

ERIC Educational Resources Information Center

Oehlke, Betsy M.; Dolliver, Holly A. S.

2011-01-01

The majority of soils in the western Wisconsin have developed from glacial sediments deposited during the Quaternary Period (2.6 million years before present). In many regions, multiple advances and retreats have left a complex landscape of diverse glacial sediments and landforms. The soils that have developed on these deposits reflect the nature…

Orbital-scale Central Arctic Ocean Temperature Records from Benthic Foraminiferal δ18O and Ostracode Mg/Ca Ratios

NASA Astrophysics Data System (ADS)

Keller, K.; Cronin, T. M.; Dwyer, G. S.; Farmer, J. R.; Poirier, R. K.; Schaller, M. F.

2017-12-01

Orbital-scale climate variability is often amplified in the polar region, for example in changes in seawater temperature, sea-ice cover, deep-water formation, ecosystems, heat storage and carbon cycling. Yet, the relationship between the Arctic Ocean and global climate remains poorly understood due largely to limited orbital-scale paleoclimate records, the complicated nature of sea-ice response to climate and limited abundance of deep sea biological proxies. Here we reconstruct central Arctic Ocean bottom temperatures over the last 600 kyr using ostracode Mg/Ca ratios (genus Krithe) and benthic foraminiferal oxygen isotope ratios (δ18Obf - I. teretis, O. tener, P. bulloides, C. reniforme, C. wuellerstorfi) in six sediment cores recovered from the Mendeleev and Northwind Ridges (700- 2726 m water depth). We examined glacial-interglacial cycles in Arctic seawater temperatures and Arctic δ18Obf chronostratigraphy to reconcile effects of changing bottom water temperature, ice volume and regional hydrography on δ18Obf records. Results show lower ( 10-12 mmol/mol) interglacial and higher ( 16-23 mmol/mol) glacial Mg/Ca ratios, signifying intermediate depth ocean warming during glacials of up to 2 ºC. These temperature maxima are likely related to a deepening of the halocline and the corresponding deeper influence of warm Atlantic water. Glacial-interglacial δ18Obf ranges are smaller in the Arctic ( 0.8-1‰ VPDB) than in the global ocean ( 1.8 ‰). However, when the distinct glacial-interglacial temperature histories of the Arctic (glacial warming) and global ocean (glacial cooling) are accounted for, both Arctic and global ocean seawater δ18O values (δ18Osw) exhibit similar 1.2-1.3 ‰ glacial-interglacial ranges. Thus, Arctic δ18Obf confirms glacial Arctic warming inferred from ostracode Mg/Ca. This study will discuss the strengths and limitations of applying paired Mg/Ca and oxygen isotope proxies in reconstructing more robust paleoceanographic changes in the Arctic Ocean.

The SE sector of the Middle Weichselian Eurasian Ice Sheet was much smaller than assumed

NASA Astrophysics Data System (ADS)

Räsänen, Matti E.; Huitti, Janne V.; Bhattarai, Saroj; Harvey, Jerry; Huttunen, Sanna

2015-08-01

Quaternary climatic and glacial history must be known in order to understand future environments. Reconstructions of the last Weichselian glacial cycle 117,000-11,700 years (kyr) ago propose that S Finland, adjacent Russia and the Baltic countries in the SE sector of the Eurasian Ice Sheet (EIS), were glaciated during the Middle Weichselian time [marine isotope stage (MIS) 4, 71-57 kyr ago] and that this glaciation was preceded in S Finland by an Early Weichselian interstadial (MIS 5c, 105-93 kyr ago) with pine forest. We apply glacial sequence stratigraphy to isolated Late Pleistocene onshore outcrop sections and show, that these events did not take place. The one Late Weichselian glaciation (MIS 2, 29-11 kyr ago) was preceded in S Finland by a nearly 90 kyr non-glacial period, featuring tundra with permafrost and probably birch forest. Our new Middle Weichselian paleoenvironmental scenario revises the configuration and hydrology of the S part of EIS and gives new setting for the evolution of Scandinavian biota. If future development during the coming glacial cycle proves to be similar, the high-level nuclear waste stored in the bedrock of SW Finland should be located deeper than currently planned, i.e. below any possible future permafrost.

The Lake Towuti Drilling Project: A New, 1-Million Year Record of Indo-Pacific Hydroclimate

NASA Astrophysics Data System (ADS)

Russell, J. M.; Bijaksana, S.; Vogel, H.; Melles, M.; Crowe, S.; Fajar, S. J.; Hasberg, A. K.; Ivory, S.; Kallmeyer, J.; Kelly, C. S.; Kirana, K. H.; Morlock, M.; Tamuntuan, G. H.; Wicaksono, S. A.

2015-12-01

­The Indo-Pacific region plays an integral role in the Earth's climate system. Changes in local insolation, greenhouse gas concentrations, ice volume, and local sea level are each hypothesized to exert a dominant control on Indo-Pacific hydroclimate variations through the Pleistocene, yet existing records from the region are generally short and exhibit fundamental differences in orbital-scale patterns that limit our understanding of the regional climate responses to these global forcings. New paleoclimate records spanning multiple glacial-interglacial cycles are therefore required to document the region's hydroclimatic response to the full range of global climate boundary conditions observed during the late Quaternary. Lake Towuti is located in central Indonesia and is the only known terrestrial sedimentary archive in the region that spans multiple glacial-interglacial cycles. From May - July, 2015, the Towuti Drilling Project, consisting of nearly 40 scientists from eight countries, recovered over 1,000 meters of new sediment core from Lake Towuti. This includes cores though the entire sediment column to bedrock, which likely provide a >1-million-year records of regional hydroclimate. On-site borehole and sediment core logging data document major shifts in sediment composition, including transitions from lake clays to peats, calcareous sediments, and gravels. These data show excellent agreement with major lithological transitions recorded in seismic reflection data, and indicate large changes in lake levels and hydroclimate through the late Quaternary. Prior work on Lake Towuti indicated a dominant control by global ice volume on regional hydroclimate, a hypothesis we aim to test through the analysis of these new cores. This presentation will review existing records from the region and show the first long geochemical and sedimentological records from Lake Towuti to understand orbital-scale hydrologic change during the last ~1 million years.

Reconstructing Deep Ocean Circulation in the North Atlantic from Bermuda Rise, and Beyond

NASA Astrophysics Data System (ADS)

McManus, J. F.

2016-12-01

The large-scale subsurface circulation of the ocean is an important component of the Earth's climate system, and contributes to the global and regional transport of heat and mass. Assessing how this system has changed in the past is thus a priority for understanding natural climate variability. A long-coring campaign on Bermuda Rise has provided additional abundant high-quality sediments from this site of rapid accumulation in the deep western basin, situated beneath the subtropical gyre of the North Atlantic Ocean. These sediments allow the high-resolution reconstruction of deepwater chemistry and export from this key location throughout the last 150,000 years, covering the entire last glacial cycle in a continuous section of 35 meters in core KNR191-CDH19. The suite of proxy indicators analyzed includes uranium-series disequilibria, neodymium isotopes, and benthic stable isotopes. Combined with multiple previous studies of nearby cores on Bermuda Rise, the published and new proxy data from CDH19 confirm the variability of the deep circulation in the Atlantic Ocean in association with past climate changes. The multiple indicators, along with complementary data from other locations, display coherent evidence for contrasts between deep circulation during glacial and interglacial intervals, with persistent strong, deep ventilation only within the peak interglacial of marine isotope stage 5e (MIS 5e) and the Holocene. In contrast, repeated, dramatic variability in deep ocean circulation accompanied the millennial climate changes of the last glaciation and deglaciation. The largest magnitude circulation shifts occurred at the transitions into stadials associated with the Hudson strait iceberg discharges and between them and the ensuing northern interstadial warmings, significantly exceeding that of the overall glacial-interglacial difference, highlighting the potential oceanographic and climatic importance of short-term perturbations to the deep ocean circulation.

Lithologic composition and rock weathering potential of forested, glacial-till soils

Treesearch

Scott W. Bailey; James W. Hornbeck; James W. Hornbeck

1992-01-01

Describes methods for predicting lithologies present in soils developed on glacial till, and the potential weathering contributions from rock particles >2 mm in diameter. The methods are not quantitative in terms of providing weathering rates, but provide information that can further the understanding of forest nutrient cycles, and possibly assist with decisions...

Methane release from the southern Brazilian margin during the last glacial.

PubMed

Portilho-Ramos, R C; Cruz, A P S; Barbosa, C F; Rathburn, A E; Mulitza, S; Venancio, I M; Schwenk, T; Rühlemann, C; Vidal, L; Chiessi, C M; Silveira, C S

2018-04-13

Seafloor methane release can significantly affect the global carbon cycle and climate. Appreciable quantities of methane are stored in continental margin sediments as shallow gas and hydrate deposits, and changes in pressure, temperature and/or bottom-currents can liberate significant amounts of this greenhouse gas. Understanding the spatial and temporal dynamics of marine methane deposits and their relationships to environmental change are critical for assessing past and future carbon cycle and climate change. Here we present foraminiferal stable carbon isotope and sediment mineralogy records suggesting for the first time that seafloor methane release occurred along the southern Brazilian margin during the last glacial period (40-20 cal ka BP). Our results show that shallow gas deposits on the southern Brazilian margin responded to glacial-interglacial paleoceanographic changes releasing methane due to the synergy of sea level lowstand, warmer bottom waters and vigorous bottom currents during the last glacial period. High sea level during the Holocene resulted in an upslope shift of the Brazil Current, cooling the bottom waters and reducing bottom current strength, reducing methane emissions from the southern Brazilian margin.

Antarctic Ocean Nutrient Conditions During the Last Two Glacial Cycles

NASA Astrophysics Data System (ADS)

Studer, A.; Sigman, D. M.; Martinez-Garcia, A.; Benz, V.; Winckler, G.; Kuhn, G.; Esper, O.; Lamy, F.; Jaccard, S.; Wacker, L.; Oleynik, S.; Gersonde, R.; Haug, G. H.

2014-12-01

The high concentration of the major nutrients nitrate and phosphate in the Antarctic Zone of the Southern Ocean dictates the nature of Southern Ocean ecosystems and permits these nutrients to be carried from the deep ocean into the nutrient-limited low latitudes. Incomplete nutrient consumption in the Antarctic also allows the leakage of deeply sequestered carbon dioxide (CO2) back to the atmosphere, and changes in this leakage may have driven glacial/interglacial cycles in atmospheric CO2. In a sediment core from the Pacific sector of the Antarctic Ocean, we report diatom-bound N isotope (δ15Ndb) records for total recoverable diatoms and two assemblages of diatom species. These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ15Ndb (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Measurements in the same sediment core indicate that export production was reduced during ice ages, pointing to an ice age reduction in the supply of deep ocean-sourced nitrate to the Antarctic Ocean surface. The reduced export production of peak ice ages also implies a weaker winter-to-summer decline (i.e. reduced seasonality) in mixed layer nitrate concentration, providing a plausible explanation for an observed reduction in the inter-assemblage δ15Ndb difference during these coldest times. Despite the weak summertime productivity, the reduction in wintertime nitrate supply from deep waters left the Antarctic mixed layer with a low nitrate concentration, and this wintertime change also would have reduced the outgassing of CO2. Relief of light limitation fails to explain the intermediate degree of nitrate consumption that characterizes early glacial conditions, as improved light limitation coincident with reduced nitrate supply would drive nitrate consumption to completion. Thus, the data favor iron availability as the dominant control on annual Antarctic Ocean export production over glacial cycles.

Methane Hydrate Formation from Enhanced Organic Carbon Burial During Glacial Lowstands: Examples from the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A.; Daigle, H.; Oryan, B.

2017-12-01

Methane hydrates in fine-grained marine sediments are often found within veins and fractures occupying discrete depth intervals that are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the methane hydrate stability zone (MHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. We investigate here the hypothesis that these hydrate deposits form in sediments that were deposited during glacial lowstands and contain higher amounts of labile particulate organic carbon (POC), leading to enhanced microbial methanogenesis. During Pleistocene lowstands, river loads are deposited near the steep top of the continental slope and turbidity currents transport organic-rich, fine-grained sediments to deep waters. Faster sedimentation rates during glacial periods result in better preservation of POC because of decreased exposure times to oxic conditions. The net result is that more labile POC enters the methanogenic zone and more methane is generated in these sediments. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent deposition of labile POC at the seafloor controlled by glacioeustatic sea level variations in the last 250 kyr. The model is run for parameters estimated at three sites drilled by the 2009 Gulf of Mexico Joint Industry Project: Walker Ridge in the Terrebonne Basin (WR313-G and WR313-H) and Green Canyon near the canyon embayment into the Sigsbee Escarpment (GC955-H). In the model, gas hydrate forms in sediments with higher labile POC content deposited during the glacial cycle between 230 and 130 kyr (marine isotope stages 6 and 7). The corresponding depth intervals in the three sites contain hydrates, as shown by high bulk electrical resistivities and resistive subvertical fracture fills. This match supports the hypothesis that enhanced POC burial during glacial lowstands can result in hydrate formation from in situ microbial methanogenesis. Our results have implications for carbon cycling during glacial/interglacial cycles and for hydrate accumulation in the MHSZ. In particular, once hydrate-bearing intervals formed during glacial periods are buried beneath the MHSZ and dissociate, gas bubbles can rise and recycle microbial methane into the MHSZ.

Explosive ice age diversification of kiwi.

PubMed

Weir, Jason T; Haddrath, Oliver; Robertson, Hugh A; Colbourne, Rogan M; Baker, Allan J

2016-09-20

Molecular dating largely overturned the paradigm that global cooling during recent Pleistocene glacial cycles resulted in a burst of species diversification although some evidence exists that speciation was commonly promoted in habitats near the expanding and retracting ice sheets. Here, we used a genome-wide dataset of more than half a million base pairs of DNA to test for a glacially induced burst of diversification in kiwi, an avian family distributed within several hundred kilometers of the expanding and retracting glaciers of the Southern Alps of New Zealand. By sampling across the geographic range of the five kiwi species, we discovered many cryptic lineages, bringing the total number of kiwi taxa that currently exist to 11 and the number that existed just before human arrival to 16 or 17. We found that 80% of kiwi diversification events date to the major glacial advances of the Middle and Late Pleistocene. During this period, New Zealand was repeatedly fragmented by glaciers into a series of refugia, with the tiny geographic ranges of many kiwi lineages currently distributed in areas adjacent to these refugia. Estimates of effective population size through time show a dramatic bottleneck during the last glacial cycle in all but one kiwi lineage, as expected if kiwi were isolated in glacially induced refugia. Our results support a fivefold increase in diversification rates during key glacial periods, comparable with levels observed in classic adaptive radiations, and confirm that at least some lineages distributed near glaciated regions underwent rapid ice age diversification.

Soil profile of Yellow-brown Earth overlying Red Clay in southern Anhui Province: A pedogenic response to the Last Glacial - Interglacial cycle in mid-subtropical China

NASA Astrophysics Data System (ADS)

Hu, Xue-Feng; Du, Yan

2013-04-01

Soil profile of Yellow-brown Earth (YBE) overlying Red Clay (RC) is commonly seen along the Yangtze River in mid-subtropical China. To study its paleoclimatic implications, one YBE - RC profile in Langxi county, southern Anhui Province, were dated with the optically stimulated luminescence (OSL) method in detail. The results indicated that the dual - layered profile is actually a pedogenic response to a great climatic change during the Last Glacial - Last Interglacial cycle: The YBE is homogenous to the aeolian Xiashu Loess widely distributed along the Yangtze River and was dated from 12.2 ka to 57.1 ka; and the underlying RC approximately from 60 ka to 132.8 ka, which fully suggests that the YBE is really the Last Glacial loess, correlated with the Malan Loess in the Chinese Loess Plateau, Northwest China, and the RC was mainly formed during the Last Interglacial. Two sub-class events of the Last Glacial, the Last Glacial Maximum (LGM) and the Last Glacial Optimum (LGO), correlated with the marine oxygen isotopic stage (MIS) 2 and 3, can be separated and identified in the YBE. Likewise, the RC can be divided into the Uniform Red Clay (URC) and Reticulate Red Clay (RRC). The URC was formed during the transitional time from the Last Interglacial to the Last Glacial, and the RRC mainly during the Last Interglacial, MIS 5. The RC is highly weathered but still shows aeolian-dust characteristics. The duplicate information implies that the paleoclimate during the Last Interglacial is instable and might also oscillate between warm and cold, but sub-class paleoclimatic events, potential correlated with MIS 5 a - 5 e, cannot be identified in the RRC possibly due to the overlapped paleoclimatic information caused by highly chemical weathering. A great climatic transfer during the Last Glacial - Interglacial cycle left soil parent materials diversified in the study areas and hence caused the parallel distribution of different zonal soils in a small scale. Two surface soils, Yellow-brown Soils (Acrisols), derived from the YBE, and Red Soils (Plinthosols), derived from the RC, often coexist in the areas. The Red Soils are really relict and not correlated with the current soil-forming conditions. Sometimes, the influence of climatic change on the pedogenesis is so significant that it should never be neglected.

Orbital Drivers of Climate Change on Earth and Mars

NASA Astrophysics Data System (ADS)

Zent, A. P.

Oscillations of orbital elements and spin axis orientation affect the climate of both Earth and Mars by redistributing solar power both latitudinally and seasonally, often resulting in secondary changes in reflected and emitted radiation (radiative forcing). Multiple feedback loops between different climatic elements operate on both planets, with the result that climate response is generally nonlinear with simple changes in solar energy. Both insolation history and geochemical climate proxies can be treated as time series data, and analyzed in terms of component frequencies. The correspondence between frequencies measured in climate proxies and orbital oscillations is the key to relating orbital cause and climatic effect. Discussions of both Earth and Mars focus on the last 5-10 m.y., because this is the period in which the orbital history and geologic record are best understood. The terrestrial climate is an extraordinarily complex system, and a vast amount of data is available for analysis. While the geologic record strongly supports the role of Milankovitch cycles as the underlying cause of glacial cycles, orbitally driven insolation changes alone cannot explain the observations in detail. Early Pleistocene glacial cycles responded linearly to the 41-k.y. oscillations in obliquity. However, over the last 1 m.y., glacial/interglacial oscillations have become more extreme as the climate has cooled. Long cooling intervals marked by an oscillating buildup of ice sheets are now followed by brief, intense periods of warming. At the same time, glacial/interglacial cycles have shifted from 41 k.y. to ~100 k.y. No such changes occurred in the solar forcing due to orbital oscillations. While orbital oscillations still appear to pace glacial cycles, their subtle interplay with ice-sheet dynamics and shifts in ocean circulation have come to dominate the late Pleistocene climate system. In contrast to Earth, the martian climate is ostensibly a much simpler system about which we have almost no quantitative data. Lacking climate proxies and chronological data, we are forced to rely on climate modeling and whatever constraints can be extracted from the predominantly remote sensing data available. Obliquity oscillations account for most of the power in historical insolation. Unfortunately, the last 5 m.y. are an anomalous period in Mars' climate history due to a secular decrease in Mars' obliquity. Subsequent to that, however, models and observations are consistent with the hypothesis that during periods of higher obliquity, enhanced polar summer insolation increases atmospheric water vapor and dust content, and ice stability shifted toward the equator. Polar caps become thermodynamically unstable, and much of the surface H2O inventory migrates from high latitudes to the tropics. As obliquity decreases, ice returns to the poles, leaving unstable ice-rich deposits in the mid latitudes that are mantled by dust. Low-obliquity periods entail — at least on occasion — collapse of the atmosphere onto the poles and high-latitude CO2 glaciers. During protracted nodes in obliquity, mid-latitude ice undergoes slow but sustained sublimation and redistribution to the poles. Because of the tremendous breadth of the subject matter, this chapter necessarily presents a high-level overview, and the reader will be compelled to investigate the copious references for a more rigorous explanation of most topics.

Reconstructing the Mineralogy and Bioavailability of Dust-Borne Iron Deposited to the Southern Ocean through the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Shoenfelt, E. M.; Winckler, G.; Lamy, F.; Bostick, B. C.

2017-12-01

The iron (Fe) in dust deposited to the Fe-limited Southern Ocean plays an important role in ocean biogeochemistry and global climate. For instance, increases in dust-borne Fe deposition in the subantarctic Southern Ocean have been linked to increases in productivity and part of the CO2 drawdown of the last glacial cycle [1]. Notably, bioavailable Fe impacts productivity rather than total Fe. While it has long been understood that Fe mineralogy impacts Fe bioavailability in general, our understanding of the mineralogy of Fe in dust in specific is limited to that in modern dust sources. Reduced mineral Fe in dust has been shown to be more bioavailable than oxidized mineral iron, as it is more readily dissolved [2], and it is more easily utilized directly by a model diatom [3]. Our previous work focusing on South American dust sources shows that glacial activity is associated with higher Fe(II) fractions in dust-borne minerals, due to the physical weathering of Fe(II)-rich silicates in bedrock [3]. Thus, we hypothesize that there were higher Fe(II) fractions in dust deposited during cold glacial periods where ice sheets were more widespread. Using synchrotron-based X-ray absorption spectroscopy, we have reconstructed the mineralogy of Fe deposited to Southern Ocean sediment cores from the subantarctic South Atlantic (TN057-6/ODP Site 1090) and South Pacific (PS7/56-1) through the last glacial cycle, creating the first paleorecord of Fe mineralogy and its associated bioavailability. During cold glacial periods there is a higher fraction of reduced Fe - in the form of Fe(II) silicates - deposited to the sediments compared to warm interglacial periods. Thus, Fe(II) content is directly correlated with dust input. The presence of Fe(II) silicates rather than products of diagenesis such as pyrite suggests that these Fe(II) minerals are physically weathered from bedrock and preserved rather than produced in the sediment. This result suggests that not only was there more dust and Fe deposited to the Southern Ocean during glacial periods, glacial Fe was also more bioavailable due to the importance of glacial activity to high latitude dust formation. [1] A. Martinez-Garcia et al., Science 343 (2014). [2] A. W. Schroth et al., Nat. Geosci. 2 (2009). [3] E. M. Shoenfelt et al., Sci. Adv. 3(6), DOI:10.1126/sciadv.1700314 (2017).

Interplay between climatic and tectonic processes in the St. Elias foreland, southern Alaska: Evolution of a glaciated convergent margin since the mid-Pleistocene

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Gulick, S. P.; Ridgway, K. R.; Jaeger, J. M.; Cowan, E. A.; Slagle, A. L.; Forwick, M.

2013-12-01

The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Ongoing collision of the Yakutat (YAK) microplate with North America (NA) has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. The sub-seafloor architecture of the Bering Trough region is defined by a regional unconformity that marks the first glacial advance to the shelf edge. Below the unconformity, the shelf is constructed by multiple aggradational packages that are likely a series of pro-glacial outer shelf/slope fans. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), all of which is younger than 0.781 Ma. Preliminary age models for the Bering Trough region indicate that the entire outer shelf and shelf edge environment have been built since the Mid-Pleistocene Transition (MPT), and is possibly even younger. In stark contrast to previous interpretations, the shelf environment, in addition to the proximal deep-sea fan system, appears to be a primary glacial depocenter since the MPT, with an average accumulation rate >1.3 mm/yr. Additionally, initiation of active deformation away from the Bering Trough depocenter likely occurred since ~1 Ma. These observations suggest that possible tectonic reorganization due to mass redistribution by glacial processes occurs at time scales on the order of 100kyr-1Myr. It follows that the St. Elias orogenic system may be more sensitive to glacial-interglacial cycles than previously recognized.

Out of the tropics: the Pacific, Great Basin lakes, and late Pleistocene water cycle in the western United States

USGS Publications Warehouse

Lyle, Mitchell; Heusser, Linda; Ravelo, Christina; Yamamoto, Masanobu; Barron, John; Diffenbaugh, Noah S.; Herbert, Timothy; Andreasen, Dyke

2012-01-01

The water cycle in the western U.S. changed dramatically over glacial cycles. In the last 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation is hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.

Out of the tropics: the Pacific, Great Basin lakes, and late Pleistocene water cycle in the western United States.

PubMed

Lyle, Mitchell; Heusser, Linda; Ravelo, Christina; Yamamoto, Masanobu; Barron, John; Diffenbaugh, Noah S; Herbert, Timothy; Andreasen, Dyke

2012-09-28

The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.

Geomorphical and Geochronological Constrains of the Last Glacial Period in Southern Patagonia, Southern South America

NASA Astrophysics Data System (ADS)

García, J.; Hall, B. L.; Kaplan, M. R.; Vega, R. M.; Binnie, S. A.; Hein, A.; Gómez, G. N.; Ferrada, J. J.

2013-12-01

Despite the outer limits of the former Patagonian ice sheet (PIS, ~38-55S) having been extensively mapped, it remains unknown if the Patagonian glaciers fluctuated synchronously or asynchronously during the last glacial period. Previous work has revealed asynchronous spatiotemporal ice dynamics along the eastern and western ice-margins at the end of the last glaciation but it is not well understood if the northern and southern parts of the PIS reached concurrent maximum glaciation during the last glacial cycle. The Patagonian Andes is the only landmass involving the southern westerly wind belt latitudinal range, which is thought to have played a key role in past glacial and climate changes. Therefore, reconstructing southern Andes glacier history constitutes a key element for understanding the cause of glaciations in Patagonia and the role of the westerlies in climate change. Here, we discuss paleoglaciological and paleoclimatological implications of new 10Be and 14C data obtained from moraines and strategically selected mires in two contiguous glacially molded basins of south Patagonia (48-55S): Torres del Paine (51S) and Última Esperanza (52S). In this region, we focused our 10Be cosmogenic-dating efforts in the previously undated outer moraines deposited (supposedly) during the last glacial cycle. In order to crosscheck cosmogenic data we collected boulders embedded in moraines and cobbles from the main glaciofluvial plains grading from the outermost moraines. Geomorphic and cosmogenic dating affords evidence for glacial maximum conditions occurring between 40-50 ka (ka = thousand of years before present) in southern Patagonia, which is different from other chronologies within southern South America. We obtained 14C basal ages from sites located within moraine depressions and on former paleolake shorelines and thus these may provide key data on deglaciation and debated regional paleolake history.

Critical insolation-CO2 relation for diagnosing past and future glacial inception.

PubMed

Ganopolski, A; Winkelmann, R; Schellnhuber, H J

2016-01-14

The past rapid growth of Northern Hemisphere continental ice sheets, which terminated warm and stable climate periods, is generally attributed to reduced summer insolation in boreal latitudes. Yet such summer insolation is near to its minimum at present, and there are no signs of a new ice age. This challenges our understanding of the mechanisms driving glacial cycles and our ability to predict the next glacial inception. Here we propose a critical functional relationship between boreal summer insolation and global carbon dioxide (CO2) concentration, which explains the beginning of the past eight glacial cycles and might anticipate future periods of glacial inception. Using an ensemble of simulations generated by an Earth system model of intermediate complexity constrained by palaeoclimatic data, we suggest that glacial inception was narrowly missed before the beginning of the Industrial Revolution. The missed inception can be accounted for by the combined effect of relatively high late-Holocene CO2 concentrations and the low orbital eccentricity of the Earth. Additionally, our analysis suggests that even in the absence of human perturbations no substantial build-up of ice sheets would occur within the next several thousand years and that the current interglacial would probably last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at least 100,000 years. Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time.

Similar millennial climate variability on the Iberian margin during two early Pleistocene glacials and MIS 3

NASA Astrophysics Data System (ADS)

Birner, B.; Hodell, D. A.; Tzedakis, P. C.; Skinner, L. C.

2016-01-01

Although millennial-scale climate variability (<10 ka) has been well studied during the last glacial cycles, little is known about this important aspect of climate in the early Pleistocene, prior to the Middle Pleistocene Transition. Here we present an early Pleistocene climate record at centennial resolution for two representative glacials (marine isotope stages (MIS) 37-41 from approximately 1235 to 1320 ka) during the "41 ka world" at Integrated Ocean Drilling Program Site U1385 (the "Shackleton Site") on the southwest Iberian margin. Millennial-scale climate variability was suppressed during interglacial periods (MIS 37, MIS 39, and MIS 41) and activated during glacial inceptions when benthic δ18O exceeded 3.2‰. Millennial variability during glacials MIS 38 and MIS 40 closely resembled Dansgaard-Oeschger events from the last glacial (MIS 3) in amplitude, shape, and pacing. The phasing of oxygen and carbon isotope variability is consistent with an active oceanic thermal bipolar see-saw between the Northern and Southern Hemispheres during most of the prominent stadials. Surface cooling was associated with systematic decreases in benthic carbon isotopes, indicating concomitant changes in the meridional overturning circulation. A comparison to other North Atlantic records of ice rafting during the early Pleistocene suggests that freshwater forcing, as proposed for the late Pleistocene, was involved in triggering or amplifying perturbations of the North Atlantic circulation that elicited a bipolar see-saw response. Our findings support similarities in the operation of the climate system occurring on millennial time scales before and after the Middle Pleistocene Transition despite the increases in global ice volume and duration of the glacial cycles.

Effects of mantle rheologies on viscous heating induced by Glacial Isostatic Adjustment

NASA Astrophysics Data System (ADS)

Huang, PingPing; Wu, Patrick; van der Wal, Wouter

2018-04-01

It has been argued that viscous dissipation from mantle flow in response to surface loading during glacial cycles can result in short-term heating and thus trigger transient volcanism or changes in mantle properties, which may in turn affect mantle dynamics. Furthermore, heating near the Earth's surface can also affect the stability of ice sheets. We have studied the magnitude and spatial-temporal distribution of viscous heating induced in the mantle by the realistic ice model ICE-6G and gravitationally consistent ocean loads. Three types of mantle rheologies, including linear, non-linear and composite rheologies are considered to see if non-linear creep can induce larger viscous heating than linear rheology. We used the Coupled-Laplace-Finite-Element model of Glacial Isostatic Adjustment (GIA) to compute the strain, stress and shear heating during a glacial cycle. We also investigated the upper bound of temperature change and surface heat flux change due to viscous heating. We found that maximum viscous heating occurs near the end of deglaciation near the edge of the ice sheet with amplitude as high as 120 times larger than that of the chondritic radioactive heating. The maximum heat flux due to viscous heating can reach 30 mW m-2, but the area with large heat flux is small and the timescale of heating is short. As a result, the upper bound of temperature change due to viscous heating is small. Even if 30 glacial cycles are included, the largest temperature change can be of the order of 0.3 °C. Thus, viscous heating induced by GIA cannot induce volcanism and cannot significantly affect mantle material properties, mantle dynamics nor ice-sheet stability.

Seasonality intensification and long-term winter cooling as a part of the Late Pliocene climate development

NASA Astrophysics Data System (ADS)

Klotz, Stefan; Fauquette, Séverine; Combourieu-Nebout, Nathalie; Uhl, Dieter; Suc, Jean-Pierre; Mosbrugger, Volker

2006-01-01

A mutual climatic range method is applied to the Mediterranean marine pollen record of Semaforo (Vrica section, Calabria, Italy) covering the period from ∼2.46 Ma to ∼2.11 Ma. The method yields detailed information on summer, annual and winter temperatures and on precipitation during the nine obliquity and precession-controlled 'glacial' periods (marine isotope stages 96 to 80) and eight 'interglacial' periods (marine isotope stages 95 to 81) characterising this time interval. The reconstruction reveals higher temperatures of at least 2.8 °C in mean annual and 2.2 °C in winter temperatures, and 500 mm in precipitation during the 'interglacials' as compared to the present-day climate in the study area. During the 'glacials', temperatures are generally lower as compared to the present-day climate in the region, but precipitation is equivalent. Along the consecutive 'interglacials', a trend toward a reduction in annual and winter temperatures by more than 2.3 °C, and toward a higher seasonality is observed. Along the consecutive 'glacials', a trend toward a strong reduction in all temperature parameters of at least 1.6 °C is reconstructed. Climatic amplitudes of 'interglacial-glacial' transitions increase from the older to the younger cycles for summer and annual temperatures. The cross-spectral analyses suggest obliquity related warm/humid-cold/dry 'interglacial-glacial' cycles which are superimposed by precession related warm/dry- cold/humid cycles. A time displacement in the development of temperatures and precipitation is indicated for the obliquity band by temperatures generally leading precipitation change at ∼4 kyr, and on the precession band of ∼9.6 kyr in maximum.

Trends in stomatal density and 13C/12C ratios of Pinus flexilis needles during last glacial-interglacial cycle

USGS Publications Warehouse

Van De Water, Peter K.; Leavitt, Steven W.; Betancourt, J.L.

1994-01-01

Measurements of stomatal density and ?? 13C of limber pine (Pinus flexilis) needles (leaves) preserved in pack rat middens from the Great Basin reveal shifts in plant physiology and leaf morphology during the last 30,000 years. Sites were selected so as to offset glacial to Holocene climatic differences and thus to isolate the effects of changing atmospheric CO2 levels. Stomatal density decreased ~17 percent and ?? 13C decreased ~1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO2. Water-use efficiency increased ~15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO2 and ?? 13C of past atmospheres are accurate. The ??13C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and biosphere during the last glacial-interglacial cycle.

The history of Antarctic Peninsula glaciation

USGS Publications Warehouse

Barker, Peter F.

2007-01-01

As Co-Chief Scientist on DSDP Leg 35 in 1974, Cam Craddock (1930-2006) produced the first useful information on Cenozoic Antarctic Peninsula glaciation - an early middle Miocene (15-17 Ma) apparent glacial onset. Subsequent work, onshore and offshore, has greatly extended our knowledge but that early conclusion stands today. Cenozoic Antarctic Peninsula palaeoclimate as presently known is broadly consistent with global palaeoclimate proxies. Initial glacial onset was within the Eocene-Oligocene boundary interval (although earlier, short-lived glaciations have been proposed, from indirect measurements) and the peninsula probably became deglaciated in the earliest Miocene (ca. 24 Ma). The renewed middle Miocene glaciation probably continued to the present and, for the last 9 Myr at least, has persisted through glacial (orbital) cycles, with grounded ice advance to the shelf edge during maxima. Although orbital cyclicity affected earlier AP palaeoclimate also, the level of glaciation through a complete cycle is uncertain.

New chronological data for the timing of the Saalian- and Elsterian glacial cycle in Europe - studies on a key site within the type area

NASA Astrophysics Data System (ADS)

Lauer, Tobias; Weiß, Marcel; Wansa, Stefan

2017-04-01

The type area for the Elsterian- and Saalian glacial cycles is located in central Germany (Saxony, Saxony-Anhalt and Thuringia) where the gravel deposits of the rivers Saale- and Elster interfinger with tills and meltwater deposits of both glacial cycles in proximity to the maximum extensions of the Middle-Pleistocene Scandinavian ice-sheets in Central Europe. The Elsterian- and Saalian glacial cycles, including the corresponding interglacial periods are also correlated with first human appearance in the area (see Haidle and Pawlik 2010). Nevertheless, the timing of these glacial cycles is still unclear due to a lack of resilient chronological data on sediments representing the advance- and retreat of the glaciers. The Elsterian is defined to be terminated by the Holsteinian, but for the latter, a correlation to MIS 9 or 11 is still a matter of debate (e. g. Sirocko et al. 2006; Nitychoruk et al. 2007). Consequently, a correlation of the Elsterian to MIS 10 or 12 is possible. Within the last decades, new luminescence dating techniques such as pIRIR-luminescence protocols or infrared-radiofluorescence dating made it possible to extent the datable age range and hence, it is now possible to establish reliable chronologies also for deposits beyond the last glacial-/interglacial cycle. In the present study, we dated the quaternary sequence of Uichteritz (close to the Saale-river near Weissenfels, Saxony-Anhalt) using luminescence and infrared-radiofluorescence dating. The base of the quaternary layers consists of Elsterian sediments pre-dating the first Elsterian ice advance. This is evidenced mainly by the lithology, especially the absence of Nordic components in the composition of the gravel. Additionally, remains of the advancing Saalian ice sheet, represented by fluvial sediments from the Middle-Pleistocene river Saale, as well as till, glaciofluvial and glaciolacustrine sediments, cover the Elsterian succession. The upper part of the fluvial Elsterian sediments also includes a palaeosol (Bt-horizon, Meng & Wansa 2005), exposed below Saalian meltwater sediments and till. Furthermore, the Middle-Pleistocene sediments yielded Lower/Middle Palaeolithic stone artefacts (Rudolph et al. 2005), probably representing the earliest human appearance in central Germany. In conclusion, the sequence of Uichteritz has the potential to provide important new chronological data for the timing of the Elsterian and Saalian glacial cycles as well as the presence of humans in Central Europe. References Haidle, M. N., Pawlik, A. F., 2010. The earliest settlement of Germany: Is there anything out there? Quaternary International 223-224, 143-153. Meng, S., Wansa, S., 2005. Lithologie, Stratigraphie und Paläoökologie des Mittelpleistozäns im Markröhlitzer Tal (Lkr. Weißenfels/Sachsen-Anhalt). Eiszeitalter und Gegenwart (Quaternary Science Journal) 55, 174-214. Nitychoruk, J., Bińka, K., Ruppert, H., Schneider, J., 2005. Holsteinian Interglacial = Marine Isotope Stage 11? Quaternary Science Reviews 25, 2678-2681. Rudolph, A., Laurat, T. & Bernhardt, W., 2005. Die altpaläolithischen Artefaktfunde von Uichteritz, Ldkr. Weißenfels. Eiszeitalter und Gegenwart (Quaternary Science Journal) 55, 215-226. Sirocko, F. et al., 2006. Chronology and climate forcing of the last four interglacials. In: Sirocko, F., Claussen, Sánchez Goñi, M.F., Litt, T. (Eds.). The Climate of Past Interglacials. Developments in Quaternary Science 7, Amsterdam, Elsevier, pp. 597-614.

Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

USGS Publications Warehouse

Marzen, Rachel; DeNinno, Lauren H.; Cronin, Thomas M.

2016-01-01

Microfaunal and geochemical proxies from marine sediment records from central Arctic Ocean (CAO) submarine ridges suggest a close relationship over the last 550 thousand years (kyr) between orbital-scale climatic oscillations, sea-ice cover, marine biological productivity and other parameters. Multiple paleoclimate proxies record glacial to interglacial cycles. To understand the climate-cryosphere-productivity relationship, we examined the cyclostratigraphy of calcareous microfossils and constructed a composite Arctic Paleoclimate Index (API) "stack" from benthic foraminiferal and ostracode density from 14 sediment cores. Following the hypothesis that API is driven mainly by changes in sea-ice related productivity, the API stack shows the Arctic experienced a series of highly productive interglacials and interstadials every ∼20 kyr. These periods signify minimal ice shelf and sea-ice cover and maximum marine productivity. Rapid transitions in productivity are seen during shifts from interglacial to glacial climate states. Discrepancies between the Arctic API curves and various global climatic, sea-level and ice-volume curves suggest abrupt growth and decay of Arctic ice shelves related to climatic and sea level oscillations.

The Salzach Valley overdeeping: A most precise bedrock model of a major alpine glacial basin

NASA Astrophysics Data System (ADS)

Pomper, Johannes; Salcher, Bernhard; Eichkitz, Christoph

2016-04-01

Overdeepenings are impressive phenomena related to the erosion in the ablation zone of major glaciers. They are common features in glaciated and deglaciated regions worldwide and their sedimentary fillings may act as important archives for regional environmental change and glaciation history. Sedimentary fillings are also important targets of geotechnical exploration and construction including groundwater resource management, shallow geothermal exploitation, tunneling and the foundation of buildings. This is especially true in densely populated areas such as the European Alps and their foreland areas, regions which have been multiply glaciated during the last million years. However, due depths often exceeding some hundreds of meters, the overall knowledge on their geometry, formation and sedimentary content is still poor and commonly tied to some local spots. Here we present a bedrock model of the overall lower Salzach Valley, one of the largest glacial overdeepings in the European Alps. We utilized seismic sections from hydrocarbon exploration surveys and deep drillings together with topographic and modelling data to construct a 3D bedrock model. Through the existence of seismic inline and crossline valley sections, multiple drillings reaching the bedrock surface, log and abundant outcrop data we were, as far to our knowledge, able to create the most accurate digital bedrock topography of an alpine major overdeepening. We furthermore analyzed the sedimentary content of the valley as recorded by driller's lithologic logs. Our results suggest that the valley is far from being a regular U-shaped trough with constant depth, rather highlighting highs and lows of different magnitude and underground valley widths of variable extent. Data also indicates that the largest overdeepening of bedrock, reaching around 450 m below the alluvial fill, is not situated after a major glacial confluence following a prominent bedrock gorge but shifted several km down the valley. The sedimentary succession, representing multiple cycles of massive gravels and lacustrine fines, indicate that the valley was not fully excavated during the last glacial coverage at the LGM. Through its model accuracy related to a comprehensive geodatabase and a relatively homogenous rock erodibility, the Salzach Valley overdeepening might be a highly suitable testing site for future numerical simulations.

Southern Ocean dust-climate coupling over the past four million years.

PubMed

Martínez-Garcia, Alfredo; Rosell-Melé, Antoni; Jaccard, Samuel L; Geibert, Walter; Sigman, Daniel M; Haug, Gerald H

2011-08-03

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles. So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles, providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

Evolution of the early Antarctic ice ages

PubMed Central

de Bakker, Anouk T. M.; Beddow, Helen M.; Wilson, Paul A.; Bohaty, Steven M.; Pälike, Heiko; Batenburg, Sietske J.; Hilgen, Frederik J.; Hodell, David A.; Huck, Claire E.; Kroon, Dick; Raffi, Isabella; Saes, Mischa J. M.; van Dijk, Arnold E.; Lourens, Lucas J.

2017-01-01

Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions. PMID:28348211

Coupled Northern Hemisphere permafrost-ice-sheet evolution over the last glacial cycle

NASA Astrophysics Data System (ADS)

Willeit, M.; Ganopolski, A.

2015-09-01

Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost-ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM) agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200-500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

Ocean and atmosphere teleconnections modulate east tropical Pacific productivity at late to middle Pleistocene terminations

NASA Astrophysics Data System (ADS)

Diz, Paula; Hernández-Almeida, Iván; Bernárdez, Patricia; Pérez-Arlucea, Marta; Hall, Ian R.

2018-07-01

The modern Eastern Equatorial Pacific (EEP) is a key oceanographic region for regulating the Earth's climate system, accounting for between 5-10% of global marine production whilst also representing a major source of carbon dioxide efflux to the atmosphere. Changes in ocean dynamics linked to the nutrient supply from the Southern Ocean have been suggested to have played a dominant role in regulating EEP productivity over glacial-interglacial timescales of the past 500 ka. Yet, the full extent of the climate and oceanic teleconnections and the mechanisms promoting the observed increase of productivity occurring at glacial terminations remain poorly understood. Here we present multi-proxy, micropaleontological, geochemical and sedimentological records from the easternmost EEP to infer changes in atmospheric patterns and oceanic processes potentially influencing regional primary productivity over glacial-interglacial cycles of the mid-late Pleistocene (∼0-650 ka). These proxy data support a leading role for the north-south migration of the Intertropical Convergence Zone (ITCZ) in shaping past productivity variability in the EEP. Productivity increases during glacial periods and notably peaks at major and "extra" glacial terminations (those occurring 1-2 precession cycles after some major terminations) coincident with the inferred southernmost position of the ITCZ. The comparison of our reconstructions with proxy records of climate variability suggests the intensification of related extratropical atmospheric and oceanic teleconnections during deglaciation events. These processes may have re-activated the supply of southern sourced nutrients to the EEP, potentially contributing to enhanced productivity in the EEP and thus counterbalancing the oceanic carbon dioxide outgassing at glacial terminations.

Geomorphologic Mapping of a Last Glacial Maximum Moraine Sequence in the Far Eastern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Lindsay, B. J.; Putnam, A. E.; Strand, P.; Radue, M. J.; Dong, G.; Kong, X.; Li, M.; Sheriff, M.; Stevens, J.

2017-12-01

The abrupt millennial-scale climate events of the last glacial cycle constitute an important component of the ice-age puzzle. A complete explanation of glacial cycles, and their rapid terminations, must account for these millennial climatic `flickers'. Here we present a glacial geomorphologic map of a moraine system in a formerly glaciated valley within the mountains of Litang County in the eastern Tibetan Plateau of China. Geomorphologic mapping was conducted by interpreting satellite imagery, structure-from-motion imagery and digital elevation models, and field observations. This map provides context for a parallel ongoing 10Be exposure-dating effort, the preliminary results of which may be available by the time of this 2017 AGU Fall Meeting. We interpret the mapped moraines to document the millennial-scale pulsebeat of glacier advances in this region during the peak of the last ice age. Because changes in mountain glacier extent in this region are driven by atmospheric temperature, these moraines record past millennial climate changes. Altogether this mapping and exposure-dating approach will provide insight into the mechanisms for millennial-scale glacier and climate fluctuations in the interior of Asia.

Microbial formation of labile organic carbon in Antarctic glacial environments

USGS Publications Warehouse

Smith, H.J.; Foster, R.; McKnight, D.M.; Lisle, John T.; Littmann, S.; Kuypers, M.M.M.; Foreman, C.M.

2017-01-01

Roughly six petagrams of organic carbon are stored within ice worldwide. This organic carbon is thought to be of old age and highly bioavailable. Along with storage of ancient and new atmospherically deposited organic carbon, microorganisms may contribute substantially to the glacial organic carbon pool. Models of glacial microbial carbon cycling vary from net respiration to net carbon fixation. Supraglacial streams have not been considered in models although they are amongst the largest ecosystems on most glaciers and are inhabited by diverse microbial communities. Here we investigate the biogeochemical sequence of organic carbon production and uptake in an Antarctic supraglacial stream in the McMurdo Dry Valleys using nanometre-scale secondary ion mass spectrometry, fluorescence spectroscopy, stable isotope analysis and incubation experiments. We find that heterotrophic production relies on highly labile organic carbon freshly derived from photosynthetic bacteria rather than legacy organic carbon. Exudates from primary production were utilized by heterotrophs within 24 h, and supported bacterial growth demands. The tight coupling of microbially released organic carbon and rapid uptake by heterotrophs suggests a dynamic local carbon cycle. Moreover, as temperatures increase there is the potential for positive feedback between glacial melt and microbial transformations of organic carbon.

Dynamic Hydrological Discharge Modelling for Fully Coupled Paleoclimate Runs of the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Riddick, Thomas; Brovkin, Victor; Hagemann, Stefan; Mikolajewicz, Uwe

2017-04-01

The continually evolving large ice sheets present in the Northern Hemisphere during the last glacial cycle caused significant changes to river pathways both through directly blocking rivers and through glacial isostatic adjustment. These river pathway changes are believed to of had a significant impact on the evolution of ocean circulation through changing the pattern of fresh water discharge into the oceans. A fully coupled ESM simulation of the last glacial cycle thus requires a hydrological discharge model that uses a set of river pathways that evolve with the earth's changing orography while being able to reproduce the known present-day river network given the present-day orography. Here we present a method for dynamically modelling hydrological discharge that meets such requirements by applying relative manual corrections to an evolving fine scale orography (accounting for the changing ice sheets and isostatic rebound) each time the river directions are recalculated. The corrected orography thus produced is then used to create a set of fine scale river pathways and these are then upscaled to a course scale. An existing present-day hydrological discharge model within the JSBACH3 land surface model is run using the course scale river pathways generated. This method will be used in fully coupled paleoclimate runs made using MPI-ESM1 as part of the PalMod project. Tests show this procedure reproduces the known present-day river network to a sufficient degree of accuracy.

A review of the evidence for a human role in the extinction of Australian megafauna and an alternative interpretation

NASA Astrophysics Data System (ADS)

Wroe, Stephen; Field, Judith

2006-11-01

Arguments that megafaunal extinctions in Australia were anthropogenically mediated have focused on establishing terminal appearance ages. This approach has been underpinned by three principle tenets: (1) if megafauna disappeared before significant climate change, but after human colonisation, then it can be inferred that extinctions were human mediated; (2) climate change within the last glacial cycle was unremarkable relative to previous cycles; and (3) all or most Pleistocene megafauna were present when people arrived on the continent. We review the evidence for human causation and note mounting evidence suggesting that the last 400-300 ka in Australia has been characterised by escalating aridity and climatic variability, culminating in the breach of a hydrological threshold within the last glacial cycle. Only 21 species (35%) of megafauna whose disappearance has been attributed to human activity are known to have persisted after the Penultimate Glacial Maximum, a time of undoubtedly severe climate change. Thus, 39 species of megafauna (65%) cannot be reliably placed within 85,000 years of firm evidence for human arrival, ca 50-43 ka. At most eight species (13%) were clearly present at this time. Four or more persisted until the onset of full glacial conditions at ca 30 ka. We argue for a falsifiable model of staggered extinction in which most megafaunal extinctions predated human arrival and with the influence of people as a minor superimposition on broader trends in train since middle Pleistocene times.

Understanding the dust cycle at high latitudes: integrating models and observations

NASA Astrophysics Data System (ADS)

Albani, S.; Mahowald, N. M.; Maggi, V.; Delmonte, B.; Winckler, G.; Potenza, M. A. C.; Baccolo, G.; Balkanski, Y.

2017-12-01

Changing climate conditions affect dust emissions and the global dust cycle, which in turn affects climate and biogeochemistry. Paleodust archives from land, ocean, and ice sheets preserve the history of dust deposition for a range of spatial scales from close to the major hemispheric sources to remote sinks such as the polar ice sheets. In each hemisphere common features on the glacial-interglacial time scale mark the baseline evolution of the dust cycle, and inspired the hypothesis that increased dust deposition to ocean stimulated the glacial biological pump contributing to the reduction of atmospheric carbon dioxide levels. On the other hand finer geographical and temporal scales features are superposed to these glacial-interglacial trends, providing the chance of a more sophisticated understanding of the dust cycle, for instance allowing distinctions in terms of source availability or transport patterns as recorded by different records. As such paleodust archives can prove invaluable sources of information, especially when characterized by a quantitative estimation of the mass accumulation rates, and interpreted in connection with climate models. We review our past work and present ongoing research showing how climate models can help in the interpretation of paleodust records, as well as the potential of the same observations for constraining the representation of the global dust cycle embedded in Earth System Models, both in terms of magnitude and physical parameters related to particle sizes and optical properties. Finally we show the impacts on climate, based on this kind of observationally constrained model simulations.

A geochemical record of polycyclic aromatic hydrocarbons (PAHs) during the late Paleozoic Ice Age: The relationship between atmospheric pCO2, climate and fire.

NASA Astrophysics Data System (ADS)

Hren, M. T.; Harris, G.; Montanez, I. P.; DiMichele, W.; Eley, Y.; White, J. D.; Wilson, J. P.; McElwain, J.; Poulsen, C. J.

2017-12-01

The late Paleozoic Ice Age (LPIA) represents a dynamic period of widespread glacial/interglacial cycling as the earth underwent a major transition from an icehouse to greenhouse climate. During this transition period, pCO2 is shown to have varied by several hundred ppm and within the predicted range for anthropogenic change. Glacial/interglacial changes in atmospheric pCO2 during this time are associated with restructuring of tropical forests and carbon cycle dynamics. At present however, there is considerable debate over the potential hydrologic and fire-frequency feedbacks associated with this climatic variability. Polycyclic aromatic hydrocarbons (PAHs) are produced from the incomplete combustion of organic matter and are shown to be preserved over hundreds of millions of years. Thus, these organic compounds provide a potential record of the feedbacks between global biogeochemical systems and fire. We analyzed sedimentary organic matter from the Illinois Basin spanning the late Carboniferous glacial-interglacial cycles to assess the evolution of fire during this period. Our data show a decrease in the overall abundance of high molecular weight PAHs (HMW) from 312 to 304 Myr with significant variability that is coincident with the general timing of pCO2 cycling. Decreasing PAH abundance is also coincident with a proposed long-term change in pO2 and may reflect the influence of atmospheric oxygen in regulating fire occurrence and hydrologic cycling in tropical ecosystems in the late Carboniferous.

A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin

NASA Astrophysics Data System (ADS)

Hodell, D.; Lourens, L.; Crowhurst, S.; Konijnendijk, T.; Tjallingii, R.; Jiménez-Espejo, F.; Skinner, L.; Tzedakis, P. C.; Abrantes, Fatima; Acton, Gary D.; Alvarez Zarikian, Carlos A.; Bahr, André; Balestra, Barbara; Barranco, Estefanìa Llave; Carrara, Gabriela; Ducassou, Emmanuelle; Flood, Roger D.; Flores, José-Abel; Furota, Satoshi; Grimalt, Joan; Grunert, Patrick; Hernández-Molina, Javier; Kim, Jin Kyoung; Krissek, Lawrence A.; Kuroda, Junichiro; Li, Baohua; Lofi, Johanna; Margari, Vasiliki; Martrat, Belen; Miller, Madeline D.; Nanayama, Futoshi; Nishida, Naohisa; Richter, Carl; Rodrigues, Teresa; Rodríguez-Tovar, Francisco J.; Roque, Ana Cristina Freixo; Sanchez Goñi, Maria F.; Sierro Sánchez, Francisco J.; Singh, Arun D.; Sloss, Craig R.; Stow, Dorrik A. V.; Takashimizu, Yasuhiro; Tzanova, Alexandrina; Voelker, Antje; Xuan, Chuang; Williams, Trevor

2015-10-01

We produced a composite depth scale and chronology for Site U1385 on the SW Iberian Margin. Using log(Ca/Ti) measured by core scanning XRF at 1-cm resolution in all holes, a composite section was constructed to 166.5 meter composite depth (mcd) that corrects for stretching and squeezing in each core. Oxygen isotopes of benthic foraminifera were correlated to a stacked δ18O reference signal (LR04) to produce an oxygen isotope stratigraphy and age model. Variations in sediment color contain very strong precession signals at Site U1385, and the amplitude modulation of these cycles provides a powerful tool for developing an orbitally-tuned age model. We tuned the U1385 record by correlating peaks in L* to the local summer insolation maxima at 37°N. The benthic δ18O record of Site U1385, when placed on the tuned age model, generally agrees with other time scales within their respective chronologic uncertainties. The age model is transferred to down-core data to produce a continuous time series of log(Ca/Ti) that reflect relative changes of biogenic carbonate and detrital sediment. Biogenic carbonate increases during interglacial and interstadial climate states and decreases during glacial and stadial periods. Much of the variance in the log(Ca/Ti) is explained by a linear combination of orbital frequencies (precession, tilt and eccentricity), whereas the residual signal reflects suborbital climate variability. The strong correlation between suborbital log(Ca/Ti) variability and Greenland temperature over the last glacial cycle at Site U1385 suggests that this signal can be used as a proxy for millennial-scale climate variability over the past 1.5 Ma. Millennial climate variability, as expressed by log(Ca/Ti) at Site U1385, was a persistent feature of glacial climates over the past 1.5 Ma, including glacial periods of the early Pleistocene ('41-kyr world') when boundary conditions differed significantly from those of the late Pleistocene ('100-kyr world'). Suborbital variability was suppressed during interglacial stages and enhanced during glacial periods, especially when benthic δ18O surpassed 3.3-3.5‰. Each glacial inception was marked by appearance of strong millennial variability and each deglaciation was preceded by a terminal stadial event. Suborbital variability may be a symptomatic feature of glacial climate or, alternatively, may play a more active role in the inception and/or termination of glacial cycles.

Vegetation dynamics during the Last Interglacial-Glacial cycle in the Arno coastal plain (Tuscany, western Italy): location of a new tree refuge

NASA Astrophysics Data System (ADS)

Lucchi, M. Ricci

2008-12-01

Pollen analysis of the pre-Last Glacial Maximum succession of a 105 m-long continuous core from Tirrenia (Tuscany) provides evidence for the existence of an area of relatively high ecological stability where the effects of climate change were mitigated. The chronological framework of the vegetation record, spanning the Last Interglacial-Glacial cycle, was established by (i) AMS 14C dating, (ii) correlation with well-dated pollen sequences, and (iii) local stratigraphical constraints. A high lithological and sedimentological variability, with facies associations changing from fluvial to alluvial and coastal plain, enhances the palaeoenvironmental control on pollen distribution, thus helping to discriminate the impact of local factors on vegetation history. The most remarkable evidence, however, is represented by the continuous record of temperate trees throughout the whole glacial period, which provides useful indications on the location and nature of cold stage refugia. Most of the vegetation changes recorded in the core can be compared to the vegetation history of the Last Interglacial-Glacial cycle from southern Europe as a whole. In addition, local geographic and environmental features account for a more complex and varied floristic composition. Only the last phase of the Penultimate Glacial (MIS6), which was characterized by the diffusion of an arid steppe tundra, is recorded at the base of the core. The subsequent Last Interglacial (MIS5e) interval shows a poor and scattered pollen content due to the instability of the sedimentary environment. Nevertheless, it provides evidence of both global and local controls on vegetation dynamics, as indicated by the initial expansion of thermophilous forests and the remarkably late diffusion of conifers ( Pinus-Abies-Picea forests), respectively. Similarly, the transition to the Last Glacial (MIS5b and 5a in the core) is characterized by a reduced vegetation response to the typical stadial/interstadial climate variability. This is because the diffusion of a characteristic pioneer vegetation (mainly represented by Hippophae cf. rhamnoides) helped to confer to the local environment a high ecological stability, buffering vegetation changes. Finally, during the Last Glacial, mixed broad-leaved deciduous and Pinus forests widely occupied the Arno coastal plain, demonstrating that this area acted as an important tree refuge. Local ecological conditions favourable to tree survival were determined mainly by (i) high precipitation, as a function of orographic uplift of air charged with moisture from the nearby Tyrrhenian Sea, (ii) mild temperatures, which were also influenced by proximity to the sea, and (iii) high topographic variability, providing a series of suitable microenvironments.

Methane Hydrate Formation from Enhanced Organic Carbon Burial During Glacial Lowstands: Examples from the Gulf of Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, Alberto; Cook, Ann; Daigle, Hugh

Methane hydrates in fine-grained marine sediments are often found within veins and fractures occupying discrete depth intervals that are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the methane hydrate stability zone (MHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. We investigate here the hypothesis that these hydrate deposits form in sediments that were deposited during glacial lowstands and contain higher amounts of labile particulate organic carbon (POC), leading to enhanced microbial methanogenesis. During Pleistocene lowstands, river loads are deposited near the steep top ofmore » the continental slope and turbidity currents transport organic-rich, fine-grained sediments to deep waters. Faster sedimentation rates during glacial periods result in better preservation of POC because of decreased exposure times to oxic conditions. The net result is that more labile POC enters the methanogenic zone and more methane is generated in these sediments. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent deposition of labile POC at the seafloor controlled by glacioeustatic sea level variations in the last 250 kyr. The model is run for parameters estimated at three sites drilled by the 2009 Gulf of Mexico Joint Industry Project: Walker Ridge in the Terrebonne Basin (WR313-G and WR313-H) and Green Canyon near the canyon embayment into the Sigsbee Escarpment (GC955-H). In the model, gas hydrate forms in sediments with higher labile POC content deposited during the glacial cycle between 230 and 130 kyr (marine isotope stages 6 and 7). The corresponding depth intervals in the three sites contain hydrates, as shown by high bulk electrical resistivities and resistive subvertical fracture fills. This match supports the hypothesis that enhanced POC burial during glacial lowstands can result in hydrate formation from in situ microbial methanogenesis. Our results have implications for carbon cycling during glacial/interglacial cycles and for hydrate accumulation in the MHSZ. In particular, once hydrate-bearing intervals formed during glacial periods are buried beneath the MHSZ and dissociate, gas bubbles can rise and recycle microbial methane into the MHSZ.« less

Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial-Interglacial cycle

NASA Astrophysics Data System (ADS)

Prothero, Donald R.; Syverson, Valerie J.; Raymond, Kristina R.; Madan, Meena; Molina, Sarah; Fragomeni, Ashley; DeSantis, Sylvana; Sutyagina, Anastasiya; Gage, Gina L.

2012-11-01

Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures. Yet since 1863 it has been well known that Pleistocene animals and plants do not show much morphological change or speciation in response to the glacial-interglacial climate cycles. We tested this hypothesis with all of the common birds (condors, golden and bald eagles, turkeys, caracaras) and mammals (dire wolves, saber-toothed cats, giant lions, horses, camels, bison, and ground sloths) from Rancho La Brea tar pits in Los Angeles, California, which preserves large samples of many bones from many well-dated pits spanning the 35,000 years of the Last Glacial-Interglacial cycle. Pollen evidence showed the climate changed from chaparral/oaks 35,000 years ago to snowy piñon-juniper forests at the peak glacial 20,000 years ago, then back to the modern chaparral since the glacial-interglacial transition. Based on Bergmann's rule, we would expect peak glacial specimens to have larger body sizes, and based on Allen's rule, peak glacial samples should have shorter and more robust limbs. Yet statistical analysis (ANOVA for parametric samples; Kruskal-Wallis test for non-parametric samples) showed that none of the Pleistocene pit samples is statistically distinct from the rest, indicating complete stasis from 35 ka to 9 ka. The sole exception was the Pit 13 sample of dire wolves (16 ka), which was significantly smaller than the rest, but this did not occur in response to climate change. We also performed a time series analysis of the pit samples. None showed directional change; all were either static or showed a random walk. Thus, the data show that birds and mammals at Rancho La Brea show complete stasis and were unresponsive to the major climate change that occurred at 20 ka, consistent with other studies of Pleistocene animals and plants. Most explanations for such stasis (stabilizing selection, canalization) fail in this setting where climate is changing. One possible explanation is that most large birds and mammals are very broadly adapted and relatively insensitive to changes in their environments, although even the small mammals of the Pleistocene show stasis during climate change, too.

From the Last Interglacial to the Anthropocene: Modelling a Complete Glacial Cycle (PalMod)

NASA Astrophysics Data System (ADS)

Brücher, Tim; Latif, Mojib

2017-04-01

We will give a short overview and update on the current status of the national climate modelling initiative PalMod (Paleo Modelling, www.palmod.de). PalMod focuses on the understanding of the climate system dynamics and its variability during the last glacial cycle. The initiative is funded by the German Federal Ministry of Education and Research (BMBF) and its specific topics are: (i) to identify and quantify the relative contributions of the fundamental processes which determined the Earth's climate trajectory and variability during the last glacial cycle, (ii) to simulate with comprehensive Earth System Models (ESMs) the climate from the peak of the last interglacial - the Eemian warm period - up to the present, including the changes in the spectrum of variability, and (iii) to assess possible future climate trajectories beyond this century during the next millennia with sophisticated ESMs tested in such a way. The research is intended to be conducted over a period of 10 years, but with shorter funding cycles. PalMod kicked off in February 2016. The first phase focuses on the last deglaciation (app. the last 23.000 years). From the ESM perspective PalMod pushes forward model development by coupling ESM with dynamical ice sheet models. Computer scientists work on speeding up climate models using different concepts (like parallelisation in time) and one working group is dedicated to perform a comprehensive data synthesis to validate model performance. The envisioned approach is innovative in three respects. First, the consortium aims at simulating a full glacial cycle in transient mode and with comprehensive ESMs which allow full interactions between the physical and biogeochemical components of the Earth system, including ice sheets. Second, we shall address climate variability during the last glacial cycle on a large range of time scales, from interannual to multi-millennial, and attempt to quantify the relative contributions of external forcing and processes internal to the Earth system to climate variability at different time scales. Third, in order to achieve a higher level of understanding of natural climate variability at time scales of millennia, its governing processes and implications for the future climate, we bring together three different research communities: the Earth system modeling community, the proxy data community and the computational science community. The consortium consists of 18 partners including all major modelling centers within Germany. The funding comprises approximately 65 PostDoc positions and more than 120 scientists are involved. PalMod is coordinated at the Helmholtz Centre for Ocean Research Kiel (GEOMAR).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archer, D.

A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbonmore » (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time scales, decreasing the efficiency of bubble transit through the water column. The methane cycle on the shelf responds to climate change on a long time constant of thousands of years, because hydrate is excluded thermodynamically from the permafrost zone by water limitation, leaving the hydrate stability zone at least 300 m below the sediment surface.« less

Climate sensitivity of Tibetan Plateau glaciers - past and future implications

NASA Astrophysics Data System (ADS)

Heyman, Jakob; Hubbard, Alun; Stroeven, Arjen P.; Harbor, Jonathan M.

2013-04-01

The Tibetan Plateau is one of the most extensively glaciated, non-Polar regions of the world, and its mountain glaciers are the primary source of melt water for several of the largest Asian rivers. During glacial cycles, Tibetan Plateau glaciers advanced and retreated multiple times, but remained restricted to the highest mountain areas as valley glaciers and ice caps. Because glacier extent is dominantly controlled by climate, the past extent of Tibetan glaciers provide information on regional climate. Here we present a study analyzing the past maximum extents of glaciers on the Tibetan Plateau with the output of a 3D glacier model, in an effort to quantify Tibetan Plateau climate. We have mapped present-day glaciers and glacial landforms deposited by formerly more extensive glaciers in eight mountain regions across the Tibetan Plateau, allowing us to define present-day and past maximum glacier outlines. Using a high-resolution (250 m) higher-order glacier model calibrated against present-day glacier extents, we have quantified the climate perturbations required to expand present-day glaciers to their past maximum extents. We find that a modest cooling of at most 6°C for a few thousand years is enough to attain past maximum extents, even with 25-75% precipitation reduction. This evidence for limited cooling indicates that the temperature of the Tibetan Plateau remained relatively stable over Quaternary glacial cycles. Given the significant sensitivity to temperature change, the expectation is perhaps that a future warmer climate might result in intense glacier reduction. We have tested this hypothesis and modeled the future glacier development for the three mountain regions with the largest present-day glacier cover using a projected warming of 2.8 to 6.2°C within 100 years (envelope limits from IPCC). These scenarios result in dramatic glacier reductions, including 24-100% ice volume loss after 100 years and 77-100% ice volume loss after 300 years.

Climate Change in Lowland Central America During the Late Deglacial and Early Holocene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hillesheim, M B; Hodell, D A; Leyden, B W

2005-02-08

The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition ({approx}11,250 to 7,500 cal yr BP) inferred from sediment cores retrieved in Lake Peten Itza, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by {approx}11,250 cal yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11,250 to 10,350 cal yr BP, during the Preboreal period, lithologic changes in sedimentsmore » from deep-water cores (>50 m below modern water level) indicate several wet-dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1-4) occurred at 11,200, 10,900, 10,700, and 10,400 cal yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10,350 cal yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Peten Itza with other records from the circum-Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high-latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores-Bermuda high-pressure system. This mechanism operated on millennial-to-submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC).« less

A stochastic, evolutionary model for range shifts and richness on tropical elevational gradients under Quaternary glacial cycles

PubMed Central

Colwell, Robert K.; Rangel, Thiago F.

2010-01-01

Quaternary glacial–interglacial cycles repeatedly forced thermal zones up and down the slopes of mountains, at all latitudes. Although no one doubts that these temperature cycles have left their signature on contemporary patterns of geography and phylogeny, the relative roles of ecology and evolution are not well understood, especially for the tropics. To explore key mechanisms and their interactions in the context of chance events, we constructed a geographical range-based, stochastic simulation model that incorporates speciation, anagenetic evolution, niche conservatism, range shifts and extinctions under late Quaternary temperature cycles along tropical elevational gradients. In the model, elevational patterns of species richness arise from the differential survival of founder lineages, consolidated by speciation and the inheritance of thermal niche characteristics. The model yields a surprisingly rich variety of realistic patterns of phylogeny and biogeography, including close matches to a variety of contemporary elevational richness profiles from an elevational transect in Costa Rica. Mountaintop extinctions during interglacials and lowland extinctions at glacial maxima favour mid-elevation lineages, especially under the constraints of niche conservatism. Asymmetry in temperature (greater duration of glacial than of interglacial episodes) and in lateral area (greater land area at low than at high elevations) have opposing effects on lowland extinctions and the elevational pattern of species richness in the model—and perhaps in nature, as well. PMID:20980317

The Growth Response of Two Diatom Species to Atmospheric Dust from the Last Glacial Maximum.

PubMed

Conway, Tim M; Hoffmann, Linn J; Breitbarth, Eike; Strzepek, Robert F; Wolff, Eric W

2016-01-01

Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO2). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cycle. However, understanding the role of enhanced atmospheric Fe supply in biogeochemical cycles is limited by knowledge of the fluxes and 'bioavailability' of atmospheric Fe during glacial intervals. Here, we assess the effect of Fe fertilization by dust, dry-extracted from the Last Glacial Maximum portion of the EPICA Dome C Antarctic ice core, on the Antarctic diatom species Eucampia antarctica and Proboscia inermis. Both species showed strong but differing reactions to dust addition. E. antarctica increased cell number (3880 vs. 786 cells mL-1), chlorophyll a (51 vs. 3.9 μg mL-1) and particulate organic carbon (POC; 1.68 vs. 0.28 μg mL-1) production in response to dust compared to controls. P. inermis did not increase cell number in response to dust, but chlorophyll a and POC per cell both strongly increased compared to controls (39 vs. 15 and 2.13 vs. 0.95 ng cell-1 respectively). The net result of both responses was a greater production of POC and chlorophyll a, as well as decreased Si:C and Si:N incorporation ratios within cells. However, E, antarctica decreased silicate uptake for the same nitrate and carbon uptake, while P. inermis increased carbon and nitrate uptake for the same silicate uptake. This suggests that nutrient utilization changes in response to Fe addition could be driven by different underlying mechanisms between different diatom species. Enhanced supply of atmospheric dust to the surface ocean during glacial intervals could therefore have driven nutrient-utilization changes which could permit greater carbon fixation for lower silica utilization. Additionally, both species responded more strongly to lower amounts of direct Fe chloride addition than they did to dust, suggesting that not all the Fe released from dust was in a bioavailable form available for uptake by diatoms.

The Growth Response of Two Diatom Species to Atmospheric Dust from the Last Glacial Maximum

PubMed Central

Hoffmann, Linn J.; Breitbarth, Eike; Strzepek, Robert F.; Wolff, Eric W.

2016-01-01

Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO2). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cycle. However, understanding the role of enhanced atmospheric Fe supply in biogeochemical cycles is limited by knowledge of the fluxes and ‘bioavailability’ of atmospheric Fe during glacial intervals. Here, we assess the effect of Fe fertilization by dust, dry-extracted from the Last Glacial Maximum portion of the EPICA Dome C Antarctic ice core, on the Antarctic diatom species Eucampia antarctica and Proboscia inermis. Both species showed strong but differing reactions to dust addition. E. antarctica increased cell number (3880 vs. 786 cells mL-1), chlorophyll a (51 vs. 3.9 μg mL-1) and particulate organic carbon (POC; 1.68 vs. 0.28 μg mL-1) production in response to dust compared to controls. P. inermis did not increase cell number in response to dust, but chlorophyll a and POC per cell both strongly increased compared to controls (39 vs. 15 and 2.13 vs. 0.95 ng cell-1 respectively). The net result of both responses was a greater production of POC and chlorophyll a, as well as decreased Si:C and Si:N incorporation ratios within cells. However, E, antarctica decreased silicate uptake for the same nitrate and carbon uptake, while P. inermis increased carbon and nitrate uptake for the same silicate uptake. This suggests that nutrient utilization changes in response to Fe addition could be driven by different underlying mechanisms between different diatom species. Enhanced supply of atmospheric dust to the surface ocean during glacial intervals could therefore have driven nutrient-utilization changes which could permit greater carbon fixation for lower silica utilization. Additionally, both species responded more strongly to lower amounts of direct Fe chloride addition than they did to dust, suggesting that not all the Fe released from dust was in a bioavailable form available for uptake by diatoms. PMID:27384948

Ice Age Reboot: Thermohaline Circulation Crisis during the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Pena, L.; Goldstein, S. L.

2014-12-01

The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41- to 100-kyr cycles and developed higher amplitude climate variability. Because it took place without significant changes in the Milankovitch forcing, this fundamental change must reflect either non-linear responses of the climate system to these external forcings, or internal changes in the ocean-atmosphere-cryosphere system that led to longer periodicities and more intense glacial periods. We document using Nd isotopes a major disruption of the ocean thermohaline circulation (THC) system during the MPT between MIS 25-21 at ~950-860 ka, which effectively marks the first 100-kyr cycle, including an exceptional weakening through critical interglacial MIS 23 at ~900 ka. The data are from ODP Sites 1088 (41°8.163'S, 13°33.77'E, 2082m) and 1090 (42°54.82'S, 8°53.98E', 3702m) in the SE Atlantic Subantarctic Zone, near the upper and lower boundaries of NADW and Circumpolar Deep Water (CDW). Given evidence for nearly stable NADW and North Pacific Water (NPW) ɛNd-values over the last 2 Ma, we interpret the ɛNd variations to reflect changes in the NADW:NPW mixing fractions. During the studied pre-MPT 41-kyr world (MIS 31-25, 1,100-950 ka), at both sites the differences in glacial and interglacial ɛNd-values are small, indicating strong glacial as well as interglacial export of NADW. A major weakening of NADW export occurred during MIS 24-22, including MIS 23, which is unique as the only known interglacial in which the THC did not strengthen, and thus can be considered as a 'trans-glacial' period. The recovery into the post-MPT 100-kyr world is characterized by continued weak glacial THC. We conclude that the MPT ocean circulation crisis 'rebooted' the pacing and intensity of ice ages and facilitated the coeval drawdown of atmospheric CO2 and high latitude ice sheet growth, generating the conditions that stabilized 100-kyr cycles.

Quantifying the influence of the terrestrial biosphere on glacial-interglacial climate dynamics

NASA Astrophysics Data System (ADS)

Davies-Barnard, Taraka; Ridgwell, Andy; Singarayer, Joy; Valdes, Paul

2017-10-01

The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeo-record. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial-interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphere-ocean-vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional -0.91 °C global mean cooling, with regional cooling as large as -5 °C, but with considerable variability across the glacial-interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 °C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a -0.26 °C effect on temperature, with -0.58 °C at the Last Glacial Maximum. Depending on assumptions made about the destination of terrestrial carbon under ice sheets and where sea level has changed, the average terrestrial biosphere contribution over the last 120 kyr could be as much as -50 °C and -0.83 °C at the Last Glacial Maximum.

Weathering pits as indicators of the relative age of granite surfaces in the Cairngorm mountains, Scotland

USGS Publications Warehouse

Hall, A.M.; Phillips, W.M.

2006-01-01

Weathering pits 1-140 cm deep occur on granite surfaces in the Cairngorms associated with a range of landforms, including tors, glacially exposed slabs, large erratics and blockfields. Pit depth is positively correlated with cosmogenic exposure age, and both measures show consistent relationships on individual rock landforms. Rates of pit deepening are non-linear and a best fit is provided by the sigmoidal function D = b1+ exp(b2+b3/t). The deepest pits occur on unmodified tor summits, where 10 Be exposure ages indicate that surfaces have been exposed to weathering for a minimum of 52-297 ka. Glacially exposed surfaces with pits 10-46 cm deep have given 10 Be exposure durations of 21-79 ka, indicating exposure by glacial erosion before the last glacial cycle. The combination of cosmogenic exposure ages with weathering pit depths greatly extends the area over which inferences can be made regarding the ages of granite surfaces in the Cairngorms. Well-developed weathering pits on glacially exposed surfaces in other granite areas are potential indicators of glacial erosion before the Last Glacial Maximum. ?? Swedish Society for Anthropology and Geography.

Geomorphic and shallow-acoustic investigation of an Antarctic Peninsula fjord system using high-resolution ROV and shipboard geophysical observations: Ice dynamics and behaviour since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

García, Marga; Dowdeswell, J. A.; Noormets, R.; Hogan, K. A.; Evans, J.; Ó Cofaigh, C.; Larter, R. D.

2016-12-01

Detailed bathymetric and sub-bottom acoustic observations in Bourgeois Fjord (Marguerite Bay, Antarctic Peninsula) provide evidence on sedimentary processes and glacier dynamics during the last glacial cycle. Submarine landforms observed in the 50 km-long fjord, from the margins of modern tidewater glaciers to the now ice-distal Marguerite Bay, are described and interpreted. The landforms are grouped into four morpho-sedimentary systems: (i) glacial advance and full-glacial; (ii) subglacial and ice-marginal meltwater; (iii) glacial retreat and neoglaciation; and (iv) Holocene mass-wasting. These morpho-sedimentary systems have been integrated with morphological studies of the Marguerite Bay continental shelf and analysed in terms of the specific sedimentary processes and/or stages of the glacial cycle. They demonstrate the action of an ice-sheet outlet glacier that produced drumlins and crag-and-tail features in the main and outer fjord. Meltwater processes eroded bedrock channels and ponds infilled by fine-grained sediments. Following the last deglaciation of the fjord at about 9000 yr BP, subsequent Holocene neoglacial activity involved minor readvances of a tidewater glacier terminus in Blind Bay. Recent stillstands and/or minor readvances are inferred from the presence of a major transverse moraine that indicates grounded ice stabilization, probably during the Little Ice Age, and a series of smaller landforms that reveal intermittent minor readvances. Mass-wasting processes also affected the walls of the fjord and produced scars and fan-shaped deposits during the Holocene. Glacier-terminus changes during the last six decades, derived from satellite images and aerial photographs, reveal variable behaviour of adjacent tidewater glaciers. The smaller glaciers show the most marked recent retreat, influenced by regional physiography and catchment-area size.

Elemental concentration variations in Plio-Pleistocene sediments from ODP Site 1143 (southern South China Sea) obtained by XRF analyses

NASA Astrophysics Data System (ADS)

Tian, J.; Xie, X.; Jin, H.; Wang, P.; Jian, Z.

2009-12-01

Energy dispersive X-ray fluorescence (XRF) scanning technology provides the most accurate and most economic analytical methods for the determination of major and minor elements of the deep-sea sediment ranging from sodium (11) to uranium (92). Scanning on the smooth core surface by XRF Core scanner is reliable and non-destructive to the sediment, requiring little or no time to prepare the core. This method overcomes the drawback of the traditional analytical method by ICP-AES or ICP-MS which requires long time for sample preparation. Thus, it makes it viable to reconstruct long and high-resolution elemental time series from sediment cores. We have performed relatively elemental concentration analyses on the deep sea sediment cores from ODP site 1143 (southern SCS) down to 190.77 mcd (meters composite depth) by XRF core scanner. The depth resolution of the scanning is 1 cm, equivalent to a time resolution of ~250 years. The age model is based on tuning the benthic foraminiferal d18O at Site 1143 to obliquity and precession (Tian et al., 2002) which indicates that the 190.77 meters long sediment spans the past 5 Myr. We compared the records between 99.5 and 136.46 mcd with the elemental records from the same site obtained by Philips PW 2400 X-ray spectrometer (Wehausen et al., online publication). Comparison reveals, regardless of the absolute changes of the elements, that the elemental records (Si, Ti, Al, Fe, Mn, Ca, K, P, Ba, Rb, Sr) obtained by two methods are nearly the same. Results show that the relative concentration variations of the productivity related elements such as Ba and Ca display distinctive glacial-interglacial cycles for the past 5 Myr. These productivity cycles recorded show one-on-one relationship with the glacial-interglacial cycles of the global ice volume change recorded in the benthic foraminiferal d18O. The glacial-interglacial cycles in productivity and global ice volume changes are consistent with each other not only in amplitude but also in secular variations. The benthic d18O implies the final formation of the northern hemisphere glaciation between ~2.5 Ma and ~3.3 Ma, as indicated by gradually increased values of d18O. During this period, both Ba and Ca show gradually increased values of relative concentration, indicating increased productivity which was probably caused by intensified East Asia summer monsoon. The close relationship of the productivity related elemental variations with benthic foraminiferal d18O reveals that the Plio-Pleistocene variations of the East Asian monsoon have been greatly dominated by global ice volume change. Although the elements related to terrigenous detrital matter composition of site 1143 such as Ti, Fe, As, Co and Ni display distinct glacial-interglacial cycles for the past 5 Myr, they display different patterns in secular variation with that of the benthic foraminiferal d18O. The mismatch indicates that besides northern hemisphere glaciation other multiple processes including changes in provenance and weathering intensity caused by monsoonal climate variability and sea level fluctuations could have affected the terrigenous detrital matter composition of site 1143.

Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

NASA Astrophysics Data System (ADS)

Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farias, Laura; Gallardo, Laura; De Pol-Holz, Ricardo

2015-07-01

Mineral dust aerosols play a major role in present and past climates. To date, we rely on climate models for estimates of dust fluxes to calculate the impact of airborne micronutrients on biogeochemical cycles. Here we provide a new global dust flux data set for Holocene and Last Glacial Maximum (LGM) conditions based on observational data. A comparison with dust flux simulations highlights regional differences between observations and models. By forcing a biogeochemical model with our new data set and using this model's results to guide a millennial-scale Earth System Model simulation, we calculate the impact of enhanced glacial oceanic iron deposition on the LGM-Holocene carbon cycle. On centennial timescales, the higher LGM dust deposition results in a weak reduction of <10 ppm in atmospheric CO2 due to enhanced efficiency of the biological pump. This is followed by a further ~10 ppm reduction over millennial timescales due to greater carbon burial and carbonate compensation.

Deglaciation and glacial erosion: a joint control on magma productivity by continental unloading

NASA Astrophysics Data System (ADS)

Sternai, Pietro; Caricchi, Luca; Castelltort, Sebastien

2016-04-01

Glacial-interglacial cycles affect the processes through which water and rocks are redistributed across the Earth's surface, thereby linking solid-Earth and climate dynamics. Regional and global scale studies suggest that continental lithospheric unloading due to ice melting during the transition to interglacials leads to increased continental magmatic, volcanic and degassing activity. Such a climatic forcing on the melting of the Earth's interior, however, has always been evaluated without considering the additional continental unloading associated with erosion. Current datasets relating to the evolution of erosion rates are typically limited by temporal resolutions that are too low or span too short time intervals to allow for direct comparisons between the contributions from ice melting and erosion to continental unloading at the timescale of the late Pleistocene glacial cycles. Yet, they provide a fundamental observational basis on which to calibrate numerical predictions. Here, we present and discuss numerical results involving synthetic but realistic topographies, ice caps and glacial erosion rates suggesting that erosion may be as important as deglaciation in affecting continental unloading, sub-continental decompression melting and magma productivity. Thus, the timing and magnitude of deglaciation and erosion must be characterized if the forcing of climate change on the continental magmatic/volcanic activity is to be extracted from the remnants of eroded volcanic centers. Our study represents an additional step towards a more general understanding of the links between a changing climate, glacial processes and the melting of the solid Earth.

Magnetic Properties of Bermuda Rise Sediments Controlled by Glacial Cycles During the Late Pleistocene

NASA Astrophysics Data System (ADS)

Roud, S.

2015-12-01

Sediments from ODP site 1063 (Bermuda Rise, North Atlantic) contain a high-resolution record of geomagnetic field behavior during the Brunhes Chron. We present rock magnetic data of the upper 160 mcd (<900 ka) from hole 1063D that show magnetic properties vary in concert with glacial cycles. Magnetite appears to be the main magnetic carrier in the carbonate-dominated interglacial horizons, yet exhibits contrasting grain size distributions depending on the redox state of the horizons. Higher contributions of single domain magnetite exist above the present day sulfate reduction zone (ca. 44 mcd) with relatively higher multidomain magnetite components below that likely arise from the partial dissolution of SD magnetite in the deeper, anoxic horizons. Glacial horizons on the other hand, characterized by enhanced terrigenous deposition, show no evidence for diagenetic dissolution but do indicate the presence of authigenic greigite close to glacial maxima (acquisition of gyro-remanence, strong magnetostatic interactions and SD properties). Glacial horizons contain hematite (maxima in HIRM and S-Ratio consistent with a reddish hue) and exhibit higher ARM anisotropy and pronounced sedimentary fabrics. We infer that post depositional processes affected the magnetic grain size and mineralogy of Bermuda rise sediments deposited during the late Pleistocene. Hematite concentration is interpreted to reflect primary terrigenous input that is likely derived from the Canadian Maritime Provinces. A close correlation between HIRM and magnetic foliation suggests that changes in sediment composition (terrigenous vs. marine biogenic) were accompanied by changes in the depositional processes at the site.

Quaternary glaciation of the Lato Massif, Zanskar Range of the NW Himalaya

NASA Astrophysics Data System (ADS)

Orr, Elizabeth N.; Owen, Lewis A.; Saha, Sourav; Caffee, Marc W.; Murari, Madhav K.

2018-03-01

The glacial chronostratigraphy and history of the Lato Massif of Zanskar northern India is defined for the first time using geomorphic mapping and 10Be surface exposure dating. Three local glacial stages, the Lato, Shiyul and Kyambu, are dated to 244-49, 25-15 and 3.4-0.2 ka, respectively. The Lato glacial stage was the most extensive period of glaciation, characterized by expanded ice caps with glaciers advancing to ∼16 km from their present position. Large till deposits are associated with this glacial stage, which represent a time of heightened glacial erosion and localized incision, and increased rates of sediment transfer and deposition. The glacial style transitioned to entrenched valley glaciation during the Shiyul glacial stage. Hummocky moraine complexes reflecting fluctuating glacier margins characterize this glaciation. Glaciers have been confined to the cirques and headwalls of the massif during and since the Kyambu glacial stage. Equilibrium-line altitude (ELA) reconstructions help define the shifts in glaciation over time, with ELA depressions changing from 470 ± 140, 270 ± 80 to 100 ± 30 m for the Lato, Shiyul and Kyambu glacial stages, respectively. The change of glacial style during the latter part of the Quaternary is similar to other regions of the Transhimalaya and Tibet suggesting that this pattern of glaciation may reflect regional climatic forcing. The evolution of the Lato Massif from an isolated alpine plateau to a steeply incised massif over the last several glacial-interglacial cycles may have also influenced the shifts from ice cap to valley glaciation.

The movement of pre-adapted cool taxa in north-central Amazonia during the last glacial

NASA Astrophysics Data System (ADS)

D'Apolito, Carlos; Absy, Maria Lúcia; Latrubesse, Edgardo M.

2017-08-01

The effects of climate change on the lowland vegetation of Amazonia during the last glacial cycle are partially known for the middle and late Pleniglacial intervals (late MIS 3, 59-24 ka and MIS 2, 24-11 ka), but are still unclear for older stages of the last glacial and during the last interglacial. It is known that a more seasonal dry-wet climate caused marginal forest retraction and together with cooling rearranged forest composition to some extent. This is observed in pollen records across Amazonia depicting presence of taxa at glacial times in localities where they do not live presently. The understanding of taxa migration is hindered by the lack of continuous interglacial-glacial lowland records. We present new data from a known locality in NW Amazonia (Six Lakes Hill), showing a vegetation record that probably started during MIS 5 (130-71 ka) and lasted until the onset of the Holocene. The vegetation record unravels a novel pattern in tree taxa migration: (1) from the beginning of this cycle Podocarpus and Myrsine are recorded and (2) only later do Hedyosmum and Alnus appear. The latter group is largely restricted to montane biomes or more distant locations outside Amazonia, whereas the first is found in lowlands close to the study site on sandy soils. These findings imply that Podocarpus and Myrsine responded to environmental changes equally and this reflects their concomitant niche use in NW Amazonia. Temperature drop is not discarded as a trigger of internal forest composition change, but its effects are clearer later in the Pleniglacial rather than the Early Glacial. Therefore early climatic/environmental changes had a first order effect on vegetation that invoke alternative explanations. We claim last glacial climate-induced modifications on forest composition favoured the expansion of geomorphologic-soil related processes that initiated forest rearrangement.

Pleistocene range shifts, refugia and the origin of widespread species in western Palaearctic water beetles.

PubMed

García-Vázquez, David; Bilton, David T; Foster, Garth N; Ribera, I

2017-09-01

Quaternary glacial cycles drove major shifts in both the extent and location of the geographical ranges of many organisms. During glacial maxima, large areas of central and northern Europe were inhospitable to temperate species, and these areas are generally assumed to have been recolonized during interglacials by range expansions from Mediterranean refugia. An alternative is that this recolonization was from non-Mediterranean refugia, in central Europe or western Asia, but data on the origin of widespread central and north European species remain fragmentary, especially for insects. We studied three widely distributed lineages of freshwater beetles (the Platambus maculatus complex, the Hydraena gracilis complex, and the genus Oreodytes), all restricted to running waters and including both narrowly distributed southern endemics and widespread European species, some with distributions spanning the Palearctic. Our main goal was to determine the role of the Pleistocene glaciations in shaping the diversification and current distribution of these lineages. We sequenced four mitochondrial and two nuclear genes in populations drawn from across the ranges of these taxa, and used Bayesian probabilities and Maximum Likelihood to reconstruct their phylogenetic relationships, age and geographical origin. Our results suggest that all extant species in these groups are of Pleistocene origin. In the H. gracilis complex, the widespread European H. gracilis has experienced a rapid, recent range expansion from northern Anatolia, to occupy almost the whole of Europe. However, in the other two groups widespread central and northern European taxa appear to originate from central Asia, rather than the Mediterranean. These widespread species of eastern origin typically have peripherally isolated forms in the southern Mediterranean peninsulas, which may be remnants of earlier expansion-diversification cycles or result from incipient isolation of populations during the most recent Holocene expansion. The accumulation of narrow endemics of such lineages in the Mediterranean may result from successive cycles of range expansion, with subsequent speciation (and local extinction in glaciated areas) through multiple Pleistocene climatic cycles. Copyright © 2017 Elsevier Inc. All rights reserved.

Ice and water on Newberry Volcano, central Oregon

USGS Publications Warehouse

Donnelly-Nolan, Julie M.; Jensen, Robert A.; O'Connor, Jim; Madin, Ian P.; Dorsey, Rebecca

2009-01-01

Newberry Volcano in central Oregon is dry over much of its vast area, except for the lakes in the caldera and the single creek that drains them. Despite the lack of obvious glacial striations and well-formed glacial moraines, evidence indicates that Newberry was glaciated. Meter-sized foreign blocks, commonly with smoothed shapes, are found on cinder cones as far as 7 km from the caldera rim. These cones also show evidence of shaping by flowing ice. In addition, multiple dry channels likely cut by glacial meltwater are common features of the eastern and western flanks of the volcano. On the older eastern flank of the volcano, a complex depositional and erosional history is recorded by lava flows, some of which flowed down channels, and interbedded sediments of probable glacial origin. Postglacial lava flows have subsequently filled some of the channels cut into the sediments. The evidence suggests that Newberry Volcano has been subjected to multiple glaciations.

Dansgaard-Oeschger cycles observed in the Greenland ReCAP ice core project

NASA Astrophysics Data System (ADS)

Kjær, Helle Astrid; Vallelonga, Paul; Vinther, Bo; Simonsen, Marius; Maffezzoli, Niccoló; Gkinis, Vasileios; Svensson, Anders; Jensen, Camilla Marie; Dallmayr, Remi; Spolaor, Andrea; Edwards, Ross

2017-04-01

The new REnland ice CAP (RECAP) ice core was drilled in summer 2015 in Greenland and measured by means of Continuous flow analysis (CFA) during the last 3 months of 2015. The Renland ice core was obtained as part of the ReCAP project, extending 584.11 meters to the bottom of the Renland ice cap located in east Greenland. The unique position on a mountain saddle above 2000 meters altitude, but close to the coast, ensures that the Renland ice core offers high accumulation, but also reaches far back in time. Results show that despite the short length the RECAP ice core holds ice all the way back to the past warm interglacial period, the Eemian. The glacial section is strongly thinned and covers on 20 meters of the ReCAP core, but nonetheless due to the high resolution of the measurements all 25 expected DO events could be identified. The record was analyzed for multiple elements including the water isotopes, forest fire tracers NH4+ and black carbon, insoluble dust particles by means of Abakus laser particle counter and the dust ion Ca2+, sea salt Na+, and sea ice proxies as well as acidity useful for finding volcanic layers to date the core. Below the glacial section another 20 meters of warm Eemian ice have been analysed. Here we present the chemistry results as obtained by continuous flow analysis (CFA) and compare the glacial section with the chemistry profile from other Greenland ice cores.

A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

DOE PAGES

Archer, D.

2014-06-03

A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbonmore » (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time scales, decreasing the efficiency of bubble transit through the water column. The methane cycle on the shelf responds to climate change on a long time constant of thousands of years, because hydrate is excluded thermodynamically from the permafrost zone by water limitation, leaving the hydrate stability zone at least 300 m below the sediment surface.« less

Glacial-Interglacial and Holocene N2O Stable Isotope Changes Constrain Terrestrial N Cycling

NASA Astrophysics Data System (ADS)

Schmitt, J.; Spahni, R.; Bock, M.; Seth, B.; Stocker, B. D.; Ri, X.; Schilt, A.; Brook, E.; Otto-Bliesner, B. L.; Liu, Z.; Prentice, I. C.; Fischer, H.; Joos, F.

2015-12-01

The land biosphere contributes most to the natural source of the long-lived greenhouse gas nitrous oxide (N2O), with N2O emissions being dependent on the turnover rate of both the terrestrial nitrogen (N) and carbon (C) cycle. The C:N stoichiometry of vegetation and soil organic matter links the cycles intimately. Sustained plant productivity increase must be supported by biological N fixation. Intensified N cycling in turn enhances N loss and thereby N2O emissions. The temporal and spatial dynamics of terrestrial N and C cycles and related terrestrial N2O emissions are poorly constrained over the glacial-interglacial transition and the Holocene. Here we reconstruct increased terrestrial N2O emissions since the Last Glacial Maximum based on N2O concentration and isotope measurements on several ice cores and show that this N2O increase can be explained by N cycle modelling - provided N fixation is allowed to respond dynamically to increasing N demand and turnover. The Ice core reconstructions suggest a deglacial increase of 1.1 ± 0.4 Tg N/yr in terrestrial and 0.6 ± 0.4 Tg/yr in oceanic N2O emissions, but relatively constant terrestrial emissions over the Holocene. Transient simulations with a Dynamic Global Vegetation Model are shown to represent the climate and CO2 induced changes in terrestrial N2O emission, and suggest a deglacial increase in biological N fixation by 20%, independently of its absolute magnitude. Deciphering the response of biological N fixation during climatic changes is an important factor for our understanding of plant growth and the land carbon sink, alongside anthropogenic greenhouse gas emissions.

Repeated sedimentation and exposure of glacial Lake Missoula sediments: A lake-level history at Garden Gulch, Montana, USA

NASA Astrophysics Data System (ADS)

Smith, Larry N.

2017-01-01

Glaciolacustrine sediments record lake transgression, regression, and subaerial modification of the silty lake-bottom of glacial Lake Missoula in the Clark Fork River valley. The sequence preserved at Garden Gulch, MT documents lake-level fluctuations at >65% of its full-pool volume. Twelve sedimentary cycles fine upwards from (1) very fine-grained sandy silt to (2) silt with climbing ripples to (3) rhythmically laminated silt and some clay. The cycles are fine-grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops. The gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake-level lowerings. Periglacial wedges, small rotational faults, involutions, and clastic dikes deform the tops of eleven cycles. The wedges are 10-30 cm wide, penetrate 30-70 cm deep, are spaced <1 m apart, and contain vertically oriented gravel and massive to laminated sediment. Wedges split and taper in plan view. A few thin silt-filled dikes, which branch and taper downwards from wedges, are interpreted as filled frost cracks. One 10-20 cm-wide sand-filled dike protrudes upward from a sand bed; it is interpreted as a liquefaction feature consistent with a filling and draining lake. The deformed cycle tops preserve evidence of periglacial cold, subaerial exposure, seasonal frost heave, and the incipient formation of sorted polygons. The lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles. The Garden Gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial Lake Missoula.

Evolution of Temperature and Carbon Storage Within the Deep Southeast Atlantic Ocean Across the Last Glacial/Interglacial Cycle Inferred from a Highly-Resolved Sedimentary Depth Transect

NASA Astrophysics Data System (ADS)

Foreman, A. D.; Charles, C. D.; Rae, J. W. B.; Adkins, J. F.; Slowey, N. C.

2015-12-01

Many models show that the relative intensity of stratification is a primary variable governing the sequestration and release of carbon from the ocean over ice ages. The wide-scale observations necessary to test these model-derived hypotheses are not yet sufficient, but sedimentary depth transects represent a promising approach for making progress. Here we present paired stable isotopic (d18O, d13C) and trace metal data (Mg/Ca, B/Ca) from benthic foraminifera collected from a highly vertically-resolved depth transect from the mid-depth and deep SE Atlantic. These observations, which cover Marine Isotope Stages 5e, 5d, 5a, 4, and the Last Glacial Maximum, document the evolution of glacial conditions from the previous interglacial, and provide detailed observations regarding the magnitude and timing of changes in temperature and salinity within the deep ocean at key time points over the last glacial/interglacial cycle. Furthermore, the comparison between purely 'physical' tracers (i.e. Mg/Ca, d18O) and tracers sensitive to the carbon cycle (i.e. d13C and B/Ca) provides critical insight into the relationship between deep/mid-depth stratification and global carbon dynamics. Notably among our observations, the paired stable isotope and trace metal results strongly suggest that much of the ice-age cooling of deep South Atlantic occurred at the MIS 5e/5d transition, while the onset of salinity stratification in the mid-depth South Atlantic occurred at the MIS 5/4 transition.

Ice stream behaviour in the western sector of the North Sea during the end of the last glacial cycle

NASA Astrophysics Data System (ADS)

Roberts, David; Evans, David; Clark, Chris; Bateman, Mark; Livingstone, Stephen; Medialdea, Alicia; Cofaigh, Colm O.; Grimoldi, Elena; Callard, Louise; Dove, Dayton; Stewart, Heather; Davies, Bethan; Chiverell, Richard

2016-04-01

During the last glacial cycle the East coast of the UK was overrun by the British-Irish Ice Sheet (BIIS) flowing eastwards and southwards. In recent years it has become evident that several ice streams including the Tweed, Tyne, and Stainmore Gap ice streams, as well as the late stage North Sea Lobe (NSL), all played a role in shaping the glacial landscape during this period, but understanding the flow phasing of these ice streams during advance and collapse has proved challenging. Here we present new data from the seafloor collected during recent work undertaken by the Britice Chrono and Glanam project teams during cruise JC123 in the North Sea. Sub-bottom seafloor data together with new swath data clearly show that the final phases of the collapse of the NSL were controlled by ice sourced from the Firth of Forth ice stream which deglaciated in a NNW trajectory. Other ice streams being fed from the west (e.g. Stainmore, Tyne, Tweed) were not influential in final phase ice retreat from the southern North Sea. The Forth ice imprint is characterised by several grounding zone/till wedges marking dynamic, oscillatory retreat of the ice as it retreated along an offshore corridor between North Yorkshire and Northumberland. Repeated packages of tills, ice marginal and glaciomarine sediments, which drape glacially scoured bedrock terrain and drumlins along this corridor, point to marine inundation accompanying ice retreat. New TCN ages suggest decoupling of the Tyne Gap ice stream and NSL between 17.8 and 16.5 ka and this coincides with rapid, regional collapse of the NSL between 17.2 and 16.0 ka along the Yorkshire and Durham coasts (new OSL ages; Britice Chrono). Hence, both the central and northern sectors of the BIIS were being strongly influenced by marine margin instability during the latter phases of the last glacial cycle.

Glacial-Interglacial, Orbital and Millennial-Scale Climate Variability for the Last Glacial Cycle at Shackleton Site U1385 based on Dinoflagellate Cysts

NASA Astrophysics Data System (ADS)

Datema, M.

2015-12-01

The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying Site U1385 is to establish a marine reference section of Pleistocene climate change. We generated (sub)millennial-scale (~600 year interval) dinoflagellate cyst (dinocyst) assemblage records from Shackleton Site U1385 (IODP Expedition 339) to reconstruct sea surface temperature (SST) and productivity/upwelling over the last 152 kyrs. In addition, our approach allows for detailed land-sea correlations, because we also counted assemblages of pollen and spores from higher plants. Dinocyst SST and upwelling proxies, as well as warm/cold pollen proxies from Site U1385 show glacial-interglacial, orbital and stadial-interstadial climate variability and correlate very well to Uk'37, planktic foraminifer δ18O and Ca/Ti proxies of previously drilled Shackleton Sites and Greenland Ice Core δ18O. The palynological proxies capture (almost) all Dansgaard-Oeschger events of the last glacial cycle, also before ~70 ka, where millennial-scale variability is overprinted by precession. We compare the performance and results of the palynology of Site U1385 to proxies of previously drilled Shackleton Sites and conclude that palynology strengthens the potential of this site to form a multi-proxy reference section for millennial scale climate variability across the Pleistocene-Holocene. Finally, we will present a long-term paleoceanographic perspective down to ~150 ka.

Beyond Rayleigh Distillation: Reconstructing Glacial Nutrient Cycles using a Seasonal Model of the Southern Ocean

NASA Astrophysics Data System (ADS)

Kemeny, P. C.; Kast, E.; Fawcett, S. E.; Hain, M.; Sigman, D. M.

2016-12-01

The nitrogen (N) isotope ratios of diatom-bound organic matter recovered from Southern Ocean sediment cores have been used to investigate N cycling and the global carbon cycle over glacial-interglacial transitions. Increases in diatom-bound 15N/14N (δ15N) and decreases in export production have qualitatively been interpreted to reflect elevated nitrate (NO3-) consumption and decreased nutrient supply during glacial intervals; however, studies have yet to quantitatively relate paleoceanographic δ15N records to the surface NO3- concentration of ancient oceans. Furthermore, recent studies of the N and oxygen (O) isotope ratios of seawater NO3- reveal that seasonal processes may impact the isotopic signal of exported organic matter. The connection between diatom-bound δ15N and paleoceanographic NO3- availability is explored using a seasonally-resolved 1-dimension model of the Southern Ocean upper water column. The model parameterizes summer and winter physical and biogeochemical processes in the surface mixed layer and the temperature minimum layer. When calibrated to modern conditions, the model reproduces observed deviations from Rayleigh dynamics in the mixed layer, which result from a combination of summertime remineralization, late-summer N recycling, and wintertime nitrification. In glacial simulations, we observe an increase in diatom-bound δ15N that results dominantly from enhanced summertime NO3- consumption, as opposed to resulting from a rise in the δ15N of wintertime NO3-. Yet wintertime mixed layer (and thus initial spring/summer) NO3- concentration is greatly reduced under ice age conditions, such that export production, which has been observed to be lower during glacial intervals, was nevertheless able to consume almost all of the gross nitrate supply. The model suggests that observed differences in δ15N between centric and pennate diatom assemblages can be explained by the near-complete consumption of NO3- in the ice age summer mixed layer.

Evolution of ice sheets in the early Quaternary of the central North Sea: 2.58 Ma to 0.78 Ma

NASA Astrophysics Data System (ADS)

Lamb, R.; Huuse, M.; Stewart, M.; Brocklehurst, S. H.

2016-12-01

Integration of chronostratigraphic proxies with 3D seismic and well-log data has allowed for a basin-wide re-interpretation of the onset of glaciation in the central North Sea during the Quaternary. Mapping of seismic geomorphology, calculations of water depth and sediment accumulation rates, and other basin analysis techniques unravel the evolution of the North Sea basin during the early Pleistocene, a period of dramatic global cooling and rapid 41 kyr glacial-interglacial cycles, identifying a system which is increasingly dominated by large, continental-scale ice sheets. Prior to this study continental-scale ice sheets were generally not considered able to grow in a 41 kyr cycle and the earliest date for such an ice sheet in the North Sea was identified at the onset of tunnel valley formation in the Elsterian (0.48 Ma; MIS 12) which forms a large regional-scale glacial unconformity. At the onset of the Pleistocene at 2.58 Ma the North Sea basin was an elongate `mega-fjord' with water depths of up to 350 m, infilling rapidly as the European river systems deposited a large clinoform complex in the southern end of the basin. This period corresponds to the preservation of large scale ice-berg scouring on clinoform topsets, suggesting the presence of marine-terminating ice sheets with repeated calving events. As the Pleistocene progressed and global climate became increasingly colder the North Sea became smaller and shallower due to the continual infill of the basin. At 1.72 Ma the basin reached a critical point between the cold climate and the shallowing of the basin and the first evidence for grounded glaciation in the form of mega-scale glacial lineations is seen at this level. Between 1.72 and 0.48 Ma there is evidence for ice-streaming in the form of multiple MSGL flow sets re-occupying the central North Sea, as well as a large glaciotectonic complex. The glacial geomorphological evidence presented pushes back the date of grounded glaciation in the central North Sea by over one million years relative to the existing models. This raises important questions about the completeness of glaciation histories of Europe and other high and mid latitude land areas that can only be addressed by in depth scrutiny of their adjacent offshore sedimentary records.

The effect of ocean alkalinity and carbon transfer on deep-sea carbonate ion concentration during the past five glacial cycles

NASA Astrophysics Data System (ADS)

Kerr, Joanna; Rickaby, Rosalind; Yu, Jimin; Elderfield, Henry; Sadekov, Aleksey Yu.

2017-08-01

Glacial-interglacial deep Indo-Pacific carbonate ion concentration ([CO32-]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciation caused by a carbonate deposition reduction on shelves (i.e., the coral reef hypothesis), and 2) transient carbonate compensation responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [CO32-] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructions, we suggest that the shelf-to-basin shift of carbonate deposition raised deep-water [CO32-], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciations. Oceanic carbon reorganisations during major climatic transitions caused deep-water [CO32-] deviations away from the long-term trend, and carbonate compensation processes subsequently acted to restore the ocean carbonate system to new steady state conditions. Deep-water [CO32-] showed similar patterns to sediment carbonate content (%CaCO3) records on glacial-interglacial timescales, suggesting that past seafloor %CaCO3 variations were dominated by deep-water carbonate preservation changes at our studied sites.

Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

NASA Astrophysics Data System (ADS)

Vidstrand, Patrik; Follin, Sven; Selroos, Jan-Olof; Näslund, Jens-Ove

2014-09-01

The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.

The initial break-up of Pangæa elicited by Late Palæozoic deglaciation.

PubMed

Yeh, Meng-Wan; Shellnutt, J Gregory

2016-08-11

The break-up of Pangæa was principally facilitated by tensional plate stress acting on pre-existing suture zones. The rifting of Pangæa began during the Early Permian along the southern Tethys margin and produced the lenticular-shaped continent known as Cimmeria. A mantle-plume model is ascribed to explain the rift-related volcanism but the NW-SE oriented Cimmerian rifts do not correlate well with pre-existing suture zones or 'structural heterogeneities' but appear to have a pertinent spatial and temporal association with Late Palæozoic glacial-interglacial cycles. Mantle potential temperature estimates of Cimmerian rift-related basalts (1410 °C ± 50 °C) are similar to ambient mantle conditions rather than an active mantle-plume rift as previously suggested. Moreover, we find that the distribution of glacial deposits shows significant temporal and spatial concurrence between the glacial retreat margins and rifting sites. We conclude that the location and timing of Cimmerian rifting resulted from the exploitation of structural heterogeneities within the crust that formed due to repeated glacial-interglacial cycles during the Late Palæozoic. Such effects of continental deglaciation helped to create the lenticular shape of Cimmeria and Neotethys Ocean suggesting that, in some instances, climate change may directly influence the location of rifting.

Glacial/interglacial changes in subarctic north pacific stratification.

PubMed

Jaccard, S L; Haug, G H; Sigman, D M; Pedersen, T F; Thierstein, H R; Röhl, U

2005-05-13

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.

Present-day secular variations in the zonal harmonics of earth's geopotential

NASA Technical Reports Server (NTRS)

Mitrovica, J. X.; Peltier, W. R.

1993-01-01

The mathematical formulation required for predicting secular variation in the geopotential is developed for the case of a spherically symmetric, self-gravitating, viscoelastic earth model and an arbitrary surface load which can include a gravitational self-consistent ocean loading component. The theory is specifically applied to predict the present-day secular variation in the zonal harmonics of the geopotenial arising from the surface mass loading associated with the late Pleistocene glacial cycles. A procedure is outlined in which predictions of the present-day geopotential signal due to the late Pleistocene glacial cycles may be used to derive bounds on the net present-day mass flux from the Antarctic and Greenland ice sheets to the local oceans.

Estuarine removal of glacial iron and implications for iron fluxes to the ocean

USGS Publications Warehouse

Schroth, Andrew W.; Crusius, John; Hoyer, Ian; Campbell, Robert

2014-01-01

While recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans, the role of high-latitude estuary environments as a potential sink of glacial iron is unknown. Here we present the first quantitative description of iron removal in a meltwater-dominated estuary. We find that 85% of “dissolved” Fe is removed in the low-salinity region of the estuary along with 41% of “total dissolvable” iron associated with glacial flour. We couple these findings with hydrologic and geochemical data from Gulf of Alaska (GoA) glacierized catchments to calculate meltwater-derived fluxes of size and species partitioned Fe to the GoA. Iron flux data indicate that labile iron in the glacial flour and associated Fe minerals dominate the meltwater contribution to the Fe budget of the GoA. As such, GoA nutrient cycles and related ecosystems could be strongly influenced by continued ice loss in its watershed.

Simulated Impact of Glacial Runoff on CO2 Uptake in the Gulf of Alaska

NASA Astrophysics Data System (ADS)

Pilcher, Darren J.; Siedlecki, Samantha A.; Hermann, Albert J.; Coyle, Kenneth O.; Mathis, Jeremy T.; Evans, Wiley

2018-01-01

The Gulf of Alaska (GOA) receives substantial summer freshwater runoff from glacial meltwater. The alkalinity of this runoff is highly dependent on the glacial source and can modify the coastal carbon cycle. We use a regional ocean biogeochemical model to simulate CO2 uptake in the GOA under different alkalinity-loading scenarios. The GOA is identified as a current net sink of carbon, though low-alkalinity tidewater glacial runoff suppresses summer coastal carbon uptake. Our model shows that increasing the alkalinity generates an increase in annual CO2 uptake of 1.9-2.7 TgC/yr. This transition is comparable to a projected change in glacial runoff composition (i.e., from tidewater to land-terminating) due to continued climate warming. Our results demonstrate an important local carbon-climate feedback that can significantly increase coastal carbon uptake via enhanced air-sea exchange, with potential implications to the coastal ecosystems in glaciated areas around the world.

Thermohaline circulation crisis and impacts during the mid-Pleistocene transition.

PubMed

Pena, Leopoldo D; Goldstein, Steven L

2014-07-18

The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41-thousand-year to 100-thousand-year cycles and developed higher-amplitude climate variability without substantial changes in the Milankovitch forcing. Here, we document, by using Nd isotopes, a major disruption of the ocean thermohaline circulation (THC) system during the MPT between marine isotope stages (MISs) 25 and 21 at ~950 to 860 thousand years ago, which effectively marks the first 100-thousand-year cycle, including an exceptional weakening through a critical interglacial (MIS 23) at ~900 thousand years ago. Its recovery into the post-MPT 100-thousand-year world is characterized by continued weak glacial THC. The MPT ocean circulation crisis facilitated the coeval drawdown of atmospheric CO2 and high-latitude ice sheet growth, generating the conditions that stabilized 100-thousand-year cycles. Copyright © 2014, American Association for the Advancement of Science.

Coastal barium cycling at the West Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Pyle, K. M.; Hendry, K. R.; Sherrell, R. M.; Meredith, M. P.; Venables, H.; Lagerström, M.; Morte-Ródenas, A.

2017-05-01

Barium cycling in the ocean is associated with a number of processes, including the production and recycling of organic matter, freshwater fluxes, and phenomena that affect alkalinity. As a result, the biogeochemical cycle of barium offers insights into past and present oceanic conditions, with barium currently used in various forms as a palaeoproxy for components of organic and inorganic carbon storage, and as a quasi-conservative water mass tracer. However, the nature of the oceanic barium cycle is not fully understood, particularly in cases where multiple processes may be interacting simultaneously with the dissolved and particulate barium pools. This is particularly the case in coastal polar regions such as the West Antarctic Peninsula, where biological drawdown and remineralisation occur in tandem with sea ice formation and melting, glacial meltwater input, and potential fluxes from shelf sediments. Here, we use a high-precision dataset of dissolved barium (Bad) from a grid of stations adjacent to the West Antarctic Peninsula in conjunction with silicic acid (Si(OH)4), the oxygen isotope composition of water, and salinity measurements, to determine the relative control of various coastal processes on the barium cycle throughout the water column. There is a strong correlation between Bad and Si(OH)4 present in deeper samples, but nevertheless persists significantly in surface waters. This indicates that the link between biogenic opal and barium is not solely due to barite precipitation and dissolution at depth, but is supplemented by an association between Bad and diatom tests in surface waters, possibly due to barite formation within diatom-dominated phytodetritus present in the photic zone. Sea-ice meltwater appears to exert a significant secondary control on barium concentrations, likely due to non-conservative biotic or abiotic processes acting as a sink for Bad within the sea ice itself, or sea-ice meltwater stimulating non-siliceous productivity that acts as a Bad sink. Meteoric water input, conversely, exerts little or no control on local barium levels, indicating that glacial meltwater is not a significant coastal source of barium to the West Antarctic Peninsula shelf waters.

Multilocus phylogeography and systematic revision of North American water shrews (genus: Sorex)

USGS Publications Warehouse

Hope, Andrew G.; Panter, Nicholas; Cook, Joseph A.; Talbot, Sandra L.; Nagorsen, David W.

2014-01-01

North American water shrews, which have traditionally included Sorex alaskanus, S. bendirii, and S. palustris, are widely distributed through Nearctic boreal forests and adapted for life in semiaquatic environments. Molecular mitochondrial signatures for these species have recorded an evolutionary history with variable levels of regional divergence, suggesting a strong role of Quaternary environmental change in speciation processes. We expanded molecular analyses, including more-comprehensive rangewide sampling of specimens representing North American water shrew taxa, except S. alaskanus, and sequencing of 4 independent loci from the nuclear and mitochondrial genomes. We investigated relative divergence of insular populations along the North Pacific Coast, and newly recognized diversity from southwestern montane locations, potentially representing refugial isolates. Congruent independent genealogies, lack of definitive evidence for contemporary gene flow, and high support from coalescent species trees indicated differentiation of 4 major geographic lineages over multiple glacial cycles of the late Quaternary, similar to a growing number of boreal taxa. Limited divergence of insular populations suggested colonization following the last glacial. Characterization of southwestern montane diversity will require further sampling but divergence over multiple loci is indicative of a relictual sky-island fauna. We have reviewed and revised North American water shrew taxonomy including the recognition of 3 species within what was previously known as S. palustris. The possibility of gene flow between most distantly related North American water shrew lineages coupled with unresolved early diversification of this group and other sibling species reflects a complex but potentially productive system for investigating speciation processes.

The timing and cause of glacial activity during the last glacial in central Tibet based on 10Be surface exposure dating east of Mount Jaggang, the Xainza range

NASA Astrophysics Data System (ADS)

Dong, Guocheng; Zhou, Weijian; Yi, Chaolu; Fu, Yunchong; Zhang, Li; Li, Ming

2018-04-01

Mountain glaciers are sensitive to climate change, and can provide valuable information for inferring former climates on the Tibetan Plateau (TP). The increasing glacial chronologies indicate that the timing of the local Last Glacial Maximum (LGM) recorded across the TP is asynchronous, implying different local influences of the mid-latitude westerlies and Asian Summer Monsoon in triggering glacier advances. However, the well-dated sites are still too few, especially in the transition zone between regions controlled by the two climate systems. Here we present detailed last glacial chronologies for the Mount Jaggang area, in the Xainza range, central Tibet, with forty-three apparent 10Be exposure-ages ranging from 12.4 ± 0.8 ka to 61.9 ± 3.8 ka. These exposure-ages indicate that at least seven glacial episodes occurred during the last glacial cycle east of Mount Jaggang. These include: a local LGM that occurred at ∼61.9 ± 3.8 ka, possibly corresponding to Marine Isotope Stage 4 (MIS 4); subsequent glacial advances at ∼43.2 ± 2.6 ka and ∼35.1 ± 2.1 ka during MIS 3; one glacial re-advance/standstill at MIS3/2 transition (∼29.8 ± 1.8 ka); and three glacial re-advances/standstills that occurred following MIS 3 at ∼27.9 ± 1.7 ka, ∼21.8 ± 1.3 ka, and ∼15.1 ± 0.9 ka. The timing of these glacial activities is roughly in agreement with North Atlantic millennial-scale climate oscillations (Heinrich events), suggesting the potential correlations between these abrupt climate changes and glacial fluctuations in the Mount Jaggang area. The successively reduced glacial extent might have resulted from an overall decrease in Asian Summer Monsoon intensity over this timeframe.

Alteration of Oceanic Nitrification Under Elevated Carbon Dioxide Concentrations

NASA Astrophysics Data System (ADS)

Beman, J.; Chow, C. E.; Popp, B. N.; Fuhrman, J. A.; Feng, Y.; Hutchins, D. A.

2008-12-01

Atmospheric carbon dioxide (CO2) concentrations are increasing exponentially and expected to double by the year 2100. Dissolution of excess CO2 in the upper ocean reduces pH, alters carbonate chemistry, and also represents a potential resource for autotrophic organisms that convert inorganic carbon into biomass--including a broad spectrum of marine microbes. These bacteria and archaea drive global biogeochemical cycles of carbon and nitrogen and constitute the vast majority of biomass in the sea, yet their responses to reduced pH and increased pCO2 remain largely undocumented. Here we show that elevated pCO2 may sharply reduce nitrification rates and populations of nitrifying microorganisms in the ocean. Multiple experiments were performed in the Sargasso Sea and the Southern California Bight under glacial maximum (193 ppm), present day (390 ppm), and projected (750 ppm) pCO2 concentrations, over time scales from hours to multiple days, and at depths of 45 m to 240 m. Measurement of nitrification rates using isotopically-labeled nitrogen showed 2-5 fold reduction under elevated pCO2--as well as an increase under glacial maximum pCO2. Marine Crenarchaeota are likely involved in nitrification as ammonia-oxidizing archaea (AOA) and are among the most abundant microbial groups in the ocean, yet this group decreased by 40-80% under increased pCO2, based on quantification of both 16S rRNA and ammonia monooxygenase (amoA) gene copies. Crenarchaeota also steadily declined over the course of multiple days under elevated pCO2, whereas ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) were more variable in their responses or were not detected. These findings suggest that projected increases in pCO2 and subsequent decreases in pH may strongly influence marine biogeochemistry and microbial community structure in the sea.

Environmental drivers of microbial abundance and composition in Arctic sediments, Kongsfjorden and Van Keulenfjorden, Svalbard (79°N): Evidence from stable and radioactive isotopes

NASA Astrophysics Data System (ADS)

Buongiorno, J.; Szynkiewicz, A.; Faiia, A. M.; Yeager, K. M.; Schindler, K.; Lloyd, K. G.

2017-12-01

The continued rise of global atmospheric temperatures in response to greenhouse gas concentrations is responsible for pronounced glacial retreat (Hanna et al., 2008), which is occurring at an increasingly rapid pace in the Arctic due in part to polar amplification (Hagan et al., 2003; Kohler et al., 2007). How glacial recession will impact biogeochemical cycling and ecosystem diversity remains a standing question in the Arctic. At 79°N, Svalbard is among the most glaciated areas in the Arctic. Changes in glacial hydrology are likely to decrease sediment delivery rate to Svalbard fjords (Wehrmann et al., 2014). This, in turn, may alter primary production as well as biological sinks for important oxidized dissolved metals. Here, we compared molecular data with dissolved chemicals near glaciers within Kongsfjorden (KF) and Van Keulenfjorden (VK), Svalbard. Quantitative PCR (qPCR) and 16S rRNA were used to assess depth profiles of microbial abundance and diversity within the context of geochemical parameters, including total organic carbon (%TOC) and C/N ratios. δ13Corg and δ15Norg of sedimentary organic matter were interpreted within the framework of molecular data. Finally, 137Cs and 210Pb were used to connect molecular and geochemical data to paleoenvironment. Bacterial copy numbers range from 3.7 × 106 to 9.2 × 1010 copies/g sediment in KF and 2.2 × 105 to 8.2 × 1010 copies/g sediment in VK. At glacially-influenced sites, the lowest copy numbers are observed at 11-12 cm depth. We hypothesized that sedimentary organic carbon drives microbial abundance at this interval. In KF, %TOC is between 0.3 wt% and 0.7 wt% and is between 1.2 wt% and 1.8 wt% in VK. Trends in %TOC do not correlate with copy number at glacially-influenced sites. However, increased abundance at a distal site in VK is related to elevated %TOC as well as decreased C/N. This suggests there are multiple controls on microbial abundance, including proximity to the glacier and organic matter quality.

Plant molecular phylogeography in China and adjacent regions: Tracing the genetic imprints of Quaternary climate and environmental change in the world's most diverse temperate flora.

PubMed

Qiu, Ying-Xiong; Fu, Cheng-Xing; Comes, Hans Peter

2011-04-01

The Sino-Japanese Floristic Region (SJFR) of East Asia harbors the most diverse of the world's temperate flora, and was the most important glacial refuge for its Tertiary representatives ('relics') throughout Quaternary ice-age cycles. A steadily increasing number of phylogeographic studies in the SJFR of mainland China and adjacent areas, including the Qinghai-Tibetan-Plateau (QTP) and Sino-Himalayan region, have documented the population histories of temperate plant species in these regions. Here we review this current literature that challenges the oft-stated view of the SJFR as a glacial sanctuary for temperate plants, instead revealing profound effects of Quaternary changes in climate, topography, and/or sea level on the current genetic structure of such organisms. There are three recurrent phylogeographic scenarios identified by different case studies that broadly agree with longstanding biogeographic or palaeo-ecological hypotheses: (i) postglacial re-colonization of the QTP from (south-)eastern glacial refugia; (ii) population isolation and endemic species formation in Southwest China due to tectonic shifts and river course dynamics; and (iii) long-term isolation and species survival in multiple localized refugia of (warm-)temperate deciduous forest habitats in subtropical (Central/East/South) China. However, in four additional instances, phylogeographic findings seem to conflict with a priori predictions raised by palaeo-data, suggesting instead: (iv) glacial in situ survival of some hardy alpine herbs and forest trees on the QTP platform itself; (v) long-term refugial isolation of (warm-)temperate evergreen taxa in subtropical China; (vi) 'cryptic' glacial survival of (cool-)temperate deciduous forest trees in North China; and (vii) unexpectedly deep (Late Tertiary/early-to-mid Pleistocene) allopatric-vicariant differentiation of disjunct lineages in the East China-Japan-Korea region due to past sea transgressions. We discuss these and other consequences of the main phylogeographic findings in light of palaeo-environmental evidence, emphasize notable gaps in our knowledge, and outline future research prospects for disentangling the evolution and biogeographic history of the region's extremely diverse temperate flora. Copyright © 2011 Elsevier Inc. All rights reserved.

The Acoustic Signature of Glaciated Margins

NASA Astrophysics Data System (ADS)

Newton, A. M. W.; Huuse, M.

2016-12-01

As climate warms it has become increasingly clear that, in order to fully understand how it might evolve in the future, we need to look for examples of how climate has changed in the past. The Late Cenozoic history of the Arctic Ocean and its surrounding seas has been dominated by glacial-interglacials cycles. This has resulted in major environmental changes in relative sea levels, ice volumes, sea ice conditions, and ocean circulation as marine and terrestrially-based ice sheets waxed and waned. In this work, the acoustic signatures of several glaciated margins in the Northern Hemisphere are investigated and compared. This includes: NW Greenland, West Greenland, East Greenland, mid-Norway, Northern Norway, and the North Sea. These shelf successions preserve a geomorphological record of multiple glaciations and are imaged using seismic reflection data. To date, the majority of work in these areas has tended to focus on the most recent glaciations, which are well known. Here, the focus of the work is to look at the overall stratigraphic setting and how it influences (and is influenced by) the evolution of ice sheets throughout the glacial succession. Landform records are imaged using seismic data to provide a long-term insight into the styles of glaciation on each margin and what relation this may have had on climate, whilst the stratigraphic architectures across each site demonstrate how the inherited geology and tectonic setting can provide a fundamental control on the ice sheet and depositional styles. For example, Scoresby Sund is characterised by significant aggradation that is likely related to subsidence induced by lithospheric cooling rather than rapid glacial deposition, whilst the subsidence of the mid-Norwegian margin can be related to rapid glacial deposition and trapping of sediments behind inversion structures such as the Helland-Hansen Arch. The insights from this multi-margin study allow for regional, basin-wide, glaciological records to be developed and to investigate how marine, marginal-marine, and grounded glacial signatures vary across margins with different geological histories and whether these margins evolved with any synchronicity.

Influence of Pleistocene glacial/interglacial cycles on the genetic structure of the mistletoe cactus Rhipsalis baccifera (Cactaceae) in Mesoamerica.

PubMed

Ornelas, Juan Francisco; Rodríguez-Gómez, Flor

2015-01-01

Phylogeographical work on cloud forest-adapted species provides inconsistent evidence on cloud forest dynamics during glacial cycles. A study of Rhipsalis baccifera (Cactaceae), a bird-dispersed epiphytic mistletoe cactus, was conducted to investigate genetic variation at sequence data from nuclear [internal transcribed spacer (ITS), 677 bp] and chloroplast (rpl32-trnL, 1092bp) DNA for 154 individuals across the species range in Mesoamerica to determine if such patterns are consistent with the expansion/contraction model of cloud forest during glacial cycles. We conducted population and spatial genetic analyses as well as gene flow and divergence time estimates between 24 populations comprising the distribution of R. baccifera in Mexico and Guatemala to gain insight of the evolutionary history of these populations, and a complementary species distribution modeling approach to frame information derived from the genetic analyses into an explicit paleoecological context. The results revealed a phylogeographical break at the Isthmus of Tehuantepec, and high levels of genetic diversity among populations and cloud forest areas. Despite the genetic differentiation of some R. baccifera populations, the widespread ITS ribotypes suggest effective nuclear gene flow via pollen and population differentiation shown by the rpl32-trnL suggests more restricted seed flow. Predictions of species distribution models under past last glacial maximum (LGM) climatic conditions and a significant signal of demographic expansion suggest that R. baccifera populations experienced a range expansion tracking the conditions of the cloud forest distribution and shifted to the lowlands with population connectivity during the LGM. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Meltwater input to the southern ocean during the last glacial maximum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shemesh, A.; Burckle, L.H.; Hays, J.D.

1994-12-02

Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climaticmore » cycles at the same cores.« less

Radiocarbon constraints on the glacial ocean circulation and its impact on atmospheric CO2

PubMed Central

Skinner, L. C.; Primeau, F.; Freeman, E.; de la Fuente, M.; Goodwin, P. A.; Gottschalk, J.; Huang, E.; McCave, I. N.; Noble, T. L.; Scrivner, A. E.

2017-01-01

While the ocean’s large-scale overturning circulation is thought to have been significantly different under the climatic conditions of the Last Glacial Maximum (LGM), the exact nature of the glacial circulation and its implications for global carbon cycling continue to be debated. Here we use a global array of ocean–atmosphere radiocarbon disequilibrium estimates to demonstrate a ∼689±53 14C-yr increase in the average residence time of carbon in the deep ocean at the LGM. A predominantly southern-sourced abyssal overturning limb that was more isolated from its shallower northern counterparts is interpreted to have extended from the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the deep ocean of a fast escape route for accumulating respired carbon. While the exact magnitude of the resulting carbon cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency of the biological carbon pump that could have accounted for as much as half of the glacial–interglacial CO2 change. PMID:28703126

Rapid shifts in South American montane climates driven by pCO2 and ice volume changes over the last two glacial cycles

NASA Astrophysics Data System (ADS)

Groot, M. H. M.; Bogotá, R. G.; Lourens, L. J.; Hooghiemstra, H.; Vriend, M.; Berrio, J. C.; Tuenter, E.; van der Plicht, J.; van Geel, B.; Ziegler, M.; Weber, S. L.; Betancourt, A.; Contreras, L.; Gaviria, S.; Giraldo, C.; González, N.; Jansen, J. H. F.; Konert, M.; Ortega, D.; Rangel, O.; Sarmiento, G.; Vandenberghe, J.; van der Hammen, T.; van der Linden, M.; Westerhoff, W.

2010-10-01

Tropical montane biome migration patterns in the northern Andes are found to be coupled to glacial-induced mean annual temperature (MAT) changes; however, the accuracy and resolution of current records are insufficient to fully explore their magnitude and rates of change. Here we present a ~60-year resolution pollen record over the past 284 000 years from Lake Fúquene (5° N) in Colombia. This record shows rapid and extreme MAT changes at 2540 m elevation of up to 10 ± 2 °C within a few hundred of years that concur with the ~100 and 41-kyr (obliquity) paced glacial cycles and North Atlantic abrupt climatic events as documented in ice cores and marine sediments. Using transient climate modelling experiments we demonstrate that insolation-controlled ice volume and greenhouse gasses are the major forcing agents causing the orbital MAT changes, but that the model simulations significantly underestimate changes in lapse rates and local hydrology and vegetation feedbacks within the studied region due to its low spatial resolution.

Development of a glacially dominated shelf-slope-fan system in tectonically active southeast Alaska: Results of IODP Expedition 341 core-log-seismic integrated studies at glacial cycle resolution

NASA Astrophysics Data System (ADS)

Gulick, Sean; Jaeger, John; Mix, Alan; Swartz, John; Worthington, Lindsay; Reece, Robert

2014-05-01

Collision of the Yakutat microplate with North American formed the St. Elias Mountains in coastal Gulf of Alaska. While the tectonic driver for orogenesis has been ongoing since the Miocene, results from the Integrated Ocean Drilling Program Expedition 341 suggests that direct climatic perturbation of active orogenesis through glacial erosion is non-linear. Geophysical studies of the glaciated continental margin, slope, and adjacent deep-sea Surveyor Fan allow examination of the glaciated orogen from source to sink. Using high-resolution and crustal-scale seismic data and through comparison with other glaciated margins, we can identify key diagnostic seismic morphologies and facies indicative of glacial proximity and sediment routing. Expedition drilling results calibrated these images suggesting a timeline for initial advances of the Cordilleran ice sheet related glacial systems onto the shelf and a further timeline for the development of ice streams that reach the shelf edge. Comparisons can be made within this single margin between evolution of the tectonic-glacial system where erosion and sediment transport are occurring within a fold and thrust belt versus on a more stable shelf region. Onshore the Bering-Bagley glacial system in the west flows across the Yakataga fold and thrust belt, allowing examination of whether glacial erosion can cause tectonic feedbacks, whereas offshore the Bering-Bagley system interacts with the Pamplona Zone thrusts in a region of significant sediment accommodation. Results from Expedition 341 imply that timing of glacial advance to the shelf edge in this region may be driven by the necessity of filling up the accommodation through aggradation followed by progradation and thus is autogenic. In contrast the Malaspina-Hubbard glacial system to the east encountered significantly less accommodation and more directly responded to climatic forcing including showing outer shelf glacial occupation since the mid-Pleistocene transition-MPT to 100 kyr glacial-interglacial cycles. Examination of the sink for both of these systems, which includes the Surveyor Fan and Aleutian Trench wedge, demonstrates a clear climatic driver for sediment flux to the deep sea. The first appearance of ice-rafted debris at our distal drill site closely approximates the start of the Pleistocene and a doubling of sediment accumulation accompanies the MPT. Converting sediment volumes just within the deep-sea sinks back to erosion rates in the orogen and correlating with changes in exhumation rates from thermochronology demonstrates a lack of accelerated tectonic response to the intensification of Northern Hemisphere glaciations at the start of the Pleistocene but increased shortening and exhumation of sediments at the MPT. The form of tectonic response differs between out-of-sequence thrusting or antiformal stacking within the fold and thrust belt to the west and a near vertical advection of material in a tectonic aneurysm in the core of the orogen to the east.

Tropical Climate Variability From the Last Glacial Maximum to the Present

DTIC Science & Technology

2005-09-01

between the tropics and extrat- ropics remains an open question. Over the course of the glacial-interglacial cycles of the past 800,000 years, the high...roughly 80% of the total CSEs. The remaining 12 Younger Dryas in the Cariaco Basin. CSE peaks are consistently smaller than those mentioned [29] CSEs I...33] CSEs 8 and 15 remain unidentified. It is evident record. Identification and downcore analysis of these CSE from their downcore trends, however

Phylogeography in Galaxias maculatus (Jenyns, 1848) along Two Biogeographical Provinces in the Chilean Coast

PubMed Central

González-Wevar, Claudio A.; Salinas, Pilar; Hüne, Mathias; Segovia, Nicolás I.; Vargas-Chacoff, Luis; Astorga, Marcela; Cañete, Juan I.; Poulin, Elie

2015-01-01

Major geologic and climatic changes during the Quaternary exerted a major role in shaping past and contemporary distribution of genetic diversity and structure of aquatic organisms in southern South America. In fact, the northern glacial limit along the Pacific coast, an area of major environmental changes in terms of topography, currents, and water salinity, represents a major biogeographic transition for marine and freshwater species. We used mitochondrial DNA sequences (D-loop) to investigate the consequences of Quaternary glacial cycles over the pattern of genetic diversity and structure of G. maculatus (Pisces: Galaxiidae) along two biogeographical provinces in the Chilean coast. Extreme levels of genetic diversity and strong phylogeographic structure characterize the species suggesting a low amount of influence of the last glacial cycle over its demography. However, we recognized contrasting patterns of genetic diversity and structure between main biogeographical areas here analyzed. Along the Intermediate Area (38°–41° S) each estuarine population constitutes a different unit. In contrast, Magellanic populations (43°–53° S) exhibited low levels of genetic differentiation. Contrasting patterns of genetic diversity and structure recorded in the species between the analyzed biogeographic areas are consistent with the marked differences in abiotic factors (i.e., different coastal configurations, Quaternary glacial histories, and oceanographic regimes) and to inherent characteristics of the species (i.e., salt-tolerance, physiology, and reproductive behavior). PMID:26161896

Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age.

PubMed

Jaccard, Samuel L; Galbraith, Eric D; Martínez-García, Alfredo; Anderson, Robert F

2016-02-11

No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO2) concentration variability over glacial-interglacial cycles. A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum. However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace-metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO2 concentration increased rapidly, reflecting--at least in part--a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our records show that the observed covariation between atmospheric CO2 concentration and abyssal Southern Ocean oxygenation was maintained throughout most of the past 80,000 years. This suggests that on millennial timescales deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in modifying atmospheric CO2 concentration.

Small Mammals as Indicators of Climate, Biodiversity, and Ecosystem Change

USGS Publications Warehouse

Hope, Andrew G.; Waltari, Eric; Morse, Nathan R.; Flamme, M.J.; Cook, Joseph A.; Talbot, Sandra L.

2017-01-01

Climate is a driving evolutionary force for biodiversity in high-latitude Alaska. This region is complex and dynamic with high annual variation in temperature and light. Through deeper time, Alaska has experienced major climate extremes over much longer periodicity. For example, the Quaternary Period (the last ~2.5 million years), commonly known as the Ice Age, was punctuated by more than 20 major glacial-interglacial cycles. During glacial phases, water was locked up in ice sheets that covered much of North America, and the resulting lower sea levels exposed a land connection between Alaska and Siberia, a combined region known as Beringia (Figure 1). This isthmus provided vast expanses of land for species to inhabit, provided they could withstand potentially harsh polar conditions. Each extended glacial phase periodically transitioned into a shorter interglacial warm phase. These climate reversals melted continental ice sheets to expose corridors for reinvasion of terrestrial species, particularly those associated with forested habitats further south. Those species that survived at northern latitudes through repeated glacial-interglacial cycles formed the Arctic tundra communities that persist today. At present, Alaska supports diverse communities associated with both tundra and forests (Figure 2). These communities often interact with one another across latitudinal and elevational gradients, with tundra species generally found further north or higher in elevation. Alaska’s climate is continuing to change today, strongly influencing local environments and the distribution and dynamics of wildlife species.

The initial break-up of Pangæa elicited by Late Palæozoic deglaciation

PubMed Central

Yeh, Meng-Wan; Shellnutt, J. Gregory

2016-01-01

The break-up of Pangæa was principally facilitated by tensional plate stress acting on pre-existing suture zones. The rifting of Pangæa began during the Early Permian along the southern Tethys margin and produced the lenticular-shaped continent known as Cimmeria. A mantle-plume model is ascribed to explain the rift-related volcanism but the NW-SE oriented Cimmerian rifts do not correlate well with pre-existing suture zones or ‘structural heterogeneities’ but appear to have a pertinent spatial and temporal association with Late Palæozoic glacial-interglacial cycles. Mantle potential temperature estimates of Cimmerian rift-related basalts (1410 °C ± 50 °C) are similar to ambient mantle conditions rather than an active mantle-plume rift as previously suggested. Moreover, we find that the distribution of glacial deposits shows significant temporal and spatial concurrence between the glacial retreat margins and rifting sites. We conclude that the location and timing of Cimmerian rifting resulted from the exploitation of structural heterogeneities within the crust that formed due to repeated glacial-interglacial cycles during the Late Palæozoic. Such effects of continental deglaciation helped to create the lenticular shape of Cimmeria and Neotethys Ocean suggesting that, in some instances, climate change may directly influence the location of rifting. PMID:27511791

Climate oscillations reflected in the Arabian Sea subseafloor microbiome

NASA Astrophysics Data System (ADS)

Orsi, William; Coolen, Marco; He, Lijun; Wuchter, Cornelia; Irigoien, Xabier; Chust, Guillem; Johnson, Carl; Hemingway, Jordon; Lee, Mitchell; Galy, Valier; Giosan, Liviu

2016-04-01

Marine sediment contains a vast microbial biosphere that influences global biogeochemical cycles over geological timescales. However, the environmental factors controlling the stratigraphy of subseafloor microbial communities are poorly understood. We studied a sediment core directly underlying the Arabian Sea oxygen minimum zone (OMZ), which exhibits organic carbon rich sapropelic laminae deposited under low oxygen conditions. Consistent with several other cores from the same location, age dating revealed the sapropelic layers coincide with warm North Atlantic millennial-scale Dansgaard-Oeschger events, indicating a direct link between the strength of the OMZ and paleoclimate. A total of 214 samples spanning 13 m and 52 Kyr of deposition were selected for geochemical analyses and paleoclimate proxy measurements, as well as high-throughput metagenomic DNA sequencing of bacteria and archaea. A novel DNA extraction protocol was developed that allowed for direct (unamplified) metagenomic sequencing of DNA from each sample. This dataset represents the highest resolved sedimentary metagenomic sampling profile to date. Analysis of these data together with multiple paleoceanographic proxies show that millennial-scale paleoenvironmental conditions correlate with the metabolism and diversity of bacteria and archaea over the last glacial-interglacial cycle in the Arabian Sea. The metabolic potential for bacterial denitrification correlates with climate-driven OMZ strength and concomitant nitrogen stable isotope fractionation, whereas catabolic potential reflects changing marine organic matter sources across the Last Glacial Maximum. These results indicate that the subsisting microbial communities had been stratified to a large extent by paleoceanographic conditions at the time of deposition. Paleoenvironmental conditions should thus be considered as a mechanism that can help explain microbiome stratigraphy in marine sediment.

Reconstruction of the North Atlantic end-member of the thermohaline circulation across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Kim, J.; Seguí, M. J.; Yehudai, M.; Goldstein, S. L.; Pena, L. D.; Raymo, M. E.; Ford, H. L.; Haynes, L.; Farmer, J. R.; Hoenisch, B.

2016-12-01

The dominant periodicity of glacial and interglacial cycles shifted from 41 ky to 100 ky at 1.2-0.8 Ma, marking the Mid-Pleistocene Transition (MPT). Pena and Goldstein (Science, 2014) investigated changes in the Earth's global thermohaline circulation (THC), focusing on South Atlantic cores, and concluded that the THC experienced major disruptions between 950-850 ka (MIS 25 to 21), which generated the climatic conditions that intensified cold periods, prolonged their duration, and stabilized 100 ky cycles. However, knowledge of the coeval North Atlantic is key for interpreting data from the Middle and South Atlantic. We report Nd isotope ratios on Fe-Mn oxide encrusted foraminifera and fish debris from DSDP Site 607 (41.001N; 32.957W, 3427m) between 1.2-0.4 Ma, as a representative of the deep North Atlantic. Pre-MPT results (MIS 35-25) show interglacial ɛNd-values of -13.5 to -14.0, similar to today, and glacial-interglacial variability of 1 ɛNd-unit. Post-MPT results after MIS 19 also show interglacial ɛNd-values of -13.5 to -14.0, but greater glacial-interglacial variability of 2 ɛNd-units. Interglacial-to-glacial transitions throughout the core shift to higher ɛNd-values indicative of weakening THC, except for MIS 26, which is uniquely more negative than the neighboring interglacials, with ɛNd reaching -14.5. During the critical MPT interval of MIS 25-21 recognized by Pena and Goldstein (2014), and continuing beyond it through MIS 19, DSDP 607 ɛNd shows higher values of -11.5 to -12.5, like post-MPT glacials. Thus for the North Atlantic, from the point of view of ɛNd in DSDP 607, post-MPT and pre-MPT interglacials are similar, and post-MPT glacials and MPT glacials are similar. Moreover, comparison to the Pena and Goldstein (2014) South Atlantic data indicates that disruptions to North Atlantic overturning may have begun as early as MIS 27, and the recovery to the pre-MPT interglacial conditions may have been delayed beyond MIS 19.

Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

NASA Astrophysics Data System (ADS)

Bischoff, James L.; Menking, Kirsten M.; Fitts, Jeffrey P.; Fitzpatrick, John A.

1997-11-01

Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs 2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na 2O, TiO 2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO 3and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the δ 18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation.

Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92

USGS Publications Warehouse

Bischoff, J.L.; Menking, K.M.; Fitts, J.P.; Fitzpatrick, J.A.

1997-01-01

Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na2O, TiO2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO3 and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the ??18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation. ?? 1997 University of Washington.

Reinterpretation of the Quaternary sedimentary infill of the Ría de Vigo, NW Iberian Peninsula, as a compound incised valley

NASA Astrophysics Data System (ADS)

Martínez-Carreño, N.; García-Gil, S.

2017-10-01

Seismic data have been used to investigate the stratigraphy of the Galician rias for more than two decades. Here, we present a new interpretation of the sedimentary infill of an incised valley (Ría de Vigo, NW Iberian Peninsula), based on high-resolution seismic profiles, core sediment analysis, and radiocarbon 14C data. The new data indicate that the stratigraphic architecture of the Galician rias result from multiple incision/infill phases and, therefore, they are reclassified as compound rather than simple incised valleys. Seven seismic units were identified: one of Tertiary age (U1), four of Pleistocene age (U2-U5) which are interpreted as 4th-order sequences deposited between MIS 11 and MIS 2, and Late Pleistocene (U6) and Holocene (U7) units corresponding with post-glacial sedimentation. The sedimentary infill overlies a highly faulted irregular granitic and metamorphic basement; the inherited morphology is shown to be important for controlling the pathway and evolution of the fluvial network as well as preservation of the sedimentary deposits during several glacial/interglacial cycles. The presence of a rocky barrier at the mouth of the ria is a distinctive feature that conditions sedimentation and exchange of sediment between the ria and the adjacent shelf. For the first time, faults and tilted blocks affecting Late Pleistocene (MIS 3) deposits have been identified. The new data presented here provide the opportunity to reconstruct the evolution of the sedimentary infill of a ria, with especially high-resolution during the last post-glacial transgression.

The George V Land Continental Margin (East Antarctica): new Insights Into Bottom Water Production and Quaternary Glacial Processes from the WEGA project

NASA Astrophysics Data System (ADS)

Caburlotto, A.; de Santis, L.; Lucchi, R. G.; Giorgetti, G.; Damiani, D.; Macri', P.; Tolotti, R.; Presti, M.; Armand, L.; Harris, P.

2004-12-01

The George Vth Land represents the ending of one of the largest subglacial basin (Wilkes Basin) of the East Antarctic Ice Sheet (EAIS). Furthermore, its coastal areas are zone of significant production of High Salinity Shelf Water (HSSW). Piston and gravity cores and high resolution echo-sounding (3.5 kHz) and Chirp profiles collected in the frame of the joint Australian and Italian WEGA (WilkEs Basin GlAcial History) project provide new insights into the Quaternary history of the EAIS and the HSSW across this margin: from the sediment record filling and draping valleys and banks along the continental shelf, to the continuous sedimentary section of the mound-channel system on the continental rise. The discovery of a current-lain sediment drift (Mertz Drift, MD) provides clues to understanding the age of the last glacial erosive events, as well as to infer flow-pathways of bottom-water masses changes. The MD shows disrupted, fluted reflectors due to glacial advance during the LGM (Last Glacial Maximum) in shallow water, while undisturbed sediment drift deposited at greater water depth, indicates that during the LGM the ice shelf was floating over the deep sector of the basin. The main sedimentary environment characterising the modern conditions of the continental rise is dominated by the turbiditic processes with a minor contribution of contour currents action. Nevertheless, some areas (WEGA Channel) are currently characterised by transport and settling of sediment through HSSW, originating in the shelf area. This particular environment likely persisted since pre-LGM times. It could indicate a continuous supply of sedimentary material from HSSW during the most recent both glacial and interglacial cycles. This would be consistent with the results obtained in the continental shelf suggesting that the Ice Sheet was not grounding over some parts of the continental shelf. Furthermore, the comparison of the studied area with other Antarctic margins indicate that, contrary to what happens on the Antarctic Peninsula margin, the relation between the Quaternary sedimentation and the glacial - interglacial cycles are less evident in the lithofacies observed on the continental rise area. This characteristic suggests a different glacial dynamic along the Wilkes Land continental margin that is less sensitive to the small climatic changes, with respect to the western (Antarctic Peninsula) margin.

Changes in Fe Oxidation Rate in Hydrothermal Plumes as a Potential Driver of Enhanced Hydrothermal Input to Near-Ridge Sediments During Glacial Terminations

NASA Astrophysics Data System (ADS)

Cullen, J. T.; Coogan, L. A.

2017-12-01

Recent studies have hypothesized that changes in sea level due to glacial-interglacial cycles lead to changes in the rate of melt addition to the crust at mid-ocean ridges with globally significant consequences. Arguably the most compelling evidence for this comes from increases in the hydrothermal component in near-ridge sediments during glacial-interglacial transitions. Here we explore the hypothesis that changes in ocean bottom water [O2] and pH across glacial-interglacial transitions would lead to changes in the rate of Fe oxidation in hydrothermal plumes. A simple model shows that a several fold increase in the rate of Fe oxidation is expected at glacial-interglacial transitions. Uncertainty in bottom water chemistry and the relationship between oxidation and sedimentation rates prevent direct comparison of the model and data. However, it appears that the null hypothesis of invariant hydrothermal vent fluxes into ocean bottom water that changed in O2 content and pH across these transitions cannot currently be discounted.

Quaternary glaciation and hydrologic variation in the South American tropics as reconstructed from the Lake Titicaca drilling project

NASA Astrophysics Data System (ADS)

Fritz, Sherilyn C.; Baker, Paul A.; Seltzer, Geoffrey O.; Ballantyne, Ashley; Tapia, Pedro; Cheng, Hai; Edwards, R. Lawrence

2007-11-01

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon.

Late Cenozoic surficial deposits and valley evolution of unglaciated northern New Jersey

USGS Publications Warehouse

Stanford, S.D.

1993-01-01

Multiple alluvial, colluvial, and eolian deposits in unglaciated northern New Jersey, and the eroded bedrock surfaces on which they rest, provide evidence of both long-term valley evolution driven by sustained eustatic baselevel lowering and short-term filling and excavation of valleys during glacial and interglacial climate cycles. The long-term changes occur over durations of 106 years, the short-term features evolve over durations of 104 to 105 years. Direct glacial effects, including blockage of valleys by glacial ice and sediment, and valley gradient reversals induced by crustal depression, are relatively sudden changes that account for several major Pleistocene drainage shifts. After deposition of the Beacon Hill fluvial gravel in the Late Miocene, lowering of sea level, perhaps in response to growth of the Antarctic ice sheet, led to almost complete dissection of the gravel. A suite of alluvial, colluvial, and eolian sediments was deposited in the dissected landscape. The fluvial Bridgeton Formation was deposited in the Raritan lowland, in the Amboy-Trenton lowland, and in the Delaware valley. Following southeastward diversion of the main Bridgeton river, perhaps during Late Pliocene or Early Pleistocene glaciation, northeastward drainage was established on the inactive Bridgeton fluvial plain. About 30 to 45 m of entrenchment followed, forming narrow, incised valleys within which Late Pleistocene deposits rest. This entrenchment may have occurred in response to lowered sea level caused by growth of ice sheets in the northern hemisphere. Under periglacial conditions in the Middle and Late Pleistocene, valleys were partially filled with alluvium and colluvium. During interglacials slopes were stabilized by vegetation and the alluvial and colluvial valley-fill was excavated by gullying, bank erosion, and spring sapping. During Illinoian and late Wisconsinan glaciation, the lower Raritan River was diverted when glacial deposits blocked its valley, and the Delaware River was partially diverted down the isostatically-steepened lower Millstone valley. ?? 1993.

Phylogeographic Insights into a Peripheral Refugium: The Importance of Cumulative Effect of Glaciation on the Genetic Structure of Two Endemic Plants

PubMed Central

Zecca, Giovanni; Minuto, Luigi

2016-01-01

Quaternary glaciations and mostly last glacial maximum have shaped the contemporary distribution of many species in the Alps. However, in the Maritime and Ligurian Alps a more complex picture is suggested by the presence of many Tertiary paleoendemisms and by the divergence time between lineages in one endemic species predating the Late Pleistocene glaciation. The low number of endemic species studied limits the understanding of the processes that took place within this region. We used species distribution models and phylogeographical methods to infer glacial refugia and to reconstruct the phylogeographical pattern of Silene cordifolia All. and Viola argenteria Moraldo & Forneris. The predicted suitable area for last glacial maximum roughly fitted current known distribution. Our results suggest that separation of the major clades predates the last glacial maximum and the following repeated glacial and interglacial periods probably drove differentiations. The complex phylogeographical pattern observed in the study species suggests that both populations and genotypes extinction was minimal during the last glacial maximum, probably due to the low impact of glaciations and to topographic complexity in this area. This study underlines the importance of cumulative effect of previous glacial cycles in shaping the genetic structure of plant species in Maritime and Ligurian Alps, as expected for a Mediterranean mountain region more than for an Alpine region. PMID:27870888

Causes of ice age intensification across the Mid-Pleistocene Transition

PubMed Central

Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-01-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets. PMID:29180424

Causes of ice age intensification across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Chalk, Thomas B.; Hain, Mathis P.; Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Badger, Marcus P. S.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Jaccard, Samuel L.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-12-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ˜40,000 (˜40 ky) to ˜100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ˜43 to ˜75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

Glacial CO2 Cycles: A Composite Scenario

NASA Astrophysics Data System (ADS)

Broecker, W. S.

2015-12-01

There are three main contributors to the glacial drawdown of atmospheric CO2 content: starvation of the supply of carbon to the ocean-atmosphere reservoir, excess CO2 storage in the deep sea, and surface-ocean cooling. In this talk, I explore a scenario in which all three play significant roles. Key to this scenario is the assumption that deep ocean storage is related to the extent of nutrient stratification of the deep Atlantic. The stronger this stratification, the larger the storage of respiration CO2. Further, it is my contention that the link between Milankovitch insolation cycles and climate is reorganizations of the ocean's thermohaline circulation leading to changes in the deep ocean's CO2 storage. If this is the case, the deep Atlantic d13C record kept in benthic foraminifera shells tells us that deep ocean CO2 storage follows Northern Hemisphere summer insolation cycles and thus lacks the downward ramp so prominent in the records of sea level, benthic 18O and CO2. Rather, the ramp is created by the damping of planetary CO2 emissions during glacial time intervals. As it is premature to present a specific scenario, I provide an example as to how these three contributors might be combined. As their magnitudes and shapes remain largely unconstrained, the intent of this exercise is to provoke creative thinking.

Effects of climatic and geological processes during the pleistocene on the evolutionary history of the northern cavefish, Amblyopsis spelaea (teleostei: amblyopsidae).

PubMed

Niemiller, Matthew L; McCandless, James R; Reynolds, R Graham; Caddle, James; Near, Thomas J; Tillquist, Christopher R; Pearson, William D; Fitzpatrick, Benjamin M

2013-04-01

Climatic and geological processes associated with glaciation cycles during the Pleistocene have been implicated in influencing patterns of genetic variation and promoting speciation of temperate flora and fauna. However, determining the factors promoting divergence and speciation is often difficult in many groups because of our limited understanding of potential vicariant barriers and connectivity between populations. Pleistocene glacial cycles are thought to have significantly influenced the distribution and diversity of subterranean invertebrates; however, impacts on subterranean aquatic vertebrates are less clear. We employed several hypothesis-driven approaches to assess the impacts of Pleistocene climatic and geological changes on the Northern Cavefish, Amblyopsis spelaea, whose current distribution occurs near the southern extent of glacial advances in North America. Our results show that the modern Ohio River has been a significant barrier to dispersal and is correlated with patterns of genetic divergence. We infer that populations were isolated in two refugia located north and south of the Ohio River during the most recent two glacial cycles with evidence of demographic expansion in the northern isolate. Finally, we conclude that climatic and geological processes have resulted in the formation of cryptic forms and advocate recognition of two distinct phylogenetic lineages currently recognized as A. spelaea. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

Loess deposits in Beijing and their paleoclimatic implications during the last interglacial-glacial cycle

NASA Astrophysics Data System (ADS)

Tian, Shengchen; Sun, Jimin; Gong, Zhijun

2017-12-01

Loess-paleosol sequences are important terrestrial paleoclimatic archives in the semi-arid region of north-central China. Compared with the numerous studies on the loess of the Chinese Loess Plateau, the eolian deposits, near Beijing, have not been well studied. A new loess section in the northeast suburb of Beijing provides an opportunity for reconstructing paleoenvironmental changes in this region. An optically stimulated luminescence (OSL) chronology yields ages of 145.1 to 20.5 ka, demonstrating that the loess deposits accumulated during the last interglacial-glacial cycle. High-resolution climatic proxies, including color-index, particle size and magnetic parameters, reveal orbital-scale climatic cycles, corresponding to marine oxygen isotope stages (MIS) 6 to MIS 2. In contrast to the loess deposits of the central Loess Plateau, loess near Beijing is a mixture of distal dust materials from gobi and sand deserts in the arid part of northwestern China and proximal, local alluvial sediments. Climatic change in Beijing during the last interglacial-glacial cycle was controlled primarily by the changing strength of the East Asian monsoon. Paleosols developed during the last interglacial complex (between 144.0 and 73.0 ka) and the interstadial of the last glaciation (between 44.6 and 36.2 ka), being associated with an enhanced summer monsoon in response to increased low-latitude insolation and a weakened Siberia High. Loess accumulation occurred during cold-dry stages of the last glaciation, in response to the intensified winter monsoon driven by the strengthened Siberia High and its longer residence time.

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

NASA Astrophysics Data System (ADS)

Grämiger, Lorenz M.; Moore, Jeffrey R.; Gischig, Valentin S.; Ivy-Ochs, Susan; Loew, Simon

2017-04-01

Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

2017-05-01

Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

Transient Deformation Patterns in Response to Quaternary Glacial Advance-Retreat Across the Offshore St. Elias Mountains, southern Alaska

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Clary, W. A.; Daigle, H.; Koons, P. O.; Gulick, S. P. S.; Jaeger, J. M.

2016-12-01

The southern Alaska margin, home to the St. Elias Mountains, the highest coastal mountain range on Earth experiencing the highest erosion rates on Earth, provides a superb setting for evaluating competing influences of rheological and climate control on orogen development. Previous studies have recognized this potential, but conclusions were limited due to the absence of information on the time-dependent behavior of climate and rheological processes. These limitations can now be surpassed due to 1) the recent availability of high-precision age constraints on the structural and stratigraphic evolution of offshore sediments and structures and 2) geotechnical information on the extent of dewatering and related spatial changes in the material properties of these sediments. We correlate emerging results from Integrated Ocean Drilling Program (IODP) Expedition 341 Sites U1420 and U1421 with regional seismic data across the continental shelf and slope to determine the spatial and temporal evolution of thrusting in response to Yakutat-North American convergence. Our mapping shows that the pattern of faulting changed from distributed across the shelf to highly localized away from the primary glacial depocenter over the course of one glacial cycle. Core samples suggest that the glacially derived sediment is overpressured, with pore pressures possibly reaching >90% of lithostatic stress. Elevated pore pressures develop rapidly in response to focused glaciomarine sedimentation, in addition to direct ice loading, and may induce a transient state of wedge reorganization manifested as a change in localization of deformation. This relationship suggests that the additive response of pore pressure variations over glacial cycles throughout the Pleistocene and Holocene result in constant reorganization of deformation style and location.

Coupled energy-balance/ice-sheet model simulations of the glacial cycle: A possible connection between terminations and terrigenous dust

NASA Astrophysics Data System (ADS)

Peltier, W. Richard; Marshall, Shawn

1995-07-01

We apply a coupled energy-balance/ice-sheet climate model in an investigation of northern hemisphere ice-sheet advance and retreat over the last glacial cycle. When driven only by orbital insolation variations, the model predicts ice-sheet advances over the continents of North America and Eurasia that are in good agreement with geological reconstructions in terms of the timescale of advance and the spatial positioning of the main ice masses. The orbital forcing alone, however, is unable to induce the observed rapid ice-sheet retreat, and we conclude that additional climatic feedbacks not explicitly included in the basic model must be acting. In the analyses presented here we have parameterized a number of potentially important effects in order to test their relative influence on the process of glacial termination. These include marine instability, thermohaline circulation effects, carbon dioxide variations, and snow albedo changes caused by dust loading during periods of high atmospheric aerosol concentration. For the purpose of these analyses the temporal changes in the latter two variables were inferred from ice core records. Of these various influences, our analyses suggest that the albedo variations in the ice-sheet ablation zone caused by dust loading may represent an extremely important ablation mechanism. Using our parameterization of "dirty" snow in the ablation zone we find glacial retreat to be strongly accelerated, such that complete collapse of the otherwise stable Laurentide ice sheet ensues. The last glacial maximum configurations of the Laurentide and Fennoscandian complexes are also brought into much closer accord with the ICE-3G reconstruction of Tushingham and Peltier (1991,1992) and the ICE-4G reconstruction of Peltier (1994) when this effect is reasonably introduced.

