Science.gov

Sample records for 100-kyr glacial cycle

  1. Plio-Pleistocene time evolution of the 100-kyr cycle in marine paleoclimate records

    NASA Technical Reports Server (NTRS)

    Park, Jeffrey; Maasch, Kirk A.

    1993-01-01

    A new time-series analysis technique (called envelope inversion), which is based on multiple taper spectral analysis, is used to address the question of an abrupt versus a gradual onset of the 100-kyr ice-age periodicity in the middle Pleistocene. Three long (greater than 2.6 m.y.) time series from Deep Sea Drilling Project site 607 (midlatitude Atlantic) and Ocean Drilling Program site 677 (equatorial Pacific) were analyzed using delta(O-18) records. Results do not yield compelling evidence for an abrupt change in the 100-kyr delta(O-18) signal. Rather, the results suggest that the 100-kyr delta(O-18) cycle is phase-locked with the 124-kyr eccentricity cycle some 300-400 kyr prior to its late Pleistocene growth in amplitude and phase lock with the 95-kyr eccentricity cycle.

  2. Frequency variations of the earth's obliquity and the 100-kyr ice-age cycles

    NASA Technical Reports Server (NTRS)

    Liu, Han-Shou

    1992-01-01

    Changes in the earth's climate are induced by variations in the earth's orbital parameters which modulate the seasonal distribution of solar radiation. Periodicities in the geological climate record with cycles of 100, 41, and 23 kyr have been linked with changes in obliquity, eccentricity, and precession of the equinoxes. The effect of variations of eccentricity during a 100 kyr period is weak relative to the signals from obliquity and precession variations and it may therefore be expected that the 100 kyr signal in the climate record would be of low intensity. However, this signal dominates the climate record and internal nonlinear processes within the climate system have previously been proposed to account for this fact. The author shows that variations in the frequency of the obliquity cycle can give rise to strong 100-kyr forcing of climate.

  3. An explanation of the 100 kyr ice age cycle using a simple box model

    NASA Astrophysics Data System (ADS)

    Fowler, A. C.; Rickaby, R. E. M.; Wolff, E. W.

    2012-04-01

    We have developed a conceptually simple box model, similar in philosophy to those of Saltzman, with a view to explaining the 100 kyr period of the most recent ice age signals. Here we explain in detail how and why the various components of the model have been constructed, and we show how the model can be analysed in order to explain its behaviour. We find that the model can explain the 100 kyr cycles as a self-sustaining oscillation, and in addition we can explain the 40 kyr -100 kyr transition, and indeed the post-Eocene cooling, through the variation of weathering rate over geologic time. The central component of the model is an ocean carbon balance, which receives input from the weathering of silicates and carbonates, and loses CaCO3 by the burial of calcareous biomass. It is therefore necessary to also balance calcium and biomass, and thence phosphorus, which we take to be rate limiting. Charge balance is effected through estimates of the conservative ions Na+, Cl-, etc. To this ocean chemistry model we add a simple ice sheet model of the Weertman/Oerlemans/Ghil type, and we allow for rapid deglaciation through an enhanced wastage rate associated with the growth of proglacial lakes like Agassiz. The oscillations which result are due to the interaction of the hysteretic ice sheet growth (allowing for the elevation-accumulation feedback), and a similar hysteresis in the proglacial lake volume. The effect of this on the atmospheric carbon is controlled by the lowering of the carbonate ion which results when the ice sheet meltwater flows into the ocean.

  4. Changes in the occurrence of heavy metals in polar ice during the last climatic cycles, with special emphasis on the possible link between cosmic dust accretion rate and the 100kyr cycle

    NASA Astrophysics Data System (ADS)

    Gabrielli, P.; Barbante, C.; Planchon, F. A. M.; Ferrant, C. P.; Delmonte, B.; Boutron, C. F.

    2003-05-01

    During the last decades, ice cores drilled in Antarctica and in Greenland have provided time series of data that have allowed the characterisation of variations of natural and anthropogenic heavy metals in the past atmosphere. Nevertheless, the interactions of heavy metals with climate change and their transport patterns remain largely unknown during the last climatic cycles. Hereafter we present our project dealing with the assessment of past changes of various heavy metals in Antarctic and Greenland ice during the past = 500kyr anticipating some preliminary Zn measurements in the EPICA Dome C ice core back to about 200000years. In our project special emphasis is given to Pt group elements (PGE) that are tracers of interplanetary dust particles (IDPs). Tracers of crustal material, volcanic activity and ocean paleoproductivity are also investigated. At the moment we are focusing especially on the ongoing EPICA Dome C Antarctic ice core, decontaminating mechanically some section and perfonning preliminary measurements of Zn and Al using Graphite Fumace Atomic Absorption Spectrometry and adopting ultraclean procedures. These data confinn the prominent continental origin of Zn in the East Antarctic ice during the last and penultimate glacial period.

  5. Late Neogene East Asian monsoon: from winter to summer dominated sub-regime and periodicity transition from 100 kyr to 41 kyr

    NASA Astrophysics Data System (ADS)

    Li, F.; Rousseau, D.-D.; Wu, N.; Hao, Q.; Pei, Y.

    2009-04-01

    More and more evidence indicates that the onset of the East Asian (EA) monsoon can be traced back to the Oligocene-Miocene boundary (at about 23 Ma). However, the process of its evolution is still less well known until now. Here we investigate its late Neogene evolution by analyzing a terrestrial mollusk sequence, from the Chinese Loess Plateau (CLP), covering the period between 7.1 and 3.5 Ma. Considering the modern ecological requirements of these organisms, we were able to define two groups of cold-aridiphilous (CA) and thermo-humidiphilous (TH) species, representing the EA winter and summer monsoon variations, respectively, as previously defined in the Quaternary glacial-interglacial cycles. Variations in these two groups indicate two different monsoon dominated periods during 7.1-3.5 Ma. First, between 7.1 and 5.5 Ma, the EA winter monsoon, with a 100 kyr periodicity, was dominant. Second, between 5.1 and 4 Ma, the EA summer monsoon dominated, with a 41 kyr periodicity. Furthermore, our mollusk record yields valuable evidence for a late Miocene-Pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated, associated with a periodicity transition from weak 100 kyr to 41 kyr. The strengthened winter monsoon interval, with a 100 kyr periodicity, is coeval with orbital-scale global ice volume changes, in conjunction with the uplift of the Tibetan Plateau which probably reinforced the winter monsoon sub-regime. Conversely, closures of the Panama and Indonesian seaways, associated with changes in obliquity between 5.1 and 4 Ma, are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency, favoring heat and moisture transports between low and high latitudes to allow TH mollusks to grow and develop in the CLP. The transition from a 100 kyr dominated interval towards a 41 kyr dominated one is contrary to the mid-Pleistocene transition (MPT), which corresponds to ice volume expansion at high

  6. 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.

  7. Tracing the glacial sulphur cycle

    NASA Astrophysics Data System (ADS)

    Hansson, M. E.; Jonsell, U.; Bigler, M.; de Angelis, M.; Fischer, H.; Siggaard-Andersen, M.-L.; Steffensen, J. P.; Udisti, R.; Wolff, E.

    2003-04-01

    Sulphate aerosols are playing a major role in climate forcing in the present atmosphere and therefore possibly also during other climatic stages. The deposition of sulphur-containing species onto polar ice sheets provides a tool for determining variations in the sulphur cycle in the past. Relatively short atmospheric residence times for sulphate aerosols cause spatial gradients and a high sensitivity to variations in the general circulation of the atmosphere and the hydrological cycle. Several factors may influence the air-snow transfer functions and post-depositional process may modify the deposited signal. Therefore, both a large spatial and temporal coverage is needed to identify significant changes in the sulphur cycle in the past. The EPICA Dome C ice core from Antarctica is providing the longest records ever, spanning several glacial cycles. Unique high-resolution chemical records, from discontinuous samples analysed by Ion Chromatography (IC), are gradually evolving from the cooperation between the laboratories in the EPICA Chemistry Consortium. The EPICA DML ice core is analysed in parallel by the same laboratories and the profiles are growing with the progress of the drilling each season. The sulphate and methane sulphonate records are here in focus and will be presented as far as they reach at present. High-resolution chemical records are now also available from the NorthGRIP ice core from Greenland spanning the last glacial cycle. An interhemispheric comparison of sulphur-containing species during the glacial period will be presented, using both new high-resolution data and previous ice core data from a few locations as well as initial results from sulphur isotope measurements, with the aim to increase our understanding of variations in the global sulphur cycle with climate change.

  8. Glacial cycles and astronomical forcing

    SciTech Connect

    Muller, R.A.; MacDonald, G.J.

    1997-07-11

    Narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces. Two million years ago, the cycles match the 41,000-year period of Earth`s obliquity. This supports the Croll/Milankovitch theory, which attributes the cycles to variations in insolation. But for the past million years, the spectrum is dominated by a single 100,000-year feature and is a poor match to the predictions of insolation models. The spectrum can be accounted for by a theory that derives the cycles of glaciation from variations in the inclination of Earth`s orbital plane.

  9. Controls of the Northern Hemisphere Hadley circulation over the last five glacial cycles

    NASA Astrophysics Data System (ADS)

    Meckler, A. N.; Roehl, U.; Adkins, J. F.; Haug, G. H.

    2012-12-01

    Sediments off the coast of Mauritania have proven to be sensitive recorders of climate in the adjacent Sahel zone and Saharan desert. It has been shown that climate in this region is highly sensitive to both local insolation forcing, dominated by orbital precession, and high latitude millennial-scale cooling events. However, most available high-resolution records are relatively short, covering at most the last glacial cycle. Here we extend the existing grain-size-based humidity record from core GeoB7920-2 (Tjallingii et al., Nature Geoscience, 2008) back to 550 kyr BP, using sediments from ODP Site 658 at the same location. We employ the XRF-scanning-derived Zr/Al ratio as a proxy for grain-size, which corresponds well to the published humidity index over the last 110 kyr. Grain-size is expected to be a mixed signal of continental aridity and wind strength, whereby the Northeasterly trade winds are the dominant source of dust at this site. The data from Site 658 should therefore reflect the northern components of the low-latitude Hadley circulation, with larger grain-sizes reflecting stronger NE trade winds and/or increased aridity (related to atmospheric subsidence). Reconstructions of precipitation in tropical Borneo (Meckler et al., Science, 2012), at the heart of the convective limb of the Hadley cell, show many similarities. In combination, the two data sets therefore likely reflect variations in strength of the Northern Hemisphere Hadley circulation. The records show clear precession-related cyclicity. In addition, the 100-kyr glacial-interglacial cycles are also apparent, with maxima in grain-size at Site 658 characterizing all glacial periods. Finally, shorter, millennial-scale events are evident at both locations. The presented data therefore reveal a persistent triumvirate of forcing factors, consisting of local insolation, high-latitude ice volume, and millennial-scale high-latitude cooling.

  10. Variations in mid-ocean ridge CO2 emissions driven by glacial cycles

    NASA Astrophysics Data System (ADS)

    Burley, Jonathan M. A.; Katz, Richard F.

    2015-09-01

    The geological record documents links between glacial cycles and volcanic productivity, both subaerially and, tentatively, at mid-ocean ridges. Sea-level-driven pressure changes could also affect chemical properties of mid-ocean ridge volcanism. We consider how changing sea-level could alter the CO2 emissions rate from mid-ocean ridges on both the segment and global scale. We develop a simplified transport model for a highly incompatible trace element moving through a homogeneous mantle; variations in the concentration and the emission rate of the element are the result of changes in the depth of first silicate melting. The model predicts an average global mid-ocean ridge CO2 emissions rate of 53 Mt/yr or 91 Mt/yr for an average source mantle CO2 concentration of 125 or 215 ppm by weight, in line with other estimates. We show that falling sea level would cause an increase in ridge CO2 emissions about 100 kyrs after the causative sea level change. The lag and amplitude of the response are sensitive to mantle permeability and plate spreading rate. For a reconstructed sea-level time series of the past million years, we predict variations of up to 12% in global mid-ocean ridge CO2 emissions.

  11. 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.

  12. Modelling 100 kyr of transient climate change during the Pliocene (MIS M2 to MIS KM5c)

    NASA Astrophysics Data System (ADS)

    Hunter, S. J.; Dolan, A. M.; Haywood, A. M.

    2014-12-01

    The mid-Pliocene warm period (3.264-3.025 Ma) is a key target for palaeoclimate modellers in the investigation of warm intervals in Earth history. This research is driven by the need to evaluate climate models against geological data in order to assess model performance in warmer than present climates. The mid-Pliocene has generally been modelled using fixed-boundary condition climate model experiments, such as those performed for the Pliocene Model Intercomparison Project (PlioMIP). This means that orbital-timescale variability in climate is often overlooked. In the past data-model comparisons have primarily focussed on comparing snap-shot experiments (fixed boundary conditions) with time-averaged data (for example PRISM3 data which is representative of an average of ~250,000 years). In order to improve the validity of proxy-data and model comparisons it is critical that we move towards climate simulations that better capture changing bounding conditions occurring over orbital timescales and compare these with timeseries data. Here, we present two sets of transient simulations; the first is centred on the warm interglacial peak, MIS KM5c (+/-20 kyr) whilst the second runs from the glacial peak MIS M2 through to MIS KM5c (~100 kyr). We use the full-complexity intermediate-resolution FAMOUS climate model driven by PRISM3 boundary conditions (which were also used in PlioMIP phase 1). Our initial experiments apply a changing orbit, with and without dynamic vegetation. We present an overview of climate variability during these time windows, but also discuss the difficulties that have been faced in such modelling and detail some ideal future directions to explore

  13. Fault slip during a glacial cycle

    NASA Astrophysics Data System (ADS)

    Steffen, Rebekka; Wu, Patrick; Steffen, Holger; Eaton, Dave

    2013-04-01

    Areas affected by glacial isostatic adjustment (GIA) generally show uplift after deglaciation. These regions are also characterized by a moderate past and present-day seismicity, at seismic moment release rates that exceed those expected under stable tectonic conditions. Several faults have been found in North America and Europe, which have been activated during or after the last deglaciation. Large-magnitude earthquakes have generated fault offsets of up to 120 m. Due to the recent melting of Greenland and Antarctic ice sheets, an understanding of the occurrence of these earthquakes is important. With a new finite-element model, we are able to estimate, for the first time, fault slip during a glacial cycle for continental ice sheets. A two-dimensional earth model based on former GIA studies is developed, which is loaded with a hyperbolic ice sheet. The fault is able to move in a stress field consisting of rebound stress, tectonic background stress, and lithostatic stress. The sensitivity of this fault is tested regarding lithospheric and crustal thickness, viscosity structure of upper and lower mantle, ice-sheet thickness and width, and fault parameters including coefficient of friction, depth, angle and location. Fault throws of up to 30 m are obtained using a fault of 45° dipping below the ice sheet centre. The thickness of the crust is one of the major parameters affecting the total fault throw, e.g. higher values for a thinner crust. Most faults start to move close to the end of deglaciation, and movement stops after one thrusting/reverse earthquake. However, certain conditions may also lead to several fault movements after the end of glaciations.

  14. 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

  15. 100 Kyr Old Desert of Western India: Morhodynamics and Environmental Significance

    NASA Astrophysics Data System (ADS)

    Bhatt, N.

    2012-04-01

    The Late Quaternary oscillations in sea levels and resultant changes in the coastal environment have remained a popular aspect of study amongst the earthscientists and archaeologists. The Saurashtra peninsula of the western India that lies on the southwestern side of the Thar Desert, has archived a fascinating record of such environmental changes since last interglacial (~120kyr) in the form of a fossil desert exhibiting various aeolian land forms constituted by the sand largely derived from the coastal areas due to an oscillatory sea level change. A variety of dunes viz., coastal transverse, parabolic, longitudinal, barchans, climbing and falling dunes along with valley fills and sand sheets have been mapped. Being biogenic calcium carbonate rich, the sands have been lithified under the influence of an increase in moisture and thus the dune and bed forms are preserved in its best shape. The intense aeolian activities are also evident in the form of desert varnish on rocky outcrops. The sequence comprises smaller climate perturbations in the form of stabilization, erosion and karstification of older dunes and deposition of fluvial sediments in between. The paper deals with the mode of occurrence, response of sediments to wind dynamics and palaeo topography, internal structures, later modifications of sediments and significance of the geochronologically constrained aeolianites in understanding of environmental changes since 100kyr in the region.

  16. Geothermal activity helps life survive glacial cycles.

    PubMed

    Fraser, Ceridwen I; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L

    2014-04-15

    Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species.

  17. Geothermal activity helps life survive glacial cycles

    PubMed Central

    Fraser, Ceridwen I.; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L.

    2014-01-01

    Climate change has played a critical role in the evolution and structure of Earth’s biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this “geothermal glacial refugia” hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  18. Geothermal activity helps life survive glacial cycles.

    PubMed

    Fraser, Ceridwen I; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L

    2014-04-15

    Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  19. 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

  20. Precise prediction of glacial cycle with its rhythm

    NASA Astrophysics Data System (ADS)

    Lai, C.; Tseng, Y.; Yu, W.; Chueh, P.

    2010-12-01

    An ability to explain and predict the paleoclimatic cycles is one of necessary conditions for reliable predictions of future climate without and with anthropogenic forcing. Here, we solved a big puzzle. Quaternary glacial cycles, as represented by climate proxy data of benthic δ18O, can be divided into four typical periods (TP) with four characteristic points (CP). The cyclic sequence of them goes in the following order: (1) Onset point of glacial termination, (2) Glacial termination period, (3) Zip point of glacial termination, (4) Inter-glacial period, (5) Inception point of glaciations, (6) Period for glacial maturation, (7) Glacial maximum point, and (8) Period for glacial hibernation. The glacial termination (GT) is a swift transition period of about 6,500 years only. A precise prediction of its onset point is a great challenge to the theorem of orbital-forcing that is being developed since Milankovitch. We consider the climate system as a stack of heat capacitors that get warmed up by absorbing part of the insolation and cooled down via gray-body radiation. Part of the insolation is transformed into chemical energy through photosynthesis (CETP) and eventually gets accumulated in the clathrate hydrate (CH) in seawater. We found that, during the last 1.7 million years, every Onset point of GT falls in a very precise time-window defined with three conditions: (1) the eccentricity (E) of Earth’s orbit is increasing, (2) the obliquity (T) is also increasing, and (3) the phase angle of precession (P) falls between 7π/8 and 5π/4. The CETP is converted into sensible heat via oxidation of gases released from dissociated CH. The dissociation of CH depends on its floating level and dissociating level. Those levels are controlled by seawater temperature and the density of CH. The Zip point of GT comes when the average temperature of seawater at 150 m depth is about 18 C, which is mostly influenced by the H2S in the CH. We define the Inception point of glaciations as

  1. Glacial cycles drive variations in the production of oceanic crust.

    PubMed

    Crowley, John W; Katz, Richard F; Huybers, Peter; Langmuir, Charles H; Park, Sung-Hyun

    2015-03-13

    Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth's interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor. PMID:25766231

  2. Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland

    NASA Astrophysics Data System (ADS)

    Löwemark, Ludvig; Chao, Weng-Si; Gyllencreutz, Richard; Hanebuth, Till J. J.; Chiu, Pin-Yao; Yang, Tien-Nan; Su, Chih-Chieh; Chuang, Chih-Kai; León Dominguez, Dora Carolina; Jakobsson, Martin

    2016-09-01

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<<5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10-20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MIS 5 appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a

  3. Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing

    NASA Astrophysics Data System (ADS)

    Huybers, Peter

    2006-07-01

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun.

  4. Early Pleistocene glacial cycles and the integrated summer insolation forcing.

    PubMed

    Huybers, Peter

    2006-07-28

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun. PMID:16794041

  5. Testing hypotheses about glacial cycles against the observational record

    NASA Astrophysics Data System (ADS)

    Kaufmann, Robert K.; Juselius, Katarina

    2013-01-01

    We estimate an identified cointegrated vector autoregression model of the climate system to test hypotheses about the physical mechanisms that may drive glacial cycles during the late Pleistocene. Results indicate that a permanent doubling of CO2 generates a 11.1°C rise in Antarctic temperature. Large variations in atmospheric CO2 over glacial cycles are driven by changes in sea ice and sea surface temperature in southern oceans and marine biological activity. The latter can be represented by a two-step process in which iron dust increases biological activity and the increase in biological activity reduces CO2 concentrations. Glacial variations in ice volume, as proxied by δ18O are driven by changes in CO2 concentrations, global and high latitude solar insolation, latitudinal gradients in solar insolation, and the atmospheric concentration of CO2. The model is able to quantify the effects of ice volume and temperature on sea level, such that in the long-run, sea level rises 14 m per 0.11‰ δ18O and about 17 m/°C of sea surface temperature in southern oceans. Beyond these specific results, the multivariate model suggests omitted variables may bias bivariate analyses of these mechanisms.

  6. 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

    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.

  7. Volcanic evolution of an active magmatic rift segment on a 100 Kyr timescale: exposure dating of lavas from the Manda Hararo/Dabbahu segment of the Afar Rift

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Williams, A.; Pik, R.; Burnard, P.; Vye, C.; France, L.; Ayalew, D.; Yirgu, G.

    2012-12-01

    In the Afar depression (Ethiopia), extension is already organised along rift segments which morphologically resemble oceanic rifts. Segmentation here results from interactions between dyke injection and volcanism, as observed during the well documented 2005 event on the Dabbahu rift segment. During this tectono-volcanic crisis, a megadyke was injected, followed by 12 subsequent dike intrusions, sometimes associated with fissure flow eruptions. Despite the accurate surveying of the magmatic and tectonic interplay during this event via remote sensing techniques, there is a lack of data on timescales of 1 to 100 kyr, the period over which the main morphology of a rift is acquired. The Dabbahu rift segment represents an ideal natural laboratory to study the evolution of rift morphology as a response to volcanic and tectonic influences. It is possible to constrain the timing of fault growth relative to the infilling of the rift axial depression by lava flows, and to assess the influence of the different magma bodies involved in lava production along the rift-segment. We use cosmogenic nuclides (3He) to determine the ages of young (<100 kyr) lava flows and to date the initiation and movement of fault scarps which cut the lavas. Combined with major & trace element compositions, field mapping and digital cartography (Landsat, ASTER and SPOT imagery), the rift geomorphology can be linked to the magmatic and tectonic history defined by surface exposure dating. The results show that over the last 100 ka the Northern part of the Dabbahu segment was supplied by two different magma reservoirs which can be identified based on their distinctive chemistries. The main reservoir is located beneath Dabbahu volcano, and has been supplied with magma for at least 72 ka. This magmatic centre supplies magma to most of the northern third of the rift segment. The second reservoir is located further south, on the axis, close to the current mid-segment magma chamber, which was responsible for

  8. Global Ice-loading History Reconstructed Over Five Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Williams, F. H.; Grant, K. M.; Tamisiea, M. E.; Rohling, E. J.; Hibbert, F. D.

    2014-12-01

    High resolution ice-loading reconstructions are a vital tool not only for palaeoclimate studies, but also for providing a palaeoenvironmental context to human development. Here we present a global ice-loading history developed using the high resolution, Red Sea relative sea-level (RSL) record. (Siddall et al. 2003, Rohling et al. 2009, Grant et al. in submission) We use glacial isostatic adjustment modelling to determine a set of corrections to the Red Sea RSL record, which is then translated into a global mean sea level. This global mean sea level allows us to calculate a global ice volume. Global ice volume is geographically distributed within our ice-loading history according to currently available data regarding ice margins, their timing, and constraints on maximum ice load. Where constraints are sparse we use a combination of ICE-5G (Peltier, 2004) and the de Boer coupled ice sheet model (de Boer et al, 2014) as a template for ice distribution. Although an ice-loading history for the past 5 Myr exists, this is the first time that geographic constraints have been applied to global ice volumes over 5 glacial cycles. Our ice-loading reconstruction is further supported by the high resolution of our source RSL data. Our ice-loading history is tested against a global compilation of coral sea-level indicators (Hibbert et al., in prep.), and compared with ice histories developed from alternate ice volume reconstructions or RSL records, including a global ice history based on that developed by de Boer et al. (2014), the sea-level record of Waelbroeck et al. (2002) and a simple ice history based on the δ18O stack of Lisiecki and Raymo (2005).

  9. Sea-level variability over five glacial cycles.

    PubMed

    Grant, K M; Rohling, E J; Ramsey, C Bronk; Cheng, H; Edwards, R L; Florindo, F; Heslop, D; Marra, F; Roberts, A P; Tamisiea, M E; Williams, F

    2014-09-25

    Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2 m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2 kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records.

  10. Sea-level variability over five glacial cycles.

    PubMed

    Grant, K M; Rohling, E J; Ramsey, C Bronk; Cheng, H; Edwards, R L; Florindo, F; Heslop, D; Marra, F; Roberts, A P; Tamisiea, M E; Williams, F

    2014-01-01

    Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2 m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2 kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records. PMID:25254503

  11. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Headley, R. M.; Ehlers, T. A.

    2015-03-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological timescales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model yields erosion rates that vary spatially and by almost an order of magnitude from those of the SIA model. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered area that are greater than 30% those of the SIA model, again with larger differences for temperate ice. Over multiple glaciations and long timescales, these results suggest that higher-order glacial physics should be considered, particularly in temperate, mountainous settings.

  12. Modelling of Gas Hydrate Dissociation During The Glacial-Inter-glacial Cycles, Case Study The Chatham Rise, New Zealand

    NASA Astrophysics Data System (ADS)

    Oluwunmi, P.; Pecher, I. A.; Archer, R.; Moridis, G. J.; Reagan, M. T.

    2015-12-01

    Seafloor depressions covering an area of >20,000 km2 on the Chatham Rise, south east of New Zealand, have been interpreted as pockmarks which are related to past fluid releases. It is proposed that the seafloor depressions were caused by sudden escape of overpressured gas generated by gas hydrate dissociation during glacial sea-level lowering. We are attempting to simulate the evolution of the gas hydrate system through glacial-interglacial cycles in the study area using TOUGH-Hydrate. The Chatham Rise offers a unique opportunity for studying the effect of depressurization from sealevel lowering to gas hydrate systems because it is a bathymetric barrier preventing the Subtropical Front separating subtropical and subantarctic waters from migrating during glacial-interglacial cycles. Hence, bottom-water temperatures can be assumed to remain constant. Recent results from paleoceanographic studies however, indicate that bottom-temperature may have varied locally. These temperature changes may have a more significant effect on the shallow gas hydrate system in the study area than the relatively gradual decrease of pressure associated with sealevel lowering.

  13. 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). PMID:25517093

  14. Laurentide Ice Sheet basal temperatures during the last glacial cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Pickler, C.; Beltrami, H.; Mareschal, J.-C.

    2016-01-01

    Thirteen temperature-depth profiles ( ≥ 1500 m) measured in boreholes in eastern and central Canada were inverted to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region that was covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0 °C throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, allowed basal flow and fast flowing ice streams at the base of the Laurentide Ice Sheet. Despite such conditions, which have been inferred from geomorphological data, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  15. Laurentide Ice Sheet basal temperatures at the Last Glacial Cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Pickler, C.; Beltrami, H.; Mareschal, J.-C.

    2015-08-01

    Thirteen temperature-depth profiles (≥ 1500 m) measured in boreholes in eastern and central Canada were inverted to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0 °C throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, allowed basal flow and fast flowing ice streams at the base of the Laurentide Ice Sheet. Despite such conditions, which have been inferred from geomorphological data, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  16. Laurentide Ice Sheet basal temperatures at the Last Glacial Cycle as inferred from borehole data

    NASA Astrophysics Data System (ADS)

    Mareschal, Jean-Claude; Pickler, Carolyne; Beltrami, Hugo

    2016-04-01

    We measured and inverted thirteen temperature-depth profiles (≥1500 m) in boreholes in eastern and central Canada to determine the ground surface temperature histories during and after the last glacial cycle. The sites are located in the southern part of the region covered by the Laurentide Ice Sheet. The inversions yield ground surface temperatures ranging from -1.4 to 3.0oC throughout the last glacial cycle. These temperatures, near the pressure melting point of ice, demonstrate that the southern portion of the Laurentide Ice Sheet was not frozen to the bed, allowing for basal flow and fast flowing ice streams at the base. Despite such conditions, which have been inferred from geomorphological data and models, the ice sheet persisted throughout the last glacial cycle. Our results suggest some regional trends in basal temperatures with possible control by internal heat flow.

  17. Deep Arctic Ocean warming during the last glacial cycle

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Farmer, J.; Bauch, H.A.; Spielhagen, R.F.; Jakobsson, M.; Nilsson, J.; Briggs, W.M.; Stepanova, A.

    2012-01-01

    In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1–2 °C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

  18. Seasonality in the Arabian Sea over glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    de Nooijer, L. J.; Tjallingii, R.; Brummer, G. J.; Reichart, G. J.

    2012-04-01

    The Indian monsoon system controls seasonal precipitation alterations over the Indian continent and upwelling of nutrient-rich waters to the surface in the northern Arabian Sea. Functioning and strength of this weather system due to climate change is one of the important issues in predicting the effects of global warming on the region's economy, agriculture and social welfare. The strength of the Indian monsoon system through time can be studied by changes in seawater temperature and chemistry from single-specimen analysis of planktic foraminiferal calcite. Temperature reconstructions based on many single specimens allow reconstruction of past seasonal sea water temperatures ranges and thus seasonal temperature variability. . Here we present seawater reconstructions based on single-specimen Mg/Ca of the surface dweller Globigerinoides ruber and the deeper-living G. dutertrei of two sediment cores of the western equatorial Indian Ocean off Tanzania and the northern Arabian Sea. From both cores, specimens are analyzed for calcitic Mg/Ca using laser ablation-ICP-MS of time-intervals representing the Holocene optimum, Last Glacial Maximum, Marine Isotope Stage 4, MIS 5 and MIS6. The resulting temperature ranges allow reconstruction of variability in the strength of the Indian Monsoon as well as cross-equatorial heat transport during glacials and interglacials.

  19. Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles

    NASA Astrophysics Data System (ADS)

    Wilson, David J.; Piotrowski, Alexander M.; Galy, Albert; Banakar, Virupaxa K.

    2015-06-01

    Changes in ocean circulation structure, together with biological cycling, have been proposed for trapping carbon in the deep ocean during glacial periods of the Late Pleistocene, but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles. In this study, we use neodymium (Nd) and carbon isotopes from a deep Indian Ocean sediment core to reconstruct water mass mixing and carbon cycling in Circumpolar Deep Water over the past 250 thousand years, a period encompassing two full glacial cycles and including a range of orbital forcing. Building on recent studies, we use reductive sediment leaching supported by measurements on isolated phases (foraminifera and fish teeth) in order to obtain a robust seawater Nd isotope reconstruction. Neodymium isotopes record a changing North Atlantic Deep Water (NADW) component in the deep Indian Ocean that bears a striking resemblance to Northern Hemisphere climate records. In particular, we identify both an approximately in-phase link to Northern Hemisphere summer insolation in the precession band and a longer-term reduction of NADW contributions over the course of glacial cycles. The orbital timescale changes may record the influence of insolation forcing, for example via NADW temperature and/or Antarctic sea ice extent, on deep stratification and mixing in the Southern Ocean, leading to isolation of the global deep oceans from an NADW source during times of low Northern Hemisphere summer insolation. That evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions. However, mid-depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods, and a return to an interglacial-like circulation state during marine isotope stage (MIS) 6.5 was accompanied by only minor changes in atmospheric CO2. Although a gradual reduction of NADW export through glacial periods may have produced slow climate feedbacks

  20. Indonesian Throughflow variability over the last glacial cycle (Invited)

    NASA Astrophysics Data System (ADS)

    Holbourn, A. E.; Kuhnt, W.; Regenberg, M.; Xu, J.; Hendrizan, M.; Schröder, J.

    2013-12-01

    The transfer of surface and intermediate waters from the Pacific Ocean to the Indian Ocean through the Indonesian archipelago (Indonesian Throughflow: ITF) strongly influences the heat and freshwater budgets of tropical water masses, in turn affecting global climate. Key areas for monitoring past ITF variations through this critical gateway are the narrow passages through the Makassar Strait and Flores Sea and the main outflow area within the Timor Sea. Here, we integrate high-resolution sea surface temperature and salinity reconstructions (based on paired planktic foraminiferal Mg/Ca and δ18O) with X-ray fluorescence runoff data and benthic isotopes from marine sediment cores retrieved in these regions during several cruises with RV'Sonne' and RV'Marion Dufresne'. Our results show that high latitude climate variability strongly influenced ITF intensity on millennial to centennial timescales as well as on longer glacial-interglacial timescales. Marked declines in ITF strength occurred during Heinrich events and the Younger Dryas, most likely related to slowdown of the global thermohaline circulation during colder northern hemisphere climate spells, when deep water production decreased and the deep ocean became more stratified. Additionally, the surface component of the ITF strongly reflects regional windstress and rainfall patterns, and thus the spatial extent and intensity of the tropical convection over the Indonesian archipelago. Our runoff and salinity estimates reveal that the development of the tropical convection was intricately linked to the latitudinal migration of the Inter Tropical Convergence Zone (ITCZ). In particular, our data show that the Australian monsoon intensified during the major deglacial atmospheric CO2 rise through the Younger Dryas and earliest Holocene (12.9-10 ka). This massive intensification of the Australian monsoon coincided with a southward shift of the ITCZ, linked to southern hemisphere warming and enhanced greenhouse forcing

  1. Role of marine biology in glacial-interglacial CO2 cycles.

    PubMed

    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.

  2. The first Greenland ice core record of methanesulfonate and sulfate over a full glacial cycle

    SciTech Connect

    Hansson, M.E.; Saltzman, E.S. )

    1993-06-18

    The authors report on methanesulfonate and non-seasalt sulfate found in an artic ice core from Greenland. The ice core record stretches back in time roughly 130,000 years, through a full glacial cycle. This record reveals a decreasing concentration of MSA with the advance of the glacial period, and a drop in temperatures, while the non-seasalt sulfate increased in concentration. The MSA data is in contrast to similar measurements from the southern hemisphere. The ratio of MSA to non-seasalt sulfate is found to have a strong linear relationship to the temperature, higher ratios being associated with warmer climatic periods.

  3. 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).

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

    NASA Astrophysics Data System (ADS)

    Seguinot, J.; Rogozhina, I.; Stroeven, A. P.; Margold, M.; Kleman, J.

    2015-08-01

    Despite more than a century of geological observations, the Cordilleran ice sheet of North America remains poorly understood in terms of its former extent, volume and dynamics. Although geomorphological evidence is abundant, its complexity is such that whole ice-sheet 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 (61.9-56.5 ka) and 2 (23.2-16.8 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 (6.6-6.2 ka).

  5. Millennial-scale climate variability in response to changing glacial and orbital boundary conditions during the Mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon; Drysdale, Russell; Bajo, Petra; Barbante, Carlo

    2016-04-01

    The Mid-Pleistocene transition represents perhaps the most important climate transition in the Quaternary period, yet it is one of the most poorly understood. Although the exact timing and mechanism of the onset of the "100 kyr" regime remain a matter of debate, it is well established that the overall periodicity of the glacial-interglacial cycles changed from a dominant 41 kyr obliquity periodicity prior to ~0.9 Ma to a dominant late Pleistocene 100 kyr variance. This change in the frequency domain was associated with an increase in the amplitude of global ice volume variations that, superimposed on a long-term climatic trend towards more glacial conditions over millions of years, produced some of the most extreme glaciations recorded. This interval of time has often been considered to be important in relation to long-term Milankovitch-scale climate variability. In contrast, here, special emphasis will be placed on assessing the presence and the characteristics of the suborbital-scale variability, and reconstructing the evolution of millennial-scale climate variability as the average climate state evolve toward generally colder conditions with larger ice sheets, and the spectral character of climate variability shifted from dominantly 41 kyr to 100 kyr. Appealing evidence suggests that millennial-scale climate variability is amplified during times of intense forcing changes, but this rapid variability has not been thoroughly explored yet at the time when the major changes in climate periodicity occurred. To address these questions, we have examined the record of climatic conditions from Marine Isotope Stages 25 to 16 (~970-650 ka) using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess millennial-scale changes in sea-surface and deep-water conditions, the dynamics of thermohaline deep-water circulation

  6. Technical Note: Glacial influence in tropical mountain hydrosystems evidenced by the diurnal cycle in water levels

    NASA Astrophysics Data System (ADS)

    Cauvy-Fraunié, S.; Condom, T.; Rabatel, A.; Villacis, M.; Jacobsen, D.; Dangles, O.

    2013-12-01

    Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Determining the influence of glacial runoff to streams is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose quantifying the diurnal cycle amplitude of the streamflow to determine the glacial influence in glacierized catchments. We performed water-level measurements using water pressure loggers over 10 months at 30 min time steps in 15 stream sites in 2 glacier-fed catchments in the Ecuadorian Andes (> 4000 m a.s.l.) where no perennial snow cover is observed outside the glaciers. For each stream site, we performed wavelet analyses on water-level time series, determined the scale-averaged wavelet power spectrum at 24 h scale and defined three metrics, namely the power, frequency and temporal clustering of the diurnal flow variation. The three metrics were then compared to the percentage of the glacier cover in the catchments, a metric of glacial influence widely used in the literature. As expected, we found that the diurnal variation power of glacier-fed streams decreased downstream with the addition of non-glacial tributaries. We also found that the diurnal variation power and the percentage of the glacier cover in the catchment were significantly positively correlated. Furthermore, we found that our method permits the detection of glacial signal in supposedly non-glacial sites, thereby revealing glacial meltwater resurgence. While we specifically focused on the tropical Andes in this paper, our approach to determine glacial influence may have potential applications in temperate and arctic glacierized catchments. The measure of diurnal water

  7. Paraglacial rock mass damage during repeat glacial cycles in preparing slope instabilities (Aletsch region, Switzerland)

    NASA Astrophysics Data System (ADS)

    Grämiger, Lorenz; Moore, Jeffrey R.; Gischig, Valentin S.; Loew, Simon

    2016-04-01

    Glacier advance and retreat imposes mechanical stress cycles on underlying bedrock. Stress changes propagate rock mass damage and act as preparatory factors for slope instabilities, however, the mechanics of paraglacial rock slope damage remains poorly understood. In this study, we present results of detailed, conceptual numerical models, based on extensive field mapping and characterization at our Aletsch valley study site, Switzerland. We illustrate how simple stress changes associated with repeat glacial cycles can propagate fractures, enhance slip along discontinuities, and lead to failure of intact rock bridges, conditioning adjacent valley slopes for failure. We describe the timing and location of induced damage, stress redistribution, and displacement associated with Late Pleistocene and Holocene glacial cycles, and compare numerical predictions with the spatial and temporal distribution of landslides around the Great Aletsch Glacier. Our results help clarify mechanical linkages between glacial cycles and damage propagation in alpine valley rock slopes. In our simulations, most damage occurs during first deglaciation. This is in good agreement with the relative initiation timing (post-LGM / post-Egesen) for the majority of identified landslides at Aletsch. Large Holocene glacial cycles with high amplitude ice elevation changes in our models have a significant impact on displacement patterns in adjacent slopes. This correlates with a concentrated area of landslides located around the present-day glacier terminus, where the Great Aletsch Glacier fluctuated most during the Holocene. The kinematics and dimensions of an unstable rock slope produced in our models also generally resembles field observations of toppling-mode landslides on the eastern slope. No substantial displacement was generated on the western slope, although compound rock slides are observed on the western flank in the Aletsch.