Age scatter in cosmogenic exposure-age chronologies in the McMurdo Dry Valleys, Antarctica: implications for regional glacial history and sampling strategies

NASA Astrophysics Data System (ADS)

Swanger, K. M.; Schaefer, J. M.; Winckler, G.; Lamp, J. L.; Marchant, D. R.

2016-12-01

Based on surface exposure dating of moraines and drifts, East Antarctic outlet glaciers in the McMurdo Dry Valleys (MDV) advanced during the mid-Pliocene and/or early-Pleistocene. However, scatter in exposure ages is common for these deposits (and other glacial drifts throughout Antarctica), making it difficult to tie glacial advances to specific climate intervals. In order to constrain the sources of scatter, we mapped and dated 15 cold-based drifts in Taylor Valley and the Olympus Range in the MDV. A secondary goal was to build a regional climate record, for comparison with fluctuations of the local outlet glaciers. Our alpine drift record is confined to the late-Pleistocene, with glacial advances during interglacial periods. Based on 54 3He exposure dates on alpine drifts, age scatter is common in the MDV on both recent and ancient deposits. Where it occurs, age scatter is likely caused by inheritance of cosmogenic nuclides previous to glacial entrainment and stacking of multiple cold-based drifts. Nuclide inheritance of >1 Myr is possible, but this is relatively rare and confined to regions where englacial debris is sourced from stable, high-elevation plateaus. On the other hand, drifts associated with glaciers bound by steep cirque headwalls and arêtes exhibit significantly less age scatter. Given the cold-based nature of MDV alpine and outlet glaciers, deposition of multiple stacked drift sheets also contributes to age scatter, with the implication that it might be possible to date multiple advances of cold-based ice. These results serve to inform better sampling strategies on cold-based drifts throughout Antarctica.

Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus)

PubMed Central

Newman, Catherine E.; Austin, Christopher C.

2015-01-01

The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a “one-size-fits-all” model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species. PMID:26132077

Nonlinear climatic sensitivity to greenhouse gases over past 4 glacial/interglacial cycles.

PubMed

Lo, Li; Chang, Sheng-Pu; Wei, Kuo-Yen; Lee, Shih-Yu; Ou, Tsong-Hua; Chen, Yi-Chi; Chuang, Chih-Kai; Mii, Horng-Sheng; Burr, George S; Chen, Min-Te; Tung, Ying-Hung; Tsai, Meng-Chieh; Hodell, David A; Shen, Chuan-Chou

2017-07-04

The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2-4 at atmospheric CO 2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO 2 levels reach threshold levels.

Glacial History of Southernmost South America and Implications for Movement of the Westerlies and Antarctic Frontal Zone

NASA Astrophysics Data System (ADS)

Kaplan, M. R.; Fogwill, C. J.; Hulton, N. R.; Sugden, D. E.; Peter, K. W.

2004-12-01

The ~1 Myr glacial geologic record in southern South American is one of the few available terrestrial paleoclimate proxies at orbital and suborbital time scales in the middle latitudes of the Southern Hemisphere. Presently, southernmost Patagonia lies about 3\\deg north of the Antarctic frontal zone and within the middle latitude westerlies and the climate is controlled by the surrounding maritime conditions. Thus, the long-term glacial record provides insight into the history of climatic boundaries over the middle and high latitude southern ocean, including the upwind SE Pacific Ocean, tectonic-glacial evolution of the Andes, and global climate. To date, cosmogenic nuclide and 14C dating have focused on glacial fluctuations between 51 and 53\\deg S (Torres del Paine to northern Tierra del Fuego) during the last glacial cycle, including the late glacial period. At least 4 advances occurred between ca. 25 and 17 ka, with the maximum expansion of ice ca. 25-24 ka. Major deglaciation commenced after ca. 17.5 ka, which was interrupted by a major glacial-climate event ca. 14-12 ka. Modelling experiments suggest that the ice mass needed to form the glacial maximum moraines required about a 6\\deg cooling and a slight drying relative to the present. Such a fundamental temperature reduction, despite high summer isolation, strongly suggests northward movement of the westerlies and the polar front on millennial timescales. The Patagonian record also indicates that on orbital timescales equatorward movement of climate boundaries and glacial growth was in phase with major Northern Hemisphere ice volume change, despite high local summer insolation. At suborbital timescales, the picture is more complex. While major facets of the last glacial maximum appear to be in phase between the hemispheres, at least some late glacial events may be in step with Antarctic climate change. Present and future research will further constrain the timing of glacial events over the last 1 Myr and the relation with mountain valley evolution and Southern Hemisphere climate change.

Gone with the currents: lack of genetic differentiation at the circum-continental scale in the Antarctic krill Euphausia superba

PubMed Central

2011-01-01

Background Southern Ocean fauna represent a significant amount of global biodiversity, whose origin may be linked to glacial cycles determining local extinction/eradication with ice advance, survival of refugee populations and post-glacial re-colonization. This pattern implies high potential for differentiation in benthic shelf species with limited dispersal, yet consequences for pelagic organisms are less clear. The present study investigates levels of genetic variation and population structure of the Antarctic krill Euphausia superba using mitochondrial DNA and EST-linked microsatellite markers for an unprecedentedly comprehensive sampling of its populations over a circum-Antarctic range. Results MtDNA (ND1) sequences and EST-linked microsatellite markers indicated no clear sign of genetic structure among populations over large geographic scales, despite considerable power to detect differences inferred from forward-time simulations. Based on ND1, few instances of genetic heterogeneity, not significant after correction for multiple tests, were detected between geographic or temporal samples. Neutrality tests and mismatch distribution based on mtDNA sequences revealed strong evidence of past population expansion. Significant positive values of the parameter g (a measure of population growth) were obtained from microsatellite markers using a coalescent-based genealogical method and suggested a recent start (60 000 - 40 000 years ago) for the expansion. Conclusions The results provide evidence of lack of genetic heterogeneity of Antarctic krill at large geographic scales and unequivocal support for recent population expansion. Lack of genetic structuring likely reflects the tight link between krill and circum-Antarctic ocean currents and is consistent with the hypothesis that differentiation processes in Antarctic species are largely influenced by dispersal potential, whereas small-scale spatial and temporal differentiation might be due to local conditions leading to genetic patchiness. The signal of recent population growth suggests differential impact of glacial cycles on pelagic Antarctic species, which experienced population expansion during glaciations with increased available habitat, versus sedentary benthic shelf species. EST-linked microsatellites provide new perspectives to complement the results based on mtDNA and suggest that data-mining of EST libraries will be a useful approach to facilitate use of microsatellites for additional species. PMID:21486439

Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

NASA Astrophysics Data System (ADS)

Dupont, L. M.; Caley, T.; Kim, J.-H.; Castañeda, I.; Malaizé, B.; Giraudeau, J.

2011-11-01

Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ∼120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.

Unstable AMOC during glacial intervals and millennial variability: The role of mean sea ice extent

NASA Astrophysics Data System (ADS)

Sévellec, Florian; Fedorov, Alexey V.

2015-11-01

A striking feature of paleoclimate records is the greater stability of the Holocene epoch relative to the preceding glacial interval, especially apparent in the North Atlantic region. In particular, strong irregular variability with an approximately 1500 yr period, known as the Dansgaard-Oeschger (D-O) events, punctuates the last glaciation, but is absent during the interglacial. Prevailing theories, modeling and data suggest that these events, seen as abrupt warming episodes in Greenland ice cores and sea surface temperature records in the North Atlantic, are linked to reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). In this study, using a new low-order ocean model that reproduces a realistic power spectrum of millennial variability, we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene (1 kyr = 1000 yr). Previous modeling studies show that the edge of sea ice in the North Atlantic shifts southward during glacial intervals, moving the region of the North Atlantic Deep Water formation and the AMOC also southward. Here we demonstrate that, by shifting the AMOC with respect to the mean atmospheric precipitation field, such a displacement makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials.

A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

NASA Astrophysics Data System (ADS)

Archer, D.

2015-05-01

A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial-interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial-interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere-ocean-terrestrial carbon cycle.

Glacial Age Correlations and Pedogenesis Rates at Long Valley, Costilla Masif, Northern New Mexico

NASA Astrophysics Data System (ADS)

Feldman, A. D.

2017-12-01

New Mexico represents the southernmost extent of glacial activity in the United States. As such an enhanced understanding of glacial climate cycles in the region as expressed through the relict landscapes they leave behind can enhance our understanding of the evolution of high altitude landscapes and soils throughout the Quaternary period. The Sangre De Cristo mountain range in northern New Mexico exhibits some of the southernmost expansion of glacial activity in the Southwest during the Quaternary; yet the range has had only limited correlation of its glacial chronology performed to date. In this study a detailed investigation into soil pedogenesis on relict moraine features is used to fit the Long Valley glacial sequence extending eastward from the Costilla Masif into the established Rocky Mountain glacial chronology. Analyzed soil development characteristics are particle size, organic carbon, and iron oxide distributions including total iron, ferric iron, ferrous iron, citrate dithionite, hydroxylamine for amorphous ferrihydrite, and pyrophosphate for organically bound iron. In addition, soils developement will be analyzed in situ for computation of a modified Harden soil profile development index. A secondary purpose of the study is to establish better constraints on the rates of soil pedogenesis in these high altitude glacial features. Soil profile developement and pedogenesis rates will be compared with previously published data from areas both further south in the Sangre De Cristo's as well as throughout the more northern sections of the Rocky Mountains to correlate moraine ages as well as to constrain how the particular climate of the Long Valley has affected soil development during the Quaternary.

Mid-Ocean Ridge Melt Supply and Glacial Cycles: A 3D EPR Study of Crustal Thickness, Layer 2A, and Bathymetry

NASA Astrophysics Data System (ADS)

Boulahanis, B.; Aghaei, O.; Carbotte, S. M.; Huybers, P. J.; Langmuir, C. H.; Nedimovic, M. R.; Carton, H. D.; Canales, J. P.

2017-12-01

Recent studies suggest that eustatic sea level fluctuations induced by glacial cycles in the Pleistocene may influence mantle-melting and volcanic eruptions at mid-ocean ridges (MOR), with models predicting variation in oceanic crustal thickness linked to sea level change. Previous analyses of seafloor bathymetry as a proxy for crustal thickness show significant spectral energy at frequencies linked to Milankovitch cycles of 1/23, 1/41, and 1/100 ky-1, however the effects of faulting in seafloor relief and its spectral characteristics are difficult to separate from climatic signals. Here we investigate the hypothesis of climate driven periodicity in MOR magmatism through spectral analysis, time series comparisons, and statistical characterization of bathymetry data, seismic layer 2A thickness (as a proxy for extrusive volcanism), and seafloor-to-Moho thickness (as a proxy for total magma production). We utilize information from a three-dimensional multichannel seismic study of the East Pacific Rise and its flanks from 9°36`N to 9°57`N. We compare these datasets to the paleoclimate "LR04" benthic δ18O stack. The seismic dataset covers 770 km2 and provides resolution of Moho for 92% of the imaged region. This is the only existing high-resolution 3-D image across oceanic crust, making it ideal for assessing the possibility that glacial cycles modulate magma supply at fast spreading MORs. The layer 2A grid extends 9 km (170 ky) from the ridge axis, while Moho imaging extends to a maximum of 16 km (310 ky). Initial results from the East Pacific Rise show a relationship between sea level and both crustal thickness and sea floor depth, consistent with the hypothesis that magma supply to MORs may be modulated by glacial cycles. Analysis of crustal thickness and bathymetry data reveals spectral peaks at Milankovitch frequencies of 1/100 ky-1 and 1/41 ky-1 where datasets extend sufficiently far from the ridge. The layer 2A grid does not extend sufficiently far from the ridge to be conclusive. Correlations between sea level and crustal thickness suggest a lag of 65 ky between sea level forcing and crustal thickness response. A further lag of 25 ky is observed between crustal thickness variations and seafloor depth change, which we attribute to the finite width of the crustal formation zone.

Multiple crossings of a large glacial river by Canada Lynx (Lynx canadensis)

Treesearch

D. Feierabend; K. Kielland

2014-01-01

Rivers may act as barriers to the movement of terrestrial mammals, which could limit dispersal and gene flow. Glacial rivers are particularly hazardous because of the cold water temperature and swift current. Yet, we determined that 2 Canada Lynx (Lynx canadensis) equipped with GPS collars repeatedly swam across the main channel of the Tanana River in interior Alaska...

Diversification, Biogeographic Pattern, and Demographic History of Taiwanese Scutellaria Species Inferred from Nuclear and Chloroplast DNA

PubMed Central

Liao, Pei-Chun

2012-01-01

The ragged topography created by orogenesis generates diversified habitats for plants in Taiwan. In addition to colonization from nearby mainland China, high species diversity and endemism of plants is also present in Taiwan. Five of the seven Scutellaria species (Lamiaceae) in Taiwan, for example, are endemic to the island. Hypotheses of multiple sources or in situ radiation have arisen to explain the high endemism of Taiwanese species. In this study, phylogenetic analyses using both nuclear and chloroplast markers revealed the multiple sources of Taiwanese Scutellaria species and confirmed the rapid and recent speciation of endemic species, especially those of the “indica group” composed of S. indica, S. austrotaiwanensis, S. tashiroi, and S. playfairii. The common ancestors of the indica group colonized first in northern Taiwan and dispersed regionally southward and eastward. Climate changes during glacial/interglacial cycles led to gradual colonization and variance events in the ancestors of these species, resulting in the present distribution and genetic differentiation of extant populations. Population decline was also detected in S. indica, which might reflect a bottleneck effect from the glacials. In contrast, the recently speciated endemic members of the indica group have not had enough time to accumulate much genetic variation and are thus genetically insensitive to demographic fluctuations, but the extant lineages were spatially expanded in the coalescent process. This study integrated phylogenetic and population genetic analyses to illustrate the evolutionary history of Taiwanese Scutellaria of high endemism and may be indicative of the diversification mechanism of plants on continental islands. PMID:23226402

Quaternary glaciations : from observations to theories (Milankovic Medal Lecture)

NASA Astrophysics Data System (ADS)

Paillard, Didier

2013-04-01

Since the mid-nineteenth century, the idea that climate may change through time has been substantiated by the observation of past glacial periods. During this time, two alternative views of glaciations have dominated the scientific debates : astronomical theories and geochemical ones involving changes in greenhouse gas concentrations. In the last decades, the validity of the Milankovitch theory has been clearly demonstrated, though several problems have been pointed out, most notably the difficulty to explain the 100-kyr cycles in simple versions of this theory. Besides, changes in atmospheric CO2 concentration have been documented, and they appear tightly linked to glaciation cycles. A central question of Quaternary Climate Sciences is therefore to understand the respective roles of the astronomical and geochemical changes, and how they can be dynamically combined in order to explain paleoclimatic observations. After some historical background, I will address this question from the viewpoint of conceptual models. I will highlight their predictive power and their limitations. Most importantly, these models are helping us to formulate hypotheses in order to unravel the required dynamical structure of the astronomical-glaciological-geochemical-climatical problem. I will discuss in some details how the model of Paillard (1998) leads naturally to the counter-intuitive idea that full glaciations should trigger oceanic CO2 degassing and thus to the model of Paillard and Parrenin (2004), by using the underlying mechanism of brine rejection during sea ice formation around Antarctica. Then I will present results from a more complex model (CLIMBER-2) that validate this mechanism through the comparison of simulated and observed paleoclimatic tracer distributions of 13C and 14C (Bouttes et al., 2011; Mariotti et al. 2013). The model simulation of the last deglaciation (Bouttes et al., 2012) predicts that, when brine formation is stopped, atmospheric CO2 and Antarctic temperatures should start rising together at the exact same time. This fact has now been confirmed from Antarctic ice core analysis (Parrenin et al, 2013). It seems therefore that we are getting closer to a full synthesis of the astronomical and geochemical theories of Quaternary Climate. Paillard D. (1998) The timing of Pleistocene glaciations from a simple multiple-state climate model. Nature, vol. 391 pp. 378-381. Paillard D., Parrenin F. (2004) The Antarctic ice-sheet and the triggering of deglaciations. Earth Planet. Sci. Lett. ,vol. 227 (3-4) pp. 263-271. Bouttes N. et al. (2011) Last Glacial Maximum CO2 and δ13C successfully reconciled. Geophys. Res. Lett., vol. 38 (2) pp. 1-5. Bouttes N. et al. (2012) Impact of oceanic processes on the carbon cycle during the last termination. Clim Past, vol. 8 (1) pp. 149-170. Mariotti V. et al., (accepted) Simulated Last Glacial Maximum ?14CATM and the deep glacial ocean carbon reservoir, Radiocarbon. Parrenin F. et al., (in press) Synchronous change of atmospheric CO2 and Antarctic temperature during the last deglacial warming, Science.

Exposure dating and glacial reconstruction at Mt. Field, Tasmania, Australia, identifies MIS 3 and MIS 2 glacial advances and climatic variability

NASA Astrophysics Data System (ADS)

Mackintosh, A. N.; Barrows, T. T.; Colhoun, E. A.; Fifield, L. K.

2006-05-01

Tasmania is important for understanding Quaternary climatic change because it is one of only three areas that experienced extensive mid-latitude Southern Hemisphere glaciation and it lies in a dominantly oceanic environment at a great distance from Northern Hemisphere ice sheet feedbacks. We applied exposure dating using 36Cl to an extensive sequence of moraines from the last glacial at Mt. Field, Tasmania. Glaciers advanced at 41-44 ka during Marine oxygen Isotope Stage (MIS) 3 and at 18 ka during MIS 2. Both advances occurred in response to an ELA lowering greater than 1100 m below the present-day mean summer freezing level, and a possible temperature reduction of 7-8°C. Deglaciation was rapid and complete by ca. 16 ka. The overall story emerging from studies of former Tasmanian glaciers is that the MIS 2 glaciation was of limited extent and that some glaciers were more extensive during earlier parts of the last glacial cycle. Copyright

Enhanced subarctic Pacific stratification and nutrient utilization during glacials over the last 1.2 Myr

NASA Astrophysics Data System (ADS)

Knudson, Karla P.; Ravelo, Ana Christina

2015-11-01

The relationship between climate, biological productivity, and nutrient flux is of considerable interest in the subarctic Pacific, which represents an important high-nitrate, low-chlorophyll region. While previous studies suggest that changes in iron supply and/or physical ocean stratification could hypothetically explain orbital-scale fluctuations in subarctic Pacific nutrient utilization and productivity, previous records of nutrient utilization are too short to evaluate these relationships over many glacial-interglacial cycles. We present new, high-resolution records of sedimentary δ15N, which offer the first opportunity to evaluate systematic, orbital-scale variations in subarctic Pacific nitrate utilization from 1.2 Ma. Nitrate utilization was enhanced during all glacials, varied with orbital-scale periodicity since the mid-Pleistocene transition, was strongly correlated with enhanced aeolian dust and low atmospheric CO2, but was not correlated with productivity. These results suggest that glacial stratification, rather than iron fertilization, systematically exerted an important regional control on nutrient utilization and air-sea carbon flux.

Ice stream reorganization and glacial retreat on the northwest Greenland shelf

NASA Astrophysics Data System (ADS)

Newton, A. M. W.; Knutz, P. C.; Huuse, M.; Gannon, P.; Brocklehurst, S. H.; Clausen, O. R.; Gong, Y.

2017-08-01

Understanding conditions at the grounding-line of marine-based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2-D and 3-D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega-scale glacial lineations, grounding-zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of 80 km across the outer shelf, the margin stabilized in a mid-shelf position, possibly during the Younger Dryas (12.9-11.7 ka). The ice sheet then decoupled from the seafloor and retreated to a coast-proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.

The influence of Antarctic subglacial volcanism on the global iron cycle during the Last Glacial Maximum

PubMed Central

Frisia, Silvia; Weyrich, Laura S.; Hellstrom, John; Borsato, Andrea; Golledge, Nicholas R.; Anesio, Alexandre M.; Bajo, Petra; Drysdale, Russell N.; Augustinus, Paul C.; Rivard, Camille; Cooper, Alan

2017-01-01

Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice-Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean. Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions. PMID:28598412

Molecular data and ecological niche modelling reveal the phylogeographic pattern of Cotinus coggygria (Anacardiaceae) in China's warm-temperate zone.

PubMed

Wang, W; Tian, C Y; Li, Y H; Li, Y

2014-11-01

The phylogeography of common and widespread species helps to elucidate the history of local flora and vegetation. In this study, we selected Cotinus coggygria, a species widely distributed in China's warm-temperate zone. One chloroplast DNA (cpDNA) region and ecological niche modelling were used to examine the phylogeographic pattern of C. coggygria. The cpDNA data revealed two phylogeographic groups (Southern and Northern) corresponding to the geographic regions. Divergence time analyses revealed that divergence of the two groups occurred at approximately 147,000 years before the present (BP), which coincided with the formation of the downstream area of the Yellow River, indicating that the Yellow River was a weak phylogeographic divide for C. coggygria. The molecular data and ecological niche modelling also indicated that C. coggyria did not experience population expansion after glaciations. This study thus supports the fact that Pleistocene glacial cycles only slightly affected C. coggygria, which survived in situ and occupied multiple localised glacial refugia during glaciations. This finding is contrary to the hypothesis of large-scale range habitat contraction and retreat into a few main refugia. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

Glacial Extent in the Western Ross Sea During the Early Miocene Climatic Optimum (18-16 Ma): Results From The ANDRILL AND-2A Drillcore, Southern McMurdo Sound Project, Antarctica

NASA Astrophysics Data System (ADS)

Pekar, S. F.; Hauptvogel, D.; Florindo, F.

2012-12-01

Litho- and sequence stratigraphic results from the ANDRILL Southern McMurdo Sound AND-2A Project indicate large variations in glacial conditions in the western Ross Sea, between the two isotopic Mi events (i.e., inferred glacioeustasy), Mi1b (17.8 Ma) and Mi2 (16.1 Ma). Most of this interval had not been previously recovered from the Antarctic continental margin providing the first opportunity to develop direct evidence on the evolution of the ice sheet during this time. During the 2007 austral spring/summer, the ANtarctic Geological DRILLing Program (ANDRILL) Southern McMurdo Sound (SMS) AND-2A drill hole cored 1138 meters of sediments, with ~98% recovery. The interval between 780 and 390 mbsf has high sedimentation rates (133-477 m/ my) and excellent age control, based on radiometric ages and magnetostratigraphy, providing an exceptional record of glacial advances and retreats deposited in a shallow water environment in Antarctica between 18 and 16 Ma. Approximately 34 sequences were identified, which contain bounding surfaces characterized by a pronounced shift in lithofacies, with typically more ice distal facies below and more proximal facies above. Lithofacies and grain size analysis suggest that these cycles are controlled by a combination of ice proximity and water depth. The timing of the sequence boundaries in the upper 300 meters are controlled by the obliquity cycle, with sequences in the lower 100 meters controlled by the precessional and eccentricity cycles. A surface at 774.94 mbsf contains a hiatus spanning 17.8-18.7 Ma, which encompasses the isotopic events Mi1b (17.8 Ma) and Mi1ab (18.3 Ma). This surface separates a prolonged interval of glacial advance over this site above, based on lithofacies and sediment deformation above and more ice distal environments below. A sharp surface at 398.25 mbsf (~16.2±0.2 Ma) interpreted to represent glacial advance to perhaps near or over the site, contains a possible short hiatus and is correlated to the Mi2 event. In contrast, between 400 and 645 mbsf, little evidence exists for subglacial grounding over the site, with sequence boundary formation generally controlled by local sea-level changes, with glacial processes being subdominant. This interval correlates to the early Miocene Climatic Optimum (17.3-16.3 Ma).

Glacial isostatic stress shadowing by the Antarctic ice sheet

NASA Technical Reports Server (NTRS)

Ivins, E. R.; James, T. S.; Klemann, V.

2005-01-01

Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

Palaeolithic landscapes of Europe and environs, 150,000-25,000 years ago: An overview

NASA Astrophysics Data System (ADS)

Van Andel, T. H.; Tzedakis, P. C.

When considering the evolution and migrations of Neandertalers and early modem human beings, the harsh conditions of the last glacial maximum are often implicitly or explicitly assumed as their environmental background. This perception is false: the conditions of the high glacial apply to a small fraction of late Pleistocene time. Here we review the palaeoenvironmental history of Europe from 150,000 to 25,000 years ago with the aid of data from long cores of ice and marine and continental sediments. The results are displayed in four sketch maps that illustrate the landscapes of an interglacial-glacial cycle. The maps, connected by palaeoenvironmental histories, show that especially between 60,000 and 25,000 years ago, a critical part of the Palaeolithic, the glacial landscapes were for much of the time less barren than is generally assumed, but numerous climate changes on a scale of several millennia are evident, placing a premium on accurate dating of the co-evolution of humans and landscape. Moreover, during the glacial interval abrupt climatic changes lasting from a century to a few millennia were common. Their importance for landscape changes and their impact on human activity remain to be ascertained.

Spawning distribution of sockeye salmon in a glacially influenced watershed: The importance of glacial habitats

USGS Publications Warehouse

Young, Daniel B.; Woody, C.A.

2007-01-01

The spawning distribution of sockeye salmon Oncorhynchus nerka was compared between clear and glacially turbid habitats in Lake Clark, Alaska, with the use of radiotelemetry. Tracking of 241 adult sockeye salmon to 27 spawning locations revealed both essential habitats and the relationship between spawn timing and seasonal turbidity cycles. Sixty-six percent of radio-tagged sockeye salmon spawned in turbid waters (???5 nephelometric turbidity units) where visual observation was difficult. Spawning in turbid habitats coincided with seasonal temperature declines and associated declines in turbidity and suspended sediment concentration. Because spawn timing is heritable and influenced by temperature, the observed behavior suggests an adaptive response to glacier-fed habitats, as it would reduce embryonic exposure to the adverse effects of fine sediments. ?? Copyright by the American Fisheries Society 2007.

Arsenic stress after the Proterozoic glaciations

NASA Astrophysics Data System (ADS)

Chi Fru, Ernest; Arvestål, Emma; Callac, Nolwenn; El Albani, Abderrazak; Kilias, Stephanos; Argyraki, Ariadne; Jakobsson, Martin

2015-12-01

Protection against arsenic damage in organisms positioned deep in the tree of life points to early evolutionary sensitization. Here, marine sedimentary records reveal a Proterozoic arsenic concentration patterned to glacial-interglacial ages. The low glacial and high interglacial sedimentary arsenic concentrations, suggest deteriorating habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago. A similar intensification of near continental margin sedimentary arsenic levels after the Cryogenian glaciations is also associated with amplified continental weathering. However, interpreted atmospheric oxygen increase at this time, suggests that the marine biosphere had widely adapted to the reorganization of global marine elemental cycles by glaciations. Such a glacially induced biogeochemical bridge would have produced physiologically robust communities that enabled increased oxygenation of the ocean-atmosphere system and the radiation of the complex Ediacaran-Cambrian life.

Arsenic stress after the Proterozoic glaciations.

PubMed

Fru, Ernest Chi; Arvestål, Emma; Callac, Nolwenn; El Albani, Abderrazak; Kilias, Stephanos; Argyraki, Ariadne; Jakobsson, Martin

2015-12-04

Protection against arsenic damage in organisms positioned deep in the tree of life points to early evolutionary sensitization. Here, marine sedimentary records reveal a Proterozoic arsenic concentration patterned to glacial-interglacial ages. The low glacial and high interglacial sedimentary arsenic concentrations, suggest deteriorating habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago. A similar intensification of near continental margin sedimentary arsenic levels after the Cryogenian glaciations is also associated with amplified continental weathering. However, interpreted atmospheric oxygen increase at this time, suggests that the marine biosphere had widely adapted to the reorganization of global marine elemental cycles by glaciations. Such a glacially induced biogeochemical bridge would have produced physiologically robust communities that enabled increased oxygenation of the ocean-atmosphere system and the radiation of the complex Ediacaran-Cambrian life.

Eight glacial cycles from an Antarctic ice core.

PubMed

Augustin, Laurent; Barbante, Carlo; Barnes, Piers R F; Barnola, Jean Marc; Bigler, Matthias; Castellano, Emiliano; Cattani, Olivier; Chappellaz, Jerome; Dahl-Jensen, Dorthe; Delmonte, Barbara; Dreyfus, Gabrielle; Durand, Gael; Falourd, Sonia; Fischer, Hubertus; Flückiger, Jacqueline; Hansson, Margareta E; Huybrechts, Philippe; Jugie, Gérard; Johnsen, Sigfus J; Jouzel, Jean; Kaufmann, Patrik; Kipfstuhl, Josef; Lambert, Fabrice; Lipenkov, Vladimir Y; Littot, Geneviève C; Longinelli, Antonio; Lorrain, Reginald; Maggi, Valter; Masson-Delmotte, Valerie; Miller, Heinz; Mulvaney, Robert; Oerlemans, Johannes; Oerter, Hans; Orombelli, Giuseppe; Parrenin, Frederic; Peel, David A; Petit, Jean-Robert; Raynaud, Dominique; Ritz, Catherine; Ruth, Urs; Schwander, Jakob; Siegenthaler, Urs; Souchez, Roland; Stauffer, Bernhard; Steffensen, Jorgen Peder; Stenni, Barbara; Stocker, Thomas F; Tabacco, Ignazio E; Udisti, Roberto; Van De Wal, Roderik S W; Van Den Broeke, Michiel; Weiss, Jerome; Wilhelms, Frank; Winther, Jan-Gunnar; Wolff, Eric W; Zucchelli, Mario

2004-06-10

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long--28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

Can energy fluxes be used to interpret glacial/interglacial precipitation changes in the tropics?

NASA Astrophysics Data System (ADS)

Roberts, W. H. G.; Valdes, P. J.; Singarayer, J. S.

2017-06-01

Recent theoretical advances in the relationship between heat transport and the position of the Intertropical Convergence Zone (ITCZ) present an elegant framework through which to interpret past changes in tropical precipitation patterns. Using a very large ensemble of climate model simulations, we investigate whether it is possible to use this framework to interpret changes in the position of the ITCZ in response to glacial and interglacial boundary conditions. We find that the centroid of tropical precipitation, which represents the evolution of precipitation in the whole tropics, is best correlated with heat transport changes. We find that the response of the annual mean ITCZ to glacial and interglacial boundary conditions is quite different to the response of the climatological annual cycle of the ITCZ to the seasonal cycle of insolation. We show that the reason for this is that while the Hadley Circulation plays a dominant role in transporting heat over the seasonal cycle, in the annual mean response to forcing, the Hadley Circulation is not dominant. When we look regionally, rather than at the zonal mean, we find that local precipitation is poorly related either to the zonal mean ITCZ or to meridional heat transport. We demonstrate that precipitation is spatially highly variable even when the zonal mean ITCZ is in the same location. This suggests only limited use for heat transport in explaining local precipitation records; thus, there is limited scope for using heat transport changes to explain individual paleoprecipitation records.

Assessing the deep drilling potential of Lago de Tota, Colombia, with a seismic survey

NASA Astrophysics Data System (ADS)

Bird, B. W.; Wattrus, N. J.; Fonseca, H.; Velasco, F.; Escobar, J.

2015-12-01

Reconciling orbital-scale patterns of inter-hemispheric South American climate during the Quaternary requires continuous, high-resolution paleoclimate records that span multiple glacial cycles from both hemispheres. Southern Andean Quaternary climates are represented by multi-proxy results from Lake Titicaca (Peru-Bolivia) spanning the last 400 ka and by pending results from the Lago Junin Drilling Project (Peru). Although Northern Andean sediment records spanning the last few million years have been retrieved from the Bogota and Fúquene Basins in the Eastern Cordillera of the Colombian Andes, climatic reconstructions based on these cores have thus far been limited to pollen-based investigations. When viewed together with the Southern Hemisphere results, these records suggest an anti-phased hemispheric climatic response during glacial cycles. In order to better assess orbital-scale climate responses, however, independent temperature and hydroclimate proxies from the Northern Hemisphere are needed in addition to vegetation histories. As part of this objective, an effort is underway to develop a paleoclimate record from Lago de Tota (3030 m asl), the largest lake in Colombia and the third largest lake in the Andes. One of 17 highland tectonic basins in Eastern Cordillera, Lago de Tota formed during Tertiary uplift that deformed pre-foreland megasequences, synrift and back-arc megasequences. The precise age and thickness of sediments in the Lago de Tota basin has not previously been established. Here, we present results from a recent single-channel seismic reflection survey collected with a small (5 cubic inch) air gun and high-resolution CHIRP sub-bottom data. With these data, we examine the depositional history and sequence stratigraphy of Lago de Tota and assess its potential as a deep drilling target.

Ancient geographical gaps and paleo-climate shape the phylogeography of an endemic bird in the sky islands of southern India.

PubMed

Robin, V V; Sinha, Anindya; Ramakrishnan, Uma

2010-10-13

Sky islands, formed by the highest reaches of mountain tracts physically isolated from one another, represent one of the biodiversity-rich regions of the world. Comparative studies of geographically isolated populations on such islands can provide valuable insights into the biogeography and evolution of species on these islands. The Western Ghats mountains of southern India form a sky island system, where the relationship between the island structure and the evolution of its species remains virtually unknown despite a few population genetic studies. We investigated how ancient geographic gaps and glacial cycles have partitioned genetic variation in modern populations of a threatened endemic bird, the White-bellied Shortwing Brachypteryx major, across the montane Shola forests on these islands and also inferred its evolutionary history. We used bayesian and maximum likelihood-based phylogenetic and population-genetic analyses on data from three mitochondrial markers and one nuclear marker (totally 2594 bp) obtained from 33 White-bellied Shortwing individuals across five islands. Genetic differentiation between populations of the species correlated with the locations of deep valleys in the Western Ghats but not with geographical distance between these populations. All populations revealed demographic histories consistent with population founding and expansion during the Last Glacial Maximum. Given the level of genetic differentiation north and south of the Palghat Gap, we suggest that these populations be considered two different taxonomic species. Our results show that the physiography and paleo-climate of this region historically resulted in multiple glacial refugia that may have subsequently driven the evolutionary history and current population structure of this bird. The first avian genetic study from this biodiversity hotspot, our results provide insights into processes that may have impacted the speciation and evolution of the endemic fauna of this region.

Millennial Variability of Eastern Equatorial Bottom Water Oxygenation and Atmospheric CO2 over the past 100 kyr

NASA Astrophysics Data System (ADS)

Marcantonio, F.; Loveley, M.; Wisler, M.; Hostak, R.; Hertzberg, J. E.; Schmidt, M. W.; Lyle, M. W.

2017-12-01

Storage of respired carbon in the deep ocean may play a significant role in lowering atmospheric CO2 concentrations by about 80 ppm during the last glacial maximum compared to pre-industrial times. The cause of this sequestration and the subsequent release of the deep respired carbon pool at the last termination remains elusive. Within the last glacial period, on millennial timescales, the relationship between the CO2 cycle and any waxing and waning of a deep respired pool also remains unclear. To further our understanding of the millennial variability in the storage of a deep-ocean respired carbon pool during the last glacial, we measure authigenic uranium and 230Th-derived non-lithogenic barium fluxes (xsBa flux) in two high-sedimentation-rate cores from the Panama Basin of the Eastern Equatorial Pacific (EEP) (8JC, 6° 14.0' N, 86° 02.6' W; 1993 m water depth; 17JC 00° 10.8' S, 85° 52.0' W; 2846 m water depth). Sediment authigenic U concentrations are controlled by the redox state of sediments which, in turn, is a function of the rain of organic material from the surface ocean and the oxygen content of bottom waters. At both 8JC and 17JC, the mismatch between xsBa fluxes, a proxy for the reconstruction of oceanic productivity, and authigenic uranium concentrations suggests that the primary control of the latter values is changes in bottom water oxygenation. Peak authigenic uranium concentrations occur during glacial periods MIS 2, 3, and 4, respectively, and are two to three times higher than those during interglacial periods, MIS 1 and 5. EEP bottom waters were likely suboxic during times of the last glacial period when atmospheric CO2 concentrations were at their lowest concentrations. In addition, the pattern of increased deep-water oxygenation during times of higher CO2 during the last glacial is similar to that reported in a study of authigenic U in sediments from the Antarctic Zone of the Southern Ocean (Jaccard et al., 2016). We suggest that a respired carbon pool existed within a large swath of the abyssal Southern and Pacific Oceans throughout the entire last glacial cycle, and that this respired carbon was periodically released through increased ventilation of deep ocean waters. Jaccard et al. (2016) Nature 530, 207-210.

Glacial cycles drive variations in the production of oceanic crust

NASA Astrophysics Data System (ADS)

Crowley, J. W.; Katz, R. F.; Langmuir, C. H.; Huybers, P. J.

2013-12-01

Changes in sea level accompanying glacial cycles affect the static pressure within the asthenosphere; these variations could modulate melting rates beneath the mid-ocean ridge system as well as crustal thickness. These effects can be investigated and quantified using models of ridges based on conservation of mass, momentum, energy, and composition for two phases (magma & mantle) and two thermodynamic components (enriched & depleted). The models predict that the sensitivity of crustal thickness to oscillations in sea-level depends on the period of oscillation, the spreading rate of the ridge, and the assumed permeability scale of the melting regime. In contrast to previous studies (Huybers & Langmuir, 2009 and Lund & Asimow, 2011), the new results indicate that effects are larger for ridges with faster spreading rates. They also show that the dominant period of variations in crustal thickness changes with spreading rate and permeability. Sea-level variations with periods in the range of 10 ky - 100 ky can result in significant changes in crustal thickness that are orders of magnitude larger than the sea-level variations that drive them. Accurately modelling this process requires the inclusion of two previously unaccounted for processes: (1) determining the volume of the melting regime that is consistent with the ridge spreading rate and (2) properly treating the transport of melt. These enable us to capture the non-linear dependencies on spreading rate and other model parameters. Spectral analysis of bathymetry at two ridge segments that have a symmetric bathymetric signal and hence are undisturbed by off-axis volcanism or ridge jumps reveals the presence of variability at frequencies associated with precession, obliquity, and the 100 ky glacial/inter-glacial variability. Furthermore, the faster spreading ridge has larger amplitude responses to changes in sea level and shows a proportionately greater response at higher frequencies. These observations reinforce the possible links among climate cycles at the surface, mantle melting at depth and the crustal fabric of the sea floor.

Pleistocene to holocene expansion of the black-belt cichlid in Central America, Vieja maculicauda (Teleostei: Cichlidae)

PubMed Central

Ginger, Luke; Cage, Marcy; David, Kyle T.; Chakrabarty, Prosanta; Johnston, Mark; Matamoros, Wilfredo A.

2017-01-01

The distributions of many Northern Hemisphere organisms have been influenced by fluctuations in sea level and climatic conditions during Pleistocene interglacial periods. These cycles are associated with range contraction and refugia for northern-distributed organisms as a response to glaciers. However, lower sea levels in the tropics and sub-tropics created available habitat for expansion of the ranges of freshwater organisms. The goal of this study was to use ecological niche modeling to test the hypothesis of north to south range expansion of Vieja maculicauda associated with Pleistocene glacial cycles. Understanding the biogeography of this widespread species may help us better understand the geology and interconnectivity of Central American freshwaters. Occurrence data for V. maculicauda was based on georeferencing of all museum records of specimens recovered from FishNet2. General patterns of phylogeographic structure were assessed with mtDNA. Present day niche models were generated and subsequently projected onto paleoclimatic maps of the region during the Last Interglacial, Last Glacial Maximum, and mid-Holocene. Phylogenetic analysis of mtDNA sequence data showed no phylogeographic structure throughout the range of this widespread species. Present day niche models were congruent with the observed distribution of V. maculicauda in Central America. Results showed a lack of suitable freshwater habitat in northern Central America and Mexico during the Last Interglacial, with greatest range expansion during the Last Glacial Maximum and mid-Holocene. Results support the hypothesis of a north to south range expansion of V. maculicauda associated with glacial cycles. The wide distribution of this species compared to other closely related cichlids indicates the latter did not respond to the degree of V. maculicauda in expansion of their distributions. Future work aimed at comparisons with other species and modeling of future climatic scenarios will be a fruitful area of investigation. PMID:28558052

Late Pleistocene paleoproductivity patterns during the last climatic cycle in the Guyana Basin as revealed by calcareous nannoplankton

NASA Astrophysics Data System (ADS)

López-Otálvaro, G.-E.; Flores, J. A.; Sierro, F. J.; Cacho, I.; Grimalt, J.-O.; Michel, E.; Cortijo, E.; Labeyrie, L.

2008-03-01

Variations in the assemblages and abundances of calcareous nannoplankton have allowed us to interpret changes in oceanic and atmospheric dynamics in the Guyana Basin, mainly linked to the southeast trades over the last climatic cycle. Records of the paleoproductivity index of coccolithophores (N ratio) allowed us to monitor the nutri-thermocline fluctuations. Additionally, nannofossil accumulation rates vary closely with the N ratio, indicating a strong correlation between these two paleoproductivity proxies. The dominance of upper (small Noelaerhabdaceae, Emiliania huxleyi and Gephyrocapsa oceanica), over lower photic zone dwellers (Florisphaera profunda) during Termination II and interglacial substages 5.1 and 5.3 is related to eutrophic conditions due to a shoaling of the nutri-thermocline as a consequence of enhanced southeast Trade Winds. This activated an upwelling at the continental margin of the Guyana Basin. Low N ratio values and the dominance of F. profunda over the glacial substages of MIS 5 and glacial MIS 2-4 are linked to a deep nutri-thermocline (deep stratification of the mixed layer), at times of low influence of the southeast Trade Winds, and a weak upwelling. However, the N ratio during MIS 2-4 was slightly higher than those seen for the MIS 4/5 boundary and glacial substages 5.2 and 5.4. These micropaleontological proxies follow the insolation at high northern latitude (65° N): the high N ratio and NAR data from the Guyana Basin during Termination II and interglacials 5.1. and 5.3 are correlated with high insolation values, and low values of the N ratio and NAR during the MIS 4/5 boundary, glacials 5.2, 5.4 and MIS 2-4 are correlated with low insolation at the same latitudes. This situation suggests a link between the ITCZ, the southeast Trade Wind dynamics and the Northern Hemisphere climate changes during the last climatic cycle.

Middle and Late Pleistocene glaciations in the southwestern Pamir and their effects on topography

USGS Publications Warehouse

Stubner, Konstanze; Grin, Elena; Hidy, Alan J.; Schaller, Mirjam; Gold, Ryan D.; Ratschbacher, Lothar; Ehlers, Todd

2017-01-01

Glacial chronologies provide insight into the evolution of paleo-landscapes, paleoclimate, topography, and the erosion processes that shape mountain ranges. In the Pamir of Central Asia, glacial morphologies and deposits indicate extensive past glaciations, whose timing and extent remain poorly constrained. Geomorphic data and 15 new 10Be exposure ages from moraine boulders and roches moutonnées in the southwestern Pamir document multiple Pleistocene glacial stages. The oldest exposure ages, , underestimate the age of the earliest preserved glacial advance and imply that the modern relief of the southwestern Pamir (peaks at ∼5000–6000 m a.s.l.; valleys at ∼2000–3000 m a.s.l.) already existed in the late Middle Pleistocene. Younger exposure ages (∼40–80 ka, ∼30 ka) complement the existing Central Asian glacial chronology and reflect successively less extensive Late Pleistocene glaciations. The topography of the Pamir and the glacial chronologies suggest that, in the Middle Pleistocene, an ice cap or ice field occupied the eastern Pamir high-altitude plateau, whereas westward flowing valley glaciers incised the southwestern Pamir. Since the Late Pleistocene deglaciation, the rivers of the southwestern Pamir adjusted to the glacially shaped landscape. Localized rapid fluvial incision and drainage network reorganization reflect the transient nature of the deglaciated landscape.

Paleoclimatic modeling and phylogeography of least killifish, Heterandria formosa: insights into Pleistocene expansion-contraction dynamics and evolutionary history of North American Coastal Plain freshwater biota.

PubMed

Bagley, Justin C; Sandel, Michael; Travis, Joseph; Lozano-Vilano, María de Lourdes; Johnson, Jerald B

2013-10-09

Climatic and sea-level fluctuations throughout the last Pleistocene glacial cycle (~130-0 ka) profoundly influenced present-day distributions and genetic diversity of Northern Hemisphere biotas by forcing range contractions in many species during the glacial advance and allowing expansion following glacial retreat ('expansion-contraction' model). Evidence for such range dynamics and refugia in the unglaciated Gulf-Atlantic Coastal Plain stems largely from terrestrial species, and aquatic species Pleistocene responses remain relatively uninvestigated. Heterandria formosa, a wide-ranging regional endemic, presents an ideal system to test the expansion-contraction model within this biota. By integrating ecological niche modeling and phylogeography, we infer the Pleistocene history of this livebearing fish (Poeciliidae) and test for several predicted distributional and genetic effects of the last glaciation. Paleoclimatic models predicted range contraction to a single southwest Florida peninsula refugium during the Last Glacial Maximum, followed by northward expansion. We inferred spatial-population subdivision into four groups that reflect genetic barriers outside this refuge. Several other features of the genetic data were consistent with predictions derived from an expansion-contraction model: limited intraspecific divergence (e.g. mean mtDNA p-distance = 0.66%); a pattern of mtDNA diversity (mean Hd = 0.934; mean π = 0.007) consistent with rapid, recent population expansion; a lack of mtDNA isolation-by-distance; and clinal variation in allozyme diversity with higher diversity at lower latitudes near the predicted refugium. Statistical tests of mismatch distributions and coalescent simulations of the gene tree lent greater support to a scenario of post-glacial expansion and diversification from a single refugium than to any other model examined (e.g. multiple-refugia scenarios). Congruent results from diverse data indicate H. formosa fits the classic Pleistocene expansion-contraction model, even as the genetic data suggest additional ecological influences on population structure. While evidence for Plio-Pleistocene Gulf Coast vicariance is well described for many freshwater species presently codistributed with H. formosa, this species demography and diversification departs notably from this pattern. Species-specific expansion-contraction dynamics may therefore have figured more prominently in shaping Coastal Plain evolutionary history than previously thought. Our findings bolster growing appreciation for the complexity of phylogeographical structuring within North America's southern refugia, including responses of Coastal Plain freshwater biota to Pleistocene climatic fluctuations.

Constraining Quaternary ice covers and erosion rates using cosmogenic 26Al/10Be nuclide concentrations

NASA Astrophysics Data System (ADS)

Knudsen, Mads Faurschou; Egholm, David Lundbek

2018-02-01

Paired cosmogenic nuclides are often used to constrain the exposure/burial history of landforms repeatedly covered by ice during the Quaternary, including tors, high-elevation surfaces, and steep alpine summits in the circum-Arctic regions. The approach generally exploits the different production rates and half-lives of 10Be and 26Al to infer past exposure/burial histories. However, the two-stage minimum-limiting exposure and burial model regularly used to interpret the nuclides ignores the effect of variable erosion rates, which potentially may bias the interpretation. In this study, we use a Monte Carlo model approach to investigate systematically how the exposure/burial and erosion history, including variable erosion and the timing of erosion events, influence concentrations of 10Be and 26Al. The results show that low 26Al/10Be ratios are not uniquely associated with prolonged burial under ice, but may as well reflect ice covers that were limited to the coldest part of the late Pleistocene combined with recent exhumation of the sample, e.g. due to glacial plucking during the last glacial period. As an example, we simulate published 26Al/10Be data from Svalbard and show that it is possible that the steep alpine summits experienced ice-free conditions during large parts of the late Pleistocene and varying amounts of glacial erosion. This scenario, which contrasts with the original interpretation of more-or-less continuous burial under non-erosive ice over the last ∼1 Myr, thus challenge the conventional interpretation of such data. On the other hand, high 26Al/10Be ratios do not necessarily reflect limited burial under ice, which is the common interpretation of high ratios. In fact, high 26Al/10Be ratios may also reflect extensive burial under ice, combined with a change from burial under erosive ice, which brought the sample close to the surface, to burial under non-erosive ice at some point during the mid-Pleistocene. Importantly, by allowing for variable erosion rates, the model results may reconcile spatially varying 26Al/10Be data from bedrock surfaces preserved over multiple glacial cycles, suggesting that samples from the same high-elevation surface or neighbouring alpine summits may have experienced similar long-term burial under ice, but varying amounts of glacial erosion.

Unstable AMOC during glacial intervals and millennial variability: The role of mean sea ice extent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sevellec, Florian; Fedorov, Alexey V.

A striking feature of paleoclimate records is the greater stability of the Holocene epoch relative to the preceding glacial interval, especially apparent in the North Atlantic region. In particular, strong irregular variability with an approximately 1500 yr period, known as the Dansgaard-Oeschger (D-O) events, punctuates the last glaciation, but is absent during the interglacial. Prevailing theories, modeling and data suggest that these events, seen as abrupt warming episodes in Greenland ice cores and sea surface temperature records in the North Atlantic, are linked to reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). In this study, using a new low-order oceanmore » model that reproduces a realistic power spectrum of millennial variability, we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene (1 kyr = 1000 yr). Previous modeling studies show that the edge of sea ice in the North Atlantic shifts southward during glacial intervals, moving the region of the North Atlantic Deep Water formation and the AMOC also southward. Finally, here we demonstrate that, by shifting the AMOC with respect to the mean atmospheric precipitation field, such a displacement makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials.« less

Unstable AMOC during glacial intervals and millennial variability: The role of mean sea ice extent

DOE PAGES

Sevellec, Florian; Fedorov, Alexey V.

2015-11-01

A striking feature of paleoclimate records is the greater stability of the Holocene epoch relative to the preceding glacial interval, especially apparent in the North Atlantic region. In particular, strong irregular variability with an approximately 1500 yr period, known as the Dansgaard-Oeschger (D-O) events, punctuates the last glaciation, but is absent during the interglacial. Prevailing theories, modeling and data suggest that these events, seen as abrupt warming episodes in Greenland ice cores and sea surface temperature records in the North Atlantic, are linked to reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). In this study, using a new low-order oceanmore » model that reproduces a realistic power spectrum of millennial variability, we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene (1 kyr = 1000 yr). Previous modeling studies show that the edge of sea ice in the North Atlantic shifts southward during glacial intervals, moving the region of the North Atlantic Deep Water formation and the AMOC also southward. Finally, here we demonstrate that, by shifting the AMOC with respect to the mean atmospheric precipitation field, such a displacement makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials.« less

Groundwater reorganization in the Floridan aquifer following Holocene sea-level rise

NASA Astrophysics Data System (ADS)

Morrissey, Sheila K.; Clark, Jordan F.; Bennett, Michael; Richardson, Emily; Stute, Martin

2010-10-01

Sea-level fluctuations, particularly those associated with glacial-interglacial cycles, can have profound impacts on the flow and circulation of coastal groundwater: the water found at present in many coastal aquifers may have been recharged during the last glacial period, when sea level was over 100m lower than present, and thus is not in equilibrium with present recharge conditions. Here we show that the geochemistry of the groundwater found in the Floridan Aquifer System in south Florida is best explained by a reorganization of groundwater flow following the sea-level rise at the end of the Last Glacial Maximum approximately 18,000 years ago. We find that the geochemistry of the fresh water found in the upper aquifers at present is consistent with recharge from meteoric water during the last glacial period. The lower aquifer, however, consists of post-sea-level-rise salt water that is most similar to that of the Straits of Florida, though with some dilution from the residual fresh water from the last glacial period circulation. We therefore suggest that during the last glacial period, the entire Floridan Aquifer System was recharged with meteoric waters. After sea level rose, the increased hydraulic head reduced the velocity of the groundwater flow. This velocity reduction trapped the fresh water in the upper aquifers and initiated saltwater circulation in the lower aquifer.

Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

DOE PAGES

Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; ...

2015-05-19

The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission,more » atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, 2 times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.« less

Late Quaternary cooling rate constrained by multiple IRSL thermochronometers of potassium feldspars for granites from Kongur Shan, Chinese Pamir

NASA Astrophysics Data System (ADS)

Qin, Jintang; Chen, Jie; Valla, Pierre; Herman, Frédéric

2015-04-01

The Kongur Shan (East Pamir), located at the northwestern Tibetan Plateau, is one of the most active orogens on Earth, where both tectonic processes along major active faults and climatic forcing (extensive glaciers coverage) are contributing to the regional landscape evolution. The exhumation rates since late Miocene was constrained to be ~6.5 - 4.2 mm/yr. However, it is still debated whether the exhumation rate accelerated since the Quaternary, of which the climate was featured by the cyclic glaciations with periods of 100 ka and 40 ka. In this study, we tried to employ luminescence thermochronology, which is a still in developing method, to resolve the impact of glacial cycles on exhumation rate. Our study site is located ~10 km to the east of the active Kongur normal fault, along the major valley of Gez river. We sampled three granite rocks from a sub-horizontal tunnel across the granite massif; one was from the entrance of the tunnel, and other two samples were from inside of the tunnel, where the measured ambient temperature is as high as 60-70 ° C. The distances of these samples are within 2 km. Four types of IRSL signals extracted from potassium feldspars (K-feldspars) were measured for each individual sample, and the results of isothermal decay experiments indicated these signals were of different thermal stabilities. Therefore, they may serve as four thermochronometers with different closure temperature. We employ these multiple thermochronometers together for each single sample to constrain their cooling rates. Our preliminary results, which are based on the simplified luminescence model of K-feldspars, suggest that the averaged cooling rate of the last 200 ka is as high as 1.4 oC/ka, which corresponds to an exhumation rate of ~ 2.3 to 0.9 cm/yr with the geothermal gradient assumed to be 60 to 150 oC/km. It seems to imply that the glacial cycles during the Quaternary substantially accelerated the exhumation rate of granite massif of Kongur Shan.

Sediment Production and Storage Through a Glacial-Interglacial Cycle on a Cool-Temperate Glaciated Margin

NASA Astrophysics Data System (ADS)

Powell, R. D.

2001-12-01

The southern Alaska margin has high coastal mountains, which coupled with temperate glaciation, result in extremely high modern erosion rates (e.g. Jaeger et al., 2001), possibly exceeding rates of orogenic uplift (Meigs and Sauber, 2000). Where measured, modern sediment yields are among the highest of any basin worldwide (Hallet et al., 1996; Elverhoi et al., 1998; Jaeger et al., 1998). In Muir Inlet, Glacier Bay, sediment yields from slowly retreating glaciers decrease logarithmically with decreasing drainage basin area (Powell, 1991), a trend also reflected in regional data synthesized in Hallet et al. (1996). Alley (1997) then hypothesized that if erosion increases with basin area then where two tributaries join, deeper erosion would ensue, which is consistent with linear erosional troughs and hanging valleys. The idea is also consistent with the general downglacier increase in water flux at the glacier bed. However over longer periods, data from seismic profiles of the Gulf of Alaska shelf, show sediment yields are nearly the same through a glacial-interglacial cycle; regional data from other glaciated basins appear to confirm that trend (Elverhoi et al., 1998). If yields are continuously high from bedrock erosion, then why are mountains not eroded to base level because erosion rates are higher than isostatic uplift? Why are trends in yields apparently different during recent retreats with decreasing basin sizes than during longer term glacial cycles? Answers to these questions may be numerous and compound; however, one possibility will be evaluated. We know there is significant modern bedrock erosion occurring during glacial retreat and that also appears to have been the case during advance. Native stories describing the last (Little Ice Age) advance in Glacier Bay describe a large amount of sediment being produced (Powell et al., 1995) indicating that significant erosion was occurring. Fjord-wall stratigraphy shows that sediment had infilled much of the Bay up to ca. 200 m above modern sea level (Goldthwait,1986) prior to the LIA. During that advance, all sediments were then eroded down to bedrock, locally up to 400-500 m below sea level (Powell and Molnia, 1989), and then dumped at the Bay entrance, the site of maximum advance Powell et al., 1995). By inference, because most sediment packages on the shelf are deposited during glacially advanced phases, they probably mostly include sediment redistributed from fjords and inner shelf with a minor component from freshly eroded mountain bedrock. The ELA, under which most erosion may occur (Meigs and Sauber, 2000), lies over fjords during glacial maxima where the glacier is probably thickest with pressure melting and melting/freezing occurring at the bed. Erosion of sediment deposited there during a retreat phase may be enhanced, as may fjord over-deepening, whereas, thinner ice over mountains is likely to be cold at the bed, limiting erosion. As the glacier retreats the ELA moves toward the mountains as may the center of erosion, which then occurs mainly on bedrock. Mountain uplift may be enhanced during interglacials when glacio-isostatic rebound occurs and increased erosion adds to the isostatic effect. Therefore, during glacial-interglacial cycles average sediment yields from a glacier may not vary significantly, but the main centers of erosion change through time as does the eroding substrate and locations of depocenters.

The nitrogen cycles on Pluto over seasonal and astronomical timescales

NASA Astrophysics Data System (ADS)

Bertrand, T.; Forget, F.; Umurhan, O. M.; Grundy, W. M.; Schmitt, B.; Protopapa, S.; Zangari, A. M.; White, O. L.; Schenk, P. M.; Singer, K. N.; Stern, A.; Weaver, H. A.; Young, L. A.; Ennico, K.; Olkin, C. B.

2018-07-01

Pluto's landscape is shaped by the endless condensation and sublimation cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia ice sheet, which is thought to be the main reservoir of nitrogen ice, displays a large diversity of terrains, with bright and dark plains, small pits and troughs, topographic depressions and evidences of recent and past glacial flows. Outside Sputnik Planitia, New Horizons also revealed numerous nitrogen ice deposits, in the eastern side of Tombaugh Regio and at mid-northern latitudes. These observations suggest a complex history involving volatile and glacial processes occurring on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model designed to simulate the nitrogen cycle over millions of years, taking into account the changes of obliquity, solar longitude of perihelion and eccentricity as experienced by Pluto. Using this model, we first explore how the volatile and glacial activity of nitrogen within Sputnik Planitia has been impacted by the diurnal, seasonal and astronomical cycles of Pluto. Results show that the obliquity dominates the N2 cycle and that over one obliquity cycle, the latitudes of Sputnik Planitia between 25°S-30°N are dominated by N2 condensation, while the northern regions between 30°N and -50°N are dominated by N2 sublimation. We find that a net amount of 1 km of ice has sublimed at the northern edge of Sputnik Planitia during the last 2 millions of years. It must have been compensated by a viscous flow of the thick ice sheet. By comparing these results with the observed geology of Sputnik Planitia, we can relate the formation of the small pits and the brightness of the ice at the center of Sputnik Planitia to the sublimation and condensation of ice occurring at the annual timescale, while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are instead related to the astronomical timescale. We also perform simulations including a glacial flow scheme which shows that the Sputnik Planitia ice sheet is currently at its minimum extent at the northern and southern edges. We also explore the stability of N2 ice deposits outside the latitudes and longitudes of the Sputnik Planitia basin. Results show that N2 ice is not stable at the poles but rather in the equatorial regions, in particular in depressions, where thick deposits may persist over tens of millions of years, before being trapped in Sputnik Planitia. Finally, another key result is that the minimum and maximum surface pressures obtained over the simulated millions of years remain in the range of milli-Pascals and Pascals, respectively. This suggests that Pluto never encountered conditions allowing liquid nitrogen to flow directly on its surface. Instead, we suggest that the numerous geomorphological evidences of past liquid flow observed on Pluto's surface are the result of liquid nitrogen that flowed at the base of thick ancient nitrogen glaciers, which have since disappeared.

Late Quaternary landscape evolution in the Kunlun Mountains and Qaidam Basin, Northern Tibet: A framework for examining the links between glaciation, lake level changes and alluvial fan formation

USGS Publications Warehouse

Owen, L.A.; Finkel, R.C.; Haizhou, M.; Barnard, P.L.

2006-01-01

The Qaidam Basin in Northern Tibet is one of the largest hyper-arid intermontane basins on Earth. Alluvial fans, pediment surfaces, shorelines and a thick succession of sediments within the basin, coupled with moraines and associated landforms in the adjacent high mountain catchments of the Kunlun Mountains, record a complex history of Late Quaternary paleoenvironmental change and landscape evolution. The region provides an ideal natural laboratory to examine the interaction between tectonics and climate within a continent-continent collision zone, and to quantify rates of landscape evolution as controlled by climate and the associated glacial and hydrological changes in hyper-arid and adjacent high-altitude environments. Geomorphic mapping, analysis of landforms and sediments, and terrestrial cosmogenic radionuclide surface exposure and optically stimulated luminescence dating serve to define the timing of formation of Late Quaternary landforms along the southern and northwestern margins of the Qaidam Basin, and in the Burhan Budai Shan of the Kunlun Mountains adjacent to the basin on the south. These dates provide a framework that suggests links between climatic amelioration, deglaciation, lake desiccation and alluvial fan evolution. At least three glacial advances are defined in the Burham Budai Shan of the Kunlun Mountains. On the northern side of this range these occurred in the penultimate glacial cycle or early in the last glacial cycle, during the Last Glacial Maximum (LGM)/Lateglacial and during the Holocene. On the south side of the range, advances occurred during the penultimate glacial cycle, MIS-3, and possibly the LGM, Lateglacial or Holocene. Several distinct phases of alluvial fan sedimentation are likewise defined. Alluvial fans formed on the southern side of the Kunlun Mountains prior to 200 ka. Ice-contact alluvial fans formed during the penultimate glacial and during MIS-3. Extensive incised alluvial fans that form the main valley fills north of the Burham Budai and extend into the Qaidam Basin are dated to ???30 ka. These ages suggest that there was a period of alluvial fan aggradation and valley filling that persisted until desiccation of the large lakes in the Qaidam Basin post ???30 ka led to base level lowering and active incision of streams into the valley fills. The continued Lateglacial and Holocene desiccation likely led to further degradation of the valley fills. Ice wedge casts in the Qaidam Basin date to ???15 ka, indicating significant Lateglacial climatic amelioration, while Holocene loess deposits north of the Burham Bdudai suggest that aridity has increased in the region since the early Holocene. From these observations, we infer that the major landscape changes within high glaciated mountains and their adjacent hyper-arid intermontane basins, such as the Kunlun Mountains and Qaidam Basin, occur rapidly over millennial timescales during periods of climatic instability. ?? 2006 Elsevier Ltd and INQUA.

Environmental evolution in Picos de Europa (Cantabrian Mountains, Northern Spain) since the last glacial cycle.

NASA Astrophysics Data System (ADS)

Nieuwendam, Alexandre; Ruiz-Fernández, Jesús; Oliva, Marc; Lopes, Vera; Cruces, Anabela; da Conceição Freitas, Maria

2015-04-01

The Western Massif of the Picos de Europa includes some of the highest elevations of the Cantabrian Mountains. The maximum ice expansion in this limestone range during the last glacial cycle preceded the global Last Glacial Maximum. A 5.4 m long sedimentary sequence was collected from Belbín, a depression damned by a moraine in a mid-altitude environment of this massif. Using a combination of several approaches we have reconstructed the environmental stages and intensity of cryogenic processes since that period until today: (1) geomorphological mapping combining field evidences, aerial photographs and topographic maps; (2) lithostratigraphic description of the cores identifying different sedimentary units; (3) Grain-size analyses of the fine fraction by laser diffraction; and (4) quartz grains using Cailleux (1942) analysis with modifications from Mycielska-Dowgiałło and Woronko (1998). The studied accumulative kame terrace has preserved a Late Quaternary record with geomorphological and climatic events, variable accumulation rates, and distinct grain properties resulting from frost and chemical weathering. The basal dating of the sediments of this section shows that the maximum glacial extent occurred prior to 37.2 ka cal BP. The lithostratigraphic analysis of the section shows evidence of four major stages regarding the environmental evolution in the area: (1) from 37.2 to 29 ka there was a phase with intense periglacial activity and deposition of slope deposits; (2) from 29 to 22 ka, the depression of Belbín gradually infilled; (3) from 22 to 8 ka, a paleolake was present in the study site; (4) since 8 ka, the lake became infilled. Besides, human-induced fires started at 4.9 ka probably for grazing purposes. Based on the sediment stratigraphy the data presented, demonstrates that in Belbín area there have been persistent cryogenic conditions since the last glacial cycle until present-day, with different degrees of intensity and type of weathering processes. However, in some cases there are uncertainties between the time of climatic transition and geomorphic adjustment to changing climate conditions. The combination of silt abundance and peculiar quartz grain micromorphology can be an instrument for tracing cryogenic weathering in sedimentary archives. This demonstrates that depending on local conditions these analyses may be very useful indicators of past geomorphological events and interpretation can determine climatic conditions during quartz grains formation.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle.

PubMed

Ren, Haojia; Sigman, Daniel M; Martínez-García, Alfredo; Anderson, Robert F; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T F; Haug, Gerald H

2017-08-15

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N 2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen ("fixed N") from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N 2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N 2 fixation covaried with sea level. The N 2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N-a "sluggish" ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

NASA Astrophysics Data System (ADS)

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-08-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems.

Impact of glacial/interglacial sea level change on the ocean nitrogen cycle

PubMed Central

Ren, Haojia; Sigman, Daniel M.; Martínez-García, Alfredo; Anderson, Robert F.; Chen, Min-Te; Ravelo, Ana Christina; Straub, Marietta; Wong, George T. F.; Haug, Gerald H.

2017-01-01

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen (“fixed N”) from the ocean. The emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification. Denitrification leads to the occurrence of phosphorus-bearing, N-depleted surface waters, which encourages N2 fixation, the dominant N input to the ocean. An 860,000-y record of foraminifera shell-bound N isotopes from the South China Sea indicates that N2 fixation covaried with sea level. The N2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level-driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves. This hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed N input and loss and a longer residence time for oceanic fixed N—a “sluggish” ocean N budget during ice ages. In addition, this work provides a clear sign of sea level-driven glacial/interglacial oscillations in biogeochemical fluxes at and near the ocean margins, with implications for coastal organisms and ecosystems. PMID:28760968

Glaciological constraints on current ice mass changes from modelling the ice sheets over the glacial cycles

NASA Astrophysics Data System (ADS)

Huybrechts, P.

2003-04-01

The evolution of continental ice sheets introduces a long time scale in the climate system. Large ice sheets have a memory of millenia, hence the present-day ice sheets of Greenland and Antarctica are still adjusting to climatic variations extending back to the last glacial period. This trend is separate from the direct response to mass-balance changes on decadal time scales and needs to be correctly accounted for when assessing current and future contributions to sea level. One way to obtain estimates of current ice mass changes is to model the past history of the ice sheets and their underlying beds over the glacial cycles. Such calculations assist to distinguish between the longer-term ice-dynamic evolution and short-term mass-balance changes when interpreting altimetry data, and are helpful to isolate the effects of postglacial rebound from gravity and altimetry trends. The presentation will discuss results obtained from 3-D thermomechanical ice-sheet/lithosphere/bedrock models applied to the Antarctic and Greenland ice sheets. The simulations are forced by time-dependent boundary conditions derived from sediment and ice core records and are constrained by geomorphological and glacial-geological data of past ice sheet and sea-level stands. Current simulations suggest that the Greenland ice sheet is close to balance, while the Antarctic ice sheet is still losing mass, mainly due to incomplete grounding-line retreat of the West Antarctic ice sheet since the LGM. The results indicate that altimetry trends are likely dominated by ice thickness changes but that the gravitational signal mainly reflects postglacial rebound.

Climatic vs. tectonic control on glacial relief

NASA Astrophysics Data System (ADS)

Prasicek, Günther; Herman, Frederic; Robl, Jörg

2017-04-01

The limiting effect of a climatically-induced glacial buzz-saw on the height of mountain ranges has been extensively discussed in the geosciences. The buzz-saw concept assumes that solely climate controls the amount of topography present above the equilibrium line altitude (ELA), while the rock uplift rate plays no relevant role. This view is supported by analyses of hypsometric patterns in orogens worldwide. Furthermore, numerical landscape evolution models show that glacial erosion modifies the hypsometry and reduces the overall relief of mountain landscapes. However, such models often do not incorporate tectonic uplift and can only simulate glacial erosion over a limited amount of time, typically one or several glacial cycles. Constraints on glacial end-member landscapes from analytical, time-independent models are widely lacking. Here we present a steady-state solution for a glacier equilibrium profile in an active orogen modified from the mathematical conception presented by Headley et al. (2012). Our approach combines a glacial erosion law with the shallow ice approximation, specifically the formulations of ice sliding and deformation velocities and ice flux, to calculate ice surface and bed topography from prescribed specific mass balance and rock uplift rate. This solution allows the application of both linear and non-linear erosion laws and can be iteratively fitted to a predefined gradient of specific mass balance with elevation. We tested the influence of climate (fixed rock uplift rate, different ELAs) and tectonic forcing (fixed ELA, different rock uplift rates) on steady-state relief. Our results show that, similar to fluvial orogens, both climate and rock uplift rate exert a strong influence on glacial relief and that the relation among rock uplift rate and relief is governed by the glacial erosion law. This finding can provide an explanation for the presence of high relief in high latitudes. Headley, R.M., Roe, G., Hallet, B., 2012. Glacier longitudinal profiles in regions of active uplift. Earth and Planetary Science Letters, 317-318, 354-362.

Earth system model simulations show different feedback strengths of the terrestrial carbon cycle under glacial and interglacial conditions

NASA Astrophysics Data System (ADS)

Adloff, Markus; Reick, Christian H.; Claussen, Martin

2018-04-01

In simulations with the MPI Earth System Model, we study the feedback between the terrestrial carbon cycle and atmospheric CO2 concentrations under ice age and interglacial conditions. We find different sensitivities of terrestrial carbon storage to rising CO2 concentrations in the two settings. This result is obtained by comparing the transient response of the terrestrial carbon cycle to a fast and strong atmospheric CO2 concentration increase (roughly 900 ppm) in Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP)-type simulations starting from climates representing the Last Glacial Maximum (LGM) and pre-industrial times (PI). In this set-up we disentangle terrestrial contributions to the feedback from the carbon-concentration effect, acting biogeochemically via enhanced photosynthetic productivity when CO2 concentrations increase, and the carbon-climate effect, which affects the carbon cycle via greenhouse warming. We find that the carbon-concentration effect is larger under LGM than PI conditions because photosynthetic productivity is more sensitive when starting from the lower, glacial CO2 concentration and CO2 fertilization saturates later. This leads to a larger productivity increase in the LGM experiment. Concerning the carbon-climate effect, it is the PI experiment in which land carbon responds more sensitively to the warming under rising CO2 because at the already initially higher temperatures, tropical plant productivity deteriorates more strongly and extratropical carbon is respired more effectively. Consequently, land carbon losses increase faster in the PI than in the LGM case. Separating the carbon-climate and carbon-concentration effects, we find that they are almost additive for our model set-up; i.e. their synergy is small in the global sum of carbon changes. Together, the two effects result in an overall strength of the terrestrial carbon cycle feedback that is almost twice as large in the LGM experiment as in the PI experiment. For PI, ocean and land contributions to the total feedback are of similar size, while in the LGM case the terrestrial feedback is dominant.

Quaternary geology of the Boston area: Glacial events from Lake Charles to Lake Aberjona

USGS Publications Warehouse

Stone, Byron D.; Lane, John W.

2014-01-01

The multiple-glacial and glaciomarine Quaternary history of the Boston, Massachusetts area has been known generally since the earliest studies of the then newly recognized glacial deposits described by Prof. Louis Agassiz in the late1840’s and fossil marine shells in the drift in the 1850’s. Attention then turned to possible glacial erosional effects on the preglacial bedrock physiography, as related to rock units and structure, and to the challenges of defining useful physical and lithic characteristics of the drift by Prof. W.O. Crosby and others, 1880-1900. The problems of deducing the relative stratigraphic order among such small, fossil-barren surficial sedimentary deposits, and extending knowledge gained from studies of postulated ancient glacial lakes to a regional understanding of the history of many lakes during the retreat of the ice sheet required field work and use of geologic maps. With the advent of modern topographic maps in the 1880’s, the early period of discovery included field studies of glacial lake deposits in local river basins in the Boston region, basins that drain northward, thereby creating glacial lake basins dammed by the ice margin as it retreated to the north. Guided by M.I.T. and Harvard professors W.O. Crosby, N.S. Shaler, J.B. Woodworth, W.M. Davis, and others in the 1880-1920 period, the first Quaternary glacial stratigraphers were students (e.g. Crosby and Grabau, 1896, Clapp, 1905, Fuller 1905, Goldthwaite 1906, Grabau, 1906, Taylor, Tight).

Impacts of abrupt climate changes in the Levant from Last Glacial Dead Sea levels

NASA Astrophysics Data System (ADS)

Torfstein, Adi; Goldstein, Steven L.; Stein, Mordechai; Enzel, Yehouda

2013-06-01

A new, detailed lake level curve for Lake Lisan (the Last Glacial Dead Sea) reveals a high frequency of abrupt fluctuations during Marine Isotope Stage 3 (MIS3) compared to the relatively high stand characterizing MIS2, and the significantly lower Holocene lake. The lake level fluctuations reflect the hydrological conditions in the large watershed of the lake, which in turn reflects the hydro-climatic conditions in the central Levant region. The new curve shows that the fluctuations coincide on millennial timescales with temperature variations recorded in Greenland. Four patterns of correlation are observed through the last ice age: (1) maximum lake elevations were reached during MIS2, the coldest interval; (2) abrupt lake level drops to the lowest elevations coincided with the occurrence of Heinrich (H) events; (3) the lake returned to higher-stand conditions along with warming in Greenland that followed H-events; (4) significant lake level fluctuations coincided with virtually every Greenland stadial-interstadial cycle. Over glacial-interglacial time-scales, Northern Hemisphere glacial cooling induces extreme wetness in the Levant, with high lake levels reaching ˜160 m below mean sea level (mbmsl), approximately 240 m above typical Holocene levels of ˜400 mbmsl. These orbital time-scale shifts are driven by expansions of the European ice sheet, which deflect westerly storm tracks southward to the Eastern Mediterranean, resulting in increased sea-air temperature gradients that invoke increased cyclogenesis, and enhanced moisture delivery to the Levant. The millennial-scale lake level drops associated with Greenland stadials are most extreme during Heinrich stadials and reflect abrupt cooling of the Eastern Mediterranean atmosphere and sea-surface, which weaken the cyclogenic rain engine and cause extreme Levant droughts. During the recovery from the effect of Heinrich stadials, the regional climate configuration resumed typical glacial conditions, with enhanced Levant precipitation and a rise in Lake Lisan levels. Similar cyclicity in the transfer of moisture to the Levant affected lake levels during all of the non-Heinrich stadial-interstadial cycles.

Stratigraphy and palaeoclimatic significance of Late Quaternary loess-palaeosol sequences of the Last Interglacial-Glacial cycle in central Alaska

USGS Publications Warehouse

Muhs, D.R.; Ager, T.A.; Bettis, E. Arthur; McGeehin, J.; Been, J.M.; Beget, J.E.; Pavich, M.J.; Stafford, Thomas W.; Stevens, D.A.S.P.

2003-01-01

Loess is one of the most widespread subaerial deposits in Alaska and adjacent Yukon Territory and may have a history that goes back 3 Ma. Based on mineralogy and major and trace element chemistry, central Alaskan loess has a composition that is distinctive from other loess bodies of the world, although it is quartz-dominated. Central Alaskan loess was probably derived from a variety of rock types, including granites, metabasalts and schists. Detailed stratigraphic data and pedologic criteria indicate that, contrary to early studies, many palaeosols are present in central Alaskan loess sections. The buried soils indicate that loess sedimentation was episodic, or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input. As in China, loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess/soil formation cycle. Loess deposition in central Alaska took place before, and probably during the last interglacial period, during stadials of the mid-Wisconsin period, during the last glacial period and during the Holocene. An unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period. Our studies lead us to conclude that vegetation plays a key role in loess accumulation in Alaska. Factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods. The most important of these is vegetation; boreal forest serves as an effective loess trap, but sparsely distributed herb tundra does not. Thus, thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central Alaska. Much of the stratigraphic diversity of North American loess, including that found in the Central Lowlands, the Great Plains, and Alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors.

Habitat modeling and genetic signatures of postglacial recolonization for tidal estuaries

NASA Astrophysics Data System (ADS)

Dolby, G. A.; Jacobs, D. K.

2014-12-01

Pleistocene glacial cycles are a foremost influence on the genetic diversity and species distribution patterns observed today. Though much work has centered on biotic response to such climatic forcing, little of it has regarded estuarine or other aquatic coastal taxa whose habitat formation is a function of sea level, hydrography, and coastal geomorphology. These physical parameters required for habitat formation suggest that glacial cycles impart a significant effect on such taxa through glacially driven eustatic changes. Additionally, the steepened coastline and rainfall-limited Mediterranean climate suggest limited glacial habitat for estuarine species in southern and Baja California. Here we present GIS modeled habitat for tidal estuaries for three co-distributed estuarine fishes (Gillichthys mirabilis, Quietula y-cauda, Fundulus parvipinnis) since the last glacial maximum. Parameterization of sea level and slope enables biologically relevant temporal resolution of near-millennial scale. At lowstand our approach reveals two refuges along the coast at 1000km distance from each other, with habitat rapidly increasing 15 - 12 ka during meltwater pulse 1A. Habitat area peaked in the early Holocene and began decreasing with the current stillstand roughly 7 ka, probably as a result of coastal maturation towards less tidal systems. To target the postglacial recolonization process we applied discriminant function analysis to highly polymorphic microsatellite data to partition out the alleles associated with refuges identified a priori by habitat modeling. The frequencies of these alleles were calculated for all individuals at intervening populations and regressed against geographic distance. This analysis revealed nonlinear mixing curves, suggesting uneven allelic mixing efficiency along the coastline, perhaps as a result of differential habitat origination times as indicated by the habitat models. These results highlight the dynamism of estuarine habitat in recent geologic time, and the widespread extirpation-recolonization dynamic that may be common to species isolated in habitat 'islands' populations. Finally, this interdisciplinary approach afforded a more thorough view of estuarine system evolutionary dynamics through time than achievable through either discipline alone.

Late Pleistocene Magnitude Glacial Incursions of Southern Component Water to the Deep North Atlantic Resolved Using Nd Isotopes during the Intensification of Northern Hemisphere Glaciation (3.3 to 2.4 Ma)

NASA Astrophysics Data System (ADS)

Lang, D.; Bailey, I.; Wilson, P. A.; Foster, G. L.; Gutjahr, M.

2014-12-01

The ocean, through its ability to globally redistribute heat and partition carbon dioxide, is believed to play a key role in driving and amplifying climate change during Quaternary glaciations on orbital to millennial timescales. Relatively little is known, however, about changes in Atlantic Meridional Overturning Circulation (AMOC) associated with the Pliocene intensification of Northern Hemisphere glaciation (iNHG). To help fill this gap in our knowledge we present a new high resolution (~6 ka) record of the Nd isotope composition of the deep North Atlantic between ~3.3 and 2.4 Ma, measured on fish debris at IODP Site U1313 (3426 m, 41°N, 32.5°W). This record represents the first orbital-resolution record of variations in watermass mixing in this region for iNHG independent of changes in the carbon cycle and, in contrast to existing benthic foraminiferal δ13C records for this time interval, our Nd dataset contains evidence for late Pleistocene magnitude incursions of Southern Component Waters to the deep North Atlantic Ocean during key glacial periods through this time. We therefore infer an important role for AMOC variability in amplifying Quaternary glacial-interglacial cycles

Drainage capture and discharge variations driven by glaciation in the Southern Alps, New Zealand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ann V. Rowan; Mitchell A. Plummer; Simon H. Brocklehurst

Sediment flux in proglacial fluvial settings is primarily controlled by discharge, which usually varies predictably over a glacial–interglacial cycle. However, glaciers can flow against the topographic gradient to cross drainage divides, reshaping fluvial drainage networks and dramatically altering discharge. In turn, these variations in discharge will be recorded by proglacial stratigraphy. Glacial-drainage capture often occurs in alpine environments where ice caps straddle range divides, and more subtly where shallow drainage divides cross valley floors. We investigate discharge variations resulting from glacial-drainage capture over the past 40 k.y. for the adjacent Ashburton, Rangitata, and Rakaia basins in the Southern Alps, Newmore » Zealand. Although glacial-drainage capture has previously been inferred in the range, our numerical glacier model provides the first quantitative demonstration that this process drives larger variations in discharge for a longer duration than those that occur due to climate change alone. During the Last Glacial Maximum, the effective drainage area of the Ashburton catchment increased to 160% of the interglacial value with drainage capture, driving an increase in discharge exceeding that resulting from glacier recession. Glacial-drainage capture is distinct from traditional (base level–driven) drainage capture and is often unrecognized in proglacial deposits, complicating interpretation of the sedimentary record of climate change.« less

Ventilation History of the Tropical Atlantic Thermocline: New Insights From the Sensitivity of Foraminifera to Water Mass Nutrient Concentrations

NASA Astrophysics Data System (ADS)

Sexton, P. F.; Norris, R. D.

2008-12-01

The sensitivity of certain species of foraminifera to nutrient distributions throughout today's oceans highlights their potential for reconstructing water mass nutrient distributions in the past. Applying these new insights to reconstructed abundances of several key species during the last glacial, we find that thermocline waters throughout the entire tropical Atlantic were better ventilated than today. These findings are in line with independent evidence for stronger intermediate-depth ventilation driven by widespread Glacial North Atlantic Intermediate Water (GNAIW), supporting the validity of our new approach. Our results also suggest that well- ventilated GNAIW penetrated at least as far as 25 degrees South, thereby confining the northernmost glacial limits of poorly ventilated Antarctic Intermediate Water (AAIW) to the southernmost Atlantic. We show that the glacial Atlantic thermocline switched to its modern, more poorly ventilated state (probably indicative of a return of AAIW dominance) in a two-step process: a transient reduction in ventilation during the Bolling/Allerod, with the definitive switch to a regime of poor thermocline ventilation occurring at the close of the Younger Dryas. Furthermore, longer-term reconstructions of past distributions of these several key foraminiferal species suggest that a major and enduring impact of glacial-interglacial cycles on Atlantic hydrography has been this vacillating behaviour in tropical thermocline ventilation.

A preliminary estimate of changing calcrete carbon storage on land since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Adams, J. M.; Post, W. M.

1999-05-01

The glacial-to-interglacial shift in land carbon storage is important in understanding the global carbon cycle and history of the climate system. While organic carbon storage on land appears to have been much less than present during the cold, dry glacial maximum, calcrete (soil carbonate) carbon storage would have been greater. Here we attempt a global estimation of this change; we use published figures for present soil carbonate by biome to estimate changing global soil carbonate storage, on the basis of reconstruction of vegetation areas for four timeslices since the Last Glacial Maximum. It appears that there would most likely have been around a 30-45% decrease in calcrete carbon on land accompanying the transition between glacial and interglacial conditions. This represents a change of about 500-400 GtC (outer error limits are estimated at 750-200 GtC) . In order to be weathered into dissolved bicarbonate, this would take up an additional 500-400 GtC (750-200 GtC) in CO 2 from ocean/atmosphere sources. An equivalent amount to the carbonate leaving the caliche reservoir on land may have accumulated in coral reefs and other calcareous marine sediments during the Holocene, liberating an equimolar quantity of CO 2 back into the ocean-atmosphere system as the bicarbonate ion breaks up.

Mountain glaciation and paleoclimate reconstruction in the Picos de Europa (Iberian Peninsula, SW Europe)

NASA Astrophysics Data System (ADS)

Serrano, Enrique; González-Trueba, Juan José; González-García, María

2012-09-01

Geomorphic mapping and stratigraphic analysis of a lake core document the late Quaternary glacial history of the Central and Eastern Massifs of the Picos de Europa, northwestern Spain. The distribution of glacial deposits indicates that at their most advanced positions glaciers occupied 9.1 km2, extended as far as 7 km down-valley and had an estimated equilibrium-line altitude (ELA) ranging between 1666 and 1722 m. Radiocarbon dating of sediment deposited in a lake dammed by moraines of this advance show that the maximum glacial extent was prior to 35,280 ± 440 cal yr BP. This advance was followed by two subsequent but less extensive late Pleistocene advances, recorded by multiple moraines flanking both massifs and sedimentary characteristics in the lake deposits. The last recognized glacial episode is the 19th-century maximum extent of small Little Ice Age glaciers in the highest cirques above 2200 m.

Tectonic control on the persistence of glacially sculpted topography

PubMed Central

Prasicek, Günther; Larsen, Isaac J.; Montgomery, David R.

2015-01-01

One of the most fundamental insights for understanding how landscapes evolve is based on determining the extent to which topography was shaped by glaciers or by rivers. More than 104 years after the last major glaciation the topography of mountain ranges worldwide remains dominated by characteristic glacial landforms such as U-shaped valleys, but an understanding of the persistence of such landforms is lacking. Here we use digital topographic data to analyse valley shapes at sites worldwide to demonstrate that the persistence of U-shaped valleys is controlled by the erosional response to tectonic forcing. Our findings indicate that glacial topography in Earth's most rapidly uplifting mountain ranges is rapidly replaced by fluvial topography and hence valley forms do not reflect the cumulative action of multiple glacial periods, implying that the classic physiographic signature of glaciated landscapes is best expressed in, and indeed limited by, the extent of relatively low-uplift terrain. PMID:26271245

Paleodistribution modeling suggests glacial refugia in Scandinavia and out-of-Tibet range expansion of the Arctic fox.

PubMed

Fuentes-Hurtado, Marcelo; Hof, Anouschka R; Jansson, Roland

2016-01-01

Quaternary glacial cycles have shaped the geographic distributions and evolution of numerous species in the Arctic. Ancient DNA suggests that the Arctic fox went extinct in Europe at the end of the Pleistocene and that Scandinavia was subsequently recolonized from Siberia, indicating inability to track its habitat through space as climate changed. Using ecological niche modeling, we found that climatically suitable conditions for Arctic fox were found in Scandinavia both during the last glacial maximum (LGM) and the mid-Holocene. Our results are supported by fossil occurrences from the last glacial. Furthermore, the model projection for the LGM, validated with fossil records, suggested an approximate distance of 2000 km between suitable Arctic conditions and the Tibetan Plateau well within the dispersal distance of the species, supporting the recently proposed hypothesis of range expansion from an origin on the Tibetan Plateau to the rest of Eurasia. The fact that the Arctic fox disappeared from Scandinavia despite suitable conditions suggests that extant populations may be more sensitive to climate change than previously thought.

Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles

NASA Astrophysics Data System (ADS)

Bense, V. F.; Person, M. A.

2008-12-01

The hydrodynamic consequences of a glaciation/deglaciation cycle within an intercratonic sedimentary basin on subsurface transport processes is assessed using numerical models. In our analysis we consider the effects of mechanical ice sheet loading, permafrost formation, variable density fluids, and lithospheric flexure on solute/isotope transport, groundwater residence times, and transient hydraulic head distributions. The simulations are intended to apply, in a generic sense, to intercratonic sedimentary basins that would have been near the southern limit of the Laurentide Ice Sheet during the last glacial maximum (˜20 ka B.P.), such as the Williston, Michigan, and Illinois basins. We show that in such basins fluid flow and recharge rates are strongly elevated during glaciation as compared to nonglacial periods. Furthermore, our results illustrate that steady state hydrodynamic conditions in these basins are probably never reached during a 32.5 ka cycle of advance and retreat of a wet-based ice sheet. Present-day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of the last glaciation and associated processes that ended locally more than 10 ka B.P. Our results reveal characteristic spatial patterns of underpressure and overpressure that occur in aquitards and aquifers, respectively, as a result of recent glaciation. The calculated emplacement of low salinity, isotopically light glacial meltwater along basin margins is roughly consistent with observations from formerly glaciated basins in North America. The modeling presented in this study will help to improve the management of groundwater resources in formerly glaciated basins as well as to evaluate the viability on geological timescales of nuclear waste repositories located at high latitudes.

Weak overturning circulation and increased iron fertilization maximized carbon storage in the glacial ocean

NASA Astrophysics Data System (ADS)

Muglia, J.; Skinner, L.; Schmittner, A.

2017-12-01

Circulation changes have been suggested to play an important role in the sequestration of atmospheric CO2 in the glacial ocean. However, previous studies have resulted in contradictory results regarding the strength of the Atlantic Meridional Overturning Circulation (AMOC) and three-dimensional, quantitative reconstructions of the glacial ocean constrained by multiple proxies remain lacking. Here we simulate the modern and glacial ocean using a coupled, global, three-dimensional, physical-biogeochemical model constrained simultaneously by d13C, radiocarbon, and d15N to explore the effects of AMOC differences and Southern Ocean iron fertilization on the distributions of these isotopes and ocean carbon storage. We show that d13C and radiocarbon data sparsely sampled at the locations of existing glacial sediment cores can be used to reconstruct the modern AMOC accurately. Applying this method to the glacial ocean we find that a surprisingly weak (6-9 Sv or about half of today's) and shallow AMOC maximizes carbon storage and best reproduces the sediment data. Increasing the atmospheric soluble iron flux in the model's Southern Ocean intensifies export production, carbon storage, and improves agreement with d13C and d15N reconstructions. Our best fitting model is a significant improvement compared with previous studies. It suggests that a weak and shallow AMOC and enhanced iron fertilization conspired to maximize carbon storage in the glacial ocean.

SSMILES.

ERIC Educational Resources Information Center

Sunal, Dennis W.; Tracy, Dyanne M., Eds.

1991-01-01

A learning cycle activity which allows students to practice process skills by sieving different size fractions of sediments is described. Science topics include weathering, erosion, streams, sedimentation, sedimentary rocks, soils, beaches, dunes, or glacial deposits. Mathematics topics include number lines, ordinal numbers, greater than/less…

Environmental influences on speleothem growth in southwestern Oregon during the last 380, 000 years

USGS Publications Warehouse

Ersek, Vasile; Hostetler, Steven W.; Cheng, Hai; Clark, Peter U.; Anslow, Faron S.; Mix, Alan C.; Edwards, R. Lawrence

2009-01-01

The growth of carbonate formations in caves (speleothems) is sensitive to changes in environmental conditions at the surface (temperature, precipitation and vegetation) and can provide useful paleoclimatic and paleoenvironmental information. We use 73 230Th dates from speleothems collected from a cave in southwestern Oregon (USA) to constrain speleothem growth for the past 380 000 years. Most speleothem growth occurred during interglacial periods, whereas little growth occurred during glacial intervals. To evaluate potential environmental controls on speleothem growth we use two new modeling approaches: i) a one-dimensional thermal advection–diffusion model to estimate cave temperatures during the last glacial cycle, and ii) a regional climate model simulation for the Last Glacial Maximum (21 000 years before present) that assesses a range of potential controls on speleothem growth under peak glacial conditions. The two models are mutually consistent in indicating that permafrost formation did not influence speleothem growth during glacial periods. Instead, the regional climate model simulation combined with proxy data suggest that the influence of the Laurentide and Cordilleran ice sheets on atmospheric circulation induced substantial changes in water balance in the Pacific Northwest and affected speleothem growth at our location. The overall drier conditions during glacial intervals and associated periods of frozen topsoil at times of maximum surface runoff likely induced drastic changes in cave recharge and limited speleothem growth. This mechanism could have affected speleothem growth in other mid-latitude caves without requiring the presence of permafrost.

Erosion patterns produced by the paleo Haizishan ice cap, SE Tibetan Plateau

NASA Astrophysics Data System (ADS)

Fu, P.; Stroeven, A. P.; Harbor, J.; Hättestrand, C.; Heyman, J.; Caffee, M. W.

2017-12-01

Erosion is a primary driver of landscape evolution, topographic relief production, geochemical cycles, and climate change. Combining in situ 10Be and 26Al exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4,000 km2 paleo Haizishan ice cap on the southeastern Tibetan Plateau. Our results show that ice caps on the low relief Haizishan Plateau produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with the last deglaciation, complete resetting of the cosmogenic exposure age clock indicates glacial erosion of at least a few meters. However, older apparent exposure ages on bedrock in areas known to have been covered by the paleo ice cap during the Last Glacial Maximum indicate inheritance and thus limited glacial erosion. Inferred surface exposure ages from cosmogenic depth profiles through two saprolites vary from resetting and thus saprolite profile truncation to nuclide inheritance indicating limited erosion. Finally, significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate limited glacial erosion during the last glaciation. Hence, for the first time, our study shows clear evidence of preservation under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the paleo Haizishan ice cap during the LGM.

Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Wickert, Andrew D.

2016-11-01

Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and sometimes delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combining models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins - the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of observational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex.

Orbital and Millennial-scale Variability Reflected on Continental-scale Vegetation Changes in the Southern Subtropics between MIS 6 and 3

NASA Astrophysics Data System (ADS)

Urrego, D. H.; Sanchez Goni, M.; Daniau, A.; Martinez, P.

2011-12-01

While our understanding of the effects of orbital and millennial-scale variability on the vegetation has grown during the past decades, empirical data from some climatically important periods and regions are still lacking. Scarce data exist for instance for deep-time glacial-interglacial cycles that could provide suitable analogs for current climate-change. Recent global-scale reconstructions of vegetation responses to rapid events during the last glacial cycle have been useful, however, these global compilations clearly show that some regions, namely the southern tropics and subtropics, remain understudied. Here we present results from one of the few available continental-scale vegetation records from southwestern Africa spanning the last glacial-interglacial cycle. We have conducted multiproxy analyses of marine core MD96 2098 (25°36'S, 12°38'E), retrieved from the Lüderitz slope off the coast of Namibia. Preservation of pollen and other terrestrial microfossils is facilitated at this site by the Benguela upwelling system and the proximity to the Orange River mouth. Chronological control has been derived from radiocarbon dates and marine isotope stratigraphy. We have used pollen analyses, benthic foraminifer d18O (1), X-ray Fluorescence, geochemistry (2), foraminifer assemblages and microcharcoal quantification (3) to reconstruct the terrestrial vegetation and climatic history of the southwestern part of Africa and offshore between 190 and 30 ka. We find that MIS 6 and 4 are characterized by expanding Semidesert and Fynbos vegetation, while expanding grasslands characterized MIS 5. The termination of MIS 5 is also punctuated by an expansion of humid forests. At millennial timescales, variations in grasslands are generally coupled with stadials and interstadials. The expansion of semidesert is associated with decreased continental humidity caused by the strengthening of the Benguela upwelling during MIS 6 and 4. The expansion of grasslands during the interglacial results from increased rainfall associated with enhanced Agulhas leakage and southward movement of the maximum westerlies. Our results shed light on the relationships between millennial and orbital-scale vegetation variations and atmospheric and oceanic climatic mechanisms in the southern subtropics during the previous glacial-interglacial cycle. References 1. L. Pichevin, P. Bertrand, M. Boussafir, J.-R. Disnar, Organic Geochemistry 35, 543 (2004). 2. L. Pichevin, M. Cremer, J. Giraudeau, P. Bertrand, Marine Geology 218, 81 (2005). 3. A. L. Daniau et al, Nature Climate Change, (submitted).

Causes of strong ocean heating during glacial periods

NASA Astrophysics Data System (ADS)

Zimov, N.; Zimov, S. A.

2013-12-01

During the last deglaciation period, the strongest climate changes occurred across the North Atlantic regions. Analyses of borehole temperatures from the Greenland ice sheet have yielded air temperature change estimates of 25°C over the deglaciation period (Dahl-Jensen et al. 1998). Such huge temperature changes cannot currently be explained in the frames of modern knowledge about climate. We propose that glacial-interglacial cycles are connected with gradual warming of ocean interior waters over the course of glaciations and quick transport of accumulated heat from ocean to the atmosphere during the deglaciation periods. Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic and filling up the ocean interior with cold and heavy water. However during the glaciation thermal circulation stopped and ocean circulation was driven by 'haline pumps' -Red and Mediterranean seas connected with ocean with only narrow but deep straights acts as evaporative basins, separating ocean water into fresh water which returns to the ocean surface (precipitation) and warm but salty, and therefore heavy, water which flows down to the ocean floor. This haline pump is stratifying the ocean, allowing warmer water locate under the colder water and thus stopping thermal convection in the ocean. Additional ocean interior warming is driven by geothermal heat flux and decomposition of organic rain. To test the hypothesis we present simple ocean box model that describes thermohaline circulation in the World Ocean. The first box is the Red and Mediterranean sea, the second is united high-latitude seas, the third is the ocean surface, and the fourth the ocean interior. The volume of these water masses and straight cross-sections are taken to be close to real values. We have accepted that the exchange of water between boxes is proportional to the difference in water density in these boxes, Sun energy inputs to the ocean and sea surface are taken as constant. Energy income to the interior box from the geothermal heat flux is also taken as constant. Even though energy inputs are taken as constants, the model manages to recreate the glacial-interglacial cycles. In the glacial periods only haline circulation takes place, the ocean is strongly stratified, and the interior box accumulates heat, while high-latitudes accumulate ice. 112,000 years after glaciation starts, water density on the ocean bottom becomes equal to the density of water in high-latitude seas, strong thermal convection take place, and the ocean quickly (within 14,600 years) releases the heat. The magnitude and duration of such cycles correspond with magnitudes and durations reconstructed for actual glacial-interglacial cycles. From the proposed mechanism it follows that during the glaciations it is likely that the Arctic Ocean was a big reservoir of isotopically light fresh ice. If in a glacial period, the World Ocean were half filled with warm water from the Red Sea and bioproductivity of the ocean declined because of the slow circulation, then carbon storage within the ocean reservoir would decline by ~2000 Pg (10^15 g) of carbon.

QUANTIFICATION OF GLACIAL EROSION IN THE ALPS USING VERY LOW-TEMPERATURE THERMOCHRONOLOGY (OSL & AHe)

NASA Astrophysics Data System (ADS)

Champagnac, J.; Herman, F.; Rhodes, E. J.; Fellin, M.; Jaiswal, M.; Schwenninger, J.; Reverman, R. L.

2009-12-01

The impact of glaciations on the topography of the Alps is still unclear: Long-term denudation rate determined by low-T thermochronology are in the range of 0.2 to 1 mm/yr, and increased during the Plio-Quaternary by 3 fold (Vernon et al., 2008). Such an increase is also documented by peri-alpine sediment budget (Kuhleman, 2000), with a similar increase in sediment yields since 5-3 Ma. This increase was considered as evidence of a climatically-driven surface process change, attributed to increased precipitation (Cederbom et al., 2004) and erosion by glacial processes (Champagnac et al., 2007). The timing of the onset of intense glacial erosion as well as its rates are still ambiguous. The glacial erosion seems to have accelerated around 0.9 Ma as suggested by the ten fold increase of incision rates of a valley in the Central Alps (Häuselmann et al., 2007), and by information about vegetation and sedimentologic changes (Muttoni et al., 2003). There is however no direct quantification of topographic change during the Plio-Quaternary. We present here how we use OSL-thermochronology, a new thermochronometer of exceptionally low closure temperature (about 30°-40°C) (Herman et al subm.), new {U-Th}/He on apatites data, and a glacial erosion model (Herman and Braun 2008) to estimate topographic changes in the Alps in response to glaciations. Because of their low closure temperature, OSL and AHe thermochronology enables quantification of events of less than 1 Ma at very small wavelength of the topography. We collected two vertical profiles, one in the Zermatt Valley (Valais) and one in Maurienne Valley (Savoy). We infer from these results changes in topography, date and quantify relief creation under glacial-interglacial cycles. Cederbom, C.E, et al., Climate induced rebound and exhumation of the European Alps. Geology 32, 709-712 (2000). Champagnac, J.-D., et al., Quaternary erosion-induced isostatic rebound in the western Alps. Geology 35, 195-198 (2007). Haüselmann P., et al.,et al. Abrupt glacial valley incision at 0.8 Ma dated from cave deposits in Switzerland. Geology 35, 33-42 (2007). Herman F. and Braun J. Evolution of the glacial landscape of the Southern Alps of New Zealand: Insights from a glacial erosion model, J. Geophys. Res., 113, F02009, doi:10.1029/2007JF000807 (2008). Herman F., Rhodes E.J. and Braun J. A new thermochronometer reveals steady state relief and exhumation in a small active orogen during the last glacial cycle, submitted. Kuhlemann J., et al., Quantifying tectonic versus erosive denudation by the sediment budget: the Miocene core complexes of the Alps, Tectonophysics 330, 1-23 (2000). Muttoni G., et al., Onset of major Pleistocene glaciations in the Alps. Geology 31, 989-992 (2003). Vernon, A.J., et al., Increase in late Neogene denudation of the European Alps confirmed by analysis of a fission-track thermochronology database. Earth and Planetary Science Letters, 270 (3-4), pp. 316-329 (2008).

New exposure ages for the Last Glacial Cycle in the Sanabria Lake region (northwestern Spain)

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María Jose; Rinterknecht, Vincent; Pallàs, Raimon; Braucher, Régis; Bourlès, Didier; Valero-Garcés, Blas

2013-04-01

The Sanabria Lake region is located in the Trevinca Massif, a mid-latitude mountain area up to 2128 m asl in the northwest corner of the Iberian Peninsula (42oN 6oW). An ice cap glaciation took place during the Last Glacial Cycle in this massif, with an equilibrium line altitude of 1687 m for the Tera glacial outlet at its local maximum (Cowton et al., 2009). A well preserved glacial sequence occurs on an area of 45 km2 around the present Sanabria Lake (1000 m asl) and is composed by lateral and end moraines in close relationship with glaciolacustrine deposits. This sequence shows the ice snout oscillations of the former Tera glacier during the Last Glacial Cycle and offers a good opportunity to compare radiocarbon and OSL- based chronological models with new cosmogenic isotope dates. The new dataset of 10Be exposure ages presented here for the Sanabria Lake moraines is based on measurements conducted on 23 boulders and is compared with previous radiocarbon and OSL data conducted on ice related deposits (Pérez-Alberti et al., 2011; Rodríguez-Rodríguez et al., 2011). Our results are coherent with the available deglaciation radiocarbon chronology, and support a last deglaciation origin for the whole set of end moraines that are downstream the Sanabria Lake (19.2 - 15.7 10Be ka). Discrepancies between results of the different dating methods concern the timing of the local glacial maximum, with the cosmogenic exposure method always yielding the youngest minimum ages. As proposed to explain similar observations made elsewhere (Palacios et al., 2012), reconciling the ages from different dating methods would imply the occurrence of two glacial advances close enough in extent to generate an overlapping polygenic moraine. Cowton, T., Hughes, P.D., Gibbard, P.L., 2009. Palaeoglaciation of Parque Natural Lago de Sanabria, northwest Spain. Geomorphology 108, 282-291. Rodríguez-Rodríguez, L., Jiménez-Sánchez, M., Domínguez-Cuesta, M.J., Rico, M.T., Valero-Garcés, B., 2011. Last deglaciation in northwestern Spain: New chronological and geomorphologic evidence from the Sanabria region. Geomorphology 135, 48-65. Palacios, D., Andrés, N., Úbeda, J., Alcalá, J., Marcos, J., Vázquez-Selem, L., 2012. The importance of poligenic moraines in the paleoclimatic interpretation from cosmogenic dating. Geophysical Research Abstracts 14, EGU2012-3759-1. Pérez-Alberti, A., Valcárcel-Díaz, M., Martini, I.P., Pascucci, V., Andrucci, S., 2011. Upper Pleistocene glacial valley-junction sediments at Pias, Trevinca Mountains, NW Spain. In: Martini, I.P., French, H.M., Pérez-Alberti, A. (Eds.), Ice-Marginal and Periglacial Processes and Sediments. Geological Society (London) Special Publication 354, pp. 93-110. Research funded by the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/CLI), LIMNOCAL (CGL2006-13327-C04-01) and GRACCIE (CSD2007-00067) of the Spanish Inter-Ministry Commission of Science and Technology (CICYT). Additional funding was provided by the Fundación Patrimonio Natural de Castilla y León through the project "La investigacion en el Lago de Sanabria dentro del proyecto CALIBRE: perspectivas y posibilidades", and by the projects Consolider Ingenio 2006 (CSD2006-0041, Topo-Iberia), 2003 PIRA 00256, HF02.4, and RISKNAT (2009SGR520). L. Rodríguez-Rodríguez has developed her research under a Severo Ochoa Programme fellowship (FICYT- Asturias).

Post-glacial phylogeography and evolution of a wide-ranging highly-exploited keystone forest tree, eastern white pine (Pinus strobus) in North America: single refugium, multiple routes.

PubMed

Zinck, John W R; Rajora, Om P

2016-03-02

Knowledge of the historical distribution and postglacial phylogeography and evolution of a species is important to better understand its current distribution and population structure and potential fate in the future, especially under climate change conditions, and conservation of its genetic resources. We have addressed this issue in a wide-ranging and heavily exploited keystone forest tree species of eastern North America, eastern white pine (Pinus strobus). We examined the range-wide population genetic structure, tested various hypothetical population history and evolutionary scenarios and inferred the location of glacial refugium and post-glacial recolonization routes. Our hypothesis was that eastern white pine survived in a single glacial refugium and expanded through multiple post-glacial recolonization routes. We studied the range-wide genetic diversity and population structure of 33 eastern white pine populations using 12 nuclear and 3 chloroplast microsatellite DNA markers. We used Approximate Bayesian Computation approach to test various evolutionary scenarios. We observed high levels of genetic diversity, and significant genetic differentiation (F ST = 0.104) and population structure among eastern white pine populations across its range. A south to north trend of declining genetic diversity existed, consistent with repeated founder effects during post-glaciation migration northwards. We observed broad consensus from nuclear and chloroplast genetic markers supporting the presence of two main post-glacial recolonization routes that originated from a single southern refugium in the mid-Atlantic plain. One route gave rise to populations at the western margin of the species' range in Minnesota and western Ontario. The second route gave rise to central-eastern populations, which branched into two subgroups: central and eastern. We observed minimal sharing of chloroplast haplotypes between recolonization routes but there was evidence of admixture between the western and west-central populations. Our study reveals a single southern refugium, two recolonization routes and three genetically distinguishable lineages in eastern white pine that we suggest to be treated as separate Evolutionarily Significant Units. Like many wide-ranging North American species, eastern white pine retains the genetic signatures of post-glacial recolonization and evolution, and its contemporary population genetic structure reflects not just the modern distribution and effects of heavy exploitation but also routes northward from its glacial refugium.

Wasatch and Uinta Mountains Ecoregion: Chapter 9 in Status and trends of land change in the Western United States--1973 to 2000

USGS Publications Warehouse

Brooks, Mark S.

2012-01-01

The Wasatch and Uinta Mountains Ecoregion covers approximately 44,176 km2 (17, 057 mi2) (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). With the exception of a small part of the ecoregion extending into southern Wyoming and southern Idaho, the vast majority of the ecoregion is located along the eastern mountain ranges of Utah. The ecoregion is situated between the Wyoming Basin and Colorado Plateaus Ecoregions to the east and south and the Central Basin and Range Ecoregion to the west; in addition, the Middle Rockies, Snake River Basin, and Northern Basin and Range Ecoregions are nearby to the north. Considered the western front of the Rocky Mountains, the two major mountain ranges that define the Wasatch and Uinta Mountains Ecoregion include the north-south-trending Wasatch Range and east-west- trending Uinta Mountains. Both mountain ranges have been altered by multiple mountain building and burial cycles since the Precambrian era 2.6 billion years ago, and they have been shaped by glacial processes as early as 1.6 million years ago. The terrain is defined by sharp ridgelines, glacial lakes, and narrow canyons, with elevations ranging from 1,829 m in the lower canyons to 4,123 m at Kings Peak, the highest point in Utah (Milligan, 2010).

Climatic Instability and Regional Glacial Advances in the Late Ediacaran

NASA Astrophysics Data System (ADS)

Hannah, J. L.; Stein, H. J.; Marolf, N.; Bingen, B.

2014-12-01

The Ediacaran Period closed out the environmentally raucous Neoproterozoic Era with the last of multiple glacial events and the first ephemeral glimmer of multicellular life. As such, evolution of Earth's biosphere and the marine environments that nurtured this nascent biota are of particular interest. Because the Ediacaran biota appear in the stratigraphic record just above tillites in many localities, inferences are naturally drawn to link glaciation to bioevolution. Here we review known controls on the timing and extent of the late Ediacaran Gaskier and Varanger glacial events, bolstered by new constraints on the Moelv tillite of South Norway. The elusive mid-Ediacaran glacial strata are poorly dated, patchy in distribution, and relatively limited in thickness. The type Gaskier glaciogenic units in Newfoundland are 582 to 584 Ma, based on U-Pb zircon ages from intercalated ash beds [1]. The Varanger glaciogenic deposits in northern Norway, in contrast, remain only roughly constrained to ca. 630 to 560 Ma. Post-Gaskier negative carbon isotope excursions (CIEs) have been reported from multiple localities in both China and SW United States, suggesting climatic instability in the late Ediacaran. Although most localities lack solid geochronology, paleontologic constraints place the Hongtiegou glacial diamictite and accompanying CIE in the Chaidam Basin, NW China, in the latest Ediacaran, ca. 555 Ma [2]. We previously suggested that the Moelv tillite in south Norway was roughly equivalent to the Gaskier, based on an imprecise Re-Os age of ~560 Ma [3] for the underlying Biri shale. Reanalysis of these data shows that the upper part of the shale section was disturbed by a redox front during the Caledonian orogeny. The undisturbed lower part of the section yields a more precise Model 1 isochron age of 559.5 ± 6.2 Ma, clearly post-dating the Gaskier event well outside analytical uncertainty. These new results bolster arguments that the Gaskier glaciation was not a global "snowball Earth" event; rather, there may have been multiple Ediacaran glacial advances - perhaps only at high latitudes - marked by tillites of regional, but not global extent. [1] Bowring et al. 2002, Astrobiology 2: 457-458. [2] Shen et al. 2010, Prec. Res. 177: 241-252. [3] Hannah et al. 2007, Geochim. Cosmochim. Acta 71: A378.

A 600,000 year long continental pollen record from Lake Van, eastern Turkey

NASA Astrophysics Data System (ADS)

Litt, T.; Pickarski, N.; Heumann, G.

2014-12-01

Lake Van is the fourth largest terminal lake in the world (38.5°N, 43 °E, volume 607 km3, area 3570 km2, maximum water depth 460 m), extending for 130 km WSW-ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, obtains a long and continuous continental sequence that covers multiple interglacial-glacial cycles. Promoted by the potential of the sedimentary sequence for reconstructing the paleoecological and paleoclimate development of the Near East, a deep drilling operation was carried out in 2010 supported by the International Continental Scientific Drilling Program (ICDP). The 119 m long continental record is based on a well-dated composite profile drilled on the so-called Ahlat Ridge in water depth of 360 m encompassing the last 600,000 years. It contains the longest continuous continental pollen record of the Quaternary in the entire Near East and central Asia obtained to date. It documents glacial and interglacial stages as well as pronounced interstadials encompassing the entire 600 ka of the sedimentary record. The cold-adapted vegetation in the Lake Van region during glacial stages and stadial substages can be described as dwarf-shrub steppe and desert steppe very similar to each other. The climax vegetation of the interglacial stages in the Lake Van region is characterized by an oak steppe-forest with pistachio and juniper. It is interesting to note that, in contrast to the atmospheric CO2 concentration from Antarctic ice cores or marine isotope values based on benthic foraminifera, there is no clear subdivision in the Lake Van pollen record between low-amplitude interglacials (cooler cycles) prior the mid-Brunhes event (MBE) at 430 ka and high-amplitude, post MBE interglacials. Lower CO2 concentrations in the atmosphere might be compensated by stronger insolation forcing during Marine Isotope Stages (MIS) 13a and 15a. A similar pattern can be observed during the triplicate interglacial complex MIS 7 when AP and oak values reach maximum values during MIS 7c instead of MIS 7e. This underlines the different environmental response to global climate change in the continental Lake Van region compared to the global ice volume and/or greenhouse-gas amounts.

Geochemistry of glacial sediments in the area of the Bend massive sulfide deposit, north-central Wisconsin

USGS Publications Warehouse

Woodruff, L.G.; Attig, J.W.; Cannon, W.F.

2004-01-01

Geochemical exploration in northern Wisconsin has been problematic because of thick glacial overburden and complex stratigraphic record of glacial history. To assess till geochemical exploration in an area of thick glacial cover and complex stratigraphy samples of glacial materials were collected from cores from five rotasonic boreholes near a known massive sulfide deposit, the Bend deposit in north-central Wisconsin. Diamond drilling in the Bend area has defined a long, thin zone of mineralization at least partly intersected at the bedrock surface beneath 30-40 m of unconsolidated glacial sediments. The bedrock surface has remnant regolith and saprolite resulting from pre-Pleistocene weathering. Massive sulfide and mineralized rock collected from diamond drill core from the deposit contain high (10s to 10,000s ppm) concentrations of Ag, As, Au, Bi, Cu, Hg, Se, Te, and Tl. Geochemical properties of the glacial stratigraphic units helped clarify the sequence and source areas of several glacial ice advances preserved in the section. At least two till sheets are recognized. Over the zone of mineralization, saprolite and preglacial alluvial and lacustrine samples are preserved on the bedrock surface in a paleoriver valley. The overlying till sheet is a gray, silty carbonate till with a source hundreds of kilometers to the northwest of the study area. This gray till is overlain by red, sandy till with a source to the north in Proterozoic rocks of the Lake Superior area. The complex glacial stratigraphy confounds down-ice geochemical till exploration. The presence of remnant saprolite, preglacial sediment, and far-traveled carbonate till minimized glacial erosion of mineralized material. As a result, little evidence of down-ice glacial dispersion of lithologic or mineralogic indicators of Bend massive sulfide mineralization was found in the samples from the rotasonic cores. This study points out the importance of determining glacial stratigraphy and history, and identifying favorable lithologies required for geochemical exploration. Drift prospecting in Wisconsin and other areas near the outer limits of the Pleistocene ice sheets may not be unsuccessful, in part, because of complex stratigraphic sequences of multiple glaciations where deposition dominates over erosion. ?? 2004 Elsevier B.V. All rights reserved.

Using 81Kr and noble gases to characterize and date groundwater and brines in the Baltic Artesian Basin on the one-million-year timescale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerber, Christoph; Vaikmae, Rein; Aeschbach, Werner

Analyses for 81Kr and noble gases on groundwater from the deepest aquifer system of the Baltic Artesian Basin (BAB) were performed to determine groundwater ages and uncover the flow dynamics of the system on a timescale of several hundred thousand years. We find that the system is controlled by mixing of three distinct water masses: Interglacial or recent meteoric water (δ 18O ≈ –10.4‰) with a poorly evolved chemical and noble gas signature, glacial meltwater (δ 18O ≤ –18‰) with elevated noble gas concentrations, and an old, high-salinity brine component (δ 18O ≥ –4.5‰, ≥ 90 g Cl –/L) withmore » strongly depleted atmospheric noble gas concentrations. The 81Kr measurements are interpreted within this mixing framework to estimate the age of the end-members. Deconvoluted 81Kr ages range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and glacial meltwater. For the brine component, ages exceed the dating range of the ATTA-3 instrument of 1.3 Ma. The radiogenic noble gas components 4He* and 40Ar* are less conclusive but also support an age of > 1 Ma for the brine. Based on the chemical and noble gas concentrations and the dating results, we conclude that the brine originates from evaporated seawater that has been modified by later water–rock interaction. Furthermore, as the obtained tracer ages cover several glacial cycles, we discuss the impact of the glacial cycles on flow patterns in the studied aquifer system.« less

Primary productivity of supraglacial snow algae communities on stratovolcanoes of the Pacific Northwest

NASA Astrophysics Data System (ADS)

Hamilton, T. L.; Havig, J. R.

2016-12-01

The majority of geomicrobiological research conducted on glacial systems to date have focused on glaciers that override primarily carbonate or granitic bedrock types, with little known of the processes that support microbial life in glacial systems overriding volcanic terrains (e.g., basalt or andesite). To better constrain the role of the supraglacial ecosystems in the carbon and nitrogen cycles, to gain insight into microbiome composition and function in alpine glacial systems overriding volcanic terrains, and to constrain potential elemental sequestration or release through weathering processes associated with snow algae communities, we examined the microbial community structure and primary productivity in snow on and near alpine glaciers on stratovolcanoes in the Cascade Range of the Pacific Northwest. Here we present the first published values for carbon fixation rates of snow algae communities on alpine glaciers in the Pacific Northwest. We observed varying levels of light-dependent carbon fixation on snowfields on or near glaciers on Mt Hood, Mt Adams and North Sister. Recovery of algal 18S rRNA transcripts is consistent with previous studies indicating the majority of primary productivity on snow and ice can be attributed to photoautotrophic algae. In contrast to previous observations of glacial ecosystems, our geochemical, isotopic and microcosm data suggest these assemblages are not limited by phosphorus or fixed nitrogen availability. Furthermore, our data indicate these snow assemblages actively sequester Fe, Mn, and P leached from minerals sourced from the local rocks. Our observations of light-dependent primary productivity on snow are consistent with similar studies in polar ecosystems; however, our data underscore the need for similar studies on glacier surfaces and seasonal snowfields to better constrain the role of local bedrock and nutrient delivery on carbon fixation and biogeochemical cycling in these ecosystems.

Climate Stability: Pathway to understand abrupt glacial climate shifts

NASA Astrophysics Data System (ADS)

Zhang, X.; Knorr, G.; Barker, S.; Lohmann, G.

2017-12-01

Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger (DO) cycles that have been linked to variations in the Atlantic meridional overturning circulation (AMOC). The most pronounced stadial coolings, Heinrich Stadials (HSs), are associated with massive iceberg discharges to the North Atlantic. This motivates scientists to consider that the North Atlantic freshwater perturbations is a common trigger of the associated abrupt transitions between weak and strong AMOC states. However, recent studies suggest that the Heinrich ice-surging events are triggered by ocean subsurface warming associated with an AMOC slow-down. Furthermore, the duration of ice-rafting events does not systematically coincide with the beginning and end of the pronounced cold conditions during HSs. In this context, we show that both, changes in atmospheric CO2 and ice sheet configuration can provide important control on the stability of the AMOC, using a coupled atmosphere-ocean model. Our simulations reveal that gradual changes in Northern Hemisphere ice sheet height and atmospheric CO2 can act as a trigger of abrupt glacial/deglacial climate changes. The simulated global climate responses—including abrupt warming in the North Atlantic, a northward shift of the tropical rain belts, and Southern Hemisphere cooling related to the bipolar seesaw—are generally consistent with empirical evidence. We further find that under a delicate configuration of atmospheric CO2 and ice sheet height the AMOC can be characterized by a self-oscillation (resonance) feature (Hopf Bifucation) with a 1000-year cycle that is comparable with observed small DO events during the MIS 3. This provides an alternative explanation for millennial-scale DO variability during glacial periods.

Using 81Kr and noble gases to characterize and date groundwater and brines in the Baltic Artesian Basin on the one-million-year timescale

DOE PAGES

Gerber, Christoph; Vaikmae, Rein; Aeschbach, Werner; ...

2017-01-31

Analyses for 81Kr and noble gases on groundwater from the deepest aquifer system of the Baltic Artesian Basin (BAB) were performed to determine groundwater ages and uncover the flow dynamics of the system on a timescale of several hundred thousand years. We find that the system is controlled by mixing of three distinct water masses: Interglacial or recent meteoric water (δ 18O ≈ –10.4‰) with a poorly evolved chemical and noble gas signature, glacial meltwater (δ 18O ≤ –18‰) with elevated noble gas concentrations, and an old, high-salinity brine component (δ 18O ≥ –4.5‰, ≥ 90 g Cl –/L) withmore » strongly depleted atmospheric noble gas concentrations. The 81Kr measurements are interpreted within this mixing framework to estimate the age of the end-members. Deconvoluted 81Kr ages range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and glacial meltwater. For the brine component, ages exceed the dating range of the ATTA-3 instrument of 1.3 Ma. The radiogenic noble gas components 4He* and 40Ar* are less conclusive but also support an age of > 1 Ma for the brine. Based on the chemical and noble gas concentrations and the dating results, we conclude that the brine originates from evaporated seawater that has been modified by later water–rock interaction. Furthermore, as the obtained tracer ages cover several glacial cycles, we discuss the impact of the glacial cycles on flow patterns in the studied aquifer system.« less

Glacial Isostatic Adjustment Derived Boundary Conditions for Paleoclimate Simulation: the Refined ICE-6G_D (VM5a) Model and the Dansgaard-Oeschger Oscillation

NASA Astrophysics Data System (ADS)

Peltier, W. R.; Vettoretti, G.; Argus, D. F.

2017-12-01

Global models of the glacial isostatic adjustment (GIA) process are designed to fit a wide range of geophysical and geomorphological observations that simultaneously constrain the internal viscoelastic structure of Earths interior and the history of grounded ice thickness variations that has occurred over the most recent ice-age cycle of the Late Quaternary interval of time. The most recent refinement of the ICE-NG (VMX) series of such global models from the University of Toronto, ICE-6G_C (VM5a), has recently been slightly modified insofar as its Antarctic component is concerned to produce a "_D" version of the structure. This has been chosen to provide the boundary conditions for the next round of model-data inter-comparisons in the context of the international Paleoclimate Modeling Inter-comparison Project (PMIP). The output of PMIP will contribute to the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change which is now under way. A highly significant test of the utility of this latest model has recently been performed that is focused upon the Dansgaard-Oeschger oscillation that was the primary source of climate variability during Marine Isotope Stage 3 (MIS3) of the most recent glacial cycle. By introducing the surface boundary conditions for paleotopography and paleobathymetry, land-sea mask and surface albedo into the NCAR CESM1 coupled climate model configured at full one degree by one degree CMIP5 resolution, together with the appropriate trace gas and orbital insolation forcing, we show that the millennium timescale Dansgard-Oeschger oscillation naturally develops following spin- up of the model into the glacial state.

Terrestrial soil pH and MAAT records based on the MBT/CBT in the southern South China Sea: implications for the atmospheric CO2 evolution in Southeast Asia

NASA Astrophysics Data System (ADS)

Dong, L.; Li, L.; Li, Q.; Zhang, C.

2013-12-01

Liang Dong1, Li Li1, Qianyu Li1,2, Chuanlun L. Zhang1,3 1State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China 2School of Earth and Environment Sciences, University of Adelaide, SA 5005, Australia 3Department of Marine Sciences, University of Georgia, Athens, GA 30602, USA The methylation index of branched tetraethers (MBT) and/or the cyclization ratio of branched tetraethers (CBT) are derived from the branched glycerol dialkyl Glycerol tetraethers (GDGTs) of bacterial origin and are widely used to reconstruct the terrestrial soil pH and mean annual air temperature (MAAT); however, these proxies are less frequently used in the oceanic settings. Here we provide the first high resolution records of soil pH and MAAT since the last glacial maximum based on the sedimentary core of MD05-2896 in the southern South China Sea. The MAAT record exhibited typical glacial and interglacial cycles and was consistent with the winter insolation variation. The pH values were lower (6.4-7) in the glacial time and higher (7-8.4) in the interglacial time. Changes in soil pH allowed the evaluation of changes in soil CO2 based on the atmosphere-soil CO2 balance. The results imply that the lower winter MAAT variation with a lower winter atmospheric CO2 concentration might have resulted in a higher pH in the interglacial period. Our records provide a new insight into the evolution of atmospheric CO2 between glacial and interglacial cycles in East Asia. Key words: South China Sea, MBT/CBT, b-GDGTs, MAAT, pH

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception

NASA Astrophysics Data System (ADS)

Schneider, R.; Schmitt, J.; Köhler, P.; Joos, F.; Fischer, H.

2013-11-01

The reconstruction of the stable carbon isotope evolution in atmospheric CO2 (δ13Catm), as archived in Antarctic ice cores, bears the potential to disentangle the contributions of the different carbon cycle fluxes causing past CO2 variations. Here we present a new record of δ13Catm before, during and after the Marine Isotope Stage 5.5 (155 000 to 105 000 yr BP). The dataset is archived on the data repository PANGEA® (www.pangea.de) under 10.1594/PANGAEA.817041. The record was derived with a well established sublimation method using ice from the EPICA Dome C (EDC) and the Talos Dome ice cores in East Antarctica. We find a 0.4‰ shift to heavier values between the mean δ13Catm level in the Penultimate (~ 140 000 yr BP) and Last Glacial Maximum (~ 22 000 yr BP), which can be explained by either (i) changes in the isotopic composition or (ii) intensity of the carbon input fluxes to the combined ocean/atmosphere carbon reservoir or (iii) by long-term peat buildup. Our isotopic data suggest that the carbon cycle evolution along Termination II and the subsequent interglacial was controlled by essentially the same processes as during the last 24 000 yr, but with different phasing and magnitudes. Furthermore, a 5000 yr lag in the CO2 decline relative to EDC temperatures is confirmed during the glacial inception at the end of MIS5.5 (120 000 yr BP). Based on our isotopic data this lag can be explained by terrestrial carbon release and carbonate compensation.

Paleoglaciology of the Ala-Archa and Ak-Shyrak areas, Kyrgyz Tian Shan

NASA Astrophysics Data System (ADS)

Blomdin, R.; Beel, C.; Caffee, M. W.; Codilean, A.; Gribenski, N.; Harbor, J.; Heyman, J.; Hattestrand, C.; Ivanov, M.; Kassab, C.; Lifton, N. A.; Petrakov, D.; Rogozhina, I.; Stroeven, A. P.; Usubaliev, R.

2012-12-01

We employed detailed glacial geomorphological mapping of the Ala-Archa and Ak-Shyrak areas, Kyrgyz Tian Shan (Shan = Mountains) to build a paleoglaciological reconstruction. These two areas were selected because their glaciers constitute important freshwater reservoirs for downstream communities (the Kyrgyz capital Bishkek, and cities along the Syr Darja which drains towards the Aral Sea, respectively), and because fluctuations in their extent cause both variations in water supply and risks for glacial hazards. Five landform categories were mapped; glacial valleys, marginal moraines, glacial lineations, hummocky terrain, and melt-water channels. These landforms were mapped using a SRTM digital elevation model (DEM) with a 90 m resolution, Landsat 7 ETM+ satellite imagery with a 30 m resolution, Aster GDEM with a 30 m resolution, and Google Earth. This remotely sensed mapping was also checked and complemented by field mapping. The distribution of mapped landforms indicates restricted glaciations, mainly concentrated to the mountain areas. In both ranges marginal moraines extend beyond the furthest extent of glacial valleys. Furthermore, extensive areas of hummocky moraine in Ak-Shyrak extending beyond montane glacial valleys indicate glacial extents into the intermontane basins. Several series of lateral and terminal moraines in the Ala-Archa and Ak-Shyrak ranges have been identified and sampled for cosmogenic nuclide 10Be dating, while associated glaciofluvial sediment was sampled for optically-stimulated luminescence (OSL) and electron spin resonance (ESR) dating. Future work will involve using these samples to build a consistent chronology for glaciation and investigation of contrasts between paleoglaciological reconstructions of valleys within a single range but with different aspects, as well as between ranges. In the final stages of the project we will use intermediate complexity glacier flow models to examine paleoclimatic implications of the observed spatial and temporal patterns of glacier changes, focused in particular on the last glacial cycle.

Climatic impact of glacial cycle polar motion: Coupled oscillations of ice sheet mass and rotation pole position

USGS Publications Warehouse

Bills, Bruce G.; James, Thomas S.; Mengel, John G.

1999-01-01

Precessional motion of Earth's rotation axis relative to its orbit is a well-known source of long-period climatic variation. It is less well appreciated that growth and decay of polar ice sheets perturb the symmetry of the global mass distribution enough that the geographic location of the rotation axis will change by at least 15 km and possibly as much as 100 km during a single glacial cycle. This motion of the pole will change the seasonal and latitudinal pattern of temperatures. We present calculations, based on a diurnal average energy balance, which compare the summer and winter temperature anomalies due to a 1° decrease in obliquity with those due to a 1° motion of the rotation pole toward Hudson Bay. Both effects result in peak temperature perturbations of about 1° Celsius. The obliquity change primarily influences the amplitude of the seasonal cycle, while the polar motion primarily changes the annual mean temperatures. The polar motion induced temperature anomaly is such that it will act as a powerful negative feedback on ice sheet growth. We also explore the evolution of the coupled system composed of ice sheet mass and pole position. Oscillatory solutions result from the conflicting constraints of rotational and thermal stability. A positive mass anomaly on an otherwise featureless Earth is in rotational equilibrium only at the poles or the equator. The two polar equilibria are rotationally unstable, and the equatorial equilibrium, though rotationally stable, is thermally unstable. We find that with a plausible choice for the strength of coupling between the thermal and rotational systems, relatively modest external forcing can produce significant response at periods of 104–106 years, but it strongly attenuates polar motion at longer periods. We suggest that these coupled oscillations may contribute to the observed dominance of 100 kyr glacial cycles since the mid-Pleistocene and will tend to stabilize geographic patterns that are suitable to glaciations.

A wet-geology and cold-climate Mars model: Punctuation of a slow dynamic approach to equilibrium

NASA Technical Reports Server (NTRS)

Kargel, J. S.

1993-01-01

It was suggested that Mars may have possessed a relatively warm humid climate and a vigorous hydrological cycle involving meteoric precipitation, oceans, and continental ice sheets. Baker hypothesized that these geologically active conditions may have been repeated several times; each of these dynamic epochs was followed by a collapse of the climate and hydrologic cycle of Mars into essentially current conditions, completing what is termed a 'Baker cycle'. The purpose is to present an endmember possibility that Martian glacial landscapes, including some that were previously considered to have formed under warm climatic conditions, might be explained by processes compatible with an extremely cold surface. Two aspects of hypothesized Martian glacial terrains were cited as favoring a warm climate during Baker cycles: (1) the formation of some landscapes, including possible eskers, tunnel channels, drumlins, and outwash plains, appears to have required liquid water, and (2) a liquid-surfaced ocean was probably necessary to feed the glaciers. The requirement for liquid water, if these features were correctly interpreted, is difficult to avoid; it is entirely possible that a comparatively warm climate was involved, but it is not clear that formation of landforms by wet-based glaciers actually requires a warm climate. Even less certain is the supposed requirement for liquid oceans. Formation of glaciers only requires a source of water or ice to supply an amount of precipitation that exceeds losses due to melting and sublimation. At Martian temperatures precipitation is very low, but so are melting and sublimation, so a large body of ice that is unstable with respect to sublimation may take the role of Earth's oceans in feeding the glaciers. Recent models suggest that even current Martian polar caps, long thought to be static bodies of ice and dust, might actually be slow-moving, cryogenic continental glaciers. Is it possible that subglacial processes beneath cryogenic (but wetbased) ice sheets formed the hypothesized Martian glacial landscapes?

Geomorphic controls on Pleistocene knickpoint migration in Alpine valleys

NASA Astrophysics Data System (ADS)

Leith, Kerry; Fox, Matt; Moore, Jeffrey R.; Brosda, Julian; Krautblatter, Michael; Loew, Simon

2014-05-01

Recent insights into sub-glacial bedrock stress conditions suggest that the erosional efficiency of glaciers may reduce markedly following a major erosional cycle [Leith et al., 2013]. This implies that the formation of large glacial valleys within the Alps is likely to have occurred shortly after the onset of 100 ky glacial-interglacial cycles (at the mid-Pleistocene Revolution (MPR)). The majority of landscape change since this time may have therefore been driven by sub-aerial processes. This hypothesis is supported by observations of hillslope and channel morphology within Canton Valais (Switzerland), where major tributary valleys display a common morphology along their length, hinting at a shared geomorphic history. Glaciers currently occupy the headwaters of many catchments, while the upper reaches of rivers flow across extensive alluvial planes before abruptly transitioning to steep channels consisting of mixed bedrock and talus fan deposits. The rivers then converge to flow out over the alluvial plane of the Rhone Valley. Characteristically rough topographies within the region are suggested to mark the progressive transition from a glacial to fluvially-dominated landscape, and correlate well with steepened river channel sections determined from a 2.5 m resolution LiDAR DEM. We envisage a landscape in which ongoing tectonic uplift drives the emergence of Alpine bedrock through massive sedimentary valley infills (currently concentrated in the Rhone Valley), whose elevation is fixed by the consistent fluvial baselevel at Lake Geneva. As fluvial incision ceases at the onset of glaciation, continued uplift causes the formation of knickpoints at the former transition from bedrock to sedimentary infill. These knickpoints will then propagate upstream during subsequent interglacial periods. By investigating channel morphologies using an approach based on the steady-state form of the stream power equation, we can correlate steepened channel reaches (degraded knickpoints) across most major tributaries south of the Rhone River. The timing of apparent uplift events correlates well with that of cool Marine Isotope Stages derived from global oxygen isotope data up to the beginning of MIS 12. A weak correlation up to the beginning of MIS 18 suggests initial glacial incision may have occurred some time during MIS 14 - 20, and valley development has since been driven by fluvial processes. Leith, K., J. R. Moore, F. Amann, and S. Loew (2013), Sub-glacial extensional fracture development and implications for Alpine valley evolution, J. Geophys. Res. Earth Surf., doi:10.1002/2012JF002691.

Ice-Sheet Dynamics and Millennial-Scale Climate Variability in the North Atlantic across the Middle Pleistocene Transition (Invited)

NASA Astrophysics Data System (ADS)

Hodell, D. A.; Nicholl, J.

2013-12-01

During the Middle Pleistocene Transition (MPT), the climate system evolved from a more linear response to insolation forcing in the '41-kyr world' to one that was decidedly non-linear in the '100-kyr world'. Smaller ice sheets in the early Pleistocene gave way to larger ice sheets in the late Pleistocene with an accompanying change in ice sheet dynamics. We studied Sites U1308 (49° 52.7'N, 24° 14.3'W; 3871 m) and U1304 (53° 3.4'N, 33° 31.8'W; 3024 m) in the North Atlantic to determine how ice sheet dynamics and millennial-scale climate variability evolved as glacial boundary conditions changed across the MPT. The frequency of ice-rafted detritus (IRD) in the North Atlantic was greater during glacial stages prior to 650 ka (MIS 16), reflecting more frequent crossing of an ice volume threshold when the climate system spent more time in the 'intermediate ice volume' window, resulting in persistent millennial scale variability. The rarity of Heinrich Events containing detrital carbonate and more frequent occurrence of IRD events prior to 650 ka may indicate the presence of 'low-slung, slippery ice sheets' that flowed more readily than their post-MPT counterparts (Bailey et al., 2010). Ice volume surpassed a critical threshold across the MPT that permitted ice sheets to survive boreal summer insolation maxima, thereby increasing ice volume and thickness, lengthening glacial cycles, and activating the dynamical processes responsible for Laurentide Ice Sheet instability in the region of Hudson Strait (i.e., Heinrich events). The excess ice volume during post-MPT glacial maxima provided a large, unstable reservoir of freshwater to be released to the North Atlantic during glacial terminations with the potential to perturb Atlantic Meridional Overtunring Circulation. We speculate that orbital- and millennial-scale variability co-evolved across the MPT and the interaction of processes on orbital and suborbital time scales gave rise to the changing patterns of glacial-interglacial cycles through the Quaternary. Bailey, I., Bolton, C.T., DeConto, R.M., Pollard, D., Schiebel, R. and Wilson, P.A. (2010) A low threshold for North Atlantic ice rafting from "low-slung slippery" late Pliocene ice sheets. Paleoceanography, 25, PA1212-[14pp]. (doi:10.1029/2009PA001736).

Quantitative interpretation of atmospheric carbon records over the last glacial termination

NASA Astrophysics Data System (ADS)

KöHler, Peter; Fischer, Hubertus; Munhoven, Guy; Zeebe, Richard E.

2005-12-01

The glacial/interglacial rise in atmospheric pCO2 is one of the best known changes in paleoclimate research, yet the cause for it is still unknown. Forcing the coupled ocean-atmosphere-biosphere box model of the global carbon cycle BICYCLE with proxy data over the last glacial termination, we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (δ13C, Δ14C) observed in natural climate archives. The sensitivity of the Box model of the Isotopic Carbon cYCLE (BICYCLE) to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models, respectively. The processes considered here ranked by their contribution to the glacial/interglacial rise in pCO2 in decreasing order are: the rise in Southern Ocean vertical mixing rates (>30 ppmv), decreases in alkalinity and carbon inventories (>30 ppmv), the reduction of the biological pump (˜20 ppmv), the rise in ocean temperatures (15-20 ppmv), the resumption of ocean circulation (15-20 ppmv), and coral reef growth (<5 ppmv). The regrowth of the terrestrial biosphere, sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction, decreasing pCO2 during Termination I by ˜30 ppmv. According to our model the sequence of events during Termination I might have been the following: a reduction of aeolian iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase. After these events the reduced North Atlantic Deep Water (NADW) formation during the Heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the Bølling-Allerød warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of Termination I. We further deduce that a complete shutdown of the NADW formation during the Younger Dryas was very unlikely. Changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric δ13C after the Bølling-Allerød warm interval.

Modelled Growth and Decay of the Cordilleran Ice Sheet Through the Last Glacial Cycle

NASA Astrophysics Data System (ADS)

Marshall, S. J.; Banwell, A.

2015-12-01

The Cordilleran Ice Sheet in western North America had an enigmatic evolution during the last glacial cycle, developing out of sync with the larger Laurentide and global glaciation. The geological record suggests that the ice sheet emerged late, ca. 45 ka, growing to be a fully-established ice sheet in isotope stages 3 and 2 and deglaciating late in the glacial cycle. This has been a challenge to model, and is a paleoclimatic curiosity, because the western Cordillera of North America is heavily glacierized today, and one would intuitively expect it to act as an inception centre for the Pleistocene ice sheets. The region receives heavy precipitation, and modest cooling should induce large-scale glacier expansion. Indeed, a Cordilleran Ice Sheet quickly nucleates in isotope substage 5d in most ice sheet modeling studies to date, and is a resilient feature throughout the glaciation. The fact that a full-scale Cordilleran Ice Sheet did not develop until relatively late argues for either: (a) ice sheet models that have been inadequate in resolving the process of alpine-style glaciation, i.e., the coalescence of alpine icefields, or (b) a climatic history in western North America that deviated strongly from the hemispheric-scale cooling which drove the growth of the Laurentide and Scandinavian Ice Sheets, as recorded in Greenland. We argue that reasonable reconstructions of Cordilleran Ice Sheet growth and decay implicate a combination of these two considerations. Sufficient model resolution is required to capture the valley-bottom melt that suppresses icefield coalescence, while early-glacial cooling must have been modest in the Pacific sector of North America. We argue for a persistent warm, dry climate relative to that in eastern North America and the Atlantic sector, likely associated with positive feedbacks between atmospheric circulation and the nascent Laurentide Ice Sheet (i.e., peristent circulation patterns similar to those of 2014-2015). This must have been disrupted as the Laurentide thickened and advanced southward, allowing the Cordilleran Ice Sheet to emerge from numerous isolated icefield complexes.

Middle and Late Pleistocene glaciations in the southwestern Pamir and their effects on topography [Topography of the SW Pamir shaped by middle-late Pleistocene glaciation

DOE PAGES

Stübner, Konstanze; Grin, Elena; Hidy, Alan J.; ...

2017-03-27

Glacial chronologies provide insight into the evolution of paleo-landscapes, paleoclimate, topography, and the erosion processes that shape mountain ranges. In the Pamir of Central Asia, glacial morphologies and deposits indicate extensive past glaciations, whose timing and extent remain poorly constrained. Geomorphic data and 15 new 10Be exposure ages from moraine boulders and roches moutonnées in the southwestern Pamir document multiple Pleistocene glacial stages. The oldest exposure ages, View the MathML source113 ± 10ka, underestimate the age of the earliest preserved glacial advance and imply that the modern relief of the southwestern Pamir (peaks at ~5000–6000 m a.s.l.; valleys at ~2000–3000more » m a.s.l.) already existed in the late Middle Pleistocene. Younger exposure ages (~40–80 ka, ~30 ka) complement the existing Central Asian glacial chronology and reflect successively less extensive Late Pleistocene glaciations. The topography of the Pamir and the glacial chronologies suggest that, in the Middle Pleistocene, an ice cap or ice field occupied the eastern Pamir high-altitude plateau, whereas westward flowing valley glaciers incised the southwestern Pamir. Since the Late Pleistocene deglaciation, the rivers of the southwestern Pamir adjusted to the glacially shaped landscape. As a result, localized rapid fluvial incision and drainage network reorganization reflect the transient nature of the deglaciated landscape.« less

Middle and Late Pleistocene glaciations in the southwestern Pamir and their effects on topography [Topography of the SW Pamir shaped by middle-late Pleistocene glaciation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stübner, Konstanze; Grin, Elena; Hidy, Alan J.

Glacial chronologies provide insight into the evolution of paleo-landscapes, paleoclimate, topography, and the erosion processes that shape mountain ranges. In the Pamir of Central Asia, glacial morphologies and deposits indicate extensive past glaciations, whose timing and extent remain poorly constrained. Geomorphic data and 15 new 10Be exposure ages from moraine boulders and roches moutonnées in the southwestern Pamir document multiple Pleistocene glacial stages. The oldest exposure ages, View the MathML source113 ± 10ka, underestimate the age of the earliest preserved glacial advance and imply that the modern relief of the southwestern Pamir (peaks at ~5000–6000 m a.s.l.; valleys at ~2000–3000more » m a.s.l.) already existed in the late Middle Pleistocene. Younger exposure ages (~40–80 ka, ~30 ka) complement the existing Central Asian glacial chronology and reflect successively less extensive Late Pleistocene glaciations. The topography of the Pamir and the glacial chronologies suggest that, in the Middle Pleistocene, an ice cap or ice field occupied the eastern Pamir high-altitude plateau, whereas westward flowing valley glaciers incised the southwestern Pamir. Since the Late Pleistocene deglaciation, the rivers of the southwestern Pamir adjusted to the glacially shaped landscape. As a result, localized rapid fluvial incision and drainage network reorganization reflect the transient nature of the deglaciated landscape.« less

Change in atmospheric mineral aerosols in response to climate: Last glacial period, preindustrial, modern, and doubled carbon dioxide climates

USGS Publications Warehouse

Mahowald, N.M.; Muhs, D.R.; Levis, S.; Rasch, P.J.; Yoshioka, M.; Zender, C.S.; Luo, C.

2006-01-01

Desert dust simulations generated by the National Center for Atmospheric Research's Community Climate System Model for the current climate are shown to be consistent with present day satellite and deposition data. The response of the dust cycle to last glacial maximum, preindustrial, modern, and doubled-carbon dioxide climates is analyzed. Only natural (non-land use related) dust sources are included in this simulation. Similar to some previous studies, dust production mainly responds to changes in the source areas from vegetation changes, not from winds or soil moisture changes alone. This model simulates a +92%, +33%, and -60% change in dust loading for the last glacial maximum, preindustrial, and doubled-carbon dioxide climate, respectively, when impacts of carbon dioxide fertilization on vegetation are included in the model. Terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions, probably due to the lack of simulation of glaciogenic dust sources. In order to include the glaciogenic dust sources as a first approximation, we designate the location of these sources, and infer the size of the sources using an inversion method that best matches the available data. The inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2.1 to 3.3 times current deposition. Copyright 2006 by the American Geophysical Union.

Influences of glacial melt and permafrost thaw on the age of dissolved organic carbon in the Yukon River basin

USGS Publications Warehouse

Aiken, George R.; Spencer, Robert G.M.; Striegl, Robert G.; Schuster, Paul F.; Raymond, Peter A.

2014-01-01

Responses of near-surface permafrost and glacial ice to climate change are of particular significance for understanding long-term effects on global carbon cycling and carbon export by high-latitude northern rivers. Here we report Δ14C-dissolved organic carbon (DOC) values and dissolved organic matter optical data for the Yukon River, 15 tributaries of the Yukon River, glacial meltwater, and groundwater and soil water end-member sources draining to the Yukon River, with the goal of assessing mobilization of aged DOC within the watershed. Ancient DOC was associated with glacial meltwater and groundwater sources. In contrast, DOC from watersheds dominated by peat soils and underlain by permafrost was typically enriched in Δ14C indicating that degradation of ancient carbon stores is currently not occurring at large enough scales to quantitatively influence bulk DOC exports from those landscapes. On an annual basis, DOC exported was predominantly modern during the spring period throughout the Yukon River basin and became older through summer-fall and winter periods, suggesting that contributions of older DOC from soils, glacial meltwaters, and groundwater are significant during these months. Our data indicate that rapidly receding glaciers and increasing groundwater inputs will likely result in greater contributions of older DOC in the Yukon River and its tributaries in coming decades.

Glacial cold-water coral growth in the Gulf of Cádiz: Implications of increased palaeo-productivity

NASA Astrophysics Data System (ADS)

Wienberg, Claudia; Frank, Norbert; Mertens, Kenneth N.; Stuut, Jan-Berend; Marchant, Margarita; Fietzke, Jan; Mienis, Furu; Hebbeln, Dierk

2010-10-01

A set of 40 Uranium-series datings obtained on the reef-forming scleractinian cold-water corals Lophelia pertusa and Madrepora oculata revealed that during the past 400 kyr their occurrence in the Gulf of Cádiz (GoC) was almost exclusively restricted to glacial periods. This result strengthens the outcomes of former studies that coral growth in the temperate NE Atlantic encompassing the French, Iberian and Moroccan margins dominated during glacial periods, whereas in the higher latitudes (Irish and Norwegian margins) extended coral growth prevailed during interglacial periods. Thus it appears that the biogeographical limits for sustained cold-water coral growth along the NE Atlantic margin are strongly related to climate change. By focussing on the last glacial-interglacial cycle, this study shows that palaeo-productivity was increased during the last glacial. This was likely driven by the fertilisation effect of an increased input of aeolian dust and locally intensified upwelling. After the Younger Dryas cold event, the input of aeolian dust and productivity significantly decreased concurrent with an increase in water temperatures in the GoC. This primarily resulted in reduced food availability and caused a widespread demise of the formerly thriving coral ecosystems. Moreover, these climate induced changes most likely caused a latitudinal shift of areas with optimum coral growth conditions towards the northern NE Atlantic where more suitable environmental conditions established with the onset of the Holocene.

Non-synchronous climate change along the western margin of North America during glacial terminations

NASA Astrophysics Data System (ADS)

Herbert, T. D.; Liu, Z.; Barron, J.; Heusser, L.; Lyle, M.; Mix, A.; Ravelo, A. C.

2003-04-01

A regional set of cores now exists to study the evolution of ocean surface temperatures and other paleoclimatic signals along the west coast of North America. Core locations range from Vancouver Island to the north, to the tip of Baja California to the south. We report on the evolution of sea surface temperatures and marine productivity, as recorded by alkenones. Several sites also have pollen records, allowing us to compare marine and terrestrial responses. We find that surface climate signals covary tightly with global climate, as represented by benthic d18O, through 80% of a typical glacial-interglacial cycle. However, the associations during glacial maxima and terminations break into three regional patterns. North of Point Conception (heart of the California Current), SST patterns are very similar to benthic d18O and to Greenland ice core surface temperature data to at least 30 ka (ODP Site 1019). In the California borderland region, warmings begin during peak glacial conditions, and significantly precede the deglacial sea level rise. Off Baja California, SST follows benthic d18O, but without the high frequency oscillations of temperature observed in Greenland. These changes outline regional reorganizations of surface winds and currents during times of maximum ice volume. Our data suggests that the geographic extent and intensity of the California Current system was much reduced during glacial maxima in comparison to modern conditions.

High regional climate sensitivity over continental China constrained by glacial-recent changes in temperature and the hydrological cycle.

PubMed

Eagle, Robert A; Risi, Camille; Mitchell, Jonathan L; Eiler, John M; Seibt, Ulrike; Neelin, J David; Li, Gaojun; Tripati, Aradhna K

2013-05-28

The East Asian monsoon is one of Earth's most significant climatic phenomena, and numerous paleoclimate archives have revealed that it exhibits variations on orbital and suborbital time scales. Quantitative constraints on the climate changes associated with these past variations are limited, yet are needed to constrain sensitivity of the region to changes in greenhouse gas levels. Here, we show central China is a region that experienced a much larger temperature change since the Last Glacial Maximum than typically simulated by climate models. We applied clumped isotope thermometry to carbonates from the central Chinese Loess Plateau to reconstruct temperature and water isotope shifts from the Last Glacial Maximum to present. We find a summertime temperature change of 6-7 °C that is reproduced by climate model simulations presented here. Proxy data reveal evidence for a shift to lighter isotopic composition of meteoric waters in glacial times, which is also captured by our model. Analysis of model outputs suggests that glacial cooling over continental China is significantly amplified by the influence of stationary waves, which, in turn, are enhanced by continental ice sheets. These results not only support high regional climate sensitivity in Central China but highlight the fundamental role of planetary-scale atmospheric dynamics in the sensitivity of regional climates to continental glaciation, changing greenhouse gas levels, and insolation.

Paleoclimatic modeling and phylogeography of least killifish, Heterandria formosa: insights into Pleistocene expansion-contraction dynamics and evolutionary history of North American Coastal Plain freshwater biota

PubMed Central

2013-01-01

Background Climatic and sea-level fluctuations throughout the last Pleistocene glacial cycle (~130-0 ka) profoundly influenced present-day distributions and genetic diversity of Northern Hemisphere biotas by forcing range contractions in many species during the glacial advance and allowing expansion following glacial retreat ('expansion-contraction’ model). Evidence for such range dynamics and refugia in the unglaciated Gulf-Atlantic Coastal Plain stems largely from terrestrial species, and aquatic species Pleistocene responses remain relatively uninvestigated. Heterandria formosa, a wide-ranging regional endemic, presents an ideal system to test the expansion-contraction model within this biota. By integrating ecological niche modeling and phylogeography, we infer the Pleistocene history of this livebearing fish (Poeciliidae) and test for several predicted distributional and genetic effects of the last glaciation. Results Paleoclimatic models predicted range contraction to a single southwest Florida peninsula refugium during the Last Glacial Maximum, followed by northward expansion. We inferred spatial-population subdivision into four groups that reflect genetic barriers outside this refuge. Several other features of the genetic data were consistent with predictions derived from an expansion-contraction model: limited intraspecific divergence (e.g. mean mtDNA p-distance = 0.66%); a pattern of mtDNA diversity (mean Hd = 0.934; mean π = 0.007) consistent with rapid, recent population expansion; a lack of mtDNA isolation-by-distance; and clinal variation in allozyme diversity with higher diversity at lower latitudes near the predicted refugium. Statistical tests of mismatch distributions and coalescent simulations of the gene tree lent greater support to a scenario of post-glacial expansion and diversification from a single refugium than to any other model examined (e.g. multiple-refugia scenarios). Conclusions Congruent results from diverse data indicate H. formosa fits the classic Pleistocene expansion-contraction model, even as the genetic data suggest additional ecological influences on population structure. While evidence for Plio-Pleistocene Gulf Coast vicariance is well described for many freshwater species presently codistributed with H. formosa, this species demography and diversification departs notably from this pattern. Species-specific expansion-contraction dynamics may therefore have figured more prominently in shaping Coastal Plain evolutionary history than previously thought. Our findings bolster growing appreciation for the complexity of phylogeographical structuring within North America’s southern refugia, including responses of Coastal Plain freshwater biota to Pleistocene climatic fluctuations. PMID:24107245

Millennial-scale variations in western Sierra Nevada precipitation during the last glacial cycle MIS 4/3 transition

NASA Astrophysics Data System (ADS)

Oster, Jessica L.; Montañez, Isabel P.; Mertz-Kraus, Regina; Sharp, Warren D.; Stock, Greg M.; Spero, Howard J.; Tinsley, John; Zachos, James C.

2014-07-01

Dansgaard-Oeschger (D-O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D-O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55-67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D-O interstadials (15-18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15-18), signified by elevated δ18O, δ13C, reflectance, and trace element concentrations, and less radiogenic 87Sr/86Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.

Snowfall less sensitive to warming in Karakoram than in Himalayas due to a unique seasonal cycle

USGS Publications Warehouse

Kapnick, Sarah B.; Delworth, Thomas L.; Ashfaq, Moetasim; Malyshev, Sergey; Milly, Paul C.D.

2014-01-01

The high mountains of Asia, including the Karakoram, Himalayas and Tibetan Plateau, combine to form a region of perplexing hydroclimate changes. Glaciers have exhibited mass stability or even expansion in the Karakoram region1, 2, 3, contrasting with glacial mass loss across the nearby Himalayas and Tibetan Plateau1, 4, a pattern that has been termed the Karakoram anomaly. However, the remote location, complex terrain and multi-country fabric of high-mountain Asia have made it difficult to maintain longer-term monitoring systems of the meteorological components that may have influenced glacial change. Here we compare a set of high-resolution climate model simulations from 1861 to 2100 with the latest available observations to focus on the distinct seasonal cycles and resulting climate change signatures of Asia’s high-mountain ranges. We find that the Karakoram seasonal cycle is dominated by non-monsoonal winter precipitation, which uniquely protects it from reductions in annual snowfall under climate warming over the twenty-first century. The simulations show that climate change signals are detectable only with long and continuous records, and at specific elevations. Our findings suggest a meteorological mechanism for regional differences in the glacier response to climate warming.

An improved land biosphere module for use in the DCESS Earth system model (version 1.1) with application to the last glacial termination

NASA Astrophysics Data System (ADS)

Eichinger, Roland; Shaffer, Gary; Albarrán, Nelson; Rojas, Maisa; Lambert, Fabrice

2017-09-01

Interactions between the land biosphere and the atmosphere play an important role for the Earth's carbon cycle and thus should be considered in studies of global carbon cycling and climate. Simple approaches are a useful first step in this direction but may not be applicable for certain climatic conditions. To improve the ability of the reduced-complexity Danish Center for Earth System Science (DCESS) Earth system model DCESS to address cold climate conditions, we reformulated the model's land biosphere module by extending it to include three dynamically varying vegetation zones as well as a permafrost component. The vegetation zones are formulated by emulating the behaviour of a complex land biosphere model. We show that with the new module, the size and timing of carbon exchanges between atmosphere and land are represented more realistically in cooling and warming experiments. In particular, we use the new module to address carbon cycling and climate change across the last glacial transition. Within the constraints provided by various proxy data records, we tune the DCESS model to a Last Glacial Maximum state and then conduct transient sensitivity experiments across the transition under the application of explicit transition functions for high-latitude ocean exchange, atmospheric dust, and the land ice sheet extent. We compare simulated time evolutions of global mean temperature, pCO2, atmospheric and oceanic carbon isotopes as well as ocean dissolved oxygen concentrations with proxy data records. In this way we estimate the importance of different processes across the transition with emphasis on the role of land biosphere variations and show that carbon outgassing from permafrost and uptake of carbon by the land biosphere broadly compensate for each other during the temperature rise of the early last deglaciation.

Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.

PubMed

Loulergue, Laetitia; Schilt, Adrian; Spahni, Renato; Masson-Delmotte, Valérie; Blunier, Thomas; Lemieux, Bénédicte; Barnola, Jean-Marc; Raynaud, Dominique; Stocker, Thomas F; Chappellaz, Jérôme

2008-05-15

Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between approximately 350 and approximately 800 parts per 10(9) by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of approximately 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is approximately 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by approximately 100,000 yr glacial-interglacial cycles up to approximately 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.

Testing the fidelity of laminations as a proxy for oxygen concentration in the Bering Sea over millennial to orbital timescales

NASA Astrophysics Data System (ADS)

Black, A. E.; Baranow, N.; Amdur, S.; Cook, M. S.

2017-12-01

Ocean circulation and biological productivity play an important role in the climate system through their contribution to global heat transport and air-sea exchange of CO­2. Oceanic oxygen concentration provides insight to ocean circulation and biological productivity. Sediment laminations provide a valuable proxy for local oceanic oxygen concentration. Many sediment cores from the Pacific Ocean are laminated from the last deglaciation, but previous studies have not provided an in-depth examination of laminations over many glacial and interglacial (G/IG) cycles. Typically, studies to date that consider bioturbation as a proxy for oxygen concentration have only considered one sediment core from a site, leaving ambiguity as to whether laminations faithfully record local oxygen levels. With sediment cores from three different holes (A, C, D) on the northern Bering Slope from IODP site U1345 (1008m), we investigate how faithfully laminations record oxygen concentration. We assign a bioturbation index from 1 to 4 for 1-cm intervals for the cores from each of the three holes and align the holes based on physical properties data. We find that the bioturbation is relatively consistent (within one bioturbation unit) between holes, suggesting that laminations may be a faithful, if not perfect, proxy for local oxygen concentration. After examining laminations from a complete hole, representing over 500,000 years, there seems to be no consistent pattern of laminations during the past five glacial cycles, suggesting there is no consistent pattern to oxygen concentration during glacial periods in the northern Bering Slope. Thus, hypotheses on ocean circulation and productivity in the northern Bering Sea from the last deglaciation may not apply to previous G/IG cycles.

Persistent genetic signatures of historic climatic events in an Antarctic octopus.

PubMed

Strugnell, J M; Watts, P C; Smith, P J; Allcock, A L

2012-06-01

Repeated cycles of glaciation have had major impacts on the distribution of genetic diversity of the Antarctic marine fauna. During glacial periods, ice cover limited the amount of benthic habitat on the continental shelf. Conversely, more habitat and possibly altered seaways were available during interglacials when the ice receded and the sea level was higher. We used microsatellites and partial sequences of the mitochondrial cytochrome oxidase 1 gene to examine genetic structure in the direct-developing, endemic Southern Ocean octopod Pareledone turqueti sampled from a broad range of areas that circumvent Antarctica. We find that, unusually for a species with poor dispersal potential, P. turqueti has a circumpolar distribution and is also found off the islands of South Georgia and Shag Rocks. The overriding pattern of spatial genetic structure can be explained by hydrographic (with ocean currents both facilitating and hindering gene flow) and bathymetric features. The Antarctic Peninsula region displays a complex population structure, consistent with its varied topographic and oceanographic influences. Genetic similarities between the Ross and Weddell Seas, however, are interpreted as a persistent historic genetic signature of connectivity during the hypothesized Pleistocene West Antarctic Ice Sheet collapses. A calibrated molecular clock indicates two major lineages within P. turqueti, a continental lineage and a sub-Antarctic lineage, that diverged in the mid-Pliocene with no subsequent gene flow. Both lineages survived subsequent major glacial cycles. Our data are indicative of potential refugia at Shag Rocks and South Georgia and also around the Antarctic continent within the Ross Sea, Weddell Sea and off Adélie Land. The mean age of mtDNA diversity within these main continental lineages coincides with Pleistocene glacial cycles. © 2012 Blackwell Publishing Ltd.