  8. Changes in ocean denitrification during Late Carboniferous glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Algeo, Thomas; Rowe, Harry; Hower, James C.; Schwark, Lorenz; Herrmann, Achim; Heckel, Phil

    2008-10-01

    Denitrification (the process by which nitrate and nitrite are reduced to nitrogen gas) in the oxygen-minimum zones of modern oceans is an important part of the global nitrogen cycle. Variations in rates of denitrification over Quaternary glacial-interglacial timescales may have affected global climate. Evidence of denitrification has been reported from some older marine systems, but it is unclear whether denitrification rates varied during pre-Quaternary glacial cycles. Here we present ratios of organic carbon to nitrogen and nitrogen isotope data from the Upper Carboniferous black shales of the North American mid-continent. In these cyclic deposits, we find evidence of variations in the intensity of denitrification in the eastern tropical Panthalassic Ocean associated with glacially driven sea-level changes. Sedimentary δ15N increases during the interval of rapid sea-level rise in each cycle, indicative of intensified denitrification, before returning to background levels as sea level stabilized during the interglacial phase. Nearly identical patterns of denitrification have been observed in the eastern tropical Pacific during the Quaternary period. We therefore conclude that ice ages have produced similar oceanographic conditions and nitrogen cycle dynamics in these regions over the past 300million years.

  9. The Dole effect over the last two glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Malaizé, B.; Paillard, D.; Jouzel, J.; Raynaud, D.

    1999-06-01

    Detailed measurements of δ18O of atmospheric oxygen performed on air trapped in the Vostok ice cores (Antarctica) are used to extend the record of the Dole effect over two climatic cycles (back to 240 kyr B.P.). Except for glacial terminations I and II and for an unexpected minimum occurring around 175 kyr, the Dole effect shows small variations (ΔDole within ± 0.5‰). These small variations, however, show a well-marked 23 kyr precessional periodicity, thus confirming the results obtained by Bender et al. [1994a] for the first climatic cycle. To explain the minimum value reached around 175 kyr, we invoke the possibility of a peak in the oceanic productivity linked to climatic events induced at low latitudes under glacial conditions.

  10. Glacial cycles and solar insolation: the role of orbital, seasonal, and spatial variations

    NASA Astrophysics Data System (ADS)

    Kaufmann, R. K.; Juselius, K.

    2010-11-01

    We use a statistical model, the cointegrated vector autoregressive model, to evaluate the relative roles that orbital, seasonal, and spatial variations in solar insolation play in glacial cycles during the late Quaternary (390kyr - present). To do so, we estimate models of varying complexity and compare the accuracy of their in-sample simulations. Results indicate that variations in solar insolation associated with changes in Earth's orbit have the greatest explanatory power and that obliquity, precession, and eccentricity are needed to generate an accurate simulation of glacial cycles. Seasonal variations in insolation play a lesser role, while cumulative summer-time insolation has little explanatory power. Finally, solar insolation in the Northern Hemisphere generates the more accurate in-sample simulation of surface temperature while ice volume is simulated most accurately by solar insolation in the Southern Hemisphere.

  11. Periodic orbits for a discontinuous vector field arising from a conceptual model of glacial cycles

    NASA Astrophysics Data System (ADS)

    Walsh, James; Widiasih, Esther; Hahn, Jonathan; McGehee, Richard

    2016-06-01

    Conceptual climate models provide an approach to understanding climate processes through a mathematical analysis of an approximation to reality. Recently, these models have also provided interesting examples of nonsmooth dynamical systems. Here we develop a new conceptual model of glacial cycles consisting of a system of three ordinary differential equations defining a discontinuous vector field. Our model provides a dynamical systems framework for a mechanism previously shown to play a crucial role in glacial cycle patterns, namely, an increased ice sheet ablation rate during deglaciations. We use ad hoc singular perturbation techniques to prove the existence of a large periodic orbit crossing the discontinuity boundary, provided the ice sheet edge moves sufficiently slowly relative to changes in the snow line and temperature. Numerical explorations reveal the periodic orbit exists when the time constant for the ice sheet edge has more moderate values.

  12. Dust: A diagnostic of the hydrologic cycle during the last glacial maximum

    SciTech Connect

    Yuk L. Yung; Typhoon Lee; Chung-Ho Wang; Ying-Tzung Shieh

    1996-02-16

    Dust concentrations in ice of the last glacial maximum (LGM) are high in ice cores from Greenland and Antarctica. The magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the LGM was about half of that at present. This notion is consistent with a large decrease (5{degrees}C) in ocean temperature during the LGM, as recently deduced from measurements of strontium and calcium in corals. 24 refs., 1 fig.

  13. A Climactic Feedback? Variations in Mid-Ocean Ridge CO2 Emissions Driven by Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Burley, J. M.; Katz, R. F.; Huybers, P. J.

    2015-12-01

    Changes in sea level associated with glacial cycles affect the pressure beneath a mid-ocean ridge (MOR) [1,2,3]. Pressure controls the depth of first melting, and therefore the rate of change of pressure controls the rate of change of the depth of first melting. The changing depth of first melting alters the effective rate at which mantle, and thus CO2, enters the melting region. Melt then transports CO2 to the ridge axis, where it enters the climate system. We calculate that the lag between sea level change and consequent variation in MOR CO2 emissions is 40-120 kyrs[4], similar to the timescale of glacial cycles. Could these variations in MOR CO2 emissions feed back on climate and lead to ice-age pacing at a small multiple of the obliquity period? [5]To test this hypothesis we begin with a climate model comprised of a global energy balance and a 1D ice sheet. The ice sheet flows under its own weight, accumulates due to precipitation, and melts in response to the local energy balance[6]. This model broadly replicates Early Pleistocene 40 kyr glacial cycles. We extend the model to include a variable greenhouse effect, according to atmospheric CO2, and variable MOR CO2 emissions driven by sea level. The lag between sea level change and MOR CO2 emissions is controlled by mantle permeability. If this model does not demonstrate MOR CO2 emissions altering glacial cycles, it would suggest this hypothesised feedback mechanism can be rejected. References[1] Huybers & Langmuir 2009; 10.1016/j.epsl.2009.07.014[2] Lund & Asimow 2011; 10.1029/2011GC003693[3] Crowley et al 2015; 10.1126/science.1261508[4] Burley & Katz 2015; 10.1016/j.epsl.2015.06.031[5] Huybers (in prep.)[6] Huybers & Tziperman 2008; 10.1029/2007PA001463

  14. Impact of brine-induced stratification on the glacial carbon cycle

    NASA Astrophysics Data System (ADS)

    Bouttes, N.; Paillard, D.; Roche, D. M.

    2010-04-01

    During the cold period of the Last Glacial Maximum (LGM, about 21 000 years ago) atmospheric CO2 was around 190 ppm (Monnin et al., 2001), much lower than the pre-industrial concentration of 280 ppm. The causes of this substantial drop remain partially unresolved, despite intense research. Understanding the origin of reduced atmospheric CO2 during glacial times is crucial to comprehend the evolution of the different carbon reservoirs within the Earth system (atmosphere, terrestrial biosphere and ocean). In this context, the ocean is believed to play a major role as it can store large amounts of carbon (Sigman and Boyle, 2000), especially in the abyss, which is a carbon reservoir that is thought to have expanded during glacial times. To create this larger reservoir, one possible mechanism is to produce very dense glacial waters, thereby stratifying the deep ocean and reducing the carbon exchange between the deep and surface ocean (Paillard and Parrenin, 2004). The existence of such very dense waters has been inferred in the LGM deep Atlantic from sediment pore water salinity (Adkins et al., 2002). Based on these observations, we study the impact of a brine mechanism on the glacial carbon cycle. This mechanism relies on the formation and rapid sinking of brines, very salty water released during sea ice formation, which brings salty dense water down to the bottom of the ocean. It provides two major features: a direct link from the surface to the deep ocean along with an efficient way of setting a strong stratification. We show with the CLIMBER-2 coupled carbon-climate model (Petoukhov et al., 2000) that such a brine mechanism can account for a significant decrease in atmospheric CO2 and contribute to the glacial-interglacial change. This mechanism can be amplified by low vertical diffusion resulting from the brine-induced stratification. The results obtained substantially improve the modeled glacial distribution of oceanic δ13C as well as the deep ocean salinity in

  15. 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.

  16. Two middle Pleistocene glacial-interglacial cycles from the Valle Grande, Jemez Mountains, northern New Mexico

    USGS Publications Warehouse

    Fawcett, Peter J.; Heikoop, Jeff; Goff, Fraser; Anderson, R. Scott; Donohoo-Hurley, L.; Geissman, John William; WoldeGabriel, Giday; Allen, Craig D.; Johnson, Catrina M.; Smith, Susan J.; Fessenden-Rahn, Julianna

    2006-01-01

    A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud were recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 ka, a correlation of major climatic changes in the core with other long Pleistocene records (deep sea oxygen isotope records and long Antarctic ice core records), and the recognition of two geomagnetic field polarity events in the core which can be correlated with globally recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 ka) to MIS 10 (~360 ka), at which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses, including core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotope ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). This record includes glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11. In the VC-3 record, both of these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records. The glacial terminations are quite abrupt in this record with notable changes in sedimentation, organic carbon content, C/N ratios and watershed vegetation type. Termination V is the largest climate change evident in this part of the middle Pleistocene. The glacial inceptions tend to be more gradual, on the order of a few thousand years.

  17. Terrigenous biomarker record off Morocco over the last five glacial cycles

    NASA Astrophysics Data System (ADS)

    Rostek, Frauke; Bard, Edouard; Nave, Silvia

    2013-04-01

    We present a record of terrigenous biomarkers - long chain n-alkanes - supplied to Moroccan coastal sediments over the past 500 kyr representing the last five glacial-interglacial cycles (MD08-3178, 31°17.09'N/11°29.20'W, 2184 m water depth). The eolian n-alkane supply along the eastern margin off the coast of NW Africa originates mainly from the Atlas Mountain region and the Moroccan coastal plain and partly from the northern Sahara. The new geochemical profiles record changes in vegetation cover, wind strength and fluvial transport from the Atlas Mountains. Marine biological productivity proxies and n-alkane concentrations increase during glacial periods suggesting that stronger winds induce upwelling in the ocean and transport hydrocarbons from the continent. Chain-length distribution of n-alkanes points to variations in the relative input of terrestrial C3 and C4 plants. These variations are clearly paced by glacial cycles due to orbital variations as illustrated by their correlation with the alkenone sea surface temperature record measured on the same core (see companion poster by Nave et al.). The relative abundance of C3 plants is seen to be higher during glacial periods whereas the abundance of C4 plants is higher during warmer interglacial periods. Our results suggest that important vegetation changes have occurred in this part of NW Africa during the last 500 kyr. These changes could be due to latitudinal migrations of vegetation belts, with plants adapted to a more humid Mediterranean climate in the north contrasting with arid Saharan vegetation in the south. In addition, the observed changes may also be related to relative changes of source regions of n-alkanes due to wind strength variations.

  18. Sensitivity simulations with direct radiative forcing by aeolian dust during glacial cycles

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Ganopolski, A.

    2014-01-01

    Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first time with an Earth system model of intermediate complexity over the late Pleistocene period. Correlations between climate variables and dust deposits suggest that aeolian dust potentially plays an important role for the evolution of glacial cycles. Here climatic effects from the dust direct radiative forcing (DRF) caused by absorption and scattering of solar radiation are investigated. Key factors controlling the dust DRF are the atmospheric dust distribution and the absorption-scattering efficiency of dust aerosols. Effective physical parameters in the description of these factors are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters are reasonably constrained by use of these studies, the simulated dust DRF spans a wide uncertainty range related to nonlinear dependencies. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several W m-2 in regions close to major dust sources and negligible values elsewhere. In case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In case of low absorption efficiency, the dust DRF can produce a significant global cooling in glacial periods which leads to a doubling of the maximum glacial ice volume relative to the case with small dust DRF. DRF-induced temperature and precipitation changes can either be attenuated or amplified through a feedback loop involving the dust cycle. The sensitivity experiments suggest that depending on dust optical parameters the DRF has the potential to either damp or reinforce glacial-interglacial climate changes.

  19. Sensitivity simulations with direct shortwave radiative forcing by aeolian dust during glacial cycles

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Ganopolski, A.

    2014-07-01

    Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first time with an Earth system model of intermediate complexity over the late Pleistocene period. Correlations between climate and dust deposition records suggest that aeolian dust potentially plays an important role for the evolution of glacial cycles. Here climatic effects from the dust direct radiative forcing (DRF) caused by absorption and scattering of solar radiation are investigated. Key elements controlling the dust DRF are the atmospheric dust distribution and the absorption-scattering efficiency of dust aerosols. Effective physical parameters in the description of these elements are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters can be reasonably constrained, the simulated dust DRF spans a~wide uncertainty range related to the strong nonlinearity of the Earth system. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several watts per square metre in regions close to major dust sources and negligible values elsewhere. In the case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In the case of low absorption efficiency, the dust DRF can produce a significant global cooling in glacial periods, which leads to a doubling of the maximum glacial ice volume relative to the case with small dust DRF. DRF-induced temperature and precipitation changes can either be attenuated or amplified through a feedback loop involving the dust cycle. The sensitivity experiments suggest that depending on dust optical parameters, dust DRF has the potential to either damp or reinforce glacial-interglacial climate changes.

  20. Automated reconstruction of drainage basins and water discharge to the sea through glacial cycles

    NASA Astrophysics Data System (ADS)

    Wickert, Andrew

    2015-04-01

    Over glacial cycles, ice masses and their geophysical impacts on surface topography dramatically changed drainage patterns and river discharges. These changes impacted meltwater discharge to the ocean, geomorphology, and climate. As the river systems'the threads that tied the ice sheets to the sea'were stretched, severed, and rearranged during deglaciation, they also shrank and swelled with the pulse of meltwater inputs and proglacial lake dynamics. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges. I automate these calculations within GRASS GIS to take advantage of rapid solution techniques for drainage networks in an open-source and compute-cluster-ready environment. I combine modern topography and bathymetry with ice sheet reconstructions from the last glacial cycle and a global glacial isostatic adjustment model to build digital elevation models of the past Earth surface. I then sum ice sheet mass balance with computed precipitation and evapotranspiration from a paleoclimate general circulation model to produce grids of water input. I combine these topographic and hydrologic inputs to compute past river networks and discharges through time. These paleodrainage reconstructions connect ice sheets, sea level, and climate models to fluvial systems, which in turn generate measurable terrace and sedimentary records as they carry physical, compositional, and isotopic signatures of ice sheet melt and landscape change through their channels and to the sea. Therefore, this work provides a self-consistent paleogeographic framework within which models and geologic records may be quantitatively compared to build new insights into past glacial systems.

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

    NASA Astrophysics Data System (ADS)

    Brücher, Tim; Latif, Mojib; Claussen, Martin; Schulz, Michael

    2016-04-01

    We will give a short overview of the national climate modelling initiative (PalMod - Paleo Modelling, www.palmod.de) on the understanding of the climate system dynamics and its variability during the last glacial cycle. PalMod 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. 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

  2. Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis aperta.

    PubMed

    Ayoub, Nadia A; Riechert, Susan E

    2004-11-01

    The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. aperta. PMID:15488003

  3. Orbital control of western North America atmospheric circulation and climate over two glacial cycles

    NASA Astrophysics Data System (ADS)

    Lachniet, Matthew S.; Denniston, Rhawn F.; Asmerom, Yemane; Polyak, Victor J.

    2014-05-01

    The now arid Great Basin of western North America hosted expansive late Quaternary pluvial lakes, yet the climate forcings that sustained large ice age hydrologic variations remain controversial. Here we present a 175,000 year oxygen isotope record from precisely-dated speleothems that documents a previously unrecognized and highly sensitive link between Great Basin climate and orbital forcing. Our data match the phasing and amplitudes of 65°N summer insolation, including the classic saw-tooth pattern of global ice volume and on-time terminations. Together with the observation of cold conditions during the marine isotope substage 5d glacial inception, our data document a strong precessional-scale Milankovitch forcing of southwestern paleoclimate. Because the expansion of pluvial lakes was associated with cold glacial conditions, the reappearance of large lakes in the Great Basin is unlikely until ca. 55,000 years into the future as climate remains in a mild non-glacial state over the next half eccentricity cycle.

  4. Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis aperta.

    PubMed

    Ayoub, Nadia A; Riechert, Susan E

    2004-11-01

    The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. aperta.

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

    NASA Astrophysics Data System (ADS)

    Willeit, Matteo; Ganopolski, Andrey

    2015-04-01

    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 modelling 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 kya (1000 years ago). 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. 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.

  6. 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.

  7. The Emsian - Eifelian (Lower - Middle Devonian) boundary occurs in a 100-kyr eccentricity maximum: A potentially useful secondary marker for the GSSP section (Wetteldorf Richtschnitt, Germany).

    NASA Astrophysics Data System (ADS)

    De Vleeschouwer, D.; Makarona, C.; Linnemann, U.; Königshof, P.; Claeys, P. F.

    2015-12-01

    . We observe a mixed forcing of obliquity and eccentricity-modulated precession. Moreover, the Emsian - Eifelian boundary clearly occurs shortly after a 100-kyr eccentricity maximum. This cyclostratigraphic observation can be used as an additional mean in future long-distance correlations between Emsian - Eifelian boundary sections.

  8. 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.

  9. 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

  10. The interglacial-glacial cycle and geochemical evolution of Canadian and Fennoscandian Shield groundwaters

    NASA Astrophysics Data System (ADS)

    Stotler, R. L.; Frape, S. K.; Ruskeeniemi, T.; Pitkänen, P.; Blowes, D. W.

    2012-01-01

    Results from cryogenic column experiments are compared with the geochemical data collected in the Canadian and Fennoscandian Shields over the past 25 years to investigate the relative influence of the glacial-interglacial cycle; specifically, the impact of continental glaciers, permafrost, and methane hydrate, on the evolution of groundwater from crystalline shield environments. Several different geochemical indicators of freezing processes (either glacial or permafrost-related) were utilized: comparisons of Na/Cl and Br/Cl ratios, δ 18O and δ 2H values, and δ 18O values and Cl - concentration. During freezing, fluids with different dominant cations follow distinctly different linear trends when Na/Cl and Br/Cl ratios are compared. Significantly, none of the freezing trends follows the trend hypothesized by Herut et al. (1990) for the evolution of seawater chemistry during freezing. Intrusion of glacial meltwater and in situ freezing (i.e., permafrost formation) result in a similar end-member when comparing δ 18O values and Cl - concentration. The geochemical influence of a freezing process on fresh, brackish, and some saline fluids was identified at some, but not all Canadian Shield sites, regardless of site location with respect to modern-day permafrost. Appreciably, physical and geochemical data do not support the formation of brines through any freezing process in the Canadian and Fennoscandian Shields, as hypothesized by Starinsky and Katz (2003). Rather, on all diagnostic freezing plots, brines are an end-member, indicating a different evolutionary pathway. Significant depletions in 18O with respect to modern precipitation, an indication of either glacial meltwater or a freezing process, were identified at depths of up to 1 km at some sites in the Canadian Shield, and to shallower depths in the Fennoscandian Shield. The potential of this fluid to reach such depths could be attributable to artificial gradients and mixing, glacial recharge, permafrost or

  11. Glacial landscape evolution and sediment export: insights from digital topographic analyses and numerical modelling (Invited)

    NASA Astrophysics Data System (ADS)

    Brocklehurst, S. H.; MacGregor, K. R.

    2013-12-01

    Sediment accumulation rates in the Gulf of Alaska and low-temperature thermochronology from the European Alps, amongst other lines of evidence, indicate accelerated glacial incision and sediment export associated with the Middle Pleistocene Transition (MPT), ~1 Ma. At this time, the change from symmetrical 40-kyr temperature cycles to larger amplitude, asymmetric 100-kyr cycles would have allowed larger, longer lived glaciers to develop, which is inferred as a key contributor to accelerated glacial erosion. Digital topographic analyses comparing glaciated drainage basins of different sizes in the Southern Alps, New Zealand, and Teton Range, western US, amongst others, indicate the importance of scale in glacial landscape development. In smaller drainage basins, or those at the limit of glaciation, landscape modification is primarily restricted to carving characteristic cirques at the heads of valleys. Glaciers may have occasionally spilled from these to carve U-shaped cross-sections downvalley, but without substantial vertical incision. In larger drainage basins with a longer history of glacial occupation, glacial incision has produced shallower downvalley profiles with characteristic glacial steps, presumably accompanied by greater sediment export. A numerical glacial longitudinal profile evolution model, driven by temperature cycles representing either side of the MPT, is used to compare glacial erosion and sediment export from initial Pleistocene glaciations with post-MPT behaviour. The modelled landscape response to the MPT is strongly dependent on the tectonic setting and the behaviour of the fluvial system downstream of the glacier. With no imposed tectonic rock uplift, the major change in the landscape is the carving of cirque forms and glacial longitudinal profiles at the start of the Pleistocene; the MPT would have had little impact on landscape morphology or sediment export. Imposing tectonic as well as isostatic rock uplift, alongside inefficient fluvial

  12. Optically Stimulated Luminescence Dating of Glacial Outwash Spanning the Last Glacial Cycle on the Western Olympic Peninsula, Washington, USA

    NASA Astrophysics Data System (ADS)

    Marshall, K. J.; Thackray, G. D.; Rittenour, T. M.

    2012-12-01

    Valley glaciers in the Olympic Mountains, Washington coalesced and advanced onto the Pacific coastal lowlands six times during Late Pleistocene time. With each advance, the valley glaciers constructed extensive landforms and thick stratigraphic sequences. Along the coast of the Olympic Peninsula, between the Hoh and Queets Rivers, wave-cut sea cliffs expose alternating sequences of outwash fans formed during periods of glacial advance and marine transgressive facies formed during periods of sea-level high stand. Previous work, encompassing geomorphic mapping of inland and coastal outcrops, stratigraphy, stratigraphic correlation, and radiocarbon dating, established a provisional glacial chronology for the Olympic coast, but was limited to the range of radiocarbon dating. Within the sea cliffs, three primary units of outwash were identified: the Hoh Oxbow (MIS 3), Lyman Rapids (MIS 4 or 5b), and Steamboat Creek outwash (MIS 6 or older). The outwash units are generally bounded by interglacial sea-level high stand sediments or interstadial terrestrial sediment. Our new investigations utilize detailed sedimentology and stratigraphy, mapping of geomorphic sequences, and optically stimulated luminescence (OSL) dating to extend and solidify the coastal glacial chronology. OSL methods provide a means to date outwash sequences directly and enable dating of previously undateable older sediments. The quartz in these sediments appears to be fully bleached and retains the luminescence signal. Furthermore, at two locations where both radiocarbon and OSL methods were applied on the same sediments, the ages are indistinguishable, indicating that OSL is reliable in these settings. Preliminary OSL ages from the outwash units indicate valley glacier advances on the Olympic Peninsula during Hoh Oxbow (MIS 3, ca. 30-50 ka), Lyman Rapids (MIS 4, ca. 50-80 ka), and Steamboat Creek (MIS 5d or older, >/= 105 ka). Additionally, general sediment fining up-section suggests a decrease in

  13. Seismic characteristics of Pleistocene glacial cycles near shelf edge, offshore Louisiana, Gulf of Mexico

    SciTech Connect

    Watkins, J.S.; Schneider, L.; Hilterman, F.

    1987-05-01

    Seismic stratigraphic studies of the shelf edge and the upper slope basins in the southern parts of the South Marsh Island, Eugene Island, Ship Shoal, and Green Canyon areas of the Louisiana outer continental shelf reveal at least four Pleistocene seismic stratigraphic cycles. These apparently reflect cyclic depositional patterns associated with glacially driven highstands and lowstands of sea level during this time. In the upper slope basins, a strong continuous reflector probably of turbiditic origin marks the base of each cycle. This reflector is thought caused by initial slumping occurring as sea level begins to fall. Overlying this reflector is a zone of chaotic-to-hummocky reflectors thought caused by slumping associated with knick-point erosion and channel-cutting during falling sea level. The upper portion of the cycle is largely reflectorless or weakly reflective punctuated with occasional strong, continuous turbidite reflectors. The reflectorless portion of the cycles is thought to represent homogeneous hemipelagic sedimentation during highstands. Shelf reflectors are usually moderately strong and continuous. A strong reflection(s), identified in some instances with gas sands, marks several sea level lowstands. Erosion is locally evident during lowstands. Otherwise, shelf reflectors are relatively uniform and show few characteristics associated with rising, falling, or highstanding parts of the sea level cycle.

  14. The role of sea ice in the temperature-precipitation feedback of glacial cycles

    NASA Astrophysics Data System (ADS)

    Gildor, Hezi; Ashkenazy, Yosef; Tziperman, Eli; Lev, Ilit

    2014-08-01

    The response of the hydrological cycle to climate variability and change is a critical open question, where model reliability is still unsatisfactory, yet upon which past climate history can shed some light. Sea ice is a key player in the climate system and in the hydrological cycle, due to its strong albedo effect and its insulating effect on local evaporation and air-sea heat flux. Using an atmospheric general circulation model with specified sea surface temperature and sea-ice distribution, the role of sea ice in the hydrological cycle is investigated under last glacial maximum (LGM) and present day conditions, and by studying its contribution to the "temperature-precipitation feedback". By conducting a set of sensitivity experiments in which the albedo and thickness of the sea ice are varied, the various effects of sea ice in the hydrological cycle are isolated. It is demonstrated that for a cold LGM like state, a warmer climate (as a result of reduced sea-ice cover) leads to an increase in snow precipitation over the ice sheets. The insulating effect of the sea ice on the hydrological cycle is found to be larger than the albedo effect. These two effects interact in a nonlinear way and their total effect is not equal to summing their separate contribution.

  15. Evolution of the stable carbon isotope composition of atmospheric CO2 over the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Eggleston, S.; Schmitt, J.; Bereiter, B.; Schneider, R.; Fischer, H.

    2016-03-01

    We present new δ13C measurements of atmospheric CO2 covering the last glacial/interglacial cycle, complementing previous records covering Terminations I and II. Most prominent in the new record is a significant depletion in δ13C(atm) of 0.5‰ occurring during marine isotope stage (MIS) 4, followed by an enrichment of the same magnitude at the beginning of MIS 3. Such a significant excursion in the record is otherwise only observed at glacial terminations, suggesting that similar processes were at play, such as changing sea surface temperatures, changes in marine biological export in the Southern Ocean (SO) due to variations in aeolian iron fluxes, changes in the Atlantic meridional overturning circulation, upwelling of deep water in the SO, and long-term trends in terrestrial carbon storage. Based on previous modeling studies, we propose constraints on some of these processes during specific time intervals. The decrease in δ13C(atm) at the end of MIS 4 starting approximately 64 kyr B.P. was accompanied by increasing [CO2]. This period is also marked by a decrease in aeolian iron flux to the SO, followed by an increase in SO upwelling during Heinrich event 6, indicating that it is likely that a large amount of δ13C-depleted carbon was transferred to the deep oceans previously, i.e., at the onset of MIS 4. Apart from the upwelling event at the end of MIS 4 (and potentially smaller events during Heinrich events in MIS 3), upwelling of deep water in the SO remained reduced until the last glacial termination, whereupon a second pulse of isotopically light carbon was released into the atmosphere.

  16. The impact of the North American glacial topography on the evolution of the Eurasian ice sheet over the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Liakka, Johan; Löfverström, Marcus; Colleoni, Florence

    2016-05-01

    Modeling studies have shown that the continental-scale ice sheets in North America and Eurasia in the last glacial cycle had a large influence on the atmospheric circulation and thus yielded a climate distinctly different from the present. However, to what extent the two ice sheets influenced each others' growth trajectories remains largely unexplored. In this study we investigate how an ice sheet in North America influences the downstream evolution of the Eurasian ice sheet, using a thermomechanical ice-sheet model forced by climate data from atmospheric snapshot experiments of three distinctly different phases of the last glacial cycle: the Marine Isotope Stages 5b, 4, and 2 (Last Glacial Maximum - LGM). Owing to the large uncertainty associated with glacial changes in the Atlantic meridional overturning circulation, each atmospheric snapshot experiment was conducted using two distinctly different ocean heat transport representations. Our results suggest that changes in the North American paleo-topography may have largely controlled the zonal distribution of the Eurasian ice sheet. In the MIS4 and LGM experiments, the Eurasian ice sheet migrates westward towards the Atlantic sector - largely consistent with geological data and contemporary ice-sheet reconstructions - due to a low wave number stationary wave response, which yields a cooling in Europe and a warming in northeastern Siberia. The expansion of the North American ice sheet between MIS4 and the LGM amplifies the Siberian warm anomaly, which limits the glaciation there and may therefore help explain the progressive westward migration of the Eurasian ice sheet in this time period. The ocean heat transport only has a small influence on the stationary wave response to the North American glacial topography; however, because temperature anomalies have a smaller influence on an ice sheet's ablation in a colder climate than in a warmer one, the impact of the North American glacial topography on the Eurasian ice

  17. Dual modes of the carbon cycle since the Last Glacial Maximum.

    PubMed

    Smith, H J; Fischer, H; Wahlen, M; Mastroianni, D; Deck, B

    1999-07-15

    The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling. During the last four transitions from glacial to interglacial conditions, over which such abrupt warmings occur, ice records indicate that the CO2 concentration of the atmosphere increased by roughly 80 to 100 parts per million by volume. But the causes of the atmospheric CO2 concentration increases are unclear. Here we present the stable-carbon-isotope composition (delta 13 CO2) of CO2 extracted from air trapped in ice at Taylor Dome, Antarctica, from the Last Glacial Maximum to the onset of Holocene times. The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years, one when climate was changing relatively slowly and another when warming was rapid, each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans. delta 13 CO2 increased between 16.5 and 9 thousand years ago by slightly more than would be estimated to be caused by the physical effects of a 5 degrees C rise in global average sea surface temperature driving a CO2 efflux from the ocean, but our data do not allow specific causes to be constrained.

  18. Initiation age and incision rates of inner gorges: Do they record multiple glacial-interglacial cycles?

    NASA Astrophysics Data System (ADS)

    Delunel, Romain; Casagrande, Jan; Schlunegger, Fritz; Akçar, Naki; Kubik, Peter W.

    2015-04-01

    gorges over multiple interglacial cycles and a relative preservation of Alpine landscapes during glacial periods.

  19. 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

  20. Variations in Mid-Ocean Ridge CO2 Emissions Driven By Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Burley, J. M.; Katz, R. F.; Huybers, P. J.

    2014-12-01

    Glacial cycles impact continental volcanism through pressure changes associated with growth and retreat of ice sheets [e.g. Iceland - Jull, 1996]. Similarly, changes in sea level accompanying glacial cycles modulate mid-ocean ridge (MOR) volcanism by pressure changes and their influence on melt production [Crowley 2014; Lund 2011; Huybers 2009]. CO2 transport through the upper mantle is sensitive to mantle melting because CO2 partitions completely into the melt phase when present. Melt then transports CO2 to the ridge axis, where it enters the climate system. We present models of CO2 transport that investigate how sea level modulates the rate of CO2 emission from MORs. The total carbon reservoir in the mantle is circa 10^7 GtC [Dasgupta 2010], orders of magnitude more than the oceans (40,000 GtC) and atmosphere (600 GtC). Changes in the rate of CO2 emission from the solid Earth therefore have the potential to significantly affect the surface carbon system. We have developed an analytical model of CO2 transport from the depth of first silicate melting (~60km) to the ridge axis, enabling a calculation of CO2 emission rate for a generic section of MOR. The model assumes homogeneous mantle and energy-conserving melt production from a simplified 2-component mantle; CO2 is taken as a perfectly incompatible trace element. Pressure variations modulate the depth of initial silicate melting and hence the flux of CO2 into the melting regime. The model can also be applied to any species that is strongly partitioned into the melt (eg. Uranium, Thorium, Niobium, Barium, Rubidium). Results suggest that changing sea level over the past Myr could have altered the CO2 emissions from MOR by ~8%. The magnitude of variation in emissions is sensitive to the mantle permeability, the ridge spreading rate, and the rate of change of sea level. The travel time of melt through the mantle causes a delay between sea-level change and the CO2 response of the MOR. This delay is sensitive to plate

  1. 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

  2. Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model.

    PubMed

    Braun, Holger; Christl, Marcus; Rahmstorf, Stefan; Ganopolski, Andrey; Mangini, Augusto; Kubatzki, Claudia; Roth, Kurt; Kromer, Bernd

    2005-11-10

    Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle. PMID:16281042

  3. Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model.

    PubMed

    Braun, Holger; Christl, Marcus; Rahmstorf, Stefan; Ganopolski, Andrey; Mangini, Augusto; Kubatzki, Claudia; Roth, Kurt; Kromer, Bernd

    2005-11-10

    Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.

  4. An episode of rapid bedrock channel incision during the last glacial cycle, measured with 10Be

    USGS Publications Warehouse

    Reusser, L.; Bierman, P.; Pavich, M.; Larsen, J.; Finkel, R.

    2006-01-01

    We use 10Be to infer when, how fast, and why the Susquehanna River incised through bedrock along the U.S. Atlantic seaboard, one of the world's most prominent and ancient passive margins. Although the rate at which large rivers incise rock is a fundamental control on the development of landscapes, relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins. Exposure ages of fluvially carve d, bedrock strath terraces, preserved along the lower Susquehanna River, demonstrate that even along a passive margin, large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions, such as the Himalayas. Over eighty samples, collected along and between three prominent levels of strath terraces within Holtwood Gorge, indicate that the Susquehanna River incised more than 10 meters into the Appalachian Piedmont during the last glacial cycle. Beginning ???36 ka, incision rates increased dramatically, and remained elevated until ???14 ka. The northern half of the Susquehanna basin was glaciated during the late Wisconsinan; however, similar rates and timing of incision occurred in the unglaciated Potomac River basin immediately to the south. The concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision. Instead, it appears that changing climatic conditions during the late Pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion, thus enabling a short-lived episode of rapid incision into rock. Although this study has constraine d the timing and rate of bedrock incision along the largest river draining the Atlantic passive margin, the dates alone cannot explain fully why, or by what processes, this incision occurred. However, cosmogenic dating offers

  5. Exploiting multi-proxy analysis of marine sediments in the southeast Atlantic: Intensification of Agulhas leakage tied to the start of the 100ka cycles.

    NASA Astrophysics Data System (ADS)

    Petrick, Benjamin; McClymont, Erin; Marret, Fabienne

    2013-04-01

    The transition in orbital forcing from a 41 ka world to a 100 ka world was a major change in the climate regime over the last 1.5 Ma but its causes and its impacts are still being investigated. Here, we present reconstructions of sea-surface temperature (SST), salinity, and plankton assemblages obtained from a single core, ODP site 1087 (31°28'S, 15°19'E, 1374m water depth) spanning the last 1.5 Ma. Our hypothesis is that the response and position of the Agulhas leakage, which transfers heat and salt to the SE Atlantic region, has shifted as a result of changes in the dominant periodicity of orbital forcing. We draw on evidence from the alkenone (U37K') proxy for SST, dinoflagllate species analysis, and foraminifera oxygen isotopes for salinity and ice volume, to identify changes in the input of the Agulhas leakage to the SE Atlantic. We present the first continuous record of SE Atlantic SSTs reaching to 1.5 Ma which spans both the 41 kyr and 100 kyr glacial cycles. We identify large changes in SST and salinity on glacial-interglacial timescales, but show that there is a consistent pattern of SSTs leading salinity and then global ice volume change, so that deglaciation occurs some 5-10 kyr after the onset of rapid warming in the SE Atlantic during the recent glacials and interglacials. This early warming pattern, which characterizes the most recent cycles, began to develop as early at 900 ka, as the 100 kyr cycles became dominant. Before this time there is little evidence of Agulhas leakage in the ODP1087 record. We also show that over the last 600 ka there has been a strengthening of the Agulhas Leakage which has led to warmer interglacials over this time period. Overall the record shows that the strength and location of the Agulhas leakage is sensitive to changes in the dominant cycles in the climate.

  6. New insights into West Greenland ice sheet/stream dynamics during the last glacial cycle.

    NASA Astrophysics Data System (ADS)

    Roberts, David; Lane, Tim; Rea, Brice; Cofaigh, Colm O.; Jamieson, Stewart; Vieli, Andreas; Rodes, Angel

    2015-04-01

    Onshore and offshore geomorphological mapping and deglacial chronologies from West Greenland constrain the nature and magnitude of ice advance and decay of the Greenland Ice Sheet (GrIS) during the last glacial cycle. Several ice stream troughs are known to have fed ice to the shelf edge during the last glacial cycle. Their offshore expression suggests that many were coalescent systems fed by smaller outlet glaciers and ice streams onshore but their central flow pathways were also controlled by geology and preglacial topography. The bed morphology of these large ice streams shows they operated over soft, deforming beds with drumlins, mega-scale glacial lineations and grounding zone wedges marking an offshore transition from predominant areal scour onshore. Records of offshore deglacial chronology remain sparse but the Uummannaq and Disko Bugt ice stream corridors are now well constrained. The Uummannaq ice stream (UIS) completely deglaciated from the continental shelf between 14.8 ka and 11.0 ka in response to rising air temperatures, increasing JJA solar radiation and sea-level rise, but temporary standstills and the asynchronous retreat history of its feeder zones suggest that topography/bathymetry strongly modulated retreat rates as ice became 'locked' back into the coastal fjord system. Initial reconstructions of behaviour UIS discounted an oceanic role in early deglaciation and favoured retreat from the mid-shelf and inner-shelf prior to the Younger Dryas but both these concepts remain under investigation. In Disko Bugt, Jakobshavn Isbrae deglaciated later than the UIS and remained on the outer shelf during the Younger Dyras stadial (12.8 - 11.7 cal. kyrs BP) only reaching in the inner coast fjords at approximately 10.0 ka. The later deglaciation of the Disko system (despite similar external forcing mechanisms) was controlled by regional topographic/bathymetric contrasts in their respective trough morphologies. This hypothesis is supported by recent model

  7. Polyploid evolution and Pleistocene glacial cycles: A case study from the alpine primrose Primula marginata (Primulaceae)

    PubMed Central

    2012-01-01

    Background Recent studies highlighted the role of Pleistocene climatic cycles in polyploid speciation and of southern Alpine refugia as reservoirs of diversity during glacial maxima. The polyploid Primula marginata, endemic to the southwestern Alps, includes both hexaploid and dodecaploid cytotypes that show no ecological or morphological differences. We used flow cytometry to determine variation and geographic distribution of cytotypes within and between populations and analyses of chloroplast (cp) and nuclear ribosomal (nr) DNA sequences from the Internal Transcribed Spacer (ITS) region to infer the evolutionary history of the two cytotypes and the auto- vs. allopolyploid origin of dodecaploid populations. Results We did not detect any intermediate cytotypes or variation of ploidy levels within populations. Hexaploids occur in the western and dodecaploids in the eastern part of the distributional range, respectively. The cpDNA and nrDNA topologies are in conflict, for the former supports shared ancestry between P. marginata and P. latifolia, while the latter implies common origins between at least some ITS clones of P. marginata and P. allionii. Conclusions Our results suggest an initial episode of chloroplast capture involving ancestral lineages of P. latifolia and P. marginata, followed by polyploidization between P. marginata-like and P. allionii-like lineages in a southern refugium of the Maritime Alps. The higher proportion of ITS polymorphisms in dodecaploid than in hexaploid accessions of P. marginata and higher total nucleotide diversity of ITS clones in dodecaploid vs. hexaploid individuals sequences are congruent with the allopolyploid hypothesis of dodecaploid origin. PMID:22530870

  8. Subsurface geology of Kansai International Airport: sequence related to global glacial - interglacial cycles and island tectonics

    NASA Astrophysics Data System (ADS)

    Takemura, K.; Kitada, N.; Furudoi, T.; Nakaseko, K.