Evolution of the Northern Rockweed, Fucus distichus, in a Regime of Glacial Cycling: Implications for Benthic Algal Phylogenetics.

PubMed

Laughinghouse, Haywood Dail; Müller, Kirsten M; Adey, Walter H; Lara, Yannick; Young, Robert; Johnson, Gabriel

2015-01-01

Northern hemisphere rockweeds (Fucus) are thought to have evolved in the North Pacific and then spread to the North Atlantic following the opening of the Bering Strait. They have dispersed and widely speciated in the North Atlantic and its tributary seas. Fucus distichus is likely near the ancestral member of this genus, and studies have shown that there are several species/subspecies in this complex (i.e. F. evanescens and F. gardneri). We used phylogenetic and haplotype analyses to test the phylogenetic relationships and biogeography of F. distichus. Our data and subsequent analyses demonstrate that, unlike previous studies that lacked samples from an extensive geographical area of the Arctic and Subarctic, there is a distinct Arctic haplotype that is the source of subspecies in both the North Pacific and North Atlantic. Fucus distichus occupies a low tide zone habitat, and in Arctic/Subarctic regions it is adapted to the severe stress of sea ice coverage and disturbance during many months per year. We hypothesize that the very large geographic area of Arctic and Subarctic rocky shores available to this species during interglacials, supported by large Arctic/Subarctic fringe areas as well as unglaciated refugia during glacial cycles, provided a robust population and gene pool (described by the Thermogeographic Model). This gene pool dilutes that of the more fragmented and area-limited Temperate/Boreal area populations when they are brought together during glacial cycles. We suggest that similar subspecies complexes for a variety of Arctic/Subarctic shore biota should be examined further in this context, rather than arbitrarily being split up into numerous species.

Deglacial climate, carbon cycle and ocean chemistry changes in response to a terrestrial carbon release

NASA Astrophysics Data System (ADS)

Simmons, C. T.; Matthews, H. D.; Mysak, L. A.

2016-02-01

Researchers have proposed that a significant portion of the post-glacial rise in atmospheric CO2 could be due to the respiration of permafrost carbon stocks that formed over the course of glaciation. In this paper, we used the University of Victoria Earth System Climate Model v. 2.9 to simulate the deglacial and interglacial carbon cycle from the last glacial maximum to the present. The model's sensitivity to mid and high latitude terrestrial carbon storage is evaluated by including a 600 Pg C carbon pool parameterized to respire in concert with decreases in ice sheet surface area. The respiration of this stored carbon during the early stages of deglaciation had a large effect on the carbon cycle in these simulations, allowing atmospheric CO2 to increase by 40 ppmv in the model, with an additional 20 ppmv increase occurring in the case of a more realistic, prescribed CO2 radiative warming. These increases occurred prior to large-scale carbon uptake due to the reestablishment of boreal forests and peatlands in the proxy record (beginning in the early Holocene). Surprisingly, the large external carbon input to the atmosphere and oceans did not increase sediment dissolution and mean ocean alkalinity relative to a control simulation without the high latitude carbon reservoir. In addition, our simulations suggest that an early deglacial terrestrial carbon release may come closer to explaining some observed deglacial changes in deep-ocean carbonate concentrations than simulations without such a release. We conclude that the respiration of glacial soil carbon stores may have been an important contributor to the deglacial CO2 rise, particularly in the early stages of deglaciation.

Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge

USGS Publications Warehouse

O'Regan, M.; King, J.; Backman, J.; Jakobsson, M.; Palike, H.; Moran, K.; Heil, C.; Sakamoto, T.; Cronin, T. M.; Jordan, R.W.

2008-01-01

Despite its importance in the global climate system, age-calibrated marine geologic records reflecting the evolultion of glacial cycles through the Pleistocene are largely absent from the central Arctic Ocean. This is especially true for sediments older than 200 ka. Three sites cored during the Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), provide a 27 m continuous sedimentary section from the Lomonosov Ridge in the central Arctic Ocean. Two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the Cobb Mountain subchron (1215 ka). Beyond 1215 ka, two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change. Within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted Milankovitch frequencies. These cyclic variations record "glacial" and "interglacial" modes of sediment deposition on the Lomonosov Ridge as evident in studies of ice-rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model. Potential errors, which largely arise from uncertainties in the nature of downhole paleomagnetic variability, and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions. Copyright 2008 by the American Geophysical Union.

100- kyr cyclicity in volcanic ash emplacement: evidence from a 1.1 Myr tephra record from the NW Pacific.

PubMed

Schindlbeck, Julie C; Jegen, Marion; Freundt, Armin; Kutterolf, Steffen; Straub, Susanne M; Mleneck-Vautravers, Maryline J; McManus, Jerry F

2018-03-13

It is a longstanding observation that the frequency of volcanism periodically changes at times of global climate change. The existence of causal links between volcanism and Earth's climate remains highly controversial, partly because most related studies only cover one glacial cycle. Longer records are available from marine sediment profiles in which the distribution of tephras records frequency changes of explosive arc volcanism with high resolution and time precision. Here we show that tephras of IODP Hole U1437B (northwest Pacific) record a cyclicity of explosive volcanism within the last 1.1 Myr. A spectral analysis of the dataset yields a statistically significant spectral peak at the ~100 kyr period, which dominates the global climate cycles since the Middle Pleistocene. A time-domain analysis of the entire eruption and δ 18 O record of benthic foraminifera as climate/sea level proxy shows that volcanism peaks after the glacial maximum and ∼13 ± 2 kyr before the δ 18 O minimum right at the glacial/interglacial transition. The correlation is especially good for the last 0.7 Myr. For the period 0.7-1.1 Ma, during the Middle Pleistocene Transition (MPT), the correlation is weaker, since the 100 kyr periodicity in the δ 18 O record diminishes, while the tephra record maintains its strong 100 kyr periodicity.

Evidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years

NASA Astrophysics Data System (ADS)

Hein, Andrew S.; Woodward, John; Marrero, Shasta M.; Dunning, Stuart A.; Steig, Eric J.; Freeman, Stewart P. H. T.; Stuart, Finlay M.; Winter, Kate; Westoby, Matthew J.; Sugden, David E.

2016-02-01

Past fluctuations of the West Antarctic Ice Sheet (WAIS) are of fundamental interest because of the possibility of WAIS collapse in the future and a consequent rise in global sea level. However, the configuration and stability of the ice sheet during past interglacial periods remains uncertain. Here we present geomorphological evidence and multiple cosmogenic nuclide data from the southern Ellsworth Mountains to suggest that the divide of the WAIS has fluctuated only modestly in location and thickness for at least the last 1.4 million years. Fluctuations during glacial-interglacial cycles appear superimposed on a long-term trajectory of ice-surface lowering relative to the mountains. This implies that as a minimum, a regional ice sheet centred on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods. If so, it constrains the WAIS contribution to global sea level rise during interglacials to about 3.3 m above present.

Desert wetlands—Archives of a wetter past

USGS Publications Warehouse

Pigati, Jeffery S.; Springer, Kathleen B.; Manker, Craig R.

2015-12-16

Scientists from the U.S. Geological Survey (USGS) are finding evidence of a much wetter past in the deserts of the American Southwest using a most unlikely source—wetlands. Wetlands form in arid environments where water tables approach or breach the ground surface. Often thought of as stagnant and unchanging, new evidence suggests that springs and wetlands responded dynamically to past episodes of abrupt climate change. Multiple cycles of deposition, erosion, and soil formation show that wetlands in the southwestern United States expanded and contracted many times during the past 35,000 years or so, before disappearing altogether as the last glacial period came to a close. USGS scientists are now studying the deposits to determine how closely conditions in the desert were tied to regional and global climate patterns in the past, and what it might mean for the fragile ecosystems in light of anticipated climate change in the future.

Increased seasonality in the Western Mediterranean during the last glacial from limpet shell geochemistry

NASA Astrophysics Data System (ADS)

Ferguson, Julie E.; Henderson, Gideon M.; Fa, Darren A.; Finlayson, J. Clive; Charnley, Norman R.

2011-08-01

The seasonal cycle is a fundamental aspect of climate, with a significant influence on mean climate and on human societies. Assessing seasonality in different climate states is therefore important but, outside the tropics, very few palaeoclimate records with seasonal resolution exist and there are currently no glacial-age seasonal-resolution sea-surface-temperature (SST) records at mid to high latitudes. Here we show that both Mg/Ca and oxygen isotope (δ 18O) ratios in modern limpet ( Patella) shells record the seasonal range of SST in the western Mediterranean — a region particularly susceptible to seasonal change. Analysis of a suite of fossil limpet shells from Gibraltar shows that SST seasonality was greater during the last glacial by ~ 2 °C as a result of greater winter cooling. These extra-tropical seasonal-resolution SST records for the last glacial suggest that the presence of large ice-sheets in the northern hemisphere enhances winter cooling. This result also indicates that seasonality in the Mediterranean is not well-represented in most palaeoclimate models, which typically show little change in seasonal amplitude, and provides a new test for the accuracy of climate models.

Surficial geologic map of Berrien County, Michigan, and the adjacent offshore area of Lake Michigan

USGS Publications Warehouse

Stone, Byron D.; Kincare, Kevin A.; O'Leary, Dennis W.; Newell, Wayne L.; Taylor, Emily M.; Williams, Van S.; Lundstrom, Scott C.; Abraham, Jared E.; Powers, Michael H.

2017-12-13

The surficial geologic map of Berrien County, southwestern Michigan (sheet 1), shows the distribution of glacial and postglacial deposits at the land surface and in the adjacent offshore area of Lake Michigan. The geologic map differentiates surficial materials of Quaternary age on the basis of their lithologic characteristics, stratigraphic relationships, and age. Drill-hole information correlated in cross sections provides details of typical stratigraphic sequences that compose one or more penetrated geologic map units. A new bedrock geologic map (on sheet 2) includes contours of the altitude of the eroded top of bedrock and shows the distribution of middle Paleozoic shale and carbonate units in the subcrop. A sediment thickness map (also on sheet 2) portrays the extent of as much as 150 meters of surficial materials that overlie the bedrock surface.The major physical features of the county are related principally to deposits of the last Laurentide ice sheet that advanced and then retreated back through the region from about 19,000 to 14,000 radiocarbon years before present. Glacial and postglacial deposits underlie the entire county; shale bedrock crops out only in the adjacent offshore area on the bottom of Lake Michigan. All glacial deposits and glacial meltwater deposits in Berrien County are related to the late Wisconsinan glacial advances of the Lake Michigan ice lobe and its three regional recessional moraines, which cross the county as three north-northeast-trending belts.From east to west (oldest to youngest), the three moraine belts are known as the Kalamazoo, Valparaiso, and Lake Border morainic systems. The till-ridge morainic systems (Lake Border and local Valparaiso morainic systems) consist of multiple, elongate moraine ridges separated by till plains and lake-bottom plains. Tills in ground and end moraines in Berrien County are distinguished as informal units, and are correlated with three proposed regional till units in southwestern Michigan, characterized as clayey till, loamy till, or sandy loamy till that are based in part on correlation of silty tills and clay mineralogy. The stratified morainic systems (local Valparaiso and Kalamazoo morainic systems) are composed of multiple ice-marginal glacial-lake deltas and glaciolacustrine fans that form a contiguous array of deposits, welded together at their onlapping contacts, further related by the accordant altitudes of their delta topset plains. Their bounding ice-contact slopes repeatedly are aligned parallel to the regional trend of the receding ice margin. Ice-marginal (ice-contact) deltas were deposited in glacial lakes that expanded northward as the ice sheet retreated. Glaciofluvial topset beds, which overlie deltaic foreset and bottomset facies, fine away from the ice margin. Stratified deposits associated with the Valparaiso moraine were deposited in glacial Lakes Madron and Dowagiac. Subsequent deposits of glacial Lake Baroda preceded basin-wide deposits associated with various levels of Lake Michigan.Sheet 2 includes a series of 10 map figures that show cut-away three-dimensional time slices of the stratigraphic succession, from basal tills on bedrock, to ice-marginal deltas in the three large proglacial lakes, to stacked till/lake-bottom deposits related to the Lake Border ice margin readvances, to young deposits of glacial Lake Chicago and younger phases of other glacial lakes and the Chippewa lake lowstand.The pamphlet contains a discussion of the stratigraphic framework, descriptions of each depositional unit, and graphic logs of U.S. Geological Survey stratigraphic drill holes. The pamphlet also relates the geologic history of Berrien County, beginning with bedrock Paleozoic marine deposits, continuing through erosional effects of multiple glaciations and the detailed steps of late Wisconsinan ice-margin recession as recorded in the moraines, and the rise and fall of postglacial lake levels in the Lake Michigan basin.

Evolution of periodicity in periodical cicadas.

PubMed

Ito, Hiromu; Kakishima, Satoshi; Uehara, Takashi; Morita, Satoru; Koyama, Takuya; Sota, Teiji; Cooley, John R; Yoshimura, Jin

2015-09-14

Periodical cicadas (Magicicada spp.) in the USA are famous for their unique prime-numbered life cycles of 13 and 17 years and their nearly perfectly synchronized mass emergences. Because almost all known species of cicada are non-periodical, periodicity is assumed to be a derived state. A leading hypothesis for the evolution of periodicity in Magicicada implicates the decline in average temperature during glacial periods. During the evolution of periodicity, the determinant of maturation in ancestral cicadas is hypothesized to have switched from size dependence to time (period) dependence. The selection for the prime-numbered cycles should have taken place only after the fixation of periodicity. Here, we build an individual-based model of cicadas under conditions of climatic cooling to explore the fixation of periodicity. In our model, under cold environments, extremely long juvenile stages lead to extremely low adult densities, limiting mating opportunities and favouring the evolution of synchronized emergence. Our results indicate that these changes, which were triggered by glacial cooling, could have led to the fixation of periodicity in the non-periodical ancestors.

Bacteriophage in polar inland waters

USGS Publications Warehouse

Säwström, Christin; Lisle, John; Anesio, A.M.; Priscu, John C.; Laybourn-Parry, J.

2008-01-01

Bacteriophages are found wherever microbial life is present and play a significant role in aquatic ecosystems. They mediate microbial abundance, production, respiration, diversity, genetic transfer, nutrient cycling and particle size distribution. Most studies of bacteriophage ecology have been undertaken at temperate latitudes. Data on bacteriophages in polar inland waters are scant but the indications are that they play an active and dynamic role in these microbially dominated polar ecosystems. This review summarises what is presently known about polar inland bacteriophages, ranging from subglacial Antarctic lakes to glacial ecosystems in the Arctic. The review examines interactions between bacteriophages and their hosts and the abiotic and biotic variables that influence these interactions in polar inland waters. In addition, we consider the proportion of the bacteria in Arctic and Antarctic lake and glacial waters that are lysogenic and visibly infected with viruses. We assess the relevance of bacteriophages in the microbial loop in the extreme environments of Antarctic and Arctic inland waters with an emphasis on carbon cycling.

Ocean export production and foraminiferal stable isotopes in the Antarctic Southern Ocean across the mid-Pleistocene transition

NASA Astrophysics Data System (ADS)

Hasenfratz, A. P.; Martinez-Garcia, A.; Jaccard, S.; Hodell, D. A.; Vance, D.; Bernasconi, S. M.; Greaves, M.; Haug, G. H.

2014-12-01

Changes in buoyancy forcing in the Antarctic Zone (AZ) of the Southern Ocean are believed to play an instrumental role in modulating atmospheric CO2 concentrations during glacial cycles by regulating the transfer of carbon between the ocean interior and the atmosphere. Indeed, a million-year-spanning high-resolution excess Barium record from the AZ of the South Atlantic (ODP 1094), which traces changes in export production, shows decreased export production during cold periods suggesting decreased overturning. Here, we extend this AZ export production record back to 1.6 Myr. In addition, we present new carbon and oxygen isotope records of benthic and planktic foraminifera from the same site, complemented by Mg/Ca measurements in some intervals. The interpretation of these new data in the context of other South Atlantic records contributes to a better understanding of Southern Ocean hydrography and its role in modulating glacial/interglacial cycles over the past 1.6 Myr.

Overdeeping and stratigraphy of a typical Alpine foreland glacier

NASA Astrophysics Data System (ADS)

Salcher, Bernhard; Reinhard, Starnberger; Götz, Joachim

2015-04-01

The Northern Alpine Foreland was repeatedly covered by massive piedmont glaciers during Quaternary peak glacial periods. Remnants of the Salzach foreland glacier (Austria/Germany) represent the easternmost of a series of piedmont glaciers entering the Foreland by major Alpine valleys reaching far into the Alpine Molasse. The area of the former Salzach foreland glacier (SFG) marks a unique place as remnants of at least 4 glacial maxima meet an abundant geodatabase including information on the digital topography and the internal built up of glacial deposits derived from outcrops and several hundreds of drillings. During the LGM, it covered an area of more than 1000 km² and was even more extensive during older peak glacial periods. The lack of absolute ages as well as systemic investigation of the internal built up did so far impede the reconstruction on its dynamics. Here we aim to bring more light into the erosional and depositional history of a typical north Alpine piedmont glacier, the SFG, by analyzing drill log data, field outcrops, topography and the depositional ages of sediments. We focus on the proximal (axial) and distal parts of the SFG lobe. Some of the major unresolved questions regarding the Quaternary evolution of the major Alpine foreland glaciers are: Is the glacial erosion of Miocene bedrock the consequence of one glacial cycle or does it rather reflect successive erosional events during each glacial period? What is the spatial variability and potential depth of erosion? What is the structure and internal built up these deposits? The intent of this study is not to answer these questions in detail but to deliver important constraints: Our results indicate that more than 300- 400 m of bedrock were eroded during an early peak glacial period (such as antepenultimate glacial period or even earlier). Erosion was rather uniform across the lobe with larger values only occurring in the center (axis) of the glacier. Accumulation of more than 100 m of deposits occurred later, potentially during the antepenultimate and penultimate glacial maximum (MIS 6). Deposits suggest a characteristic stratigraphy of glaciofluvial sediments and basal tills, with the lithofacies of fluvial sediments varying from the proximal to distal lobe parts. The general impact of the LGM (MIS2) seems to be minor.

Simulated Last Glacial Maximum Δ14CATM and the Deep Glacial Ocean Reservoir

NASA Astrophysics Data System (ADS)

Mariotti, V.; Paillard, D.; Roche, D. M.; Bouttes, N.; Bopp, L.

2012-12-01

Δ14Catm has been estimated at 420 ± 80‰ (INTCAL09) during the Last Glacial Maximum (LGM) compared to preindustrial times (0‰), but mechanisms explaining this difference are not yet resolved. Δ14Catm is a function of cosmogenic production in high atmosphere and of carbon cycling in the Earth system (through carbon exchange with the superficial reservoirs, ocean and continental biosphere). 10Be-based reconstructions show a contribution of the cosmogenic production term of only 200 ± 200‰ at the LGM. The remaining 220‰ of Δ14Catm variation between the LGM and preindustrial times have thus to be explained by changes in the carbon cycle. Recently, Bouttes et al. (2010) proposed to explain most of the difference in atmospheric pCO2 between glacial and interglacial times by brine-induced ocean stratification in the Southern Ocean. This mechanism involves the formation of very saline water masses that can store Dissolved Inorganic Carbon (DIC) in the deep ocean. During glacial times, the sinking of brines is enhanced and more DIC is stored in the deep ocean, lowering atmospheric pCO2. Such an isolated ocean reservoir would be characterized by a low Δ14C signature. Evidence of such 14C-depleted deep waters during the LGM has recently been found in the Southern Ocean (Skinner et al., 2010). The degassing of this carbon with low Δ14C would then reduce Δ14Catm throughout the deglaciation. We have further developed the CLIMBER-2 model to include a cosmogenic production of 14C as well as an interactive atmospheric 14C reservoir. We investigate the role of both sinking of brines and cosmogenic production, alongside iron and vertical diffusion mechanisms to explain changes in Δ14Catm during the last deglaciation. In our simulations, not only the sinking of brine mechanism is consistent with past Δ14C data but also it explains most of the differences in atmospheric pCO2 and Δ14C between LGM and preindustrial times.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.

The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission,more » atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, 2 times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.« less

The Last Interglacial-Glacial cycle (MIS 5-2) re-examined based on long proxy records from central and northern Europe

NASA Astrophysics Data System (ADS)

Helmens, Karin F.

2014-02-01

Current multi-proxy studies on a long sediment sequence preserved at Sokli (N Finland), i.e. in the central area of Fennoscandian glaciations, are drastically changing classic ideas of glaciations, vegetation and climate in northern Europe during the Late Pleistocene. The sediments in the Sokli basin have escaped major glacial erosion due to non-typical bedrock conditions. In this review, the Sokli record is compared in great detail with other long proxy records from central, temperate and northern, boreal Europe. These comprise the classic records of La Grande Pile (E France) and Oerel (N Germany) and more recently obtained records from Horoszki Duże (E Poland) and Lake Yamozero (NW Russia). The focus of the review is on pollen, lithology and macrofossil- and insect-based temperature inferences. The long records are further compared with recent proxy data from nearby terrestrial sites as well as with the rapidly accumulating high-resolution proxy data from the ocean realm. The comparison allows a re-examination of the environmental history and climate evolution of the Last Interglacial-Glacial (LI-G) cycle (MIS 5-2). It shows that environmental and climate conditions during MIS 5 (ca 130-70 ka BP) were distinctly different from those during MIS 4-2 (ca 70-15 ka BP). MIS 5 is characterized by three long forested intervals (broadly corresponding to MIS 5e, 5c, 5a), both in temperate and northern boreal Europe. These mild periods were interrupted by two short, relatively cold and dry intervals (MIS 5d and 5b) with mountain-centered glaciation in Fennoscandia. Millennial scale climate events were superimposed upon these longer lasting climate fluctuations. The time interval encompassing MIS 4-2 shows open vegetation. It is characterized by two glacial maxima (MIS 4 and 2) with sub-continental scale glaciation over northern Europe and dry conditions in strongly continental eastern European settings. High amplitude climate oscillations of millennial duration characterized the climate variability of MIS 3. Mild climate conditions in early MIS 3 caused large-scale deglaciation of the Fennoscandian Ice Sheet, and ice-free conditions with Betula-dominated vegetation (including tree birch) persisted over large parts of Fennoscandia, possibly interrupted by glaciation, during major part of MIS 3 till ca 35 ka BP. Overall, MIS 5 was mostly mild with warmest or peak interglacial conditions at the very start during MIS 5e. MIS 4-2 was mostly cold with most extreme or peak glacial conditions in the closing phase during MIS 2. This points to a subdivision of the last climate cycle into an early, overall mild interglacial half and a late, overall cold glacial half, each with duration of ca 50 ka. This review also shows that the climate variability in central and northern Europe during the LI-G cycle was mostly in degrees of continentality with major shifts in winter temperature and precipitation values; summer temperatures, on the other hand, remained largely unchanged. It points to the waxing and waning of sea-ice over the North Atlantic Ocean as a possible characteristic feature of the Late Pleistocene. The present compilation, based on long terrestrial sequences, high-resolution multi-proxy data from the oceans, and quantified paleo-climate data, strongly favors a definition of entire Marine Oxygen Isotope Stage 5 as the Last Interglacial similar as in the original marine stratigraphy and the stratigraphy at La Grande Pile in France. The proxy-based climate data places the start of the Last Glacial at the base of MIS 4 and the northwest European Pleniglacial. It shows that the division between the Eemian (MIS 5e) and the Early Weichselian (MIS 5d-a) is not useful, as not relevant from a climate point of view.

Glaciation and Hydrologic Variability in Tropical South America During the Last 400,000 Years

NASA Astrophysics Data System (ADS)

Fritz, S. C.; Baker, P. A.; Seltzer, G. O.; Ekdahl, E. J.; Ballantyne, A.

2005-12-01

The expansion and contraction of northern continental ice sheets is a fundamental characteristic of the Quaternary. However, the extent of tropical glaciation is poorly constrained, particularly for periods prior to the Last Glacial Maximum (LGM). Similarly, the magnitude and timing of hydrologic variation in tropical South America is not clearly defined over multiple glacial cycles. Thus, the relative roles of global temperature change and insolation control of the South American Summer Monsoon (SASM) are unclear. We have reconstructed the timing of glaciation and precipitation variability in the tropical Andes of South America from drill cores from Lake Titicaca, Bolivia/Peru. The longest core (site LT01-2B, 235 m water depth) is 136 m and consists of four major silt-dominated units with high magnetic susceptibility, low organic carbon concentration, and no carbonate, which are indicative of extensive glacial activity in the cordillera surrounding the lake. These units alternate with laminated low-susceptibility units, with high carbonate and organic carbon concentrations, which reflect times when detrital input from the watershed was low and lake-level was lowered to below the outlet threshold, driving carbonate precipitation. Thus, the stratigraphy suggests that the core spans four major periods of glaciation and the subsequent interstadials. Core chronology is based on radiocarbon in the uppermost 25m, U-series dates on aragonite laminae, and tuning of the calcium carbonate stratigraphy in the lowermost sediments to the Vostok CO2 record. High-resolution (ca. 100 yr) sampling of sediments spanning the last glacial stage shows distinct millennial-scale variability from 20 - 65 kyr BP. This variability is evident in the periodic deposition of turbidites, which are characterized by low biogenic silica concentrations, elevated benthic diatom abundances, heavy carbon isotopic values, high C/N ratios, and an increase in mean grain size - a composite signal indicative of enhanced input to this deepwater site of material originally deposited in nearshore regions of the lake. U-series ages at the top of the penultimate (pre-Holocene) unit of laminated sediments suggest that the last major low stand of Lake Titicaca dates from MIS 5.5. Diatom data indicate that this was the most saline interval in the recovered sequence and thus suggest that MIS5.5 was the time of maximum aridity. The tuned drill-core magnetic susceptibility record suggests that glacial stages in the tropical Andes were approximately synchronous with high-latitude glacial stages and globally cold climate, with increased glacial activity in the periods 370-322, 300-238, 230-213, 188-139, and 65-15 kyr BP. Overall, the intervals of increased glaciation are periods when Lake Titicaca was deep, fresh, and overflowing, as inferred from calcium carbonate concentration, carbon isotopic values, and the diatom composition. The timing of lake-level change relative to high-latitude climate and insolation variation suggests that the water balance of the tropical Andes was at least as strongly influenced by global temperature change and global-scale boundary conditions as by insolation control of the SASM.

Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA)

NASA Astrophysics Data System (ADS)

Sasgen, Ingo; Martín-Español, Alba; Horvath, Alexander; Klemann, Volker; Petrie, Elizabeth J.; Wouters, Bert; Horwath, Martin; Pail, Roland; Bamber, Jonathan L.; Clarke, Peter J.; Konrad, Hannes; Drinkwater, Mark R.

2017-12-01

A major uncertainty in determining the mass balance of the Antarctic ice sheet from measurements of satellite gravimetry, and to a lesser extent satellite altimetry, is the poorly known correction for the ongoing deformation of the solid Earth caused by glacial isostatic adjustment (GIA). Although much progress has been made in consistently modeling the ice-sheet evolution throughout the last glacial cycle, as well as the induced bedrock deformation caused by these load changes, forward models of GIA remain ambiguous due to the lack of observational constraints on the ice sheet's past extent and thickness and mantle rheology beneath the continent. As an alternative to forward-modeling GIA, we estimate GIA from multiple space-geodetic observations: Gravity Recovery and Climate Experiment (GRACE), Envisat/ICESat and Global Positioning System (GPS). Making use of the different sensitivities of the respective satellite observations to current and past surface-mass (ice mass) change and solid Earth processes, we estimate GIA based on viscoelastic response functions to disc load forcing. We calculate and distribute the viscoelastic response functions according to estimates of the variability of lithosphere thickness and mantle viscosity in Antarctica. We compare our GIA estimate with published GIA corrections and evaluate its impact in determining the ice-mass balance in Antarctica from GRACE and satellite altimetry. Particular focus is applied to the Amundsen Sea Sector in West Antarctica, where uplift rates of several centimetres per year have been measured by GPS. We show that most of this uplift is caused by the rapid viscoelastic response to recent ice-load changes, enabled by the presence of a low-viscosity upper mantle in West Antarctica. This paper presents the second and final contributions summarizing the work carried out within a European Space Agency funded study, REGINA (www.regina-science.eu).

Searching for Last Glacial Deep-Sea Polar Carbonates in the Ross Sea Continental slope and Their Relevance to Chronological Constraints

NASA Astrophysics Data System (ADS)

Brambati, A.; Bonaccorsi, R.; Quaia, T.; Busetti, M.

2003-12-01

Ice-proximal glacial marine sediments from the Antarctic continental margin retain ice rafting events as proxy record for change in the volume and extension of the Antarctic ice sheet throughout glacial-interglacial cycles. However, the sedimentary sequences from the Ross Sea continental margin remain relatively poorly understood and most research has been focused mainly on continental shelf sequences during the last past decades. We present a data set (i.e., X-ray lithology, Multi Sensor Core Logger physical data, and preservation of biogenic carbonates), obtained from six deep-sea cores (1991-1999 Italian Antarctic Research Programme, PNRA - Summer cruises). Specifically, the cores were collected from a) the central Eastern sector (i.e., Core ANTA95-89C, depth: 2056 m, length: 401 cm and Core ANTA99-c22, depth: 2650 m, length: 851 cm); b) the central Western sector (i.e., Core ANTA99-c23; water depth: 2158 m, length: 548 cm; and ANTA99-c24, water depth: 2750 m, length: 811 cm); and c) the North Western sector (i.e., Core ANTA91-08C, and ANTA91-02C) of the Ross Sea Continental slope. Well-preserved calcareous foraminifers (N. pachyderma, sx) in coarse-grained IRD materials sparsely occur and/or are concentrated in discrete layers (i.e., up to 22 cm-thick) of at least three cores (i.e., Cores ANTA91-08, ANTA91-02, and ANTA95-89C, e.g., at 217-238 cm-depth). Some carbonate layers were deposited during a period of time bracketing Stage3/Stage2. In Core 89C foraminifers are associated to multiple ice rafting episodes and likely occurred with oceanographic changes in the properties of slope water masses. The search of well-preserved, in situ-deposited, polar carbonates is demanded for a reliable C-14 AMS dating of late Pleistocene events in the Ross Sea.

Paleodrainage insights into the fluvial and glacial history of the western Chukchi margin, Arctic Alaska

NASA Astrophysics Data System (ADS)

Stockmaster, B. A.; Hill, J. C.; Klotsko, S.; Driscoll, N. W.

2016-12-01

CHIRP subbottom data collected from the Chukchi shelf offshore of northwest Alaska reveal extensive paleodrainage networks that incised the margin during sea level lowstands. These features are cut into folded Cretaceous bedrock strata and likely represent multiple sea level cycles. Several large incised valleys, 10s of km wide and up to 50m deep, as well as numerous smaller, individual channels have been identified. Possible sources of fluvial input include drainage from the Hope Valley to the south, as well as several smaller rivers on the northwest Alaskan coast such as the Utukok, Kokolik, Kukpowruk, and Kuk Rivers. Correlation of sediment infill patterns provides insight to paleochannels and paleovalleys as well as outlining potential drainage networks. This new data will be used to examine sediment infill and erosion patterns to assess whether some of the valleys were formed by non-fluvial (i.e. glacial) processes. Preliminary results indicate the presence of six paleodrainage networks across the eastern Chukchi shelf, based on shape, size and infill of the paleovalleys: Incised Valley, Middle Valley, Northern Valley, Borderlands Valley, the Hanna Bank Valley and the Barrow Valley. All of the paleodrainage valleys are oriented perpendicular to the coast except for Barrow Valley, which follows the northwest coastline, and the Hanna Bank Valley, which is oriented parallel. The Barrow Valley also displays several interesting features in the subsurface. In all of the profiles across this paleovalley, the fluvial infill is overlain by high amplitude, acoustically laminated reflectors that appear to represent hemipelagic marine sediment, indicating rapid sea level rise flooded the shelf. There also appears to be 1 m erosional relief on the transgressive surface, which suggests there may have been an additional source of erosion within the Barrow Valley during sea level rise, possibly from an ice shelf or other glacial features. The presence of ice could also possibly explain the occupation of Barrow Canyon that would have diverted the Barrow Valley drainage.

Oxygen isotope constraints on the sulfur cycle over the past 10 million years.

PubMed

Turchyn, Alexandra V; Schrag, Daniel P

2004-03-26

Oxygen isotopes in marine sulfate (delta18O(SO4)) measured in marine barite show variability over the past 10 million years, including a 5 per mil decrease during the Plio-Pleistocene, with near-constant values during the Miocene that are slightly enriched over the modern ocean. A numerical model suggests that sea level fluctuations during Plio-Pleistocene glacial cycles affected the sulfur cycle by reducing the area of continental shelves and increasing the oxidative weathering of pyrite. The data also require that sulfate concentrations were 10 to 20% lower in the late Miocene than today.

Quaternary history of an endemic passerine bird on Corsica Island: Glacial refugium and impact of recent forest regression

NASA Astrophysics Data System (ADS)

Thibault, Jean-Claude; Cibois, Alice; Prodon, Roger; Pasquet, Eric

2016-03-01

Molecular studies support the hypothesis that Corsica Island was a glacial refugium for a number of forest birds during the Pleistocene. We focused on the Corsican nuthatch (Sitta whiteheadi), an endemic passerine strongly associated with the laricio pine (Pinus nigra laricio). The range of laricio pine has been impacted by the Pleistocene glacial periods and forest has been recently fragmented by cutting and fires. Using both molecular (mitochondrial and nuclear) and morphological characters, we assessed the variation within the nuthatch population. Our results are consistent with the hypothesis that the Corsican nuthatch endured through the late Pleistocene and Holocene climatic variations, and sustained the subsequent cycles of forests reduction/expansion. The results also suggest that the recent anthropization of the landscape resulted in the isolation of a cluster of populations in the northern part of the island. The fragmentation of the habitat of the nuthatch may impede the future of the bird by creating isolated population units between which the gene flow is reduced.

The sensitivity of the Greenland Ice Sheet to glacial-interglacial oceanic forcing

NASA Astrophysics Data System (ADS)

Tabone, Ilaria; Blasco, Javier; Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

2018-04-01

Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet-shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial-interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.

Extensive MIS 3 glaciation in southernmost Patagonia revealed by cosmogenic nuclide dating of outwash sediments

NASA Astrophysics Data System (ADS)

Darvill, Christopher M.; Bentley, Michael J.; Stokes, Chris R.; Hein, Andrew S.; Rodés, Ángel

2015-11-01

The timing and extent of former glacial advances can demonstrate leads and lags during periods of climatic change and their forcing, but this requires robust glacial chronologies. In parts of southernmost Patagonia, dating pre-global Last Glacial Maximum (gLGM) ice limits has proven difficult due to post-deposition processes affecting the build-up of cosmogenic nuclides in moraine boulders. Here we provide ages for the Río Cullen and San Sebastián glacial limits of the former Bahía Inútil-San Sebastián (BI-SSb) ice lobe on Tierra del Fuego (53-54°S), previously hypothesised to represent advances during Marine Isotope Stages (MIS) 12 and 10, respectively. Our approach uses cosmogenic 10Be and 26Al exposure dating, but targets glacial outwash associated with these limits and uses depth-profiles and surface cobble samples, thereby accounting for surface deflation and inheritance. The data reveal that the limits formed more recently than previously thought, giving ages of 45.6 ka (+139.9/-14.3) for the Río Cullen, and 30.1 ka (+45.6/-23.1) for the San Sebastián limits. These dates indicate extensive glaciation in southern Patagonia during MIS 3, prior to the well-constrained, but much less extensive MIS 2 (gLGM) limit. This suggests the pattern of ice advances in the region was different to northern Patagonia, with the terrestrial limits relating to the last glacial cycle, rather than progressively less extensive glaciations over hundreds of thousands of years. However, the dates are consistent with MIS 3 glaciation elsewhere in the southern mid-latitudes, and the combination of cooler summers and warmer winters with increased precipitation, may have caused extensive glaciation prior to the gLGM.

Sensitivity of Photosynthetic Gas Exchange and Growth of Lodgepole Pine to Climate Variability Depends on the Age of Pleistocene Glacial Surfaces

NASA Astrophysics Data System (ADS)

Osborn, B.; Chapple, W.; Ewers, B. E.; Williams, D. G.

2014-12-01

The interaction between soil conditions and climate variability plays a central role in the ecohydrological functions of montane conifer forests. Although soil moisture availability to trees is largely dependent on climate, the depth and texture of soil exerts a key secondary influence. Multiple Pleistocene glacial events have shaped the landscape of the central Rocky Mountains creating a patchwork of soils differing in age and textural classification. This mosaic of soil conditions impacts hydrological properties, and montane conifer forests potentially respond to climate variability quite differently depending on the age of glacial till and soil development. We hypothesized that the age of glacial till and associated soil textural changes exert strong control on growth and photosynthetic gas exchange of lodgepole pine. We examined physiological and growth responses of lodgepole pine to interannual variation in maximum annual snow water equivalence (SWEmax) of montane snowpack and growing season air temperature (Tair) and vapor pressure deficit (VPD) across a chronosequence of Pleistocene glacial tills ranging in age from 700k to 12k years. Soil textural differences across the glacial tills illustrate the varying degrees of weathering with the most well developed soils with highest clay content on the oldest till surfaces. We show that sensitivity of growth and carbon isotope discrimination, an integrated measure of canopy gas exchange properties, to interannual variation SWEmax , Tair and VPD is greatest on young till surfaces, whereas trees on old glacial tills with well-developed soils are mostly insensitive to these interannual climate fluctuations. Tree-ring widths were most sensitive to changes in SWEmax on young glacial tills (p < 0.01), and less sensitive on the oldest till (p < 0.05). Tair correlates strongly with δ13C values on the oldest and youngest tills sites, but shows no significant relationship on the middle aged glacial till. It is clear that growth and photosynthetic gas exchange parameters are sensitive to glacial till surfaces, which is evident by the different responses to SWEmax and Tair across sites.

Chronology of Late Quaternary Glacial Cycles in the Bering Trough, Gulf of Alaska: Constraints from Core-Log-Seismic Integration across the Continental Shelf and Slope

NASA Astrophysics Data System (ADS)

Clary, W. A.; Worthington, L. L.; Daigle, H.; Slagle, A. L.; Gulick, S. P. S.

2016-12-01

Sediments offshore Southern Alaska offer a natural laboratory to study glacial erosion, sediment deposition, and orogenesis. A major goal of Integrated Ocean Drilling Program (IODP) Expedition 341 was investigation of interrelationships among tectonic processes, paleoclimate, and glacial activity. Here, we focus on core-log-seismic integration of IODP Sites U1420 and U1421 on the shallow shelf and slope near the Bering Trough, a glacially derived shelf-crossing landform. These sites sample glacial and marine sediments that record a history of sedimentation following the onset of glacial intensification near the mid-Pleistocene transition (1.2 Ma) and Yakutat microplate convergence with North America. Ocean drilling provides important stratigraphic, physical properties, and age data in depth which support development of a stratigraphic model that can be extended across the shelf if carefully calibrated to local and regional seismic surveys. We use high resolution multichannel seismic, core, and logging data to develop a time-depth relationship (TDR) and update the developing chronostratigraphic model based on correlation of seismic sequence boundaries and drilling-related data, including biostratigraphic and paleomagnetic age controls. We calibrate, combine, and interpolate core and logging data at each site to minimize gaps in physical property information and generate synthetic seismic traces. At Site U1421, vertical seismic profiling further constrains the TDR, and provides input for the initial velocity model during the tie. Finally, we match reflectors in the synthetic trace with events in nearby seismic reflection data to establish a TDR at each site. We can use this relationship to better interpret the development of the Bering Trough, a recurring and favored path for ice streams and glacial advance. Initial results suggest late Pleistocene sedimentation rates of at least 1 km/m.y. on average, and variable sedimentation rates which are possibly correlated with paleoenvironmental indicators such as sea ice related species of diatoms.

Reconstruction of the glacial maximum recorded in the central Cantabrian Mountains (N Iberia)

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María

2014-05-01

The Cantabrian Mountains is a coastal range up to 2648 m altitude trending parallel to northern Iberian Peninsula edge at a maximum distance of 100 km inland (~43oN 5oW). Glacial sediments and landforms are generally well-preserved at altitudes higher than 1600 m, evidencing the occurrence of former glaciations. Previous research supports a regional glacial maximum prior to ca 38 cal ka BP and an advanced state of deglaciation by the time of the global Last Glacial Maximum (Jiménez-Sánchez et al., 2013). A geomorphological database has been produced in ArcGIS (1:25,000 scale) for an area about 800 km2 that partially covers the Redes Natural Reservation and Picos de Europa Regional Park. A reconstruction of the ice extent and flow pattern of the former glaciers is presented for this area, showing that an ice field was developed on the study area during the local glacial maximum. The maximum length of the ice tongues that drained this icefield was remarkably asymmetric between both slopes, recording 1 to 6 km-long in the northern slope and up to 19 km-long in southern one. The altitude difference between the glacier fronts of both mountain slopes was ca 100 m. This asymmetric character of the ice tongues is related to geologic and topo-climatic factors. Jiménez-Sánchez, M., Rodríguez-Rodríguez, L., García-Ruiz, J.M., Domínguez-Cuesta, M.J., Farias, P., Valero-Garcés, B., Moreno, A., Rico, M., Valcárcel, M., 2013. A review of glacial geomorphology and chronology in northern Spain: timing and regional variability during the last glacial cycle. Geomorphology 196, 50-64. Research funded by the CANDELA project (MINECO-CGL2012-31938). L. Rodríguez-Rodríguez is a PhD student with a grant from the Spanish national FPU Program (MECD).

Quaternary glacial geomorphosites from the Cantabrian Mountains (northern Iberian Peninsula): the Redes Natural Reservation and Picos de Europa Regional Park

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María

2013-04-01

The Cantabrian Mountains is a mountain range 480 km-long and up to 2,648 m altitude (Torre Cerredo Peak) trending parallel to the Cantabrian Coastline between Pyrenees and the northwest corner of the Iberian Peninsula (~43oN 5oW). This mountain range is an outstanding area to research the climatic patterns across South Europe during the Quaternary glaciations since well-preserved glacial features evidence the occurrence of past mountain glaciations in a climatic environment marked by the transition from a maritime climate (Atlantic) to Mediterranean one across the mountain range. The available studies in the Cantabrian Mountains stand that the regional glacial maximum recorded here is prior to ca 38, and that glaciers were in some locations remarkably retreated by the time of the global Last Glacial Maximum (Jiménez-Sánchez et al., in press; Serrano et al., in press). This study is focused on an area about 800 km2 that includes 36 peaks over 2,000 m (Pico Mampodre; 2,192 m) and partially covers the Redes Natural Reservation and Picos de Europa Regional Park. A geomorphologic database in ArcGIS was produced for this area as a previous step to reconstruct in detail the extent, flow pattern and chronology of the former glaciers (PhD under progress). Here we present a selection of 18 glacial geomorphosites classified according to genetic criteria in sites that show: (i) a nicely preserved moraine sequence recording the transition from glacial to periglacial conditions; (ii) glacial erosion features; (iii) glacial and ice related deposits (like moraines, ice-dammed deposits, erratic boulders or fluvio-glacial deposits); (iv) slope instability related to glacial debuttressing (complex landslides and rock avalanches); and (v) the interaction between the landscape and human activity. The interest of the geomorphosites is supported by its good quality of preservation, allowing its use as a basis to reconstruct the glacial and paraglacial processes in this region during the Quaternary glaciations, especially after the last local glacial maximum. Jiménez-Sánchez, M., Rodríguez-Rodríguez, L., García-Ruiz, J.M., Domínguez-Cuesta, M.J., Farias, P., Valero-Garcés, B., Moreno, A., Rico, M., Valcárcel, M., in press. A review of glacial geomorphology and chronology in northern Spain: timing and regional variability during the last glacial cycle. Geomorphology, doi: 10.1016/j.geomorph.2012.06.009. Serrano, E., González-Trueba, J.J., Pellitero, R., González-García, M., Gómez-Lende, M., in press. Quaternary glacial evolution in the Central Cantabrian Mountains (Northern Spain). Geomorphology, doi:10.1016/j.geomorph.2012.05.001. Research funded by the project CANDELA (CGL2012-31938) of the Spanish national research program in Earth Sciences and Hydric Resources (MICINN) and the project FC-11-PC-10-14 (FICYT-Asturias). L. Rodríguez-Rodríguez has developed her research under a grant of the Severo Ochoa Program (FICYT- Asturias).

A rock-magnetic record from Lake Baikal, Siberia: Evidence for Late Quaternary climate change

USGS Publications Warehouse

Peck, J.A.; King, J.W.; Colman, Steven M.; Kravchinsky, V.A.

1994-01-01

Rock-magnetic measurements of sediment cores from the Academician Ridge region of Lake Baikal, Siberia show variations related to Late Quaternary climate change. Based upon the well-dated last glacial-interglacial transition, variations in magnetic concentration and mineralogy are related to glacial-interglacial cycles using a conceptual model. Interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals. Glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals. The variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods. We also infer an increased contribution of eolian sediment during the colder, windier, and more arid glacial conditions when extensive loess deposits were formed throughout Europe and Asia. Eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals. Variations in magnetic concentration and mineralogy of Lake Baikal sediment correlate to the SPECMAP marine oxygen-isotope record. The high degree of correlation between Baikal magnetic concentration/mineralogy and the SPECMAP oxygen-isotope record indicates that Lake Baikal sediment preserves a history of climate change in central Asia for the last 250 ka. This correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method. Future work must include providing better age control and additional climate proxy data, thereby strengthening the correlation of continental and marine climate records. ?? 1994.

Regional mid-Pleistocene glaciation in central Patagonia

NASA Astrophysics Data System (ADS)

Hein, Andrew S.; Cogez, Antoine; Darvill, Christopher M.; Mendelova, Monika; Kaplan, Michael R.; Herman, Frédéric; Dunai, Tibor J.; Norton, Kevin; Xu, Sheng; Christl, Marcus; Rodés, Ángel

2017-05-01

Southern South America contains a glacial geomorphological record that spans the past million years and has the potential to provide palaeoclimate information for several glacial periods in Earth's history. In central Patagonia, two major outlet glaciers of the former Patagonian Ice Sheet carved deep basins ∼50 km wide and extending over 100 km into the Andean plain east of the mountain front. A succession of nested glacial moraines offers the possibility of determining when the ice lobes advanced and whether such advances occurred synchronously. The existing chronology, which was obtained using different methods in each valley, indicates the penultimate moraines differ in age by a full glacial cycle. Here, we test this hypothesis further using a uniform methodology that combines cosmogenic nuclide ages from moraine boulders, moraine cobbles and outwash cobbles. 10Be concentrations in eighteen outwash cobbles from the Moreno outwash terrace in the Lago Buenos Aires valley yield surface exposure ages of 169-269 ka. We find 10Be inheritance is low and therefore use the oldest surface cobbles to date the deposit at 260-270 ka, which is indistinguishable from the age obtained in the neighbouring Lago Pueyrredón valley. This suggests a regionally significant glaciation during Marine Isotope Stage 8, and broad interhemispheric synchrony of glacial maxima during the mid to late Pleistocene. Finally, we find the dated outwash terrace is 70-100 ka older than the associated moraines. On the basis of geomorphological observations, we suggest this difference can be explained by exhumation of moraine boulders.

HISTORICAL PATTERNS OF HABITAT CHANGES AND GENETIC DIVERGENCE IN THE DESERT AND SHORT HORNED LIZARDS

EPA Science Inventory

Historical environmental change is thought to have played an important role in the diversification of the biota of western North America. Many patterns of diversification have been associated with glacial-interglacial cycles of the latest Pleistocene. To evaluate the relativ...

200,000 years of monsoonal history recorded on the lower Bengal Fan - strong response to insolation forcing

NASA Astrophysics Data System (ADS)

Weber, Michael E.; Lantzsch, Hendrik; Dekens, Petra; Das, Supriyo K.; Reilly, Brendan T.; Martos, Yasmina M.; Meyer-Jacob, Carsten; Agrahari, Sandip; Ekblad, Alf; Titschack, Jürgen; Holmes, Beth; Wolfgramm, Philipp

2018-07-01

We conducted a multidisciplinary study to provide the stratigraphic and palaeoclimatic context of monsoonal rainfall dynamics and their responses to orbital forcing for the Bay of Bengal. Using sediment lightness we established an age model at orbital resolution for International Ocean Discovery Programme (IODP) Core U1452C-1H that covers the last 200 ka in the lower Bengal Fan. The low-resolution δ18O of G. sacculifer is consistent with global δ18O records, at least for major glacial-to-interglacial transitions. The variability of total organic carbon, total nitrogen, and the δ13C composition of organic matter indicate the marine origin of organic matter. Marine primary productivity likely increased during insolation minima, indicative for an enhanced NE monsoon during glacials and stadials. Pristine insolation forcing is also documented for wet-bulk density, red-green color variability, and grain-size variations, indicating that darker and coarser-grained material deposited at higher sedimentation rates during insolation minima. Stronger NE monsoon likely amplified ocean-atmosphere interactions over the Indian Ocean, leading to stronger upwelling through shoaling the thermocline, and higher delivery of sediment to the Bay of Bengal due to higher soil erosion on land. In addition, lower glacial and stadial sea levels as well as stronger westward surface circulation favored delivery of coarser-grained fluvial material to the lower Bengal Fan. At the same time the stronger NE monsoon might have increased the aeolian supply. Total inorganic carbon, the Ca/Ti ratio, and biogenic silica vary dominantly on obliquity frequencies, suggesting mobilization and transport of lithogenic material primarily during lowered sea levels and/or higher influence of the Northern Hemisphere westerlies on the dust transport from the Tibetan Plateau. The close resemblance of sediment lightness and the climate record of Antarctic ice cores over multiple glacial cycles indicate close relationship between high southern latitude and tropical Asian climate through shifts in position of the Intertropical Convergence Zone. The Bengal Fan monsoonal record shows very clear and strict responses to insolation forcing in the lower part from 200 ka to the Younger Toba Tuff during Marine Isotope Stage (MIS) 7 - 5, and less distinct response patterns after deposition of the ash during MIS 4 - 2, consistent with low-amplitude changes in insolation.

Glacier meltwater flow paths and storage in a geomorphologically complex glacial foreland: The case of the Tapado glacier, dry Andes of Chile (30°S)

NASA Astrophysics Data System (ADS)

Pourrier, J.; Jourde, H.; Kinnard, C.; Gascoin, S.; Monnier, S.

2014-11-01

The Tapado catchment is located in the upper Elqui river basin (4000-5550 m) in northern Chile. It comprises the Tapado glacial complex, which is an assemblage of the Tapado glacier and the glacial foreland (debris-covered glacier, rock glacier, and moraines). Although the hydrological functioning of this catchment is poorly known, it is assumed to actively supply water to the lower semi-arid areas of the Elqui river basin. To improve our knowledge of the interactions and water transfers between the cryospheric compartment (glacier, debris-covered glacier, and rock glacier) and the hydrological compartment (aquifers, streams), the results of monitoring of meteorological conditions, as well as discharge, conductivity and temperature of streams and springs located in the Tapado catchment were analyzed. The hydrological results are compared to results inferred from a ground penetrating radar (GPR) survey of the underground structure of the glacial foreland. Water production from the Tapado glacier was shown to be highly correlated with daily and monthly weather conditions, particularly solar radiation and temperature. The resulting daily and monthly streamflow cycles were buffered by the glacial foreland, where underground transfers took place through complex flow paths. However, the development of a thermokarst drainage network in a portion of the glacial foreland enabled rapid concentrated water transfers that reduced the buffer effect. The glacial foreland was shown to act as a reservoir, storing water during high melt periods and supplying water to downstream compartments during low melt periods. GPR observations revealed the heterogeneity of the internal structure of the glacial foreland, which is composed of a mixture of ice and rock debris mixture, with variable spatial ice content, including massive ice lenses. This heterogeneity may explain the abovementioned hydrological behaviors. Finally, calculation of a partial hydrological budget confirmed the importance of the Tapado catchment in supplying water to lower areas of the Elqui river basin. Water production from, and transfer through, cryospheric compartments, and its subsequent interactions with hydrological compartments are key processes driving the summer water supply from the Tapado catchment.

Multiple tropical Andean glaciations during a period of late Pliocene warmth

NASA Astrophysics Data System (ADS)

Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.

2017-02-01

The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene.

Inferences about winter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert

USGS Publications Warehouse

Holmgren, Camille A.; Norris, Jodi; Betancourt, Julio L.

2007-01-01

Late Quaternary histories of two North American desert biomes—C4 grasslands and C3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000cal.yrBP. Bioclimatic envelopes for select C4 and C3 species are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C4 grasses, whereas winters were probably too cold (or too wet) for C3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000cal.yrBP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillation variability.

Thermohaline Circulation Crisis and Changes Through the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Goldstein, S. L.; Pena, L.

2013-12-01

The Mid-Pleistocene Transition (MPT) marked a fundamental change in glacial-interglacial periodicity, transitioning from ~41,000 to 100,000 year cycles, accompanied by higher amplitude climate variability. It occurred without a significant change in orbital forcing, and thus its causes are poorly understood. We report major changes in the pre- and post-MPT mode of the ocean thermohaline circulation (THC), and a THC crisis during the MPT, from Nd isotopes in ODP Sites 1088 (~42S, 2082m) and 1090 (~43S, 3702m). The core locations are at the transition between the South Atlantic and the Southern oceans, a major gateway for the exchange of northern- and southern-sourced water masses. The new data show that in the ';40-kyr world' prior to the MPT, NADW export was strong during both interglacials and glacials. At ~900 ka the THC system underwent a major crisis, with an unprecedented weakening in NADW export during Marine Isotope Stages (MIS) 22-24. The recovery of the THC system in the post-MPT ';100-kyr world' is characterized by strong THC during interglacials, similar to pre-MPT interglacials, but much weaker THC during glacials. The ';THC crisis' interval includes MIS 23, which is unique as an interglacial where the THC operated in the same weak mode as post-MPT glacials. The MIS 22-24 interval has been recognized as a time of abrupt atmospheric pCO2 drawdown (Hoenisch et al. 2009) and significant cooling of ocean deep water, and Antarctic ice sheet expansion (Elderfield et al. Science 2012). Our data indicate that THC changes played an important role as a primary driving force, and helped to generate a series of positive feedbacks. This drastic change in deep-ocean circulation had important implications for the coeval drawdown of atmospheric pCO2, and the absence of a strong THC system through a glacial-to-interglacial-to-glacial cycle had a major impact on high latitude ice sheet growth. We suggest that the weak NADW export during MIS 24-22 resulted in reduced vertical exchange between Antarctic surface and deep waters, which helped to induce the drop in atmospheric pCO2, and in turn generated significant cooling which facilitated ice sheet expansion. These impacts were amplified by anomalously low Southern Hemisphere summer insolation during MIS 23, which resulted in suppressed ice sheet melting. Increased sea-ice coverage around the Antarctic continent during this time period may have generated increased AABW formation, which would have further drawn down CO2 from the atmosphere.

Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

NASA Astrophysics Data System (ADS)

Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

2018-05-01

Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations, controlled by the sub-ice-shelf melting which was dictated by the RSL forcing and the glacial history of the IIS and LIS. In contrast, the southwestern part of the ice sheet was insensitive to these forcings, with a uniform response in all simulations controlled by the surface air temperature, derived from ice cores.

Glacial vs. Interglacial Period Contrasts in Midlatitude Fluvial Systems, with Examples from Western Europe and the Texas Coastal Plain

NASA Astrophysics Data System (ADS)

Blum, M.

2001-12-01

Mixed bedrock-alluvial valleys are the conveyor belts for sediment delivery to passive continental margins. Mapping, stratigraphic and sedimentologic investigations, and development of geochronological frameworks for large midlatitude rivers of this type, in Western Europe and the Texas Coastal Plain, provide for evaluation of fluvial responses to climate change over the last glacial-interglacial period, and the foundations for future quantitative evaluation of long profile evolution, changes through time in flood magnitude, and changes in storage and flux of sediments. This paper focuses on two issues. First, glacial vs. interglacial period fluvial systems are fundamentally different in terms of channel geometry, depositional style, and patterns of sediment storage. Glacial-period systems were dominated by coarse-grained channel belts (braided channels in Europe, large-wavelength meandering in Texas), and lacked fine-grained flood-plain deposits, whereas Holocene units, especially those of late Holocene age, contain appreciable thicknesses of flood-plain facies. Hence, extreme overbank flooding was not significant during the long glacial period, most flood events were contained within bankfull channel perimeters, and fine sediments were bypassed through the system to marine basins. By contrast, extreme overbank floods have been increasingly important during the relatively short Holocene, and a significant volume of fine sediment is sequestered in flood-plain settings. Second, glacial vs. interglacial systems exhibit different amplitudes and frequencies of fluvial adjustment to climate change. High-amplitude but low-frequency adjustments characterized the long glacial period, with 2-3 extended periods of lateral migration and sediment storage puncuated by episodes of valley incision. Low-amplitude but high-frequency adjustments have been more typical of the short Holocene, when there has been little net valley incision or net changes in sediment storage, but frequent changes in the magnitude and frequency of floods and periods of overbank flooding. This high-frequency signal is absent in landforms and deposits from the glacial period. Glacial vs. interglacial contrasts in process and stratigraphic results are the rule in most large unglaciated fluvial systems. 70-80 percent or more of any 100 kyr glacial-interglacial cycle is characterized by significant ice volume, cooler temperatures, mid-shelf or lower sea-level positions, and cooler-smaller ocean basins. A glacial-period process regime is therefore the norm, and an interglacial regime like that of the late Holocene is relatively unique and non-representative. Large unglaciated midlatitude fluvial systems may be in long-term equilibrium with a glacial-period environment, with long profiles graded to glacial-period sea-level positions, so fluvial systems respond to major changes in climate, discharge regimes, and sediment loads, but they appear to have been relatively insensitive to higher-frequency changes. Short interglacials like the Holocene are, by comparison, periods of abnormally high sea levels and relatively low-amplitude climate changes, but fluvial systems appear to exhibit a greatly increased sensitivity to subtle changes in discharge regimes that produce frequent periods of disequilibrium.

Annually laminated sequences in the internal structure of some Belgian stalagmites -- Importance for paleoclimatology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Genty, D.; Quinif, Y.

1996-01-01

Fifteen stalagmites from four caves and one sealed tunnel in southern Belgium are composed of alternations of annually deposited white-porous and dark-compact laminae. This is demonstrated by comparing the number of laminae with the local history of the site for modern stalagmites and with radioisotopic ages for Late Glacial and Holocene stalagmites. Annual cyclicity in the internal structure of these speleothems is explained by the highly seasonal variations of the water excess, which influences underground water flow. Comparison between climatic data and modern stalagmites of a closed tunnel shows that growth laminae can record climatic variations: (1) there is amore » good correlation (R = 0.84) between lamina thickness in a stalagmite and water excess; (2) during years with a high water excess, dark-compact laminae are more developed, which makes the speleothem darker. Vertical successions of several laminae represent microsequences that may have recorded climatic variations with a time resolution of 1/2 year. In a Late Glacial stalagmite, successive laminae microsequences form very regular cycles of 11 years separated by a thick dark-compact lamina. It is supported that, as for modern stalagmites, the thick dark-compact lamina corresponds to a period of high water excess. Hence, this 11-year cycle may reflect a climatic cycle.« less

Expansion of the North Pacific subpolar gyre during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Gray, W. R.; Rae, J. W. B.; Wills, R. C.; Burke, A.; Taylor, B.

2017-12-01

Due to the opposite sign of the wind-stress forcing in the Pacific subpolar and subtropical gyres, the two gyres are characterised by vastly different nutrient and temperature regimes; the subpolar gyre is cold and nutrient-rich, whereas the subtropical gyre is warm and nutrient poor. The relative extent of the gyres therefore exerts a first order control on biogeochemistry and meridional ocean heat transport in the North Pacific Ocean. Here, by compiling all previously published planktic foraminferal d18O and sea-surface temperature data from across the North Pacific, we show a striking and hitherto unknown feature of the Glacial North Pacific; the southward expansion of the subpolar gyre by 5 degrees. We show, in the PMIP3 ensemble of state-of-the-art climate models, that this expansion is associated with a strengthening of the westerly winds. The southward expansion of the subpolar gyre would have brought nutrient-rich waters further south, providing a solution to the long-standing question of why, while productivity decreased throughout the subpolar gyre during Last Glacial Maximum, it increased in the transition zone between the gyres. The expansion and contraction of the subpolar/subtropical gyres over glacial-interglacial cycles could provide a mechanism to modulate meridional ocean heat transport.

A diatom record of climate and hydrology for the past 200 KA from Owens Lake, California with comparison to other Breat Basin records

USGS Publications Warehouse

Bradbury, J.P.

1997-01-01

Diatoms from lake sediments beneath Owens Lake playa, Inyo County, California, document a nearly continuous paleolimnological record of climate and hydrologic change since the penultimate glacial-interglacial cycle based on a chronology established by radiocarbon, tephrochronology, and paleomagnetic control. Freshwater planktic diatoms (especially species of Stephanodiscus), plagioclase feldspar-rich sediments with high magnetic susceptibility, and Juniperus-type pollen characterized the penultimate glaciation at Owens Lake. Saline diatoms dominated in the following interglacial period, and there are several episodes during which freshwater planktic diatoms became abundant between 100 and 50 ka that may represent interstadial climatic conditions. Saline diatoms fell to low values after 50 ka, but warm-season Aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of Owens Lake prior to the last glacial maximum. By 25 ka, glacial environments were again characterized by abundant Juniperus, plagioclase feldspar, and Stephanodiscus species. Generally and Holocene climates were recorded in Owens Lake by short-term fluctuations of saline and freshwater diatoms, desiccation, and oolitic sediments barren of diatoms. Comparison to paleoclimate records both north and south of Owens Lake suggest a southerly displacement of storm tracks originating from the Aleutian Low during glacial episodes.

Reply to comment received from J. Herget et al. regarding ;Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai; by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-305

NASA Astrophysics Data System (ADS)

Gribenski, Natacha; Lukas, Sven; Stroeven, Arjen P.; Jansson, Krister N.; Harbor, Jonathan M.; Blomdin, Robin; Ivanov, Mikhail N.; Heyman, Jakob; Petrakov, Dmitry A.; Rudoy, Alexei; Clifton, Tom; Lifton, Nathaniel A.; Caffee, Marc W.

2017-07-01

We thank Herget et al. (2017) for their keen interest in our study about the paleoglacial history of the Chagan Uzun Valley, in the Russian Altai (Gribenski et al., 2016). In our study, we proposed a detailed chronological and glaciodynamic reconstruction of a succession of glacial events represented by prominent moraine complexes, based on remotely-sensed data and field-geomorphological mapping, sedimentological logging, and cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. Herget et al. (2017) express skepticism about the outermost moraine complex dated in our study (CUMC 1; Gribenski et al., 2016), which slightly predates 19 thousand years (ka), during marine isotope stage (MIS) 2. To quote: "we suspect that their claim of regional climatic significance-that the ∼19 ka Chagan-Uzun moraine they dated can be used to show that the local LGM and regional LGM were the same, and occurred during MIS 2-may be premature" (Herget et al., 2017: p. 1). Their comment appears to relate to an ongoing debate regarding the timing of maximum glaciation in Central Asia during the last glacial cycle, however it is based on misinterpretations of our paper.

Implications of Δ33S for Evolution of Earth's Sulfur Cycle and Atmosphere

NASA Astrophysics Data System (ADS)

Farquhar, J.; Wing, B. A.

2002-12-01

The recent observation of large magnitude Δ33S anomalies in parts of the rock record has changed the way that we view the sulfur cycle. On the basis of Δ33S we can divide the sulfur cycle into three distinct phases - an Archean phase, an early Paleoproterozoic phase, and a modern phase. The occurrence of large magnitude Δ33S anomalies in rocks of Archean age (>2.45 Ga) is attributed to deep UV photolysis of sulfur dioxide in an atmosphere that was largely anoxic with <= 10-5 PAL O2. The presence of multiple exit channels for both oxidized and reduced atmospheric sulfur allowed efficient transfer of sulfur isotope anomalies to the Earth's surface reservoirs under these conditions (see Pavlov and Kasting, 2002). The absence of an active cycle of surface oxidation and bacterial (?) sulfate reduction insured preservation of the anomalies in the rock record. During the early Paleoproterozoic (<2.45 Ga but > 2.1 Ga) the occurrence of isotopic anomalies with substantially smaller magnitudes points to an atmosphere with higher but probably still diminutive levels of oxygen. As suggested by variations in Δ33S associated with rocks representing global glacial intervals, oxygen levels were probably fluctuating during this interval and reflect the preference of Earth's atmosphere for either a stable reduced or oxidized state. The absence of measurable anomalies in the rock record after 2.1 Ga points to an atmosphere that has been largely oxidized (> 10-5 to 10-2 PAL O2) since then. New Δ33S data from a variety of terrestrial rock samples provide unique insights into the nature of Earth's early surface environment and allow well-constrained speculation about the evolution of Earth's sulfur cycle.

Biogeochemical Cycling and Sea Ice Dynamics in the Bering Sea across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Detlef, H.; Sosdian, S. M.; Belt, S. T.; Smik, L.; Lear, C. H.; Hall, I. R.; Kender, S.; Leng, M. J.; Husum, K.; Cabedo-Sanz, P.

2017-12-01

Today the Bering Sea is characterized by high primary productivity (PP) along the eastern shelf, maintained by CO2 and nutrient rich upwelled deep waters and nutrient release during spring sea ice melting. As such, low oxygen concentrations are pervasive in mid-depth waters. Changes in ventilation and export productivity in the past have been shown to impact this oxygen minimum zone. On glacial/interglacial (G/IG) timescales sea ice formation plays a pivotal role on intermediate water ventilation with evidence pointing to the formation of North Pacific Intermediate Water (NPIW) in the Bering Sea during Pleistocene glacial intervals. In addition, sea ice plays a significant role in both long- and short-term climate change via associated feedback mechanisms. Thus, records of sea ice dynamics and biogeochemical cycling in the Bering Sea are necessary to fully understand the interaction between PP, circulation patterns, and past G/IG climates with potential implications for the North Pacific carbon cycle. Here we use a multi-proxy approach to study sea ice dynamics and bottom water oxygenation, across three intervals prior to, across, and after the Mid-Pleistocene Transition (MPT, 1.2-0.7 Ma) from International Ocean Discovery Program Site U1343. The MPT, most likely driven by internal climate mechanisms, is ideal to study changes in sea ice dynamics and sedimentary redox conditions on orbital timescales and to investigate the implications for associated feedback mechanisms. The sea ice record, based on various biomarkers, including IP25, shows substantial increase in sea ice extent across the MPT and the occurrence of a late-glacial/deglacial sea ice spike, with consequences for glacial NPIW formation and land glacier retreat via the temperature-precipitation feedback. U/Mn of foraminiferal authigenic coatings, a novel proxy for bottom water oxygenation, also shows distinct variability on G/IG timescales across the MPT, most likely a result of PP and water mass changes in relation to sea ice dynamics. Additional records of benthic foraminiferal assemblages and biogenic opal accumulation rates further elucidate the influence of PP on U/Mn, which can help to investigate the strength of NPIW formation along the eastern Bering slope, important for CO2 outgassing and abyssal North Pacific carbon storage.

Land-sea coupling of early Pleistocene glacial cycles in the southern North Sea exhibit dominant Northern Hemisphere forcing

NASA Astrophysics Data System (ADS)

Donders, Timme H.; van Helmond, Niels A. G. M.; Verreussel, Roel; Munsterman, Dirk; ten Veen, Johan; Speijer, Robert P.; Weijers, Johan W. H.; Sangiorgi, Francesca; Peterse, Francien; Reichart, Gert-Jan; Sinninghe Damsté, Jaap S.; Lourens, Lucas; Kuhlmann, Gesa; Brinkhuis, Henk

2018-03-01

We assess the disputed phase relations between forcing and climatic response in the early Pleistocene with a spliced Gelasian (˜ 2.6-1.8 Ma) multi-proxy record from the southern North Sea basin. The cored sections couple climate evolution on both land and sea during the intensification of Northern Hemisphere glaciation (NHG) in NW Europe, providing the first well-constrained stratigraphic sequence of the classic terrestrial Praetiglian stage. Terrestrial signals were derived from the Eridanos paleoriver, a major fluvial system that contributed a large amount of freshwater to the northeast Atlantic. Due to its latitudinal position, the Eridanos catchment was likely affected by early Pleistocene NHG, leading to intermittent shutdown and reactivation of river flow and sediment transport. Here we apply organic geochemistry, palynology, carbonate isotope geochemistry, and seismostratigraphy to document both vegetation changes in the Eridanos catchment and regional surface water conditions and relate them to early Pleistocene glacial-interglacial cycles and relative sea level changes. Paleomagnetic and palynological data provide a solid integrated timeframe that ties the obliquity cycles, expressed in the borehole geophysical logs, to Marine Isotope Stages (MIS) 103 to 92, independently confirmed by a local benthic oxygen isotope record. Marine and terrestrial palynological and organic geochemical records provide high-resolution reconstructions of relative terrestrial and sea surface temperature (TT and SST), vegetation, relative sea level, and coastal influence.During the prominent cold stages MIS 98 and 96, as well as 94, the record indicates increased non-arboreal vegetation, low SST and TT, and low relative sea level. During the warm stages MIS 99, 97, and 95 we infer increased stratification of the water column together with a higher percentage of arboreal vegetation, high SST, and relative sea level maxima. The early Pleistocene distinct warm-cold alterations are synchronous between land and sea, but lead the relative sea level change by 3000-8000 years. The record provides evidence for a dominantly Northern Hemisphere-driven cooling that leads the glacial buildup and varies on the obliquity timescale. Southward migration of Arctic surface water masses during glacials, indicated by cool-water dinoflagellate cyst assemblages, is furthermore relevant for the discussion on the relation between the intensity of the Atlantic meridional overturning circulation and ice sheet growth.

Assessing Deep Ocean Carbon Storage Across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Haynes, L.; Hoenisch, B.; Farmer, J. R.; Ford, H. L.; Raymo, M. E.; Yehudai, M.; Goldstein, S. L.; Pena, L. D.; Bickert, T.

2017-12-01

The Mid-Pleistocene Transition (MPT) was a profound reorganization of the climate system between 0.8 to 1.2 million years ago (Ma) that led to the establishment of 100 thousand year (kyr)-paced glacial cycles. At the midpoint of the transition at around 900 ka (the "900 ka event"), observations of a globally synchronous decrease in benthic δ13C suggest a large-scale perturbation to the oceanic carbon cycle. While the cause of the MPT remains elusive, recent geochemical evidence suggests that this δ13C minimum was concurrent with an increased presence of Southern Sourced Waters (SSW) in the South Atlantic, a decrease in Δ[CO32-] in the deep North Atlantic, and a decrease in glacial atmospheric CO2, pointing to increased carbon storage in the deep ocean as a possible amplifier for glacial intensification. Here we utilize the B/Ca proxy for carbonate saturation ( Δ[CO32-]) in the benthic foraminifer C. wuellerstorfi to investigate the storage of carbon in the deep western equatorial Atlantic at ODP sites 925 and 926 (3040 and 3590 m water depths, respectively). Reconstructed Δ[CO32-] covaries with benthic δ13C and follows the slope anticipated from the Redfield relationship predicted from organic matter degradation, suggesting control of respired CO2 content on the deep ocean's saturation state. Data spanning the 900-ka event suggest a decrease in minimum Δ[CO32-] of deep waters during glacial periods, concurrent with the documented expansion of SSW as captured by records of ɛNd. The coherence between shifts in δ13C, ɛNd, and Δ[CO32-] point to ocean circulation as a partial driver for increased oceanic CO2 storage. Comparison of Atlantic data to new records from the deep Pacific will explore the consequences of weakening Atlantic overturning across the MPT for CO2 storage in this expansive deep ocean reservoir.

Changes in Equatorial Atlantic Ocean Thermohaline Circulation Across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Yehudai, M.; Kim, J.; Seguí, M. J.; Goldstein, S. L.; Pena, L. D.; Haynes, L.; Hoenisch, B.; Farmer, J. R.; Ford, H. L.; Raymo, M. E.; Bickert, T.

2016-12-01

The Mid-Pleistocene Transition (MPT) marked a change in the duration of glacial-interglacial cycles from 41 to 100kyr between 1.3-0.7 Ma. A recent study (Pena and Goldstein, Science, 2014) from the Southern Atlantic Ocean found evidence for major disruptions in the global thermohaline circulation (THC) between MIS 25-21 ( 950-850ka), which may have triggered intensified glacial periods and the onset of the 100 kyr cycles. We report new Nd isotope data on Fe-Mn oxide encrusted foraminifera and fish debris from ODP Site 926 (3.719N, 42.908W, 3598m) between 1.2-0.4 Ma, in order to evaluate changes in the THC in the equatorial Atlantic, through comparison with North and South Atlantic sites. The ODP 926 ɛNd values fall in-between those in the North Atlantic (DSDP 607) and South Atlantic (ODP 1088 and 1090) throughout the studied interval, consistent with mixing between northern and southern end-members, and supporting the interpretation that the data represent the THC signal at this site. Pre-MPT data show smaller glacial-interglacial differences compared to the greater post-MPT glacial-interglacial variability. As Pena and Goldstein (2014) observed in the South Atlantic, during MIS 23 at 900 ka, ɛNd values do not shift significantly toward North Atlantic more negative values, consistent with a weak THC through this critical weak interglacial. Comparing ODP 926 and DSDP 607 data, ɛNd values converge during most interglacial peaks (excepting MIS 23) and diverge otherwise. This observation indicates that northern-sourced water masses dominate the site during peak interglacials, and confirms that the THC has been strongest during peak interglacials throughout the studied interval. Otherwise, diverging ɛNd values indicate a stronger southern-source signal and weaker northern-source signal at the ODP 926 site. This confirms that there was an active but variable THC system before, during, and after the MPT, with stronger deep water export from the North Atlantic during interglacials.

Neogene ice sheet, paleoclimatic and geological history of the McMurdo Sound region, Victoria Land Basin, Antarctica: overview of ANDRILL's first two drilling projects

NASA Astrophysics Data System (ADS)

Powell, R.; Naish, T.; Harwood, D.; Florindo, F.; Levy, R.; Teams, M. S.

2008-12-01

The ANtarctic geological DRILLing Program (ANDRILL), an international collaboration within IPY, has recovered 2 cores: from under the Ross Ice Shelf (McMurdo Ice Shelf Project (MIS) - AND-1B), and from the land-fast sea-ice of McMurdo Sound (Southern McMurdo Sound Project (SMS) - AND-2A). Drill cores reached respective total depths of 1285mbsf in c. 850m of water (MIS) and 1138.54mbsf in c. 380m of water (SMS). Repetitive facies successions in AND-1B core imply at least 60 fluctuations, of probable Milankovitch- duration, between subglacial, ice proximal and ice distal open marine environments. These are grouped into 3 types of facies cycles corresponding to glacial-interglacial variability during climatically distinct periods of Late Neogene: (1) cold-polar climate and ice (late Miocene and Pleistocene); (2) relatively warmer climate, polythermal ice and interglacials dominated by pelagic diatomite (Pliocene); (3) warmer climate, polythermal ice with interglacials dominated by hemipelagites (early late Miocene). A c. 80m-thick interval of diatomite of mid to late Pliocene age shows no apparent glacial cyclicity and represents an extended period of ice-free conditions indicating reduced or absent WAIS. Late Pliocene glacial-interglacial cycles characterized by abrupt alternations between subglacial/ice-proximal facies and open marine diatomite units imply significant WAIS dynamism, and contribution to global ice volume changes coeval with the initiation of Northern Hemisphere glaciations. A c. 4m-thick interval of diatomaceous mudstone in the mid-Pleistocene also represents warm-interglacial ice-free conditions. Intriguingly, glacial deposits interrupted by periodic, small- scale grounding-line retreats dominate the last 1m.y. Inter-hemispheric ice sheet coupling was probably controlled by Northern Hemispheric insolation and consequent glacial eustasy to account for much of the orbital-scale WAIS variability since 2.5Ma. A further expansion of WAIS occurred across the Mid-Pleistocene Climate Transition to establish the present WAIS mode. The AND-2A drillcore recovered several distinct intervals separated by disconformities: (1) a lower Miocene interval (1138.54-c. 800mbsf); (2) a 600m-thick early and middle Miocene interval (800-223mbsf), including an expanded section through two Miocene climatic optima, is truncated by a disconformity that spans c. 7m.y.; and (3) an upper Miocene-Recent interval (223-0mbsf) that is thinner but correlative to parts of the AND-1B drillcore. Shallow marine deposits dominate the lower AND-2A section until c.1.5Ma when the basin deepened rapidly from volcanic loading by Mt Erebus. Lower and middle Miocene strata record repeating lithological changes reflecting variation in sea level, glacial proximity, and climate fluctuations on the shallow marine coast of the Transantarctic Mountains. Sediments deposited close to or beneath grounded glaciers (likely flowing from East Antarctica) alternate with fine-grained marine sediments, providing clear evidence for cycles of ice advance then substantial retreat during climate transitions to warmer conditions. Fossils suggest non-polar climate conditions similar to southern New Zealand today, influenced by high sediment discharge from river run-off, and high coastal turbidity.

The late Cenozoic diatom stratigraphy and paleolimnology of Tule Lake, Siskiyou Co. California

USGS Publications Warehouse

Bradbury, J.P.