    2007-12-01

    Tectonic sedimentary basins aligned in the central part of Japan during Quaternary . Thick sediments deposited in these basins provide useful records of climatic changes and tectonics throughout Quaternary. The Osaka sedimentary basin including Osaka Bay and area of Kansai International Airport is one of them. The Quaternary Osaka sedimentary basin has developed at an eastern contractional bend of a major transcurrent fault system named the Median Tectonic Line, which divides the southwest Japan arc. The thickness of Pliocene - Pleistocene sediments reaches to ca 3500m at the deepest part. These sequences are called the Osaka Group and are distributed in the Osaka Bay and exposed in the surrounding mountain areas. The Osaka Group is characterized by alternating sequences of marine and nonmarine strata. The subsurface sediments of Kansai International Airport (KIA) is composed mainly of Pliocene - Pleistocene sediments, which is characterized by alternating sequences of marine and nonmarine strata related to glacial - interglacial cycles. . The stratigraphy at KIA was established by micropaleontological, tephrochronological and magnetostratigraphical method. The sedimentary sequence at KIX is divided into two main units (Kukojima and Sennanoki Formations in ascending order) with the uncomformity within two units. Although thick marine clay units are mainly of the subsurface sequence, characteristics of coarser sediment units have an important role of moving of water during construction of the reclaimed land.

  9. Periodicity in a Conceptual Model of Glacial Cycles in the Absence of Milankovitch Forcing

    NASA Astrophysics Data System (ADS)

    Hahn, J.; Walsh, J.; Widiasih, E.; McGehee, R.

    2015-12-01

    Previously, McGehee and Widiasih coupled Budyko's Energy Balance Model with dynamics of a latitudinal ice-line incorporating the albedo feedback effect. They reduced this model to a two-dimensional equation of global mean temperature and a latitudinal ice-line. With this conceptual model, we now include dynamics of the ablation and accumulation of ice, to form a three-dimensional system that partitions the regions of the Earth latitudinally into an accumulation zone, ablation zone, and ice-free zone. Motivated by the findings of Abe-Ouchi et al that the fast retreat of ice-sheets is due to an increased rate of ablation via the effects of delayed isostatic rebound, we incorporate a simple switching mechanism to the model which increases the rate of ablation during periods of glacial retreat. This forms a discontinuous system of the Earth's temperature and ice-volume in which we find a stable periodic orbit. This can be interpreted as a intrinsic cycling of the Earth's climate in the absence of Milankovitch forcing.

  10. Nitrogen Cycling in the Black Sea on Glacial-Interglacial Time Scales

    NASA Astrophysics Data System (ADS)

    Quan, T. M.; Wright, J. D.; Falkowski, P. G.

    2010-12-01

    On geological time scales, the nitrogen cycle consists of three main processes: nitrogen fixation, nitrification, and denitrification/anammox, all of which are affected by the amount of oxygen present in the water column. The balance between nitrogen fixation and denitrification/anammox controls the pool of fixed inorganic nitrogen, and can be traced using nitrogen isotopes. We have previously proposed a conceptual model that relates sedimentary δ15N to deep water oxygen concentrations using a simple, non-linear curve. Provided that the sediment record is well-preserved, the nitrogen isotopic profile at a given location reflects history of the relative contributions of nitrogen fixation to denitrifiation and thus the past redox environment. Our goal was to test this model using deep sea sediments from the Black Sea, which alternates from an anoxic, stratified, marine water body during interglacial periods to a less saline, oxygenated lake during glacial events. We find that the measured δ15N profile in general corresponds to the changes in redox state as determined by trace metal concentrations and micropaleontology. Higher δ15N values occur during suboxic transitional periods, with lower δ15N values appearing under anoxic and oxic conditions, supporting our hypothesis that the nitrogen cycle is regulated by oxygen concentration. We also identify some intervals where the correlation between redox proxies appears to fail. While the lack of ancillary data from the paleo-Black Sea makes interpretation difficult, we believe analysis of these intervals may provide more information about Black Sea paleoenvironmental and paleoredox conditions.

  11. Inter-Tropical Convergence Zone Shifts During the Last Glacial Cycle Near the Line Islands Ridge.

    NASA Astrophysics Data System (ADS)

    Reimi Sipala, M. A.; Marcantonio, F.

    2015-12-01

    This research focuses on the shift in the inter-tropical convergence zone (ITCZ) during the last glacial cycle. Deep sea sediments from the Central Equatorial Pacific (CEP) are used to quantify and isolate the sources and sinks of atmospheric dust. Dust records and influences climate affecting a wide range of process from Earth's Albedo to carbon export. Our aim is to determine the provenance of windblown dust deposited in the CEP near the Line Islands Ridge using radiogenic Nd and Pb isotopes, and to infer the location of the ITCZ and the changes of atmospheric transport through ice-age climate transitions. We focus on three cores from the CEP, along a meridional transect at approximately 160° W --- 0° 28' N (ML1208-17PC), 4° 41' N (ML1208-31BB), and 7 ° 2'N (ML1208-31BB). Radiogenic isotopes (Sr, Nd, Pb) have been successfully used to distinguish between different potential dust sources in the aluminosilicates fractions of Pacific Sediments. Our preliminary data suggest that the equatorial core (17PC) predominantly receives its dust from South America and South American volcanics South America (206Pb/204Pb = 18.62, 207Pb/204Pb = 15.63, 208Pb/204Pb = 38.62; ; ɛNd = ~ -5). The middle core, which more closely reflects the modern position of the ITCZ, has varied dust provenance through time, at times consistent with Asian Loess (average ratios are 206Pb/204Pb = 18.88, 207Pb/204Pb = 15.69, 208Pb/204Pb = 39.06; ɛNd = ~ -7) and Asian Volcanics (ɛNd = ~-1) suggesting a shift in the ITCZ south of 4N before the LGM. Our results for the most northern core are forthcoming. Prior to Holocene time, the changes in Pb isotope ratios in both cores appear to be in anti-phase; the northern core becomes less radiogenic up to the LGM, while the southern core becomes more radiogenic. This is potentially due to a weakening of the ITCZ during glacial times. A secondary aim of this work is to determine if the ITCZ migrated further south than core 17PC during Heinrich stage II.

  12. Western Atlantic Intertropical Convergence Zone Variability Over the Last Full Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Drenzek, N.; Hughen, K.; Sessions, A.; Bice, M.; Eglinton, T.

    2006-12-01

    Precipitation associated with the modern Intertropical Convergence Zone (ITCZ) in the Atlantic Basin is sensitive to fluctuations in both local insolation1 and remote North Atlantic2,3 and equatorial Pacific4 climate. Reconstructing the pattern and timing of precipitation change in regions influenced by the ITCZ may therefore clarify the mechanisms driving Quaternary climate change in, and the teleconnections between, low and high latitudes. In order to establish a record of ITCZ variability in the western tropical Atlantic, we measured the stable carbon and hydrogen isotopic compositions of individual vascular plant lipids preserved in Cariaco Basin sediments at sub-millennial resolution over the last glacial cycle. High frequency oscillations in the δ13C values of long chain fatty acids during Marine Isotope Stage 3, reflecting changes in the relative proportion of C3 vs C4 vegetation, and hence humidity, in northern South America, appear to coincide with Dansgaard- Oeschger (D-O) variability in high latitude ice cores. Positive (negative) excursions occur during stadial (interstadial) periods, with the largest enrichments associated with Heinrich Events in the North Atlantic. Corresponding D/H ratios also indicate rapid shifts in ambient humidity, although more work is needed to fully constrain the effect of glacial conditions on the isotopic composition of paleoprecipitation. These millennial scale fluctuations are superimposed upon a longer term oscillation with significant power near the 21 kyr spectral band. Together, these data imply that the ITCZ in this region of the tropics responded to both high and low latitude forcing over the late Quaternary. For example, the proportion of C4 plants rapidly increased at the onset of stadial periods in the North Atlantic, suggesting that a southward deflection of the ITCZ gave rise to more arid conditions in northern South America. The converse was true for interstadials. Moreover, the amplitude of these millennial

  13. Paleoceanographic history of the Lower Bengal Fan during the last glacial cycle - IODP Expedition 354

    NASA Astrophysics Data System (ADS)

    Dekens, P. S.; Weber, M. E.; Lantzsch, H.; Das, S. K.; Williams, T.; Adhikari, R. R.; Jia, G.; Fox, L. R.; Ge, J.; Manoj, M. C.; Savian, J. F.; Reilly, B. T.; Selkin, P. A.; Meynadier, L.; Spiess, V.; France-Lanord, C.; Sharma, B.

    2015-12-01

    IODP Expedition 354 drilled a ~320 km long transect of seven sites on the Lower Bengal Fan at 8o N in the Northern Indian Ocean. The sediments cores recovered record a complex relationship between turbiditic and hemipelagic environments. This variability offers a unique opportunity to link our understanding of tectonic and terrestrial processes with climate and oceanography. With the exception the westernmost Site U1454, all sites show a several meter thick, hemipelagic top layer, usually representing Late Quaternary sediment. We present physical, geochemical and stable isotopic properties of this interval to establish a time frame and assess the paleoceanographic development of the region during the last glacial cycle. We sampled Site U1452C-1H continuously for the uppermost 480 cm of hemipelagic sediment in 2-cm increments. Preliminary results indicate the Toba Ash 1 (0.74 ka) is a distinct time marker in all physical properties. Furthermore, wet-bulk density as well as color reflectance b* (the red-green component) and L* (the lightness) show a dominant precession cyclicity. Hence, we are able to provide an insolation-tuned chronology for the last 200 ka (MIS1 - 7) as a preliminary age model. These records agree well with d18O records retrieved from Chinese caves. We will present a preliminary paleoceanographic proxy data to reconstruct sea-surface temperature (SST), sea-surface salinity (SSS), ice volume, marine biological productivity, nutrient supply, and deep-water circulation. These oceanographic and climate conditions are linked to changes in monsoonal strength and terrestrial input using sedimentary proxies to reconstruct chemical weathering and sediment sources and transport time. This work addresses one of the primary cruise objectives - linking monsoon variability, regional and global climate, and Bay of Bengal sediment deposition.

  14. Paleoceanography of the Okhotsk Sea During the Last Glacial Cycle Deduced From Radiolarian Record

    NASA Astrophysics Data System (ADS)

    Takahashi, K.; Okazaki, Y.; Yoshitani, H.

    2001-05-01

    Paleoceanographic record contained in the Okhotsk Sea sediments provide pertinent information on global climate change during the late Pleistocene. This stems from its unique oceanographic nature with seasonal sea-ice cover in this relatively low latitude setting resulting in formation of the North Pacific Intermediate Water (NPIW). In order to unravel siliceous microfossil record in the Okhotsk Sea, we have acquired four piston-cores and more than a dozen multiple cores, together with flux materials from four time-series sediment traps at two locations, were obtained in the area during the 1998-1999 periods on board R/V Professor Khromov, Far East Hydrometeological Institute, Russia, as part of "Joint Japanese-Russian-U. S. Study of the Sea of Okhotsk". Seasonal fluxes of radiolarians (No. shells m-2 day-1) showed significant maxima during summer through autumn at both trap stations. The radiolarian fluxes during August to November accounted for 60-87 percent of total annual flux, suggesting that the radiolarian production is significantly controlled by the sea-ice coverage. The radiolarian accumulation rates (RAR: No. shells cm-2 kyr-1) from piston cores, varied substantially, roughly corresponding to the glacial-interglacial cycles. Especially the RAR of Cycladophora davisiana, the dominant radiolarian taxon in the Holocene Okhotsk Sea sediments, contributed much to this trend. The last occurrence (LO) of Lychnocanomma nipponica sakaii in the Okhotsk Sea is at about 50ky BP, which is synchronous with that in the North Pacific. Such a synchronous nature of the LO of this species is important for biostratigraphy of the North Pacific and the northern marginal seas for the late Pleistocene.

  15. Variations in mid-ocean ridge magmatism and carbon emissions driven by glacial cycles

    NASA Astrophysics Data System (ADS)

    Katz, R. F.; Burley, J. M.; Huybers, P. J.; Langmuir, C. H.; Crowley, J. W.; Park, S. H.; Carbotte, S. M.; Ferguson, D.; Proistosescu, C.; Boulahanis, B.

    2015-12-01

    Glacial cycles transfer ˜5×10^19 kg of water between the oceans and ice sheets, causing pressure changes in the upper mantle with consequences for the melting of Earth's interior. Forced with Plio-Pleistocene sea-level variations, theoretical models of mid-ocean ridge magma/mantle dynamics predict temporal variations up to 10% in melt supply to the base of the crust. Moreover, a transport model for a perfectly incompatible element suggests that CO2 emissions from mid-ocean ridges could vary by a similar proportion, though with a longer time-lag.Bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills record the magmatic response to changes in sea level. The mechanism by which variations in the rate of melt supply are expressed in the bathymetry is not understood.The same pressure variations that modulate the melting rate could also modulate the depth of the onset of silicate melting. As ice sheets grow and sea level drops, this onset deepens, causing melting at the base of the silicate melting regime. Excess highly incompatible elements like CO2 enter the melt and begin their journey to the ridge axis. Tens of thousands of years later, this additional CO2 flux is emitted into the climate system. Because of its delay with respect to sea-level change, the predicted variation in CO2 emissions could represent a restoring force on climate (and sea-level) excursions. This mechanism has a response time determined by the time scale of melt transport; it potentially introduces a resonant frequency into the climate system.

  16. Millennial-Scale Climate Variability for the Last Glacial Cycle along the Iberian Margin based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.; Sangiorgi, F.; Reichart, G. J.; Lourens, L. J.; Sluijs, A.

    2014-12-01

    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 millennial-scale dinoflagellate cyst (dinocyst) assemblage records from the Shackleton Site (IODP Expedition 339) to reconstruct upwelling, sea surface temperature (SST) and productivity across the last two glacial-interglacial cycles. We quantify the validity of dinocyst-based paleoenvironmental reconstructions based on multivariate statistics on dinocyst assemblages and multi-proxy data from regional core-tops and the last glacial cycle. This allows us to conclude that the strength of the West Iberian Margin upwelling system changed from relatively intense upwelling during the last glacial to upwelling relaxation during the Holocene as a result of reduced (strength of the) Portuguese trade winds. Secondly, SST, productivity/upwelling, strength of Portuguese trade winds and climate on the Iberian Peninsula co-vary on stadial-interstadial timescales and correspond to Greenland stadial-interstadial variability (δ18O). Finally, we will present a long-term paleoceanographic perspective down to ~120 ka.

  17. Persistent millennial-scale climate variability in the eastern tropical North Pacific over the last two glacial cycles

    NASA Astrophysics Data System (ADS)

    Arellano-Torres, Elsa; Ganeshram, Raja S.; Pichevin, Laetitia E.; Salas-de-Leon, David Alberto

    2015-06-01

    High-resolution sediment records from the eastern tropical North Pacific (ETNP) spanning the last ~240 ka B.P. were studied to document the nature of millennial-scale climatic events in the tropical Pacific and to investigate teleconnection mechanisms. We present organic carbon (%OC) and diffuse spectral reflectivity records as indicative of upwelling and productivity changes off NW Mexico over the middle to late Pleistocene. The new productivity records document the persistence of abrupt millennial-scale changes over the last two glacial cycles. Detailed spectral and wavelet time series analyses show the predominance of longer climatic cycles (2-6 ka) during the last and the penultimate glacial periods. The persistence of millennial variability during the penultimate glacial, in absence of large ice rafted debris events in the North Atlantic, suggests that freshwater input through ice sheet dynamics is not essential for millennial-scale climate variability. Given the worldwide emerging picture of remarkable similar millennial-scale records over long time periods, we suggest that the pacing of this climate variability may represent a natural resonance in the climate system, amplified by a tightly coupled oceanic and atmospheric teleconnection processes. We present a schematic scenario of millennial-scale climate change depicting the role of the tropical Pacific in this global teleconnection system by linking productivity and upwelling changes in the ETNP with shifts in the position of the Intertropical Convergence Zone and the strength of the subtropical North Pacific High.

  18. 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.

  19. 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.

  20. 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.

  1. Modelling of glacial isostatic adjustment in the Barents Sea region: Earth rheology inferred from various ice load scenarios for the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Auriac, Amandine; Whitehouse, Pippa L.; Bentley, Michael J.; Patton, Henry; Hubbard, Alun; Lloyd, Jerry M.

    2015-04-01

    The Barents Sea, bordered by Norway to the south, Svalbard to the north and Novaya Zemlya to the east, was covered by ice during the last glacial cycle. The extent and thickness of the marine-based ice sheet as well as timing of glaciation / deglaciation are, however, difficult to constrain, partly due to the few terrestrial areas available. There are various models for the ice load history in this region, but large discrepancies remain between them depending on the dataset used as constraint (e.g. sea-level data, temperature record or geomorphology data). Our aim here is to compare and find the best ice load scenario for this region over the last glacial cycle and solve for the Earth structure in the area. To achieve this, we model the present-day crustal deformation and sea-level variations during the last deglaciation by solving the sea-level equation. We use a wide range of Earth models, where we vary the lithosphere thickness and the upper and lower mantle viscosities, as well as four ice load scenarios. The first three ice load scenarios come from published studies, and include the ICE-5G model as well as models from M. Siegert and J.-O. Näslund, while the last one is currently being developed at the University of Tromsø, Norway. We compare the modelled sea-level predictions to relative sea-level curves at key locations around the Barents Sea using chi square, which enables us to infer the best Earth structure and ice history. We also compare the predicted surface deformation from our best model with GPS observations from stations located around the Barents Sea. The GPS provides a constraint on the present-day evolution of deformation in the area and is complementary to the relative sea-level data, which constrain the long-term deformation. First results show that the published ice load scenarios are not accurate enough to reproduce the sea level curves around the Barents Sea, regardless of the Earth model tried. However, the last model, currently being

  2. Co-variation of nitrogen isotopes and redox states through glacial-interglacial cycles in the Black Sea

    NASA Astrophysics Data System (ADS)

    Quan, Tracy M.; Wright, James D.; Falkowski, Paul G.

    2013-07-01

    In all aquatic environments, nitrogen cycling within the water column is strongly influenced by oxygen. We hypothesize that the nitrogen isotopic composition (δ15N) of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition. We tested the hypothesis by measuring the bulk sedimentary δ15N values in a drill core from the Black Sea, a basin that alternates between oxic, less saline conditions and anoxic, marine conditions on glacial-interglacial time scales. We reconstructed these changes in Black Sea redox conditions using sedimentary δ15N, total organic carbon (TOC), total nitrogen (TN), redox-sensitive metals, and micropaleontological data from a deep-sea core (DSDP Site 380). The sedimentary data reveal that during the transitions between oxic and anoxic conditions, δ15N values increased relative to the preceding and succeeding quasi-steady-state oxic and anoxic periods. The results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification; during the quasi-stable oxic and anoxic states (characterized by glacial fresh water and interglacial marine conditions) nitrification and complete nitrate utilization, respectively, dominate the nitrogen cycle. While other factors may influence the δ15N record, our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the Black Sea subphotic zone on glacial-interglacial time scales, and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems. Our model suggests that the nitrogen isotopic composition of marine sediments, on geological time scales, can be used to reconstruct the redox state of the overlying water column.

  3. 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

  4. Distinction of glacial and interglacial cycles in Feni and Gardar drifts, North Atlantic

    SciTech Connect

    Eggers, M.R.; Ehrlich, R.

    1985-02-01

    The Feni and Gardar drifts of the North Atlantic are thought to represent large accumulations of current-deposited material and should record changes through time in direction and intensity of overflows in the Norwegian Sea and Iceland-Faereo Ridge, respectively. Both drifts were drilled by DSDP Leg 94. Initial shipboard examination revealed no visual differences between these sediments and typical pelagic North Atlantic sediments. Fourier shape analysis on quartz silts, augmented by SEM, showed that each sample consists of a mixture of 3 grain populations. One grain type is covered with surface fractures unmodified by subsequent abrasion. Lack of such abrasion and the fact that the abundance of these grains varies independently of other shape types suggest a glacial-ice rafted origin. A second shape family is covered with irregular, platy silica overgrowths, typical of diagenesis in a poorly sorted, clay-rich environment and is likely the production of erosion of submarine lutites. A third grain type, plastered with fine-grained silica, is characterized by protuberences and indentations typical of primary continental source terranes. These last 2 grain types vary inversely with one another, implying that at glacial maxima, bottom currents deposited first-generation continental material, but at glacial minima, they eroded material from the sea bottom and redeposited it as drift sediments.

  5. Correlation and interpretation of paleosols and loess across European Russia and Asia over the last interglacial-glacial cycle

    NASA Astrophysics Data System (ADS)

    Rutter, Nathaniel W.; Rokosh, Dean; Evans, Michael E.; Little, Edward C.; Chlachula, Jiri; Velichko, Andrei

    2003-07-01

    Loess-paleosol sequences of the last interglacial-glacial cycle are correlated from European Russia to central Siberia and the Chinese Loess Plateau. During cold periods represented by marine oxygen isotope stages (OIS) 2 and 4, loess deposition dominated in the Russian Plain and the Loess Plateau. In central Siberia, loess deposition took place also, but five to seven thin, weakly developed paleosols are identified in both stages. OIS 3, in the Chinese Loess Plateau near Yangchang, consists of a loess bed that is flanked by two weakly developed paleosols. At Kurtak, Siberia, OIS 3 is represented by two distinct, stacked paleosols with no loess bed separating the paleosols. In the Russian Plain, OIS 3 consists of a single, possibly welded paleosol, representing upper and lower stage-3 climates. Brunisols and Chernozems dominate the profiles in China and Siberia, whereas Regosols, Luvisols, and Chernozems are evident in the northern and southern Russian Plain, respectively. OIS 5 is represented in China and the Russian Plain by pedo complexes in a series of welded soils, whereas in contrast, the Kurtak site consists of six paleosols with interbedded loess. The paleosols consist largely of Brunisols and Chernozems. Although the three areas examined have different climates, geographical settings, and loess source areas, they all had similar climate changes during the last interglacial-glacial cycle.

  6. Sequence and chronology of the Cuerpo de Hombre paleoglacier (Iberian Central System) during the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Carrasco, Rosa M.; Pedraza, Javier; Domínguez-Villar, David; Willenbring, Jane K.; Villa, Javier

    2015-12-01

    The Cuerpo de Hombre paleoglacier occupies the upper sector of the Cuerpo de Hombre river basin, located on the northwest slope of the Sierra de Béjar Mountains (Iberian Central System). At the stage of the maximum ice extent during the last glacial cycle, this paleoglacier was one of the longest tongues emerging from the Sierra de Béjar plateau glacier. The study of the morphostratigraphic succession and the geometric and genetic relations between the geomorphological indicators of this paleoglacier has revealed its evolutionary sequence during the last glacial cycle. The comparison between this sequence and the one previously established by a regional evolutionary pattern shows that although they both coincide in general terms, some stages/substages of this pattern must be corrected or more clearly defined. The absolute chronology of the different stages was obtained using terrestrial cosmogenic nuclides (10Be). The maximum ice extent of Cuerpo de Hombre paleoglacier has been dated to ˜25.0 ka (MIS2 and concurrent with the LGM). This chronology coincides with date obtained for other paleoglaciers in the Iberian Central System, but is slightly more modern than the regional chronology estimated as most likely for the maximum ice extent in these areas. Subsequent to reaching the maximum extent, the glacier had a retreat (minimum age ˜20.6 ka), followed by another stage of expansion or readvance, after which it stabilised until the start of the deglaciation stage (˜17.8 ka). In all previous work, the deglaciation stages in the Iberian Central System have been described as one continuous recession process. However, in the Cuerpo de Hombre paleoglacier, all the data point to stabilisations of considerable magnitude, and particularly to another stage of readvance of the glacier. Based on its chronology (minimum age ˜11.1 ka) and its evolutionary significance, this new readvance has been correlated with the Older Dryas stadial. Finally, the evolutionary context

  7. Extra-long interglacial in Northern Hemisphere during MISs 15-13 arising from limited extent of Arctic ice sheets in glacial MIS 14.

    PubMed

    Hao, Qingzhen; Wang, Luo; Oldfield, Frank; Guo, Zhengtang

    2015-01-01

    Knowledge of the behavior of Northern Hemisphere (NH) ice sheets over the past million years is crucial for understanding the role of orbitally driven insolation changes on glacial/interglacial cycles. Here, based on the demonstrable link between changes in Chinese loess grain-size and NH ice-sheet extent, we use loess grain-size records to confirm that northern ice-sheets were restricted during marine oxygen isotope stage (MIS) 14. Thus, an unusually long NH interglacial climate of over 100 kyr persisted during MISs 15-13, much longer than expected from marine oxygen isotope records. Taking a global view of the paleoclimate records, MIS 14 inception seems to be a response to changes in Antarctic ice-sheets rather than to NH cooling. Orbital configuration in the two Polar regions shows that the onset of MIS 14 was forced by austral insolation changes, rather than by boreal summer insolation, as Milankovitch theory proposes. Our analysis of MIS 14 raises the possibility that southern insolation forcing may have played an important role in the inception of several other glacials. We suggest that the extra-long NH interglacial climate during MISs 15-13 provided favorable conditions for the second major dispersal episode of African hominins into Eurasia.

  8. Temporal relationships of carbon cycling and ocean circulation at glacial boundaries.

    PubMed

    Piotrowski, Alexander M; Goldstein, Steven L; Hemming, Sidney R; Fairbanks, Richard G

    2005-03-25

    Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets.

  9. Temporal relationships of carbon cycling and ocean circulation at glacial boundaries.

    PubMed

    Piotrowski, Alexander M; Goldstein, Steven L; Hemming, Sidney R; Fairbanks, Richard G

    2005-03-25

    Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets. PMID:15790848

  10. The timing and cause of glacial advances in the southern mid-latitudes during the last glacial cycle based on a synthesis of exposure ages from Patagonia and New Zealand

    NASA Astrophysics Data System (ADS)

    Darvill, Christopher M.; Bentley, Michael J.; Stokes, Chris R.; Shulmeister, James

    2016-10-01

    Glacier advances in the southern mid-latitudes during the last glacial cycle (ca. 110-10 ka) were controlled by changes in temperature and precipitation linked to several important ocean-climate systems. As such, the timing of glacial advance and retreat can yield important insights into the mechanisms of Southern Hemisphere climate change. This is particularly important given that several recent studies have demonstrated significant glacial advances prior to the global Last Glacial Maximum (gLGM) in Patagonia and New Zealand, the cause of which are uncertain. The recent increase in chronological studies in these regions offers the opportunity to compare regional trends in glacial activity. Here, we compile the first consistent 10Be exposure-dating chronologies for Patagonia and New Zealand to highlight the broad pattern of mid-latitude glacial activity over the last glacial cycle. Our results show that advances or still stands culminated at 26-27 ka, 18-19 ka and 13-14 ka in both Patagonia and New Zealand and were broadly synchronous, but with an offset between regions of up to 900 years that cannot be explained by age calculation or physically plausible erosion differences. Furthermore, there is evidence in both regions for glacial advances culminating from at least 45 ka, during the latter half of Marine Isotope Stage (MIS) 3. Glacial activity prior to the gLGM differed from the large Northern Hemisphere ice sheets, likely due to favourable Southern Hemisphere conditions during late MIS 3: summer insolation reached a minimum, seasonality was reduced, winter duration was increasing, and sea ice had expanded significantly, inducing stratification of the ocean and triggering northward migration of oceanic fronts and the Southern Westerly Winds. Glacial advances in Patagonia and New Zealand during the gLGM were probably primed by underlying orbital parameters. However, the precise timing is likely to have been intrinsically linked to migration of the coupled ocean

  11. New Benthic δ18o Stacks and Age Models for the Last Glacial Cycle (0-150 kyr ago)

    NASA Astrophysics Data System (ADS)

    Lisiecki, L. E.; Stern, J. V.

    2014-12-01

    The δ18O of formainiferal calcite is a common paleoceanographic proxy, which measures ice volume and deep water temperature change. Foraminiferal δ18O is also often used to create marine sediment core age models by aligning down-core variations in δ18O to a global stack, or average. However, the most commonly used stack, known as "LR04," has an outdated age model, assumes global benthic δ18O synchrony, and is biased to the Atlantic [Lisiecki and Raymo, 2005]. Here we present six regional benthic δ18O stacks of the last glacial cycle (0-150 kyr) that are combined to form a volume-weighted global stack with data from 263 sites. We develop new benthic δ18O age models using regional radiocarbon dates from 0-40 ka and correlations to the GICC05 layer-counted Greenland age model from 40-56 ka [Svensson et al., 2008] and U-Th-dated Chinese speleothems from 56-150 kyr [Wang et al., 2001; Cheng et al., 2009; Barker et al, 2011]. Additional features of the new stacks are diachronous benthic δ18O changes during the last two glacial terminations and explicit age uncertainty estimates throughout. Our new global stack indicates that some portions of the LR04 stack are up to 4 kyr too young. We estimate corrections to the LR04 age model throughout the Pleistocene that imply faster climate responses to orbital forcing than previously estimated.

  12. Changes in the occurence of heavy metals in Antarctic ice during the last climatic cycles

    NASA Astrophysics Data System (ADS)

    Gabrielli, P.; Barbante, C.; Planchon, F.; Ferrari, C.; Delmonte, B.; Boutron, C. F.

    2003-04-01

    During the last decades ice cores drilled in Antarctica and in Greenland have provided time series of data that have allowed the characterisation of variations of natural and anthropogenic heavy metals in the past atmosphere. Nevertheless, the interactions of heavy metals with climate change and their transport patterns remain largely unknown for the last climatic cycles. Our aim is to assess past changes of various heavy metals in polar ice during the past ª500 kyr. Special emphasis is given to Pt, Pd, Rh, Ir, Os and Ru which are tracers of interplanetary dust particles (IDPs). It has in fact been shown that the accretion flux of IDPs would change in parallel with the period of 100 kyr, possibly affecting climate and/or contributing to the observed 100 kyr cycle in climate records. These tracers could also allow us to identify the impact of larger size bodies which might have strongly influenced the stratospheric ozone layer. Tracers of crustal material (Pb isotopes, Pb, Ba, Fe, Co, Ti, Mn, V), volcanic activity (Cd, Bi, Sb, As) and ocean paleoproductivity (Hg, Se) are also investigated. At the moment we are focusing especially on the ongoing EPICA Dome C Antarctic ice core. We are decontaminating mechanically each section and we are performing preliminary measurements of Zn and Al using Graphite Furnace Atomic Absorption Spectrometry and ultraclean procedures. These data confirm the prominent continental origin of Zn in the East Antarctic ice during the last and penultimate glacial period back to about 200,,000 years B.P.. The other analyses are going to be performed using Inductively Coupled Plasma Sector Field Mass Spectrometry, Thermal Ionisation Mass Spectrometry, and Cold Vapour Atomic Absorption Spectrometry, adopting ultraclean procedures.

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

    PubMed Central

    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. PMID:26630571

  14. 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. PMID:26630571

  15. 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

  16. Changes in atmospheric carbon dioxide during the last glacial inception: High-resolution data and its implications for changes in the carbon cycle

    NASA Astrophysics Data System (ADS)

    Bereiter, B.; Lüthi, D.; Siegrist, M.; Schüpbach, S.; Stocker, T. F.; Fischer, H.

    2011-12-01

    Atmospheric carbon dioxide concentrations (CO2) are strongly linked to temperatures reconstructed from Antarctic ice cores on timescales of glacial-interglacial cycles. However, the linking mechanisms are not fully understood. During the last glacial period several abrupt climate variations occurred, causing the southern and northern hemisphere temperatures to change on millennial timescales (known as AIM-events in the southern hemisphere and DO-events in the northern hemisphere). Hence, the evolution of CO2 during the glacial period provides important insight in the long-scale glacial changes as well as in responses to millennial-scale variations of the carbon cycle during these natural climate variations. New, high-resolution CO2 records from two Antarctic ice cores (Talos Dome and EPICA Dronning Maud Land), covering the time period from 38,000 to 115,000 years BP, allow us to investigate the interplay of long-term and millennial-scale climate variations during the last glacial inception. An overlay of the two records of about 20,000 years and measurements with different analytical techniques enable a test of the robustness and analytical dependence of these CO2 reconstructions. For the climatic interpretation we use highly resolved records of methane concentration from both ice cores to compare the relationship between DO-events and CO2. The long-scale change of CO2 towards glacial values seen in the records shows a stepwise decrease. On millennial timescales the records show the strong link of southern hemisphere temperatures and CO2, found in earlier studies, also during the early glacial period and less distinct variations. However, the data show that the link is decoupled during most pronounced Greenlandic interstadial phases between 38,000 to 60,000 years BP. We conclude that both the stepwise decrease and decoupling to southern temperatures of CO2 is mainly caused by ocean circulation and carbon stock changes and provide a hypothesis about the mechanism

  17. Mid-Ocean Ridge Magma Supply and Glacial Cycles: Long Time Series Studies of Crustal Thickness and Seafloor Topography

    NASA Astrophysics Data System (ADS)

    Boulahanis, B.; Carbotte, S. M.; Huybers, P. J.; Langmuir, C. H.; Han, S.; Aghaei, O.; Canales, J. P.; Nedimovic, M. R.; Menke, W. H.

    2015-12-01

    Glacial loading has been shown to modulate volcanic melt generation in subaerial systems, and recent studies suggest that eustatic sea level fluctuations induced by glacial cycles may influence mantle-melting regimes at mid-ocean ridges. Models predict temporal variation in crustal thickness, and seafloor topography, linked to sea level change. Recent studies of bathymetry as a proxy for crustal thickness show significant spectral energy at periodicities linked to Milankovitch cycles of 23, 41, and 100ka (Crowley et al., 2015; Tolstoy, M., 2015). In this study we investigate climate driven periodicity in mid-ocean ridge magma supply utilizing basement topography and crustal thickness data. We use multichannel seismic reflection (MCS) data from two prior studies of the flanks of the Juan de Fuca (JdF) ridge, and 3D MCS data from the Northern East Pacific Rise (EPR) 9°37-57'N. The JdF datasets extend to crustal ages up to 8.78 Ma, and EPR data to ~180 ka. By performing spectral analysis on these data along with dO18 climate records from Lisiecki and Raymo (2005) for the last 5.32ma and Zachos et al. (2001) for earlier times we investigate intervals of similar periodicities in order to identify potential links between climate and magma supply to mid-ocean ridges. Further analysis is undertaken to determine whether depth to basement and crustal thickness are correlated within and across datasets, and whether significant spectral peaks occur in basement and crustal thickness data outside of known climate cycles. Initial results show significant spectral energy in basement depth at the 100ky cycle in the 0-1Ma time series, when eccentricity is understood to have the most impact. Long-term temporal variability is apparent in JdF data, with low relief abyssal hills (~70m on average) present 1-3.2Ma and 6-8.78Ma, but higher relief bathymetry (~200m) from 3.2-6Ma. These subsets align well with previously identified climatic subgroups (Zachos et al., 2001), correlating both

  18. South Pole ice stream temporal and spatial evolution in the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Blankenship, D. D.; Cavitte, M. G.; Young, D. A.; Carter, S. P.; Gutowski, G.; Bingham, R. G.; Siegert, M. J.

    2012-12-01

    While considered to be the most stable part of the Antarctic continent, recent studies show East Antarctic ice sheet has a high potential for rapid change and significant sea level contribution. Airborne radar sounding has shown that major ice stream tributaries have disrupted ice at the South Pole, portraying a complex evolution for the East Antarctic ice sheet. We confirm the temporal and spatial extent of these flow regime changes through the analysis of dated internal layers observed using airborne sounding data. Layering is time-registered to the local dust record from ICE CUBE boreholes and the SPRESSO core, which constrains ice stream transient penetration between 50 ka and about 10 ka, corresponding to the last glacial maximum. The ice stream margin position has migrated through time, initially at 10 km grid north of the South Pole, and migrated to the grid south by 40km before shutting off. The active portion of the ice sheet has undergone significant melting, bringing ice from the MIS 5e interglacial very close to the bedrock with respect to the inactive portion to the grid north. Shear heating from the ice stream margin migration is consistent with subglacial lakes previously observed in the area (Peters et al, 2008). This ice stream is further evidence for a substantial, rapid sea level contribution from the deep interior of the East Antarctic Ice Sheet.

  19. Peregrinations of the Greenland Ice Sheet divide in the last glacial cycle: implications for central Greenland ice cores

    NASA Astrophysics Data System (ADS)

    Marshall, Shawn J.; Cuffey, Kurt M.

    2000-06-01

    The superb quality of the climate chronology archived in the Summit, Greenland ice cores (GRIP, GISP2) testifies that the Greenland Ice Sheet divide has been generally stable through the last glacial cycle. The ice sheet has experienced a broad range of paleoclimate conditions, ice sheet margin configurations, and internal dynamical adjustments in glacial-interglacial transitions, however. It is unlikely that the Summit region escaped shifts in ice divide position, geometry, elevation, and flow characteristics. Details of this dynamical history are important to several aspects of ice core studies. The magnitudes of pure and simple shearing, reconstruction of vertical ice velocity, the explicit location of the ice divide, and the divide 'residence time' at different locations are all of interest in interpretation of climatic variables and physical properties of ice in the ice cores. We apply a three-dimensional, thermomechanical ice sheet model to examine the evolution of these dynamical variables over the last 160 kyr in central Greenland. While a high-elevation ice dome is present in the Summit region throughout the simulation, ice divide migrations of up to 150 km are predicted. All points in the vicinity of the Summit ice cores, including the modern divide, have been subject to flowline shifts and variable, non-zero shear deformation during the adjustment from glacial to Holocene conditions, from ca. 10 ka to the present. Modelled divide peregrinations and strain rate history are consistent with the observed disturbance of deep ice in the GRIP and GISP2 ice cores, which has muddled paleoclimate reconstructions for the last interglacial (Eemian) period in Greenland. Dynamical excursions are also evident north of the modern summit, where the NGRIP ice core is currently being drilled [Dahl-Jensen et al., J. Glaciol. 43 (1997) 300-306]. However, the prevailing flow direction and deformation regime at the NGRIP site are much more stable than those at GRIP and GISP2

  20. Isotopic record of Pleistocene glacial/interglacial cycles in pelagic carbonates: Revisiting historical data from the Caribbean Sea

    NASA Astrophysics Data System (ADS)

    Hermoso, Michaël

    2016-04-01

    The glacial/interglacial cycles of the Pleistocene were first recognised by variations in the oxygen isotopic composition of planktonic foraminifera from cores in the Caribbean Sea. Since this pioneering work by Emiliani, this proxy has been extensively applied to a variety of carbonate biominerals over the entirety of the Meso-Cenozoic. However, palaeoceanographic studies have overwhelmingly focused on foraminifera compared to other calcifying microorganism fossils, such as the coccoliths. In this study, I revisit coccolith stable isotopic data obtained from the classic P6304-4 core in light of recent developments in the biogeochemistry of coccolithophores. In particular, I show that the coccolith stable isotope record of the last 13 Marine Isotope Stages (∼480 kyrs) is significantly biased by large vital effects. The magnitude of coccolith carbon and oxygen isotope vital effects is not uniform, but shows remarkable co-variance with the Vostok CO2 ice record. During periods of relatively elevated CO2 (interstadials), the expression of the vital effect is relatively small, whereas it can as high as +3‰ for the oxygen isotopes during glacial stadials, which I argue is a result of enhanced CO2 limitation of coccolithophores. Using this paradigm, I propose that coccolithophore vital effects are not a complicating factor, but rather the signal of interest. As the magnitude of the coccolith vital effect is shown to scale with pCO2, coccolith carbon and oxygen isotopes may be used in conjunction with foraminifera data to reconstruct and refine aqueous CO2 concentrations in the past.

  1. Chronology of glaciations in the Cantabrian Mountains (NW Iberia) during the Last Glacial Cycle based on in situ-produced 10Be

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María José; Rinterknecht, Vincent; Pallàs, Raimon; Bourlès, Didier

    2016-04-01

    The mountain ranges of the Iberian Peninsula preserve a valuable record of past glaciations that may help reconstruct past atmospheric circulation patterns in response to cooling events in the North Atlantic Ocean. Available chronologies for the glacial record of the Cantabrian Mountains, which are mainly based on radiocarbon and luminescence dating of glacial-related sediments, suggest that glaciers recorded their Glacial Maximum (GM) during MIS 3 and experienced a later Last Glacial Maximum (LGM) advance. This LGM extent is not established yet, preventing a fair correlation with available Cosmic Ray Exposure (CRE) based chronologies for the glacial record of the Pyrenees and the Sistema Central. We present a glacial reconstruction and a 10Be CRE chronology for the Porma valley, in the southern slope of the central Cantabrian Mountains. Glacial evidence at the lowest altitudes correspond to erratic boulders and composite moraines whose minimum 10Be CRE age of 113.9 ± 7.1 ka suggests that glaciers were at their maximum extent during MIS 5d, most likely in response to the minima in summertime insolation of the Last Glacial Cycle. Recessional moraines preserved within the glacial maximum limits allow the assessment of subsequent glacier advances or stagnations. The most remarkable advance took place prior to 55.7 ± 4.0 ka (probably at the end of MIS 4), consistently with minimum radiocarbon ages previously reported for lacustrine glacial-related deposits in the Cantabrian Mountains. A limited number of 10Be CRE ages from a composite moraine suggest a possible advance of the Porma glacier coeval with the global LGM; the glacier front attributed to the LGM would be placed within the margins of the previous GM like in the western Pyrenees. Erratic boulders perched on an ice-moulded bedrock surface provided a mean 10Be CRE age of 17.7 ± 1.0 ka, suggesting that part of the recessional moraine sequence corresponds to minor advances or stagnations of the glacier fronts

  2. Thermocline temperature variability in the Timor Strait over the last two glacial cycles

    NASA Astrophysics Data System (ADS)

    Lo Giudice Cappelli, E.; Holbourn, A. E.; Kuhnt, W.; Regenberg, M.; Garbe-Schoenberg, C.

    2012-12-01

    *Lo Giudice Cappelli, E elgc@gpi.uni-kiel.de Institute of Geosciences, Christian-Albrechts-University, Kiel, Germany Holbourn, A ah@gpi.uni-kiel.de Institute of Geosciences, Christian-Albrechts-University, Kiel, Germany Kuhnt, W wk@gpi.uni-kiel.de Institute of Geosciences, Christian-Albrechts-University, Kiel, Germany Regenberg, M regenberg@gpi.uni-kiel.de Institute of Geosciences, Christian-Albrechts-University, Kiel, Germany Garbe- Schönberg, D dgs@gpi.uni-kiel.de Institute of Geosciences, Christian-Albrechts-University, Kiel, Germany Seafloor temperature variations within the path of the Indonesian Throughflow are mainly influenced by the intensity of the cool throughflow and by glacial-interglacial sea-level changes. We present a study based on core 18471 (9°21.987' S, 129°58.983' E, 485m water depth, 13.5m long) and 30 core tops retrieved in the Timor Sea during the R/V Sonne Cruise 185 ("VITAL"). Multicorer core tops were retrieved along two transects between 130 and 2400m water depths, representing a range of present day bottom water temperatures between 2 and 21°C. For the downcore study, we measured Mg/Ca-ratios in ~10 tests of the benthic foraminifera Hoeglundina elegans, Cibicidoides wuellerstorfi and Hyalinea balthica in 10cm intervals (1-2kyr time resolution). The preservation of tests was checked with a scanning electron microscope. Cibicidoides wuellerstorfi and H. balthica were used in one interval, where H. elegans was rare. Duplicate samples were analyzed to inter-calibrate the three species. Mg/Ca ratios were converted into temperature using published calibrations and our regional calibration based on Timor Sea core tops. Preliminary results show that Mg/Ca ratios in H. elegans vary between 0.8 and 2.2mmol mol-1 corresponding to a temperature range between 4 and 10.5°C, in contrast to a modern annual average temperature of 7.9°C at 400m. 22-paired analyses in H. elegans give a reproducibility of 0.16mmol mol-1 (standard deviation

  3. Penultimate and last glacial cycles in the western Bering Sea: evidence from micropaleontological and sedimentary records

    NASA Astrophysics Data System (ADS)

    Ovsepyan, Ekaterina; Ivanova, Elena; Murdmaa, Ivar

    2014-05-01

    The short- and long-term variability of sea-surface bioproductivity, intermediate-water oxygenation, sea ice conditions and bottom current velocities are inferred from the high-resolution multi-proxy study based on benthic (BF) and planktonic (PF) foraminiferal assemblages and sedimentary record of the 18m-long Core SO201-2-85KL (western Bering Sea). Early MIS 6 is characterized by a very low seasonal bioproductivity, moderate bottom-water oxygenation, and expanded seasonal sea ice conditions, as documented by the abundant phytodetritus species Alabaminella weddelensis, Islandiella norcrossi and Epistominella arctica, suboxic group of BF, and high accumulation rates of gravel grains, respectively. Middle MIS 6 is represented by intercalation of green diatomaceous ooze and grey clayey silt layers with sharp peaks of BF abundance in green interbeds. These spikes might result either from short-term events of enhanced sea surface bioproductivity or from lateral BF transport by intensified bottom currents, as it is demonstrated by high-amplitude variations of the clay/silt ratio. Rather high seasonal productivity and northward migration of the sea ice margin are reconstructed for the late MIS 6 that is also characterized by a slight increase in the Northern Hemisphere summer insolation. Strong dissolution of calcareous microfossils is revealed for MIS 5.5-5.1 when the Bering Strait was open. Dissolution might be caused by an excess of carbon dioxide in the bottom-water due to an abundant organic matter decay and/or to an influence of the old CO2-rich deep water. MIS 4 - early Termination I is characterized by a dominance of glacial benthic foraminiferal assemblages that implies low bioproductivity conditions. A prevalence of suboxic BF group suggests moderate bottom-water oxygenation. Sea ice rafting occurred in the western Bering Sea during MIS 4 - early Termination I but the drifted ice was not so dense as during MIS 6. The well-known productivity spikes at B

  4. Understanding past climatic and hydrological variability in the Mediterranean from Lake Prespa sediment isotope and geochemical record over the Last Glacial cycle

    NASA Astrophysics Data System (ADS)

    Leng, Melanie J.; Wagner, Bernd; Boehm, Anne; Panagiotopoulos, Konstantinos; Vane, Christopher H.; Snelling, Andrea; Haidon, Cheryl; Woodley, Ewan; Vogel, Hendrik; Zanchetta, Gianni; Baneschi, Ilaria

    2013-04-01

    Here we present stable isotope and geochemical data from Lake Prespa (Macedonia/Albania border) over the Last Glacial cycle (Marine Isotope Stages 5-1) and discuss past lake hydrology and climate (TIC, oxygen and carbon isotopes), as well as responses to climate of terrestrial and aquatic vegetation (TOC, Rock Eval pyrolysis, carbon isotopes, pollen). The Lake Prespa sediments broadly fall into 5 zones based on their sedimentology, geochemistry, palynology and the existing chronology. The Glacial sediments suggest low supply of carbon to the lake, but high summer productivity; intermittent siderite layers suggest that although the lake was likely to have mixed regularly leading to enhanced oxidation of organic matter, there must have been within sediment reducing conditions and methanogenesis. MIS 5 and 1 sediments suggest much more productivity, higher rates of organic material preservation possibly due to more limited mixing with longer periods of oxygen-depleted bottom waters. We also calculated lakewater δ18O from siderite (authigenic/Glacial) and calcite (endogenic/Holocene) and show much lower lakewater δ18O values in the Glacial when compared to the Holocene, suggesting the lake was less evaporative in the Glacial, probably as a consequence of cooler summers and longer winter ice cover. In the Holocene the oxygen isotope data suggests general humidity, with just 2 marked arid phases, features observed in other Eastern and Central Mediterranean lakes.

  5. Comment on “Glacial cycles drive variations in the production of oceanic crust”

    NASA Astrophysics Data System (ADS)

    Goff, John A.

    2015-09-01

    Crowley et al. (Reports, 13 March 2015, p. 1237) propose that abyssal hill topography can be generated by variations in volcanism at mid-ocean ridges modulated by Milankovitch cycle-driven changes in sea level. Published values for abyssal hill characteristic widths versus spreading rate do not generally support this hypothesis. I argue that abyssal hills are primarily fault-generated rather than volcanically generated features.

  6. Comment on "Glacial cycles drive variations in the production of oceanic crust".

    PubMed

    Goff, John A

    2015-09-01

    Crowley et al. (Reports, 13 March 2015, p. 1237) propose that abyssal hill topography can be generated by variations in volcanism at mid-ocean ridges modulated by Milankovitch cycle-driven changes in sea level. Published values for abyssal hill characteristic widths versus spreading rate do not generally support this hypothesis. I argue that abyssal hills are primarily fault-generated rather than volcanically generated features.

  7. Extreme events from hundreds years to glacial cycle: insights from Quaternary terraces across the Taiwan mountain belt

    NASA Astrophysics Data System (ADS)

    Lee, J. C.; Chan, Y. C.; Chang, Q. M.; Siame, L. L.

    2015-12-01

    Based on different age determinations on Quaternary fluvial terraces distributed across the Taiwan mountain belt, we provide insights on possible and intriguing extreme events, tectonic and/or climate, at different time scales from hundreds years to glacial cycles (i.e., hundreds of thousands years). First in the foreland foothills of western Taiwan, based on Be10 cosmogenic and C14 dating the Puakua tableland reveals a recurrent time of about 100-120 Ka of terrace deposits, which are characterized by 4-5 levels of lateritic terraces, with a long-term uplift rate of 1.5-2 mm/yr in the last 450 Ka. Secondly in the eastern Central Range of the Hsinwulyu River, based on linear tilting model and GPS short-term geodetic rate, it exhibits 8-10 levels of recurrent river terrace deposits occurred about every 5 thousands years in the past 50 Ka or so, under a regional uplift rate of 2-8 mm/yr. Finally in the Longitudinal Valley, a plate suture between the rapid moving Philippine Sea plate and the stable Eurasian plate, based on the C14 dating and abundant geodetic data, including leveling, GPS and creep meter, we infer a recurrent time of about 400-600 years for 8-10 levels of uplifted fluvial terraces on the hanging wall of the Longitudinal Valley fault with an uplift rate of 2-3 cm/yr during the past 5-6 Ka. It is still too early to draw any conclusion on scientific explanations for these three types of possible extreme events at a recurrent time of 0.5 ka, 5 ka and 11 ka, respectively. However, possible scenario and causative mechanisms might be anticipated, for instance the global climate influence such as glacial cycle, or regional tectonic effect such as cluster of mega earthquakes in different areas of the Taiwan mountain belt. On the other hand, comparing the terraces in the three different geological/tectonic setting, we found that the recurrent time of terrace deposits shows an inverse proportional relationship to the uplift rate in the local areas, which requires

  8. 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.

  9. The rock magnetic characteristics of last glacial cycle loess from the island of Susak (Adriatic Sea, Croatia)

    NASA Astrophysics Data System (ADS)

    Hambach, Ulrich; Duchoslav, Maguerita; Rolf, Christian; Wacha, Lara; Frechen, Manfred; Galovic, Lidija

    2010-05-01

    palaeosols occur at 3 and 5.5 metre depth and two macroscopically visible volcanic tephra layers are intercalated in the upper part of the section. At present, we assume that the sequence represents the entire last glacial cycle (11-130 kyr). The concentration dependent magnetic parameters (e.g. magnetic low field susceptibility, SIRM) do not at all resemble the lithology. Volume susceptibility in unaltered loess exceeds even 1*10-3 SI which is at least 3 times higher compared to loess from the middle Danube basin only a few hundreds of kilometres to the East (Markovic et al. 2009). Grain size dependent magnetic parameters (e.g. frequency dependent magnetic susceptibility, S-ratio, etc.) reveal the relative enhancement of superparamagnetic particles and the formation of high-coercivity minerals in the pedogenetically altered horizons. However, in general the magnetic signal seems to be controlled by the primarily detrital minerals and climatically governed relatively weak alterations occur only in the macroscopically visible pedohorizons. During the last glacial cycle, the sea level of the Adriatic Sea was lowered by several decametres at least. As a consequence, the alluvial plain of the Po River extended far to the Southeast and provided the sand and silt which were blown to the shallow mountain ranges forming today the islands of the Dalmatian archipelago (Cremaschi 1990). Pleistocene and recent floodplain deposits of the Po River in North Italy contain large amounts of heavy minerals from the metamorphic series of the Central Alps. This detritus may control the magnetic properties of the aeolian deposits on the island of Susak. Further petrographical and mineral magnetic studies are necessary to prove our hypothesis.

  10. The role of glacial cycles in promoting genetic diversity in the Neotropics: the case of cloud forests during the Last Glacial Maximum.

    PubMed

    Ramírez-Barahona, Santiago; Eguiarte, Luis E

    2013-03-01

    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

  11. A loess-paleosol record of climate and glacial history over the past two glacial-interglacial cycles (~ 150 ka), southern Jackson Hole, Wyoming

    NASA Astrophysics Data System (ADS)

    Pierce, Kenneth L.; Muhs, Daniel R.; Fosberg, Maynard A.; Mahan, Shannon A.; Rosenbaum, Joseph G.; Licciardi, Joseph M.; Pavich, Milan J.

    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 10Be accumulation in soils, and cosmogenic 10Be 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 (~ 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (~ 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.

  12. 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

  13. 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.

  14. The Taimyr Peninsula and the Severnaya Zemlya archipelago, Arctic Russia: a synthesis of glacial history and palaeo-environmental change during the Last Glacial cycle (MIS 5e-2)

    NASA Astrophysics Data System (ADS)

    Möller, Per; Alexanderson, Helena; Funder, Svend; Hjort, Christian

    2015-01-01

    We here suggest a glacial and climate history of the Taimyr Peninsula and Severnaya Zemlya archipelago in arctic Siberia for the last about 150 000 years (ka). Primarily it is based on results from seven field seasons between 1996 and 2012, to a large extent already published in papers referred to in the text - and on data presented by Russian workers from the 1930s to our days and by German colleagues working there since the 1990s. Although glaciations even up here often started in the local mountains, their culminations in this region invariably seems to have centred on the shallow Kara Sea continental shelf - most likely due to expanding marine ice-shelves grounding there, as a combined effect of thickening ice and eustatically lowered sea-levels. The most extensive glaciation so far identified in this region (named the Taz glaciation) took place during Marine Isotope Stage 6 (MIS 6), i.e. being an equivalent to the late Saale/Illinoian glaciations. It reached c. 400 km southeast of the Kara Sea coast, across and well beyond the Byrranga Mountain range and ended c. 130 ka. It was followed by the MIS 5e (Karginsky/Eemian) interglacial, with an extensive marine transgression to 140 m above present sea level - facilitated by strong isostatic downloading during the preceding glaciation. During the latest (Zyryankan/Weichselian/Wisconsinan) glacial cycle followed a series of major glacial advances. The earliest and most extensive, culminating c. 110-100 ka (MIS 5d-5e), also reached south of the Byrranga mountains and its post-glacial marine limit there was c. 100 m a.s.l. The later glacial phases (around 70-60 ka and 20 ka) terminated at the North Taimyr Ice Marginal Zone (NTZ), along or some distance inland from the present northwest coast of Taimyr. They dammed glacial lakes, which caused the Taimyr River to flow southwards where to-day it flows northwards into the Kara Sea. The c. 20 ka glacial phase, contemporary with the maximum (LGM) glaciation in NW Europe

  15. 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

  16. Interglacial-glacial cycles recorded in the deposit sequence at Kruzhyky on the Dniester River (East Carpathian Foreland)

    NASA Astrophysics Data System (ADS)

    Łanczont, Maria; Boguckyj, Aandrij; Mroczek, Przemysław; Zieliński, Paweł; Jacyszyn, Andrij; Pidek, Agnieszka I.; Urban, Danuta; Kulesza, Piotr; Hołub, Beata

    2010-01-01

    of sands with horizontal stratification and silts with horizontal or flaser lamination; single small-scale lithofacies of sands with trough cross-stratification occur in places; single gravel grains are numerous. Two deformation horizons are found: the higher one is characterized by the occurrence of folds and flexure deflections, and the lower one-involution structures and casts of ice wedges/fissures. This complex is probably the result of deposition on the distal part of flat, periodically inundated fluvioglacial fan connected with advancing ice sheet. 4. Ablation complex-sandy or sandy-silty diamicton occurring as isolated inserts, lenses or tongues. Its lower boundary is sharp, erosional and uneven (concave). This complex represents flows of supraglacial tills, which strongly deformed the deposits of the underlying complex 3. 5. Aeolian complex-silty (loess) and sandy-silty (Table 1) deposits with distinct traces of intensive, postsedimentary alterations of pedogenesis of different ages (Tables 1 and 2). It is composed of two soil units separated by thin, primary loess layer: a) older, well-developed paleosol with several pedofeatures very typical of the Sokal (Mazovian) soil; b) younger unit developed as pedocomplex consisting of two mature soils, the upper of which ("modern" neosol) is formed in the top of relict and exhumed paleosol. The described paleosols should be recognized as at least two soils of different ages and of interglacial rank, developed in periglacial loess-like deposits. The Kruzhyky profile is unique in the Dniester River valley. On account of its situation, it supplements the former information about the terrace 5 structure, which has been determined in detail in the Halyč site. And what is most important, it is the only site on the terrace 5 where glacial deposits were found. Lithofacial analysis carried out in the profile enables us to reconstruct the following events reflecting interglacial-glacial cycles: 1. The lowest, gravelly

  17. Gradual and small decrease of glacial sea surface temperatures in the eastern equatorial Indian ocean across the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Casse, Marie; Malaize, Bruno; Bassinot, Franck; Caillon, Nicolas; Degaridel-Thoron, Thibault; Rebaubier, Hélène; Charlier, Karine; Caley, Thibaut; Marieu, Vincent; Beaufort, Luc; Rojas, Virginia; Meynadier, Laure; Valet, Jean Pierre; Reaud, Yvan

    2015-04-01

    The Mid-Pleistocene Transition (MPT), between about 1.2 and 0.7 Ma, is characterized by the emergence of asymmetric, high-amplitude 100 ka cycles, which contrast with the low amplitude, 41 kyr cycles that dominate the early Pleistocene climate. Here, we study the sediment core MD12-3409, which spans the last ~ 1.75 Ma, to document hydrographic changes across the MPT in the Eastern Equatorial Indian Ocean. Stratigraphy is based on benthic foraminifera delta18O and we reconstruct Sea Surface Temperatures (SST) using the Mg/Ca ratio of Globigerinoides ruber, a surface dwelling planktonic foraminifera. Our results reveal a progressive cooling of glacial maxima across the MPT but no long-term trend in mean SST over the last 1.75 Ma. The main periodicity of the surface temperature signal shifts from 41 kyr before the MPT, to both 100 kyr and 41 kyr for the post MPT time period. Over the last 800 ka, the strong correlation between core MD12-3409 SST fluctuations and the atmospheric CO2 record suggests a global, greenhouse forcing for the tropical Indian SST over the post-MPT time period. Within the MPT, and for earlier time interval, changes in temperature gradients between our SST record and other temperature records in, or at the edge of, the Pacific Warm Pool, could suggest reorganizations of sea surface circulation and lateral heat exchanges. Since the MPT, the amplification of sea level lowering during glacial periods might have shoaled the Indonesian Through Flow (ITF) gateway, restricting hydrographic exchanges between Pacific and Indian oceans.

  18. Sediment from the Last Two Glacial Periods Amalgamated and Re-Entrained in the Alluvial Piedmont of the North Tian Shan

    NASA Astrophysics Data System (ADS)

    Malatesta, L. C.; Avouac, J. P.; Brown, N.; Rhodes, E. J.; Prancevic, J.; Pan, J.; Chevalier, M. L.; Saint-Carlier, D.; Zhang, W.

    2015-12-01

    The history of the planet is recorded in its sedimentary basins where the product of mountain erosion is stored, reflecting climatic and tectonic forcing. Were the sediments and the signal they carry to be immediately deposited in a basin, paleo-reconstructions would be straightforward as the age and nature of a deposit would be a testimony of the source and transfer conditions. The sometime intricate path of clastic material along the sediment routing system complicates greatly the situation. We set here to investigate quantitatively the effect of an alluvial piedmont on the sediment flux that crosses it en route to a basin. We focus on the northern piedmont of the Tian Shan (Xinjiang, China). The piedmont is actively deformed by a fold-and-thrust system and experienced several cycles of incision and aggradation in the Pleistocene. We present new OSL dating of terrace and fan material. These data suggest that the most prominent terraces match three glacial maxima 100 kyr apart; thereby the landscape would primarily react to eccentricity cycles. As a consequence, a significant fraction of sediments produced in that period is temporarily deposited in the piedmont before a later incision phase can deliver it to the basin. The OSL ages of alluvial fan strata exposed and recently eroded by the incising river hint at two aggradation phases during the last two glacial periods. Furthermore lose sediment dated at 300 ka is found to be available along the transport route of the sediments and likely entrained during incision phases. We expect the modern sediment flux entering the basin to contain a significant amount of recycled material as old as 180 ka and a non-negligible amount of recycled material as old as 300 ka that can significantly skew geochemical or provenance studies if ignored.

  19. 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

  20. Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Simon, Quentin; Thouveny, Nicolas; Bourlès, Didier L.; Nuttin, Laurence; Hillaire-Marcel, Claude; St-Onge, Guillaume

    2016-05-01

    Authigenic 10Be/9Be ratios and 10Be-fluxes reconstructed using the 230Thxs normalization, proxies of the cosmogenic radionuclide 10Be production rate in the atmosphere, have been measured in a sedimentary core from Baffin Bay (North Atlantic) spanning the last 136 ka BP. The normalization applied on the exchangeable (authigenic) 10Be concentrations using the authigenic 9Be isotope and 230Thxs methods yield equivalent results strongly correlated with sedimentological parameters (grain-size and mineralogy). Lower authigenic beryllium (Be) concentrations and 10Be/9Be ratios are associated with coarse-grained carbonate-rich layers, while higher authigenic Be values are related to fine-grained felspar-rich sediments. This variability is due to: i) sediment composition control over beryllium-scavenging efficiency and, ii) glacial history that contributed to modify the 10Be concentration in Baffin Bay by input and boundary scavenging condition changes. Most paleo-denudation rates inferred from the 10Be/9Be ratio vary weakly around 220 ± 76 tons.km-2.yr-1 (0.09 ± 0.03 mm.yr-1) corresponding to relatively steady weathering fluxes over the last glacial cycle except for six brief intervals characterized by sharp increases of the denudation rate. These intervals are related to ice-surging episodes coeval with Heinrich events and the last deglaciation period. An average freshwater flux of 180.6 km3.yr-1 (0.006 Sv), consistent with recent models, has been calculated in order to sustain glacially-derived 10Be inputs into Baffin Bay. It is concluded that in such environments, the authigenic 10Be measured mainly depends on climatic effects related to the glacial dynamics, which masks the 10Be production variation modulated by geomagnetic field changes. Altogether, these results challenge the simple interpretation of 10Be-concentration variation as a proxy of Interglacial/Glacial (interstadial/stadial) cycles in Arctic and sub-Arctic regions. They rather suggest the effect

  1. Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Simon, Quentin; Thouveny, Nicolas; Bourlès, Didier L.; Nuttin, Laurence; Hillaire-Marcel, Claude; St-Onge, Guillaume

    2016-05-01

    Authigenic 10Be/9Be ratios and 10Be-fluxes reconstructed using the 230Thxs normalization, proxies of the cosmogenic radionuclide 10Be production rate in the atmosphere, have been measured in a sedimentary core from Baffin Bay (North Atlantic) spanning the last 136 ka BP. The normalization applied on the exchangeable (authigenic) 10Be concentrations using the authigenic 9Be isotope and 230Thxs methods yield equivalent results strongly correlated with sedimentological parameters (grain-size and mineralogy). Lower authigenic beryllium (Be) concentrations and 10Be/9Be ratios are associated with coarse-grained carbonate-rich layers, while higher authigenic Be values are related to fine-grained felspar-rich sediments. This variability is due to: i) sediment composition control over beryllium-scavenging efficiency and, ii) glacial history that contributed to modify the 10Be concentration in Baffin Bay by input and boundary scavenging condition changes. Most paleo-denudation rates inferred from the 10Be/9Be ratio vary weakly around 220 ± 76 tons.km-2.yr-1 (0.09 ± 0.03 mm.yr-1) corresponding to relatively steady weathering fluxes over the last glacial cycle except for six brief intervals characterized by sharp increases of the denudation rate. These intervals are related to ice-surging episodes coeval with Heinrich events and the last deglaciation period. An average freshwater flux of 180.6 km3.yr-1 (0.006 Sv), consistent with recent models, has been calculated in order to sustain glacially-derived 10Be inputs into Baffin Bay. It is concluded that in such environments, the authigenic 10Be measured mainly depends on climatic effects related to the glacial dynamics, which masks the 10Be production variation modulated by geomagnetic field changes. Altogether, these results challenge the simple interpretation of 10Be-concentration variation as a proxy of Interglacial/Glacial (interstadial/stadial) cycles in Arctic and sub-Arctic regions. They rather suggest the effect of

  2. 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

    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.

  3. Gulf of Mexico Climate, Laurentide Ice Sheet History, and Global Sea Level Change During the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Flower, B. P.; Williams, C.; Brown, E. A.; Hastings, D. W.; Hill, H.; Adams, S.; Hendrix, J.; Martin, E. E.; Biller, N. B.; Goddard, E.

    2011-12-01

    The interactions between low-latitude Atlantic climate and high-latitude ice sheet variability represent an important issue in past abrupt climate change. Specifically, Laurentide Ice Sheet (LIS) meltwater input seems to be decoupled at the millennial scale from Gulf of Mexico sea-surface temperature (SST), as well as Greenland air temperature, during the last glacial cycle. Indeed, comparison to Greenland ice core records indicate significant meltwater input during some North Atlantic cool episodes, including Heinrich Stadials 4, 3, and 1. Here we present published and new Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber from northern Gulf of Mexico sediment cores that provide detailed records of SST, δ18O of seawater (δ18Osw), and inferred salinity for the 48-10 ka interval. Age control for Orca Basin cores MD02-2550 and -2551 is based on AMS 14C dates on G. ruber and documents continuous sedimentation at rates >35 cm/kyr. Significant meltwater input is inferred from δ18Osw data during Antarctic Isotope Maxima (AIM) events and reaches a peak during the Bølling/Allerød, consistent with bipolar warming and a high sensitivity to greenhouse forcing. Furthermore, bulk sediment δ18O data show a brief spike reaching -5.5% ca. 14.5 ka during an interval barren of foraminifera. We speculate that this excursion represents fine carbonate sediment from Canadian Paleozoic marine carbonates, analogous to detrital carbonate in the North Atlantic that has a δ18O value of -5%. Radiogenic isotope data (Nd and Pb) also reach peak values at this interval, indicative of older continental material sourced from Canada vs. younger material from the Mississippi River drainage basin. Inferred major meltwater flow appears to have been associated with meltwater pulse 1a within the Bølling warm interval, consistent with a significant contribution by the LIS to rapid global sea level rise. Overall, the relations between Gulf of Mexico meltwater input, Heinrich

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

    PubMed Central

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

    2013-01-01

    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. PMID:23671087

  5. 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.

  6. Periodic isolation of the southern coastal plain of South Africa and the evolution of modern humans over late Quaternary glacial to interglacial cycles

    NASA Astrophysics Data System (ADS)

    Compton, J. S.

    2012-04-01

    Humans evolved in Africa, but where in Africa and by what mechanisms remain unclear. The evolution of modern humans over the last million years is associated with the onset of major global climate fluctuations, glacial to interglacial cycles, related to the build up and melting of large ice sheets in the Northern Hemisphere. During interglacial periods, such as today, warm and wet climates favored human expansion but during cold and dry glacial periods conditions were harsh and habitats fragmented. These large climate fluctuations periodically expanded and contracted African ecosystems and led to human migrations to more hospitable glacial refugia. Periodic isolation of relatively small numbers of humans may have allowed for their rapid evolutionary divergence from the rest of Africa. During climate transitions these divergent groups may have then dispersed and interbred with other groups (hybridization). Two areas at the opposite ends of Africa stand out as regions that were periodically isolated from the rest of Africa: North Africa (the Maghreb) and the southern coastal plain (SCP) of South Africa. The Maghreb is isolated by the Sahara Desert which periodically greens and is reconnected to the rest of Africa during the transition from glacial to interglacial periods. The SCP of South Africa is isolated from the rest of Africa by the rugged mountains of the Cape Fold Belt associated with inedible vegetation and dry climates to the north. The SCP is periodically opened when sea level falls by up to 130 m during glacial maxima to expose the present day submerged inner continental shelf. A five-fold expansion of the SCP receiving more rainfall in glacial periods may have served as a refuge to humans and large migratory herds. The expansive glacial SCP habitat abruptly contracts, by as much as one-third in 300 yr, during the rapid rise in sea level associated with glacial terminations. Rapid flooding may have increased population density and competition on the SCP to

  7. High latitude regulation of low latitude thermocline ventilation and planktic foraminifer populations across glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Sexton, Philip F.; Norris, Richard D.

    2011-11-01

    One of the earliest discoveries in palaeoceanography was the observation in 1935 that the (sub)tropical planktic foraminifer Globorotalia menardii became absent or extremely rare in the Atlantic Ocean during glacials of the late Pleistocene. Yet a mechanistic explanation for G. menardii's extraordinary biogeographic behaviour has eluded palaeoceanographers for 75 years. Here we show that modern G. menardii, along with two other species that also suffer Atlantic population collapses during glacials, track poorly ventilated waters globally in their thermocline habitats. The ventilation states of low latitude thermoclines are 'set', to a first order, by intermediate water masses originating at high latitudes. In the modern Atlantic this control on low latitude thermocline ventilation is exerted by relatively poorly ventilated, southern-sourced Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW). We suggest that the glacial Atlantic foraminifer population collapses were a consequence of a low latitude thermocline that was better ventilated during glacials than it is today, in line with geochemical evidence, and driven primarily by a well-ventilated, northern-sourced intermediate water mass. A ventilation mechanism driving the glacial population collapses is further supported by our new constraints on the precise timing of these species' Atlantic proliferation during the last deglaciation — occurring in parallel with a wholesale, bipolar reorganisation of the Atlantic's thermocline-to-abyssal overturning circulation. Our findings demonstrate that a bipolar seesaw in the formation of high latitude intermediate waters has played an important role in regulating the population dynamics of thermocline-dwelling plankton at lower latitudes.

  8. Genera variation of tropical mid-upper montane rainforest inferred from a marine pollen record in southern Philippines during the glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Bian, Y.

    2015-12-01

    Tropical vegetation is the most outstanding and obvious feature of South-East Asia, and it is expected to provide valuable information for the palaeoclmatic conditions. Pollen records from the tropical West Pacific indicate that the tropical vegetation is much sensitive to the environment and climate change, and their good correspondence with palaeocliamte change in glacial/interglacial timescales. It is shown that the range of the tropical montane rainforest was affected by the temperature change during the glacial cycle. But, from some marine core, the genera variation of tropical mid-upper montane pollen record is also distinct during the glacial cycle. In this study, examination of the pollen content of marine core MD06-3075 taken from Davao Gulf in the Southern Philippines reveals a ~116,000 year record of tropical vegetation change as well as the influence of the environment and climate variability on the ecosystem of the tropical area. Chronology was determined by 16 AMS 14C dates and a detailed oxygen isotope record. A high representation of pollen from tropical upper montane rainforest (mainly Podocarpus) (40-60%) during the last glacial period indicates that this forest type extended to lower attitudes. And the genera variations of the tropical mid-upper montane rainforest exist between the Phyllocladus and Podocarpus with the environment and climate changing. The pollen content of Phyllocladus is much high in marine isotope stage (MIS) 5, but Podocarpus is much higher in the glacial period. During the onset of MIS 5a and 5c, the percentage of Phyllocladus pollen declines dramatically. Vegetation investigation in Mindanao, shows that Podocarpus exists in altitude ranging from 1,200-1,700 m, and Phyllocladus appear in altitude range from 1700-2100 m, but is more abundant above the 2,400 m. Thus, Phyllocladus might be more sensitive to the temperature change. Then, in this study, the pollen content of is much high during the interglacial period

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

    NASA Astrophysics Data System (ADS)

    Muhs, Daniel R.; Ager, Thomas A.; Arthur Bettis, E.; McGeehin, John; Been, Josh M.; Begét, James E.; Pavich, Milan J.; Stafford, Thomas W.; Stevens, De Anne S. P.

    2003-09-01

    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

  10. 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

  11. All together now? Sensitivity, dynamics, and predictability of planktonic foraminiferal species abundance versus community structure across Plio-Pleistocene glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Hull, P. M.; Norris, R. D.; Sexton, P.

    2012-12-01

    Most studies to date of biospheric sensitivity to global change have focused on understanding the sensitivity of modern species and communities to recent or experimental environmental change. However, it is unclear how to scale these results towards predicting the response of the biosphere to ongoing global change given that i) similar species often respond individualistically the same perturbation, ii) biotic response often scales nonlinearly with the size and/or duration of environmental change, and iii) many terrestrial and marine community types known from the recent past lack modern analogs. In this context, marine microfossils from deep sea sediments hold enormous promise for furthering our understanding of biotic sensitivity as they capture temporally expanded records of paleoceanographic and biotic response across a range climatic regimes (e.g., icehouse versus greenhouse climates), disturbance types (e.g., from background climate oscillations to mass extinctions), and habitats (e.g., low vs. high latitudes, upwelling vs. gyre ecosystems, etc). Here we use the repeated glacial-interglacial cycles and longer term trend of intensifying Northern Hemisphere glaciation from the Pliocene-Pleistocene to examine issues related to the sensitivity of planktonic foraminiferal species and communities to global change in an icehouse world. More specifically, we quantify the sensitivity and predictability of changes in planktonic foraminiferal species abundance (species specific mass accumulation rates) and community structure (dissimilarity indices and community classification) to glacial-interglacial cycles in the Plio-Pleistocene in two Atlantic sites (ODP Sites 999 and 662). We first examine whether the sensitivity of species and communities to glacial-interglacial cycles in the early Pliocene (~5-3 million years ago) is predictive of i) their sensitivity to the intensification of Northern Hemisphere glaciation (~3-2 million years ago), or ii) their sensitivity to

  12. Dynamic Drainage Networks and Discharge Histories in North America over the Last Glacial Cycle: Implications for Geomorphic Change and Early Human Settlement Patterns

    NASA Astrophysics Data System (ADS)

    Wickert, A. D.; Anderson, R. S.; Mitrovica, J. X.; Kettner, A. J.; Lee, C. M.

    2011-12-01

    During the last glacial cycle, changing ice masses altered topography, moving drainages and coastlines by hundreds of kilometers or more. These changes had wide-reaching implications for geomorphic evolution and human interactions with the hydrologic system. We present results from the coupling of ice sheet histories, geophysical models, and hydrologic analyses to reconstruct flow and sediment transport as the major ice sheets grew and waned. We show how our model results compare to geological data, and how they can be used to create a predictive model of archaeological site locations as people entered the Americas. We coupled ice sheet histories with a state-of-the-art model of global response to changing surface loads [Kendall et al., 2005] to reconstruct continental-scale drainage networks and coastlines over the last glacial cycle. The combination of changes in global ocean volume, basal pressure gradients under the ice sheets, and geophysical responses to loading-including flexural isostasy, geoid deflection, and true polar wander-caused continental-scale drainage basin reorganization. We then used the model HydroTrend [Kettner and Syvitski, 2008], with ice mass balances, proglacial lake positions, and paleoclimate general circulation model results as inputs, to simulate river water and sediment discharges over the last glacial cycle through each of our reconstructed drainage basins. We compared these results to geologic data from the Mississippi River drainage basin as a case study. Our predicted time-series of water and sediment discharges correlates with the alluvial history of the Upper Mississippi and the transition of the Lower Mississippi from a braided to a meandering system. Our results also place hard numbers on water and sediment discharges to the Gulf of Mexico over the last glacial cycle. We compare these with paleoceanographic data to assess the accuracy of the ice and solid earth models that we use and to understand quantitatively the impacts of

  13. Separating the Effects of Northern Hemisphere Ice-Sheets, CO2 Concentrations and Orbital Parameters on Global Precipitation During the Late Pleistocene Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Elison Timm, O.; Friedrich, T.; Timmermann, A.; Ganopolski, A.