1991-01-01

Lacustrine diatoms are diverse, well preserved and abundant in cores of lake sediment to 334 m depth near the town of Tulelake, Siskiyou County, northern California. The cores have been dated by radiometric, tephrochronologic and paleomagnetic techniques, which indicate a basal age of about 3 million years (Ma) and a nearly continuous depositional record for the Tule Lake basin for the last 3 million years (My). Fossil diatoms document the late Cenozoic paleolimnologic and paleoclimatic history for the northwestern edge of the Basin and Range Province. During the last 3 My, Tule Lake was typically a relatively deep, extensive lake. The Pliocene is characterized by a diatom flora dominated by Aulacoseira solida suggesting more abundant summer precipitation and warmer winters. Increases in 'Fragilaria' at 2.4 Ma and between 2.0 and 1.7 Ma imply cooler summers that correlate to glacial environments recorded elsewhere in the world. Stephanodiscus niagarae and 'Fragilaria' species dominate the Pleistocene. Benthic diatoms of alkalineenriched, saline waters occur with S. niagarae between 100 and 40 m depth (0.90-0.14 Ma). Tephrochronology indicates slow deposition and possible hiatuses between about 0.6 and 0.2 Ma. Overall, the Pleistocene diatom flora reflects cooler and sometimes drier climates, especially after major glaciations began 0.85 Ma. The chronology of even-numbered oxygen isotope stages approximately matches fluctuations in the abundance in 'Fragilaria' species since 1 Ma, suggesting that glacial periods at Tule Lake were expressed by relatively cool summers with enhanced effective moisture. Interglacial periods are represented by variable mixtures of freshwater planktonic and benthic alkaline diatom assemblages that suggest seasonal environments with winter-spring precipitation and summer moisture deficits. Glacial-interglacial environments since 150 ka were distinct from, and more variable than, those occurring earlier. The last full glacial period was very dry. Aulacoseira ambigua characterizes the late glacial and early Holocene record of Tule Lake. Its distribution indicates that warmer and wetter climates began about 15 ka in this part of the Great Basin. Fluctuations in diatom concentration suggests a 41000-yr. cycle between 3.0 and 2.5 Ma and 100000-yr. cycles after 1.0 Ma. In the late Pliocene and early Pleistocene, Aulacoseira solida percentages wax and wane in an approximately 400000-yr. cycle. The apparent response of Tule Lake diatom communities to orbitally induced insolation cycles underscores the importance of this record for the study of late Cenozoic paleoclimate change. The diatom stratigraphy records the evolution and local extinction of several species that may be biochronologically important. Stephanodiscus niagarae first appeared and became common in the Tule Lake record shortly after 1.8 Ma. Stephanodiscus carconensis disappeared about 1.8 Ma, while Aulacoseira solida is rare in the core after about 1.35 Ma. Cyclotella elgeri, a diatom characteristic of some outcrops referred to the Yonna Formation (Pliocene), is common only near the base of the core at an age of about 3 Ma. Detection of local extinctions is complicated by reworking of distinctive species from Pliocene diatomites surrounding Tule Lake. A new species, Aulacoseira paucistriata, is described from Pliocene lake deposits in the Klamath Basin. ?? 1991 Kluwer Academic Publishers.

Large variation in mitochondrial DNA of sexual and parthenogenetic Dahlica triquetrella (Lepidoptera: Psychidae) shows multiple origins of parthenogenesis

PubMed Central

2013-01-01

Background Obligate parthenogenesis is relatively rare in animals. Still, in some groups it is quite common and has evolved and persisted multiple times. These groups may provide important clues to help solve the ‘paradox of sex’. Several species in the Psychidae (Lepidoptera) have obligate parthenogenesis. Dahlica triquetrella is one of those species where multiple transitions to parthenogenesis are postulated based on intensive cytological and behavioural studies. This has led to the hypothesis that multiple transitions from sexuals to diploid parthenogens occurred during and after the last glacial period, followed by transitions from parthenogenetic diploids to parthenogenetic tetraploids. Our study is the first to test these hypotheses using a molecular phylogeny based on mtDNA from multiple sexual and parthenogenetic populations from a wide geographic range. Results Parthenogenetic (and sexual) D. triquetrella are not monophyletic, and considerable sequence variation is present suggesting multiple transitions to parthenogenesis. However, we could not establish ancestral sexual haplotypes from our dataset. Our data suggest that some parthenogenetic clades have evolved, indicating origins of parthenogenesis before the last glacial period. Conclusions Multiple transitions to parthenogenesis have taken place in Dahlica triquetrella, confirming previous hypotheses. The number of different parthenogenetic clades, haplotypes and their apparent evolutionary age, clearly show that parthenogenesis has been a very successful reproductive strategy in this species over a long period. PMID:23622052

Large variation in mitochondrial DNA of sexual and parthenogenetic Dahlica triquetrella (Lepidoptera: Psychidae) shows multiple origins of parthenogenesis.

PubMed

Elzinga, Jelmer A; Jokela, Jukka; Shama, Lisa N S

2013-04-26

Obligate parthenogenesis is relatively rare in animals. Still, in some groups it is quite common and has evolved and persisted multiple times. These groups may provide important clues to help solve the 'paradox of sex'. Several species in the Psychidae (Lepidoptera) have obligate parthenogenesis. Dahlica triquetrella is one of those species where multiple transitions to parthenogenesis are postulated based on intensive cytological and behavioural studies. This has led to the hypothesis that multiple transitions from sexuals to diploid parthenogens occurred during and after the last glacial period, followed by transitions from parthenogenetic diploids to parthenogenetic tetraploids. Our study is the first to test these hypotheses using a molecular phylogeny based on mtDNA from multiple sexual and parthenogenetic populations from a wide geographic range. Parthenogenetic (and sexual) D. triquetrella are not monophyletic, and considerable sequence variation is present suggesting multiple transitions to parthenogenesis. However, we could not establish ancestral sexual haplotypes from our dataset. Our data suggest that some parthenogenetic clades have evolved, indicating origins of parthenogenesis before the last glacial period. Multiple transitions to parthenogenesis have taken place in Dahlica triquetrella, confirming previous hypotheses. The number of different parthenogenetic clades, haplotypes and their apparent evolutionary age, clearly show that parthenogenesis has been a very successful reproductive strategy in this species over a long period.

Introduction

Treesearch

V. Alaric Sample

2014-01-01

Throughout Earth’s history, its climates have been changing, and biotic systems have mutated, migrated, and otherwise adapted as tectonic shifts have reconfigured the continents and polar ice caps have ebbed and flowed across the latitudes through glacial cycles. In our own era, there is growing evidence that changes in climate that in the past have taken place over...

Evolution of periodicity in periodical cicadas

PubMed Central

Ito, Hiromu; Kakishima, Satoshi; Uehara, Takashi; Morita, Satoru; Koyama, Takuya; Sota, Teiji; Cooley, John R.; Yoshimura, Jin

2015-01-01

Periodical cicadas (Magicicada spp.) in the USA are famous for their unique prime-numbered life cycles of 13 and 17 years and their nearly perfectly synchronized mass emergences. Because almost all known species of cicada are non-periodical, periodicity is assumed to be a derived state. A leading hypothesis for the evolution of periodicity in Magicicada implicates the decline in average temperature during glacial periods. During the evolution of periodicity, the determinant of maturation in ancestral cicadas is hypothesized to have switched from size dependence to time (period) dependence. The selection for the prime-numbered cycles should have taken place only after the fixation of periodicity. Here, we build an individual-based model of cicadas under conditions of climatic cooling to explore the fixation of periodicity. In our model, under cold environments, extremely long juvenile stages lead to extremely low adult densities, limiting mating opportunities and favouring the evolution of synchronized emergence. Our results indicate that these changes, which were triggered by glacial cooling, could have led to the fixation of periodicity in the non-periodical ancestors. PMID:26365061

Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records

NASA Astrophysics Data System (ADS)

Chappell, John; Omura, Akio; Esat, Tezer; McCulloch, Malcolm; Pandolfi, John; Ota, Yoko; Pillans, Brad

1996-06-01

A major discrepancy between the Late Quaternary sea level changes derived from raised coral reef terraces at the Huon Peninsula in Papua New Guinea and from oxygen isotopes in deep sea cores is resolved. The two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka (ka = 1000 yr before present), but between 70 and 30 ka the isotopic sea levels are 20-40 m lower than the Huon Peninsula sea levels derived in earlier studies. New, high precision U-series age measurements and revised stratigraphic data for Huon Peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic δ 18O data. Using the sea level and deep sea isotopic data, oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from Greenland ice cores. The record of ice volume changes through the last glacial cycle now appears to be reasonably complete.

A Glacial Perspective on the Impact of Heinrich Stadials on North Atlantic Climate

NASA Astrophysics Data System (ADS)

Bromley, G. R.; Putnam, A. E.; Rademaker, K. M.; Balter, A.; Hall, B. L.

2017-12-01

The British Isles contain a rich geologic record of Late Pleistocene ice sheet behaviour in the NE North Atlantic basin. We are using cosmogenic 10Be surface-exposure dating, in conjunction with detailed glacial-geomorphic mapping, to reconstruct the timing and nature of cryospheric change - and thus climate variability - in northern Scotland since the Last Glacial Maximum. Our specific focus is Heinrich Stadial 1 (18,300-14,700 years ago), arguably the most significant abrupt climate event of the last glacial cycle and a major feature in global palaeoclimate records. Such constraint is needed because of currently conflicting models of how these events impact terrestrial environments and a recent hypothesis attributing this disparity to enhanced seasonality in the North Atlantic basin. To date, we have measured 10Be in > 30 samples from glacial erratics located on moraines deposited by the British Ice Sheet as it retreated from the continental shelf to its highland source regions. Our preliminary results indicate that the stadial was characterised by widespread deglaciation driven by atmospheric warming, a pattern that is suggestive of pronounced seasonality. Additionally, we report new exposure ages from moraines deposited during a subsequent phase of alpine glaciation (known locally as the Loch Lomond Readvance) that has long been attributed to the Younger Dryas stadial. With the growing focus on the full expression of stadials, and the inherent vulnerability of Europe to shifts in North Atlantic climate, developing the extant record of terrestrial glaciation and comparing these data to marine records is a critical step towards understanding the drivers of abrupt climate change.

Response of the Amazon rainforest to late Pleistocene climate variability

NASA Astrophysics Data System (ADS)

Häggi, Christoph; Chiessi, Cristiano M.; Merkel, Ute; Mulitza, Stefan; Prange, Matthias; Schulz, Michael; Schefuß, Enno

2017-12-01

Variations in Amazonian hydrology and forest cover have major consequences for the global carbon and hydrological cycles as well as for biodiversity. Yet, the climate and vegetation history of the lowland Amazon basin and its effect on biogeography remain debated due to the scarcity of suitable high-resolution paleoclimate records. Here, we use the isotopic composition (δD and δ13C) of plant-waxes from a high-resolution marine sediment core collected offshore the Amazon River to reconstruct the climate and vegetation history of the integrated lowland Amazon basin for the period from 50,000 to 12,800 yr before present. Our results show that δD values from the Last Glacial Maximum were more enriched than those from Marine Isotope Stage (MIS) 3 and the present-day. We interpret this trend to reflect long-term changes in precipitation and atmospheric circulation, with overall drier conditions during the Last Glacial Maximum. Our results thus suggest a dominant glacial forcing of the climate in lowland Amazonia. In addition to previously suggested thermodynamic mechanisms of precipitation change, which are directly related to temperature, we conclude that changes in atmospheric circulation are crucial to explain the temporal evolution of Amazonian rainfall variations, as demonstrated in climate model experiments. Our vegetation reconstruction based on δ13C values shows that the Amazon rainforest was affected by intrusions of savannah or more open vegetation types in its northern sector during Heinrich Stadials, while it was resilient to glacial drying. This suggests that biogeographic patterns in tropical South America were affected by Heinrich Stadials in addition to glacial-interglacial climate variability.

Quaternary Sedimentary Processes and Budgets in Orphan Basin, Southwestern Labrador Sea

NASA Astrophysics Data System (ADS)

Hiscott, Richard N.; Aksu, Ali E.

1996-03-01

The continental slope in Orphan Basin, northeast of Newfoundland, is underlain by several seaward-thinning debris-flow wedges alternating with acoustically stratified, regionally extensive, mainly hemipelagic sediments. δ 18O stratigraphy and volcanic ash layers in a 11.67-m core indicate that the uppermost debris-flow wedge formed during the last of several sea-level lowstands in isotopic stages 2-4. Similarly, seismic reflection correlation of dated levels at DSDP Site 111 with the Orphan Basin succession suggests that two deeper debris-flow wedges were deposited during oxygen isotopic stages 6 and 8. The oldest of the debris-flow deposits in at least three of the wedges formed well into the corresponding glacial cycle, after ice sheets had reached the edge of the continental shelf. Slower deposition by hemipelagic processes and ice rafting formed the acoustically stratified units, including Heinrich layers. The youngest three debris-flow wedges each have volumes of 1300-1650 km 3. Approximately two-thirds of this material is attributed to glacial erosion of Mesozoic and Tertiary strata beneath the Northeast Newfoundland Shelf. The remainder is believed to have been derived by glacial erosion of older bedrock that now forms the island of Newfoundland. The observed sediment volumes and the inferred basal and upper ages of the debris-flow wedges imply an average glacial denudation rate of about 0.13 mm/yr for this older bedrock, and an average of about 60 m of glacial bedrock erosion since oxygen isotope stage 22. This denudation rate is similar to estimates from the Barents Sea region off Norway.

Methane fluxes and their controlling processes in the Baltic Sea

NASA Astrophysics Data System (ADS)

Rehder, G. J.; Fossing, H.; Lapham, L.; Endler, R.; Spiess, V.; Bruchert, V.; Nguyen, T.; Gülzow, W.; Schneider von Deimling, J.; Conley, D. J.; Jorgensen, B.

2010-12-01

The Baltic Sea is an ideal natural laboratory to study the methane cycle in the framework of diagenetic processes. With its brackish character and a gradient from nearly marine to almost limnic conditions, a strong permanent haline stratification leading to large vertical redox gradients in the water column, and a sedimentation history which resulted in the deposition of organic-rich young post-glacial sediments over older glacial and post-glacial strata with very low organic content, the Baltic allows to study the role of a variety of key parameters for early diagenetic processes including the methane cycle. Within the BONUS + Project “Baltic Gas”, a 3.5 week scientific expedition of RV Maria S. Merian in August 2010 was dedicated to study the methane cycle in the various basins of the Baltic Sea, with strong emphasis on the metabolic reactions of early diagenesis and the occurrence of shallow gas deposits. Various subbottom profiling systems were used to map the thickness and structure of organic-rich deposits and build the base for a detailed coring program for biogeochemical analysis, including methane, sulfur compounds, iron, and other compounds. Methane gradients in connection with the information of the areal extend of organic-rich deposits are used to estimate the diffusive flux from the sediments into the water column and the rate of methane oxidation, with changing importance of sulfate as oxidant along the salinity gradient. On selected key stations, rate measurements of methanogenic and methanotrophic reactions were executed. The methane distribution in the water column was comprehensively assessed, revealing amongst other findings a drastic increase in bottom water methane concentration between the post bloom summer situation and the situation in the winter of 2009, in connection to the occurrence of a benthic nepheloid layer. Air-sea flux measurements were executed along the ship’s track comprising all major basins of the Baltic. The talk gives an interdisciplinary overview of the first results of this research campaign.

The polar sulfur cycle in the Werenskioldbreen, Spitsbergen: Possible implications for understanding the deposition of sulfate minerals in the North Polar Region of Mars

NASA Astrophysics Data System (ADS)

Szynkiewicz, Anna; Modelska, Magdalena; Buczyński, Sebastian; Borrok, David M.; Merrison, Jonathan P.

2013-04-01

In this study we investigated the polar cycling of sulfur (S) associated with the Werenskioldbreen glacier in Spitsbergen (Svalbard). Sulfide-derived S comprised 0.02-0.42 wt% of the fine-grained fraction of proglacial sediments. These sediments originated from glacial erosion of Precambrian sulfide-rich quartz and carbonate veins. In summer 2008, the δ34S of dissolved SO4 in glacier melt waters (+9‰ to +17‰) was consistent with SO4 generation from oxidation of primary sulfide minerals in the bedrock (+9‰ to +16‰). The calculated monthly SO4 load was ˜6881 kg/month/km2 in the main glacier stream. Subsequent evaporation and freezing of glacial waters lead to precipitation, accumulation, and temporary storage of sulfate salt efflorescences in the proglacial zone. These salts are presumably ephemeral, as they dissolve during annual snow/glacial melt events. Hydrated sulfates such as gypsum are also important constituents of the low-elevation areas around the polar ice cap of Planum Boreum on Mars. The origin of this gypsum on Mars might be better understood by using the investigated polar S cycle in Spitsbergen as a foundation. Assuming a trace sulfide content in the basaltic bedrock on Mars, the weathering of sulfides within the fine, porous texture of the ancient aeolian strata (basal unit) underlying Planum Boreum could have created elevated SO4 fluxes (and gypsum precipitation) during episodic thawing/melting events in the past. Limited water activity and prevailing dry conditions on the surface of Mars are the likely factors that accounted for the larger accumulation and preservation of polar gypsum on the surface and its broad aeolian distribution around Planum Boreum. This suggestion is also supported by an experiment showing that gypsum sand can be transported, under dry conditions, over great distances (˜2000 km) without a significant loss of mass.

Pleistocene Arid and Wet Climatic Variability: Imprint of Glacial Climate, Tectonics and Oceanographic Events in the Sediments of the se Indian Ocean, Western Australia

NASA Astrophysics Data System (ADS)

McHugh, C. M.; Castaneda, J.; Kominz, M. A.; Gallagher, S. J.; Gurnis, M.; Ishiwa, T.; Mamo, B. L.; Henderiks, J.; Christensen, B. A.; Groeneveld, J.; Yokoyama, Y.; Mustaque, S.; Iqbal, F.

2017-12-01

The interaction between the evolving tectonic configuration of the Indo Pacific region as a result of the northward migration of the Australian continent, and its collision with the Banda Arc began in the Late Miocene ( 8 Ma ago). This constriction played an important role in the diversion of the Indonesian Throughflow and initiation of the Leeuwin Current. These events coupled to Pleistocene glaciations left a significant imprint in the sediments offshore western Australia. The International Ocean Discovery Program Expedition 356 drilled in shelf depths of the Carnarvon and Perth Basins recovering a thick section of Pleistocene sediment from Sites U1461 (440 m thick) and U1460 (306 m), respectively. Analyses of the lithology (logs, grain size), chemistry (X-ray elemental analyses) and an initial age model constructed from biostratigraphy and radiocarbon ages were interpreted within the framework of multichannel seismic profiles. Radiocarbon ages provide control for MIS 1-4, and the identification of glacial cycles is based on shipboard biostratigraphy best developed for Site U1460. Arid and high productivity signals are linked with glacial stages. Wet conditions are associated with river discharge, terrigenous sediments and linked with interglacial stages. Except for one very pronounced interval the productivity signal during interglacials is low. High productivity during glacial stages is related to upwelling linked to the southward flowing Leeuwin Current. Comparison of the northernmost (U1461) with southernmost (U1460) sites reveals a strong arid and wet climatic variability beginning in the Pleistocene. This variability is most pronounced in the late Pleistocene post 0.8-1.0 Ma and can be correlated with glacial-interglacial cycles, especially in the more humid southern Site that was closer to the Subantarctic Front and influenced by the Westerlies. In Site U1461 we recovered the 135m thick Gorgon slide. Its occurrence at 1 Ma coincides with a rapid tectonic uplift event, possibly related to the ongoing collision of the Australian plate with the Java Trench. These tectonic events could have caused faulting and mass-transport affecting the western Australian margin. Nevertheless, the Pleistocene climatic signal is strong overprinting the possible effects of tectonic events.

Glacial-interglacial cycles in detrital sediment supply to the Amundsen Sea: Implications for West Antarctic Ice Sheet dynamics during the Late Pleistocene

NASA Astrophysics Data System (ADS)

Simoes Pereira, P.; van de Flierdt, T.; Hillenbrand, C. D.; Hemming, S. R.; Kuhn, G.

2017-12-01

The West Antarctic Ice Sheet (WAIS) plays a key role in the global climate system and its collapse could contribute up to 4.3 m of sea-level rise. Mass loss of this marine-based ice sheet is largely caused by ocean-driven melting of ice shelves. This is confimed by modern observational data which show significant glacier thinning and retreat of grounding lines, particularly in the Amundsen Sea area. We here apply an integrated approach to determine provenance of marine sediments, which enables us to trace erosion of different bedrock lithologies, ultimately tied to the location of the eroding ice through time. We present provenance analysis on detrital Holocene seafloor sediments from the Amundsen Sea Embayment as well as from two marine cores PS58/254 (69°19´S, 108°27´W) and PC493 (71°09´S, 119°57´W), located on the continental rise of the Amundsen Sea and covering glacial-interglacial cycles of the past 800 kyrs. We use strontium (Sr) and neodymium (Nd) isotopic compositions of fine terrigenous grains (<63μm), and 40Ar/39Ar ages on ice-rafted (>150μm) hornblende and biotite grains. Our Holocene mapping results reveal drainage pathways with distinct signatures in the eastern and western Amundsen Sea Embayment. The western embayment records a homogenous provenance signature, pointing to a local source area in the hinterland, while the eastern embayment shows a range of compositions indicating erosion of the eastern coastal margin and a distinct, but unexposed source lithology under Pine Island Glacier and/or its drainage basin. Systematic isotope variations are detected between glacial and interglacial stages in both downcore records. Core PS58/254 exhibits a radiogenic fingerprint throughout the Late Pleistocene and systematic glacial-interglacial fluctuations in the order of three ɛNd units. They correlate with physical properties of the sediments (i.e. magnetic susceptibility) and trend towards lower values during interglacials, notably during Marine Isotope Stage (MIS) 5 and MIS 7. Core PC493 exhibits similar radiogenic Nd isotope composition, but a slightly reduced magnitude of glacial-interglacial changes. Detailed analysis of our results will offer a framework for interpreting sediment records from the area, including those from a recent MeBo expedition (PS104) and upcoming IODP expedition 379.

Pleistocene Arid and Wet Climatic Variability: Imprint of Glacial Climate, Tectonics and Oceanographic Events in the Sediments of the se Indian Ocean, Western Australia

NASA Astrophysics Data System (ADS)

McHugh, C. M.; Castaneda, J.; Kominz, M. A.; Gallagher, S. J.; Gurnis, M.; Ishiwa, T.; Mamo, B. L.; Henderiks, J.; Christensen, B. A.; Groeneveld, J.; Yokoyama, Y.; Mustaque, S.; Iqbal, F.

2016-12-01

The interaction between the evolving tectonic configuration of the Indo Pacific region as a result of the northward migration of the Australian continent, and its collision with the Banda Arc began in the Late Miocene ( 8 Ma ago). This constriction played an important role in the diversion of the Indonesian Throughflow and initiation of the Leeuwin Current. These events coupled to Pleistocene glaciations left a significant imprint in the sediments offshore western Australia. The International Ocean Discovery Program Expedition 356 drilled in shelf depths of the Carnarvon and Perth Basins recovering a thick section of Pleistocene sediment from Sites U1461 (440 m thick) and U1460 (306 m), respectively. Analyses of the lithology (logs, grain size), chemistry (X-ray elemental analyses) and an initial age model constructed from biostratigraphy and radiocarbon ages were interpreted within the framework of multichannel seismic profiles. Radiocarbon ages provide control for MIS 1-4, and the identification of glacial cycles is based on shipboard biostratigraphy best developed for Site U1460. Arid and high productivity signals are linked with glacial stages. Wet conditions are associated with river discharge, terrigenous sediments and linked with interglacial stages. Except for one very pronounced interval the productivity signal during interglacials is low. High productivity during glacial stages is related to upwelling linked to the southward flowing Leeuwin Current. Comparison of the northernmost (U1461) with southernmost (U1460) sites reveals a strong arid and wet climatic variability beginning in the Pleistocene. This variability is most pronounced in the late Pleistocene post 0.8-1.0 Ma and can be correlated with glacial-interglacial cycles, especially in the more humid southern Site that was closer to the Subantarctic Front and influenced by the Westerlies. In Site U1461 we recovered the 135m thick Gorgon slide. Its occurrence at 1 Ma coincides with a rapid tectonic uplift event, possibly related to the ongoing collision of the Australian plate with the Java Trench. These tectonic events could have caused faulting and mass-transport affecting the western Australian margin. Nevertheless, the Pleistocene climatic signal is strong overprinting the possible effects of tectonic events.

Atlantic meridional overturning circulation during the Last Glacial Maximum.

PubMed

Lynch-Stieglitz, Jean; Adkins, Jess F; Curry, William B; Dokken, Trond; Hall, Ian R; Herguera, Juan Carlos; Hirschi, Joël J-M; Ivanova, Elena V; Kissel, Catherine; Marchal, Olivier; Marchitto, Thomas M; McCave, I Nicholas; McManus, Jerry F; Mulitza, Stefan; Ninnemann, Ulysses; Peeters, Frank; Yu, Ein-Fen; Zahn, Rainer

2007-04-06

The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the Atlantic only slightly greater than today. However, evidence from multiple water-mass tracers supports a different distribution of deep-water properties, including density, which is dynamically linked to circulation.

Three-Dimensional Animation Technology: a New Interactive Model Designed for the Teaching of Cryospheric Science

NASA Astrophysics Data System (ADS)

Porter, P. R.; Marunchak, A.

2011-12-01

One of the key challenges facing educators in the cryospheric sciences is to explain to students the processes that operate and the landforms that exist in relatively unfamiliar glacial environments. In many cases these environments are also largely inaccessible which can hinder field-based teaching. This is particularly the case for en-glacial and sub-glacial hydrology and the closely related topic of sub-glacial glacier dynamics, yet a full understanding of these subject areas is pivotal to overall student understanding of glaciology. An ability to visualise these unfamiliar and inaccessible environments offers a potentially powerful tool to assist student conceptualisation and comprehension. To address this we have developed a three-dimensional interactive 'virtual glacier' simulation model. Based on standards and technology established by the rapidly evolving video gaming industry, the user is presented with an interactive real-time three-dimensional environment designed to accurately portray multiple aspects of glacial environments. The user can move in all directions in the fore-field area, on the glacier surface and within en-glacial and sub-glacial drainage networks. Descent into the glacier hydrological system is via a moulin, from which the user can explore en-glacial channels linking to this moulin and ultimately descend into the sub-glacial drainage system. Various sub-glacial drainage network morphologies can then be 'explored' to aid conceptualisation and understanding and the user can navigate through drainage networks both up- and down-glacier and ultimately emerge at the portal into the fore-field environment. Interactive icons relating to features of interest are presented to the user throughout the model, prompting multimedia dialogue boxes to open. Dialogue box content (e.g. text, links to online resources, videos, journal papers, etc.) is fully customisable by the educator. This facilitates the use of the model at different academic levels. Although our model is predominantly based on the teaching of glacier hydrology, sufficient functionality has been designed into the model package to allow educators to uniquely populate other areas of the scene with interactive multimedia dialogue boxes. For example, users could explore fore-field geomorphology in a similar manner to the glacier hydrological system. We will also be developing this technology to build further suites of virtual interactive environments relevant to teaching in the earth and environmental sciences.

The Amazon reveals its secrets--partly

USGS Publications Warehouse

Betancourt, Julio L.

2000-01-01

The role of the tropics in global climate change during glacial cycles is hotly debated in paleoclimate cycles today. Records from South America have not provided a clear picture of tropical climate change. In his Perspective, Betancourt highlights the study by Maslin and Burns, who have deduced the outflow of the Amazon over the past 14,000 years. This may serve as a proxy that integrates hydrology over the entire South American tropics, although the record must be interpreted cautiously because factors other than rainfall may contribute to the variability in outflow.

Periodical climate variations and their impact on Earth rotation for the last 800Kyr

NASA Astrophysics Data System (ADS)

Chapanov, Yavor; Gambis, Daniel

2010-05-01

The Earth rotation variations are highly affected by climatic variations associated with the glacial cycles in the late Pleistocene. The processes of glaciation, followed by ice melting, are connected with significant changes of the mean sea level. These processes redistribute great amount of water masses between oceans and ice sheets, which lead to changes of the axial moment of inertia and corresponding variations of the Universal Time UT1 and Length of Day LOD, according to the law of angular momentum conservation. The climatic variations for the last 800Kyr are analyzed by means of time series of temperature changes, determined by deuterium data from Antarctica ice core. Reconstructed glacial sea level variations for the last 380Kyr, determined by the sediments from the Red sea, are used, too. Common periodicities of the temperature and mean sea level variations are determined. Time series of the long-periodical UT1 and LOD oscillations for the last 380Kyr and 800Kyr are reconstructed by means of empirical hydrological model of global water redistribution between the ocean and ice sheets during the last glacial events.

Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum

PubMed Central

Conway, T.M.; Wolff, E.W.; Röthlisberger, R.; Mulvaney, R.; Elderfield, H.E.

2015-01-01

Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial–interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial–interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1–42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01–0.84 mg m−2 per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply. PMID:26204562

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

PubMed Central

De Wever, Aaike; Leliaert, Frederik; Verleyen, Elie; Vanormelingen, Pieter; Van der Gucht, Katleen; Hodgson, Dominic A.; Sabbe, Koen; Vyverman, Wim

2009-01-01

Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial–interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30–45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events. PMID:19625320

King penguin demography since the last glaciation inferred from genome-wide data

PubMed Central

Trucchi, Emiliano; Gratton, Paolo; Whittington, Jason D.; Cristofari, Robin; Le Maho, Yvon; Stenseth, Nils Chr; Le Bohec, Céline

2014-01-01

How natural climate cycles, such as past glacial/interglacial patterns, have shaped species distributions at the high-latitude regions of the Southern Hemisphere is still largely unclear. Here, we show how the post-glacial warming following the Last Glacial Maximum (ca 18 000 years ago), allowed the (re)colonization of the fragmented sub-Antarctic habitat by an upper-level marine predator, the king penguin Aptenodytes patagonicus. Using restriction site-associated DNA sequencing and standard mitochondrial data, we tested the behaviour of subsets of anonymous nuclear loci in inferring past demography through coalescent-based and allele frequency spectrum analyses. Our results show that the king penguin population breeding on Crozet archipelago steeply increased in size, closely following the Holocene warming recorded in the Epica Dome C ice core. The following population growth can be explained by a threshold model in which the ecological requirements of this species (year-round ice-free habitat for breeding and access to a major source of food such as the Antarctic Polar Front) were met on Crozet soon after the Pleistocene/Holocene climatic transition. PMID:24920481

Sea level and ground water table depth (WTD): A biogeochemical pacemaker for glacial-interglacial cycling

NASA Astrophysics Data System (ADS)

Cowling, S. A.

2016-11-01

The role that changes in sea level have on potential carbon-climate feedbacks are discussed as a potential contributing mechanism for terminating glacial periods. Focus will be on coastal wetlands because these systems can be substantially altered by changing sea level and ground water table depth (WTD); in addition to being important moderators of the exchange of nutrients and energy between terrestrial and marine ecosystems. A hypothesis is outlined that describes how the release of carbon from formerly anaerobic wetland soils and sediments can influence climate when sea levels begin to decline. As ground WTD deepens and eventually recedes from the surface, coastal wetland basins may become isolated from their belowground source of water. With their primary source of base flow removed, coastal wetlands likely dried up, promoting decomposition of the carbon compounds buried in their sediments. Depending on the timing of basin isolation and the timing of decomposition, glacial sea level lows could have triggered a relatively large positive carbon feedback on climate warming, just at the time when a new interglacial period is about to begin.

Responses of high-elevation herbaceous plant assemblages to low glacial CO₂ concentrations revealed by fossil marmot (Marmota) teeth.

PubMed

McLean, Bryan S; Ward, Joy K; Polito, Michael J; Emslie, Steven D

2014-08-01

Atmospheric CO2 cycles of the Quaternary likely imposed major constraints on the physiology and growth of C3 plants worldwide. However, the measured record of this remains both geographically and taxonomically sparse. We present the first reconstruction of physiological responses in a late Quaternary high-elevation herbaceous plant community from the Southern Rocky Mountains, USA. We used a novel proxy-fossilized tooth enamel of yellow-bellied marmots (Marmota flaviventris)-which we developed using detailed isotopic analysis of modern individuals. Calculated C isotopic discrimination (Δ) of alpine plants was nearly 2 ‰ lower prior to the Last Glacial Maximum than at present, a response almost identical to that of nonherbaceous taxa from lower elevations. However, initial shifts in Δ aligned most closely with the onset of the late Pleistocene bipolar temperature "seesaw" rather than CO2 increase, indicating unique limitations on glacial-age high-elevation plants may have existed due to both low temperatures and low CO2. Further development of system-specific faunal proxies can help to clarify this and other plant- and ecosystem-level responses to past environmental change.

Combining cosmogenic radionuclides and amino acid racemization to date late Pliocene glacial deposits exposed on Baffin Island, Nunavut, Canada

NASA Astrophysics Data System (ADS)

Refsnider, K. A.; Miller, G. H.

2009-12-01

Sequences of glacial deposits spanning the Quaternary are valuable archives recording the effects of glaciation on landscapes through time, but determining the age of such deposits has long challenged geologists. The recent advances in cosmogenic radionuclide (CRN) measurement has made it possible to date some of these deposits, but dating buried glacial sediments in most settings remains problematic. Here we explore a new approach to date the oldest glacial deposits in the Plio-Pleistocene Clyde Foreland Formation of Baffin Island. This formation, approximately 40 m thick, includes interlayered shell-bearing marine, glaciomarine, and glacial sediments deposited along the northern margin of the Laurentide Ice Sheet and earlier continental ice sheets. Previous work on foraminifera assemblages suggests that the deposits span the last ≥2 Ma. By combining CRN measurements (10Be and 26Al) from the glacial units and measurements of the D-alloisoleucine:L-isoleucine ratios (A/I) in valves of the mollusk Hiatella arctica in the marine units overlying a particular glacial deposit, we can calculate the age of the glacial deposit. Because the post-burial temperature history for the mollusks preserved in the Clyde Foreland Formation is poorly constrained, A/I ratios alone cannot be used to determine absolute ages. Instead, we use A/I ratios to identify sediment packages of discrete ages and define a step-wise burial history function for glacial units. A/I ratios of all packages (<0.3 for the total hydrolysate fraction) fall within the A/I interval characterized by linear racemization kinetics, so the age of each package in the burial history function can simply be defined as a fractional age with respect to the total burial age for the glacial deposit of interest. The long duration of burial (26Al/10Be as low as 1.6±0.6 at 2σ) and low initial CRN inventories require that post-burial muogenic production is accounted for using the burial history function. We apply a numerical model to calculate the duration of burial from the measured CRN concentrations for a given inherited CRN inventory. But because this initial inventory is unknown, a single CRN sample/burial history combination will not provide a unique age solution. Instead, measurements from multiple localities where a particular glacial deposit has differing burial histories (i.e., the thickness of overlying units or ages of overlying units differ) are required to statistically determine the total burial age that most closely matches the observed CRN inventories and burial histories.

Framework for regional synthesis of water-quality data for the glacial aquifer system in the United States

USGS Publications Warehouse

Warner, Kelly L.; Arnold, Terri L.

2005-01-01

The glacial aquifer system is the largest principal aquifer in aerial extent and ground-water use for public supply in the United States. A principal aquifer is defined as a regionally extensive aquifer or aquifer system that has the potential to be used as a source of potable water (U.S. Geological Survey, 2003). Multiple aquifers often are grouped into large, extensive aquifer systems such as the glacial aquifer system. The glacial aquifer system is considered here to include all unconsolidated aquifers above bedrock north of the line of continental glaciation throughout the country (fig. 1). Total withdrawals from the glacial aquifer system were 3,560 million gallons per day in 2000, which constitutes almost 5 percent of total withdrawals from all aquifers in the United States (Maupin and Barber, 2005). Approximately 41 million people relied on the glacial aquifer for public supply and domestic use in 2000. The U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program began assessing the glacial aquifer system in 1991. The assessment of water-quality data on a regional scale, such as the glacial aquifer system, is coincident with the regional framework established by the Regional Aquifer-System Analysis Program (RASA) (Sun and others, 1997). From 1978 to 1995, the RASA Program systematically evaluated 25 of the Nation's most important groundwater systems including studies in the glacial aquifer system in the northeast, Midwest, and northern Midwest United States. The NAWQA Program is building on the work of the RASA Program to study the water quality of 16 of the most important ground-water systems (Lapham and others, 2005). Over 1,700 water-quality samples have been collected by the NAWQA Program from 1991 to 2004 to assess the glacial aquifer system. This large data set is unique in that the samples have been collected using a consistent sampling protocol, and multiple nested samples. The nested samples address the recently recharged shallow ground water, deeper water from principal aquifers often used for domestic supply, and source water used for public supplies within the glacial aquifer system. Information concerning the NAWQA Program including study unit boundaries is shown in figure 1 (Lapham and others, 2005). A framework for comparison of water quality across the glacial aquifer system has been developed based on two primary characteristics: intrinsic susceptibility and vulnerability. Intrinsic susceptibility, which is a measure of the ease at which water enters and moves through aquifer material, is a characteristic of the aquifer and overlying material and of the hydrologic conditions. Intrinsic susceptibility is independent of the chemical characteristics of the contaminant and its sources. In this way, intrinsic susceptibility assessments do not target specific natural or anthropogenic sources of contamination but instead consider only the physical factors affecting the flow of water to, and through the ground-water resource (Focazio and others, 2002). On a regional scale, intrinsic susceptibility is represented by the spatial distribution of fine- or coarse-grained material at the land surface, and the physical setting of the aquifer system. Vulnerability, which is a function of both intrinsic susceptibility and the proximity and characteristics of contaminant sources, includes consideration of features related to anthropogenic sources of contaminants, such as the character of the upgradient land use (for example, urban, agricultural, undeveloped, and others); as well as features related to natural sources of contaminants, such as the mineralogy of the aquifer material or the geochemical conditions within the aquifer system. The framework helps categorize this large region into areas of similar hydrogeologic characteristics for which water quality can be compared. The purpose of this report is to describe this framework and how it will be used for regional synthesis of water-quality da

Geographic and temporal dynamics of a global radiation and diversification in the killer whale.

PubMed

Morin, Phillip A; Parsons, Kim M; Archer, Frederick I; Ávila-Arcos, María C; Barrett-Lennard, Lance G; Dalla Rosa, Luciano; Duchêne, Sebastián; Durban, John W; Ellis, Graeme M; Ferguson, Steven H; Ford, John K; Ford, Michael J; Garilao, Cristina; Gilbert, M Thomas P; Kaschner, Kristin; Matkin, Craig O; Petersen, Stephen D; Robertson, Kelly M; Visser, Ingrid N; Wade, Paul R; Ho, Simon Y W; Foote, Andrew D

2015-08-01

Global climate change during the Late Pleistocene periodically encroached and then released habitat during the glacial cycles, causing range expansions and contractions in some species. These dynamics have played a major role in geographic radiations, diversification and speciation. We investigate these dynamics in the most widely distributed of marine mammals, the killer whale (Orcinus orca), using a global data set of over 450 samples. This marine top predator inhabits coastal and pelagic ecosystems ranging from the ice edge to the tropics, often exhibiting ecological, behavioural and morphological variation suggestive of local adaptation accompanied by reproductive isolation. Results suggest a rapid global radiation occurred over the last 350 000 years. Based on habitat models, we estimated there was only a 15% global contraction of core suitable habitat during the last glacial maximum, and the resources appeared to sustain a constant global effective female population size throughout the Late Pleistocene. Reconstruction of the ancestral phylogeography highlighted the high mobility of this species, identifying 22 strongly supported long-range dispersal events including interoceanic and interhemispheric movement. Despite this propensity for geographic dispersal, the increased sampling of this study uncovered very few potential examples of ancestral dispersal among ecotypes. Concordance of nuclear and mitochondrial data further confirms genetic cohesiveness, with little or no current gene flow among sympatric ecotypes. Taken as a whole, our data suggest that the glacial cycles influenced local populations in different ways, with no clear global pattern, but with secondary contact among lineages following long-range dispersal as a potential mechanism driving ecological diversification. © 2015 John Wiley & Sons Ltd.

Living in the Past: Phylogeography and Population Histories of Indo-Pacific Wrasses (Genus Halichoeres) in Shallow Lagoons versus Outer Reef Slopes

PubMed Central

Ludt, William B.; Bernal, Moisés A.; Bowen, Brian W.; Rocha, Luiz A.

2012-01-01

Sea level fluctuations during glacial cycles affect the distribution of shallow marine biota, exposing the continental shelf on a global scale, and displacing coral reef habitat to steep slopes on oceanic islands. In these circumstances we expect that species inhabiting lagoons should show shallow genetic architecture relative to species inhabiting more stable outer reefs. Here we test this expectation on an ocean-basin scale with four wrasses (genus Halichoeres): H. claudia (N = 194, with ocean-wide distribution) and H. ornatissimus (N = 346, a Hawaiian endemic) inhabit seaward reef slopes, whereas H. trimaculatus (N = 239) and H. margaritaceus (N = 118) inhabit lagoons and shallow habitats throughout the Pacific. Two mitochondrial markers (cytochrome oxidase I and control region) were sequenced to resolve population structure and history of each species. Haplotype and nucleotide diversity were similar among all four species. The outer reef species showed significantly less population structure, consistent with longer pelagic larval durations. Mismatch distributions and significant negative Fu’s F values indicate Pleistocene population expansion for all species, and (contrary to expectations) shallower histories in the outer slope species. We conclude that lagoonal wrasses may persist through glacial habitat disruptions, but are restricted to refugia during lower sea level stands. In contrast, outer reef slope species have homogeneous and well-connected populations through their entire ranges regardless of sea level fluctuations. These findings contradict the hypothesis that shallow species are less genetically diverse as a consequence of glacial cycles. PMID:22701597

The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

NASA Astrophysics Data System (ADS)

Sánchez Goñi, María Fernanda; Desprat, Stéphanie; Daniau, Anne-Laure; Bassinot, Frank C.; Polanco-Martínez, Josué M.; Harrison, Sandy P.; Allen, Judy R. M.; Anderson, R. Scott; Behling, Hermann; Bonnefille, Raymonde; Burjachs, Francesc; Carrión, José S.; Cheddadi, Rachid; Clark, James S.; Combourieu-Nebout, Nathalie; Mustaphi, Colin. J. Courtney; Debusk, Georg H.; Dupont, Lydie M.; Finch, Jemma M.; Fletcher, William J.; Giardini, Marco; González, Catalina; Gosling, William D.; Grigg, Laurie D.; Grimm, Eric C.; Hayashi, Ryoma; Helmens, Karin; Heusser, Linda E.; Hill, Trevor; Hope, Geoffrey; Huntley, Brian; Igarashi, Yaeko; Irino, Tomohisa; Jacobs, Bonnie; Jiménez-Moreno, Gonzalo; Kawai, Sayuri; Kershaw, A. Peter; Kumon, Fujio; Lawson, Ian T.; Ledru, Marie-Pierre; Lézine, Anne-Marie; Liew, Ping Mei; Magri, Donatella; Marchant, Robert; Margari, Vasiliki; Mayle, Francis E.; Merna McKenzie, G.; Moss, Patrick; Müller, Stefanie; Müller, Ulrich C.; Naughton, Filipa; Newnham, Rewi M.; Oba, Tadamichi; Pérez-Obiol, Ramón; Pini, Roberta; Ravazzi, Cesare; Roucoux, Katy H.; Rucina, Stephen M.; Scott, Louis; Takahara, Hikaru; Tzedakis, Polichronis C.; Urrego, Dunia H.; van Geel, Bas; Valencia, B. Guido; Vandergoes, Marcus J.; Vincens, Annie; Whitlock, Cathy L.; Willard, Debra A.; Yamamoto, Masanobu

2017-09-01

Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U/230Th, optically stimulated luminescence (OSL), 40Ar/39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867.

A Stratification Boomerang: Nonlinear Dependence of Deep Southern Ocean Ventilation on PCO2

NASA Astrophysics Data System (ADS)

Galbraith, E. D.; Merlis, T. M.

2014-12-01

Strong correlations between atmospheric CO2, Antarctic temperatures, and marine proxy records have hinted that ventilation of the deep Southern Ocean may have played a central role in the variations of CO2 over glacial-interglacial cycles. One proposition is that, in general, the Southern Ocean ventilates the deep more strongly under higher CO2, due to a change in winds and/or the dominance of thermal stratification in a warm ocean, which weakens ocean biological carbon storage. Here, we explore this idea with a suite of multi-millennial simulations using the GFDL CM2Mc global coupled model. The results are, indeed, consistent with increasing ventilation of the Southern Ocean as pCO2 increases above modern. However, they reveal a surprising twist under low pCO2: increased salinity of the Southern Ocean, due in part to weakening atmospheric moisture transport, actually increases ventilation rate of the deep ocean under low pCO2 as well. This implies that a nadir of Southern Ocean ventilation occurs at intermediate pCO2, which the model estimates as being close to that of the present-day. This is at odds with the interpretation that weak ventilation of the deep Southern Ocean was the unifying coupled mechanism for the glacial pCO2 cycles. Rather, it suggests that factors other than the ventilation rate of the deep Southern Ocean, such as iron fertilization, ecosystem changes, water mass distributions, and sea ice cover, were key players in the glacial-interglacial CO2 changes.

Decoding the origins of vertical land motions observed today at coasts

NASA Astrophysics Data System (ADS)

Pfeffer, J.; Spada, G.; Mémin, A.; Boy, J.-P.; Allemand, P.

2017-07-01

In recent decades, geodetic techniques have allowed detecting vertical land motions and sea-level changes of a few millimetres per year, based on measurements taken at the coast (tide gauges), on board of satellite platforms (satellite altimetry) or both (Global Navigation Satellite System). Here, contemporary vertical land motions are analysed from January 1993 to July 2013 at 849 globally distributed coastal sites. The vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic Green's functions. Special attention is paid to the effects of glacial isostatic adjustment induced by past and present-day ice melting. Various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally. In well-instrumented regions, predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres. Residual vertical land motions show a strong local variability, especially in the vicinity of plate boundaries due to the earthquake cycle. Significant residual signals are also observed at scales of a few hundred kilometres over nine well-instrumented regions forming observation windows on unmodelled geophysical processes. This study highlights the potential of our multitechnique database to detect geodynamical processes, driven by anthropogenic influence, surface mass changes (surface loading and glacial isostatic adjustment) and tectonic activity (including the earthquake cycle, sediment and volcanic loading, as well as regional tectonic constraints). Future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models.

Multiple glacial culminations from the Lateglacial to the late Holocene in central and southern Peru (Invited)

NASA Astrophysics Data System (ADS)

Licciardi, J. M.; Schaefer, J. M.; Rodbell, D. T.; Stansell, N.; Schweinsberg, A.; Finkel, R. C.; Zimmerman, S. R.

2013-12-01

Fluctuations in small tropical mountain glaciers serve as sensitive indicators of variations in past and present-day climate. Most of the world's modern tropical glaciers reside in the Peruvian Andes, where a growing number of well-dated glacial records have recently been developed. As additional records are documented, regional patterns of late Pleistocene to Holocene glacial activity have begun to emerge. Here we present a compilation of new and previously obtained 10Be surface exposure ages from boulders on well-preserved moraine successions in two glaciated Andean ranges: the Cordillera Vilcabamba of southern Peru (13°20'S, 72°32'W) and the Huaguruncho massif (10°32'S, 75°56'W), located in central Peru ~450 km northwest of the Vilcabamba. A high-resolution composite chronology that merges >100 10Be measurements on moraine sequences in five glaciated drainages of the Cordillera Vilcabamba reveals the occurrence of at least five discrete glacial culminations from the Lateglacial to the late Holocene. At the Huaguruncho massif, >20 10Be exposure ages obtained from moraine sequences in a south-facing cirque indicate at least three major glacial stages spanning the Lateglacial to the Little Ice Age. The moraine ages at Huaguruncho are broadly correlative with the Vilcabamba moraine chronologies, with some dated moraine belts exhibiting geomorphic expressions that closely resemble those of their coeval counterparts in the Vilcabamba. A recurring finding in both field areas is a mismatch between basal radiocarbon ages from bog and lake sediments and 10Be exposure ages on outboard moraines, which enclose the depositional basins. These age discrepancies suggest that cosmogenic 10Be production rates scaled to high altitudes in the tropics are substantially lower than previous estimates. While we anticipate that future refinements to scaled isotope production rates may significantly affect correlation of 10Be exposure ages in the high Andes with ages derived from other dating methods, the revised production rates should have a negligible impact on 10Be age comparisons between the Vilcabamba and Huaguruncho moraines, which lie at similar elevations. The correspondence in age between moraine sequences in these two widely separated ranges suggests regional-scale coherency of multiple glacial fluctuations across the central to southern Peruvian Andes from the Lateglacial to the late Holocene, implying spatially uniform climate drivers along this transect.

Evolution of Topography in Glaciated Mountain Ranges

NASA Technical Reports Server (NTRS)

Brocklehurst, Simon H.

2002-01-01

This thesis examines the response of alpine landscapes to the onset of glaciation. The basic approach is to compare fluvial and glacial laudscapes, since it is the change from the former to the latter that accompanies climatic cooling. This allows a detailed evaluation of hypotheses relating climate change to tectonic processes in glaciated mountain belts. Fieldwork was carried out in the eastern Sierra Nevada, California, and the Sangre de Cristo Range, Colorado, alongside digital elevation model analyses in the western US, the Southern Alps of New Zealand, and the Himalaya of northwestern Pakistan. hypothesis is overstated in its appeal to glacial erosion as a major source of relief production and subsequent peak uplift. Glaciers in the eastern Sierra Nevada and the western Sangre de Cristos have redistributed relief, but have produced only modest relief by enlarging drainage basins at the expense of low-relief topography. Glaciers have lowered valley floors and ridgelines by similar amounts, limiting the amount of "missing mass' that can be generated, and causing a decrease in drainage basin relief. The principal response of glaciated landscapes to rapid rock uplift is the development of towering cirque headwalls. This represents considerable relief production, but is not caused by glacial erosion alone. Large valley glaciers can maintain their low gradient regardless of uplift rate, which supports the "glacial buzzsaw" hypothesis. However, the inability of glaciers to erode steep hillslopes as rapidly can cause mean elevations to rise. Cosmogenic isotope dating is used to show that (i) where plucking is active, the last major glaciation removed sufficient material to reset the cosmogenic clock; and (ii) former glacial valley floors now stranded near the crest of the Sierra Nevada are at varying stages of abandonment, suggesting a cycle of drainage reorganiszation and relief inversion due to glacial erosion similar to that observed in river networks. Glaciated landscapes are quite distinct from their fluvial counterparts in both landforms and processes. Given the scarcity of purely fluvial, active mountain ranges, it is essential that glacial erosion be considered amongst the processes sculpting active orogenic belts.

Timing of maximum glacial extent and deglaciation from HualcaHualca volcano (southern Peru), obtained with cosmogenic 36Cl.

NASA Astrophysics Data System (ADS)

Alcalá, Jesus; Palacios, David; Vazquez, Lorenzo; Juan Zamorano, Jose

2015-04-01

Andean glacial deposits are key records of climate fluctuations in the southern hemisphere. During the last decades, in situ cosmogenic nuclides have provided fresh and significant dates to determine past glacier behavior in this region. But still there are many important discrepancies such as the impact of Last Glacial Maximum or the influence of Late Glacial climatic events on glacial mass balances. Furthermore, glacial chronologies from many sites are still missing, such as HualcaHualca (15° 43' S; 71° 52' W; 6,025 masl), a high volcano of the Peruvian Andes located 70 km northwest of Arequipa. The goal of this study is to establish the age of the Maximum Glacier Extent (MGE) and deglaciation at HualcaHualca volcano. To achieve this objetive, we focused in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) characterized by a well-preserved sequence of moraines and roches moutonnées. The method is based on geomorphological analysis supported by cosmogenic 36Cl surface exposure dating. 36Cl ages have been estimated with the CHLOE calculator and were compared with other central Andean glacial chronologies as well as paleoclimatological proxies. In Huayuray valley, exposure ages indicates that MGE occurred ~ 18 - 16 ka. Later, the ice mass gradually retreated but this process was interrupted by at least two readvances; the last one has been dated at ~ 12 ka. In the other hand, 36Cl result reflects a MGE age of ~ 13 ka in Mollebaya valley. Also, two samples obtained in Pujro-Huayjo and Mucurca valleys associated with MGE have an exposure age of 10-9 ka, but likely are moraine boulders affected by exhumation or erosion processes. Deglaciation in HualcaHualca volcano began abruptly ~ 11.5 ka ago according to a 36Cl age from a polished and striated bedrock in Pujro Huayjo valley, presumably as a result of reduced precipitation as well as a global increase of temperatures. The glacier evolution at HualcaHualca volcano presents a high correlation with precipitation cycles of the Altiplano (Tauca / Coipasa phases) and Heinrich 1 / Younger Dryas cold climatic events. Research funded by Cryocrisis project (CGL2012-35858), Government of Spain

The Glacial-Interglacial summer monsoon recorded in southwest Sulawesi speleothems: Evidence for sea level thresholds driving tropical monsoon strength

NASA Astrophysics Data System (ADS)

Kimbrough, A. K.; Gagan, M. K.; Dunbar, G. B.; Krause, C.; Di Nezio, P. N.; Hantoro, W. S.; Cheng, H.; Edwards, R. L.; Shen, C. C.; Sun, H.; Cai, B.; Rifai, H.

2016-12-01

Southwest Sulawesi lies within the Indo-Pacific Warm Pool (IPWP), at the center of atmospheric convection for two of the largest circulation cells on the planet, the meridional Hadley Cell and zonal Indo-Pacific Walker Circulation. Due to the geographic coincidence of these circulation cells, southwest Sulawesi serves as a hotspot for changes in tropical Pacific climate variability and Australian-Indonesian summer monsoon (AISM) strength over glacial-interglacial (G-I) timescales. The work presented here spans 386 - 127 ky BP, including glacial terminations IV ( 340 ky BP) and both phases of TIII (TIII 248 ky BP and TIIIa 217 ky BP). This record, along with previous work from southwest Sulawesi spanning the last 40 kyr, reveals coherent climatic features over three complete G-I cycles. The multi-stalagmite Sulawesi speleothem δ18O record demonstrates that on G-I timescales, the strength of the AISM is most sensitive to changes in sea level and its impact on the regional distribution of land and shallow ocean. Stalagmite δ18O and trace element (Mg/Ca) data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. TIV, TIII, TIIIa, and TI are each characterized by an abrupt 3‰ decrease in δ18O that coincides with sea level rise and flooding of the Sunda and Sahul shelves. Strong evidence for a sea level (flooding/exposure) threshold is found throughout the southwest Sulawesi record. This is most clearly demonstrated over the period 230 - 212 ky BP (MIS 7d-7c), when a sea level fall to only -80 to -60 m for 10 kyr results in a weakened AISM and glacial conditions, followed by a full termination. Taken together, both glaciations and glacial terminations imply a sea level threshold driving the AISM between two primary levels of intensity (`interglacial' & `glacial'). These massive, sea-level driven shifts in AISM strength are superimposed on precession-scale variability associated with boreal fall insolation at the equator, indicating sensitivity to tropical Pacific influence on warm pool convection.

The sedimentary evolution of the Celtic Sea during Marine Isotope Stages 1 and 2

NASA Astrophysics Data System (ADS)

Lockhart, Edward; Scourse, James; Van Landeghem, Katrien; Praeg, Daniel; Mellett, Claire; Huws, Dei; Saher, Margot; Benetti, Sara

2017-04-01

During the Last Glacial Maximum (LGM), the Celtic Sea was partially glaciated by the Irish Sea Ice Stream and is considered to have subsequently experienced a high-energy post-glacial transgression. The combination of these events resulted in the deposition, reworking and erosion of a wide range of sediment types to produce the upper stratigraphy of the shelf, including the world's largest submarine elongated ridges. These geomorphic features dominate the shelf and have been previously interpreted to have formed as a result of the tidal reworking of shelf deposits during transgression, despite not having been directly dated. Shelf-wide high-resolution geophysical data, and vibrocores, collected as part of the BRITICE-CHRONO Project, provide new information on relationships between seismic and shallow sedimentary units. A regionally extensive near-surface reflector, cored in several locations, correlates to a gravel/shell layer with an erosive base, unconformably overlying fine-grained LGM glacial sediments with undrained shear strengths in excess of 120 kPa, and in places exhibiting visibly deformed laminations. Geotechnical tests suggest these sediments to be over-consolidated, and we propose that these properties and the observed deformation can only be explained by subglacial reworking under a re-advancing Irish Sea Ice Stream, a scenario never before evidenced in reconstructions of Celtic Sea glaciation. Previous reconstructions propose a single advance-retreat cycle; therefore, a re-advance during a time of inferred retreat would represent a significant change in glacial dynamics. Seismic reflection profiles show that the regionally continuous gravel/shell layer appears to form an undulating palaeo-topography, possibly influenced by the geotechnical properties of the deposits below, on which the large surface ridges are formed. The presence of a regionally continuous reflection surface truncating LGM glacial sediments would suggest a significant erosion event after glacial deposition occurred, possibly representing transgression. This suggests that the large surface ridges may be of post-glacial tidal origin, but with significant sediment supply and morphological control influenced by the glaciation of the Celtic Sea.

A loess-paleosol record of climate and glacial history over the past two glacial-interglacial cycles (~140 ka), southern Jackson Hole, Wyoming

USGS Publications Warehouse

Pierce, Kenneth L.; Muhs, Daniel R.; Fosberg, Maynard A.; Mahan, Shannon; Rosenbaum, Joseph G.; Licciardi, Joseph M.; Pavich, Milan J.

2011-01-01

Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric Be-10 accumulation in soils, and cosmogenic Be-10 surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8,7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (similar to 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (similar to 43-51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada. Published by Elsevier Inc. on behalf of University of Washington.

75 FR 12597 - Endangered and Threatened Species; Proposed Listing of Nine Distinct Population Segments of...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-16

... result in a significant gap in the range of the taxon; (c) evidence that the discrete segment represents... appear to have shaped the evolution of these two matriarchal lineages with the onset of glacial cycles...-directional invasion by the temperate-adapted loggerheads into the respective basins (Bowen et al., 1994; J.S...

Growth, Uplift and Truncation of Indo-Burman Anticlines Paced By Glacial-Interglacial Sea Level Change

NASA Astrophysics Data System (ADS)

Gale, J.; Steckler, M. S.; Sousa, D.; Seeber, L.; Goodbred, S. L., Jr.; Ferguson, E. K.

2014-12-01

The Ganges-Brahmaputra Delta abuts the Indo-Burman Arc on the east. Subduction of the thick delta strata has generated a large subaerial accretionary prism, up to 250 km wide, with multiple ranges of anticlines composed of the folded and faulted delta sediments. As the wedge has grown, the exposed anticlines have become subject to erosion by the rivers draining the Himalaya, a local Indo-Burman drainage network, and coastal processes. Multiple lines of geophysical, geologic, and geomorphologic evidence indicate anticline truncation as a result of interaction with the rivers of the delta and sea level. Seismic lines, geologic mapping, and geomorphology reveal truncated anticlines with angular unconformities that have been arched due to continued growth of the anticline. Buried, truncated anticlines have been identified by seismic lines, tube well logs, and resistivity measurements. The truncation of these anticlines also appears to provide a pathway for high-As Holocene groundwater into the generally low-As Pleistocene groundwater. Overall, the distribution of anticline erosion and elevation in the fold belt appears to be consistent with glacial-interglacial changes in river behavior in the delta. The anticline crests are eroded during sea level highstands as rivers and the coastline sweep across the region, and excavated by local drainage during lowstands. With continued growth, the anticlines are uplifted above the delta and "survive" as topographic features. As a result, the maximum elevations of the anticlines are clustered in a pattern suggesting continued growth since their last glacial highstand truncation. An uplift rate is calculated from this paced truncation and growth that is consistent with other measurements of Indo-Burman wedge advance. This rate, combined with the proposed method of truncation, give further evidence of dynamic fluvial changes in the delta between glacial and interglacial times.

Bering Sea Nd isotope records of North Pacific Intermediate Water circulation

NASA Astrophysics Data System (ADS)

Rabbat, C.; Knudson, K. P.; Goldstein, S. L.

2017-12-01

North Pacific Intermediate Water (NPIW) is the primary water mass associated with Pacific meridional overturning circulation. While the relationship between Atlantic meridional overturning circulation and climate has been extensively studied, a lack of suitable sediment cores has limited past investigations of North Pacific climate and NPIW variability. Integrated Ocean Drilling Program Site U1342 (818 m water depth) on Bower's Ridge in the Bering Sea is located at a sensitive depth for detecting changes in NPIW, and it is the only available sub-arctic North Pacific site that offers long, continuous core recovery, relatively high sedimentation rates, excellent foraminifera preservation, and a well-constrained age model over multiple glacial-interglacial cycles. Previous work at Site U1342 from Knudson and Ravelo (2015), using non-quantitative circulation proxies, provides evidence for enhanced NPIW formation during extreme glacials associated with the closure of the Bering Strait and suggest that NPIW was formed locally within the Bering Sea. Our work builds on the potential importance of these results and applies more robust and potentially quantitative circulation proxies to constrain NPIW variability. Here, we present new records of NPIW circulation from Site U1342 based on Nd isotope analyses on fish debris and Fe-Mn encrusted foraminifera, which serve as semi-quantitative "water mass tracers." Weak Bering Sea NPIW formation and ventilation are reflected by relatively lower eNd values indicative of open subarctic North Pacific waters, which are presently predominant, whereas enhanced Bering Sea NPIW formation and ventilation are be reflected by relatively higher eNd values due to the input of Nd from regional volcanic rocks.

An Analytical Framework for the Steady State Impact of Carbonate Compensation on Atmospheric CO2

NASA Astrophysics Data System (ADS)

Omta, Anne Willem; Ferrari, Raffaele; McGee, David

2018-04-01

The deep-ocean carbonate ion concentration impacts the fraction of the marine calcium carbonate production that is buried in sediments. This gives rise to the carbonate compensation feedback, which is thought to restore the deep-ocean carbonate ion concentration on multimillennial timescales. We formulate an analytical framework to investigate the impact of carbonate compensation under various changes in the carbon cycle relevant for anthropogenic change and glacial cycles. Using this framework, we show that carbonate compensation amplifies by 15-20% changes in atmospheric CO2 resulting from a redistribution of carbon between the atmosphere and ocean (e.g., due to changes in temperature, salinity, or nutrient utilization). A counterintuitive result emerges when the impact of organic matter burial in the ocean is examined. The organic matter burial first leads to a slight decrease in atmospheric CO2 and an increase in the deep-ocean carbonate ion concentration. Subsequently, enhanced calcium carbonate burial leads to outgassing of carbon from the ocean to the atmosphere, which is quantified by our framework. Results from simulations with a multibox model including the minor acids and bases important for the ocean-atmosphere exchange of carbon are consistent with our analytical predictions. We discuss the potential role of carbonate compensation in glacial-interglacial cycles as an example of how our theoretical framework may be applied.

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands

PubMed Central

Cornejo-Romero, Amelia; Aguilar-Martínez, Gustavo F.; Medina-Sánchez, Javier; Rendón-Aguilar, Beatriz; Valverde, Pedro Luis; Zavala-Hurtado, Jose Alejandro; Serrato, Alejandra; Rivas-Arancibia, Sombra; Pérez-Hernández, Marco Aurelio; López-Ortega, Gerardo; Jiménez-Sierra, Cecilia

2017-01-01

Historic demography changes of plant species adapted to New World arid environments could be consistent with either the Glacial Refugium Hypothesis (GRH), which posits that populations contracted to refuges during the cold-dry glacial and expanded in warm-humid interglacial periods, or with the Interglacial Refugium Hypothesis (IRH), which suggests that populations contracted during interglacials and expanded in glacial times. These contrasting hypotheses are developed in the present study for the giant columnar cactus Cephalocereus columna-trajani in the intertropical Mexican drylands where the effects of Late Quaternary climatic changes on phylogeography of cacti remain largely unknown. In order to determine if the historic demography and phylogeographic structure of the species are consistent with either hypothesis, sequences of the chloroplast regions psbA-trnH and trnT-trnL from 110 individuals from 10 populations comprising the full distribution range of this species were analysed. Standard estimators of genetic diversity and structure were calculated. The historic demography was analysed using a Bayesian approach and the palaeodistribution was derived from ecological niche modelling to determine if, in the arid environments of south-central Mexico, glacial-interglacial cycles drove the genetic divergence and diversification of this species. Results reveal low but statistically significant population differentiation (FST = 0.124, P < 0.001), although very clear geographic clusters are not formed. Genetic diversity, haplotype network and Approximate Bayesian Computation (ABC) demographic analyses suggest a population expansion estimated to have taken place in the Last Interglacial (123.04 kya, 95% CI 115.3–130.03). The species palaeodistribution is consistent with the ABC analyses and indicates that the potential area of palaedistribution and climatic suitability were larger during the Last Interglacial and Holocene than in the Last Glacial Maximum. Overall, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH. PMID:28426818

Alternative glacial-interglacial refugia demographic hypotheses tested on Cephalocereus columna-trajani (Cactaceae) in the intertropical Mexican drylands.

PubMed

Cornejo-Romero, Amelia; Vargas-Mendoza, Carlos Fabián; Aguilar-Martínez, Gustavo F; Medina-Sánchez, Javier; Rendón-Aguilar, Beatriz; Valverde, Pedro Luis; Zavala-Hurtado, Jose Alejandro; Serrato, Alejandra; Rivas-Arancibia, Sombra; Pérez-Hernández, Marco Aurelio; López-Ortega, Gerardo; Jiménez-Sierra, Cecilia

2017-01-01

Historic demography changes of plant species adapted to New World arid environments could be consistent with either the Glacial Refugium Hypothesis (GRH), which posits that populations contracted to refuges during the cold-dry glacial and expanded in warm-humid interglacial periods, or with the Interglacial Refugium Hypothesis (IRH), which suggests that populations contracted during interglacials and expanded in glacial times. These contrasting hypotheses are developed in the present study for the giant columnar cactus Cephalocereus columna-trajani in the intertropical Mexican drylands where the effects of Late Quaternary climatic changes on phylogeography of cacti remain largely unknown. In order to determine if the historic demography and phylogeographic structure of the species are consistent with either hypothesis, sequences of the chloroplast regions psbA-trnH and trnT-trnL from 110 individuals from 10 populations comprising the full distribution range of this species were analysed. Standard estimators of genetic diversity and structure were calculated. The historic demography was analysed using a Bayesian approach and the palaeodistribution was derived from ecological niche modelling to determine if, in the arid environments of south-central Mexico, glacial-interglacial cycles drove the genetic divergence and diversification of this species. Results reveal low but statistically significant population differentiation (FST = 0.124, P < 0.001), although very clear geographic clusters are not formed. Genetic diversity, haplotype network and Approximate Bayesian Computation (ABC) demographic analyses suggest a population expansion estimated to have taken place in the Last Interglacial (123.04 kya, 95% CI 115.3-130.03). The species palaeodistribution is consistent with the ABC analyses and indicates that the potential area of palaedistribution and climatic suitability were larger during the Last Interglacial and Holocene than in the Last Glacial Maximum. Overall, these results suggest that C. columna-trajani experienced an expansion following the warm conditions of interglacials, in accordance with the GRH.

Aspects of late Quaternary geomorphological development in the Khangai Mountains and the Gobi Altai Mountains (Mongolia)

NASA Astrophysics Data System (ADS)

Lehmkuhl, Frank; Nottebaum, Veit; Hülle, Daniela

2018-07-01

The reconstruction of geomorphological processes as a result of environmental change is approached by investigating and dating some fluvial, aeolian and lacustrine archives at specific locations that form a N-S basin and range transect across the Khangai Mountains south to the eastern Gobi Altai mountains in Mongolia. Geomorphological processes varied a) spatially with different climatic conditions and vegetation cover in relation to different elevation and latitude and b) temporally due to climatic shifts during the late Quaternary. In total, 15 sections from three distinct sub-regions along that transect were dated by 22 OSL ages. The Khangai Mountain sub-region exhibits mainly late Glacial to Holocene aeolian silty to sandy cover sediments mainly in the upper catchment reaches (>1800 m a.s.l.). Sections in the northern and central Gobi represent river terraces and alluvial fans in basin areas as well as aeolian sediments in the mountains above 2200 m a.s.l. The oldest terrace surface found in this study (T2; NGa1) dates to the penultimate Glacial cycle. The T1 terrace surfaces, on the northern Khangai Mountain front and in the central Gobi sub-region yield a maximum accumulation during the global Last Glacial Maximum (gLGM) and late Glacial time. During the gLGM phase represents rather sheetflow dominated transport built the alluvial fans and in late Glacial times the sediments exhibit more debrisflow controlled accumulation. Incision, forming the T1-terrace edges is therefore, supposed for the Pleistocene-Holocene transition and subsequent early Holocene. The geomorphic evidence is interpreted as stronger fluvial morphodynamics induced by enhanced humidity under beginning interglacial conditions. These processes coincided with the development of aeolian mantles at higher altitudes in the Khangai and Gobi Altai mountains where higher temperatures and humidities supported the formation of a vegetation cover, that served as a dust trap at least since late Glacial times and reduced the sediment supply on the alluvial fans.

The Glacial and Relative Sea Level History of Southern Banks Island, NT, Canada

NASA Astrophysics Data System (ADS)

Vaughan, Jessica Megan

The mapping and dating of surficial glacial landforms and sediments across southern Banks Island document glaciation by the northwest Laurentide Ice Sheet (LIS) during the last glacial maximum. Geomorphic landforms confirm the operation of an ice stream at least 1000 m thick in Amundsen Gulf that was coalescent with thin, cold-based ice crossing the island's interior, both advancing offshore onto the polar continental shelf. Raised marine shorelines across western and southern Banks Island are barren, recording early withdrawal of the Amundsen Gulf Ice Stream prior to the resubmergence of Bering Strait and the re-entry of Pacific molluscs ~13,750 cal yr BP. This withdrawal resulted in a loss of ~60,000 km2 of ice --triggering drawdown from the primary northwest LIS divide and instigating changes in subsequent ice flow. The Jesse moraine belt on eastern Banks Island records a lateglacial stillstand and/or readvance of Laurentide ice in Prince of Wales Strait (13,750 -- 12,750 cal yr BP). Fossiliferous raised marine sediments that onlap the Jesse moraine belt constrain final deglaciation to ~12,600 cal yr BP, a minimum age for the breakup of the Amundsen Gulf Ice Stream. The investigation of a 30 m thick and 6 km wide stratigraphic sequence at Worth Point, southwest Banks Island, identifies an advance of the ancestral LIS during the Mid-Pleistocene (sensu lato), substantially diversifying the glacial record on Banks Island. Glacial ice emplaced during this advance has persisted through at least two glacial-interglacial cycles, demonstrating the resilience of circumpolar permafrost. Pervasive deformation of the stratigraphic sequence also records a detailed history of glaciotectonism in proglacial and subglacial settings that can result from interactions between cold-based ice and permafrost terrain. This newly recognized history rejects the long-established paleoenvironmental model of Worth Point that assumed a simple 'layer-cake' stratigraphy.

Dynamic Change in Glacial Dammed Lake Behavior of Suicide Basin, Mendenhall Glacier, Juneau Alaska

NASA Astrophysics Data System (ADS)

Jacobs, A. B.; Moran, T.; Hood, E. W.

2016-12-01

Suicide Basin Jökulhlaups, since 2011, have resulted in moderate flooding on the Mendenhall Lake and River in Juneau, AK. At this time, the USGS recorded peak streamflow of 20,000 cfs in 2014, the highest flows officially reported by the USGS which was attributed to a Suicide Basin glacial-dammed lake release. However, the USGS estimated a peak flow of 27,000 cfs in 1961 and we suspect this event is partially the result of a glacial dammed lake release. From 2011 to 2015, data indicates that yearly outburst from Suicide Basin were the norm; however, in 2015 and 2016, multiple outbursts during the summer were observed suggesting a dynamic change in glacial behavior. For public safety and awareness, the University of Alaska Southeast and U.S. Geologic Survey began monitoring real-time Suicide Basin lake levels. A real-time model was developed by the National Weather Service Alaska-Pacific River Forecast Center capable of forecasting potential timing and magnitude of the flood-wave crest from this Suicide Basin release. However, the model now is being modified because data not previously available has become available and adapted to the change in state of glacial behavior. The importance of forecasting time and level of crest on the Mendenhall River system owing to these outbursts floods is an essential aid to emergency managers and the general public to provide impact decision support services (IDSS). The National Weather Service has been able to provide 36 to 24 hour forecasts for these large events, but with the change in glacial state on the Mendenhall Glacier, the success of forecasting these events is getting more challenging. We will show the success of the hydrologic model but at the same time show the challenges we have seen with the changing glacier dynamics.

Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance

NASA Astrophysics Data System (ADS)

Rother, Henrik; Shulmeister, James; Fink, David; Alexander, David; Bell, David

2015-11-01

During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages.

N zooming into the Mediterranean outflow fossil moat during the 1.2-1.8 million years period (Early-Pleistocene) - An approach by radiogenic and stable isotopes

NASA Astrophysics Data System (ADS)

Lebreiro, Susana M.; Antón, Laura; Reguera, M. Isabel; Fernández, Marta; Conde, Estefanía; Barrado, Ana I.; Yllera, Abel

2015-12-01

The fossil Alvarez Cabral erosive Moat contains hemipelagite, contourite and turbidite facies where oceanography changes in the Mediterranean outflow are archived over the 1.2-1.8 Myr time period. Here we used Pb and Sr radiogenic isotopes to trace water masses and sediment source changes, for the first time in twenty glacial-interglacial (G-I) cycles of the Early-Pleistocene interval, and the last Glacial Maximum through Holocene cycle (including the Younger Dryas and Heinrich Stadial-1). A mixing line of Pb isotopes gives reliable low radiogenic 208Pb/204Pb, 206Pb/204Pb, and 206Pb/207Pb typical of Mediterranean Outflow Water (MOW) in one end-member and the signature of high radiogenic isotopes of Atlantic Waters (AW) towards the second end-member. The 87Sr/86Sr isotopes also display two end-members of the mixing line between eolian transport/dust source (0.71) and fluvial transport/weathering source (0.73) previously proposed in the Gulf of Cadiz. Combination of Pb and Sr radiogenic isotopes with O and C stable isotopes of planktonic and benthic foraminifera, and the response of foraminifera benthos over the Early-Pleistocene interval, reveals a direct link between water masses circulation and shifts in G-I. We found a persistent cyclic pattern of MOW circulation and fluvial deposition during glaciations and AW and aeolian influence during interglaciations. On site U1386B/C, the upper-MOW was less ventilated but productive and with high flux of organic flux matter during glacials, while Atlantic Waters were better ventilated, enriched in O, but less productive during interglacials. We infer that shifts in ocean and atmospheric processes in the Gulf of Cadiz were strongly controlled by Earth's obliquity (41 kyr-cycle) and 35°NH insolation during the Early-Pleistocene. We propose a correlation in changes in phase-relationship between precession and obliquity. In general terms, physical properties of fine sediments (glacials) show lower NGR, low reflectance and high magnetic susceptibility. These curves measured in a 20 cm sampling interval, on board ship, present a number of gaps due to non-recovery of sediment. To overcome this problem and obtain a complete lithological record the point-sensor curves of physical properties were correlated with down-hole logs of HSGR (standard total Gamma-ray in gAPI units) (Suppl. Fig. 1) and HROM (high resolution corrected bulk density in g/cm3) (IODP Expedition 339 by the Scientific Party, Logging Summaries).

Responses of the deep ocean carbonate system to carbon reorganization during the Last Glacial-interglacial cycle

NASA Astrophysics Data System (ADS)

Yu, Jimin; Anderson, Robert F.; Jin, Zhangdong; Rae, James W. B.; Opdyke, Bradley N.; Eggins, Stephen M.

2013-09-01

We present new deep water carbonate ion concentration ([CO32-]) records, reconstructed using Cibicidoides wuellerstorfi B/Ca, for one core from Caribbean Basin (water depth = 3623 m, sill depth = 1.8 km) and three cores located at 2.3-4.3 km water depth from the equatorial Pacific Ocean during the Last Glacial-interglacial cycle. The pattern of deep water [CO32-] in the Caribbean Basin roughly mirrors that of atmospheric CO2, reflecting a dominant influence from preformed [CO32-] in the North Atlantic Ocean. Compared to the amplitude of ˜65 μmol/kg in the deep Caribbean Basin, deep water [CO32-] in the equatorial Pacific Ocean has varied by no more than ˜15 μmol/kg due to effective buffering of CaCO3 on deep-sea pH in the Pacific Ocean. Our results suggest little change in the global mean deep ocean [CO32-] between the Last Glacial Maximum (LGM) and the Late Holocene. The three records from the Pacific Ocean show long-term increases in [CO32-] by ˜7 μmol/kg from Marine Isotope Stage (MIS) 5c to mid MIS 3, consistent with the response of the deep ocean carbonate system to a decline in neritic carbonate production associated with ˜60 m drop in sea-level (the “coral-reef” hypothesis). Superimposed upon the long-term trend, deep water [CO32-] in the Pacific Ocean displays transient changes, which decouple with δ13C in the same cores, at the start and end of MIS 4. These changes in [CO32-] and δ13C are consistent with what would be expected from vertical nutrient fractionation and carbonate compensation. The observed ˜4 μmol/kg [CO32-] decline in the two Pacific cores at >3.4 km water depth from MIS 3 to the LGM indicate further strengthening of deep ocean stratification, which contributed to the final step of atmospheric CO2 drawdown during the last glaciation. The striking similarity between deep water [CO32-] and 230Th-normalized CaCO3 flux at two adjacent sites from the central equatorial Pacific Ocean provides convincing evidence that deep-sea carbonate dissolution dominantly controlled CaCO3 preservation at these sites in the past. Our results offer new and quantitative constraints from deep ocean carbonate chemistry to understand roles of various mechanisms in atmospheric CO2 changes over the Last Glacial-interglacial cycle.

Late Quaternary deglacial history of the Mérida Andes, Venezuela

NASA Astrophysics Data System (ADS)

Stansell, Nathan D.; Abbott, Mark B.; Polissar, Pratigya J.; Wolfe, Alexander P.; Bezada, Maximiliano; Rull, Valentí

2005-10-01

Radiocarbon-dated sediment cores from seven lakes and two bogs spanning the Cordillera de Mérida in the Venezuelan Andes were used to identify and date the regional history of late Pleistocene and Holocene glacial activity. Coring sites were selected at different elevations across a pronounced rain shadow from southeast (wet) to northwest (dry). Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation. The local expression of the Last Glacial Maximum occurred between 22 750 and 19 960 cal. yr BP. On the wetter southeastern side of the Cordillera de Mérida, glaciers had significantly retreated by 15 700 cal. yr BP, followed by several minor glacial advances and retreats between 14 850 and 13 830 cal. yr BP. At least one major glacial readvance occurred between 13 830 and 10 000 cal. yrBP in the wetter southeastern sector of the region. The drier northwest side of the Cordillera de Mérida records initial glacial retreat by 14240cal.yrBP. Multiple sites on both sides of the Mérida Andes record a further phase of extensive deglaciation approximately 10000cal.yrBP. However, the north-northwest facing Mucubají catchment remained partially glaciated until ca. 6000cal.yrBP. Deglacial ages from the Venezuelan Andes are consistently younger than those reported from the Southern Hemisphere Andes, suggesting an inter-hemispheric deglacial lag in the northern tropics of the order of two thousand years.