    2015-12-01

    Global-scale changes in the hydrological cycle have been reconstructed in many parts of the world using various archives of proxy information. The signals found in proxies allow us to study the complex response of the global hydrological cycle to the combined forcing and feedback mechanisms. However, it remains a challenge to attribute the observed variations to specific causes, in particular, it is difficult to distinguish CO2 and ice-sheet response in time series. Here, we present new results from a set of transient paleoclimate simulation of the last eight glacial cycles (784,000 years) using accelerated forcing. In order to isolate the ice-sheet forcing from the CO2 -driven response and orbital forcing, we made use of additional transient experiments with varying forcing combinations covering the last 408,000 years: (a) keeping CO2 concentrations constant, (b) keeping the ice-sheet fixed, (c) orbital forcing only. The simulations show that orbital forcing has strongest impact in the tropical and subtropical regions. The northern hemisphere ice-sheets stamp a characteristic spatial footprint on the global precipitation variability. The ice-sheets mainly affect the extratropical northern hemisphere, but the cone of influence extends further into the North African monsoon regions, and to a weaker extent into the Asian monsoon. In an attempt to validate our model-specific results we compared our results with existing hydrological paleo proxy records. Despite the growing number of proxy archives, the aim to identify the ice-sheet influence in spatially limited networks of proxy time series remains as challenge. More records that cover at least two full glacial cycles could significantly increase the signal separation. In conclusion, our results suggest that the northern hemisphere ice-sheets played an important role in modulating the global hydrological cycle.

  14. Past seismic activity in Eastern Anatolia recorded over several glacial/interglacial cycles in the sediments of Lake Van

    NASA Astrophysics Data System (ADS)

    Stockhecke, M.; Anselmetti, F.; Sturm, M.

    2012-12-01

    Lake sediments document besides paleoenvironmental and paleoclimate conditions also paleoseismic activity through various forms of deformation structures. These are especially visible in finely-laminated sediments. Being situated in a tectonically active region, the partly annually-laminated sedimentary sequence of the terminal Lake Van, recovered in 2010 under the context of the ICDP Paleovan project, shows dozens of earthquake-triggered microdeformations that document past seismic events of the last half a million years. Lithological and multiproxy analysis revealed that the Lake Van's depositional conditions varied in correspondence to Milankovitch and sub-Milankovitch cycles. Glacial/stadial and interglacial/interstadial conditions were recorded continuously over the last half a million years excluding two discontinuities, which indicate major hydrological and geomorphological changes in Lake Van's early history. Two sites were drilled 10 km apart: A primary drill site, situated on a ridge, covers the entire lake history since its initial transgression in the middle Pleistocene; A secondary drill site, located in a more shallow northern basin, covers the past 90'000 years. Multiple coring at both drill sites allows to establish two almost complete 220 m and 145 m long composite sections, respectively. Observing deformation structures in multiple parallel cores at each site is used as a criteria to distinguish 'true' paleoseismic deformation structures from potential drilling artifacts. Deformation structures consist of i) silt-filled vertical fractures, ii) microfaults with displacements at cm-scale, iii) microfolds, iv) liquefaction structures (mushroom, pseudonodules), iv) disturbed varve laminations and v) mixed layers. While the ridge site records the paleoseismic events as microdeformations, the northern basinal site rather records seismic events through the deposition of seismo-turbidites. In some cases, individual earthquake events can even be identified

  15. 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.

  16. Numerical modelling of subglacial erosion and sediment transport and its application to the North American ice sheets over the Last Glacial cycle

    NASA Astrophysics Data System (ADS)

    Melanson, Alexandre; Bell, Trevor; Tarasov, Lev

    2013-05-01

    Present-day sediment distribution offers a potentially strong constraint on past ice sheet evolution. Glacial system models (GSMs), however, cannot address this constraint while lacking appropriate representations of subglacial sediment production and transport. Incorporating these elements in GSMs is also required in order to quantify the impact of a changing sediment cover on glacial cycle dynamics. Towards these goals, we present a subglacial process model (hereafter referred to as the sediment model) that incorporates mechanisms for sediment production, entrainment, transport, and deposition. Bedrock erosion is calculated by both Hallet's and Boulton's abrasion laws separately, and by a novel quarrying law parametrized as a function of subglacial cavity extent. These process-oriented erosion laws are compared against a simple empirical relationship between erosion rate and the work done by basal stress. Sediment entrainment is represented by Philip's law for regelation intrusion and soft-bed deformation is included as a subglacial sediment transport mechanism. The model is driven by the data-calibrated MUN (3D) GSM and a newly developed subglacial hydrology module. The sediment model is applied to the last North American glacial cycle and predicts sediment thickness and cumulative erosion patterns. Results are obtained in the context of a sensitivity analysis and are compared against the present-day distribution of glacigenic sediment and geological estimates of Laurentide Ice Sheet erosion. Given plausible ranges for the sensitivity parameters, chosen a priori based on available literature or on heuristic arguments, the calculated erosion depths overlap with the geological estimates of Laurentide erosion. Most of the runs in the sensitivity set produce unrealistically thick and continuous moraines along the eastern, southern and western margins of the North American ice complex, which suggests that the model overestimates sediment entrainment and thus

  17. Running hotter, faster, shallower: acceleration of the marine nitrogen cycle from the Last Glacial Maximum to the pre-industrial, and implications for the future

    NASA Astrophysics Data System (ADS)

    Galbraith, E. D.

    2015-12-01

    Biologically-available nitrogen is the primary limiting nutrient in the global ocean. The complex physical-biological interdependencies of nitrogen fixation and denitrification, the source and sink of bioavailable nitrogen, have led to uncertainty over their future trajectories under higher CO2. Sedimentary nitrogen isotope evidence suggests that the global rate of denitrification was on the order of 50% lower during the last glacial maximum, and reveals that significant changes in denitrification have occurred on a decadal-centennial timescale. Coupled atmosphere-ocean-biogeochemistry models simulate similar changes, through physically-driven changes in anoxia, which then feed back on nitrogen fixation through the availability of phosphorus to diazotrophs. In addition, diazotroph culture experiments suggest that nitrogen fixation was further limited during glacial maxima by low CO2, causing an additional slowdown of the nitrogen cycle. The emergent picture suggests that deglaciation accelerated both sides of the N cycle, with more rapid loss encouraged by expanded shallow anoxia, and more rapid gain encouraged by higher CO2. It will be argued that the net effect on the nitrogen inventory can be approximated by knowing the distribution of surface ocean PO4, given the observed correlation of surface PO4 concentrations on the P:C ratio of exported organic matter.

  18. 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

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

    SciTech Connect

    Van de Water, P.K.; Leavitt, S.W. ); Betancourt, J.L. )

    1994-04-08

    Measurements of stomatal density and [sigma][sup 13]C 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 CO[sub 2] levels. Stomatal density decreased [approximately]17 percent and [sigma][sup 13]C decreased [approximately]1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO[sub 2]. Water-use efficiency increased [approximately]15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO[sub 2] and [sigma][sup 13]C of past atmospheres are accurate. The [sigma][sup 13]C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and the biosphere during the last glacial-interglacial cycle.

  20. Climatic control of sediment transport from the Himalayas to the proximal NE Bengal Fan during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Joussain, Ronan; Colin, Christophe; Liu, Zhifei; Meynadier, Laure; Fournier, Léa; Fauquembergue, Kelly; Zaragosi, Sébastien; Schmidt, Frédéric; Rojas, Virginia; Bassinot, Franck

    2016-09-01

    Clay mineralogy, siliciclastic grain-size, major elements, 87Sr/86Sr, and εNd analyses of deep-sea sediments cored in the north-eastern Bay of Bengal are used to reconstruct evolution of detrital sources and sediment transport to the proximal part of the Bengal deep-sea fan during the last climatic cycle. εNd values (-13.3 to -9.7) and 87Sr/86Sr ratios (0.721-0.733) indicate a mixture of sediments originating from the Ganges-Brahmaputra rivers and the Indo-Burman ranges. Interglacial Marine Isotopic Stages (MIS) 5 and 1 are associated with a higher contribution of sediments from the Ganges-Brahmaputra river system than is the case for glacial MIS 6, 4, 3, and 2. Siliciclasitic grain-size combined with Si/Al and Si/Fe ratios indicate coarser glacial sediments with numerous turbidite layers. Glacial turbidite layers display similar clay mineralogical compositions to hemipelagic sediments. Only few of turbidite layers (MIS 6, 4, and 2) are slightly unradiogenic (εNd -13.3), suggesting a higher contribution of Ganges-Brahmaputra river sediments. Independently of changes in the sedimentary sources, the smectite/(illite + chlorite) ratio of cores located on the NE Bengal Fan indicates higher inputs of primary minerals (illite and chlorite) from the highlands of the river basins (relief) during glacial MIS 6, 4, 3, and 2 and an increased contribution of pedogenic minerals (smectite and kaolinite) during interglacial MIS 5 and 1. Maximum smectite/(illite + chlorite) ratios during the warm sub-stages of MIS 5 suggest an intensification of summer monsoon rainfall associated with higher rates of physical erosion of the Indo-Gangetic flood-plain and/or dominant summer hydrological conditions transporting a higher proportion of sediments deriving from the Ganges-Brahmaputra rivers to the NE Bengal Fan. In addition, a higher production of smectite in soils of the Indo-Gangetic flood-plain during periods of intensification of monsoon rainfall cannot be excluded.

  1. Contributions of biological domains to nitrogen biogeochemical cycling in a High Arctic glacial ecosystem during summer melt

    NASA Astrophysics Data System (ADS)

    Ansari, A. H.; Hodson, A.; Heaton, T. H.; Marca-Bell, A.

    2010-12-01

    In this study coupled investigations of solute chemistry and isotopic tracers (δ15N, δ18O-NO3 and δ18O-H2O) of snow and streams are used to reveal the competitive and diverse nature of biological process within a High Arctic glacial ecosystem (Midtre Lovénbreen, Svalbard). This includes potential mineralisation and nitrification of dissolved organic nitrogen (DON) and ammonia within subglacial flow paths and denitrification in hyporheic zone of proglacial streams. During the initial melt phase (up to mid July), most of nitrate in the proglacial streams was directly derived from snow. But as the hyporheic zone gradually became more active after mid July and its relative contribution of nitrate to the proglacial streams water increased downstream. This was evident with a considerable downstream loss of nitrate and an increase in δ15N-NO3 (-7.82 to 14.91‰) values in the proglacial meltwater streams. At the same time non-snowpack nitrate was detected in subglacial runoff indicating as significant presence of metabolically active heterotrophic microbial consortia beneath the glacier. The observed snow packs δ18O-NO3 values (76 to 80‰) were strongly diagnostic of an atmospheric origin. However with the initiation of melt, this provided subglacial and proglacial aquatic ecosystems with a major primary source of nitrogen. Therefore nitrogen leaving this glacial watershed in runoff (δ18O-NO3 values 64.44 to 3.78‰) had a markedly different composition.

  2. Carbon cycle constraints during the last glacial/interglacial cycle derived from [CO2] and δ13Catm measurements from ice cores

    NASA Astrophysics Data System (ADS)

    Eggleston, S.; Schmitt, J.; Chappellaz, J. A.; Joos, F.; Fischer, H.

    2014-12-01

    Antarctic ice cores represent an invaluable source for understanding the climate of the past. Climatically important gases, including CO2, can be extracted from the ice and measured, thus providing atmospheric records for the past 800 kyr. Research has shown that atmospheric CO2 has varied naturally in conjunction with Antarctic air temperature. Additional knowledge of the variations of the stable carbon isotope of CO2, δ13Catm, can help us better understand the processes involved in these fluctuations. Here, we present a complete δ13Catm record extending from 160 kyrBP to the present. The present record, measured primarily on ice from the EPICA Dome C and Talos Dome ice cores, demonstrates a complex interplay of the ocean, terrestrial biosphere and atmosphere carbon reservoirs. For instance, a long-term increasing trend in δ13Catm, starting at the penultimate glacial maximum, extends well into MIS 4, while CO2 shows major drops already between 115 kyrBP and the MIS 5/4 boundary. In contrast, δ13Catm evolved roughly in antiphase during the MIS 4/3 transition with the atmospheric carbon storage increasing by 50 Gt while δ13Catm decreased by 0.5‰, a signal larger than that observed during the last glacial/interglacial termination. This antiphase relationship suggests that a single natural process or multiple processes acting on similar timescales may be responsible for this change in CO2. Modelling studies have shown that the ocean has the greatest impact on the concentration and stable isotope abundance of this greenhouse gas, in particular due to changes in stratification, upwelling, or marine productivity in the Southern Ocean. Similar to the situation at the onset of the last glacial/interglacial termination (Schmitt et al., 2012), the MIS 4/3 transition is characterized by the occurrence of a Heinrich event in the North Atlantic, presumably related to changes in the Atlantic Meridional Overturning Circulation and the upwelling of old carbon enriched

  3. An investigation of carbon cycle dynamics from the Last Glacial Maximum to the present using an earth system model of intermediate complexity

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    The University of Victoria Earth System Climate Model of intermediate complexity (v. 2.9) is used in this study to investigate carbon cycle dynamics from the Last Glacial Maximum to the present, with a particular emphasis on recreating the Holocene's carbon cycle from 8000-150 years before present (BP). This particular model's strengths are its comprehensive representation of ocean circulation in an ocean GCM (with 1.8° x 3.6° resolution and 19 levels) as well as its ability to perform transient simulations over the entire period between the LGM and the present. Without the explicit representation of peatlands, coral reefs and land use change, the UVic model's natural Holocene carbon cycle produced a decline of 245-254 ppm from 8000 to 150 BP, in contrast to the increase from 260 ppm to 280 ppm actually seen during this period. The effects of deep-ocean calcite compensation (and corresponding lysocline changes) were only a few (1-2) ppm when compared to simulations that had not experienced an ocean chemistry response to thousands of years of post-glacial vegetation uptake. Our experiments thus suggest that, without the contribution of land use, peatland uptake, and coral reefs, a net decline in atmospheric CO2 would have occurred from the mid-Holocene to the beginning of the Industrial era (instead of the 20 ppm increase), regardless of the winds or initial ocean state. However, these findings were discovered to be highly sensitive to the configuration of land ice shelves near Antarctica, with more extensive land ice leading to deeper vertical circulation in the Southern Ocean and a much higher atmospheric CO2 concentration of 260 ppm at 150 BP. Furthermore, simulations forced to follow the observed CO2 trend indicate that 400 PgC would need to be released into the atmosphere by the Earth System in order to account for the 280 ppm seen by the beginning of the Industrial era. Because this would require an improbable release of terrestrial vegetation, the UVic

  4. Dust Deposition and Migration of the ITCZ through the Last Glacial Cycle in the Central Equatorial Pacific (Line Islands).

    NASA Astrophysics Data System (ADS)

    Reimi Sipala, M. A.; Marcantonio, F.

    2014-12-01

    weakening of the ITCZ during glacial times. Future work on Nd isotope will shed additional light on subtle differences in dust isotopic composition within the source regions of interest, including the different volcanic zones of South America.

  5. Glacial-interglacial cycles of erosion and sediment transport along the western North American margin constrained by reconciling geologic and climate model data sets

    NASA Astrophysics Data System (ADS)

    Vanlaningham, S.; Pisias, N. G.; Duncan, R. A.; Hostetler, S. W.; Wilson, K. L.

    2009-12-01

    This study aims to determine whether observed shifts in sediment source (indicated by bulk sediment 40Ar-39Ar and Nd isotopic tracers) at a northeast Pacific core site are in response to variations in river basin erosion or transport pathways of terrigenous sediment once it reaches the ocean. We synthesize geologic and climate model data sets to evaluate whether climate model (REGCM2) outputs of precipitation-evaporation (P-E) can be linked to observed changes in erosion and landscape evolution along the western North American margin (core site EW9504-17PC, offshore southern Oregon) over the last glacial-interglacial cycle. This site is ideally located to test this new approach as it captures the combined sediment fluxes from coastal N. California/S. Oregon and the interior Cascade Volcanic Ranges, which have drastically different 40Ar-39Ar bedrock ages (130-147 Ma versus 10-30 Ma, respectively) and different climate responses occurring on glacial-interglacial timescales. We perturb a watershed-scale model of bedrock 40Ar-39Ar ages by the P-E changes to reproduce the total range of variability observed in downcore, bulk sediment 40Ar-39Ar ages and Nd isotopic values at the core site. We find that climate model percent changes in P-E values cannot reproduce the total range of variability seen in the provenance record before 22 ka without invoking drastic reductions in Klamath Mountain and Eel River sediment sources. A relatively unconstrained variable in the source area at this time is the presence of a large pluvial lake, Lake Modoc. It is possible that discharges from it could carry large volumes of young, Cascade Mountain-derived sediments offshore. Alternatively, an offshore switch in ocean current direction or reduction (relative to present-day) could explain the downcore sedimentological changes, as material discharged from the Eel River (the largest sediment source south of the core site) would not be carried north. To reproduce the observed downcore shift in

  6. Influence of Glacial Oscillations on Deformation in the Himalayas of Central Nepal

    NASA Astrophysics Data System (ADS)

    Godard, V.; Burbank, D. W.

    2009-12-01

    Recent studies indicate that variations in surface loads associated with the evolution of ice caps or lakes can modulate the stress pattern inside the crust [e.g. Hampel et al., 2007; Luttrell et al., 2007; Turpeinen et al., 2008]. In particular these studies point out that such variations may be large enough to change the stress acting on faults and modify the timing of the seismic cycle and long-term slip rates. Glacial loads can impact the stress regime of mountain ranges in different ways, by simultaneously (1) loading with ice masses and (2) unloading it by bedrock erosion promoted by glacial processes. Furthermore, as a response to climate changes, major glacier retreats and advances occur with durations of a few kyrs, inducing fast rates of variation for the crustal stress field. An ongoing debate in Himalayan geodynamics concerns the deformation distribution inside the range and how the ~20 mm/yr of convergence that is accommodated by the orogen is partitioned between the different structures. In central Nepal, previous studies show that, over the Holocene, the MFT has accommodated ~20 mm/yr, i.e., the entire far-field convergence [Lavé and Avouac, 2001].These data support deformation models where the whole Himalayan range is overthrust along the MHT/MFT system. On the other hand, recent studies point to a Quaternary reactivation of the MCT, suggesting that the mode of deformation can substantially change at a time scale of 10-100 kyrs [e.g. Hodges et al., 2004]. The mechanisms that may lead to a shift from one behavior to another, however, are still poorly understood. We hypothesize that variations in crustal loads associated with changes in the glacial cover may induce variations in the stress pattern that are high enough to significantly modify the deformation regime of the Himalayas and the slip rate on the MCT. We first assess the range of variations in surface loads, associated with both ice loading and bedrock erosion. Then we develop

  7. Endogenic carbonate sedimentation in Bear Lake, Utah and Idaho, over the last two glacial-interglacial cycles

    USGS Publications Warehouse

    Dean, W.E.

    2009-01-01

    that is at least 50 yr old, and probably older. Apparently, the microbialite mound also stopped forming aragonite cement sometime after Bear River diversion. Because of reworking of old aragonite, the bulk mineralogy of carbonate in bottom sediments has not changed very much since the diversion. However, the diversion is marked by very distinct changes in the chemical and isotopic composition of the bulk carbonate. After the last glacial interval (LGI), a large amount of endogenic carbonate began to precipitate in Bear Lake when the Pacific moisture that filled the large pluvial lakes of the Great Basin during the LGI diminished, and Bear River apparently abandoned Bear Lake. At first, the carbonate that formed was low-Mg calcite, but ???11,000 years ago, salinity and Mg2+:Ca2+ thresholds must have been crossed because the amount of aragonite gradually increased. Aragonite is the dominant carbonate mineral that has accumulated in the lake for the past 7000 years, with the addition of high-Mg calcite after the diversion of Bear River into the lake at the beginning of the twentieth century. Copyright ?? 2009 The Geological Society of America.

  8. AGN flickering on 10-100 kyr timescales

    NASA Astrophysics Data System (ADS)

    Sartori, Lia F.; Schawinski, Kevin; Kill, Bill; Maksym, Peter; Koss, Michael; Argo, Megan; Urry, Meg; Wong, Ivy; Lintott, Chris

    2016-08-01

    The study of AGN variability on timescales of 10^4-10^5 years is important in order to understand the BH - host galaxy interaction and coevolution. The discovery of "Hanny's Voorwerp" (HV), an extended emission line region associated with the nearby galaxy IC 2497, provided us with a laboratory to study AGN variability over such timescales. HV was illuminated by a strong quasar in IC 2497, but this quasar significantly shut down in the last 200 kyrs. Thanks to its recent shutdown we can now explore the host galaxy unimpeded by the presence of a quasar dominating the observations, while the Voorwerp preserves the echoes of its past activity. Recent studies on the optical properties of hard X-ray selected AGN suggest that AGN may flicker on and off hundreds or thousands times with each burst lasting ~10^5 yrs. Systems similar to IC 2497 and HV, the so-called Voorwerpjes, allow us to constrain the last stages of the AGN lifecycle. On the other hand, we recently suggested that the switch on phase may be observed in the so-called optically elusive AGN. In this talk I will review both observational evidence and results from simulation work which support this picture, and explain how optically elusive AGN and Voorwerpjes galaxies can help us to understand different phases of the AGN lifecycle. Moreover, I will discuss possible implications for AGN feedback, BH - host galaxy coevolution, and the analogy between AGN and X-ray binaries accretion physics.

  9. Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

    NASA Astrophysics Data System (ADS)

    Kochhann, Karlos G. D.; Holbourn, Ann; Kuhnt, Wolfgang; Channell, James E. T.; Lyle, Mitch; Shackford, Julia K.; Wilkens, Roy H.; Andersen, Nils

    2016-09-01

    The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (δ18O) and carbon (δ13C) isotope records (5-12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic Ice Sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity, and X-ray fluorescence (XRF) scanner-derived carbonate records from IODP Sites U1335, U1336, U1337, and U1338 on a consistent, astronomically tuned timescale. Benthic isotope and XRF scanner-derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on δ13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with >75% carbonate loss occurring at paleodepths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (δ18O minima) and δ13C decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to δ13C maxima and δ18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

  10. Effects of midlatitude westerlies on the paleoproductivity at the Agulhas Bank slope during the penultimate glacial cycle: Evidence from coccolith Sr/Ca ratios

    NASA Astrophysics Data System (ADS)

    Mejia, Luz Maria; Ziveri, Patrizia; Cagnetti, Marilisa; Bolton, Clara; Zahn, Rainer; Marino, Gianluca; Martinez Mendez, Gema; Stoll, Heather

    2015-04-01

    Because modern primary productivity on the Agulhas Bank, off South Africa, is linked to the mid-latitude westerlies, a paleoproductivity record from this area could be used to investigate past may changes in the westerlies dynamics. Coccolith Sr/Ca is a suitable productivity indicator to explore paleoproductivity from the penultimate glacial-interglacial cycle because it is independent of preservation changes that may accompany changes in deepwater circulation. In the Agulhas Bank slope core MD96-2080, the coccolith Sr/Ca record shows that phases of depressed productivity coincided with periods of stratification in the same core, indicated by high relative abundances of the coccolithophore Florisphaera profunda, and with low relative abundances of the upwelling indicator G. bulloides in the Cape Basin. This coherence suggests that upwelling regulated productivity throughout this region. As in the present, we infer that periods of low productivity result from northward positions of the westerlies which block the upwelling-promoting easterlies. Productivity minima also coincide with periods of increased ice-rafted detritus (IRD) deposition on the Agulhas Plateau, which also indicates extreme northward positions of the westerlies. The influence of the westerlies appears to be obliquity-conditioned, as productivity minima occur during low obliquity intervals. The dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the South Indian Gyre that likewise respond sensitively to a poleward contraction of the westerlies.

  11. Radiolarian artificial neural network based paleo sea surface water temperature and salinity changes during the last glacial cycle in the Timor Sea, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Gupta, S. M.; Malmgren, B. A.

    2015-12-01

    The western Pacific water enters into the Timor Sea (tropical Indian Ocean) by the thermohaline conveyor belt, and this region is under the influence of the SW monsoon. The higher precipitation during the monsoon rains lower the surface salinity in the north-eastern Indian Ocean towards the Bay of Bengal; whereas, the Arabian Sea remains highly saline due to higher evaporation in the region surrounding Arabian deserts. The salinity contrast in the northern Indian Ocean is very unique, and the radiolarian micro-zooplanktons living in the surface water serve a very good proxy for the monsoonal changes in the surface sea-water temperature (SST) and salinity in the geological past. We studied radiolarian faunal variation in the core MD01-2378, located at ~13oS and ~121oE (1783 m water depth), at the inlet of the thermohaline circulation into the Timor Sea. We applied the modern radiolarian based artificial neural networks (ANNs) (Gupta and Malmgren, 2009) to derive the SST and salinity during August-October for the last 140 ka (the full last glacial cycle). Based on the mean estimates of the 10 ANNs, the root mean square error in prediction (RMSEP) for SST is ~1.4oC with correlation between observed and estimated values r=0.98 (Gupta and Malmgren, 2009). Similarly, the RMSEP is 0.3 psu (r=0.94) for the salinity estimates. We derived paleo-SSTs and salinity values using modern radiolarian ANNs and the fossil radiolarian data generated from the core for the last 140-ka (Fig.1). The age model of the core is based on δ18O benthic oxygen isotope stratigraphy and 21 AMS 14C ages up to ~30-ka (Holbourn et al., 2005). Paleo SST-summer varied between 22-28.5oC, and it is in very good agreement with the δ18O benthic record of Holbourn et al. (2005) defining the Last Glacial Maximum (~24 ka) and the Eemian (~125 ka) stages. The salinity fluctuated between 34-35 psu, and compared well with oxygen isotope record representing the LGM and Eemian periods. We gratefully acknowledge

  12. Spatial and temporal variations of glacial erosion in the European Alps: numerical models and implications for slope stability (Invited)

    NASA Astrophysics Data System (ADS)

    Sternai, P.; Herman, F.; Willett, S.; Champagnac, J.; Fox, M.; Valla, P.; Salcher, B.

    2013-12-01

    Glacial erosion in alpine landscapes can be highly variable in space and time and lead to significant morphologic modification and mass redistribution at virtually all scales. Because they affect the near-surface stress and strain distribution by producing cyclic variations of the surface load, removing and abrading rocks, storing/releasing sediments and affecting the surface and subsurface hydrology, glaciations have multiple effects on slope stability. Understanding how glacial erosion evolves in space and time is thus important for investigating potential feedbacks between glacial erosion and deep-seated gravitational slope deformation (DSGSD). The present-day topography of the European Alps shows evidence of intense glacial erosion. However, significant questions regarding Alpine landscape evolution during glaciations still persist. For example, large-scale topographic analyses suggest that glacial erosion is maximized at and above the glaciers' long-term Equilibrium Line Altitude. In contrast, measurements of long-term denudation rates from low-temperature thermochronology and reconstructions of the pre-glacial Alpine topography suggest high erosion towards low altitudes and formation of overdeepnenings, in turn indicating an increase of local relief in response to glacial processes. Based on sediment record, low-temperature thermochronology and burial cosmogenic nuclide dating, it has also been proposed that the mid-Pleistocene climatic transition from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations sets the onset of intense glacial erosion within the Alps. However, this climate threshold in glacial erosion has not been showed in other orogens, and positive feedbacks between climate periodicity and glacial erosion efficiency still remain to be proven. Numerical modeling provides estimates of the patterns and magnitudes of glacial erosion through time. Modeling results on an advanced reconstruction of the pre-glacial topography and the

  13. Post-glacial inflation-deflation cycles, tilting, and faulting in the Yellowstone Caldera based on Yellowstone Lake shorelines

    USGS Publications Warehouse

    Pierce, Kenneth L.; Cannon, Kenneth P.; Meyer, Grant A.; Trebesch, Matthew J.; Watts, Raymond D.

    2002-01-01

    by a ~5 m rise in lake level to S2. The lowest generally recognizable shoreline is S2. It is ~5 m above datum (3 m above S1) and is ~8 ka, as dated on both sides of the outlet. Yellowstone Lake and the river near Fishing Bridge were 5-6 m below their present level about 3-4 ka, as indicated by 14C ages from submerged beach deposits, drowned valleys, and submerged Yellowstone River gravels. Thus, the lake in the outlet region has been below or near its present level for about half the time since a 1 km-thick icecap melted from the Yellowstone Lake basin about 16 ka. The amplitude of two rises in lake and river level can be estimated based on the altitude of Le Hardys Rapids, indicators of former lake and river levels, and reconstruction of the river gradient from the outlet to Le Hardys Rapids. Both between ~9.5 ka and ~8.5 ka, and after ~3 ka, Le Hardys Rapids (LHR) was uplifted about 8 meters above the outlet, suggesting a cyclic deformation process. Older possible rises in lake level are suggested by locations where the ~10.7 ka S4 truncates older shorelines, and valleys truncated by the ~12.6 ka S5 shoreline. Using these controls, a plot of lake level through time shows 5-7 millennial-scale oscillations since 14.5 ka. Major cycles of inflation and deflation are thousands of years long. Le Hardys Rapids has twice been uplifted ~8 m relative to the lake outlet. These two locations span only the central 25% of the historic caldera doming, so that if we use historic doming as a model, total projected uplift would be ~32 m. This ?heavy breathing? of the central part of the Yellowstone caldera may reflect a combination of several possible processes: magmatic inflation, tectonic stretching and deflation, and hydrothermal fluid sealing and inflation followed by cracking of the seal, pressure release, and deflation. Over the entire postglacial period, subsidence has balanced or slightly exceeded uplift as shown by older shorelines that descend towards the caldera axis. We

  14. Responses of ocean circulation and carbon cycle to changes in the position of the Southern Hemisphere westerlies at Last Glacial Maximum

    PubMed Central

    Völker, Christoph; Köhler, Peter

    2013-01-01

    We explore the impact of a latitudinal shift in the westerly wind belt over the Southern Ocean on the Atlantic meridional overturning circulation (AMOC) and on the carbon cycle for Last Glacial Maximum background conditions using a state-of-the-art ocean general circulation model. We find that a southward (northward) shift in the westerly winds leads to an intensification (weakening) of no more than 10% of the AMOC. This response of the ocean physics to shifting winds agrees with other studies starting from preindustrial background climate, but the responsible processes are different. In our setup changes in AMOC seemed to be more pulled by upwelling in the south than pushed by downwelling in the north, opposite to what previous studies with different background climate are suggesting. The net effects of the changes in ocean circulation lead to a rise in atmospheric pCO2 of less than 10 μatm for both northward and southward shift in the winds. For northward shifted winds the zone of upwelling of carbon- and nutrient-rich waters in the Southern Ocean is expanded, leading to more CO2outgassing to the atmosphere but also to an enhanced biological pump in the subpolar region. For southward shifted winds the upwelling region contracts around Antarctica, leading to less nutrient export northward and thus a weakening of the biological pump. These model results do not support the idea that shifts in the westerly wind belt play a dominant role in coupling atmospheric CO2 rise and Antarctic temperature during deglaciation suggested by the ice core data. PMID:26074663

  15. Effects of midlatitude westerlies on the paleoproductivity at the Agulhas Bank slope during the penultimate glacial cycle: Evidence from coccolith Sr/Ca ratios

    NASA Astrophysics Data System (ADS)

    Mejía, Luz María.; Ziveri, Patrizia; Cagnetti, Marilisa; Bolton, Clara; Zahn, Rainer; Marino, Gianluca; Martínez-Méndez, Gema; Stoll, Heather

    2014-07-01

    Modern primary productivity on the Agulhas Bank, off South Africa, has been proposed to be linked to the midlatitude westerlies. A paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics. Accordingly, we produced a coccolith Sr/Ca-based paleoproductivity record from core MD96-2080 (Agulhas Bank slope) during the penultimate glacial-interglacial cycle. Deriving the productivity signal from Sr/Ca requires a correction for a temperature effect, here constrained using Mg/Ca sea surface temperatures from the foraminifer Globigerina bulloides from core MD96-2080. Phases of depressed productivity coincided with periods of stratification in the same core, indicated by high relative abundances of the coccolithophore Florisphaera profunda and with low relative abundances of the upwelling indicator G. bulloides in the nearby Cape Basin. These observations collectively suggest that productivity was regulated by upwelling throughout this region. We infer that, as in the present, periods of low productivity result from a more northerly position of the westerlies, potentially accompanied by subtropical front displacements, and blockage of upwelling promoting easterlies. Productivity minima also coincide with periods of increased ice-rafted detritus (IRD) deposition on the Agulhas Plateau, which also indicates extreme northward positions of the westerlies. The influence of the westerlies appears to be obliquity conditioned, as productivity minima (and IRD maxima) occur during low-obliquity intervals. The dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the South Indian Gyre that likewise respond sensitively to a poleward contraction of the westerlies.

  16. Glacial and marine chronology of Mars

    NASA Technical Reports Server (NTRS)

    Strom, Robert G.; Kargel, Jeffrey S.; Johnson, Natasha; Knight, Christine

    1992-01-01

    A summary is given of the glacial and marine chronology of Mars. Hydrological models of oceans and ice sheets, the cratering record, hydrological cycling, and episodic glaciation are discussed. Evidence for a Noachian ocean is evaluated.

  17. Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Schüler, Lisa; Hemp, Andreas; Zech, Wolfgang; Behling, Hermann

    2012-04-01

    The pollen, charcoal and sedimentological record from the Maundi crater, located at 2780 m elevation on the south-eastern slope of Mt Kilimanjaro, is one of the longest terrestrial records in equatorial East Africa, giving an interesting insight into the vegetation and climate dynamics back to the early last Glacial period. Our sediment record has a reliable chronology until 42 ka BP. An extrapolation of the age-depth model, as well as matching with other palaeo-records from tropical East Africa, suggest a total age of about 90 ka BP at the bottom of the record. During the last Glacial the distribution as well as the composition of the vegetation belts classified as colline savanna, submontane woodland, montane forest, ericaceous belt, and alpine vegetation changed. The early last Glacial is characterized by high amounts of Poaceae and Asteraceae pollen suggesting a climatically dry but stable phase. Based on the absence of pollen grains in samples deposited around 70 ka BP, we assume the occurrence of distinct drought periods. During the pre-LGM (Last Glacial Maximum) a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation, thus indicating a more humid period. The taxa diversity increases steadily during the recorded time span. The decent of vegetation zones indicate dry and cold conditions during the LGM and seem to have been detrimental for many taxa, especially those of the forest vegetation; however, the early last Glacial seems to have been markedly drier than the LGM. The reappearance of most of the taxa (most importantly Alchemilla, Araliaceae, Dodonea, Hagenia, Ilex, Myrsine, Moraceae, Piperaceae) during the deglacial and Holocene period suggest a shift into humid conditions. An increase in ferns and the decrease in grasses during the Holocene also indicate increasing humidity. Fire played an important role in controlling the development and elevation of the ericaceous zone and the tree

  18. Glacial-Interglacial changes in silicon cycling in the subarctic North Pacific: Insights from diatom δ30Si over Termination 1

    NASA Astrophysics Data System (ADS)

    Shevenell, A.; Emerson, S. R.; Brzezinski, M. A.; Swann, G.; Jaccard, S.

    2009-12-01

    Subarctic North Pacific Ocean paleoceanographic records reveal a breakdown of glacial surface and deepwater stratification and an increase in biogenic opal flux during each of the large deglaciations since the onset of Northern Hemisphere glaciation (2.7 Ma). The North Pacific oceanographic and biogenic changes are similar to those observed in the Southern Ocean, suggesting a potential role for the North Pacific in regulating glacial-interglacial atmospheric CO2 variations. To better understand the role of North Pacific ventilation and biological productivity in glacial-interglacial climate variability, we generated a detailed silicon isotope (δ30Si; a proxy for the extent of dissolved silicon depletion in surface waters) record from biogenic opal across Termination 1 (20-9 ka) at ODP Site 882 in the western North Pacific (50°21’N, 167°35’E; water depth: 3244 m). At present, Site 882 is situated in an iron limited High Nutrient Low Chlorophyl region of the North Pacific. The δ30Si data range between 0.04-1.54‰ with the lowest isotopic values occurring between 25 and 15 ka, when opal accumulation rates are relatively low. A 1‰ increase in δ30Si occurs between 15.3 and 14.3 ka, coincident with an increase in opal accumulation rates and the arrival of more oxygenated deep waters to Site 882. However, the increase in δ30Si begins 1500 years before the abrupt increase in opal accumulation associated with the onset of the Bolling/Allerod (B/A). Elevated δ30Si values characterize the deglacial interval between 14.4 and 10.3 ka, but decline progressively after reaching a peak value (1.54‰) at 13 ka. Holocene δ30Si values are ~1‰. Our results may reflect an increase in the percent drawdown of available silicic acid during the last glacial maximum resulting from stratification of regional surface waters and/or the addition of iron-rich dust. Low glacial δ30Si values at Site 882 and the abrupt increase at the B/A may relate to a change in regional source

  19. Extinction and recolonization of maritime Antarctica in the limpet Nacella concinna (Strebel, 1908) during the last glacial cycle: toward a model of Quaternary biogeography in shallow Antarctic invertebrates.

    PubMed

    González-Wevar, C A; Saucède, T; Morley, S A; Chown, S L; Poulin, E

    2013-10-01

    Quaternary glaciations in Antarctica drastically modified geographical ranges and population sizes of marine benthic invertebrates and thus affected the amount and distribution of intraspecific genetic variation. Here, we present new genetic information in the Antarctic limpet Nacella concinna, a dominant Antarctic benthic species along shallow ice-free rocky ecosystems. We examined the patterns of genetic diversity and structure in this broadcast spawner along maritime Antarctica and from the peri-Antarctic island of South Georgia. Genetic analyses showed that N. concinna represents a single panmictic unit in maritime Antarctic. Low levels of genetic diversity characterized this population; its median-joining haplotype network revealed a typical star-like topology with a short genealogy and a dominant haplotype broadly distributed. As previously reported with nuclear markers, we detected significant genetic differentiation between South Georgia Island and maritime Antarctica populations. Higher levels of genetic diversity, a more expanded genealogy and the presence of more private haplotypes support the hypothesis of glacial persistence in this peri-Antarctic island. Bayesian Skyline plot and mismatch distribution analyses recognized an older demographic history in South Georgia. Approximate Bayesian computations did not support the persistence of N. concinna along maritime Antarctica during the last glacial period, but indicated the resilience of the species in peri-Antarctic refugia (South Georgia Island). We proposed a model of Quaternary Biogeography for Antarctic marine benthic invertebrates with shallow and narrow bathymetric ranges including (i) extinction of maritime Antarctic populations during glacial periods; (ii) persistence of populations in peri-Antarctic refugia; and (iii) recolonization of maritime Antarctica following the deglaciation process.

  20. Paleoglaciological reconstructions for the Tibetan Plateau during the last glacial cycle: evaluating numerical ice sheet simulations driven by GCM-ensembles

    NASA Astrophysics Data System (ADS)

    Kirchner, Nina; Greve, Ralf; Stroeven, Arjen P.; Heyman, Jakob

    2011-01-01

    The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 ka), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 ka in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice-free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and

  1. 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

  2. Orbital forcing of glacial/interglacial variations in chemical weathering and silicon cycling within the upper White Nile basin, East Africa: Stable-isotope and biomarker evidence from Lakes Victoria and Edward

    NASA Astrophysics Data System (ADS)

    Cockerton, Helen E.; Street-Perrott, F. Alayne; Barker, Philip A.; Leng, Melanie J.; Sloane, Hilary J.; Ficken, Katherine J.

    2015-12-01

    On Quaternary time scales, the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae (notably diatoms, for which Si is an essential nutrient). Large tropical river systems dominate the export of Si from the continents to the oceans. Here, we investigate variations in Si cycling in the upper White Nile basin over the last 15 ka, using sediment cores from Lakes Victoria and Edward. Coupled measurements of stable O and Si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and Si cycling, while the abundances of lipid biomarkers characteristic of terrestrial/emergent higher plants, submerged/floating aquatic macrophytes and freshwater algae document past ecosystem changes. During the late-glacial to mid-Holocene, 15-5.5 ka BP, orbital forcing greatly enhanced monsoon rainfall, forest cover and chemical weathering. Riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower Si-isotope values. Since 5.5 ka BP, increasingly dry climates and more open vegetation, reinforced by the spread of agricultural cropland over the last 3-4 ka, have reduced dissolved silica inputs into the lakes. Centennial-to millennial-scale dry episodes are also evident in the isotopic records and merit further investigation.

  3. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

  4. Concurrent and opposed environmental trends during the last glacial cycle between the Carpathian Basin and the Black Sea coast: evidence from high resolution enviromagnetic loess records

    NASA Astrophysics Data System (ADS)

    Hambach, Ulrich; Zeeden, Christian; Veres, Daniel; Obreht, Igor; Bösken, Janina; Marković, Slobodan B.; Eckmeier, Eileen; Fischer, Peter; Lehmkuhl, Frank

    2015-04-01

    Danube Basin near to the Black Sea (Urluia quarry, Dobrogea, Romania). In order to investigate the potential of Danubian loess in recording millennial-scale palaeoclimate variability, a 22 m deep drill-core from the Titel loess plateau and a more than 15 metres thick LPSS from the Urluia quarry were contiguously sampled. Both sides provide improved insight into past climate evolution of the regions down to MIS 6. The presentation will focus on the down-core/down-section variability of χ and χfd as environmental proxy parameters. Based on these mineral magnetic proxies we can already draw the following conclusions: 1) The dust accumulation rates in both regions were relatively constant over the past c. 130 kyrs, even during full interglacial conditions. 2) In the studied sections, the pedo-complex S1 represents ± the Eemian and not the entire MIS 5, as previously assumed. 3) There are a lot of similarities between the mineral magnetic records of the Titel-Plateau (Vojvodina, South Carpathian Basin) and the Urluia quarry (Dobrogea, Lower Danube Basin) and also between these records and those from the Chinese Loess Plateau, but also fundamental differences. 4) During the early glacial (end of MIS5) we find no evidence for soil formation in the South Carpathian Basin whereas in the Dobrogea near to the Black Sea coast embryonic soils developed. On the contrary, during the younger part of MIS 3 (≤ 40 ka) near to the Black Sea coast soil humidity sharply decreased towards the LGM whereas in the South Carpathian Basin the mineral magnetic proxies indicate a relative maximum in pedogenesis/soil humidity. Sedimentological, geochemical, geochronological and palaeomagnetic investigations are in progress. They will provide further high quality data sets leading to an improved understanding of the Late Pleistocene environmental evolution in the Danube Basin.

  5. 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 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

  6. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

    Understanding the mechanisms of past climate changes requires modelling of the complex interaction between all major components of the Earth system: atmosphere, ocean, cryosphere, lithosphere and biosphere. This paper reviews attempts at such an integrative approach to modelling climate changes during the glacial age. In particular, the roles of different factors in shaping glacial climate are compared based on the results of simulations with an Earth-system model of intermediate complexity, CLIMBER-2. It is shown that ice sheets, changes in atmospheric compositions, vegetation cover, and reorganization of the ocean thermohaline circulation play important roles in glacial climate changes. Another example of this approach is the modelling of two major types of abrupt glacial climate changes: Dansgaard-Oeschger and Heinrich events. Our results corroborate some of the early proposed mechanisms, which relate abrupt climate changes to the internal instability of the ocean thermohaline circulation and ice sheets. At the same time, it is shown that realistic representation of the temporal evolution of the palaeoclimatic background is crucial to simulate observed features of the glacial abrupt climate changes.

  7. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

    Understanding the mechanisms of past climate changes requires modelling of the complex interaction between all major components of the Earth system: atmosphere, ocean, cryosphere, lithosphere and biosphere. This paper reviews attempts at such an integrative approach to modelling climate changes during the glacial age. In particular, the roles of different factors in shaping glacial climate are compared based on the results of simulations with an Earth-system model of intermediate complexity, CLIMBER-2. It is shown that ice sheets, changes in atmospheric compositions, vegetation cover, and reorganization of the ocean thermohaline circulation play important roles in glacial climate changes. Another example of this approach is the modelling of two major types of abrupt glacial climate changes: Dansgaard-Oeschger and Heinrich events. Our results corroborate some of the early proposed mechanisms, which relate abrupt climate changes to the internal instability of the ocean thermohaline circulation and ice sheets. At the same time, it is shown that realistic representation of the temporal evolution of the palaeoclimatic background is crucial to simulate observed features of the glacial abrupt climate changes. PMID:14558899

  8. Nature and Origin of Variations in Late-Glacial and Holocene Atmospheric CARBON-14 as Revealed by Global Carbon Cycle Modeling

    NASA Astrophysics Data System (ADS)

    Braziunas, Thomas Frank

    1990-01-01

    }, F + Q, K _{rm z} + Q) incorporates "feedback" effects which depend on the instantaneous marine ^{14}C profile and atmosphere/surface ocean ^{14}C disparity. Spectral analyses of the 9600-yr tree-ring Q history generally produce power at or near harmonics of a 420-yr cycle. Century-scale Q periodicities may reflect harmonic or nonsinusoidal solar processes. Residual ^ {14}C production and bi-decadal sunspot numbers from AD 1700 to 1840 define a preliminary history of relative sunspot numbers back to 7730 BC. "Fine-tuned" Q periodicities are used to forecast future solar behavior.

  9. 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

  10. Contrasting scaling properties of interglacial and glacial climates.

    PubMed

    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

  11. Glacial Geology of Wisconsin.

    ERIC Educational Resources Information Center

    Madison Public Schools, WI.

    This publication is a teacher's resource and guidebook for the presentation of the three filmstrips in the "Glacial Geology of Wisconsin" series. The first filmstrip is subtitled, "Evidence of the Glaciers," the second "How the Glaciers Reshaped the Landscape," and the third "Fossils of the Ice Age." Included are a list of objectives, an outline…

  12. Glacial atmospheric phosphorus deposition

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Dallmayr, Remi; Gabrieli, Jacopo; Goto-Azuma, Kumiko; Hirabayashi, Motohiro; Svensson, Anders; Vallelonga, Paul

    2016-04-01

    Phosphorus in the atmosphere is poorly studied and thus not much is known about atmospheric phosphorus and phosphate transport and deposition changes over time, though it is well known that phosphorus can be a source of long-range nutrient transport, e.g. Saharan dust transported to the tropical forests of Brazil. In glacial times it has been speculated that transport of phosphorus from exposed shelves would increase the ocean productivity by wash out. However whether the exposed shelf would also increase the atmospheric load to more remote places has not been investigated. Polar ice cores offer a unique opportunity to study the atmospheric transport of aerosols on various timescales, from glacial-interglacial periods to recent anthropogenic influences. We have for the first time determined the atmospheric transport of phosphorus to the Arctic by means of ice core analysis. Both total and dissolved reactive phosphorus were measured to investigate current and past atmospheric transport of phosphorus to the Arctic. Results show that glacial cold stadials had increased atmospheric total phosphorus mass loads of 70 times higher than in the past century, while DRP was only increased by a factor of 14. In the recent period we find evidence of a phosphorus increase over the past 50 yrs in ice cores close to human occupation likely correlated to forest fires. References: Kjær, Helle Astrid, et al. "Continuous flow analysis method for determination of dissolved reactive phosphorus in ice cores." Environmental science & technology 47.21 (2013): 12325-12332. Kjær, Helle Astrid, et al. "Greenland ice cores constrain glacial atmospheric fluxes of phosphorus." Journal of Geophysical Research: Atmospheres120.20 (2015).

  13. Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India

    USGS Publications Warehouse

    Owen, L.A.; Caffee, M.W.; Bovard, K.R.; Finkel, R.C.; Sharma, M.C.

    2006-01-01

    Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya. The glacial stages that have been identified are: the Indus Valley glacial stage, dated at older than 430 ka; the Leh glacial stage occurring in the penultimate glacial cycle or older; the Karglacial stage, occurring during the early part of the last glacial cycle; the Bazgo glacial stage, at its maximum during the middle of the last glacial cycle; and the early Holocene Khalling glacial stage. The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation. A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively. Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene. ?? 2006 Geological Society of America.

  14. Rapid Environmental Fluctuations Recorded over the Last Glacial/Interglacial Cycle in the Sediments from Borehole PRGL1-4 (Gulf of Lions; Western Mediterranean) using Radiogenic Isotopes (Sr & Nd)

    NASA Astrophysics Data System (ADS)

    Nizou, J.

    2015-12-01

    The study of sediments deposited and preserved in oceanic basins unable us to examine how terrigenous sediment supply varied through time in relation to paleoenvironmental and climatic changes on land. The geochemical and isotopic compositions of marine sediment are used to unravel its provenance, and provide information about its formation. Providing that the paleoclimatic frame is known, such data give an insight into the rock-source location and allow us to decipher between genetic processes of mechanical erosion and chemical alteration. Borehole PRGL1-4 (European project PROMESS), located in the Gulf of Lions (W Mediterranean) at 300 mwd, was investigated geochemically at high-temporal resolution over the last glacial/interglacial cycle (i.e. 130 ka) to study sediment-source variations during rapid climate changes. Besides, sediments originating from the Rhône's and the Pyreneo-Languedocian's catchment areas have been analyzed to measure the isotopic composition of five source end-members that are the Alps, the Higher Rhône valley, the Lower Rhône valley, the Languedoc and the Pyrenees. Epsilon Nd and 87Sr/86Sr were measured on 60 samples encompassing 4 marine isotopic stages with an emphasis on Heinrich events. The epsilon Nd values of PRGL1-4 lean towards the Lower Rhône valley unradiogenic end-member during cold stadial intervals, and towards the Alpine radiogenic end-member during warm interstadials. The presence of an ice cap over the crystalline Alpine watershed during cold phases could prevent the sediments originating from this region from reaching the Gulf of Lions. The same pattern is observed during the time of Heinrich events. An influence of the sea level variations on the sedimentation at the borehole site during the Heinrich events is unlikely since they are only 10 to 15 m in amplitude. Furthermore, a major isotopic shift in epsilon Nd mean values is displayed around 40 ka that coincides with the connection of the Durance to the Rhône River

  15. Glacial influence on caldera-forming eruptions

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Bindeman, Ilya

    2011-04-01

    It has been suggested that deglaciations have influenced volcanism in several areas around the world increasing productivity of mantle melting and eruptions from crustal magma chambers. However, the connection between glaciations and increased volcanism is not straightforward. Investigation of Ar-Ar, U-Pb, and 14C ages of caldera-forming eruptions for the past million years in the glaciated arc of Kamchatka has lead to the observation that the majority of large-volume ignimbrites, which are associated with the morphologically preserved calderas, correspond in time with "maximum glacial" conditions for the past several glacial cycles. In the field, the main proof is related to the fact that glaciated multi-caldera volcanoes hosted thick glacial ice caps. Additional evidence comes from clustering Kamchatka-derived marine ash layers with glacial moraines in DSDP cores. Here we present a set of new results from numerical modelling using the Finite Element Method that investigate how the glacial load dynamic may affect the conditions for ring-fault formation in such glaciated multi-caldera volcanoes. Different scenarios were simulated by varying: (1) the thickness and asymmetric distribution of the existing ice cap, (2) the depth and size of the magmatic reservoir responsible for the subsequent collapse event, (3) the thickness and mechanical properties of the roof rock due to the alteration by hydrothermal fluids, (4) the existence of a deeper and wider magmatic reservoir and (5) possible gravitational failure triggered, in part, by subglacial rock mass build up and hydrothermal alteration. The results obtained indicate that: (1) Any ice cap plays against ring fault formation; (2) Asymmetric distribution of ice may favour the initiation of trap-door type collapse calderas; (3) Glacial erosion of part of volcanic edifice or interglacial edifice failure may facilitate subsequent ring fault formation; (4) hydrothermal system under an ice cap may lead to a quite effective

  16. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle. PMID:15860623

  17. Glacial climate states and abrupt climate change in MIROC AOGCM

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, Ayako; Ohgaito, Rumi; Takahashi, Kunio; Yoshimori, Masa; Kawamura, Kenji; Oka, Akira; Chan, Wing-Le; Sherriff-Tadano, Sam

    2016-04-01

    Millennial climate change such as D-O cycles and AIM recorded in ice cores in both Hemispheres is known to show a relatively higher amplitude in the middle-level of a glacial cycle than in the interglacial state or severe glacial state. Here we ran several sensitivity experiments using a coupled atmosphere and ocean GCM (MIROC4m, renamed from MIROC3.2.2) and show that the response to fresh water release to the ocean and bipolar response is highly dependent on the background climate. The experiments were conducted with 500 years water hosing of 0.05 to 0.1 Sv (where 1 Sv is equivalent to the water flux of 10m sea level rise in 100 years) in the North Atlantic 50-70N under different basic states; modern climate state with the pre-industrial condition, middle glacial climate state and full glacial condition, mainly differing in the ice sheet configuration and atmospheric amount of Greenhouse Gases. The results under middle glacial condition show largest cooling/warming response in North Atlantic and a reasonable bipolar warming/cooling signal revealed in the ice core data of the both hemisphere. We discuss the responses under different background climates which involve the strong coupling between atmosphere, ocean and sea ice and their dependence on the configuration of ice sheet.

  18. Kennebunk glacial advance: A reappraisal

    NASA Astrophysics Data System (ADS)

    Smith, Geoffrey W.

    1981-06-01

    Evidence for the Kennebunk glacial advance (readvance) in southwestern Maine is discussed in light of recent geologic mapping. Orientations of glacially produced lineations record the response of ice to major topographic controls and do not indicate glacial readvance. Minor end moraines and large stratified end moraines associated with deformed marine sediments of the Presumpscot Formation occur throughout the southwestern coastal zone. These features outline the general pattern of ice retreat from this part of the coastal zone and suggest that withdrawal of the last ice from southwestern Maine occurred with minor stillstands and local frontal fluctuations but without significant readvance. The Kennebunk glacial advance (readvance) appears to have been one of many local fluctuations of the ice front during general recession, occurring at about 13,200 yr B.P.

  19. The last glacial maximum

    USGS Publications Warehouse

    Clark, P.U.; Dyke, A.S.; Shakun, J.D.; Carlson, A.E.; Clark, J.; Wohlfarth, B.; Mitrovica, J.X.; Hostetler, S.W.; McCabe, A.M.

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ???14.5 ka.

  20. The Last Glacial Maximum.

    PubMed

    Clark, Peter U; Dyke, Arthur S; Shakun, Jeremy D; Carlson, Anders E; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X; Hostetler, Steven W; McCabe, A Marshall

    2009-08-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level approximately 14.5 ka.

  1. Modeling glacial climates

    NASA Technical Reports Server (NTRS)

    North, G. R.; Crowley, T. J.

    1984-01-01

    Mathematical climate modelling has matured as a discipline to the point that it is useful in paleoclimatology. As an example a new two dimensional energy balance model is described and applied to several problems of current interest. The model includes the seasonal cycle and the detailed land-sea geographical distribution. By examining the changes in the seasonal cycle when external perturbations are forced upon the climate system it is possible to construct hypotheses about the origin of midlatitude ice sheets and polar ice caps. In particular the model predicts a rather sudden potential for glaciation over large areas when the Earth's orbital elements are only slightly altered. Similarly, the drift of continents or the change of atmospheric carbon dioxide over geological time induces radical changes in continental ice cover. With the advance of computer technology and improved understanding of the individual components of the climate system, these ideas will be tested in far more realistic models in the near future.

  2. Glacial marine sedimentation: Paleoclimatic significance

    SciTech Connect

    Anderson, J.B.; Ashley, G.M.

    1991-01-01

    This publication resulted from a symposium held during the 1988 Annual Meeting of the Geological Society of America. Many, but not all, contributors to the symposium have papers in this volume. This Special Paper consists of 14 chapters and a Subject/Geographic index. Each chapter has is own list of references. The papers cover a wide range of modem climate/ ocean environments, including papers on glacial marine sediments from Antarctica, the fiords of Alaska, and sediments from the Canadian High Arctic. In addition, three papers discuss [open quote]old[close quotes] glacial marine records (i.e., pre-Tertiary), and one paper discusses the Yakataga Formation of the Gulf of Alaska which is a Miocene-to-late-Pleistocene sequence. The last chapter in the book includes a survey and summary of the evidence for the paleoclimatic significance of glacial marine sediments by the two editors, John Anderson and Gail Ashley. It is worth noting that Anderson and Domack state in the Foreword that there is a considerable variation in terminology; hence they employ a series of definitions which they urge the other authors to employ. They define and explain what they mean by [open quotes]polar ice cap,[close quotes] [open quote]polar tundra (subpolar),[close quotes] and [open quotes]temperate oceanic and boreal[close quotes] in terms of the dominant glacial and glacial marine processes. Although one might quarrel with the terminology, the broad differences between these three glaciological regimes are indeed fundamental and need to be sought in the geological record. The flavor of the volume can be judged by some of the chapter titles. Contributions on Antarctica include a paper by Anderson and other entitled [open quote]Sedimentary facies associated with Antarctica's floating ice masses[close quotes] and a companion paper by Anderson and Domack which deals with the extremely complex glacial marine facies (13 facies are delimited) in McMurdo Sound, Antarctica.

  3. Sub-glacial volcanic eruptions

    USGS Publications Warehouse

    White, Donald Edward

    1956-01-01

    The literature on sub-glacial volcanic eruptions and the related flood phenomena has been reviewed as a minor part of the larger problem of convective and conductive heat transfer from intrusive magma. (See Lovering, 1955, for a review of the extensive literature on this subject.) This summary of data on sub-glacial eruptions is part of a program that the U.S. Geological Survey is conducting in connection with its Investigations of Geologic Processes project on behalf of the Division of Research, U.S. Atomic Energy Commission.

  4. Earth's glacial record and its tectonic setting

    NASA Astrophysics Data System (ADS)

    Eyles, N.

    1993-09-01

    Glaciations have occurred episodically at different time intervals and for different durations in Earth's history. Ice covers have formed in a wide range of plate tectonic and structural settings but the bulk of Earth's glacial record can be shown to have been deposited and preserved in basins within extensional settings. In such basins, source area uplift and basin subsidence fulfill the tectonic preconditions for the initiation of glaciation and the accomodation and preservation of glaciclastic sediments. Tectonic setting, in particular subsidence rates, also dictates the type of glaciclastic facies and facies successions that are deposited. Many pre-Pleistocene glaciated basins commonly contain well-defined tectonostratigraphic successions recording the interplay of tectonics and sedimentation; traditional climatostratigraphic approaches involving interpretation in terms of either ice advance/retreat cycles or glacio-eustatic sea-level change require revision. The direct record of continental glaciation in Earth history, in the form of classically-recognised continental glacial landforms and "tillites", is meagre; it is probable that more than 95% of the volume of preserved "glacial" strata are glacially-influenced marine deposits that record delivery of large amounts of glaciclastic sediment to offshore basins. This flux has been partially or completely reworked by "normal" sedimentary processes such that the record of glaciation and climate change is recorded in marine successions and is difficult to decipher. The dominant "glacial" facies in the rock record are subaqueous debris flow diamictites and turbidites recording the selective preservation of poorly-sorted glaciclastic sediment deposited in deep water basins by sediment gravity flows. However, these facies are also typical of many non-glacial settings, especially volcanically-influenced environments; numerous Archean and Proterozoic diamictites, described in the older literature as tillites, have no

  5. Tectonic stress feedback loop explains U-shaped glacial valleys

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2014-03-01

    In the shadow of the Matterhorn, the broad form of the Matter Valley—like so many throughout the Alps—is interrupted by a deep U-shaped glacial trough. Carved into a landscape reflecting millennia of tectonic uplift and river erosion, growing evidence suggests the 100-meter-deep U-shaped groove was produced shortly after a shift toward major cycles of Alpine glaciation almost a million years ago. Subsequent glaciations may have therefore had little effect on the landscape.

  6. Weathering and the mobility of phosphorus in the catchments and forefields of the Rhône and Oberaar glaciers, central Switzerland: Implications for the global phosphorus cycle on glacial-interglacial timescales

    NASA Astrophysics Data System (ADS)

    Föllmi, Karl B.; Hosein, Rachel; Arn, Kaspar; Steinmann, Philipp

    2009-04-01

    indentations on grains acting as sites of preferential dissolution. We also measured iron-bound, organic and detrital P concentrations in the chronosequence and show that organic and iron-bound P has almost completely replaced detrital P in the top layers of the YD profiles. Detrital P weathering rates are calculated as 310 and 280 kg km -2 yr -1 for LIA moraines and 10 kg km -2 yr -1 for YD tills. During the first 300 years of glacial sediment exposure P dissolution rates are shown to be approximately 70 times higher than the mean global dissolved P flux from ice-free continents. After 11.6 kyr the flux is 2.5 times the global mean. These data strengthen the argument for substantial changes in the global dissolved P flux on glacial-interglacial timescales. A crude extrapolation from the data described here suggests that the global dissolved P flux may increase by 40-45% during the first few hundred years of a deglaciation phase.

  7. Obliquity Control On Southern Hemisphere Climate During The Last Glacial

    PubMed Central

    Fogwill, C.J.; Turney, C.S.M.; Hutchinson, D.K.; Taschetto, A.S.; England, M.H.

    2015-01-01

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent. PMID:26115344

  8. Obliquity Control on Southern Hemisphere Climate during the Last Glacial

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Hutchinson, D. K.; Turney, C. S.; Taschetto, A.; England, M. H.

    2015-12-01

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent.

  9. 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.

  10. Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Graham, Alastair G. C.; Griffiths, Huw J.; Roberts, Stephen J.; Cofaigh, Colm O.; Bentley, Michael J.; Evans, David J. A.

    2014-05-01

    We present multibeam swath bathymetric surveys of the major fjords surrounding the sub-Antarctic island of South Georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat. Bathymetry data revealed a range of glacial features including terminal, retreat and truncated moraines, deep (distal) outer and shallow (proximal) inner basins and cross shelf troughs. These provide evidence of glacial advance and retreat through several glacial cycles. A near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing. A relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or Last Glacial Maximum, while deep basin moraines may date from an earlier (pre-LGM) more extensive glaciation, which we speculate corresponds to MIS6. On the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods. The cross shelf troughs, and mid-trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here, thus possibly older than MIS6. This hypothesis would suggest that South Georgia followed a glacial history similar to that of central Patagonia (46deg S)where a series of Pleistocene glaciations (of MIS 20 and younger) extended beyond LGM limits, with the most extensive glacial advance occurring at c. 1.1 Ma.

  11. Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Graham, Alastair G. C.; Griffiths, Huw J.; Roberts, Stephen J.; Cofaigh, Colm Ó.; Bentley, Michael J.; Evans, David J. A.

    2014-04-01

    We present multibeam swath bathymetric surveys of the major fjords surrounding the sub-Antarctic island of South Georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat. Bathymetry data revealed a range of glacial features including terminal, retreat and truncated moraines, deep (distal) outer and shallow (proximal) inner basins and cross shelf troughs. These provide evidence of glacial advance and retreat through several glacial cycles. A near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing. A relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or Last Glacial Maximum, while deep basin moraines may date from an earlier (pre-LGM) more extensive glaciation, which we speculate corresponds to MIS6. On the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods. The cross shelf troughs, and mid-trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here, thus possibly older than MIS6. This hypothesis would suggest that South Georgia followed a glacial history similar to that of central Patagonia (46°S) where a series of Pleistocene glaciations (of MIS 20 and younger) extended beyond LGM limits, with the most extensive glacial advance occurring at c. 1.1 Ma.

  12. Architecture of Late Ordovician glacial valleys in the Tassili N'Ajjer area (Algeria)

    NASA Astrophysics Data System (ADS)

    Deschamps, Rémy; Eschard, Rémi; Roussé, Stéphane

    2013-05-01

    The architecture of three Late Ordovician glacial valleys was studied in detail in the Tassili N'Ajjer (SE Algeria) outcrops. The valleys are oriented south-north, 2 to 5 km wide, and up to 250 m deep. The valley-fills revealed a very complex sedimentary architecture with significant lateral facies changes. Several glacial cycles induced the formation of Glacial Erosion Surfaces (GES) at the base and within the glacial valleys. The first type of GES shows a sharp and steep-angled contact without striations or associated syn-sedimentary deformation, suggesting that subglacial meltwater was the dominant erosive agent. A second type associated with the deformation of pre-glacial and syn-glacial sediment, suggests that ice was in contact with the valley floor. Four facies associations are proposed: FA1: subglacial tillite; FA2: Sub-to pro-glacial ice contact fans; FA3: Proglacial sub-aqueous gravity flows; and FA4: outwash fans. The stratigraphic architecture of three of the main valleys reveals a complex polyphase infill. At least two main cycles of ice-sheet advance and retreat can be interpreted from the sedimentary succession of each valley. Minor glacial cycles by ice oscillations also occur locally. GES morphology and the facies sequence suggest that the Iherir valleys were initiated by meltwater erosion in subglacial channels, whereas the Dider and Ouarsissen valleys were part of a large ice stream pathway. Above the valley-fill and the interfluves, a sand-rich unit of stacked lobes and channels is interpreted as submarine outwash fans deposited during final ice retreat. A glacial sequence found between two GES comprises fluvio-glacial or ice-contact fan deposits, fluvio-glacial eskers and tills. These sediments were deposited subglacially or at the glacier front during the ice maximum phase and/or the early ice retreat phase. During the ice retreat, interbedded subaqueous gravity flow deposits and diamictites filled the glacially cut topography as the sea

  13. Glacial onset predated Late Ordovician climate cooling

    NASA Astrophysics Data System (ADS)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  14. Negligible glacial-interglacial variation in continental chemical weathering rates.

    PubMed

    Foster, Gavin L; Vance, Derek

    2006-12-14

    Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide. However, variations in chemical weathering rates over glacial-interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering, but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.

  15. Large inert carbon pool in the terrestrial biosphere during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ciais, P.; Tagliabue, A.; Cuntz, M.; Bopp, L.; Scholze, M.; Hoffmann, G.; Lourantou, A.; Harrison, S. P.; Prentice, I. C.; Kelley, D. I.; Koven, C.; Piao, S. L.

    2012-01-01

    During each of the late Pleistocene glacial-interglacial transitions, atmospheric carbon dioxide concentrations rose by almost 100ppm. The sources of this carbon are unclear, and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions. Here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon-cycle modelling to estimate terrestrial and oceanic gross primary productivity during the Last Glacial Maximum. We find that the rate of gross terrestrial primary production during the Last Glacial Maximum was about 40+/-10 Pg C yr-1, half that of the pre-industrial Holocene. Despite the low levels of photosynthesis, we estimate that the late glacial terrestrial biosphere contained only 330 Pg less carbon than pre-industrial levels. We infer that the area covered by carbon-rich but unproductive biomes such as tundra and cold steppes was significantly larger during the Last Glacial Maximum, consistent with palaeoecological data. Our data also indicate the presence of an inert carbon pool of 2,300 Pg C, about 700 Pg larger than the inert carbon locked in permafrost today. We suggest that the disappearance of this carbon pool at the end of the Last Glacial Maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations.

  16. Climatic implications of intermediate sized glacial advances in New Zeland valleys during OIS3.

    NASA Astrophysics Data System (ADS)

    Shulmeister, James; Thackray, Glenn; Rittenour, Tammy

    2014-05-01

    Recent work has greatly increased the number of known glacial oscillations during the last (Otiran) glaciation in South Island, New Zealand. Here we present summary stratigraphic and age results from a tectonic basin in the upper Rangitata Valley and a trough fill in the Rakaia Valley in Canterbury, New Zealand. The deposits constrain a series of intermediate scale glacial advances during OIS 3 that are not recorded in terminal moraine sequences in these valleys. These records demonstrate that ice limits oscillated substantially during the last glacial cycle but that very significant advances occurred at times other than the LGM, with glacial extents 80-95% of the local last glacial maximum. The timings of these advances appear to coincide with fragmentary evidence for glaciation in some other settings in New Zealand and SE Australia, indicating that the advances represent regionally significant climatic events. In the talk, I will summarise the evidence for the better constrained advances, consider the climate forcing required to maintain extended ice in these valleys through much of the last glacial cycle and consider the impact of antecedent ice limits on the climatic conditions at the LGM.

  17. Intermittent glacial sliding velocities explain variations in long-timescale denudation

    NASA Astrophysics Data System (ADS)

    Yanites, Brian J.; Ehlers, Todd A.

    2016-09-01

    Quantifying controls on glacial erosion over geologic timescales is central to understanding the role of Cenozoic climate change on the development of modern mountain belts, yet the mechanisms that produce the distinct relief and topography visible in glaciated regions remain poorly constrained. We test the hypothesis that commonly assumed glacial sliding parameterizations control denudation rates over geologic timescales. We do this by modeling glacier dynamics over a glacial-interglacial cycle and compare with a dense dataset of (U-Th)/He thermochronometer derived denudation rates from the southern Coast Mountains, BC. Results indicate zones of rapid Quaternary erosion correspond to locations where the model predicts the highest averaged sliding velocities. The results are consistent with the hypothesis that sliding influences the rate of glacial erosion. Regression between sliding predicted by the model and erosion rates shows a statistically significant correlation (r2 = 0.6). The coefficient of the regression (10-5) is smaller than previous estimates based on data from much shorter timescales. The model results also reveal that for a specific location, active subglacial sliding, and hence erosion, occurs for only ∼10-20% of a glacial-interglacial cycle, suggesting high temporal variations in erosion rates. This intermittency of erosion requires instantaneous erosion rates to be greater than long term averages, explaining how timescale averaging can impact estimates of glacial erosion rates.

  18. Evidence for Obliquity Forcing of Glacial Termination II

    NASA Astrophysics Data System (ADS)

    Drysdale, R. N.; Hellstrom, J. C.; Zanchetta, G.; Fallick, A. E.; Sánchez Goñi, M. F.; Couchoud, I.; McDonald, J.; Maas, R.; Lohmann, G.; Isola, I.

    2009-09-01

    Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 ± 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth’s obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

  19. Earth's eccentricity cycles and Indian Summer Monsoon variability over the past 2 million years: Evidence from deep-sea benthic foraminifer

    NASA Astrophysics Data System (ADS)

    Gupta, Anil K.; Dhingra, Hitesh; Mélice, Jean-Luc; Anderson, David M.

    Spectral analysis of a Uvigerina proboscidea time series from DSDP Site 214 using the Lomb-Scargle method for unevenly sampled data, exhibits two dominant power peaks at 412 and 94 kyrs over the last 2 million years, which correspond to the Earth's eccentricity cycles. The results indicate that the SW monsoon varied at about 100 kyr and 400 kyr periodicities within Earth's eccentricity domain (Milankovitch range) over the past 2 million years. Wavelet transform analysis reveals the non-stationary nature of monsoon upwelling over this interval. The amplitude of the 400 kyr cycle in the U. proboscidea time series began to increase at ∼900 kyrs as has also been observed in few recent studies. We do not see a strong relation between eccentricity highs and intense summer monsoons over the studied interval.

  20. Deglaciation and glacial erosion: A joint control on magma productivity by continental unloading

    NASA Astrophysics Data System (ADS)

    Sternai, Pietro; Caricchi, Luca; Castelltort, Sébastien; Champagnac, Jean-Daniel

    2016-02-01

    Glacial-interglacial cycles affect the processes through which water and rocks are redistributed across the Earth's surface, thereby linking the 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 regardless of continental unloading by glacial erosion, albeit the density of rock exceeds that of ice by approximately 3 times. 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. Our study represents an additional step toward a more general understanding of the links between a changing climate, glacial processes, and the melting of the solid Earth.

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

    USGS Publications Warehouse

    Young, D.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.

  2. Phosphorus burial in the ocean over glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Tamburini, F.; Föllmi, K. B.

    2009-04-01

    The role of nutrients, such as phosphorus (P), and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to most recent ones that changes in the glacial ocean inventory of phosphorus were important but not influential if compared to other macronutrients, such as nitrate. Using new data coming from a selection of ODP sites, we analyzed the distribution of oceanic P sedimentary phases and calculate reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period at these sites. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) of reactive P show higher variability. If we extrapolate for the analyzed sites, we may assume that in general glacial burial fluxes of reactive P are lower than those during interglacial periods by about 8%, because the lack of burial of reactive P on the glacial shelf reduced in size, was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we evaluate their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 17-40% compared to interglacial stages. Variations in the distribution of sedimentary P phases at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations, which seems to point to P-richer waters at glacial terminations. All these findings would support the Shelf-Nutrient Hypothesis, which assumes that during glacial low stands nutrients are transferred from shallow sites to deep sea with possible

  3. 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.

  4. Microbial Succession in Glacial Foreland Soils of the Canadian Subarctic

    NASA Astrophysics Data System (ADS)

    Kazemi, S.; Lanoil, B. D.

    2014-12-01

    The Canadian arctic has experienced increasing temperatures over the past century leading to heightened rate of glacial retreat. Glacial retreat leads to subsequent exposure of foreland soils to atmospheric conditions, thus creating a sequence of change in these ecosystems. Microbes are critical for soil development and nutrient dynamics in glacial systems as they are the primary colonizers of these soils and have been demonstrated to play a role in geochemical weathering and nutrient cycling beneath the glacier. Although viable microbial communities exist beneath glaciers and are known to be important for the glacial ecosystem, the impact of glacial retreat on these communities and development of the resulting foreland ecosystem is not well understood. Here, we investigate how microbial communities respond to changing conditions brought on by glacial retreat and whether a pattern of succession, such as those found in well characterized plant systems, occurs along a soil foreland in these microbial communities. We hypothesis that time since deglaciation is the major determinant of structure and composition of microbial assemblages. To test this, soil samples were collected along two glacier forelands, Trapridge Glacier and Duke River Glacier, located in Kluane National Park, Yukon Territory. Chronosequence dating of satellite images using geographic information system software revealed sampling sites have been ice-free from ~30 years to over 60 years. Soil chemistry analysis of major nutrients revealed no change in chemical parameters along the chronosequence, suggesting that presence of microbes after exposure from subglacial environments does not significantly alter soil characteristics in the timeframe observed. Furthermore, next-generation IonTorrentTM sequencing performed on soil samples revealed over five million sequencing reads, suggesting prominent microbial presence within these soils. Further analysis on sequencing data is needed to establish the

  5. 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

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

    PubMed

    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

  7. Obsidian hydration dates glacial loading?

    PubMed

    Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

    1973-05-18

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow. PMID:17806883

  8. Obsidian hydration dates glacial loading?

    PubMed

    Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

    1973-05-18

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

  9. Obsidian hydration dates glacial loading?

    USGS Publications Warehouse

    Friedman, I.; Pierce, K.L.; Obradovich, J.D.; Long, W.D.

    1973-01-01

    Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming . The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

  10. Short length scale mantle heterogeneity beneath Iceland probed by glacial modulation of melting

    NASA Astrophysics Data System (ADS)

    Sims, Kenneth W. W.; Maclennan, John; Blichert-Toft, Janne; Mervine, Evelyn M.; Blusztajn, Jurek; Grönvold, Karl

    2013-10-01

    Glacial modulation of melting beneath Iceland provides a unique opportunity to better understand both the nature and length scale of mantle heterogeneity. At the end of the last glacial period, ∼13 000 yr BP, eruption rates were ∼20-100 times greater than in glacial or late postglacial times and geophysical modeling posits that rapid melting of the large ice sheet covering Iceland caused a transient increase in mantle decompression melting rates. Here we present the first time-series of Sr-Nd-Hf-Pb isotopic data for a full glacial cycle from a spatially confined region of basaltic volcanism in northern Iceland. Basalts and picrites erupted during the early postglacial burst of volcanic activity are systematically offset to more depleted isotopic compositions than those of lavas erupted during glacial or recent (<7 kyr) times. These new isotopic data, coupled with major and trace element data, show that the mantle underneath northern Iceland is heterogeneous on small (<100 km) length scales. The temporal response of the isotopic compositions of the basalts to glacial unloading indicates that the isotopic composition of mantle heterogeneities can be linked to their melting behavior. The present geochemical data can be accounted for by a melting model in which a lithologically heterogeneous mantle source contains an enriched component more fusible than its companion depleted component.

  11. Tentative correlation of midcontinent glacial sequence with marine chronology

    SciTech Connect

    Dube, T.E.

    1985-01-01

    A tentative glacial-interglacial 3-million-year chronology is synthesized by regional correlation of Midcontinent tills and paleosols to marine paleotemperature/eustatic cycles and oxygen isotope stages. The paleotemperature curves of Beard et al. (1982), based on planktonic foraminiferal abundances, correspond directly with eustatic cycles during the last 3 Ma. These generalized curves are shown to correlate reasonably well with standard oxygen isotope stages at least for the past 900 ka. This indicates that paleotemperature and Vail-type eustatic cycles have been glacially induced during the last 3 Ma. The chronology developed here utilizes both paleotemperature and oxygen isotope stages; however, below the Jaramillo magnetic subchron, isotope curves are more variable and only paleotemperature stages are used. Tills and paleosols at type localities in the Midcontinent area of the US are correlated to the SPECMAP oxygen isotope time scale. Because mid-Brunhes events are poorly constrained by radiometric dates, alternative correlations are possible. The oldest known Midcontinent tills correlate to the first Plio-Pleistocene cold paleotemperature stage and drop in sea level at 2.4 Ma. This Late Pliocene event also corresponds to the first major isotopic enrichment and the onset of late Cenozoic ice-rafting in the North Atlantic region.