Multi-scale curvature for automated identification of glaciated mountain landscapes

NASA Astrophysics Data System (ADS)

Prasicek, Günther; Otto, Jan-Christoph; Montgomery, David R.; Schrott, Lothar

2014-03-01

Erosion by glacial and fluvial processes shapes mountain landscapes in a long-recognized and characteristic way. Upland valleys incised by fluvial processes typically have a V-shaped cross-section with uniform and moderately steep slopes, whereas glacial valleys tend to have a U-shaped profile with a changing slope gradient. We present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi-scale curvature and drainage area. Sample catchments are delineated and multiple moving window sizes are used to calculate per-cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides. Single-scale curvature can take similar values for glaciated and non-glaciated catchments but a comparison of multi-scale curvature leads to different results according to the typical cross-sectional shapes. To adapt these differences for automated classification of mountain landscapes into areas with V- and U-shaped valleys, curvature values are correlated with drainage area and a new and simple morphometric parameter, the Difference of Minimum Curvature (DMC), is developed. At three study sites in the western United States the DMC thresholds determined from catchment analysis are used to automatically identify 5 × 5 km quadrats of glaciated and non-glaciated landscapes and the distinctions are validated by field-based geological and geomorphological maps. Our results demonstrate that DMC is a good predictor of glacial imprint, allowing automated delineation of glacially and fluvially incised mountain landscapes.

Effects of global climate change on biodiversity in forests of the Southern United States

Treesearch

Margaret S. Devall; Bernard R. Parresol

1998-01-01

Climate has not been stable in the past. Fluctuations of pine (Pinus) pollen in a 50,000-year sequence from Lake Tulane in Florida indicate that major vegetation shifts occurred during the last glacial cycle. Phases of pollen dominated by pine (indicating a wet climate) were interspersed with periods with plentiful oak (Quercus), ragweed, and marsh elder (...

Testing competing forms of the Milankovitch hypothesis: A multivariate approach

NASA Astrophysics Data System (ADS)

Kaufmann, Robert K.; Juselius, Katarina

2016-02-01

We test competing forms of the Milankovitch hypothesis by estimating the coefficients and diagnostic statistics for a cointegrated vector autoregressive model that includes 10 climate variables and four exogenous variables for solar insolation. The estimates are consistent with the physical mechanisms postulated to drive glacial cycles. They show that the climate variables are driven partly by solar insolation, determining the timing and magnitude of glaciations and terminations, and partly by internal feedback dynamics, pushing the climate variables away from equilibrium. We argue that the latter is consistent with a weak form of the Milankovitch hypothesis and that it should be restated as follows: internal climate dynamics impose perturbations on glacial cycles that are driven by solar insolation. Our results show that these perturbations are likely caused by slow adjustment between land ice volume and solar insolation. The estimated adjustment dynamics show that solar insolation affects an array of climate variables other than ice volume, each at a unique rate. This implies that previous efforts to test the strong form of the Milankovitch hypothesis by examining the relationship between solar insolation and a single climate variable are likely to suffer from omitted variable bias.

Geochronology of Middle and Upper Pleistocene Loess Sections in Hungary

NASA Astrophysics Data System (ADS)

Frechen, Manfred; Horváth, Erzsébet; Gábris, Gyula

1997-11-01

The application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied "classical" Hungarian loess/paleosol sequences from Basaharc, Mende, and Paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Based on this combined luminescence dating study a new chronology is proposed for the "Young Loess" in Hungary. Luminescence dating suggests that the loess below the MF2 horizon formed during the penultimate glaciation. The MF1 horizon probably formed during an interstade within oxygen isotope stage 3. For the youngest loess, overlying MF1, a very high accumulation rate was determined. Large time gaps occur above MF2 and MF1, indicating that most of the record of the last glaciation is missing in the standard sections at Basaharc, Mende, and Paks. Either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil-forming periods. High-resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in Hungary, although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites.

The narrow endemic Norwegian peat moss Sphagnum troendelagicum originated before the last glacial maximum

PubMed Central

Stenøien, H K; Shaw, A J; Stengrundet, K; Flatberg, K I

2011-01-01

It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years. PMID:20717162

Corrigendum to "Three climatic cycles recorded in a loess-palaeosol sequence at Semlac (Romania)-Implications for dust accumulation in south-eastern Europe" [Quat. Sci. Rev. 154C (2016) 130-142

NASA Astrophysics Data System (ADS)

Zeeden, C.; Kels, H.; Hambach, U.; Schulte, P.; Protze, J.; Eckmeier, E.; Marković, S. B.; Klasen, N.; Lehmkuhl, F.

2018-05-01

In the article 'Three climatic cycles recorded in a loess-palaeosol sequence at Semlac (Romania)-Implications for dust accumulation in south-eastern Europe' (Zeeden et al., 2016) we employed rock magnetic and grain size proxy data in combination with OSL- and correlative age models. The data and dating is combined to discuss glacial-interglacial paleoclimate variability in an Eurasian context. This dataset was also interpreted regarding the dust source in the eastern Carpathian (Middle Danube) Basin.

Mediterranean Outflow and surface water variability off southern Portugal during the early Pleistocene: A snapshot at Marine Isotope Stages 29 to 34 (1020-1135 ka)

NASA Astrophysics Data System (ADS)

Voelker, Antje H. L.; Salgueiro, Emilia; Rodrigues, Teresa; Jimenez-Espejo, Francisco J.; Bahr, André; Alberto, Ana; Loureiro, Isabel; Padilha, Maria; Rebotim, Andreia; Röhl, Ursula

2015-10-01

Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558 m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stages (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic δ18O signal follows obliquity with the exception of an additional, smaller δ18O peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3. A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065-1091 ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (< 12 °C) SST that in their climatic impact were comparable with the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show a strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes.

Timing of lake-level changes for a deep last-glacial Lake Missoula: optical dating of the Garden Gulch area, Montana, USA

NASA Astrophysics Data System (ADS)

Smith, Larry N.; Sohbati, Reza; Buylaert, Jan-Pieter; Lian, Olav B.; Murray, Andrew; Jain, Mayank

2018-03-01

Glaciolacustrine sediments in the Clark Fork River valley at Garden Gulch, near Drummond, Montana, USA record highstand positions of the ice-dammed glacial Lake Missoula and repeated subaerial exposure. During these highstands the lake was at greater than 65% of its recognized maximum capacity. The initial lake transgression deposited a basal sand unit. Subsequent cycles of lake-level fluctuations are recorded by sequences of laminated and cross laminated silt, sand, and clay deformed by periglacial processes during intervening periods of lower lake levels. Optically stimulated luminescence (OSL) dating of quartz sand grains, using single-aliquot regenerative-dose procedures, was carried out on 17 samples. Comparison of infrared stimulated luminescence (IRSL) from K-rich feldspar to OSL from quartz for all the samples suggests that they were well bleached prior to deposition and burial. Ages for the basal sand and overlying glaciolacustrine exposure surfaces are indistinguishable within one standard deviation, and give a weighted mean age of 20.9 ± 1.3 ka (n = 11). Based on sedimentological and stratigraphic analysis we infer that the initial transgression, and at least six cycles of lake-level fluctuation, occurred over time scales of decades to ∼2 ka. Bioturbated sandy slopewash dated at 10.6 ± 0.9 ka and 11.9 ± 1.2 ka unconformably overlies the upper glaciolacustrine deposits. The uppermost sediments, above the glaciolacustrine section, are younger than the Glacier Peak tephra (13.7-13.4 cal ka B.P.), which was deposited across parts of the drained lake basin, but has not been found at Garden Gulch. Our study indicates that glacial Lake Missoula reached >65 percent of maximum capacity by about 20.9 ± 1.3 ka and either partially or completely drained twelve times from this position. Rapid lowering from the lake's highstand position due to ice-dam failure likely led to scour in the downstream portions of the glacial Lake Missoula basin and megafloods in the Channeled Scabland.

Reconstructing the Glacial Cycle of the Last 150 ka in the Southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Holmes, B.; Dekens, P.; Weber, M. E.; Lantzsch, H.; Reilly, B. T.; Das, S. K.; Martos, Y. M.; Williams, T.

2017-12-01

The Himalayas and resulting monsoonal climate provide the source and mechanism for sediment deposition in the Bay of Bengal. Sediments from the distal Bengal Fan collected during IODP expedition 354, with the exception the westernmost Site U1454, show a several meter thick, hemipelagic top layer representing the Late Quaternary. This interval has abundant foraminifera throughout and therefore presents a unique opportunity to reconstruct oceanographic conditions, alongside records of terrestrial climate variability. We reconstructed oceanographic conditions at IODP site U1452 (8°N, 87°E, 3671 m water depth), in the southern Bay of Bengal. The age model was constructed by tuning the core's sediment lightness, L*, to the EDML ice core. The Toba Ash 1 (73.7 ka) is an additional constraint leading to an age model with a total of 35 tie points. We sampled the top 3.5 m of sediment at 2 cm resolution, and picked between 8 to 30 tests of the mixed surface layer planktonic foraminifera G. sacculifer from each sample. The tests were cracked open between two glass plates and the sample was homogenized before being split into separate aliquots for d18O and Mg/Ca analysis. Mg/Ca data range from 2.5 to 4.1 mmol/mol and show a SST change of 2-4°C between glacial and interglacial times. The δ18O data range from -2.63 to 0.17‰. The data shows the shift from the cooler glacial period into the warming interglacial period at 15 ka ending the LGM. The apparent late timing of the deglaciation in the record could be an artifact of lower resolution of the δ18O data (compared to the benthic stack). It is also possible the offset in the timing is due to the age model limitations and the assumption of linear sedimentation rates between tie points. We will further explore the age model implications by measuring d18O on benthic foraminifera where available in the sediment core. In collaboration with scientists from IODP Expedition 354, this data can be used to examine the link between tropical ocean conditions, monsoon strength, and glacial cycles.

Glacistore: Understanding Late Cenozoic Glaciation and Basin Processes for the Development of Secure Large Scale Offshore CO2 Storage (North Sea).

NASA Astrophysics Data System (ADS)

Stewart, H. A.; Barrio, M.; Akhurst, M.; Aagaard, P.; Alcalde, J.; Bauer, A.; Bradwell, T.; Cavanagh, A.; Faleide, J. I.; Furre, A. K.; Haszeldine, S.; Hjelstuen, B. O.; Holloway, S.; Johansen, H.; Johnson, G.; Kuerschner, W.; Mondol, N. H.; Querendez, E.; Ringrose, P. S.; Sejrup, H. P.; Stewart, M.; Stoddart, D.; Wilkinson, M.; Zalmstra, H.

2014-12-01

The sedimentary strata of the North Sea Basin (NSB) record the glacial and interglacial history of environmental change in the Northern Hemisphere, and are a proposed location for the engineered storage of carbon dioxide (CO2) captured from power plant and industrial sources to reduce greenhouse gas emissions. These aspects interact in the geomechanical and fluid flow domain, as ice sheet dynamics change the properties of potential seal and reservoir rocks that are the prospective geological storage strata for much of Europe's captured CO2. The intensification of the global glacial-interglacial cycle at the onset of the Pleistocene (2.5-2.7 Ma) was a critical tipping-point in Earth's recent climate history. The increased severity of glaciations at the Plio-Pleistocene boundary triggered the first development of large-scale continental ice sheets in the Northern Hemisphere. The central part of the NSB preserves a unique history of the depositional record spanning at least the last 3 Ma, which also forms the overburden and seal to the underlying CO2 reservoirs. There is good evidence that these ice sheets created strong feedback loops that subsequently affected the evolution of the Quaternary climate system through complex ocean-atmosphere-cryosphere linkages. Understanding NSB dynamics, including the role of fluids in controlling compaction, cementation, and diagenetic processes in shale-dominated basins, is essential for CO2 storage site characterisation to increase understanding and confidence in secure storage. An increased understanding of the overlying sequence will inform quantitative predictions of the performance of prospective CO2 storage sites in glaciated areas in Europe and worldwide; to include improved resolution of glacial cycles (depositional and chronological framework), characterise pore fluids, flow properties of glacial landforms within the sequence (e.g. tunnel valleys) and the geomechanical effects (quantify compaction, rock stiffness, strength and stress profiles) of advancing and retreating ice on the underlying strata to verify and constrain models of glaciation. This presentation describes current work and introduces a proposal submitted to the Integrated Ocean Discovery Program (852-Pre) by the authors.

Late Cenozoic lacustrine and climatic environments at Tule Lake, northern Great Basin, USA

USGS Publications Warehouse

Platt, Bradbury J.

1992-01-01

Cores of lake sediment to a depth of 334 m in the town of Tulelake, Siskiyou County, northern California, document the late Cenozoic paleolimnologic and paleoclimatic history of the northwestern edge of the Great Basin. The cores have been dated by radiometric, tephrochronologic and paleomagnetic analyses. Lacustrine diatoms are abundant throughout the record and document a nearly continuous paleolimnologic history of the Tule Lake basin for the last 3 Myr. During most of this time, this basin (Tule Lake) was a relatively deep, extensive lake. Except for a drier (and cooler?) interval recorded by Fragilaria species about 2.4 Ma, the Pliocene is characterized by a dominance of planktonic Aulacoseira solida implying a warm monomictic lake under a climatic regime of low seasonality. Much of the Pleistocene is dominated by Stephanodiscus and Fragilaria species suggesting a cooler, often drier, and highly variable climate. Benthic diatoms typical of alkaline-enriched saline waters commonly appear after 1.0 Ma, and tephrochronology indicates slow deposition and possible hiatuses between about 0.6 and 0.2 Ma. The chronology of even-numbered oxygen isotope stages approximately matches fluctuations in the abundance of Fragilaria since 800 ka indicating that glacial periods were expressed as drier environments at Tule Lake. Glacial and interglacial environments since 150 ka were distinct from, and more variable than, those occurring earlier. The last full glacial period was very dry, but shortly thereafter Tule Lake became a deep, cool lacustrine system indicating a substantial increase in precipitation. Aulacoseira ambigua characterized the latest glacial and Holocene record of Tule Lake. Its distribution indicates that warmer and wetter climates began about 15 ka in this part of the Great Basin. Diatom concentration fluctuates at 41 000 year intervals between 3.0 and 2.5 Ma and at approximately 100 000 year intervals after 1.0 Ma. In the late Pliocene and early Pleistocene, Aulacoseira solida percentages wax and wane in an approximately 400 000 year cycle. The possible response of Tule Lake diatom communities to orbitally-induced insolation cycles underscores the importance of this record for the study of late Cenozoic paleoclimate change. ?? 1992 Springer-Verlag.

Ice Elevation Changes in the Ellsworth Mountains, Antarctica Using Multiple Cosmogenic Nuclides

NASA Astrophysics Data System (ADS)

Marrero, S.; Hein, A.; Sugden, D.; Woodward, J.; Dunning, S.; Reid, K.

2014-12-01

Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Initial surface exposure ages (10Be, 26Al, 21Ne, and 36Cl ) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to 1.1 Ma in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

Using Multiple Cosmogenic Nuclides to Investigate Ice Elevation Changes in the Ellsworth Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Marrero, Shasta; Hein, Andy; Sugden, David; Woodward, John; Dunning, Stuart; Freeman, Stewart; Shanks, Richard

2015-04-01

Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Surface exposure ages (10Be, 26Al, 21Ne, and 36Cl) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to more than 1 million years in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

Investigating the present and past glacial and frost activity on Pluto with a volatile transport model

NASA Astrophysics Data System (ADS)

Bertrand, Tanguy; Forget, Francois

2016-10-01

The high obliquity and eccentricity of the orbit of Pluto induce seasonal cycles of condensation and sublimation of the main volatile ices: N2, CH4, and CO. The New Horizons spacecraft, which flew by Pluto in July 2015, revealed a complex surface composition including a thousand-kilometre nitrogen glacier in the "Sputnik Planum" plain near the Anti-Charon longitude, extensive methane frosts at mid and high latitudes, and equatorial ice-free regions. We present numerical simulations designed to model the evolution of Pluto's volatiles over thousands of years on the basis of straightforward universal physical equations.Our results explain the observed distribution of ices on the surface and the quantities of volatiles in the atmosphere. In particular the model predicts the N2 ice accumulation in the deepest low-latitude basin and the 3-fold increase of pressure observed to occur since 1988. This points to atmospheric-topographic processes at the origin of the Sputnik Planum's nitrogen glacier. The same simulations also show frosts of methane, and sometimes nitrogen, that seasonally cover the mid and high latitudes, explaining the bright northern polar cap reported in the 1990s and the observed ice distribution in 2015. The model also predicts that most of these seasonal frosts should disappear in the next decade, and thus could be tested observationally in the near future.Using prior orbital parameters of Pluto and a realistic glacial flow parametrization, we also simulate past climates of Pluto. The results show that Pluto undergoes cycles of glacial activity (over timescales of few million years) that may explain the rugged eroded-mountain landscapes surrounding Sputnik Planum and the "bladed" methane terrains east of "Tombaugh Regio".

Glacial Chemical Alteration of Mars-Like Bedrock

NASA Astrophysics Data System (ADS)

Rutledge, A. M.; Horgan, B. H. N.; Havig, J. R.; Rampe, E. B.; Scudder, N.; Hamilton, T.

2017-12-01

Mars is understood to have had a widespread and long-lived cryosphere, including glaciers and ice sheets, possibly since the Noachian. However, the contribution of glaciers to the observed alteration mineralogy of Mars is unclear. To characterize this alteration, water and rock samples were collected from glaciated volcanic bedrock of a range of compositions in the Cascade Volcanic Arc, USA: Mount Hood (silicic), Mount Adams (intermediate), North Sister (mafic), and Middle Sister (most mafic). We analyzed glacial meltwater using field meters (pH, temperature), portable spectrophotometry (dissolved silica), and ion chromatography (major ions). We analyzed proglacial rock coatings and sediments using scanning and transmission electron microscopies with energy dispersive spectroscopy (SEM, TEM, EDS), and visible/short-wave-infrared (VSWIR) and thermal-infrared (TIR) spectroscopies. Water samples are dominated by dissolved silica across a range of pH values, and dissolved silica increases significantly at more mafic sites. Rock coatings associated with glacial striations on mafic terrains include a major poorly crystalline silica component, as do proglacial sediments. This field study demonstrates that silica cycling is the dominant alteration process at glaciated volcanics, and more mafic glaciovolcanic sites have higher concentrations of dissolved silica compared to more felsic glaciovolcanic sites. Though basalts have lower silica content than more felsic volcanic rocks, they are more susceptible to silica mobility. On Mars, widespread poorly crystalline, high silica deposits have been modeled in Nothern Acidalia and Gusev Crater, and hydrated silica deposits have been identified in Nili Fossae and elsewhere. We hypothesize that these phases may be indicators of a cold climate regime on early Mars such as one dominated by large regional ice sheets. Cryosphere-driven silica cycling on low-carbonate, mafic rocks may be more important than previously thought on Mars.

Climate changes in south western Iberia and Mediterranean Outflow variations during two contrasting cycles of the last 1 Myrs: MIS 31-MIS 30 and MIS 12-MIS 11

NASA Astrophysics Data System (ADS)

Sánchez Goñi, M. F.; Llave, E.; Oliveira, D.; Naughton, F.; Desprat, S.; Ducassou, E.; Hodell, D. A.; Hernández-Molina, F. J.

2016-01-01

Grain size analysis and physical properties of Sites U1388, U1389 and U1390 collected in the Contourite Depositional System of the Gulf of Cádiz during the Integrated Ocean Drilling Program (IODP) Expedition 339 "Mediterranean Outflow" reveal relative changes in bottom current strength, a tracer of the dynamics of the Mediterranean Outflow Water (MOW), before and after the Middle Pleistocene Transition (MPT). The comparison of MOW behavior with climate changes identified by the pollen analysis and δ18O benthic foraminifera measurements of Site U1385, the Shackleton Site, collected in the south western Iberian margin shows that the interval MIS 31-MIS 30, ~ 1.1-1.05 million years ago (Ma), before the MPT, was marked by wetter climate and weaker bottom current than the interval MIS 12-MIS 11 (0.47-0.39 Ma), after the MPT. Similarly, the increase in fine particles from these glacials to interglacials and in coarse fraction from interglacials to glacials was coeval with forest and semi-desert expansions, respectively, indicating the lowering/enhancement of MOW strength during periods of regional increase/decrease of moisture. While these findings may not necessarily apply to all glacial/interglacial cycles, they nonetheless serve as excellent supporting examples of the hypothesis that aridification can serve as a good tracer for MOW intensity. The strongest regional aridity during MIS 12 coincides with a remarkable increase of coarse grain size deposition and distribution that we interpret as a maximum in MOW strength. This MOW intensification may have pre-conditioned the North Atlantic by increasing salinity, thereby triggering the strong resumption of the Meridional Overturning Circulation that could contribute to the great warmth that characterizes the MIS 11c super-interglacial.

Sedimentology and lithostratigraphy of a late Wisconsinan outer shelf delta, research consortium boring in Main Pass Block 303, Mississippi delta area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, H.H.; Bouma, A.H.; Coleman, J.M.

A 92 m continuous boring was collected in Main Pass Area, Block 303, to better understand deltaic sedimentation and facies architecture in relationship to glacio eustatic cycles. The boring was also used to calibrate sequence stratigraphy with lithology and chronostratigraphy. The boring spans six isotope stages, covering parts of the last three sea-level cycles. The basal part (92-81 m; glacial isotope Stage 6) is interpreted as a mudflow composed of a rapidly deposited shale with distorted bedding, gas-related structures, and C-13 depleted diagenetic carbonates. This glacial stage is overlain by transgressive systems tract shelf shales capped by a 4-m thickmore » nodular calcareous shale/shelly limestone, representing the interglacial isotope Stage 5 condensed section as well as part of an outer shelf high stand systems tract. Isotope Stage 4 (60-55 m), a lowstand, appears to be condensed or missing, according to benthic foraminifera and oxygen isotope data, possibly constituting a parasequence boundary. The ensuing early Stage 3 transgression (53-45 m) and maximum flooding surface at 43 m precede a distinct progradational deltaic event (43-18 m). There is no clear sedimentary record of the latter part of Stage 3. This midshelf delta has a fauna-poor, rapidly deposited prodelta shale at the base overlain by alternating thin clays, silts, and sands of the distal bar facies and topped by a thick distributary mouth bar sand with numerous layers of redistributed organics. The Stage 2 glacial maximum appears represented by an erosional contact between the fine deltaic sands and the coarse sandy and fine gravelly transgressive system tract channel deposits. There are about 3 m of Stage 1 bioturbated silts and shelly sands capping the section.« less

A closer look at the Neogene erosion and accumulation rate increase

NASA Astrophysics Data System (ADS)

Willenbring, J.; von Blanckenburg, F.

2008-12-01

Glacial erosion and Quaternary cold-stage warm-stage climate cycling have been cited as mechanisms to explain observations of increased Neogene marine sedimentation rates. Quantification of long-term glacial erosion rates from cosmogenic radionuclides from large areas mostly covered by cold-based ice during the Quaternary show very low erosion rates over several glacial cycles. In addition, isotope ratio proxies of dissolved metals in seawater, measured in chemical ocean sediments, lack clear evidence for an increase in terrigenous denudation. In particular, the stable isotope 9Be, derived from continental erosion, shows no change in its ratio to meteoric cosmogenic nuclide 10Be, derived from rain over the past 10 My. Radiogenic Pb and Nd isotopes, mainly show a change in the style of denudation from more chemical to more physical processes in the Quaternary. These data are at odds with a suggested increase in marine sedimentation rates during the late Cenozoic. In order to resolve this contradiction we have scrutinized these sedimentation rate calculations from ocean cores to identify whether they might show only apparent increases in the Neogene sections. Potential explanations are that in some cases, measured sediment thicknesses for different time intervals lack corrections for sediment compaction. Compaction of the lower portions of the cores drastically increases the apparent thickness of the more recent (Quaternary) sediment. In addition, sedimentation rates often only appear higher for recent sections in cores due to an artifact of an averaging timescale that decreases up-core. Such an averaging time scale decrease arises from better chronological resolution in recent times (Sadler et al., 1999). Cannibalization of older sediment might add to this effect. Together, these data question a clear, global-scale Quaternary climate-erosion connection that would be unique in Earth's history.

Threshold responses in runoff from sub-humid heterogeneous low relief regions

NASA Astrophysics Data System (ADS)

Devito, K.; Hokanson, K. J.; Chasmer, L.; Kettridge, N.; Lukenbach, M.; Mendoza, C. A.; Moore, P.; Peters, D.; Silins, U.

2017-12-01

We examined runoff in 20 catchments (50 to 50000 km2) over a 25 year wet and dry climate cycle to understand temporal and spatial thresholds in runoff generation responses in the water limited, glaciated continental Boreal Plains (BP) eco-region of Western Canada. Annual runoff ranged over 3 orders of magnitude (<3 mm to >300 mm/year) but was poorly correlated with annual precipitation. A threshold relationship was observed with multi-year cumulative moisture deficit (CMD) that reflected temporal and spatial differences in effective storage, antecedent moisture state and hydrologic connectivity among catchments with differing portions of land-cover (e.g. wetland vs. forestland) and glacial-deposit types. During dry states (CMD< -200 mm), catchment annual low flow ranged by over one order of magnitude (2 to 80 mm/yr), and increased with percent area of coarse textured deposits. In fine textured catchments, runoff was only observed in catchments with >30% wetland area. During mesic conditions (CMD 0 mm), runoff remained very low in catchments with large proportions of forests and poorly connected open water depressions associated with fine-textured moraines. Runoff was positively correlated with percent peatland area, suggesting that peatland networks were the primary source areas of surface water to regional runoff. During the infrequent wet states (CMD > 200 mm) of the study period, runoff coefficients were similar among all catchments indicating that both forests and peatlands contributed to catchment runoff. . Rather than estimating regional runoff from topographic drainage networks, integrating CMD with the classification of catchments based on land-cover configuration and glacial-deposit type can: 1) better represent water cycling and regional sink-source dynamics controlling regional runoff, and 2) provide an effective management framework for predicting climate and land-use impacts on regional runoff in low relief glacial landscapes such as the Boreal Plain.

Late Pliocene-Early Pleistocene oscillations in Mediterranean Overflow water: a new perspective from the Iberian Margin

NASA Astrophysics Data System (ADS)

Alonso-Garcia, M.; Salgueiro, E.; Rodrigues, T.; Alvarez Zarikian, C. A.; Kuhnert, H.; Roehl, U.; Voelker, A. H. L.; Sierro, F. J.; Abrantes, F. F. G.

2016-12-01

During the Late Pliocene to the Early Pleistocene the Earth experienced a transition from the warm Pliocene climate, with high greenhouse gases concentrations, to a colder climate with significant expansion of ice-sheets in the Northern Hemisphere and alternation between glacial and interglacial periods. Several hypotheses have been put forward to explain this climate transition, and recently, the enhancement of the Mediterranean Overflow Water (MOW) was suggested to have played a major role since it contributes high salinity water to the North Atlantic. Sedimentary records from the last glacial cycle and modelling experiments evidenced this link and suggested that the MOW injection of salty water to intermediate depths may have enhanced the upper branch of NADW, which ultimately reinvigorated the whole Atlantic Meridional overturning circulation. Here we present sedimentological and paleontological data from Site U1391 (37° N; 9° W; 1085 m water depth), recovered on the Southwest Iberian Margin during the Integrated Ocean Drilling Program (IODP) Expedition 339. This site is located in a plastered drift in the path of the MOW and offers high sedimentation rates to perform high resolution studies of past climatic and oceanographic conditions. In this study, we combined XRF geochemical data (from X-ray fluorescence core scanning) with grain-size, benthic foraminifer δ18O and δ13C, and ostracod records to reconstruct deep water circulation and climatic conditions during the Plio-Pleistocene transition. The high-resolution record of the XRF analysis indicates a switch in the response of MOW to climate changes across this transition. Early Pleistocene glacial-interglacial cycles show a stronger coupling between MOW oscillations (as indicated by the Zr/Al ratio) and sea surface temperature conditions (as indicated by the Ca/Ti ratio).

The Search for Eight Glacial Cycles of Deep-Water Temperatures and Global ice Volume From the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Ferretti, P.; Elderfield, H.; Greaves, M.; McCave, N.

2007-12-01

It has been recently suggested "a substantial portion of the marine 100-ky cycle that has been object of so much attention over the past quarter of a century is, in reality, a deep-water temperature signal and not an ice volume signal" (Shackleton, 2000). There are currently few records available of deep-water temperature variations during the Pleistocene and most of our understanding is inferred from the oxygen isotopic composition (δ18O) of benthic foraminifera from deep-sea sediments. However, variations in benthic δ18O reflect some combination of local to regional changes in water mass properties (largely deep- water temperature) as well as global changes in seawater δ18O (δ18Osw) resulting from the growth and decay of continental ice. Recent studies suggest that benthic foraminiferal Mg/Ca may be useful in reconstructing deep-water temperature changes, but the application of this method to benthic species has been hampered by a number of unresolved issues, such as uncertainties related to the calibration for benthic Mg at the coldest temperatures. Here we present deep-sea Mg/Ca and δ18O records for the past eight glacial cycles in benthic foraminiferal ( Uvigerina spp.) calcite from a marine sediment core recovered in the mid Southern latitudes. Ocean Drilling Program Site 1123 was retrieved from Chatham Rise, east of New Zealand in the Southwest Pacific Ocean (3290 m water depth). This site lies under the Deep Western Boundary Current (DWBC) that flows into the Pacific Ocean, and is responsible for most of the deep water in that ocean; DWBC strength is directly related to processes occurring around Antarctica. Temperatures derived via pore fluid modeling of the last glacial maximum are available from Site 1123 and represent an important tool to constrain deep-water temperatures estimates using Mg/Ca. In selected time slices, we measured B/Ca ratios in Uvigerina in order to gain information on the deep-water carbonate saturation state and have data of Mg/Ca and B/Ca on planktonic species, which also provides evidence on carbonate saturation state. These results permit preliminary discussion of the magnitude of the deep-water temperature changes during glacial/interglacial transitions and the interglacials themselves. In particular, our deep-water temperature estimates confirm that interglacial stages before 430 ka were characterized by less pronounced warmth - at least in the deeper southern Pacific - than those of the past four climatic cycles, a pattern previously observed in the deuterium record from EPICA Dome C. We examine the relative contributions of deep-water temperature and ice volume to the benthic δ18O signal. The phase relationship between the two signals is tentatively assessed for the middle/late Pleistocene, when different patterns of climate variability have been inferred from marine and ice cores records.

The impact of Last Glacial climate variability in west-European loess revealed by radiocarbon dating of fossil earthworm granules.

PubMed

Moine, Olivier; Antoine, Pierre; Hatté, Christine; Landais, Amaëlle; Mathieu, Jérôme; Prud'homme, Charlotte; Rousseau, Denis-Didier

2017-06-13

The characterization of Last Glacial millennial-timescale warming phases, known as interstadials or Dansgaard-Oeschger events, requires precise chronologies for the study of paleoclimate records. On the European continent, such chronologies are only available for several Last Glacial pollen and rare speleothem archives principally located in the Mediterranean domain. Farther north, in continental lowlands, numerous high-resolution records of loess and paleosols sequences show a consistent environmental response to stadial-interstadial cycles. However, the limited precision and accuracy of luminescence dating methods commonly used in loess deposits preclude exact correlations of paleosol horizons with Greenland interstadials. To overcome this problem, a radiocarbon dating protocol has been developed to date earthworm calcite granules from the reference loess sequence of Nussloch (Germany). Its application yields a consistent radiocarbon chronology of all soil horizons formed between 47 and 20 ka and unambiguously shows the correlation of every Greenland interstadial identified in isotope records with specific soil horizons. Furthermore, eight additional minor soil horizons dated between 27.5 and 21 ka only correlate with minor decreases in Greenland dust records. This dating strategy reveals the high sensitivity of loess paleoenvironments to Northern Hemisphere climate changes. A connection between loess sedimentation rate, Fennoscandian ice sheet dynamics, and sea level changes is proposed. The chronological improvements enabled by the radiocarbon "earthworm clock" thus strongly enhance our understanding of loess records to a better perception of the impact of Last Glacial climate changes on European paleoenvironments.

The role of glacial cycles in promoting genetic diversity in the Neotropics: the case of cloud forests during the Last Glacial Maximum

PubMed Central

Ramírez-Barahona, Santiago; Eguiarte, Luis E

2013-01-01

The increasing aridity during the Last Glacial Maximum (LGM) has been proposed as a major factor affecting Neotropical species. The character and intensity of this change, however, remains the subject of ongoing debate. This review proposes an approach to test contrasting paleoecological hypotheses by way of their expected demographic and genetic effects on Neotropical cloud forest species. We reviewed 48 paleoecological records encompassing the LGM in the Neotropics. The records show contrasting evidence regarding the changes in precipitation during this period. Some regions remained fairly moist and others had a significantly reduced precipitation. Many paleoecological records within the same region show apparently conflicting evidence on precipitation and forest stability. From these data, we propose and outline two demographic/genetic scenarios for cloud forests species based on opposite precipitation regimes: the dry refugia and the moist forests hypotheses. We searched for studies dealing with the population genetic structure of cloud forest and other montane taxa and compared their results with the proposed models. To date, the few available molecular studies show insufficient genetic evidence on the predominance of glacial aridity in the Neotropics. In order to disentangle the climatic history of the Neotropics, the present study calls for a general multi-disciplinary approach to conduct future phylogeographic studies. Given the contradictory paleoecological information, population genetic data on Neotropical cloud forest species should be used to explicitly test the genetic consequences of competing paleoecological models. PMID:23531632

Abrupt changes of intermediate water properties on the northeastern slope of the Bering Sea during the last glacial and deglacial period

NASA Astrophysics Data System (ADS)

Rella, Stephan F.; Tada, Ryuji; Nagashima, Kana; Ikehara, Minoru; Itaki, Takuya; Ohkushi, Ken'ichi; Sakamoto, Tatsuhiko; Harada, Naomi; Uchida, Masao

2012-09-01

Millennial-scale variability in the behavior of North Pacific Intermediate Water during the last glacial and deglacial period, and its association with Dansgaard-Oeschger (D-O) cycles and Heinrich events, are examined based on benthic foraminiferal oxygen and carbon isotopes (δ18Obf and δ13Cbf) and %CaCO3 using a sediment core recovered from the northeastern slope of the Bering Sea. A suite of positive δ18Obf excursions at intermediate depths of the Bering Sea, which seem at least in part associated with increases in the δ18Obf gradients between the Bering and Okhotsk Seas, suggest the Bering Sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period. Absence of such δ18Obf gradients during periods of high surface productivity in the Bering and Okhotsk Seas, which we correlate to D-O interstadials, suggests a reduction in intermediate water production in the Bering Sea and subsequent introduction of nutrient-rich deep waters from the North Pacific into intermediate depths of the Bering Sea. We argue that a reorganization of atmospheric circulation in the high-latitude North Pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern Bering Sea. The resulting salinity increase in the cold surface waters could have initiated intermediate (and deep) water formation that spread out to the North Pacific.

Biological Oxygen Productivity Over The Last Glacial Termination From Triple Oxygen Isotope Measurements

NASA Astrophysics Data System (ADS)

Blunier, T.; Bender, M. L.; Hendricks, M. B.

The atmospheric oxygen isotope signature of O2 is linked to the oxygen signature of seawater through photosynthesis and respiration. Fractionation during these pro- cesses is mass dependent affecting 17O about half as much as 18O. A mass indepen- dent fractionation process takes place during isotope exchange between O2 and CO2 in the stratosphere (Thiemens, 1999; Luz et al., 1999). The magnitude of the mass- independent anomaly in the triple isotope composition of O2 depends on relative rates of biological O2 cycling and photochemical reactions in the stratosphere. Variations of this anomaly thus allows us to estimate changes of mass dependent O2 production by photosynthesis versus mass independent O2-CO2 exchange in the stratosphere. We reconstruct total oxygen productivity for the past from 17O and 18O measure- ments of O2 trapped in ice cores. With a box model we estimate that the total biogenic productivity was only 76-83 % of today for the glacial and was probably still lower than today during the glacial-interglacial transition and the early Holocene. In principle we can calculate the oxygen flux from the ocean biosphere if we know the oxygen flux from the land biosphere. Calculated ocean production is very sensitive to the estimate of land biosphere production. The latter term remains uncertain, however, and we can presently only constrain glacial ocean production to 88 to 140 % of the present value.

Greenland's glacial fjords and their role in regional biogeochemical dynamics.

NASA Astrophysics Data System (ADS)

Crosby, J.; Arndt, S.

2017-12-01

Greenland's coastal fjords serve as important pathways that connect the Greenland Ice Sheet (GrIS) and the surrounding oceans. They export seasonal glacial meltwater whilst being significant sites of primary production. These fjords are home to some of the most productive ecosystems in the world and possess high socio-economic value via fisheries. A growing number of studies have proposed the GrIS as an underappreciated yet significant source of nutrients to surrounding oceans. Acting as both transfer routes and sinks for glacial nutrient export, fjords have the potential to act as significant biogeochemical processors, yet remain underexplored. Critically, an understanding of the quantitative contribution of fjords to carbon and nutrient budgets is lacking, with large uncertainties associated with limited availability of field data and the lack of robust upscaling approaches. To close this knowledge gap we developed a coupled 2D physical-biogeochemical model of the Godthåbsfjord system, a sub-Arctic sill fjord in southwest Greenland, to quantitatively assess the impact of nutrients exported from the GrIS on fjord primary productivity and biogeochemical dynamics. Glacial meltwater is found to be a key driver of fjord-scale circulation patterns, whilst tracer simulations reveal the relative nutrient contributions from meltwater-driven upwelling and meltwater export from the GrIS. Hydrodynamic circulation patterns and freshwater transit times are explored to provide a first understanding of the glacier-fjord-ocean continuum, demonstrating the complex pattern of carbon and nutrient cycling at this critical land-ocean interface.

The impact of Last Glacial climate variability in west-European loess revealed by radiocarbon dating of fossil earthworm granules

PubMed Central

Moine, Olivier; Antoine, Pierre; Hatté, Christine; Landais, Amaëlle; Mathieu, Jérôme; Prud’homme, Charlotte

2017-01-01

The characterization of Last Glacial millennial-timescale warming phases, known as interstadials or Dansgaard–Oeschger events, requires precise chronologies for the study of paleoclimate records. On the European continent, such chronologies are only available for several Last Glacial pollen and rare speleothem archives principally located in the Mediterranean domain. Farther north, in continental lowlands, numerous high-resolution records of loess and paleosols sequences show a consistent environmental response to stadial–interstadial cycles. However, the limited precision and accuracy of luminescence dating methods commonly used in loess deposits preclude exact correlations of paleosol horizons with Greenland interstadials. To overcome this problem, a radiocarbon dating protocol has been developed to date earthworm calcite granules from the reference loess sequence of Nussloch (Germany). Its application yields a consistent radiocarbon chronology of all soil horizons formed between 47 and 20 ka and unambiguously shows the correlation of every Greenland interstadial identified in isotope records with specific soil horizons. Furthermore, eight additional minor soil horizons dated between 27.5 and 21 ka only correlate with minor decreases in Greenland dust records. This dating strategy reveals the high sensitivity of loess paleoenvironments to Northern Hemisphere climate changes. A connection between loess sedimentation rate, Fennoscandian ice sheet dynamics, and sea level changes is proposed. The chronological improvements enabled by the radiocarbon “earthworm clock” thus strongly enhance our understanding of loess records to a better perception of the impact of Last Glacial climate changes on European paleoenvironments. PMID:28559353

The geologic records of dust in the Quaternary

USGS Publications Warehouse

Muhs, Daniel R.

2013-01-01

Study of geologic records of dust composition, sources and deposition rates is important for understanding the role of dust in the overall planetary radiation balance, fertilization of organisms in the world’s oceans, nutrient additions to the terrestrial biosphere and soils, and for paleoclimatic reconstructions. Both glacial and non-glacial processes produce fine-grained particles that can be transported by the wind. Geologic records of dust flux occur in a number of depositional archives for sediments: (1) loess deposits; (2) lake sediments; (3) soils; (4) deep-ocean basins; and (5) ice sheets and smaller glaciers. These archives have several characteristics that make them highly suitable for understanding the dynamics of dust entrainment, transport, and deposition. First, they are often distributed over wide geographic areas, which permits reconstruction of spatial variation of dust flux. Second, a number of dating methods can be applied to sediment archives, which allows identification of specific periods of greater or lesser dust flux. Third, aeolian sediment particle size and composition can be determined so that dust source areas can be ascertained and dust transport pathways can be reconstructed. Over much of the Earth’s surface, dust deposition rates were greater during the last glacial period than during the present interglacial period. A dustier Earth during glacial periods is likely due to increased source areas, greater aridity, less vegetation, lower soil moisture, possibly stronger winds, a decreased intensity of the hydrologic cycle, and greater production of dust-sized particles from expanded ice sheets and glaciers.

A biomarker record of temperature and phytoplankton community in Okinawa Trough since the last glacial maximum

NASA Astrophysics Data System (ADS)

Ruan, Jiaping

2017-04-01

A variety of biomarkers were examined from Ocean Drilling Program (ODP) core 1202B to reconstruct temperature and phytoplankton community structures in the southern Okinawa Trough for the past ca. 20000 years. Two molecular temperature proxies (Uk37 and TEX86) show 5-6 ℃ warming during the glacial/interglacial transition. Prior to the Holocene, the Uk37-derived temperature was generally 1-4 ℃ higher than TEX86-derived temperature. This difference, however, was reduced to <1 ℃ in the Holocene when the Kuroshio Current was intensified. Correspondingly, the phytoplankton biomarkers (e.g., C37:2 alkenone, brassicasterol, C30 1,15-diols and dinosterol) suggest a shift of planktonic community assemblages with coccolithophorids becoming more abundant in the Holocene at the expense of diatoms/dinoflagellates. Such a shift is related to the variability of nutrient, temperature and salinity in the Okinawa Trough, controlled by the sea level and the intensity of Kuroshio Current. The phytoplankton community change may have profound implications on atmospheric CO2 fluctuations during glacial/interglacial cycles since diatoms and dinoflagellates have a higher efficiency of biological pump than coccolithophorids.

Loess sedimentation in Tibet: provenance, processes, and link with Quaternary glaciations

USGS Publications Warehouse

Sun, Jielun; Li, S.-H.; Muhs, D.R.; Li, B.

2007-01-01

Well-preserved loess deposits are found on the foothills of mountains along the middle reaches of the Yarlung Zangbo River in southern Tibet. Optically stimulated luminescence (OSL) dating is used to determine loess ages by applying the single-aliquot regeneration technique. Geochemical, mineralogical, and granulometric measurements were carried out to allow a comparison between loess from Tibet and the Chinese Loess Plateau. Our results demonstrate that (i) the loess deposits have a basal age of 13-11 ka, suggesting they accumulated after the last deglaciation, (ii) loess in southern Tibet has a "glacial" origin, resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near-surface winds, and (iii) the present loess in the interior of Tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt. The lack of full-glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial. Such processes would have been repeated during each glacial-interglacial cycle of the Quaternary. ?? 2007 Elsevier Ltd. All rights reserved.

Late glacial ice advances in the Strait of Magellan, Southern Chile

NASA Astrophysics Data System (ADS)

Mcculloch, Robert D.; Bentley, Michael J.

During the last glacial cycle low gradient glaciers repeatedly drained north-eastward into the Strait of Magellan and dammed extensive proglacial lakes in the central section of the strait. This paper focuses on the two most recent glacial advances in the strait, culminating over 150 and 80 km from the present ice limits. The timing of the first of the two advances has, up to now, been ambiguous and depended on the interpretation of anomously older dates of 16,590-15,800 yr BP for deglaciation at Puerto del Hambre. Here, we show there is evidence from seismic data and truncated shorelines that the Puerto del Hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation. Several other dates show that the advance occurred sometime before 14,260 yr BP. The timing of the second advance has been investigated using a refined tephrochronology for the region, which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit. 14C dating of peat and a key tephra layer, above and below the glaciolacustrine deposits, respectively suggest that the advance culminated in the Strait of Magellan between 12,010 and 10,050 yr BP.

King penguin demography since the last glaciation inferred from genome-wide data.

PubMed

Trucchi, Emiliano; Gratton, Paolo; Whittington, Jason D; Cristofari, Robin; Le Maho, Yvon; Stenseth, Nils Chr; Le Bohec, Céline

2014-07-22

How natural climate cycles, such as past glacial/interglacial patterns, have shaped species distributions at the high-latitude regions of the Southern Hemisphere is still largely unclear. Here, we show how the post-glacial warming following the Last Glacial Maximum (ca 18 000 years ago), allowed the (re)colonization of the fragmented sub-Antarctic habitat by an upper-level marine predator, the king penguin Aptenodytes patagonicus. Using restriction site-associated DNA sequencing and standard mitochondrial data, we tested the behaviour of subsets of anonymous nuclear loci in inferring past demography through coalescent-based and allele frequency spectrum analyses. Our results show that the king penguin population breeding on Crozet archipelago steeply increased in size, closely following the Holocene warming recorded in the Epica Dome C ice core. The following population growth can be explained by a threshold model in which the ecological requirements of this species (year-round ice-free habitat for breeding and access to a major source of food such as the Antarctic Polar Front) were met on Crozet soon after the Pleistocene/Holocene climatic transition. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Relationship between dissolved organic matter quality and microbial community composition across polar glacial environments.

PubMed

Smith, H J; Dieser, M; McKnight, D M; SanClements, M D; Foreman, C M

2018-05-14

Vast expanses of Earth's surface are covered by ice, with microorganisms in these systems affecting local and global biogeochemical cycles. We examined microbial assemblages from habitats fed by glacial meltwater within the McMurdo Dry Valleys, Antarctica, and on the west Greenland Ice Sheet, (GrIS) evaluating potential physicochemical factors explaining trends in community structure. Microbial assemblages present in the different Antarctic dry valley habitats were dominated by Sphingobacteria and Flavobacteria, while Gammaproteobacteria and Sphingobacteria prevailed in west GrIS supraglacial environments. Microbial assemblages clustered by location (Canada Glacier, Cotton Glacier, west GrIS) and were separated by habitat type (i.e. ice, cryoconite holes, supraglacial lakes, sediment, and stream water). Community dissimilarities were strongly correlated with dissolved organic matter (DOM) quality. Microbial meltwater assemblages were most closely associated with different protein-like components of the DOM pool. Microbes in environments with mineral particles (i.e. stream sediments, cryoconite holes) were linked to DOM containing more humic-like fluorescence. Our results demonstrate the establishment of distinct microbial communities within ephemeral glacial meltwater habitats, with DOM-microbe interactions playing an integral role in shaping communities on local and polar spatial scales.

Iron solubility driven by speciation in dust sources to the ocean

USGS Publications Warehouse

Schroth, A.W.; Crusius, John; Sholkovitz, E.R.; Bostick, B.C.

2009-01-01

Although abundant in the Earths crust, iron is present at trace concentrations in sea water and is a limiting nutrient for phytoplankton in approximately 40% of the ocean. Current literature suggests that aerosols are the primary external source of iron to offshore waters, yet controls on iron aerosol solubility remain unclear. Here we demonstrate that iron speciation (oxidation state and bonding environment) drives iron solubility in arid region soils, glacial weathering products (flour) and oil combustion products (oil fly ash). Iron speciation varies by aerosol source, with soils in arid regions dominated by ferric (oxy)hydroxides, glacial flour by primary and secondary ferrous silicates and oil fly ash by ferric sulphate salts. Variation in iron speciation produces systematic differences in iron solubility: less than 1% of the iron in arid soils was soluble, compared with 2-3% in glacial products and 77-81% in oil combustion products, which is directly linked to fractions of more soluble phases. We conclude that spatial and temporal variations in aerosol iron speciation, driven by the distribution of deserts, glaciers and fossil-fuel combustion, could have a pronounced effect on aerosol iron solubility and therefore on biological productivity and the carbon cycle in the ocean. ?? 2009 Macmillan Publishers Limited.

Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene?

PubMed

Marshall, Jill A; Roering, Joshua J; Bartlein, Patrick J; Gavin, Daniel G; Granger, Darryl E; Rempel, Alan W; Praskievicz, Sarah J; Hales, Tristram C

2015-11-01

Understanding climatic influences on the rates and mechanisms of landscape erosion is an unresolved problem in Earth science that is important for quantifying soil formation rates, sediment and solute fluxes to oceans, and atmospheric CO2 regulation by silicate weathering. Glaciated landscapes record the erosional legacy of glacial intervals through moraine deposits and U-shaped valleys, whereas more widespread unglaciated hillslopes and rivers lack obvious climate signatures, hampering mechanistic theory for how climate sets fluxes and form. Today, periglacial processes in high-elevation settings promote vigorous bedrock-to-regolith conversion and regolith transport, but the extent to which frost processes shaped vast swaths of low- to moderate-elevation terrain during past climate regimes is not well established. By combining a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction derived from a paleo-Earth System Model, paleovegetation data, and a paleoerosion archive, we propose that frost-driven sediment production was pervasive during the LGM in our unglaciated Pacific Northwest study site, coincident with a 2.5 times increase in erosion relative to modern rates. Our findings provide a novel framework to quantify how climate modulates sediment production over glacial-interglacial cycles in mid-latitude unglaciated terrain.

Glacial magnetite dissolution in abyssal NW Pacific sediments - evidence for carbon trapping?

NASA Astrophysics Data System (ADS)

Korff, Lucia; von Dobeneck, Tilo; Frederichs, Thomas; Kasten, Sabine; Kuhn, Gerhard; Gersonde, Rainer; Diekmann, Bernhard

2016-04-01

The abyssal North Pacific Ocean's large volume, depth, and terminal position on the deep oceanic conveyor make it a candidate site for deep carbon trapping as postulated by climate theory to explain the massive glacial drawdown of atmospheric CO2. As the major basins of the North Pacific have depths of 5500-6500m, far below the modern and glacial Calcite Compensation Depths (CCD), these abyssal sediments are carbonate-free and therefore not suitable for carbonate-based paleoceanographic proxy reconstructions. Instead, paleo-, rock and environmental magnetic methods are generally well applicable to hololytic abyssal muds and clays. In 2009, the international paleoceanographic research cruise SO 202 INOPEX ('Innovative North Pacific Experiment') of the German RV SONNE collected two ocean-spanning EW sediment core transects of the North Pacific and Bering Sea recovering a total of 50 piston and gravity cores from 45 sites. Out of seven here considered abyssal Northwest Pacific piston cores collected at water depths of 5100 to 5700m with mostly coherent shipboard susceptibility logs, the 20.23m long SO202-39-3, retrieved from 5102 m water depth east of northern Shatsky Rise (38°00.70'N, 164°26.78'E), was rated as the stratigraphically most promising record of the entire core transect and selected for detailed paleo- and environmental magnetic, geochemical and sedimentological investigations. This core was dated by correlating its RPI and Ba/Ti records to well-dated reference records and obviously provides a continuous sequence of the past 940 kyrs. The most striking orck magnetic features are coherent magnetite-depleted zones corresponding to glacial periods. In the interglacial sections, detrital, volcanic and even submicron bacterial magnetite fractions are excellently preserved. These alternating magnetite preservation states seem to reflect dramatic oxygenation changes in the deep North Pacific Ocean and hint at large-scale benthic glacial carbon trapping followed by subsequent interglacial carbon burn-down and CO2 release. Abyssal Northwest Pacific sediments may have served as glacial carbon reservoir in particular since the onset of systematic 100 kyr ice age cycles at the end of the Mid-Pleistocene transition (MPT). Stagnant glacial Antarctic Bottom Water, which expanded primarily into abyssal South Atlantic basins during the MPT interim phase, thereafter seemed to flow preferentially into the deeper and larger abyssal Indo-Pacific basins, where it may have enabled more efficient carbon-trapping. More intensive scavenging of the Northwest Pacific surface ocean by enhanced glacial Asian dust flux is suggested by parallel TOC and quartz contents, enhancing glacial carbon accumulation despite potentially lower export production. The magnetic records also identify numerous partly consistent tephra layers, which can be matched between most records of the core transect.

Glaciation and regional ground-water flow in the Fennoscandian Shield: Site 94

USGS Publications Warehouse

Provost, Alden M.; Voss, Clifford I.; Neuzil, C.E.

1998-01-01

Results from a regional-scale ground-water flow model of the Fennoscandian shield suggest that ground-water flow is strongly affected by surface conditions associated with climatic change and glaciation. The model was used to run a series of numerical simulations of variable-density ground-water flow in a 1500-km-long and approximately 10-km-deep cross-section that passes through southern Sweden. Ground-water flow and shield brine transport in the cross-sectional model are controlled by an assumed time evolution of surface conditions over the next 140 ka. Simulations show that, under periglacial conditions, permafrost may locally or extensively impede the free recharge or discharge of ground water. Below cold-based glacial ice, no recharge or discharge of ground water occurs. Both of these conditions result in the settling of shield brine and consequent freshening of near-surface water in areas of natural discharge blocked by permafrost. The presence of warm-based ice with basal melting creates a potential for ground-water recharge rates much larger than under present, ice-free conditions. Recharging basal meltwater can reach depths of a few kilometers in a few thousand years. The vast majority of recharged water is accommodated through storage in the volume of bedrock below the local area of recharge; regional (lateral) redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (~10 ka). During glacial retreat, the weight of the ice overlying a given surface location decreases, and significant upward flow of ground water may occur below the ice sheet due to pressure release, despite the continued potential for recharge of basal meltwater. Excess meltwater must exit from below the glacier through subglacial cavities and channels. Subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are greatest if the loading efficiency of the shield rock is low. The maximum rate of ground-water discharge occurs at the receding ice margin, and some discharge occurs below incursive post-glacial seas. The simulation results suggest that vertical movement of deep shield brines induced by the next few glacial cycles should not increase the concentration of dissolved solids significantly above present-day levels. However, the concentration of dissolved solids should decrease significantly at depths of up to several kilometers during periods of glacial meltwater recharge. The meltwater may reside in the subsurface for periods exceeding 10 ka and may bring oxygenated conditions to an otherwise reducing chemical environment.

Palaeovegetation. Diversity of temperate plants in east Asia.

PubMed

Harrison, S P; Yu, G; Takahara, H; Prentice, I C

2001-09-13

The exceptionally broad species diversity of vascular plant genera in east Asian temperate forests, compared with their sister taxa in North America, has been attributed to the greater climatic diversity of east Asia, combined with opportunities for allopatric speciation afforded by repeated fragmentation and coalescence of populations through Late Cenozoic ice-age cycles. According to Qian and Ricklefs, these opportunities occurred in east Asia because temperate forests extended across the continental shelf to link populations in China, Korea and Japan during glacial periods, whereas higher sea levels during interglacial periods isolated these regions and warmer temperatures restricted temperate taxa to disjunct refuges. However, palaeovegetation data from east Asia show that temperate forests were considerably less extensive than today during the Last Glacial Maximum, calling into question the coalescence of tree populations required by the hypothesis of Qian and Ricklefs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Zeli; Zhuang, Qianlai; Shurpali, Narasinha J.

Recent studies indicated that Arctic lakes play an important role in receiving, processing, and storing organic carbon exported from terrestrial ecosystems. To quantify the contribution of Arctic lakes to the global carbon cycle, we developed a one-dimensional process-based Arctic Lake Biogeochemistry Model (ALBM) that explicitly simulates the dynamics of organic and inorganic carbon in Arctic lakes. By realistically modeling water mixing, carbon biogeochemistry, and permafrost carbon loading, the model can reproduce the seasonal variability of CO 2 fluxes from the study Arctic lakes. The simulated area-weighted CO 2 fluxes from yedoma thermokarst lakes, nonyedoma thermokarst lakes, and glacial lakes aremore » 29.5, 13.0, and 21.4 g C m -2 yr -1, respectively, close to the observed values (31.2, 17.2, and 16.5 ± 7.7 g C m -2 yr -1, respectively). The simulations show that the high CO 2 fluxes from yedoma thermokarst lakes are stimulated by the biomineralization of mobilized labile organic carbon from thawing yedoma permafrost. The simulations also imply that the relative contribution of glacial lakes to the global carbon cycle could be the largest because of their much larger surface area and high biomineralization and carbon loading. According to the model, sunlight-induced organic carbon degradation is more important for shallow nonyedoma thermokarst lakes but its overall contribution to the global carbon cycle could be limited. Overall, the ALBM can simulate the whole-lake carbon balance of Arctic lakes, a difficult task for field and laboratory experiments and other biogeochemistry models.« less

Mode change of millennial CO2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

PubMed Central

Bereiter, Bernhard; Lüthi, Dieter; Siegrist, Michael; Schüpbach, Simon; Stocker, Thomas F.; Fischer, Hubertus

2012-01-01

Important elements of natural climate variations during the last ice age are abrupt temperature increases over Greenland and related warming and cooling periods over Antarctica. Records from Antarctic ice cores have shown that the global carbon cycle also plays a role in these changes. The available data shows that atmospheric CO2 follows closely temperatures reconstructed from Antarctic ice cores during these variations. Here, we present new high-resolution CO2 data from Antarctic ice cores, which cover the period between 115,000 and 38,000 y before present. Our measurements show that also smaller Antarctic warming events have an imprint in CO2 concentrations. Moreover, they indicate that during Marine Isotope Stage (MIS) 5, the peak of millennial CO2 variations lags the onset of Dansgaard/Oeschger warmings by 250 ± 190 y. During MIS 3, this lag increases significantly to 870 ± 90 y. Considerations of the ocean circulation suggest that the millennial variability associated with the Atlantic Meridional Overturning Circulation (AMOC) undergoes a mode change from MIS 5 to MIS 4 and 3. Ocean carbon inventory estimates imply that during MIS 3 additional carbon is derived from an extended mass of carbon-enriched Antarctic Bottom Water. The absence of such a carbon-enriched water mass in the North Atlantic during MIS 5 can explain the smaller amount of carbon released to the atmosphere after the Antarctic temperature maximum and, hence, the shorter lag. Our new data provides further constraints for transient coupled carbon cycle-climate simulations during the entire last glacial cycle. PMID:22675123

Mode change of millennial CO2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw.

PubMed

Bereiter, Bernhard; Lüthi, Dieter; Siegrist, Michael; Schüpbach, Simon; Stocker, Thomas F; Fischer, Hubertus

2012-06-19

Important elements of natural climate variations during the last ice age are abrupt temperature increases over Greenland and related warming and cooling periods over Antarctica. Records from Antarctic ice cores have shown that the global carbon cycle also plays a role in these changes. The available data shows that atmospheric CO(2) follows closely temperatures reconstructed from Antarctic ice cores during these variations. Here, we present new high-resolution CO(2) data from Antarctic ice cores, which cover the period between 115,000 and 38,000 y before present. Our measurements show that also smaller Antarctic warming events have an imprint in CO(2) concentrations. Moreover, they indicate that during Marine Isotope Stage (MIS) 5, the peak of millennial CO(2) variations lags the onset of Dansgaard/Oeschger warmings by 250 ± 190 y. During MIS 3, this lag increases significantly to 870 ± 90 y. Considerations of the ocean circulation suggest that the millennial variability associated with the Atlantic Meridional Overturning Circulation (AMOC) undergoes a mode change from MIS 5 to MIS 4 and 3. Ocean carbon inventory estimates imply that during MIS 3 additional carbon is derived from an extended mass of carbon-enriched Antarctic Bottom Water. The absence of such a carbon-enriched water mass in the North Atlantic during MIS 5 can explain the smaller amount of carbon released to the atmosphere after the Antarctic temperature maximum and, hence, the shorter lag. Our new data provides further constraints for transient coupled carbon cycle-climate simulations during the entire last glacial cycle.

Reconstructing dust fluxes and paleoproductivity at the southern Agulhas Plateau since MIS-6

NASA Astrophysics Data System (ADS)

Frenkel, M. M.; Anderson, R. F.; Winckler, G.

2017-12-01

Understanding the mechanisms underlying glacial-interglacial cycles requires characterizing the role of oceanic feedbacks in climatic changes. For example, increased aeolian iron fluxes to Fe-limited regions of the ocean and corresponding changes in marine productivity could have improved biological pump efficiency and resulted in CO2 drawdown. Here we explore these feedbacks using marine sediment core MDO2-2588 collected from the southern Agulhas Plateau (SAP; 41°S, 26°E), located beneath the modern subtropical front. Today, diatom productivity in this region is Si-limited because high Si utilization south of the polar front (PF) means that water advected northward to our study site is Si-depleted. However, previous work has suggested that extended sea ice cover during glacial periods may have limited diatom productivity south of the PF while frontal systems shifted northward, allowing more Si to reach thermocline of the SAP. Meanwhile, increased glacial dust flux to the SAP may have simultaneously supplied more Fe, contributing to higher glacial productivity. This hypothesis has been supported by observations of higher LGM and MIS-6 productivity at MD02-2588 using bulk biogenic content and diatom assemblages (Romero et al., Paleoceanography, 30 (2015) 118-132). Gradients in d13C between benthic and planktic foraminifera have also been used to support Fe fertilization at this site on millennial timescales (Ziegler et al., Nature Geoscience, 6 (2013) 457-461). Yet, studies have yet to produce coordinated records of dust flux and export production for the SAP. Here, we present records of dust, based on 230Th-normalized 232Th fluxes, and export production using 230Th-normalized excess-Ba and opal fluxes and authigenic U through MIS-6. Preliminary results show that lithogenic fluxes to MD02-2588 were approximately twice as high during MIS-6 as MIS-5e and were concurrent with a two-fold increase in excess-Ba flux. However, this relative increase in lithogenic flux during glacials is smaller than the four-fold relative increase in glacial dust flux previously observed in the central South Atlantic (Martínez-García et al., Science, 343 (2014) 1347-1350), motivating future work to study how dust and productivity vary along a zonal transect away from a dust source between glacial and interglacial periods.

Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hu, Rong; Piotrowski, Alexander M.; Bostock, Helen C.; Crowhurst, Simon; Rennie, Victoria

2016-08-01

The deep Pacific Ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales. The circulation of the deep Pacific during the Last Glacial Maximum (LGM), however, is not well understood. Neodymium (Nd) isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography. In this study, we present Nd isotope compositions (εNd) of planktonic foraminifera for the Holocene and the LGM obtained from 55 new sites widely distributed in the Pacific Ocean. The Holocene planktonic foraminiferal εNd results agree with the proximal seawater data, indicating that they provide a reliable record of modern bottom water Nd isotopes in the deep Pacific. There is a good correlation between foraminiferal εNd and seawater phosphate concentrations (R2 = 0.80), but poorer correlation with silicate (R2 = 0.37). Our interpretation is that the radiogenic Nd isotope is added to the deep open Pacific through particle release from the upper ocean during deep water mass advection and aging. The data thus also imply the Nd isotopes in the Pacific are not likely to be controlled by silicate cycling. In the North Pacific, the glacial Nd isotopic compositions are similar to the Holocene values, indicating that the Nd isotope composition of North Pacific Deep Water (NPDW) remained constant (-3.5 to -4). During the LGM, the southwest Pacific cores throughout the water column show higher εNd corroborating previous studies which suggested a reduced inflow of North Atlantic Deep Water to the Pacific. However, the western equatorial Pacific deep water does not record a corresponding radiogenic excursion, implying reduced radiogenic boundary inputs during the LGM probably due to a shorter duration of seawater-particle interaction in a stronger glacial deep boundary current. A significant negative glacial εNd excursion is evident in mid-depth (1-2 km) cores of the eastern equatorial Pacific (EEP) which may suggest a stronger influence of NPDW return flow to the core sites and decreased local input in the EEP. Taken together, our Nd records do not support a dynamically slower glacial Pacific overturning circulation, and imply that the increased carbon inventory of Pacific deep water might be due to poor high latitude air-sea exchange and increased biological pump efficiency in glacial times.

Wolfgang Schott (1905-1989): the founder of quantitative paleoceanography

NASA Astrophysics Data System (ADS)

Dullo, Wolf-Christian; Pfaffl, Fritz A.

2016-11-01

Wolfgang Schott is the pioneer in paleoceanography and has established this research field within marine geology. His papers from the first half of the twentieth century are all published in German; therefore, the most inspiring results are given here as original quotes in English, since they paved the ground for all scientific discussions on climate stratigraphy, past ocean currents, and glacial interglacial cycles.

The carbon cycle since the LGM in the University of Victoria Earth System Climate Model: Implications of marine ice shelves and late-Holocene deforestation

NASA Astrophysics Data System (ADS)

Simmons, C. T.; Mysak, L. A.; Matthews, D.

2012-12-01

The University of Victoria Earth System Climate Model (version v.9) is used to investigate carbon cycle dynamics from the Last Glacial Maximum (21000 years Before Present (BP)) to the beginning of the Industrial Revolution (150 BP). A series of simulations with prescribed and freely-evolving CO2 infer that a combination of two factors, a faster overturning of the oceans during the interglacial and a release of carbon from deep-sea sediments, are likely responsible for a substantial proportion of the glacial-interglacial CO2 increase from 190 (23000 BP) to 280 ppm (150 BP). The simulations also indicate that a realistic glacial-interglacial change in the meridional overturning circulation can be generated without accounting for runoff from melting ice sheets. A series of model experiments also investigated the mechanisms behind the Holocene increase in CO2 after 8000 BP. Without the explicit representation of peatlands, permafrost, coral reefs, or human land use, the UVic model simulation of the natural carbon cycle over the period produced a decline in the atmospheric CO2 from 260 to around 250 ppm, in contrast to the increase from 260 to 280 ppm actually observed. Surprisingly, sensitivity simulations with global deforestation actually yielded lower CO2 concentrations (249-254 ppm) at 150 BP than the same simulations with no deforestation; however, deforestation of certain vegetation types lead to higher concentrations (~270 ppm). Even without deforestation, the decrease in CO2 is highly sensitive to the configuration of land ice shelves near Antarctica, with more extensive land ice leading to deeper local circulation in the Southern Ocean, less Antarctic-generated bottom waters globally, and a higher atmospheric CO2 concentrations (260 ppm) at 150 BP. The 5-8 ppm contribution of ice shelf extent may well be an important contributor to the higher analogue CO2 levels during the Holocene interglacial, as current data and reconstructions suggests that these ice shelves are indeed more extensive today than during many previous interglacial periods.

Sedimentary organic matter and carbonate variations in the Chukchi Borderland in association with ice sheet and ocean-atmosphere dynamics over the last 155 kyr

NASA Astrophysics Data System (ADS)

Rella, S. F.; Uchida, M.

2011-12-01

Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), CaCO3, benthic foraminiferal δ18O and the coarse grain size fraction from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on oxygen stratigraphy, radiocarbon dating and lithological constraints suggests that the piston core records paleoenvironmental changes of the last 155 kyr. TOC shows orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacial-interglacial cycles. At millennial scales, increases in TOC might correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 45 ka before present (BP) indicating a possible response to abrupt northern hemispheric temperature changes. Between 70 and 45 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC variability. CaCO3 content tends to anti-correlate with TOC on both orbital and millennial time scales, which we interpret in terms of enhanced sediment advection from the carbonate-rich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased organic carbon advection from the Siberian Arctic during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital- and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.

Sedimentary organic matter variations in the Chukchi Borderland over the last 155 kyr

NASA Astrophysics Data System (ADS)

Rella, S. F.; Uchida, M.

2011-03-01

Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), C/N and CaCO3 from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on correlation of our CaCO3 record with the benthic δ18O stack, supplemented by lithological constraints, suggests that the piston core records paleoenvironmental changes of the last 155 kyr. According to this age model, TOC and C/N show orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacial-interglacial cycles. At millennial scales, increases in TOC and C/N appear to correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 40 ka before present (BP) and thus seem to respond to abrupt northern hemispheric temperature changes. Between 65 and 40 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC and C/N variability. CaCO3 content tends to anti-correlate with TOC and C/N on both orbital and millennial time scales, which we interpret as enhanced sediment advection from the carbonate-rich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased terrestrial organic carbon advection from the Siberian Arctic during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital- and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.

Genetic signals of past demographic changes and the history of oak populations in California

NASA Astrophysics Data System (ADS)

Dodd, R. S.

2009-04-01

A retrospective view of species' demographic changes can inform on population stability through times of climatic change and the origins and spatial structure of genetic diversity in contemporary populations. The former provides the means to predict responses to future climatic change, while the latter allows us to infer the ability of populations to buffer the effects of reductions in population size and fragmentation. The approximately 1.8 my of the Pleistocene is believed to have had a significant impact on diversity through high rates of extinction during early glacial cycles and population expansions and contractions during the later cycles. In the Mediterranean basin, early emphasis on taxa with wide latitudinal ranges led to models of refugial sites and subsequent recolonization routes that could explain geographic patterns in genetic diversity, with a trend towards reduced genetic diversity in the north. More recently, the study of strictly Mediterranean taxa has revealed relictual sites that have persisted over very long periods of time, commonly relatively poor in diversity, but populations well differentiated from one site to another. In California, relatively little is known of the population dynamics of plant taxa during the Pleistocene glacial cycles, or to what extent differentiation today is a result of pre-Pleistocene events. For several animal taxa, differentiation between Coastal and Sierran taxa are believed to date to the Pliocene. Major demographic changes resulting in population isolation, bottlenecks, founder events and population expansions leave a genetic signal that can be detected through appropriate genetic markers and analyses. Such signals help to infer whether past climate fluctuations have had important effects on population demographics. Here, I will focus on key oak species of the California mediterranean climate zone. I will explore the likely effects of the last glacial maximum on oak populations using palaeoclimate and niche modeling together with analyses of population genetic structure. One of the major questions that will be addressed is whether populations have persisted over long periods of time and if the contemporary population structure has derived from events earlier than the Pleistocene. Population genetic structure will then be used to propose strategies that will optimize conservation of genetic resources.

Paleoenvironments, Evolution, and Geomicrobiology in a Tropical Pacific Lake: The Lake Towuti Drilling Project (TOWUTI)

NASA Astrophysics Data System (ADS)

Vogel, Hendrik; Russell, James M.; Bijaksana, Satria; Fowle, David; von Rintelen, Thomas; Stevenson, Janelle; Watkinson, Ian; Marwoto, Ristiyanti; Melles, Martin; Crowe, Sean; Haffner, Doug; King, John

2013-04-01

Lake Towuti (2.5°S, 121°E) is a, 560 km2, 200-m deep tectonic lake at the downstream end of the Malili lake system, a set of five, ancient (1-2 MYr) tectonic lakes in central Sulawesi, Indonesia. Lake Towuti's location in central Indonesia provides a unique opportunity to reconstruct long-term paleoclimate change in a crucially important yet understudied region- the tropical Western Pacific warm pool, heart of the El Niño-Southern Oscillation. The Malili Lakes have extraordinarily high rates of floral and faunal endemism, and the lakes are surrounded by one of the most diverse tropical forests on Earth. Drilling in Lake Towuti will identify the age and origin of the lake and the environmental and climatic context that shaped the evolution of this unique lacustrine and terrestrial ecosystem. The ultramafic (ophiolitic) rocks and lateritic soils surrounding Lake Towuti provide metal substrates that feed a diverse, exotic microbial community, analogous to the microbial ecosystems that operated in the Archean Oceans. Drill core will provide unique insight into long-term changes in this ecosystem, as well as microbial processes operating at depth in the sediment column. While the Malili Lakes have long been considered high-priority drilling sites, only now do we have the requisite site survey information to propose the development of ICDP's first lake drilling target in the tropical western Pacific. High-resolution seismic reflection data (CHIRP and airgun) combined with numerous long sediment piston cores collected from 2007-2010 demonstrate the enormous promise of Lake Towuti for an ICDP drilling campaign. Well-stratified sequences of up to 150 m thickness, uninterrupted by unconformities or erosional truncation, are present in multiple sub-basins within Towuti, providing ideal sites for long-term environmental, climatic, and limnological reconstructions. Multiproxy analyses of our piston cores document a continuous and detailed record of moisture balance variations in Lake Towuti during the past 60 kyr BP, highlighted by arid conditions during northern hemisphere stadials and the last glacial maximum, followed by a dry early and wet late Holocene. This history suggests that climate in central Indonesia responds most strongly to high-latitude climate forcing, despite Indonesia's remote location, and secondarily to southern hemisphere insolation forcing, a hypothesis we aim to test across multiple glacial-interglacial cycles through scientific drilling. Indeed, numerous high-amplitude reflectors in the upper 150 m of lacustrine fill suggest repeated cycles of moisture-balance variations in the tropical Pacific. The principal objectives of our proposed ICDP deep drilling initiative are to: (1) Document the timing, frequency, and amplitude of orbital- to millennial-scale changes in surface hydrology and terrestrial temperature in the Indo-Pacific Warm Pool across multiple glacial-interglacial cycles; (2) Understand how variations in terrestrial hydrology and temperature in central Indonesia respond to changes in the mean state of the ENSO system, the monsoons, high-latitude forcing, and insolation; (3) Analyze the long-term stability and resilience of rainforest vegetation to changes in climate, greenhouse gases, and fire frequency; (4) Study the extent, biogeography, and metabolism of microbial life in the sediments of a non-sulfidic, ferrginous basin, and their relationships to carbon cycling, redox metal deposition, and the concentration of metal ore minerals; (5) Study the effects of climate-driven changes in the aquatic environment on both lacustrine microbial populations, and the geobiosphere within the lake's sediment; (6) Determine the age of Lake Towuti, and the ensuing rates of speciation of Towuti's endemic fauna and flora; (7) Identify the timing of past lake level fluctuations in Towuti, changes in hydrological connections among the Malili Lakes, and how these influenced biological colonization events, habitat stability, and modes of speciation (sympatric, allopatric). We established an international science team, reviewed datasets from the site survey, and selected three drill sites that are best suited to address the objectives of the TOWUTI project during an ICDP and NSF sponsored workshop held in Bandung, Indonesia in March 2012. Important milestones concerning the operational and logistical preparation of a deep drilling at Lake Towuti have been achieved by the PI team in close collaboration with DOSECC, local authorities and businesses in Indonesia, and ICDP. A drilling proposal has been submitted to ICDP in January 2013 and proposals for matching funds will be submitted to national funding agencies in the course of 2013. Drilling operations are envisaged to commence in early 2015.

Late Quaternary changes in desert dust inputs to the Red Sea and Gulf of Aden from 87Sr/ 86Sr ratios in deep-sea cores

NASA Astrophysics Data System (ADS)

Stein, Mordechai; Almogi-Labin, Ahuva; Goldstein, Steven L.; Hemleben, Christoph; Starinsky, Abraham

2007-09-01

Strontium isotope ratios of the HCL-insoluble residue ("ISR") and foraminifera of cores from the Red Sea and Gulf of Aden are used to monitor effects of hydrothermal, fluvial and desert dust transport to these regions during the past ˜ 0.5 Ma. While the Gulf of Aden was open-ocean, during low glacial sea levels the Red Sea was a semi-isolated basin, allowing the possibility to study the effects regional versus global inputs during glacial-interglacial cycles. The ISR from the Gulf of Aden and the Red Sea display different ranges of 87Sr/ 86Sr ratios of 0.7085-0.7107 and 0.7062-0.7085, respectively. These reflect mixtures between three components: granitic, hydrothermal and loess strontium with representative 87Sr/ 86Sr of ˜ 0.711; ˜ 0.706 and ˜ 0.7085, respectively. Gulf of Aden ISR represent mixtures of the loess and "granitic" sources, while Red Sea ISR are mixtures of the loess and sea floor "hydrothermal" sources. In the Gulf of Aden, loess sources dominate during glacials, indicating intensification of the NE moonsonal wind regime, and granitic sources dominate during interglacials, reflecting wetter conditions related to an enhanced regional SW monsoon. Red Sea ISR show no clear glacial-interglacial distinction, but display a general temporal increase in 87Sr/ 86Sr ratios over the past 380 ka toward loess-like values, indicating increasing loess contributions toward the present day. The ranges of ISR 87Sr/ 86Sr ratios in the Red Sea and the Gulf of Aden were distinct prior to the last glacial period (< 60 ka), when they converge at loess values. The increasing loess signal may be due to increasing aridity in the dust source regions, or increasing accumulation and availability of loess with progressive glacial cycles. Superimposed on the Red Sea general trend are shifts to higher 87Sr/ 86Sr ratios following major climate transitions (at ˜ 10, ˜ 80, ˜ 130, ˜ 190, ˜ 240 and ˜ 330 ka BP) that coincide with sapropel episodes in the Eastern Mediterranean, which originated from the African monsoonal system and indicate enhanced wetness in the desert belt. 87Sr/ 86Sr ratios of foraminifera show a very narrow range from 0.70912 to 0.70917 over 530 ka, and in most samples are consistent with the contemporaneous global ocean. In the Red Sea, foraminifera and pteropods show slightly more variability than the Gulf of Aden. A few Red Sea samples fall slightly above the seawater trend (in Marine Isotope Stages 5 and 9) and below (during the last deglaciation), suggesting local effects that occurred when the flow of surface ocean water from the Gulf of Aden to the Red Sea was limited and the Red Sea behaved like an "amplifier basin".

Silicate versus carbonate weathering in Iceland: New insights from Ca isotopes

NASA Astrophysics Data System (ADS)

Jacobson, Andrew D.; Grace Andrews, M.; Lehn, Gregory O.; Holmden, Chris

2015-04-01

Several studies have measured riverine fluxes of Ca and carbonate alkalinity in Iceland with the aim of quantifying the role of basalt weathering in the long-term carbon cycle. A major assumption is that all of the Ca and alkalinity originates from the dissolution of Ca-bearing silicate minerals, such as plagioclase and clinopyroxene. However, hydrothermal calcite occurs throughout Iceland, and even trace levels are expected to impact river geochemistry owing to the mineral's high solubility and fast dissolution rate. To test this hypothesis, we used a new, high-precision Ca isotope MC-TIMS method (δ44/40Ca; 2σSD = ± 0.04 ‰) to trace sources of Ca in Icelandic rivers. We report elemental and Ca isotope data for rivers, high- and low-temperature groundwater, basalt, hydrothermal calcite (including Iceland Spar), and stilbite and heulandite, which are two types of zeolites commonly formed during low-grade metamorphism of basalt. In agreement with previous research, we find that rivers have higher δ44/40Ca values than basalt, with a maximum difference of ∼0.40‰. This difference may reflect isotope fractionation in the weathering zone, i.e., preferential uptake of 40Ca during clay mineral formation, adsorption, and other geochemical processes that cycle Ca. However, calcite δ44/40Ca values are also up to ∼0.40‰ higher than bedrock values, and on a diagram of δ44/40Ca versus Sr/Ca, nearly all waters plot within a plausible mixing domain bounded by the measured compositions of basalt and calcite, with glacial rivers plotting closer to calcite than non-glacial rivers. Calcite and heulandite form during hydrothermal alteration of basalt in the deep lava pile and often occur together in metabasalts now exposed at the surface. Because heulandite δ44/40Ca values are ∼1-2‰ lower than basalt, we suggest that 40Ca uptake by heudlandite explains the relatively high δ44/40Ca values of calcite and that calcite weathering in turn elevates riverine δ44/40Ca values. High mechanical erosion rates are known to facilitate the exposure and weathering of calcite, which explains the isotopic contrast between glacial and non-glacial watersheds. Using a mixing model, we find that calcite weathering provides ∼0-65% of the Ca in non-glacial rivers and ∼25-90% of the Ca in glacial rivers, with silicate weathering providing the remainder. Icelandic hydrothermal calcite contains mantle carbon. Noting that zeolite facies metamorphism and hydrothermal fluid circulation are ubiquitous characteristics of basaltic eruptions and assuming that hydrothermal calcite in other basaltic settings also contains mantle carbon, we suggest that the contribution of basalt weathering to long-term CO2 drawdown and climate regulation may be less significant than previously realized.