  12. Systematically enhanced subarctic Pacific stratification and nutrient utilization during glacials

    NASA Astrophysics Data System (ADS)

    Knudson, K. P.; Ravelo, A. C.

    2015-12-01

    The modern subarctic North Pacific is characterized as a high-nitrate, low-chlorophyll (HNLC) area, but evidence for increased nutrient utilization during the last glacial indicates that this region is highly dynamic. As such, this HNLC area is of particular interest in regard to understanding changes in the biological pump and carbon sequestration and predicting how biogeochemical processes will influence, or be influenced by, future climate change. While it has been suggested that changes in iron supply and/or ocean stratification could explain fluctuations in nutrient utilization and productivity in the subarctic Pacific, short records of nutrient utilization have previously hindered the evaluation of these potential mechanisms over long timescales. Here we present new, high-resolution records of bulk sediment δ15N from 0-1.2 Ma from Integrated Ocean Drilling Program Exp. 323 Site U1342, which are used to calculate Δδ15N (U1342 δ15Nbulk - ODP Site 1012 δ15Nbulk) as a nitrate utilization proxy. The unprecedented length and resolution of this new record allows us, for the first time, to determine orbital-scale systematic behavior in subarctic Pacific nutrient utilization over many glacial/interglacial cycles. Spectral analyses demonstrate that enhanced nutrient utilization was paced by climate on Milankovitch orbital cycles since the Mid-Pleistocene Transition (MPT; ~800 ka). Nitrate utilization maxima is statistically correlated with glacial maxima and enhanced dust/iron availability (represented by existing records of EPICA ice core dust, Southern Pacific Ocean sediment iron, and China loess) but shows low correlation to primary productivity, suggesting that stratification has systematically exerted an important control on subarctic Pacific nutrient utilization since the MPT. These findings imply that the presence of iron helped to change the region into a nitrate-limited, rather than iron-limited, region during glacials and that stratification, which

  13. Sedimentary architecture of the Amundsen Sea Embayment shelf, West Antarctica, from pre-glacial to glacial processes

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Uenzelmann-Neben, Gabriele; Hillenbrand, Claus-Dieter; Larter, Robert; Nitsche, Frank

    2013-04-01

    Studies of the sedimentary architecture and characteristics of Antarctic shelves provide clues of past ice sheet advance-retreat cycles and help improve constraints for paleo-ice dynamic models since early glacial periods. A first seismostratigraphic analysis of the Amundsen Sea Embayment shelf and slope of West Antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition, erosion and transport history from pre-glacial times to early glaciation and to the most recent glacial periods. The shelf geometry consists of a large pre- and syn-rift basin in the middle shelf region between outcropping basement of the inner shelf and basement ridges and highs beneath the outer shelf. A middle shelf sub-basin exists which may have formed as a result of motion along an early West Antarctic Rift System branch. At least 4 km of pre-glacial strata has been eroded from the present inner shelf and coastal hinterland by ice sheet advances since the onset of glaciation. Some of the eroded sediments were deposited as a progradational wedge extending the outer shelf by 25 to 65 km oceanward of the pre-glacial shelf-break. Comparing the observed seismic characteristics with those of other Antarctic shelf sequences, we assign an Early Cretaceous age for bottom sedimentary unit ASS-1, a Late Cretaceous to Oligocene age for unit ASS-2, an Early to Mid-Miocene age for unit ASS-3, a Mid-Miocene age for unit ASS-4, a Late Miocene to Early Pliocene age for unit ASS-5, and a Pliocene to Pleistocene age for the top unit ASS-6. The survival of buried grounding zone wedges in the upper part of unit ASS-5 of the outer shelf is consistent with the onset of a long warming phase and a retreated ice sheet in the early Pliocene as observed for the Ross Sea shelf and reconstructed from paleo-ice sheet models. Our data also reveal that the paleo-ice flow paths of the central Pine Island Trough system have remained stationary across the

  14. EPICA Dome C record of glacial and interglacial intensities

    NASA Astrophysics Data System (ADS)

    Masson-Delmotte, V.; Stenni, B.; Pol, K.; Braconnot, P.; Cattani, O.; Falourd, S.; Kageyama, M.; Jouzel, J.; Landais, A.; Minster, B.; Barnola, J. M.; Chappellaz, J.; Krinner, G.; Johnsen, S.; Röthlisberger, R.; Hansen, J.; Mikolajewicz, U.; Otto-Bliesner, B.

    2010-01-01

    Climate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800 000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile. The consistency between stable isotope-derived temperature and other environmental and climatic proxies measured along the EDC ice core is analysed at the orbital scale and compared with estimates of global ice volume. MIS 2, 12 and 16 appear as the strongest glacial maxima, while MIS 5.5 and 11 appear as the warmest interglacial maxima. The links between EDC temperature, global temperature, local and global radiative forcings are analysed. We show: (i) a strong but changing link between EDC temperature and greenhouse gas global radiative forcing in the first and second part of the record; (ii) a large residual signature of obliquity in EDC temperature with a 5 ky lag; (iii) the exceptional character of temperature variations within interglacial periods. Focusing on MIS 5.5, the warmest interglacial of EDC record, we show that orbitally forced coupled climate models only simulate a precession-induced shift of the Antarctic seasonal cycle of temperature. While they do capture annually persistent Greenland warmth, models fail to capture the warming indicated by Antarctic ice core δD. We suggest that the model-data mismatch may result from the lack of feedbacks between ice sheets and climate including both local Antarctic effects due to changes in ice sheet topography and global effects due to meltwater-thermohaline circulation interplays. An MIS 5.5 sensitivity study conducted with interactive Greenland melt indeed induces a slight Antarctic warming. We suggest that interglacial EDC optima are caused by transient heat transport redistribution comparable with

  15. High-resolution mapping of glacial landforms in the North Alpine Foreland, Austria

    NASA Astrophysics Data System (ADS)

    Salcher, Bernhard C.; Hinsch, Ralph; Wagreich, Michael

    2010-10-01

    In this study results from traditional field mapping were merged with precise elevation information from airborne LiDAR (Light detection and ranging) surveys. Morphological and sedimentological data provide new results from the Austrian (eastern) part of the Salzach piedmont glacier during times of and shortly after the Last Glacial Maximum (LGM). The variations in meltwater discharge had a major impact on the development of glacial landforms. In areas with high meltwater supply erosional or debris reworking processes play a major role, represented by drainage channels, drumlins and kettled, low relief hummocky moraine with low slope angles. Low discharge areas are associated with distinct depositional forms such as high relief end moraines (up to 30 m) and hummocky moraine (averaging 20 m) with high slope angles. Isolated conical kames may reach heights up to 45 m. Fluvial activity is supposed to rise towards the end of the glacial cycle causing high melting rates and comprehensive debris reworking. The formation of terminal lakes and associated widespread, inorganic lake clays are the last deposits within the study area before the Salzach Glacier completely receded to its main valley. The survey of glacial landforms through the combination of field mapping and high-resolution DEM derived from airborne LiDAR missions gives precise information on transport and deposition during the last glacial cycle of the eastern Salzach Glacier piedmont lobe.

  16. Record of glacial Lake Missoula floods in glacial Lake Columbia, Washington

    NASA Astrophysics Data System (ADS)

    Hanson, Michelle A.; Clague, John J.

    2016-02-01

    During the last glaciation (marine oxygen isotope stage 2), outburst floods from glacial Lake Missoula deposited diagnostic sediments within glacial Lake Columbia. Two dominant outburst flood lithofacies are present within glacial Lake Columbia deposits: a flood expansion bar facies and a finer-grained hyperpycnite facies. We conclude that the flood sediments have a glacial Lake Missoula source because: (1) current indicators indicate westward flow through the lake, and upvalley flow followed by downvalley flow in tributary valleys; (2) no flood sediments are found north of a certain point; (3) there is a dominance of Belt-Purcell Supergroup clasts in a flood expansion bar; and (4) some of the finer-grained beds have a pink colour, reflective of glacial Lake Missoula lake-bottom sediments. A new radiocarbon age of 13,400 ± 100 14C BP on plant detritus found below 37 flood beds helps constrain the timing of outburst flooding from glacial Lake Missoula.

  17. The Role of Glacial Erosion in Limiting Ice Sheet Extents

    NASA Astrophysics Data System (ADS)

    Jamieson, S.; Hulton, N.

    2007-12-01

    , the thermal regime of the ice alters and the drawdown and capture of warm ice into 'streams' causes more focussed selective erosion. The main control on the pattern of retreat is the pre-existing topography, which strongly controls erosion patterns. Ice streams retreat progressively in response to lowering valley floors and the impact of erosion induced self-limiting remains over successive glacial cycles. References: Jamieson, S.S.R., Hulton, N.R.J. and Hagdorn, M., 2007. Modelling landscape evolution under ice sheets. Geomorphology, doi:10.1016/j.geomorph.2007.02.047. Oerlemans, J., 1984. Numerical experiments on large-scale glacial erosion. Zeitschrift fur Gletscherkunde und Glazialgeologie, 20: 107-126. Payne, A.J., 1999. A thermomechanical model of ice flow in West Antarctica. Climate Dynamics, 15(2): 115-125.

  18. Controls on magmatic cycles and development of rift topography of the Manda Hararo segment (Afar, Ethiopia): Insights from cosmogenic 3He investigation of landscape evolution

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Pik, R.; Burnard, P.; Williams, A.; Vye-Brown, C.; Ferguson, D.; Blard, P.-H.; France, L.; Yirgu, G.; Seid, J. I.; Ayalew, D.; Calvert, A.

    2013-04-01

    Crustal extension at mature continental rifts and oceanic ridges occurs by a combination of normal faulting and magma injection, which interact to create rift morphology. Quantifying the relative roles of faulting and melt intrusion in accommodating extension at magmatic rifts remains difficult and requires studies at sufficient spatial and temporal scales to resolve the interaction between these processes. In this study we provide new chronological constraints based on cosmogenic exposure dating for the ˜100 kyr topographic evolution of a young and active magmatic rift segment in Afar, Ethiopia. We combine structural investigations, field mapping, geochemical analysis and cosmogenic 3He exposure dating of lava surfaces in order to investigate the interplay between volcanic activity and fault growth in the northern part of the axial depression, where the rift segment intersects a large stratovolcano. Our results allow us to determine the roles of the various magma reservoirs feeding this rift system and their interactions during accretion over the past 100 kyr. New age data for key lava units allow several magmatic cycles to be distinguished. Each cycle lasts 20-40 ka resulting in periods of high and low magma supply rate. The variations in magma supply rate at the segment extremity strongly affect the development of the rift depression, with the availability of melt controlling the morphological impact of faulting. Melts from different magma reservoirs feeding the segment are chemically distinct and geochemical analysis of lavas from the rift floor allows their respective contributions to maintaining magmatic accretion to be estimated. We propose that melts from the magma reservoir at the northern end of the segment contribute around one-third of the length of this portion of the segment, whereas the mid-segment reservoir is responsible for the remaining two-thirds of the segment accretion.

  19. The Glacial-Interglacial Monsoon Recorded by Speleothems from Sulawesi, Indonesia

    NASA Astrophysics Data System (ADS)

    Kimbrough, A. K.; Gagan, M. K.; Dunbar, G. B.; Krause, C.; Hantoro, W. S.; Cheng, H.; Edwards, R. L.; Shen, C. C.; Sun, H.; Cai, B.; Hellstrom, J. C.; Rifai, H.

    2015-12-01

    The Indo-Pacific Warm Pool is a primary source of heat and moisture to the global atmosphere and a key player in tropical and global climate variability. There is mounting evidence that atmospheric convection and oceanic processes in the tropics can modulate global climate on orbital and sub-orbital timescales. Glacial-interglacial cycles represent the largest natural climate changes over the last 800 kyr with each cycle terminated by rapid global warming and sea level rise. Our understanding of the role and response of tropical atmospheric convection during these periods of dramatic warming is limited. We present the first speleothem paleomonsoon record for southwest Sulawesi (5ºS, 119ºE), spanning two glacial-interglacial cycles, including glacial termination IV (~340 kyr BP) and both phases of termination III (~248 and ~220 kyr BP). This unique record is constructed from multiple stalagmites from two separate caves and is based on a multi-proxy approach (δ18O, δ13C, Mg/Ca, Sr/Ca) that provides insight into the mechanisms controlling Australian-Indonesian summer monsoon variability. Speleothem δ18O and trace element data indicate a rapid increase in rainfall at glacial terminations and wet interglacials. Terminations IV, III, and I are each characterized by an abrupt 3‰ decrease in δ18O. Variability in δ18O leading-in to glacial terminations is also similar, and corresponds to October insolation. Prior to deglaciation, there is a distinct shift to higher δ18O that is synchronized with weak monsoon intervals in Chinese speleothem records. The remarkably consistent pattern among terminations implies that the response of tropical convection to changing background climates is well regulated. Furthermore, we find that speleothem δ13C leads δ18O by ~5 kyr during glacial terminations. The early decrease in speleothem δ13C may reflect the response of tropical vegetation to rising atmospheric CO2 and temperature, rather than regional changes in rainfall.

  20. A fresh look at glacial foods

    USGS Publications Warehouse

    Colman, Steven M.

    2002-01-01

    Over the last 20 years, it has become clear that ice ages are characterized by glacial as well as climatic instability on millennial time scales. In his Perspective, Colman highlights two recent papers investigating the role of glacial meltwater and continental drainage in this instability. The results suggest a fundamental instability feedback between ocean circulation and ice sheet dynamics and provides an explanation for why instability was greatest at times of intermediate ice volume.

  1. Meltwater input to the southern ocean during the last glacial maximum

    SciTech Connect

    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 climatic cycles at the same cores.

  2. Mapping Glacial Lakes on the Tibetan Plateau with Landsat TM/ETM+ Imagery

    NASA Astrophysics Data System (ADS)

    Li, J.; Sheng, Y.

    2009-12-01

    With a pronounced temperature rise of 0.16oC per decade, the Tibetan plateau is one of the world’s most vulnerable areas responding to global change. Glaciers and glacial lakes serve as sensitive indicators to these regional climate and water cycle variations. Recent study shows that glaciers on the plateau have retreated dramatically, leading to the expansion of the existing glacial lakes and the emergence ofnew glacial lakes. The existence of these lakes increases the possibility of outburst floods to the downstream areas during the ice melting season. Mapping and monitoring these glacial lakes will facilitate our understanding of the glacier-related hazards and regional climate changes. However, rigorous field surveys of glacial lake dynamics are prohibitive in high-mountainous areas on the plateau due to their low accessibility. Satellite remote sensing provides an efficient and objective tool to analyze the status and variations of glacial lakes. Theoretically, lakes and other surface open water bodies are readily identified in satellite images owing to their very low reflectance in near-infrared (NIR) channels of Landsat sensors. In the mountain regions where glacial lakes are located, cloud shadows, mountain shadows, melting glaciers or even lakes under different conditions (e.g., ice lakes, salt lakes, turbid lakes) could become disturbing factors and create problems to glacial lake delineation. We use normalized difference water index (NDWI), the normalized ratio index between the green and near infrared spectral bands, to differentiate water bodies from other land features. As lake features are on the relatively flat areas, topographic features such as terrain slope and hill shades derived from digital elevation model (DEM) are also used to remove the shadows from lakes. Based on NDWI and topographic characteristics, We have developed an automated hierarchical method to monitor glacial lakes using Landsat TM/ETM+ imagery. Firstly, lakes are roughly

  3. The impact of glaciations and glacial processes on groundwater flow dynamics: a numerical investigation

    NASA Astrophysics Data System (ADS)

    Sterckx, A.; Lemieux, J. M.; Vaikmae, R.

    2015-12-01

    Numerical models are widely used to investigate the impact of glaciations on groundwater flow systems because they can simulate complex glacial processes. However, it isn't clear which of these processes are relevant to adequately capture groundwater flow dynamics. Given the complexity of representing these processes in a numerical model and the paucity of field data available for their validation, it is of prime interest to assess how they impact groundwater flow and if any of these processes could be neglected. In order to assess the specific impact of glacial processes on groundwater flow dynamics, those processes were included in the numerical model FEFLOW and simulations were conducted in a simple conceptual model representing a 21 ky glacial cycle in a sedimentary basin. The following processes have been simulated: subglacial recharge, linear and non-linear compaction of the porous medium under the weight of the ice, isostasy, proglacial lakes, as well as permafrost. Solute transport was simulated along with groundwater flow to track groundwater originating from the ice-sheet. To interpret the results, a base case scenario considering only subglacial recharge was selected and compared with the other scenarios, where individual glacial processes were simulated. When comparing the results at the end of the simulations, it appears that most of the aforementioned glacial processes don't lead to a significant difference in meltwater distribution with respect to the base case. Only hydromechanical coupling brings some noticeable change. Conversely, the type and the value of the boundary condition applied at the base of the ice-sheet play a major role in groundwater flow dynamics. The presence of confining hydrogeological units also seems to be a key to understand the long-term effect of glaciations. These results suggest that some of the glacial processes may be neglected for the simulation of groundwater flow dynamics during a glacial period.

  4. Short Length Scale Mantle Heterogeneity Beneath Iceland Probed by Glacial Modulation of Melting

    NASA Astrophysics Data System (ADS)

    Sims, K. W.; Maclennan, J.; Blichert-Toft, J.; Mervine, E. M.; Gronvold, K.

    2012-12-01

    While isotopic variability in basaltic lavas indisputably documents long-lived mantle heterogeneity, the nature of this heterogeneity (lithologic variability or cryptic metasomatism) and its length scales remain uncertain. We show that glacial modulation of melting beneath Iceland provides a unique opportunity to better understand both the nature and length scale of mantle heterogeneity. At the end of the last glacial period, ~13,000 yr BP, eruption rates were ~20-100 times greater than in glacial or late postglacial times and geophysical modeling posits that rapid melting of the large ice sheet covering Iceland caused a transient increase in decompression mantle melting. Here we present the first time-series of Sr-Nd-Hf-Pb isotopic data for a full glacial cycle (glacial-early postglacial-late postglacial/modern) from a spatially confined region of basaltic volcanism in Northern Iceland. Our new isotopic data coupled with major and trace element data for lavas from Krafla and Theistareykir allow for comparison of lava flows erupted during the early postglacial volcanic pulse, when melting rates are thought to have increased dramatically in the shallow part of the melting region, with glacial and late postglacial lavas. These new isotopic data show that the early postglacial lavas at Theistareykir and Krafla carry a larger contribution from a long-term time-averaged incompatible element-depleted source than glacial and recent lavas. This observation suggests that the mantle underneath northern Iceland is heterogeneous on small (<100 km) scales within the melting column, and that the isotopic and trace element data are best explained by melting of a lithologically heterogeneous mantle source in which the enriched component is more fusible than the depleted component. Our study of temporal variation in isotopic compositions provides important evidence of a link between isotopic and major element variations in the mantle, removing much of the ambiguity associated with

  5. Terrigenous Fe input and biogenic sedimentation in the glacial and interglacial equatorial Pacific Ocean

    SciTech Connect

    Murray, R.W.; Leinen, M.; Knowlton, C.W.

    1995-12-01

    This study was performed to determine the relationship of particulate iron from land erosion to the accumulation of biogenic matter in the equatorial Pacific Ocean. Sediment cores representing the last six glacial-interglacial cycles and previously published mineralogic records were used as data input. Total iron, terrigenous, and biogenic components were determined for three sediment cores. The study determined that there is no relationship between terrigenous iron input and sedimentary carbon sequestering. This is based on chemical, spectral, and stratigraphic anlyses which showed: (1) no consistent pattern of terrigenous input during glacial or interglacial periods, (2) a close relationshipe between the accumulation of particulate iron and the accumulation of terrigenous matter, (3) no coherent spectral correlations between glacial periodicity and iron input, (4) an inverse correlation of iron input and calcium carbonate, and (5) no spectral or linear relationship between iron accumulation and calcium carbonate, organic carbon, or opal. 55 refs., 6 figs., 3 tabs.

  6. Analyzing Glacial-Interglacial Ocean Biogeochemical States in the MPI-Earth System Model

    NASA Astrophysics Data System (ADS)

    Heinze, M.; Ilyina, T.

    2015-12-01

    There is still little consensus about the mechanisms causing the glacial - interglacial variationsin atmospheric CO2 concentrations of around 100 ppm. Some of those mechanisms aredriven by alterations in ocean biogeochemical cycles. Hence, it is crucial to understand oceanbiogeochemistry dynamics during glacial-interglacial transitions. Within the German nationalclimate modeling initiative PalMod, aiming at simulating a full glacial cycle (135k - today) intransient mode with a state-of-the-art Earth System Model (ESM), we address the oceanbiogeochemistry cycles using a comprehensive modeling approach. In order to set up themodel we start with ocean only simulations, which are based on the 3-D ocean generalcirculation model MPIOM coupled to the ocean biogeochemistry model HAMOCC.Atmospheric forcing data is derived from a fully coupled LGM simulation including theatmosphere general circulation model ECHAM6. This setup provides us a sophisticatedrepresentation of the ocean biogeochemistry during the LGM without using any kind of datarestoring,to be consistent with the biological, chemical and physical dynamics of the model.We analyze alterations in ocean biogeochemistry during the LGM in comparison to a preindustrialcontrol climate. We discuss and quantify the changes in ocean biogeochemicalcycles between these two states, as well as possible implications for carbon transfer due tochanges in ocean dynamics. In the next steps we will use the ocean biogeochemistry model aspart of the fully coupled MPI-ESM. Our results aim at improving the understanding of glacial- interglacial changes in atmospheric CO2, especially in terms of marine carbon sequestrationand release. The presented work contributes to developing comprehensive ESMs, which arecapable of simulating the climate evolution and the variability during the last glacial cycle.

  7. Glacial influence on caldera-forming eruptions

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Bindeman, Ilya

    2010-05-01

    Investigation of Ar-Ar, U-Pb, and 14C ages of caldera-forming eruptions for the past million years in glaciated arc of Kamchatka has lead to observations that the majority of large-volume ignimbrites, which are associated with the morphologically-preserved calderas, correspond in time with 'maximum glacial' conditions. The latter are defined as the highest δ18O foraminifera values on the N Pacific SPECMAP stack. Additional evidence comes from clustering Kamchatka-derived marine ash layers with glacial moraines in DSDP cores. The strongest field evidence comes from glaciated multi-caldera volcanoes that hosted thick glacial ice caps. In this paper, we investigate how glacial load dynamics may alter eruption frequency in such glaciated multicaldera volcanoes. We present results of numerical simulations that include ice cap of different thickness (ranging from 0 to 1 km) on top of calderas of relevant sizes (5 to 40 km) with magma chambers at different depths. We also study the effects of an asymmetric ice distribution, a variable pre-caldera topography, glacial overpressure on volatiles solubility, and the subglacial intracaldera hydrothermal system on changing mechanical properties of roof rock. The results are: 1) Any ice cap retard ring-fall propagation and caldera formation; 2) Asymmetric distribution of ice plays no or minor role; 3) Glacial erosion of part of volcanic edifice or interglacial edifice failure may promote ring fracture; 4) hydrothermal system under an ice cap may have more acidic hydrothermal fluids leading to more effective hydrothermal rotting of the intracaldera roof rocks; 5) short period interstadial during maximal glaciation may play most important role in pressure fluctuations/volatite saturation condition; 6) Arching influence of the ice cap on roof rock may lead to ring fracture. Overall, the maximal glacial time represent the most dynamic time in a multi-caldera volcano life promoting physical and chemical feedbacks.

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Ganopolski, Andrey; Winkelmann, Ricarda; Schellnhuber, Hans Joachim

    2016-04-01

    Past rapid growth of Northern Hemisphere continental ice sheets, which terminated rather stable and warm climate periods, is generally attributed to reduced summer insolation in boreal latitudes (Milanković , 1941; Hays et al., 1976, Paillard, 1998). Yet pertinent summer insolation is near to its minimum at present (Berger and Loutre, 2002), and there are no signs of a new ice age (Kemp et al., 2011). This challenges our scientific understanding of the mechanisms driving glacial cycles and our ability to predict the next glacial inception (Masson-Delmotte et al., 2013). Here we propose a fundamental functional relationship between boreal summer insolation and global CO2 concentration, which explains the beginning of the past eight glacial cycles and can anticipate future periods when glacial inception may occur again. Using a simulations ensemble generated by an Earth system model of intermediate complexity constrained by paleoclimatic data, we show that glacial inception was narrowly missed before the beginning of the Industrial Revolution. This can be explained by the combined effect of relatively high late-Holocene CO2 concentration and low orbital eccentricity of the Earth (Loutre and Berger, 2003). Additionally, our analysis shows that even in the absence of human perturbations no significant buildup of ice sheets would occur within the next several thousand years and that the current interglacial would likely last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1000 to 1500 GtC may already postpone the next glacial inception by at least 100,000 years (Archer and Ganopolski, 2005; Paillard, 2006). Our simulations demonstrate that under natural conditions alone the Earth system would be expected to stay in the delicate interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time.

  12. 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. PMID:26762457

  13. 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.

  14. Quaternary fluvial response to climate change in glacially influenced river systems

    NASA Astrophysics Data System (ADS)

    Cordier, Stéphane; Adamson, Kathryn; Delmas, Magali; Calvet, Marc; Harmand, Dominique

    2016-04-01

    Over the last few decades, many studies in Europe and other continents have focused on the fluvial response to climate forcing in unglaciated basins. However, glacial activity may have a profound impact on the behaviour of the fluvial systems located downstream. In comparison to ice-free basins, these systems are characterised by distinctive hydrological and sediment supply regimes. Over Quaternary timescales, the fluvial records are influenced by periglacial (in non-glaciated areas), proglacial, and paraglacial processes. Understanding the impacts of these processes on the formation and preservation of the Quaternary geomorphological and sedimentary archives is key for our understanding of glacial-fluvial interactions. We investigate the impact of Quaternary glacial activity on fluvial sediment transfer, deposition, and preservation. Using existing studies from across Europe, we create a database of glaciofluvial geomorphology, sedimentology, and geochronology. This is used to examine how glacial forcing of fluvial systems varies spatially in different basin settings, and temporally over successive Milankovitch cycles. In particular, we focus on the ways in which the primary glacial-fluvial depositional signal could be distinguished from periglacial and paraglacial reworking and redeposition.

  15. Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

    PubMed

    Rutberg; Hemming; Goldstein

    2000-06-22

    The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times--delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231Pa/230Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch. Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export. PMID:10879531

  16. History of glacial terminations from the Tiber River, Rome: Insights into glacial forcing mechanisms

    NASA Astrophysics Data System (ADS)

    Marra, Fabrizio; Florindo, Fabio; Boschi, Enzo

    2008-06-01

    We document the aggradational history of the Tiber River delta through the last 17,000 years by means of 17 new 14C ages from peat or wood collected from the delta sediment. An abrupt change in sediment clast size, grading from gravel to clay, occurred between 13.63 (±0.20) and 12.80 (±0.15) ka, indicating that it was synchronous with the last glacial termination, with no appreciable phase lag. Knowing this phase relationship enables us to reduce the magnitudes of age uncertainties for aggradational sections corresponding to glacial terminations IX through III, which we had dated previously by 40Ar/39Ar methods. Glacial terminations VIII, VI, and IV precede beyond 95% confidence the ages predicted by Northern Hemisphere summer insolation maxima. Additionally, we find that each of these seven glacial terminations follows particularly mild insolation minima, which we suggest may be regarded as the preconditioning factor to trigger a glacial termination.

  17. 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).

  18. Glacial history of Tranquilo glacier (Central Patagonia) since the Last Glacial Maximum through to the present.

    NASA Astrophysics Data System (ADS)

    Sagredo, E. A.; Araya, P. S.; Schaefer, J. M.; Kaplan, M. R.; Kelly, M. A.; Lowell, T. V.; Aravena, J. C.

    2014-12-01

    Deciphering the timing and the inter-hemispheric phasing of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we present a detailed chronology of glacial fluctuations for Río Tranquilo glacier (47°S), since the LGM, including up to the present. Río Tranquilo is a small glacial valley located on the northern flank of Monte San Lorenzo, an isolated granitic massif, ~70 km to the east of the southern limit of the Northern Patagonian Icefield. Although Mt. San Lorenzo is located on the leeward side of the Andes, it is one of the most glacierized mountains in the region, with an ice surface area of ~140 km2. Geomorphic evidence suggests that during past episodes of climate change several small glaciers that today occupy the headwalls of Río Tranquilo valley expanded and coalesced, depositing a series of moraines complexes along the flanks and bottom of the valley. We used two independent dating techniques to constrain the age of the glacial history of the area. 10Be surface exposure ages from boulders located atop moraine ridges reveal that Río Tranquilo valley underwent glacial expansion/stabilization during at least the LGM (late LGM?), Late glacial (ACR and Younger Dryas) and Mid-Holocene. Within the Mid-Holocene limits, tree-ring based chronology indicates that Río Tranquilo glacier expanded during the Late Holocene as well. Our results are the first detailed chronology of glacial fluctuations from a single valley glacier, spanning the entire period from the (end of the) LGM up to the present, in southern South America. By identifying different glacial episodes within a single alpine valley, this study provides baseline data for studying the relative magnitude of the climate events responsible for these glacial events.

  19. Origin of glacial dust in four East Antarctica ice cores

    NASA Astrophysics Data System (ADS)

    Delmonte, B.; Petit, J. R.; Basile-Doelsh, I.; Jagoutz, E.; Michard, A.; Maggi, V.; Revel-Rolland, M.

    2003-04-01

    We investigated the geographic origin of mineral aerosol (dust) windblown from the Southern Hemisphere continents and preserved in four East Antarctica ices cores using 87Sr/86Sr -143Nd/144Nd isotopic systems. For the equivalent size range (diameter < 5 micron) the isotope composition is compared to the signature of Potential Source Areas (PSAs) of the Southern Hemisphere. Our initial collection of PSA samples was recently documented by new samples of loesses, fluvial and sands deposits from South America, South Africa, New Zealand and the Antarctic Dry Valleys. In addition, the isotopic fingerprint was measured on ice core from glacial climate (corresponding to even number of marine isotopic stages) for four different ice cores from the East Antarctic Plateau: EPICA-Dome C (75^o06'S, 123^o 24'E; Stage 2,4,6), Vostok (78^o S, 106^o E; Stage 6), Dome B (77^o05' S, 94^o 55' E; Stage 2) and Komsomolskaia (74^o 05' S, 97^o 29' E, Stage 2). The Sr-Nd signature of dust from the four sites appear very close from each other, and confirm the previous results from Basile (1997) from the Vostok ice core. Altogether, they define a restricted isotopic field, and suggest provenance from the same source(s). The comparison with the isotopic signature from the PSAs allows to exclude South Africa as possible candidate, but a partial overlap arises among Southern South America (Chile, Argentina), New Zealand and the Antarctic Dry Valleys. A possible contribution from all these three sources cannot be excluded. However New Zealand and Antarctic source and contribution to Antarctic ice seem quite negligible, an hypothesis as also supported by the absence of volcanic ashes from these area in the Vostok ice core. for the last four glacial/interglacial cycles. Our data confirm previous studies (Grousset et al., 1992, Basile et al., 1997) suggesting South America as the dominant source for dust in East Antarctica in glacial times.

  20. 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.

  1. Sources of glacial moisture in Mesoamerica

    USGS Publications Warehouse

    Bradbury, J.P.

    1997-01-01

    Paleoclimatic records from Mesoamerica document the interplay between Atlantic and Pacific sources of precipitation during the last glacial stage and Holocene. Today, and throughout much of the Holocene, the entire region receives its principal moisture in the summer from an interaction of easterly trade winds with the equatorial calms. Glacial records from sites east of 95?? W in Guatemala, Florida, northern Venezuela and Colombia record dry conditions before 12 ka, however. West of 95?? W, glacial conditions were moister than in the Holocene. For example, pollen and diatom data show that Lake Pa??tzcuaro in the central Mexican highlands was cool, deep and fresh during this time and fossil pinyon needles in packrat middens in Chihuahua, Sonora, Arizona, and Texas indicate cooler glacial climates with increased winter precipitation. Cold Gulf of Mexico sea-surface temperatures and reduced strength of the equatorial calms can explain arid full and late glacial environments east of 95?? W whereas an intensified pattern of winter, westerly air flow dominated hydrologic balances as far south as 20?? N. Overall cooler temperatures may have increased effective moisture levels during dry summer months in both areas. ?? 1997 INQUA/ Elsevier Science Ltd.

  2. Last Glacial loess in the conterminous USA

    USGS Publications Warehouse

    Bettis, E. Arthur; Muhs, Daniel R.; Roberts, Helen M.; Wintle, Ann G.

    2003-01-01

    The conterminous United States contains an extensive and generally well-studied record of Last Glacial loess. The loess occurs in diverse physiographic provinces, and under a wide range of climatic and ecological conditions. Both glacial and non-glacia lloess sources are present, and many properties of the loess vary systematically with distance from loess sources. United States' mid-continent Last Glacial loess is probably the thickest in the world, and our calculated mass accumulation rates (MARs) are as high as 17,500 g/m2/yr at the Bignell Hill locality in Nebraska, and many near-source localities have MARs greater than 1500 g/m2/yr. These MARs are high relative to rates calculated in other loess provinces around the world. Recent models of LastGlacial dust sources fail to predict the extent and magnitude of dust flux from the mid-continent of the United States. A better understanding of linkages between climate, ice sheet behaviour, routing of glacial meltwater, land surface processes beyond the ice margin, and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region.

  3. Humid glacials, arid interglacials? Results from a multiproxy study of the loess-paleosol sequence Crvenka, Serbia

    NASA Astrophysics Data System (ADS)

    Zech, R.; Zech, M.; Markovic, S.; Huang, Y.

    2012-04-01

    The loess-paleosol sequences in the Carpathian Basin, southeast Europe, are up to tens of meters thick and provide valuable archives for paleoenvironmental and -climate change over several glacial-interglacial cycles. The Crvenka section spans the full last glacial cycle and is used in this multi-proxy study to reconstruct past climate conditions. Crvenka features the characteristic pattern in terms of grain size and weathering intensity, i.e. finer grain sizes and more intensive weathering in the paleosols compared to the glacial loess units. The analysis of plant-derived long-chain n-alkanes as molecular biomarkers for past vegetation indicates the presence of trees during glacials, which is consistent with other e.g. macrofossil findings and the notion that parts of southeast Europe served as tree-refugia. However, virtually tree-less grass steppes are reconstructed for the Eemian, the last interglacial. More humid conditions during glacials and more arid conditions during interglacials would be in good agreement with lake-level reconstructions from the Dead Sea, but they seem to be at odds with traditional interpretations of pollen and stable isotope records for the Mediterranean region. In order to further contribute to this issue, we performed compound-specific D/H analyses on the most abundant alkanes C29 and C31, which should mainly record past changes in the isotopic composition of precipitation. The absence of a clear signal towards more depleted values during glacials shows that the temperature-effect is not dominant and probably offset by a strong source-effect, namely the enrichment of the Mediterranean sea water during glacials. This very same source effect may generally need to be taken into account when interpreting terrestrial isotope records in the Mediterranean, which implies that more positive values during glacials may not necessarily indicate an amount-effect and more arid conditions.

  4. Iceland Dust Storms Linked to Glacial Outwash Deposits and to Sub-Glacial Flood (Jökulhlaup) Events

    NASA Astrophysics Data System (ADS)

    Prospero, J. M.; Arnalds, Ó.; Olafsson, H.; Bullard, J.; Hodgkins, R.

    2008-12-01

    Studies of Arctic snow and ice cores reveal large temporal changes in dust concentrations, especially over glacial-interglacial cycles. Most efforts to model dust variability with climate have focused on sources in tropical and mid-latitude arid regions and have neglected high latitude emissions because of a lack of information on possible sources. Here we report on aerosol measurements which show that dust storms are common on Iceland and that major events are associated with glacial sedimentary environments. In July 1991 we established an aerosol sampling site on Heimaey, a small island located 18 km off the southeast coast of Iceland, with the objective of studying the transport of pollutant species to the Arctic. We found that although concentrations of nitrate and non-sea-salt sulfate were generally quite low, there were sporadic peaks that were primarily attributed to pollutant transport from Europe [Prospero et al., 1995]. Recently we expanded our analyses to include mineral dust, covering the period 1997 through 2004. Dust is present during much of the year (annual average 3.9 μg m-3) with a strong seasonal cycle (maximum in April, 14.0 μg m-3). However there are many spikes in the dust record, some exceeding 100 μg m-3, which are not associated with pollutant transport peaks. A search of NASA satellite web archives yielded six "dust storm" images that were acquired during our data period. These show prominent dust plumes streaming off the coast of Iceland. Here we show that each image could be closely linked to a major dust peak in our record (although there were many more peaks than satellite images). Most of these dust events were associated with dust emitted from glacial outwash (sandur) deposits. Some of the largest dust peaks were linked to jökulhlaups, an Icelandic term for sub-glacially generated outburst floods. The dust clouds were typically comprised of a series of well-defined plumes emitted from large "point" sources, mostly associated with

  5. 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.

  6. Glacial sequence stratigraphy reveal the Weichselian glacial history of the SE sector of the Eurasian Ice Sheet

    NASA Astrophysics Data System (ADS)

    Räsänen, Matti

    2016-04-01

    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. Here glacial sequence stratigraphy (Powell and Cooper 2002) is applied to isolated Late Pleistocene onshore outcrop sections in S Finland. The analysed sedimentary records have traditionally been investigated, interpreted and published separately by different authors without an attempt to a methodologically more systematic survey. By putting new field data and old observations into a regional sequence stratigraphic framework it is shown how previously unnoticed regularities can be found in the lithofacies and fossil successions. It is shown that the proposed Middle Weichselian glaciation or the pine dominated interstadial did not take place at all (Räsänen et al. 2015). The one Late Weichselian glaciation (MIS 2, 29-11 kyr ago) at the SE sector of EIS was preceded in S Finland by a nearly 90 kyr long still poorly known non-glacial period, featuring tundra with permafrost and probably birch forest. The 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. References Powell, R. D., and Cooper, J. M., 2002, A glacial sequence stratigraphic model for temperate, glaciated continental shelves, in Dowdeswell, J. A., and Cofaig, C. Ó. eds., Glacier-Influenced Sedimentation on High-Latitude Continental Margins: The Geological Society of London, London, Geological Society London, Special Publication v. 203, p. 215-244. Räsänen, M.E., Huitti, J.V., Bhattarai, S. Harvey, J. and Huttunen, S. 2015, The SE sector of the Middle

  7. Glacial geography and native North American languages

    NASA Astrophysics Data System (ADS)

    Rogers, Richard A.