How well do we really know the timing and extent of glaciers during the Last Glacial Maximum in the Alps?

NASA Astrophysics Data System (ADS)

Ivy-Ochs, Susan; Braakhekke, Jochem; Monegato, Giovanni; Gianotti, Franco; Forno, Gabriella; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

2017-04-01

The Last Glacial Maximum (LGM) in the Alps saw much of the mountains inundated by ice. Several main accumulation areas comprising local ice caps and plateau icefields fit into a picture of transection glaciers flowing into huge valley glaciers. In the north the valley glaciers covered long distances (hundreds of kilometers) to reach the forelands where they spread out in fan-shaped piedmont lobes tens of kilometers across, e.g. the Rhine glacier. In the south travel distances to the mountain front were often shorter, the pathway steeper. Nevertheless, not all glaciers even reached beyond the front, as the temperatures were notably warmer in the south. For example at Orta the glacier snout remained within the mountains. Where glaciers reached the forelands they stopped abruptly and the moraine amphitheaters were constructed, e.g. at Ivrea and Rivoli-Avigliana. Sets of stacked moraines built-up as glacier advance was directly confined by the older moraines. We may temporally and spatially identify the culmination of the last glacial cycle by pinpointing the outermost moraines that date to the LGM (generally about 26-24 ka). On the other hand, the timing of abandonment of foreland positions is given by ages of the innermost, often lake-bounding, moraines (about 19-18 ka). Between the two, glacier fluctuations left the stadial moraines. In the Linth-Rhine system three stadials have been recognized: Killwangen, Schlieren and Zurich. Nevertheless, already in the Swiss sector correlation of the LGM stadials among the several foreland lobes is not unambiguous. Across the Alps, not only north to south but also west to east, how do the timing and extent of glaciers during the LGM vary? Recent glacier modelling by Seguinot et al. (2017) informs and suggests the possibility of differences in timing for reaching of the maximum extent and for the number of oscillations of individual lobes during the LGM. At present few sites in the Alps have detailed enough geomorphological constraints with well-dated ice-marginal positions for in depth discussion of outermost, innermost and in between moraines. Where locations of the LGM farthest extent are conflicting depending on author, we are trying to establish the precise location of the most extensive LGM position by directly dating moraine boulders with cosmogenic 10Be. Here we present 10Be data from the Orta and Rivoli-Avigliana amphitheatres. A key comparison is with the Tagliamento amphitheatre to the east, where dating testifies to a two-phase maximum (Monegato et al. 2007). Furthermore, comparison is made to sites north of the Alps including previously unpublished data. Monegato G. et al. 2007. Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps). Quaternary Research 68: 284-302. Seguinot J. et al. 2017. Modelling last glacial cycle ice dynamics in the Alps. EGU2017-8982

Surface Nutrient Utilisation and Productivity During Glacial-Interglacial Periods from the Equatorial Indian Ocean

NASA Astrophysics Data System (ADS)

R, C. K.; Bhushan, R.; Agnihotri, R.; Sawlani, R.; Jull, A. J. T.

2016-12-01

Seawaters and underlying sediments off Sri Lanka provide a unique marine realm affected by both branches of Northern Indian Ocean i.e. Arabian Sea (AS) and Bay of Bengal (BOB). AS and BOB are known for their distinct response to southwest monsoon. AS experiencing mainly winds and upwelling while BOB receives precipitation driven surface runoff from the Indian sub-continent. Multiple proxies were measured on a radiocarbon dated sediment core raised off Sri Lanka; their down core variations were used to understand oceanic history (nutrient utilisation, surface productivity, nature of organic matter) spanning last glacial-interglacial cycle ( 26 to 2.5 ka BP). Variations in CaCO3, biogenic silica (BSi) and δ15N from 26 ka to 12.5 ka BP indicate the region was experiencing high surface productivity with probably reduced surface nutrient utilisation efficiency. Sedimentary δ15N depth profile is decoupled from down core variations of major productivity indices (e.g. CaCO3, OC), hinting plausibly partial utilization of nutrients in the mixed layer (photic zone). δ13C of OC and C/N (wt. ratio) clearly reveal the terrestrial origin of organic matter at 15 ka BP, a period known for witnessing onset of deglaciation in northern hemisphere. δ13C minimum at 9 ka BP indicates intense monsoonal activity during this time coinciding well with solar insolation (June) maximum of the northern hemisphere. With the onset of Holocene ( 11 ka BP), δ15N variations appear to correlate with BSi and Ba/Ti indicating enhanced utilization of available nutrients at surface. Suggesting surface productivity over the region was probably micro-nutrient limited. The increased inventory of terrestrial runoff in Holocene probably demonstrates enhanced carbon sequestration capability of the region.

Habitat type and dispersal mode underlie the capacity for plant migration across an intermittent seaway.

PubMed

Worth, J R P; Holland, B R; Beeton, N J; Schönfeld, B; Rossetto, M; Vaillancourt, R E; Jordan, G J

2017-10-17

Investigating species distributions across geographic barriers is a commonly utilized method in biogeography to help understand the functional traits that allow plants to disperse successfully. Here the biogeographic pattern analysis approach is extended by using chloroplast DNA whole-genome 'mining' to examine the functional traits that have impacted the dispersal of widespread temperate forest species across an intermittent seaway, the 200 km wide Bass Strait of south-eastern Australia. Multiple, co-distributed species of both dry and wet forests were sampled from five regions on either side of the Strait to obtain insights into past dispersal of these biomes via seed. Using a next-generation sequencing-based pool-seq method, the sharing of single nucleotide polymorphisms (SNPs) was estimated between all five regions in the chloroplast genome. A total of 3335 SNPs were detected in 20 species. SNP sharing patterns between regions provided evidence for significant seed-mediated gene flow across the study area, including across Bass Strait. A higher proportion of shared SNPs in dry forest species, especially those dispersed by birds, compared with wet forest species suggests that dry forest species have undergone greater seed-mediated gene flow across the study region during past climatic oscillations and sea level changes associated with the interglacial/glacial cycles. This finding is consistent with a greater propensity for long-distance dispersal for species of open habitats and proxy evidence that expansive areas of dry vegetation occurred during times of exposure of Bass Strait during glacials. Overall, this study provides novel genetic evidence that habitat type and its interaction with dispersal traits are major influences on dispersal of plants. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Metal Deposition Along the Peru Margin Since the Last Glacial Maximum: Evidence For Regime Change at \\sim 6ka

NASA Astrophysics Data System (ADS)

Tierney, J.; Cleaveland, L.; Herbert, T.; Altabet, M.

2004-12-01

The Peru Margin upwelling zone plays a key role in regulating marine biogeochemical cycles, particularly the fate of nitrate. High biological productivity and low oxygen waters fed into the oxygen minimum zone result in intense denitrification in the modern system, the consequences of which are global in nature. It has been very difficult, however, to study the paleoclimatic history of this region because of the poor preservation of carbonate in Peru Margin sediments. Here we present records of trace metal accumulation from two cores located in the heart of the suboxic zone off the central Peru coast. Chronology comes from multiple AMS 14C dates on the alkenone fraction of the sediment, as well as correlation using major features of the \\delta 15N record in each core. ODP Site 1228 provides a high resolution, continuous sediment record from the Recent to about 14ka, while gravity core W7706-41k extends the record to the Last Glacial Maximum. Both cores were sampled at a 100 yr resolution, then analyzed for % N, \\delta 15N, alkenones, and trace metal concentration. Analysis of redox-sensitive metals (Mo and V) alongside metals associated with changes in productivity (Ni and Zn) provides perspective on the evolution of the upwelling system and distinguishes the two major factors controlling the intensity of the oxygen minimum zone. The trace metal record exhibits a notable increase in the intensity and variability of low oxygen waters and productivity beginning around 6ka and extending to the present. Within this most recent 6ka interval, the data suggest fluctuations in oxygenation and productivity occur on 1000 yr timescales. Our core records, therefore, suggest that the Peru Margin upwelling system strengthened significantly during the mid to late Holocene.

Central Tropical Pacific Variability And ENSO Response To Changing Climate Boundary Conditions: Evidence From Individual Line Island Foraminifera

NASA Astrophysics Data System (ADS)

Rustic, G. T.; Polissar, P. J.; Ravelo, A. C.; White, S. M.

2017-12-01

The El Niño Southern Oscillation (ENSO) plays a dominant role in Earth's climate variability. Paleoceanographic evidence suggests that ENSO has changed in the past, and these changes have been linked to large-scale climatic shifts. While a close relationship between ENSO evolution and climate boundary conditions has been predicted, testing these predictions remains challenging. These climate boundary conditions, including insolation, the mean surface temperature gradient of the tropical Pacific, global ice volume, and tropical thermocline depth, often co-vary and may work together to suppress or enhance the ocean-atmosphere feedbacks that drive ENSO variability. Furthermore, suitable paleo-archives spanning multiple climate states are sparse. We have aimed to test ENSO response to changing climate boundary conditions by generating new reconstructions of mixed-layer variability from sedimentary archives spanning the last three glacial-interglacial cycles from the Central Tropical Pacific Line Islands, where El Niño is strongly expressed. We analyzed Mg/Ca ratios from individual foraminifera to reconstruct mixed-layer variability at discrete time intervals representing combinations of climatic boundary conditions from the middle Holocene to Marine Isotope Stage (MIS) 8. We observe changes in the mixed-layer temperature variability during MIS 5 and during the previous interglacial (MIS 7) showing significant reductions in ENSO amplitude. Differences in variability during glacial and interglacial intervals are also observed. Additionally, we reconstructed mixed-layer and thermocline conditions using multi-species Mg/Ca and stable isotope measurements to more fully characterize the state of the Central Tropical Pacific during these intervals. These reconstructions provide us with a unique view of Central Tropical Pacific variability and water-column structure at discrete intervals under varying boundary climate conditions with which to assess factors that shape ENSO variability.

Contrasting Genetic Structure and Diversity of Galaxias maculatus (Jenyns, 1848) Along the Chilean Coast: Stock Identification for Fishery Management.

PubMed

González-Wevar, Claudio; Salinas, Pilar; Hüne, Mathias; Segovia, Nicolás; Vargas-Chacoff, Luis; Oda, Esteban; Poulin, Elie

2015-01-01

Galaxias maculatus (Pisces: Galaxiidae) commonly known as "puye" has a disjunct distribution along the Southern Hemisphere including landlocked and migratory populations at latitudes over 30°S in South America, Australia, Tasmania, and New Zealand. Chilean artisanal fishery of G. maculatus has become less important as a resource due to multiple factors including overexploitation, pollution, introduction of predators, and competitors. At the same time, the current conservation status of the species in Chile is still uncertain. Here, we used mtDNA control region sequences (925bp) to investigate main patterns of genetic diversity and structure in populations from 2 biogeographic areas along the Chilean coast. Extremely high levels of genetic diversity characterize the species, suggesting a low amount of influence of the last glacial cycle over its demography compared with other studies in freshwater and marine South American fishes. However, we recognized contrasting genetic patterns between the Intermediate Area (between 30°S and 42°S) and the Magellanic Province (between 42°S and 56°S). On the one hand, over a narrow geographical range (<200 km) each Intermediate Area estuarine population constitutes a different genetic unit. On the other hand, the Magellanic populations of the species exhibited low levels of differentiation in an area extending for more than 500 km. Such differences may be a consequence of different coastal configurations, oceanographic regimes, and Quaternary glacial histories. Finally, our results support the existence of different stock units for G. maculatus and this information should be integrated in future management strategies and aquaculture programs for this species. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

­Orbital-scale variations in Indo-Pacific hydroclimate during the mid- to late Pleistocene from Lake Towuti, Indonesia

NASA Astrophysics Data System (ADS)

Russell, J. M.; Vogel, H.; Bijaksana, S.; Melles, M.

2016-12-01

The Indo-Pacific region plays a critical role in the Earth's climate system. Changes in local insolation, greenhouse gas concentrations, ice volume, and local sea level are all hypothesized to exert a dominant control on Indo-Pacific hydroclimate, yet existing records from the region are generally short and exhibit fundamental differences in orbital-scale patterns that limit our understanding of the regional climate responses to orbital-scale forcings. In 2015 we conducted an ICDP drilling program on Lake Towuti, located near the equator in central Indonesia, one of the only terrestrial sedimentary archives in the region that continuously spans multiple glacial-interglacial cycles. We recovered over 1,000 meters of core including cores though the entire sediment sequence to bedrock. Previously published organic geochemical reconstructions of vegetation from relatively short, 60 kyr long piston from Lake Towuti exhibit strong drying during the Last Glacial Maximum, indicating that central Indonesian hydroclimate is sensitive to forcing from high-latitude ice-sheets. New, inorganic geochemical and mineralogical reconstructions of lake level also indicate a strong half-precessional climate signal during the last 60 kyr in which lake level highstands occur during austral and boreal summer insolation maxima, suggesting that equatorial rainfall varies in response to remote (likely subtropical) insolation forcing of the Asian monsoons. However, the short length of these records limits our understanding of the regional hydroclimatic response to the full range of global climate boundary conditions experienced during the late Quaternary. This presentation will discuss results from the last 60 kyr and present new geochemical reconstructions from the upper 100 m of core from Lake Towuti, dated using magnetic paleointensity, tephrachronology, and optically-stimulated luminescence to span the last 500 kyr BP.

Pleistocene evolutionary history of the Clouded Apollo (Parnassius mnemosyne): genetic signatures of climate cycles and a 'time-dependent' mitochondrial substitution rate.

PubMed

Gratton, P; Konopiński, M K; Sbordoni, V

2008-10-01

Genetic data are currently providing a large amount of new information on past distribution of species and are contributing to a new vision of Pleistocene ice ages. Nonetheless, an increasing number of studies on the 'time dependency' of mutation rates suggest that date assessments for evolutionary events of the Pleistocene might be overestimated. We analysed mitochondrial (mt) DNA (COI) sequence variation in 225 Parnassius mnemosyne individuals sampled across central and eastern Europe in order to assess (i) the existence of genetic signatures of Pleistocene climate shifts; and (ii) the timescale of demographic and evolutionary events. Our analyses reveal a phylogeographical pattern markedly influenced by the Pleistocene/Holocene climate shifts. Eastern Alpine and Balkan populations display comparatively high mtDNA diversity, suggesting multiple glacial refugia. On the other hand, three widely distributed and spatially segregated lineages occupy most of northern and eastern Europe, indicating postglacial recolonization from different refugial areas. We show that a conventional 'phylogenetic' substitution rate cannot account for the present distribution of genetic variation in this species, and we combine phylogeographical pattern and palaeoecological information in order to determine a suitable intraspecific rate through a Bayesian coalescent approach. We argue that our calibrated 'time-dependent' rate (0.096 substitutions/ million years), offers the most convincing time frame for the evolutionary events inferred from sequence data. When scaled by the new rate, estimates of divergence between Balkan and Alpine lineages point to c. 19 000 years before present (last glacial maximum), and parameters of demographic expansion for northern lineages are consistent with postglacial warming (5-11 000 years before present).

Comparison of eastern tropical Pacific TEX86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hertzberg, Jennifer E.; Schmidt, Matthew W.; Bianchi, Thomas S.; Smith, Richard W.; Shields, Michael R.; Marcantonio, Franco

2016-01-01

The use of the TEX86 temperature proxy has thus far come to differing results as to whether TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86 temperature proxy by comparing TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene TEX86H temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber, a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, TEX86H temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8 °C and 2.9 °C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at both sites based on both temperature proxies, and find that TEX86H temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86 paleothermometer in the eastern tropical Pacific.

Multi-scale curvature for automated identification of glaciated mountain landscapes☆

PubMed Central

Prasicek, Günther; Otto, Jan-Christoph; Montgomery, David R.; Schrott, Lothar

2014-01-01

Erosion by glacial and fluvial processes shapes mountain landscapes in a long-recognized and characteristic way. Upland valleys incised by fluvial processes typically have a V-shaped cross-section with uniform and moderately steep slopes, whereas glacial valleys tend to have a U-shaped profile with a changing slope gradient. We present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi-scale curvature and drainage area. Sample catchments are delineated and multiple moving window sizes are used to calculate per-cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides. Single-scale curvature can take similar values for glaciated and non-glaciated catchments but a comparison of multi-scale curvature leads to different results according to the typical cross-sectional shapes. To adapt these differences for automated classification of mountain landscapes into areas with V- and U-shaped valleys, curvature values are correlated with drainage area and a new and simple morphometric parameter, the Difference of Minimum Curvature (DMC), is developed. At three study sites in the western United States the DMC thresholds determined from catchment analysis are used to automatically identify 5 × 5 km quadrats of glaciated and non-glaciated landscapes and the distinctions are validated by field-based geological and geomorphological maps. Our results demonstrate that DMC is a good predictor of glacial imprint, allowing automated delineation of glacially and fluvially incised mountain landscapes. PMID:24748703

Patterns of glacial-interglacial vegetation and climate variability in eastern South Africa

NASA Astrophysics Data System (ADS)

Dupont, Lydie; Caley, Thibaut; Malaizé, Bruno; Giraudeau, Jacques

2010-05-01

Vegetation is an integrated part of the earth system and our understanding needs records of its glacial-interglacial variability. Although the data coverage for South Africa is slightly better than for some other parts of Africa, there are only very few records that allow us a glimpse of the vegetation history and development through one or more late Quaternary climate cycles. The existing evidence is fragmentary and in some cases contradictory. Marine sediments can offer here continuous sequences that cover large periods of time and provide a record of a signal that integrates rather large continental regions. Core MD96-2048 has been cored off the Limpopo River mouth at 26°10'S 34°01'E in 660 m water depth. This area is under the double influence of continental discharge and Agulhas current water advection. The sedimentation is slow and continuous. The upper 5 meter (down till 250 ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests with an increase of dry deciduous forest and open woodland during interglacial optima. During glacials open mountainous shrubland extended. The pattern strongly suggests a shifting of altitudinal vegetation belts in the mountains primarily depending on temperature, although the decline of forested areas during glacial times might also be the effect of low atmospheric carbon dioxide concentrations. This pattern in eastern South Africa differs from that suggested for western South Africa, where extension of the winter rain climate seems likely, and corroborates findings of increased C4 vegetation during the Glacial of eastern South Africa. The spread of dry deciduous forest and open woodland suggests a hot and dry climate during interglacial optima. The vegetation and climate of eastern South Africa seems to follow a mid to high latitude rhythm, in which the glacial-interglacial contrast is more important than the precessional forced monsoon system of tropical Africa.

Modelling the effects of ice-sheet activity on CO2 outgassing by Icelandic volcanoes

NASA Astrophysics Data System (ADS)

Armitage, J. J.; Ferguson, D.; Petersen, K. D.; Creyts, T. T.

2017-12-01

Glacial cycles may play a significant role in mediating the flux of magmatic CO2 between the Earth's mantle and atmosphere. In Iceland, it is thought that late-Pleistocene deglaciation led to a significant volcanic pulse, evidenced by increased post-glacial lava volumes and changes in melt chemistry consistent with depressurization. Investigating the extent to which glacial activity may have affected volcanic CO2 emissions from Iceland, and crucially over what timescale, requires detailed knowledge of how the magma system responded to the growth and collapse of the ice-sheet before and after the LGM. To investigate this, we coupled a model of magma generation and transport with a history of ice-sheet activity. Our results show that the emplacement and removal of the LGM ice-sheet likely led to two significant pulses of magmatic CO2. The first, and most significant of these, is associated with ice-sheet growth and occurs as the magma system recovers from glacial loading. This recovery happens from the base of the melting region upwards, producing a pulse of CO2 rich magma that is predicted to reach the surface around 20 ka after the loading event, close in time to the LGM. The second peak in CO2 output occurs abruptly following deglaciation as a consequence of increased rates of melt generation and transport in the shallow mantle. Although these post-glacial melts are relatively depleted in CO2, the increase in magma flux leads to a short-lived period of elevated CO2 emissions. Our results therefore suggest a negative feedback, whereby ice-sheet growth produces a delayed pulse of magmatic CO2, which, in addition to increased geothermal heat flux, may contribute towards driving deglaciation, which itself then causes further magmatism and CO2 outgassing. This model is consistent with the seismic structure of the asthenosphere below Iceland, and the established compositional and volumetric trends for sub- and post-glacial volcanism in Iceland. These trends show that the earliest subglacial events involved small volumes of enriched melts, while eruptions that were synchronous with or immediately followed deglaciation involved larger volumes of more depleted melts.

Large drainages from short-lived glacial lakes in the Teskey Range, Tien Shan Mountains, Central Asia

NASA Astrophysics Data System (ADS)

Narama, Chiyuki; Daiyrov, Mirlan; Duishonakunov, Murataly; Tadono, Takeo; Sato, Hayato; Kääb, Andreas; Ukita, Jinro; Abdrakhmatov, Kanatbek

2018-04-01

Four large drainages from glacial lakes occurred during 2006-2014 in the western Teskey Range, Kyrgyzstan. These floods caused extensive damage, killing people and livestock as well as destroying property and crops. Using satellite data analysis and field surveys of this area, we find that the water volume that drained at Kashkasuu glacial lake in 2006 was 194 000 m3, at western Zyndan lake in 2008 was 437 000 m3, at Jeruy lake in 2013 was 182 000 m3, and at Karateke lake in 2014 was 123 000 m3. Due to their subsurface outlet, we refer to these short-lived glacial lakes as the tunnel-type, a type that drastically grows and drains over a few months. From spring to early summer, these lakes either appear, or in some cases, significantly expand from an existing lake (but non-stationary), and then drain during summer. Our field surveys show that the short-lived lakes form when an ice tunnel through a debris landform gets blocked. The blocking is caused either by the freezing of stored water inside the tunnel during winter or by the collapse of ice and debris around the ice tunnel. The draining then occurs through an opened ice tunnel during summer. The growth-drain cycle can repeat when the ice-tunnel closure behaves like that of typical supraglacial lakes on debris-covered glaciers. We argue here that the geomorphological characteristics under which such short-lived glacial lakes appear are (i) a debris landform containing ice (ice-cored moraine complex), (ii) a depression with water supply on a debris landform as a potential lake basin, and (iii) no visible surface outflow channel from the depression, indicating the existence of an ice tunnel. Applying these characteristics, we examine 60 depressions (> 0.01 km2) in the study region and identify here 53 of them that may become short-lived glacial lakes, with 34 of these having a potential drainage exceeding 10 m3 s-1 at peak discharge.

Exhumed subglacial landscape in Uruguay: Erosional landforms, depositional environments, and paleo-ice flow in the context of the late Paleozoic Gondwanan glaciation

NASA Astrophysics Data System (ADS)

Assine, Mario Luis; de Santa Ana, Héctor; Veroslavsky, Gerardo; Vesely, Fernando F.

2018-07-01

A well-exposed glacial surface sculpted on Precambrian crystalline basement rocks occurs below the glacial succession of the San Gregorio Formation on the eastern border of the Chaco-Parana Basin in Uruguay and was formed in the context of the late Paleozoic Gondwana Ice Age. On the glacial surface are asymmetric parallel streamlined bedrock landforms interpreted as whalebacks. The downglacier (lee-side) faces of the whalebacks have gentle slopes dipping NNW with striated and sometimes polished surfaces on crystalline rocks. These landforms are covered by 10-100-cm-thick layers of tillites and shear-laminated siltstones, suggesting glacial abrasion produced mainly by subglacial till sliding. The subglacial facies are ice-molded, and exhibit meso-scale glacial lineations such as ridges and grooves up to 30 m long and 30 cm deep. The subglacial association is directly overlain by proglacial fine-grained facies (rhythmites) with dropstones indicating a subaqueous depositional environment following ice-margin retreat. The fine-grained facies are erosively cut by a succession of sandstones with wave-generated stratification resting on a basal conglomerate. Intraformational striated surfaces, NNE-oriented, were found on four distinct bedding planes within the sandstone package and interpreted as ice keel scour marks produced by floating ice. The San Gregorio deposits are partially confined in a wide and shallow subglacial trough and the stratigraphic succession is interpreted as the record of a glacial advance-retreat cycle comparable to deglacial sequences from other late Paleozoic localities. The paleo-ice flow to the NNW indicated by subglacial lineations is parallel to that verified in the southernmost Paraná Basin located north of the study area, suggesting a paleogeographic scenario in which glaciers advanced northward into a glaciomarine environment. The proposed palaeogeography does not confirm the previous hypothesis of an ice center on the Sul-Riograndense Shield but, instead, it corroborates a south-derived Uruguayan Ice Lobe advancing to the north, probably with provenance far afield in terranes of the present-day southern African.

Glacial heritage: knowledge, inventory and promotion in the Chablais area (France, Switzerland)

NASA Astrophysics Data System (ADS)

Perret, A.; Reynard, E.; Delannoy, J.-J.

2012-04-01

This study is part of an Interreg IVA project (www.123chablais.com) dealing with the promotion of different types of natural and cultural heritage in the Chablais area (French and Swiss Prealps) and is linked to the candidature of the French Chablais territory for the European Geoparks Network. The objective of the study is to develop a strategy for the promotion of the glacial heritage (landforms, deposits) in an area where the geomorphological features are highly influenced by glacial history and where key concepts in the Quaternary sciences were developed (e.g. the theory of multiple glaciations by Morlot in 1859), but that is now nearly completely deglaciated. The challenge is to find solutions to explain why the glacial heritage is so important for the regional economy and how it influences the life of inhabitants (e.g. Evian and Thonon mineral water, extraction industry, landscape and tourism), even if glaciers are not so impressive than in other parts of the Alps. The research is divided in three parts. (1) The first one aims to enhance knowledge on glacial landforms and deposits. The study area, that is quite large, has been intensively studied for more than two centuries; nevertheless, some parts have been only poorly studied. Intensive field survey was carried out to fill in the gaps of knowledge and some landforms, such as erratic boulders, have been dated in order to establish a chronology of deglaciation. All of these different elements have been included in a Geographic Information System with the aim of establishing maps of glacial stages in the Chablais area. (2) From this, an inventory of glacial geosites has been carried out, using the assessment method developed by Reynard et al. (2007). A specific focus has been on the assessment of the potential of the selected sites for educational purposes and geotourist promotion. (3) The last part has been the preparation of adapted educational and promotional supports. In particular, an exhibition will be available to regional stakeholders (municipalities, schools, geopark managers, tourist offices, etc.) for the promotion of the glacial heritage at the regional scale. Reference Reynard E., Fontana G., Kozlik L., Scapozza C. (2007). A method for assessing the scientific and additional values of geomorphosites, Geographica Helvetica, 62(3), 148-158.

A ~20,000 year history of glacial variability in the tropical Andes recorded in lake sediments from the Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Stansell, N.; Rodbell, D. T.; Moy, C. M.

2010-12-01

Pro-glacial lake sediments from the Cordillera Blanca, Peru contain continuous records of climate variability spanning the Last Glacial Maximum to present day. Here we present results from two alpine lake basins in the Queshgue Valley (9.8°S, 77.3°W) that contain high-resolution records of clastic sediment deposition for the last ~20,000 years. Radiocarbon-dated sediment cores were scanned at 0.5 to 1.0 cm resolution using a profiling x-ray fluorescence scanner for major and minor element distributions. In addition, we measured down-core variations in magnetic susceptibility, organic carbon, biogenic silica and calcium carbonate. Samples of bedrock and sediments from glacial moraines in the Queshgue watershed were analyzed using an ICP-MS in order to fingerprint and trace the source of glacial sediments deposited in the lakes. The bedrock is dominated by a combination of granodiorite with high Sr concentrations and meta-sedimentary rocks with high Zr values. Because the glacial sediments proximal to the modern glacier terminus are composed mostly of the granodiorite end-member, we interpret changes in Sr and clastic sediment concentrations in the lake sediment profiles as proxies for past glacial variability. Preliminary results indicate that glaciers retreated soon after ~14,500 cal yr BP and remained less extensive during the remaining late Glacial Stage and early Holocene. Gradually increasing clastic sediments through the middle and late Holocene indicate that glaciers became progressively larger, or more erosive towards present day. However, this overall Holocene trend of increasing glacier extent was interrupted by multiple periods of centennial- to millennial-scale ice margin retreat. For example, relative peaks in clastic sediments occurred from ~14,500 to 6000, 5600 to 5000, 4600 to 4200, 3600 to 3200, 2800 to 2700, 2400 to 2200, 1750 to 1550, 1100 to 900 cal yr BP, and during the Little Ice Age (~700 to 50 cal yr BP), while periods of low clastic sedimentary influx took place from between ~6000 to 5600, 5000 to 4600, 4200 to 3600, 3200 to 2800, 2700 to 2400, and 2200 to 1750, 1550 to 1100, and 900 to 700 cal yr BP. Periods of ice advance in the Cordillera Blanca generally correspond to times of increased moisture-balance and lower temperatures that are recorded in other regional, terrestrial proxy records.

Sea ice variations in the central Okhotsk Sea during the last two glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Lo, L.; Cabedo-Sanz, P.; Lattaud, J.; Belt, S. T.; Schouten, S.; Huang, J. J.; Timmermann, A.; Zeeden, C.; Wei, K. Y.; Shen, C. C.; Hodell, D. A.; Elderfield, H.

2016-12-01

Sea ice system as one of the critical and sensitive climate components in the Earth's climate system has experienced dramatically declination for the past few decades. Little knowledge, however, about the sea ice variations in the past orbital timescales has been obtained by paleoclimatic studies due to the lack of reliable sea ice proxy and age model constrain in the high productivity subpolar to polar regions. Here we present continuous 180,000 years subarctic northwestern Pacific sea ice and surface temperature (SST) records in the center Okhotsk Sea, the southernmost of seasonal sea ice fomration region in the Northern Hemisphere by using by using novel organic and non-destructive geochemical proxies from Site MD01-2414 (53oN, 149oE, water depth 1123 m). High resolution X-ray fluoresces scanning biogenic/terrestrial (Ba/Ti) elemental ratio represent clear glacial-interglacial cycles. Organic geochemical proxies (IP25 and TEX86) derived sea ice and SST changes in the same time resolution reveal the seasonality in the center Okhotsk Sea. Sea ice shows strong 23-kyr precession cycle control with modulation of 100-kyr eccentricity cycle during the peak interglacial periods (Marine Isotope Stage 5e and Holocene). On the other hand, SST represent global background climate change of 100-kyr cycle with very strong obliquity changes. According to the timeseries analyses, we argue that the sea ice minimum in the center of Okhotsk Sea has mainly been controlled by the local autumn insolation. SST represent annual insolation increasing due to local summer insolation and the obliquity pacing. This study firstly demonstrated clear seasonality in the same site. Further study of the relationship between sea ice and seawater thermal hisotries on the orbital timescale in the subarctic Pacific is crucial in the understanding of past major climate event, e.g. Middle Pleistocene Transition and Middle Brunhes Event.

Early Diagenesis of Trace Elements in Modern Fjord Sediments of the High Arctic

NASA Astrophysics Data System (ADS)

Herbert, L.; Riedinger, N.; Aller, R. C.; Jørgensen, B. B.; Wehrmann, L.

2017-12-01

Marine sediments are critical repositories for elements that are only available at trace concentrations in seawater, such as Fe, Mn, Co, Ni, As, Mo, and U. The behavior of these trace elements in the sediment is governed by a dynamic interplay of diagenetic reactions involving organic carbon, Fe and Mn oxides, and sulfur phases. In the Arctic fjords of Svalbard, glacial meltwater delivers large amounts of reactive Fe and Mn oxides to the sediment, while organic carbon is deposited episodically and diluted by lithogenic material. These conditions result in pronounced Fe and Mn cycling, which in turn drives other diagenetic processes such as rapid sulfide oxidation. These conditions make the Svalbard fjords ideal sites for investigating trace element diagenesis because they allow resolution of the interconnections between Fe and Mn dynamics and trace element cycling. In August 2016, we collected sediment cores from three Svalbard fjords and analyzed trace elements in the pore water and solid sediment over the top meter. Initial results reveal the dynamic nature of these fjords, which are dominated by non-steady state processes and episodic events such as meltwater pulses and phytoplankton blooms. Within this system, the distribution of As appears to be strongly linked to the Fe cycle, while Co and Ni follow Mn; thus, these three elements may be released from the sediment through diffusion and bioturbation along with Fe and Mn. The pore water profiles of U and Mo indicate removal processes that are independent from Fe or Mn, and which are rather unexpected given the apparent diagenetic conditions. Our results will help elucidate the processes controlling trace element cycling in a dynamic, glacially impacted environment and will ultimately contribute to our understanding of the role of fjords in the biogeochemical cycling of trace elements in a rapidly changing Arctic Ocean.

Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.

NASA Astrophysics Data System (ADS)

Fink, David; Joy, Kurt; Storey, Bryan

2014-05-01

It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum occurred prior to the Antarctic LGM (18-22 ka). No evidence based on cosmogenic ages for post-LGM or Holocene advances were found. These results support an extensive exposure age data set from the nearby Darwin-Hatherton Glacier system that indicates an absence of EAIS expansion across the Transantarctic Mnts during the global LGM period.

Investigating the effects of Pleistocene events on genetic divergence within Richardsonius balteatus, a widely distributed western North American minnow

PubMed Central

2014-01-01

Background Biogeographers seek to understand the influences of global climate shifts and geologic changes to the landscape on the ecology and evolution of organisms. Across both longer and shorter timeframes, the western North American landscape has experienced dynamic transformations related to various geologic processes and climatic oscillations, including events as recently as the Last Glacial Maximum (LGM; ~20 Ka) that have impacted the evolution of the North American biota. Redside shiner is a cyprinid species that is widely distributed throughout western North America. The species’ native range includes several well-documented Pleistocene refugia. Here we use mitochondrial DNA sequence data to assess phylogeography, and to test two biogeographic hypotheses regarding post-glacial colonization by redside shiner: 1) Redside shiner entered the Bonneville Basin at the time of the Bonneville Flood (Late Pleistocene; 14.5 Ka), and 2) redside shiner colonized British Columbia post-glacially from a single refugium in the Upper Columbia River drainage. Results Genetic diversification in redside shiner began in the mid to late Pleistocene, but was not associated with LGM. Different clades of redside shiner were distributed in multiple glacial age refugia, and each clade retains a signature of population expansion, with clades having secondary contact in some areas. Conclusions Divergence times between redside shiner populations in the Bonneville Basin and the Upper Snake/Columbia River drainage precedes the Bonneville Flood, thus it is unlikely that redside shiner invaded the Bonneville Basin during this flooding event. All but one British Columbia population of redside shiner are associated with the Upper Columbia River drainage with the lone exception being a population near the coast, suggesting that the province as a whole was colonized from multiple refugia, but the inland British Columbia redside shiner populations are affiliated with a refugium in the Upper Columbia River drainage. PMID:24885371

Chemical Oceanography and the Marine Carbon Cycle

NASA Astrophysics Data System (ADS)

Emerson, Steven; Hedges, John

The principles of chemical oceanography provide insight into the processes regulating the marine carbon cycle. The text offers a background in chemical oceanography and a description of how chemical elements in seawater and ocean sediments are used as tracers of physical, biological, chemical and geological processes in the ocean. The first seven chapters present basic topics of thermodynamics, isotope systematics and carbonate chemistry, and explain the influence of life on ocean chemistry and how it has evolved in the recent (glacial-interglacial) past. This is followed by topics essential to understanding the carbon cycle, including organic geochemistry, air-sea gas exchange, diffusion and reaction kinetics, the marine and atmosphere carbon cycle and diagenesis in marine sediments. Figures are available to download from www.cambridge.org/9780521833134. Ideal as a textbook for upper-level undergraduates and graduates in oceanography, environmental chemistry, geochemistry and earth science and a valuable reference for researchers in oceanography.

Simulation of groundwater flow in the glacial aquifer system of northeastern Wisconsin with variable model complexity

USGS Publications Warehouse

Juckem, Paul F.; Clark, Brian R.; Feinstein, Daniel T.

2017-05-04

The U.S. Geological Survey, National Water-Quality Assessment seeks to map estimated intrinsic susceptibility of the glacial aquifer system of the conterminous United States. Improved understanding of the hydrogeologic characteristics that explain spatial patterns of intrinsic susceptibility, commonly inferred from estimates of groundwater age distributions, is sought so that methods used for the estimation process are properly equipped. An important step beyond identifying relevant hydrogeologic datasets, such as glacial geology maps, is to evaluate how incorporation of these resources into process-based models using differing levels of detail could affect resulting simulations of groundwater age distributions and, thus, estimates of intrinsic susceptibility.This report describes the construction and calibration of three groundwater-flow models of northeastern Wisconsin that were developed with differing levels of complexity to provide a framework for subsequent evaluations of the effects of process-based model complexity on estimations of groundwater age distributions for withdrawal wells and streams. Preliminary assessments, which focused on the effects of model complexity on simulated water levels and base flows in the glacial aquifer system, illustrate that simulation of vertical gradients using multiple model layers improves simulated heads more in low-permeability units than in high-permeability units. Moreover, simulation of heterogeneous hydraulic conductivity fields in coarse-grained and some fine-grained glacial materials produced a larger improvement in simulated water levels in the glacial aquifer system compared with simulation of uniform hydraulic conductivity within zones. The relation between base flows and model complexity was less clear; however, the relation generally seemed to follow a similar pattern as water levels. Although increased model complexity resulted in improved calibrations, future application of the models using simulated particle tracking is anticipated to evaluate if these model design considerations are similarly important for understanding the primary modeling objective - to simulate reasonable groundwater age distributions.

The Paleoceanography of the Bering Sea During the Last Glacial Cycle

DTIC Science & Technology

2006-02-01

Stabeno, 1998). Water from the Bering (1995) inferred that the oxygen minimum zone Sea is relatively low salinity and rich in nutrients, (OMZ...fresher, warmer, and enriched in nutrients, particu- planktonic species Neogloboquadrina pachyderma larly silicate, which dissolves from opal- rich seafloor...2- rich 33 North Pacific intermediate water (NPIW), (2) decrease in the [02] of newly-formed NPIW without a change in ventilation rate (Crusius et al

Southern Ocean Control of Glacial AMOC Stability and Dansgaard-Oeschger Interstadial Duration

NASA Astrophysics Data System (ADS)

Buizert, C.; Schmittner, A.

2016-12-01

Glacial periods exhibit abrupt Dansgaard-Oeschger (DO) climatic oscillations that are thought to be linked to instabilities in the Atlantic meridional overturning circulation (AMOC). Great uncertainty remains regarding the dynamics of the DO cycle, as well as controls on the timing and duration of individual events. Using ice core data we show that the duration of warm (interstadial) periods is strongly correlated with Antarctic climate, and presumably with Southern Ocean (SO) temperature and the position of the Southern Hemisphere (SH) westerlies. We propose a SO control on AMOC stability and interstadial duration via the rate of Antarctic bottom water formation, meridional density/pressure gradients, Agulhas Leakage, and SO adiabatic upwelling. This hypothesis is supported by climate model experiments that demonstrate SO warming leads to a stronger AMOC that is less susceptible to freshwater perturbations. In the AMOC stability diagram, SO warming and strengthening of the SH westerlies both shift the vigorous AMOC branch toward higher freshwater values, thus raising the threshold for AMOC collapse. The proposed mechanism could provide a consistent explanation for several diverse observations, including maximum DO activity during intermediate ice volume/SH temperature, and successively shorter DO durations within each Bond cycle. It may further have implications for the fate of the AMOC under future global warming.

Red River barrier and Pleistocene climatic fluctuations shaped the genetic structure of Microhyla fissipes complex (Anura: Microhylidae) in southern China and Indochina.

PubMed

Yuan, Zhi-Yong; Suwannapoom, Chatmongkon; Yan, Fang; Poyarkov, Nikolay A; Nguyen, Sang Ngoc; Chen, Hong-Man; Chomdej, Siriwadee; Murphy, Robert W; Che, Jing

2016-12-01

South China and Indochina host striking species diversity and endemism. Complex tectonic and climatic evolutions appear to be the main drivers of the biogeographic patterns. In this study, based on the geologic history of this region, we test 2 hypotheses using the evolutionary history of Microhyla fissipes species complex. Using DNA sequence data from both mitochondrial and nuclear genes, we first test the hypothesis that the Red River is a barrier to gene flow and dispersal. Second, we test the hypothesis that Pleistocene climatic cycling affected the genetic structure and population history of these frogs. We detect 2 major genetic splits that associate with the Red River. Time estimation suggests that late Miocene tectonic movement associated with the Red River drove their diversification. Species distribution modeling (SDM) resolves significant ecological differences between sides of the Red River. Thus, ecological divergence also probably promoted and maintained the diversification. Genogeography, historical demography, and SDM associate patterns in southern China with climate changes of the last glacial maximum (LGM), but not Indochina. Differences in geography and climate between the 2 areas best explain the discovery. Responses to the Pleistocene glacial-interglacial cycling vary among species and regions.

Production of hydrogen peroxide in the atmosphere of a Snowball Earth and the origin of oxygenic photosynthesis

PubMed Central

Liang, Mao-Chang; Hartman, Hyman; Kopp, Robert E.; Kirschvink, Joseph L.; Yung, Yuk L.

2006-01-01

During Proterozoic time, Earth experienced two intervals with one or more episodes of low-latitude glaciation, which are probable “Snowball Earth” events. Although the severity of the historical glaciations is debated, theoretical “hard Snowball” conditions are associated with the nearly complete shutdown of the hydrological cycle. We show here that, during such long and severe glacial intervals, a weak hydrological cycle coupled with photochemical reactions involving water vapor would give rise to the sustained production of hydrogen peroxide. The photochemical production of hydrogen peroxide has been proposed previously as the primary mechanism for oxidizing the surface of Mars. During a Snowball, hydrogen peroxide could be stored in the ice; it would then be released directly into the ocean and the atmosphere upon melting and could mediate global oxidation events in the aftermath of the Snowball, such as that recorded in the Fe and Mn oxides of the Kalahari Manganese Field, deposited after the Paleoproterozoic low-latitude Makganyene glaciation. Low levels of peroxides and molecular oxygen generated during Archean and earliest Proterozoic non-Snowball glacial intervals could have driven the evolution of oxygen-mediating and -using enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis. PMID:17138669

Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

PubMed

Schmittner, Andreas; Galbraith, Eric D

2008-11-20

Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales.

Late-glacial recolonization and phylogeography of European red deer (Cervus elaphus L.).

PubMed

Meiri, Meirav; Lister, Adrian M; Higham, Thomas F G; Stewart, John R; Straus, Lawrence G; Obermaier, Henriette; González Morales, Manuel R; Marín-Arroyo, Ana B; Barnes, Ian

2013-09-01

The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion-contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40,000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South-East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South-Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North-West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas. © 2013 John Wiley & Sons Ltd.

Subarctic Lake Sediment Microbial Community Contributions to Methane Emission Patterns

NASA Astrophysics Data System (ADS)

Emerson, J. B.; Varner, R. K.; Parks, D.; Wik, M.; Neumann, R.; Johnson, J. E.; Singleton, C. M.; Woodcroft, B. J.; Tollerson, R., II; Owusu-Dommey, A.; Binder, M.; Freitas, N. L.; Crill, P. M.; Saleska, S. R.; Tyson, G. W.; Rich, V. I.

2017-12-01

Northern post-glacial lakes have recently been identified as a significant and increasing source of carbon to the atmosphere, largely through ebullition (bubbling) of microbially produced methane from the sediments. Ebullitive methane flux has been shown to correlate significantly with sediment surface temperatures, suggesting that solar radiation is the primary driver of methane emissions from these lakes. However, the slope of this relationship (i.e., the extent to which increasing temperature increases ebullitive methane emissions) differs spatially, both within and among lakes. As microbes are responsible for both methane generation and removal in lakes, we hypothesized that microbial communities—previously uncharacterized in post-glacial lake sediments—could be contributing to spatiotemporal differences in methane emission responses to temperature. We compared methane emission data with sediment microbial (metagenomic and amplicon), isotopic, and geochemical characterizations across two post-glacial lakes in Northern Sweden. With increasing temperatures, the increase in methane emissions was greater in lake middles (deeper water) than lake edges (shallower water), consistent with higher abundances of methanogens in sediments from lake middles than edges, along with significant differences in microbial community composition between these regions. Using sparse partial least squares statistical modeling, microbial abundances (including the abundances of methane-cycling microorganisms and of reconstructed population genomes, e.g., from Planctomycetes, Thermoplasmatales, and Candidate Phylum Aminicenantes) were better predictors of porewater methane concentrations than abiotic variables. These results suggest that, although temperature controls methane emissions, microbial community composition and function may drive the rate and magnitude of this temperature response in subarctic post-glacial lakes.

Reconstructing spatial and temporal patterns of paleoglaciation along the Tian Shan

NASA Astrophysics Data System (ADS)

Harbor, J.; Stroeven, A. P.; Beel, C.; Blomdin, R.; Caffee, M. W.; Chen, Y.; Codilean, A.; Gribenski, N.; Hattestrand, C.; Heyman, J.; Ivanov, M.; Kassab, C.; Li, Y.; Lifton, N. A.; Liu, G.; Petrakov, D.; Rogozhina, I.; Usubaliev, R.

2012-12-01

Testing and calibrating global climate models require well-constrained information on past climates of key regions around the world. Particularly important are transitional regions that provide a sensitive record of past climate change. Central Asia is an extreme continental location with glaciers and rivers that respond sensitively to temporal variations in the dominance of several major climate systems. As an international team initiative, we are reconstructing the glacial history of the Kyrgyz and Chinese Tian Shan, based on mapping and dating of key localities along the range. Remote-sensing-based geomorphological mapping, building on previous maps produced by Kyrgyz, Russian, Chinese and German scholars, is being augmented with field observations of glacial geomorphology and the maximum distribution of erratics. We are using cosmogenic nuclide (CN) 10Be dating of moraines and other landforms that constrain the former maximum extents of glaciers. Study sites include the Ala-Archa, Ak-Shyrak and Inylchek/Sary-Dzaz areas in Kyrgyzstan and the Urumqi valley (as well as its upland and southern slopes), and the Tumur and Bogeda peak areas in China. Comparing consistently dated glacial histories along and across the range will allow us to examine potential shifts in the dominance patterns of climate systems over time in Central Asia. We are also comparing ages based on CN with optically stimulated luminescence (OSL) and electron spin resonance (ESR) dates. The final stage of this project will use intermediate complexity glacier flow models to examine paleoclimatic implications of the observed spatial and temporal patterns of glacier changes across Central Asia and eastern Tibet, focused in particular on the last glacial cycle.

Precession and glacial-cycle controls of monsoon precipitation isotope changes over East Asia during the Pleistocene

NASA Astrophysics Data System (ADS)

Huang, Enqing; Chen, Yunru; Schefuß, Enno; Steinke, Stephan; Liu, Jingjing; Tian, Jun; Martínez-Méndez, Gema; Mohtadi, Mahyar

2018-07-01

Precipitation isotope reconstructions derived from speleothems and plant waxes are important archives for understanding hydroclimate dynamics. Their climatic significance in East Asia, however, remains controversial. Here we present terrestrial plant-wax stable hydrogen isotope (δDwax) records over periods covering the last four interglacials and glacial terminations from sediment cores recovered from the northern South China Sea (SCS) as an archive of regionally-integrated precipitation isotope changes in Southeast China. Combined with previous precipitation isotope reconstructions from China, we find that the SCS δDwax and Southwest-Central China stalagmite δ18O records show relatively enriched and depleted isotopic values, respectively, during interglacial peaks; but relatively similar isotopic variations during most sub-interglacials and glacial periods over the past 430 thousand years. During interglacial peaks, strong summer insolation should have intensified the convection intensity, the isotopic fractionation along moisture trajectories and the seasonality, which are all in favor of causing isotopically-depleted rainfall over the East Asian monsoon regime. These effects in combination with a relatively high proportion of Indian Ocean- versus Pacific-sourced moisture influx should have resulted in strongly depleted precipitation isotopes (stalagmite δ18O) over most parts of China. However, Southeast China should have been affected by a relatively low ratio of Indian Ocean- versus Pacific-sourced moisture influx, which dominated over effects yielding depleted precipitation isotopes and led to enriched precipitation isotopes (δDwax). It is thus concluded that glacial boundary conditions and insolation forcing are the two most important factors for causing regional differences in precipitation isotope compositions over subtropical East Asia on orbital timescales.

A transient fully coupled climate-ice-sheet simulation of the last glacial inception

NASA Astrophysics Data System (ADS)

Lofverstrom, M.; Otto-Bliesner, B. L.; Lipscomb, W. H.; Fyke, J. G.; Marshall, S.; Sacks, B.; Brady, E. C.

2017-12-01

The last glacial inception occurred around 115 ka, following a relative minimum in the Northern Hemisphere summer insolation. It is believed that small and spatially separated ice caps initially formed in the high elevation regions of northern Canada, Scandinavia, and along the Siberian Arctic coast. These ice caps subsequently migrated down in the valleys where they coalesced and formed the initial seeds of the large coherent ice masses that covered the northern parts of the North American and Eurasian continents over most of the last glacial cycle. Sea level records show that the initial growth period lasted for about 10 kyrs, and the resulting ice sheets may have lowered the global sea level by as much as 30 to 50 meters. Here we examine the transient climate system evolution over the period between 118 and 110 ka, using the fully coupled Community Earth System Model, version 2 (CESM2). This model features a two-way coupled high-resolution (4x4 km) ice-sheet component (Community Ice Sheet model, version 2; CISM2) that simulates ice sheets as an interactive component of the climate system. We impose a transient forcing protocol where the greenhouse gas concentrations and the orbital parameters follow the nominal year in the simulation; the model topography is also dynamically evolving in order to reflect changes in ice elevation throughout the simulation. The analysis focuses on how the climate system evolves over this time interval, with a special focus on glacial inception in the high-latitude continents. Results will highlight how the evolving ice sheets compare to data and previous model based reconstructions.

Paleoclimate reconstruction in the Levant region from the petrography and the geochemistry of a MIS 5 stalagmite from the Kanaan Cave, Lebanon

NASA Astrophysics Data System (ADS)

Nehme, C.; Verheyden, S.; Noble, S. R.; Farrant, A. R.; Delannoy, J. J.; Claeys, P.

2015-07-01

Lying at the transition between the temperate Mediterranean domain and subtropical deserts, the Levant is a key area to study the palaeoclimatic response over glacial-interglacial cycles. This paper presents a precisely dated last interglacial (MIS 5) stalagmite (129-84 ka) from the Kanaan Cave, Lebanon. Variations in growth rate and isotopic records indicate a warm humid phase at the onst of the last interglacial at ~129 ka that lasted until ~125 ka. A gradual shift in speleothem isotopic composition (125-122 ka) is driven mainly by the δ18O source effect of the Eastern Mediterranean surface waters during Sapropel S5. The onset of glacial inception began after ~122 ka, interrupted by a short wet pulse during Sapropel S4. Low growth rates and enriched oxygen and carbon values until ~84 ka indicate a transition to drier conditions during Northern Hemisphere glaciation.

Reconstruction of MIS 5 climate in the central Levant using a stalagmite from Kanaan Cave, Lebanon

NASA Astrophysics Data System (ADS)

Nehme, C.; Verheyden, S.; Noble, S. R.; Farrant, A. R.; Sahy, D.; Hellstrom, J.; Delannoy, J. J.; Claeys, P.

2015-12-01

Lying at the transition between the temperate Mediterranean domain and subtropical deserts, the Levant is a key area to study the palaeoclimatic response over glacial-interglacial cycles. This paper presents a precisely dated last interglacial (MIS 5) stalagmite (129-84 ka) from the Kanaan Cave, Lebanon. Variations in growth rate and isotopic records indicate a warm humid phase at the onset of the last interglacial at ~ 129 ka that lasted until ~ 125 ka. A gradual shift in speleothem isotopic composition (125-122 ka) is driven mainly by the δ18O source effect of the eastern Mediterranean surface waters during sapropel 5 (S5). The onset of glacial inception began after ~ 122 ka, interrupted by a short wet pulse during the sapropel 4 (S4) event. Low growth rates and enriched oxygen and carbon values until ~ 84 ka indicate a transition to drier conditions during Northern Hemisphere glaciation.

Geological mapping of Sputnik Planitia on Pluto

NASA Astrophysics Data System (ADS)

White, Oliver L.; Moore, Jeffrey M.; McKinnon, William B.; Spencer, John R.; Howard, Alan D.; Schenk, Paul M.; Beyer, Ross A.; Nimmo, Francis; Singer, Kelsi N.; Umurhan, Orkan M.; Stern, S. Alan; Ennico, Kimberly; Olkin, Cathy B.; Weaver, Harold A.; Young, Leslie A.; Cheng, Andrew F.; Bertrand, Tanguy; Binzel, Richard P.; Earle, Alissa M.; Grundy, Will M.; Lauer, Tod R.; Protopapa, Silvia; Robbins, Stuart J.; Schmitt, Bernard; New Horizons Science Team

2017-05-01

The geology and stratigraphy of the feature on Pluto informally named Sputnik Planitia is documented through geologic mapping at 1:2,000,000 scale. All units that have been mapped are presently being affected to some degree by the action of flowing N2 ice. The N2 ice plains of Sputnik Planitia display no impact craters, and are undergoing constant resurfacing via convection, glacial flow and sublimation. Condensation of atmospheric N2 onto the surface to form a bright mantle has occurred across broad swathes of Sputnik Planitia, and appears to be partly controlled by Pluto's obliquity cycles. The action of N2 ice has been instrumental in affecting uplands terrain surrounding Sputnik Planitia, and has played a key role in the disruption of Sputnik Planitia's western margin to form chains of blocky mountain ranges, as well in the extensive erosion by glacial flow of the uplands to the east of Sputnik Planitia.

Evidence for Multiple Late Quaternary Glaciations in the Southernmost Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Smith, J. A.; Rodbell, D. T.; Ramage, J. M.

2007-12-01

Surface-exposure dating with in-situ-produced cosmogenic isotopes has provided the basis for a growing framework of glacial chronologies in the tropical Andes. In the Peruvian Andes, long chronologies (>400 ka) with relatively small local last glacial maximum (LLGM) advances have been reported for the central Cordillera Blanca (ca. 9°30'S) and Junin Plain (11°00'S), whereas preliminary data suggest a shorter record (<40 ka) in the intervening Cordillera Huayhuash (10°15'S). These seemingly contradictory findings raise several questions: Was the LLGM a relatively minor event in the Peruvian Andes, far exceeded by bigger, older advances? Which combination of geographic and geomorphic factors increases the likelihood that evidence of older advances will be preserved? With these questions in mind, we sought a site with both high peaks and a high-altitude plateau. The glaciated Nevado Jeulla Rajo massif (10°00'S, 77°16'W, peaks ca. 5600 masl) marks the southern end of the Cordillera Blanca and the Callejon de Huaylas valley in the central Peruvian Andes. The Conococha Plain (ca. 4050 masl) borders the western side of the massif. Large lateral moraines extend onto the Conococha Plain from the west-facing valleys and multiple moraine loops lie upvalley, closer to active ice margins. Surface-exposure dating (10Be) indicates that the largest lateral moraines from Jeullesh Valley are compound features deposited during the LLGM (ca. 30 ka) and a late-glacial readvance (ca. 16 ka). The LLGM/late-glacial moraines cross-cut an older pair of lateral moraines (ca. 70 ka) that may provide evidence for a smaller advance during marine isotope stage 4. Although the LLGM/late-glacial moraines are impressively large (ca. 150 m high), they do not represent the maximum ice extent in the region. Fluvial outwash deposits beyond the termini of the moraines on the Conococha Plain are underlain by lodgement till that is up to 20 m thick and extends ca. 6 km across the width of the Plain to the Rió Santa. The wide distribution of the till suggests that at least one older glaciation was far more extensive than any of the late Quaternary advances that we have dated by 10Be. The combination of high peaks, a high-altitude plateau, and an active fault may be ideal for enhancing preservation of older moraines and till deposits.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archer, D.

A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. Theremore » is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H 2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.« less

Evidence of strong ocean heating during glacial periods

NASA Astrophysics Data System (ADS)

Zimov, S. A.; Zimov, N.

2013-12-01

Numerous hypotheses have addressed glacial-interglacial climatic dynamics, but none of them explain the sharp 25C temperature increase in Greenland in the last deglaciation (Cuffey et al. 1995; Dahl-Jensen et al. 1998). These robust data were obtained through analyzing the temperature profile in the Greenland ice sheet where cold from the last glaciation is preserved in the depth of the glacial sheet. We suggest that during glaciations the ocean accumulated energy: interior ocean water heated up to ~20-30C and during deglaciation this energy is released. In the analogy with reconstructing the ice sheet temperature profiles, the most reliable proof of ocean interior warming during the last glaciation is the heat flux profiles in the bottom sediments. In the final reports based on temperature measurements conducted during the DSDP (Deep Sea Drilling Project) it is stated that heat flux in the bottom sediments doesn't vary with depth and consequently there were no substantial temperature changes in the ocean interior during the last glacial cycle, and heat flux on the surface of the ocean bottom is the geothermal heat flux (Erickson et al., 1975, Hyndman et al., 1987). However, we have critically investigated data in all initial reports of all deep sea drilling projects and have noticed that all temperature data show that heat flow decreases strongly with depth (a minimum of 40 mW/m2), i.e. most of the heat flux detected on the surface of the ocean floor is not the geothermal heat flux but remaining heat that bottom sediments release. Sharp shifts in heat flow are seen within boreholes at depths crossing gas hydrate bottom. All this means that during the last glacial period interior water temperature was on 25-30C degrees warmer. Conversely, in isolated seas heat flow in the sediments shows little change with depth.

Response of northern hemisphere environmental and atmospheric conditions to climate changes using Greenland aerosol records from the Eemian to the Holocene

NASA Astrophysics Data System (ADS)

Fischer, H.

2017-12-01

The Northern Hemisphere experienced dramatic climate changes over the last glacial cycle, including vast ice sheet expansion and frequent abrupt climate events. Moreover, high northern latitudes during the last interglacial (Eemian) were warmer than today and may provide guidance for future climate change scenarios. However, little evidence exists regarding the environmental alterations connected to these climate changes. Using aerosol concentration records in decadal resolution from the North Greenland Eemian Ice Drilling (NEEM) over the last 128,000 years we extract quantitative information on environmental changes, including the first comparison of northern hemisphere environmental conditions between the warmer than present Eemian and the early Holocene. Separating source changes from transport effects, we find that changes in the ice concentration greatly overestimate the changes in atmospheric concentrations in the aerosol source region, the latter mirroring changes in aerosol emissions. Glacial times were characterized by a strong reduction in terrestrial biogenic emissions (only 10-20% of the early Holocene value) reflecting the net loss of vegetated area in mid to high latitudes, while rapid climate changes during the glacial had essentially no effect on terrestrial biogenic aerosol emissions. An increase in terrestrial dust emissions of approximately a factor of eight during peak glacial and cold stadial intervals indicates higher aridity and dust storm activity in Asian deserts. Glacial sea salt aerosol emissions increased only moderately (by approximately 50%), likely due to sea ice expansion, while marked stadial/interstadial variations in sea salt concentrations in the ice reflect mainly changes in wet deposition en route. Eemian ice contains lower aerosol concentrations than ice from the early Holocene, due to shortened atmospheric residence time during the warmer Eemian, suggesting that generally 2°C warmer climate in high northern latitudes did not change environmental conditions controlling aerosol formation in the source regions significantly.

Impacts of autochthonous marine branched GDGTs on related paleo- environmental proxies: a preliminary study

NASA Astrophysics Data System (ADS)

Dong, L.; Li, L.; Li, Q.; Zhang, C.

2014-12-01

Two proxies derived from branched glycerol dialkyl glycerol tetraethers (brGDGTs)-, the methylation index of branched tetraethers (MBT) and the cyclization ratio of branched tetraethers (CBT), are often used to reconstruct paleo mean annual air temperature (MAAT) and soil pH on the belief of their terrestrial origin. However, mounting evidence indicates the existence of autochthonous brGDGTs in marine environments，which may affect MAAT reconstruction and the use of other related paleoenvironmental proxies. Here we provide high resolution profiles of brGDGTs in a sedimentary core (MD05-2896/7) from the southern South China Sea, which include MBT and CBT indices as well as the branched and isoprenoid tetraether (BIT) index. The BIT results varied systematically with glacial-interglacial cycles, with values distinctly lower (<0.1) during the interglacial periods (MIS 1 and MIS 5) than during the glacial periods (MIS 2, MIS, 3, MIS 4 and MIS 6). Also distinct is the MBT/CBT-derived temperature, which show lower values during the interglacial periods but higher values during the glacial periods. We hypothesize that the lower MBT/CBT-derived temperature during the interglacial periods reflects subsurface water column temperature registered by autochthonous brGDGTs produced in situ marine conditions, whereas the higher MBT/CBT derived-temperature during the glacial periods reflects terrestrial MAAT because of the overwhelming input of brGDGTs from land when sea level was low. Similarly, the CBT-derived pH appears to have been overprinted also by the sea water signal of the interglacials but affected mostly by precipitation during the glacial intervals, showing patterns similar to or as a positive response to the southern hemispheric climate oscillation due to teleconnection. Our study demonstrates the complexity of brGDGT occurrence in marine environments and suggests that the MBT/CBT proxy should not be directly employed for the reconstruction of terrestrial MAAT at marine settings when BIT value is lower than 0.1.

Phylogeography and Post-Glacial Recolonization in Wolverines (Gulo gulo) from across Their Circumpolar Distribution

PubMed Central

Zigouris, Joanna; Schaefer, James A.; Fortin, Clément; Kyle, Christopher J.

2013-01-01

Interglacial-glacial cycles of the Quaternary are widely recognized in shaping phylogeographic structure. Patterns from cold adapted species can be especially informative - in particular, uncovering additional glacial refugia, identifying likely recolonization patterns, and increasing our understanding of species’ responses to climate change. We investigated phylogenetic structure of the wolverine, a wide-ranging cold adapted carnivore, using a 318 bp of the mitochondrial DNA control region for 983 wolverines (n = 209 this study, n = 774 from GenBank) from across their full Holarctic distribution. Bayesian phylogenetic tree reconstruction and the distribution of observed pairwise haplotype differences (mismatch distribution) provided evidence of a single rapid population expansion across the wolverine’s Holarctic range. Even though molecular evidence corroborated a single refugium, significant subdivisions of population genetic structure (0.01< ΦST <0.99, P<0.05) were detected. Pairwise ΦST estimates separated Scandinavia from Russia and Mongolia, and identified five main divisions within North America - the Central Arctic, a western region, an eastern region consisting of Ontario and Quebec/Labrador, Manitoba, and California. These data are in contrast to the nearly panmictic structure observed in northwestern North America using nuclear microsatellites, but largely support the nuclear DNA separation of contemporary Manitoba and Ontario wolverines from northern populations. Historic samples (c. 1900) from the functionally extirpated eastern population of Quebec/Labrador displayed genetic similarities to contemporary Ontario wolverines. To understand these divergence patterns, four hypotheses were tested using Approximate Bayesian Computation (ABC). The most supported hypothesis was a single Beringia incursion during the last glacial maximum that established the northwestern population, followed by a west-to-east colonization during the Holocene. This pattern is suggestive of colonization occurring in accordance with glacial retreat, and supports expansion from a single refugium. These data are significant relative to current discussions on the conservation status of this species across its range. PMID:24386287

Phylogeography and post-glacial recolonization in wolverines (Gulo gulo) from across their circumpolar distribution.

PubMed

Zigouris, Joanna; Schaefer, James A; Fortin, Clément; Kyle, Christopher J

2013-01-01

Interglacial-glacial cycles of the Quaternary are widely recognized in shaping phylogeographic structure. Patterns from cold adapted species can be especially informative - in particular, uncovering additional glacial refugia, identifying likely recolonization patterns, and increasing our understanding of species' responses to climate change. We investigated phylogenetic structure of the wolverine, a wide-ranging cold adapted carnivore, using a 318 bp of the mitochondrial DNA control region for 983 wolverines (n=209 this study, n=774 from GenBank) from across their full Holarctic distribution. Bayesian phylogenetic tree reconstruction and the distribution of observed pairwise haplotype differences (mismatch distribution) provided evidence of a single rapid population expansion across the wolverine's Holarctic range. Even though molecular evidence corroborated a single refugium, significant subdivisions of population genetic structure (0.01< ΦST <0.99, P<0.05) were detected. Pairwise ΦST estimates separated Scandinavia from Russia and Mongolia, and identified five main divisions within North America - the Central Arctic, a western region, an eastern region consisting of Ontario and Quebec/Labrador, Manitoba, and California. These data are in contrast to the nearly panmictic structure observed in northwestern North America using nuclear microsatellites, but largely support the nuclear DNA separation of contemporary Manitoba and Ontario wolverines from northern populations. Historic samples (c. 1900) from the functionally extirpated eastern population of Quebec/Labrador displayed genetic similarities to contemporary Ontario wolverines. To understand these divergence patterns, four hypotheses were tested using Approximate Bayesian Computation (ABC). The most supported hypothesis was a single Beringia incursion during the last glacial maximum that established the northwestern population, followed by a west-to-east colonization during the Holocene. This pattern is suggestive of colonization occurring in accordance with glacial retreat, and supports expansion from a single refugium. These data are significant relative to current discussions on the conservation status of this species across its range.

A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

DOE PAGES

Archer, D.

2015-05-21

A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. Theremore » is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H 2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.« less

Fire and ice: volcanic and glacial impacts on the phylogeography of the New Zealand forest fern Asplenium hookerianum.

PubMed

Shepherd, Lara D; Perrie, Leon R; Brownsey, Patrick J

2007-11-01

In the Southern Hemisphere there has been little phylogeographical investigation of forest refugia sites during the last glacial. Hooker's spleenwort, Asplenium hookerianum, is a fern that is found throughout New Zealand. It is strongly associated with forest and is a proxy for the survival of woody vegetation during the last glacial maximum. DNA sequence data from the chloroplast trnL-trnF locus were obtained from 242 samples, including c. 10 individuals from each of 21 focal populations. Most populations contained multiple, and in many cases unique, haplotypes, including those neighbouring formerly glaciated areas, while the predominant inference from nested clade analysis was restricted gene flow with isolation by distance. These results suggest that A. hookerianum survived the last glacial maximum in widespread populations of sufficient size to retain the observed phylogeography, and therefore that the sheltering woody vegetation must have been similarly abundant. This is consistent with palynological interpretations for the survival in New Zealand of thermophilous forest species at considerably smaller distances from the ice sheets than recorded for the Northern Hemisphere. Eastern and central North Island populations of A. hookerianum were characterized by a different subset of haplotypes to populations from the remainder of the country. A similar east-west phylogeographical pattern has been detected in a diverse array of taxa, and has previously been attributed to recurrent vulcanism in the central North Island.

Understanding the major transitions in Quaternary climate dynamics

NASA Astrophysics Data System (ADS)

Willeit, Matteo; Ganopolski, Andrey

2017-04-01

Climate dynamics over the past 3 million years was characterized by strong variability associated with glacial cycles and several distinct regime changes. The Pliocene-Pleistocene Transition (PPT), which happened around 2.7 million years ago, was characterized by the appearance of the large continental ice sheets over Northern Eurasia and North America. For two million years after the PPT climate variability was dominated by relatively symmetric 40 kyr cycles. At around 1 million years ago the dominant mode of climate variability experienced a relatively rapid transition from 40 kyr to strongly asymmetric 100 kyr cycles of larger amplitude (Mid-Pleistocene Transition). Additionally, during the past 800 kyr there are clear differences between the earlier and the later glacial cycles with the last five cycles characterized by larger magnitude of variability (Mid-Brunhes Event). Here, we use the Earth system model of intermediate complexity CLIMBER-2 to explore possible mechanisms that could explain these regime shifts. CLIMBER-2 incorporates all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, marine biogeochemistry and aeolian dust. The model was optimally tuned to reproduce climate, ice volume and CO2 variability over the last 400,000 years. Using the same model version, we performed a large set of simulations covering the entire Quaternary (3 million years) starting from identical initial conditions and using a parallelization in time technique which consists of starting the model at different times (every 100,000 years) and running each simulation for 500,000 years. The Earth's orbital variations are the only prescribed radiative forcing. Several sets of the Northern Hemisphere orography and sediment thickness representing different stages of landscape evolution during the Quaternary are prescribed as boundary conditions for the ice sheet model and volcanic CO2 outgassing is used as the external forcing for the carbon cycle to allow for different background atmospheric CO2 concentrations. We show that by varying only these two model boundary conditions and volcanic forcing the model is able to reproduce the major regime changes of Quaternary long-term climate dynamics.

Solving the riddle of interglacial temperatures over the last 1.5 million years with a future IPICS "Oldest Ice" ice core

NASA Astrophysics Data System (ADS)

Fischer, Hubertus

2014-05-01

The sequence of the last 8 glacial cycles is characterized by irregular 100,000 year cycles in temperature and sea level. In contrast, the time period between 1.5-1.2 million years ago is characterized by more regular cycles with an obliquity periodicity of 41,000 years. Based on a deconvolution of deep ocean temperature and ice volume contributions to benthic δ18O (Elderfield et al., Science, 2012), it is suggested that glacial sea level became progressively lower over the last 1.5 Myr, while glacial deep ocean temperatures were very similar. At the same time many interglacials prior to the Mid Brunhes event showed significantly cooler deep ocean temperatures than the Holocene, while at the same time interglacial ice volume remained essentially the same. In contrast, interglacial sea surface temperatures in the tropics changed little (Herbert et al., Science,2010) and proxy reconstructions of atmospheric CO2 using δ11B in planktic foraminifera (Hönisch et al., Science, 2009) suggest that prior to 900,000 yr before present interglacial CO2 levels did not differ substantially from those over the last 450,000 years. Accordingly, the conundrum arises how interglacials can differ in deep ocean temperature without any obvious change in ice volume or greenhouse gas forcing and what caused the change in cyclicity of glacial interglacial cycles over the Mid Pleistocene Transition. Probably the most important contribution to solve this riddle is the recovery of a 1.5 Myr old ice core from Antarctica, which among others would provide an unambiguous, high-resolution record of the greenhouse gas history over this time period. Accordingly, the international ice core community, as represented by the International Partnership for Ice Core Science (IPICS), has identified such an 'Oldest Ice' ice core as one of the most important scientific targets for the future (http://www.pages.unibe.ch/ipics/white-papers). However, finding stratigraphically undisturbed ice, which covers this time period in Antarctica, is not an easy task. Based on a simple ice and heat flow model and glaciological observations (Fischer et al., Climate of the Past, 2013), we conclude that sites in the vicinity of major domes and saddle positions on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, significantly reduced ice thickness is required to avoid bottom melting. The most critical parameter is the largely unknown geothermal heat flux at the bottom of the ice sheet. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 My old ice. If sites with lower geothermal heat flux can be found, also a higher ice thickness is allowed, alleviating the problem of potential flow disturbances in the bottom-most ice to affect a 1.5 Myr climate record.

Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene?

PubMed Central

Marshall, Jill A.; Roering, Joshua J.; Bartlein, Patrick J.; Gavin, Daniel G.; Granger, Darryl E.; Rempel, Alan W.; Praskievicz, Sarah J.; Hales, Tristram C.

2015-01-01

Understanding climatic influences on the rates and mechanisms of landscape erosion is an unresolved problem in Earth science that is important for quantifying soil formation rates, sediment and solute fluxes to oceans, and atmospheric CO2 regulation by silicate weathering. Glaciated landscapes record the erosional legacy of glacial intervals through moraine deposits and U-shaped valleys, whereas more widespread unglaciated hillslopes and rivers lack obvious climate signatures, hampering mechanistic theory for how climate sets fluxes and form. Today, periglacial processes in high-elevation settings promote vigorous bedrock-to-regolith conversion and regolith transport, but the extent to which frost processes shaped vast swaths of low- to moderate-elevation terrain during past climate regimes is not well established. By combining a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction derived from a paleo-Earth System Model, paleovegetation data, and a paleoerosion archive, we propose that frost-driven sediment production was pervasive during the LGM in our unglaciated Pacific Northwest study site, coincident with a 2.5 times increase in erosion relative to modern rates. Our findings provide a novel framework to quantify how climate modulates sediment production over glacial-interglacial cycles in mid-latitude unglaciated terrain. PMID:26702434

Biogeographical role of the Kuroshio Current in the amphibious mudskipper Periophthalmus modestus indicated by mitochondrial DNA data.

PubMed

He, Lijun; Mukai, Takahiko; Hou Chu, Ka; Ma, Qiang; Zhang, Jing

2015-10-28

Quaternary climatic cycles have influenced marine organisms' spatial distribution and population dynamics. This study aimed to elucidate the evolutionary influences of contemporary and glacial physical barriers on the population structure, demography and colonization history of the mudskipper (Periophthalmus modestus) based on a mitochondrial gene segment (ND5) from 131 individual fish sampled in the northwestern Pacific Ocean. The current Kuroshio Current and the glacial exposure of the Taiwan Strait appeared to have restricted migration among the South China Sea, coastal East China and Japan. However, genetic homogeneity (Nm>1) also suggested contemporary larval transportation by sea circulation between the East China Sea and the South China Sea or historical dispersal along the glacial exposed shoreline among China, Japan and the Ryukyu Islands. Evolutionary signals of the strengthened East Asian Summer Monsoon in the mid-Pleistocene and regional difference in intertidal primary productions were indicated by a late-Pleistocene population expansion of P. modestus with a higher effective population size in the South China Sea than in the East China Sea. Furthermore, a potential colonization origin from the South China Sea was consistently inferred by different clues, including the populations' coalescence times, the ancestral haplotype distribution, the number of private haplotypes and species/genetic diversity.

Biogeographical role of the Kuroshio Current in the amphibious mudskipper Periophthalmus modestus indicated by mitochondrial DNA data

NASA Astrophysics Data System (ADS)

He, Lijun; Mukai, Takahiko; Hou Chu, Ka; Ma, Qiang; Zhang, Jing

2015-10-01

Quaternary climatic cycles have influenced marine organisms’ spatial distribution and population dynamics. This study aimed to elucidate the evolutionary influences of contemporary and glacial physical barriers on the population structure, demography and colonization history of the mudskipper (Periophthalmus modestus) based on a mitochondrial gene segment (ND5) from 131 individual fish sampled in the northwestern Pacific Ocean. The current Kuroshio Current and the glacial exposure of the Taiwan Strait appeared to have restricted migration among the South China Sea, coastal East China and Japan. However, genetic homogeneity (Nm>1) also suggested contemporary larval transportation by sea circulation between the East China Sea and the South China Sea or historical dispersal along the glacial exposed shoreline among China, Japan and the Ryukyu Islands. Evolutionary signals of the strengthened East Asian Summer Monsoon in the mid-Pleistocene and regional difference in intertidal primary productions were indicated by a late-Pleistocene population expansion of P. modestus with a higher effective population size in the South China Sea than in the East China Sea. Furthermore, a potential colonization origin from the South China Sea was consistently inferred by different clues, including the populations’ coalescence times, the ancestral haplotype distribution, the number of private haplotypes and species/genetic diversity.

Impact of glaciers retreat on highland Andean wetlands and communities: lessons from the upper Cachi catchment (Ayacucho, Peru)

NASA Astrophysics Data System (ADS)

Angulo, Oscar; Biévre Bert, De

2017-04-01

The vulnerability of water resources under climate change scenarios in Peru is generally regarded to be connected to a diminished availability of water due to retreating glaciers. However, the impact of glacier retreat goes much beyond a decline of glacial water reserves. This article argues that another important impact is the extreme erosion in areas where glaciers have recently melted, as well as the accumulation of erosion material in highland wetlands located downslope. As a direct consequence of these changes highland Andean communities which depend on these ecosystems are affected in socio-economic terms as they find themselves forced to alter ancestral dynamics and traditional practices of land and water use. This quickly leads to a vicious cycle of risks and threats. In such a context a possibility to adapt to glacial retreat should be to protect areas affected by glacial melt in order to enable a rapid development of protective vegetation cover. In the upper catchment of the Cachi River interesting experiences of protection and water harvesting exist that could be extended to other high vulnerability areas for the benefit of highland populations as well as downstream water users, such as the irrigation system of Cachi and the city of Ayacucho.

Biogeographical role of the Kuroshio Current in the amphibious mudskipper Periophthalmus modestus indicated by mitochondrial DNA data

PubMed Central

He, Lijun; Mukai, Takahiko; Hou Chu, Ka; Ma, Qiang; Zhang, Jing

2015-01-01

Quaternary climatic cycles have influenced marine organisms’ spatial distribution and population dynamics. This study aimed to elucidate the evolutionary influences of contemporary and glacial physical barriers on the population structure, demography and colonization history of the mudskipper (Periophthalmus modestus) based on a mitochondrial gene segment (ND5) from 131 individual fish sampled in the northwestern Pacific Ocean. The current Kuroshio Current and the glacial exposure of the Taiwan Strait appeared to have restricted migration among the South China Sea, coastal East China and Japan. However, genetic homogeneity (Nm>1) also suggested contemporary larval transportation by sea circulation between the East China Sea and the South China Sea or historical dispersal along the glacial exposed shoreline among China, Japan and the Ryukyu Islands. Evolutionary signals of the strengthened East Asian Summer Monsoon in the mid-Pleistocene and regional difference in intertidal primary productions were indicated by a late-Pleistocene population expansion of P. modestus with a higher effective population size in the South China Sea than in the East China Sea. Furthermore, a potential colonization origin from the South China Sea was consistently inferred by different clues, including the populations’ coalescence times, the ancestral haplotype distribution, the number of private haplotypes and species/genetic diversity. PMID:26508474

Natural and anthropic effects on hydrochemistry and major and trace elements in the water mass of a Spanish Pyrenean glacial lake set.

PubMed

Santolaria, Zoe; Arruebo, Tomás; Pardo, Alfonso; Rodríguez-Casals, Carlos; Matesanz, José María; Lanaja, Francisco Javier; Urieta, José Santiago

2017-07-01

This study presents the key hydrochemical characteristics and concentration levels of major (Ca, Mg, Na, Si, K, Sr, Fe) and trace (Ba, Sc, Cr, Mn, Al, As, Li, Co, Cu, U, Pb, Hg, Au, Sn, Zn, Cd, Ag, Ni) elements in the water mass of four selected Pyrenean cirque glacial lakes (Sabocos, Baños, Truchas and Escalar tarns) with different catchment features, between 2010 and 2013. Resulting data set is statistically analyzed to discriminate between the natural or anthropic origin of the elements. Analyses indicate that in all cases, the main source of most major and trace elements is geological weathering, being thus individual bedrock composition the main driver of differences between lakes. Several anthropogenic sources of airborne Cu, Sc, Co, and Cr must be also considered. The shallowness of the lake is also a factor that may influence element cycling and concentration levels in its water mass. Concentrations of anthropogenic elements were low, comparable to those reported in other glacial lakes, way below the WHO, US EPA, EC, and Spanish legal limits for drinking water quality, indicating the absence of serious pollution. Toxic heavy metals Cd, Pb, Hg, and Zn were not detected in any of the tarns.