    1985-01-01

    This study tests the hypothesis that the number and distribution of some native American languages may be related to ice-margin changes of the Wisconsin glaciation. The analysis indicated that the number of languages per unit area is much greater in unglaciated areas of the last glacial maximum than in glaciated areas. The pattern of languge overlap between land areas sequentially exposed during deglaciation appears to indicate the direction of movement of populations from the periphery toward the core of the area once covered by the Wisconsin Ice Sheet. The data strongly indicate that North America was inhabited prior to the Wisconsin glacial maximum, because glacial maximum conditions apparently influenced linguistic distributions. Evidence suggests that ancestral Eskimo-Aleut and Na-Dene speakers occupied the northwestern edge of the continental ice mass, and that ancestral Algonquian speakers were south of the ice mass during the Wisconsin glacial maximum (approximately 18,000 yr ago). These three linguistic groups were the principal ones to spreas into areas exposed by the recession of the Wisconsin ice.

  8. Late glacial aridity in southern Rocky Mountains

    SciTech Connect

    Davis, O.K.; Pitblado, B.L.

    1995-09-01

    While the slopes of the present-day Colorado Rocky Mountains are characterized by large stands of subalpine and montane conifers, the Rockies of the late glacial looked dramatically different. Specifically, pollen records suggest that during the late glacial, Artemisia and Gramineae predominated throughout the mountains of Colorado. At some point between 11,000 and 10,000 B.P., however, both Artemisia and grasses underwent a dramatic decline, which can be identified in virtually every pollen diagram produced for Colorado mountain sites, including Como Lake (Sangre de Cristo Mountains), Copley Lake and Splains; Gulch (near Crested Butte), Molas Lake (San Juan Mountains), and Redrock Lake (Boulder County). Moreover, the same pattern seems to hold for pollen spectra derived for areas adjacent to Colorado, including at sites in the Chuska Mountains of New Mexico and in eastern Wyoming. The implications of this consistent finding are compelling. The closest modem analogues to the Artemisia- and Gramineae-dominated late-glacial Colorado Rockies are found in the relatively arid northern Great Basin, which suggests that annual precipitation was much lower in the late-glacial southern Rocky Mountains than it was throughout the Holocene.

  9. Potential flood volume of Himalayan glacial lakes

    NASA Astrophysics Data System (ADS)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-01-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the risk of such flooding, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes flooded. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e. the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability because it requires no particular expertise to carry out. We calculated PFVs for more than 2000 Himalayan glacial lakes using the ASTER data. The distribution follows a power-law function, and we identified 49 lakes with PFVs of over 10 million m3 that require further detailed field investigations.

  10. Central Michigan University's Glacial Park: Instruction through Landscaping.

    ERIC Educational Resources Information Center

    Pape, Bruce; Francek, Mark A.

    1992-01-01

    Describes the creation of a glacial park on a university campus. Suggests that the park is a useful instructional resource that helps students relate classroom material to outdoor phenomena by visualizing and identifying glacial landforms, recognizing their spatial relationships, and understanding how glacial features originated. Offers advice for…

  11. 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.

  12. 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.

  13. Glacial-marine and glacial-lacustrine sedimentation in Sebago Lake, Maine: Locating the marine limit

    SciTech Connect

    Johnston, R.A.; Kelley, J.T. ); Belknap, D. . Dept. of Geological Sciences)

    1993-03-01

    The marine limit in Maine marks a sea-level highstand at approximately 13 ka. It was inferred to cross Sebago Lake near Frye Island by Thompson and Borns (1985) on the Surficial Geological Map of Maine, dividing the lake into a northern glacial-lacustrine basin and a southern glacial-marine basin. This study examined the accuracy of the mapped marine limit in the lake and the nature of glacial-lacustrine and glacial-marine facies in Maine. Recognition of the marine limit is usually based on mapped shorelines, glacial-marine deltas, and contacts with glacial-marine sediments. This study, in Maine's second largest lake, collected 100 kilometers of side-scan sonar images, 100 kilometers of seismic reflection profiles, and one core. Side-scan sonar records show coarse sand and gravel and extensive boulder fields at an inferred grounding-line position near Frye Island, where the marine limit was drawn. ORE Geopulse seismic reflection profiles reveal a basal draping unit similar to glacial-marine units identified offshore. Later channels cut more than 30 m into the basal stratified unit. In addition, till and a possible glacial-tectonic grounding-line feature were identified. Slumps and possible spring disruptions are found in several locations. The top unit is an onlapping ponded Holocene lacustrine unit. Total sediment is much thicker in the southern basin; the northern basin, >97 m deep, north of the marine limit appears to have been occupied by an ice block. Retrieved sediments include 12 meters of rhythmites. Microfossil identifications and dating will resolve the environments and time of deposition in this core.

  14. Potential flood volume of Himalayan glacial lakes

    NASA Astrophysics Data System (ADS)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-07-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

  15. Glacial history of a mid-altitude mountain massif: cartography and dating in the Chablais area (France, Switzerland)

    NASA Astrophysics Data System (ADS)

    Perret, A.; Reynard, E.; Delannoy, J.-J.

    2012-04-01

    The Chablais area, considered as one of the cradles of glaciology (de Charpentier, 1841; Morlot, 1859), has been studied for a long time but several questions still remain unresolved. This study aims to reconstruct the glacial history of the massif, in order to explain the glacial landforms, which constitute an important part of the local geomorphology. The study focuses on the last glacial cycle (OIS 5 - OIS 2). The area is primarily associated with the the Valais glacier, by several local glacial flows and, to a lesser extent, by the Giffre glacier. Its position at the interface of the important Valais glacial flow and less powerful local flows is a specificity of the study area, which implies several bifurcations, penetration of the main glacier into laterals valleys, damming situations, and different responses of the various ice bodies to climatic changes. The study is divided in four steps. (1) The first step was to carry out a wide bibliographic survey to identify the state of knowledge, especially in relation to areas previously poorly studied and areas that needed to be reconsidered given developments in dating methods. (2) Field surveys allowed us to complete observations and prepare local geomorphological maps (of glacial landforms and associated phenomena). (3) The third step was to assemble heterogeneous data (old and new maps, Digital Terrain Models, aerial photographies) in a GIS to establish maps of glacial stages. (4) Finally, the absolute and relative chronology of deglaciation (Guitter, 2003) was completed by cosmogenic nuclide dating. Results have allowed us to address the conditions of glacial landform deposition and evolution in a mid-altitude mountain range, and show the need to be prudent in comparing results of different dating methods. Our results suggest that the ages obtained are overall too young in regard to 10Be ages on the northern alpine foreland (Ivy-Ochs et al., 2004) and are in conflict with 14C dates obtained in the area

  16. Glacial/Interglacial changes of southwest Pacific intermediate- and deep-water circulation over the last 350,000 years

    NASA Astrophysics Data System (ADS)

    Ronge, Thomas; Tiedemann, Ralf; Prange, Matthias; Merkel, Ute; Kuhn, Gerhard; Lamy, Frank

    2015-04-01

    On glacial/interglacial timescales, Southern Ocean air-sea gas exchange is considered to be an important factor, driving the variability of atmospheric CO2 concentrations. To understand the role of oceanic variability in the global carbon cycle, it is necessary to reconstruct changes in deep- and intermediate-water circulation and chemistry of Southern Ocean water masses. In this context, our study aims on the reconstruction of glacial/interglacial changes in the vertical expansion of southwest Pacific Antarctic Intermediate Water. For our study, we compared isotope records (δ13C and δ18O) measured on the epibenthic foraminifera Cibicidoides wuellerstorfi from the Antarctic Intermediate Water and the Upper Circumpolar Deep Water (943 - 2066 m water depth) off New Zealand. We used two sediment cores from the Tasman Sea (MD06-2990 and MD06-2986), retrieved during R/V Marion Dufresne cruise MD152, and three sediment cores from the Bounty Trough east of New Zealand (MD97-2120, SO 213-82-1 and SO 213-84-1). Comparing these records, we can monitor changes in southwest Pacific water mass circulation over the past 350,000 years. Over this time period, we record a significant shoaling of the boundary between Antarctic Intermediate Water and Upper Circumpolar Deep Water during all glacial stages. We propose that freshwater input by melting sea ice into the glacial intermediate-water increased the buoyancy difference to underlying deep-waters, thus hampering the downward expansion of southwest Pacific Antarctic Intermediate Water during glacials. This interpretation is consistent with our modeling results, based on the Community Climate System model version 3, which also indicate a shoaling of glacial intermediate waters due to the input of meltwater. The glacial upward displacement of the water mass boundary significantly increased the vertical extent of circumpolar deep-waters, consequently extending the volume of the proposed glacial deep-water carbon pool.

  17. Glacial-interglacial Changes in Ocean Carbon Chemistry constrained by Boron Isotopes, Trace Elements, and Modelling

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Deep ocean carbon storage and release is commonly invoked to explain glacial-interglacial CO2 cycles, but records of the carbonate chemistry of the glacial ocean have, until recently, been scarce. Here we present new boron isotope (δ11B) and trace metal data from benthic foraminifera from a suite of 15 cores from the South Atlantic from depths ranging from 1500 to 4000 m. These records show distinct changes in the water column depth structure of these tracers between the last glacial maximum (LGM) and late Holocene. Comparison of these paired trace element and isotope ratios reveals new insights to the shared and individual controls on tracers including Li/Ca, Sr/Ca, U/Ca, Mg/Li and δ11B. We further examine these data using a recently developed tracer fields modelling approach (Lund et al. 2011). This has previously been applied to δ18O data to investigate changes in circulation at the LGM. Here we extend this method to non-conservative isotopic and trace elemental tracers, allowing us to constrain the roles of circulation, the biological pump of organic carbon and CaCO3, and carbonate compensation, in setting deep ocean carbon storage at the LGM. Lund, D. C., J. F. Adkins, and R. Ferrari (2011), Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing, Paleoceanography, 26, PA1213, doi:10.1029/2010PA001938.

  18. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum.

    PubMed

    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.

  19. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Conway, T. M.; Wolff, E. W.; Röthlisberger, R.; Mulvaney, R.; Elderfield, H. E.

    2015-07-01

    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.

  20. 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. PMID:27037513

  1. North Atlantic Deep Water Production during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-06-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

  2. North Atlantic Deep Water Production during the Last Glacial Maximum.

    PubMed

    Howe, Jacob N W; Piotrowski, Alexander M; Noble, Taryn L; Mulitza, Stefan; Chiessi, Cristiano M; Bayon, Germain

    2016-01-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ(13)C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters. PMID:27256826

  3. High-precision radiogenic strontium isotope measurements of the modern and glacial ocean: Limits on glacial-interglacial variations in continental weathering

    NASA Astrophysics Data System (ADS)

    Mokadem, Fatima; Parkinson, Ian J.; Hathorne, Ed C.; Anand, Pallavi; Allen, John T.; Burton, Kevin W.

    2015-04-01

    Existing strontium radiogenic isotope (87Sr/86Sr) measurements for foraminifera over Quaternary glacial-interglacial climate cycles provide no evidence for variations in the isotope composition of seawater at the ±9-13 ppm level of precision. However, modelling suggests that even within this level of uncertainty significant (up to 30%) variations in chemical weathering of the continents are permitted, accounting for the longer-term rise in 87Sr/86Sr over the Quaternary, and the apparent imbalance of Sr in the oceans at the present-day. This study presents very high-precision 87Sr/86Sr isotope data for modern seawater from each of the major oceans, and a glacial-interglacial seawater record preserved by planktic foraminifera from Ocean Drilling Program (ODP) Site 758 in the north-east Indian ocean. Strontium isotope 87Sr/86Sr measurements for modern seawater from the Atlantic, Pacific and Indian Oceans are indistinguishable from one another (87Sr/86Sr = 0.7091792 ± 0.0000021, n = 17) at the level of precision obtained in this study (±4.9 ppm 2σ). This observation is consistent with the very long residence time of Sr in seawater, and underpins the utility of this element for high precision isotope stratigraphy. The 87Sr/86Sr seawater record preserved by planktic foraminifera shows no resolvable glacial-interglacial variation (87Sr/86Sr = 0.7091784 ± 0.0000035, n = 10), and limits the response of seawater to variations in the chemical weathering flux and/or composition to ±4.9 ppm or less. Calculations suggest that a variation of ±12% around the steady-state weathering flux can be accommodated by the uncertainties obtained here. The new data cannot accommodate a short-term weathering pulse during de-glaciation, although a more a diffuse weathering pulse accompanying protracted ice retreat is permissible. However, these results still indicate that modern weathering fluxes are potentially higher than average over the Quaternary, and such variations through

  4. Glacial bed forms at Findelengletscher, Zermatt, Switzerland

    NASA Astrophysics Data System (ADS)

    Madella, Andrea; Nyffenegger, Franziska; Schlüchter, Christian

    2013-04-01

    The current glacier meltdown is increasingly unveiling the glacial bed forms produced by the most recent glacial advance of the 1980ies, such as flutes, mega-flutes and drumlins. This is a challenging opportunity to study these morphologies and the processes involved in their formation; in addition, our observation suggests a new question to be answered: why can't any of these features in units belonging to previous glacial advances be recognised? Similar forms could either have been washed away already, or never been built during LGM and since. The most beautiful and evident of the forms under investigation are the flutes and mega-flutes: elongated streamlined ridges of sediments either starting from an obstacle or just sticking out of the basal lodgement till. The way flutes have been initiated and then evolve is still partially unknown, due to their variety in shape, size and material. The glacial forefield at Findelengletscher under investigation deglaciated over the past two years, offers a well-preserved variety of such forms at all scales. Their material (basal lodgement till) is homogeneous and consistent all over the site, as well as their fabric. In addition, this silty sand shows a low plasticity index. These preliminary results support the idea that flutes build up very quickly during repeated seasonal advances in thin ice conditions with retreating trend (Coray, 2007), and that they could be equally easily and rapidly washed away. References: Coray Sandro (2007): Genesis and significance of flutes at Findelengletscher, Valais, Switzerland, Institute of Geological Sciences, University of Bern.

  5. Glacial curvilineations: gradual or catastrophic origin?

    NASA Astrophysics Data System (ADS)

    Clark, Chris; Livingstone, Stephen

    2016-04-01

    Glacial curvilineations (GCLs) are enigmatic landforms that have recently been discovered in Poland (Lesemann et al., 2010, 2014). They comprise parallel sets of sinuous ridges separated by troughs that are found in tunnel valleys and replicate the morphology and pattern of the valley sides. The sedimentology for some has been reported to indicate that the sediment composition relates to a pre-GCL phase. So far just one theory for their formation exists - erosion by longitudinal-vortices within high-energy subglacial meltwater flows (Lesemann et al., 2010). Here, we provide an alternative hypothesis for their formation developed from observations of GCLs found along the southern sector of the Laurentide Ice Sheet. In all cases GCLs were found associated with tunnel valley widenings or hollows and occur as distinct parallel sets that mimic each other in terms of nicks and cusps. Using analogies from tree-rings and coral growth we take such mimicry as indicating either incremental growth or development from a template over time. Although without a strong physical explanation we find it much less likely that a series of parallel water channels would maintain such strong mimicry. We instead suggest that subglacial thawing of frozen ground in association with discrete water bodies (tunnel valleys or subglacial lakes) resulted in retrogressive bank failure, possibly along a glide plane provided by a frozen surface. References: Lesemann, J.-E., Piotrowski, J. a, Wysota, W., 2010. "Glacial curvilineations": New glacial landforms produced by longitudinal vortices in subglacial meltwater flows. Geomorphology 120, 153-161. Lesemann, J.-E., Piotrowski, J. a, Wysota, W., 2014. Genesis of the "glacial curvilineation" landscape by meltwater processes under the former Scandinavian Ice Sheet, Poland. Sediment. Geol. 312, 1-18.

  6. Glacial-Interglacial Climate Changes Recorded by Debris Flow Grain Size, Eastern Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    D'Arcy, M. K.; Whittaker, A. C.; Roda Boluda, D. C.

    2015-12-01

    Uncertainties remain about the sensitivity of eroding landscapes to climate changes over a range of frequencies and amplitudes. Numerical models suggest that simple catchment-fan systems should be responsive to glacial-interglacial climate cycles, recording them in both sediment flux and the grain size distribution of their deposits. However these models are largely untested and the propagation of climatic signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological data from 8 debris flow fans in Owens Valley, eastern California. These fans have an exceptionally well-constrained depositional record spanning the last 120 ka, which we use to examine how sediment export has varied as a function of high-amplitude climate changes. We find a strong and sustained relationship between debris flow grain size and paleoclimate proxies over an entire glacial-interglacial cycle, with significantly coarser-grained deposits correlated with warm and dry conditions. Our data suggest these systems are highly reactive to climate forcing, with a short response timescale of <10 ka and no evidence of signal buffering, which we interpret to be driven by rapid sediment transfer from source to sink. We demonstrate that debris flow grain size follows an exponential relationship with temperature, coarsening at a rate of ~10 % per °C. Using this observation, and a known relationship between temperature and storm intensity, we propose that the climate signal recorded in these fan deposits captures changing storm intensity during the last glacial-interglacial cycle. This study offers a direct test of existing models of catchment-fan systems, confirming that glacial-interglacial climate changes can be clearly expressed in their grain size records. Our results also suggest that these debris flow deposits contain a high-resolution, testable record of past storm intensity, and that storminess is the primary control on their sedimentological

  7. Constraints on the glacial erosion rule

    NASA Astrophysics Data System (ADS)

    Herman, Frédéric

    2016-04-01

    It is thought that glaciers erode their underlying bedrock mainly through abrasion and quarrying. Theories predict erosion to be proportional to ice-sliding velocity raised to some power: ˙e = Kguls (1) where ė is the erosion rate, and Kg a proportionality constant and l an exponent. By implementing such a rule in numerical models, it has been possible to reproduce typical glacial landscape features, such as U-shape valleys, hanging valleys, glacial cirques or fjords. Although there have been great advances in the level of sophistication of these models, for example through the inclusion of high-order ice dynamics and subglacial hydrology, the proportionality constant, and the exponent have remained poorly constrained parameters. Recently, two independent studies in the Antarctic Peninsula and Patagonian Andes (Koppes et al., 2015) and the Franz Josef Glacier, New Zealand (Herman et al., 2015) simultaneously collected erosion rate and ice velocity data to find that erosion depends non-linearly on sliding velocity, and that the exponent on velocity is about 2. Such a nonlinear rule is appealing because it may, in part, explain the observed variations in erosion rates globally. Furthermore, an exponent about 2 closely matches theoretical predictions for abrasion. Although it is tempting to argue that abrasion is the dominant process for fast flowing glaciers like the Franz Josef Glacier, there is a clear need for more data and better quantification for the role of quarrying. Both studies also led to very similar values for the proportionality constant Kg. These new results therefore imply that glacial erosion processes might be better constrained than previously thought. Given that glacial velocity can nowadays be measured and modeled at an unprecedented resolution, it may potentially become possible to use glacial erosion models in a predictive manner. Herman, F. et al. "Erosion by an Alpine glacier." Science 350.6257 (2015): 193-195. Koppes, M. et al. "Observed

  8. Glacial Retreat and Associated Glacial Lake Hazards in the High Tien Shan

    NASA Astrophysics Data System (ADS)

    Smith, T. T.

    2013-12-01

    A number of studies have identified glacial retreat throughout the greater Himalayan region over the past few decades, but the Karakorum region remains an anomaly with large stagnating or advancing glaciers. The glacial behavior in the Tien Shan is still unclear, as few studies have investigated mass balances in the region. This study focuses on the highest peaks of the Tien Shan mountain range, in the region of Jengish Chokusu along the Kyrgyzstan-China-Kazakhstan border. In a first step, a 30-year time series of Landsat imagery (n=27) and ASTER imagery (n=10) was developed to track glacial growth and retreat in the region. Using a combination of spectral and topographic information, glacial outlines are automatically delineated. As several important glaciers in the study region contain medium to high levels of debris cover, our algorithm also improves upon current methods of detecting debris-covered glaciers by using topography, distance weighting methods, river networks, and additional spectral data. Linked to glacial retreat are glacial lake outburst floods (GLOFs) that have become increasingly common in High Mountain Asia over the last few decades. As glaciers retreat, their melt water is often trapped by weakly bonded moraines. These moraines have been known to fail due to overtopping caused by surge waves created by avalanches, rockslides, or glacial calving. A suite of studies throughout High Mountain Asia have used remotely-sensed data to monitor the formation and growth of glacial lakes. In a second step of the work, lake-area changes over the past 15 years were tracked monthly and seasonally using dense Landsat/ASTER coverage (n=30) with an automatic procedure based on spectral and topographic information. Previous work has identified GLOFs as a significant process for infrastructural damage in the southern Tien Shan/northern Pamir, as well as in the better studied Himalaya region. Lake identification and quantification of lake-growth rates is a valuable

  9. Sea Ice Induced Glacial/Deglacial Changes in Southern Ocean Surface Structure

    NASA Astrophysics Data System (ADS)

    Abelmann, A.; Gersonde, R.; Knorr, G.; Zhang, X.; Chapligin, B.; Maier, E.; Esper, O.; Lohmann, G.; Meyer, H.; Tiedemann, R.

    2014-12-01

    Glacial/deglacial sea ice variations in the Southern Ocean are suggested to be an important factor impacting ocean's surface structure and biological productivity and thus controlling glacial/interglacial changes in atmospheric CO2. However, the description of involved mechanisms and their implication on nutrient cycling and biological productivity remains incomplete. Isotope measurements on siliceous microorganisms (diatoms and radiolarians) provide a means of reconstructing past changes in nutrient utilization and surface water structure, thus provide information on past biological and physical properties crucial to better describe and model the mechanisms regulating glacial/interglacial variability in CO2 draw down in the Southern Ocean. As diatoms belong to the phytoplankton, they present a sea surface signal. Radiolarians, by contrast, are siliceous zooplankton distributed from surface to deep waters and their stable isotope signals can provide information about deeper water layers. Here, we specify Southern Ocean surface/subsurface contrasts using combined oxygen and silicon isotope measurements of diatom and radiolarian opal obtained from two cores gathered in the sea ice-free Antarctic Zone and northern Polar Front Zone of the Atlantic Southern Ocean. Our records point to a well established glacial spring/summer stratification induced by sea-ice melt. Numerical simulations corroborate this, but also suggest that seasonal stratification was variable with relatively deep mixing that occurred during fall/winter. We discuss various aspects of nutrient utilization in surface and subsurface waters with specific emphasis on the impact of sea ice variations on mixed layer depths and biological productivity during the last glacial and deglacial transition.

  10. 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.

  11. Multi-millennial-scale climatic variations in Antarctica and their relation with orbital changes for the last eight glacial periods

    NASA Astrophysics Data System (ADS)

    Kawamura, K.; Dome Fuji Ice Core Project Members

    2011-12-01

    Climatic variability on millennial timescales including abrupt changes and associated inter-hemispheric seesaw in the last glacial period have been well documented in a variety of paleoclimatic records. Moreover, there are evidences that very large inter-hemispheric seesaw occurred during the last deglaciation. However, the frequency and magnitude of such events in the older glacial periods and terminations are still poorly constrained. We present a 720,000-yr-long ice-core isotopic record measured along the second Dome Fuji ice core, East Antarctica. Stacking this record with other Antarctic isotopic records (Dome C, Vostok, EDML, Byrd, Talos Dome) allows us to clearly identify millennial-scale Antarctic warming events, which are found to have persisted over the last eight glacial cycles. Measurement of dust proxies in Marine Isotope Stage 16 in the Dome Fuji core (oldest glacial period in this core) shows that the millennial-scale variations of dust flux are negatively correlated with temperature proxy for all identified Antarctic warming events, suggesting reduced aridity in the dust source region, presumably Patagonia, during those times. This indicates that the identified events are at least hemispheric in extent. After applying a bandpass filter (4,000 - 17,000 yr periodicities) through the stacked isotope record to account for loss of resolution in the old (deep) part of the record, we identified large Antarctic warming event with a constant criteria. We find a positive relationship between repetition period of multi-millennial-scale events and Antarctic temperature, with an exception in glacial maxima where the repetition period is long. Together with accurate Antarctic chronology over the last three glacial cycles, the data suggests a role of climatic precession, presumably through northern hemisphere summer insolation affecting ice sheet mass, in making multi-millennial-scale events infrequent in the times of high precessional forcing in early parts of

  12. A high-resolution benthic stable-isotope record for the South Atlantic: Implications for orbital-scale changes in Late Paleocene-Early Eocene climate and carbon cycling

    NASA Astrophysics Data System (ADS)

    Littler, Kate; Röhl, Ursula; Westerhold, Thomas; Zachos, James C.

    2014-09-01

    The Late Paleocene and Early Eocene were characterized by warm greenhouse climates, punctuated by a series of rapid warming and ocean acidification events known as “hyperthermals”, thought to have been paced or triggered by orbital cycles. While these hyperthermals, such as the Paleocene Eocene Thermal Maximum (PETM), have been studied in great detail, the background low-amplitude cycles seen in carbon and oxygen-isotope records throughout the Paleocene-Eocene have hitherto not been resolved. Here we present a 7.7 million year (myr) long, high-resolution, orbitally-tuned, benthic foraminiferal stable-isotope record spanning the late Paleocene and early Eocene interval (∼52.5-60.5 Ma) from Ocean Drilling Program (ODP) Site 1262, South Atlantic. This high resolution (∼2-4 kyr) record allows the changing character and phasing of orbitally-modulated cycles to be studied in unprecedented detail as it reflects the long-term trend in carbon cycle and climate over this interval. The main pacemaker in the benthic oxygen-isotope (δ18O) and carbon-isotope (δ13C) records from ODP Site 1262, are the long (405 kyr) and short (100 kyr) eccentricity cycles, and precession (21 kyr). Obliquity (41 kyr) is almost absent throughout the section except for a few brief intervals where it has a relatively weak influence. During the course of the Early Paleogene record, and particularly in the latest Paleocene, eccentricity-paced negative carbon-isotope excursions (δ13C, CIEs) and coeval negative oxygen-isotope (δ18O) excursions correspond to low carbonate (CaCO3) and coarse fraction (%CF) values due to increased carbonate dissolution, suggesting shoaling of the lysocline and accompanied changes in the global exogenic carbon cycle. These negative CIEs and δ18O events coincide with maxima in eccentricity, with changes in δ18O leading changes in δ13C by ∼6 (±5) kyr in the 405-kyr band and by ∼3 (±1) kyr in the higher frequency 100-kyr band on average. However, these

  13. Frost weathering versus glacial grinding in the micromorphology of quartz sand grains: Processes and geological implications

    NASA Astrophysics Data System (ADS)

    Woronko, Barbara

    2016-04-01

    Micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments. Two processes dominate in the glacial environment, i.e., crushing and abrasion, or a combination thereof. Their effect is a wide range of microstructures on the surface of quartz grains, e.g., chattermarks, conchoidal fractures and multiple grooves. However, the periglacial environment also effectively modifies the surface of quartz grains. The active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction (e.g., breakage blocks or conchoidal fractures), as compared to deposits which are not affected by freeze-thaw cycles. However, only a few microstructures are found in both environments. At the same time, there are several processes in subglacial environments related to freeze-thaw cycles, e.g., regelation, congelation, basal adfreezing, and glaciohydraulic supercooling. Most likely, therefore, the role of the glacial environment in the destruction of quartz grains has been misinterpreted, and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge-to-edge contacts are erroneous.

  14. Glacial and periglacial geomorphology and its paleoclimatological significance in three North Ethiopian Mountains, including a detailed geomorphological map

    NASA Astrophysics Data System (ADS)

    Hendrickx, Hanne; Jacob, Miro; Frankl, Amaury; Nyssen, Jan

    2015-10-01

    Geomorphological investigations and detailed mapping of past and present (peri)glacial landforms are required in order to understand the impact of climatic anomalies. The Ethiopian Highlands show a great variety in past and contemporary climate, and therefore, in the occurrence of glacial and periglacial landforms. However, only a few mountain areas have been studied, and detailed geomorphological understanding is lacking. In order to allow a fine reconstruction of the impact of the past glacial cycle on the geomorphology, vegetation complexes, and temperature anomalies, a detailed geomorphological map of three mountain areas (Mt. Ferrah Amba, 12°51‧N 39°29‧E; Mt. Lib Amba, 12°04‧N 39°22‧; and Mt. Abuna Yosef, 12°08‧N 39°11‧E) was produced. In all three study areas, inactive solifluction lobes, presumably from the Last Glacial Maximum (LGM), were found. In the highest study area of Abuna Yosef, three sites were discovered bearing morainic material from small late Pleistocene glaciers. These marginal glaciers occurred below the modeled snowline and existed because of local topo-climatic conditions. Evidence of such Pleistocene avalanche-fed glaciers in Ethiopia (and Africa) has not been produced earlier. Current frost action is limited to frost cracks and small-scale patterned ground phenomena. The depression of the altitudinal belts of periglacial and glacial processes during the last cold period was assessed through periglacial and glacial landform mapping and comparisons with data from other mountain areas taking latitude into account. The depression of glacial and periglacial belts of approximately 600 m implies a temperature drop around 6 °C in the last cold period. This cooling is in line with temperature depressions elsewhere in East Africa during the LGM. This study serves as a case study for all the intermediate mountains (3500-4200 m) of the North Ethiopian highlands.

  15. A Model for Interpreting 10Be Basin-Wide Erosion Rates in Post-Glacial Environments, Northwest Scotland

    NASA Astrophysics Data System (ADS)

    Fame, M. L.; Owen, L. A.; Balco, G.; Spotila, J. A.

    2015-12-01

    Meaningful interpretation of in-situ cosmogenic 10Be basin-wide erosion rates in slowly eroding postglacial catchments is complicated because 10Be is inherited through shifts between glacial and fluvial regimes and ice shielding prevents 10Be production. Such environments do not attain isotopic and landscape steady state, conditions necessary for the current method of calculating basin-wide erosion rates. We propose an alternate set of assumptions, specific to postglacial regions, which make it possible to calculate basin-wide erosion rates in the post-glacial Highlands of NW Scotland. From 20 Scottish basins basin-wide 10Be concentrations range from 2.129 x 104 to 4.870 x 104 atoms/g qtz. Average 10Be concentrations from shallow till and bank deposits within the basins are 2.856 x 104 atoms/g qtz, similar to the basin-wide concentrations, whereas average bedrock concentrations in the basins are 1.747 x 105 atoms/g qtz. This suggests that during the postglacial time most active sediment is derived from reworked deposits rather then sub-aerially eroded bedrock. Therefore, we make the simplifying assumption that most bedrock erosion occurs during glaciation. A deeply buried till that has experienced no nuclide production since deglaciation has a 10Be concentration of 6.810 x 103 atoms/g qtz and allows us to estimate how much of the 10Be in basin-wide samples was produced since deglaciation. A glacial ice thickness of only 2 m would shield all 10Be production; therefore we assume that no 10Be production occurred during glacial periods and that all production occurs during interglacial periods. Using 100 ka as the approximate duration of a Pleistocene glacial-interglacial cycle, comprised of a 15 ka interglacial period and an 85 ka glacial period, and the aforementioned assumptions we have derived a numerical model to calculate basin-wide glacial erosion rates in NW Scotland.

  16. Stratification and Circulation of the Glacial Ocean: Reconstructing Watermass Geometry and Circulation with Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Piotrowski, A. M.; Goldstein, S. L.; Hemming, S. R.

    2004-12-01

    One of the most important debates in paleoclimate research is the link between ocean circulation and climate change. On glacial-interglacial timescales, global climate is driven by Milankovich orbital cycles, though the resulting insolation variations are small and require amplifying mechanisms. Changes in the strength of global "conveyor-belt" ocean circulation is one possible amplifying mechanism, and abrupt switches between circulation modes may have triggered rapid climate changes. Understanding the ocean-climate link has been difficult because nutrient-based proxies of ocean circulation disagree with each other. During the last glacial period, benthic foraminiferal carbon isotopes suggest substantially weaker North Atlantic Deep Water (NADW) formation and export, while benthic Cd/Ca indicate a strong flow of North Atlantic -sourced water at intermediate depths. Non-circulatory effects (including fractionation during calcite dissolution, changes in global carbon budget, air-sea gas equilibration, and porewater effects) are known to overprint these proxies, likely causing this discrepancy. Neodymium isotopes can resolve this disagreement because it does not share the same sources of error as nutrient-based proxies. We report Nd isotopes measured on Fe-Mn leaches from sites located throughout the South Atlantic. These sites range in depth from 2000 - 5000 mbsl, allowing a three-dimensional perspective of South Atlantic watermass geometry. The leachates have marine Sr isotopic composition. Coretop samples have Nd isotopic compositions which match overlying bottom waters. This coretop calibration is consistent with known vertical and horizontal geometry of NADW and Antarctic Bottom Water. Samples from the last glacial maximum show a coherent glacial-interglacial pattern of circulation change which is most simply interpreted as indicating a reduction in the amount of NADW reaching the South Atlantic. The relative contribution of NADW to the glacial South Atlantic

  17. North Atlantic Deep Water Production during the Last Glacial Maximum

    PubMed Central

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-01-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters. PMID:27256826

  18. Varied response of western Pacific hydrology to climate forcings over the last glacial period.

    PubMed

    Carolin, Stacy A; Cobb, Kim M; Adkins, Jess F; Clark, Brian; Conroy, Jessica L; Lejau, Syria; Malang, Jenny; Tuen, Andrew A

    2013-06-28

    Atmospheric deep convection in the west Pacific plays a key role in the global heat and moisture budgets, yet its response to orbital and abrupt climate change events is poorly resolved. Here, we present four absolutely dated, overlapping stalagmite oxygen isotopic records from northern Borneo that span most of the last glacial cycle. The records suggest that northern Borneo's hydroclimate shifted in phase with precessional forcing but was only weakly affected by glacial-interglacial changes in global climate boundary conditions. Regional convection likely decreased during Heinrich events, but other Northern Hemisphere abrupt climate change events are notably absent. The new records suggest that the deep tropical Pacific hydroclimate variability may have played an important role in shaping the global response to the largest abrupt climate change events.

  19. Varied response of western Pacific hydrology to climate forcings over the last glacial period.

    PubMed

    Carolin, Stacy A; Cobb, Kim M; Adkins, Jess F; Clark, Brian; Conroy, Jessica L; Lejau, Syria; Malang, Jenny; Tuen, Andrew A

    2013-06-28

    Atmospheric deep convection in the west Pacific plays a key role in the global heat and moisture budgets, yet its response to orbital and abrupt climate change events is poorly resolved. Here, we present four absolutely dated, overlapping stalagmite oxygen isotopic records from northern Borneo that span most of the last glacial cycle. The records suggest that northern Borneo's hydroclimate shifted in phase with precessional forcing but was only weakly affected by glacial-interglacial changes in global climate boundary conditions. Regional convection likely decreased during Heinrich events, but other Northern Hemisphere abrupt climate change events are notably absent. The new records suggest that the deep tropical Pacific hydroclimate variability may have played an important role in shaping the global response to the largest abrupt climate change events. PMID:23744779

  20. Fire in Ice: Glacial-Interglacial biomass burning in the NEEM ice core

    NASA Astrophysics Data System (ADS)

    Zennaro, Piero; Kehrwald, Natalie; Zangrando, Roberta; Gambaro, Andrea; Barbante, Carlo

    2014-05-01

    Earth is an intrinsically flammable planet. Fire is a key Earth system process with a crucial role in biogeochemical cycles, affecting carbon cycle mechanisms, land-surface properties, atmospheric chemistry, aerosols and human activities. However, human activities may have also altered biomass burning for thousands of years, thus influencing the climate system. We analyse the specific marker levoglucosan to reconstruct past fire events in ice cores. Levoglucosan (1,6-anhydro-β-D-glucopyranose) is an organic compound that can be only released during the pyrolysis of cellulose at temperatures > 300°C. Levoglucosan is a major fire product in the fine fraction of woody vegetation combustion, can be transported over regional to global distances, and is deposited on the Greenland ice sheet. The NEEM, Greenland ice core (77 27'N, 51 3'W, 2454 masl) documents past fire activity changes from the present back to the penultimate interglacial, the Eemian. Here we present a fire activity reconstruction from both North American and Eurasian sources over the last 120,000 yrs based on levoglucosan signatures in the NEEM ice core. Biomass burning significantly increased over the boreal Northern Hemisphere since the last glacial, resulting in a maximum between 1.5 and 3.5 kyr BP yet decreasing from ~2 kyr BP until the present. Major climate parameters alone cannot explain the observed trend and thus it is not possible to rule out the hypothesis of early anthropogenic influences on fire activity. Over millennial timescales, temperature influences Arctic ice sheet extension and vegetation distribution at Northern Hemisphere high latitudes and may have altered the distance between NEEM and available fuel loads. During the last Glacial, the combination of dry and cold climate conditions, together with low boreal insolation and decreased atmospheric carbon dioxide levels may have also limited the production of available biomass. Diminished boreal forest extension and the southward

  1. Glacial isostatic uplift of the European Alps

    NASA Astrophysics Data System (ADS)

    Mey, Juergen; Scherler, Dirk; Wickert, Andrew D.; Egholm, David L.; Tesauro, Magdala; Schildgen, Taylor F.; Strecker, Manfred R.

    2016-04-01

    Present-day vertical movements of the Earth's surface are mostly due to tectonic deformation, volcanic processes, and crustal loading/unloading. In tectonically stable regions of North America and Scandinavia, vertical movements are almost entirely attributable to glacial isostatic rebound after the melting of the Laurentide and Fennoscandian ice sheets. In contrast, the Pleistocene Alpine icecap grew on a younger mountain belt that formed by collision of the European and African plates, still subject to shortening. Therefore, measured uplift is potentially a composite signal of tectonic shortening and unloading after deglaciation and concomitant erosion. Deciphering the contributions of tectonics and crustal unloading to present-day uplift rates in formerly-glaciated mountain belts is a prerequisite to using uplift data to estimate the viscosity structure of the Earth's mantle, a key variable in geodynamics. We evaluate the post-LGM glacial-isostatic rebound of the Alps following a 4-tiered procedure. First, we estimated the thickness distribution of sedimentary valley fills to create a bedrock map of the entire mountain belt. Second, this map was used as topographic basis for the reconstruction of the Alpine icecap using a numerical ice-flow model. Third, we estimated the equilibrium deflection of the Alpine lithosphere, using the combined loads of ice and sediments with a variable effective elastic thickness. Finally, we used an exponential decay function to infer the residual deflection and the present-day uplift rate for a range of upper mantle viscosities. Our analysis shows that virtually all of the geodetically measured surface uplift in the Swiss and the Austrian Alps can be attributed to glacial unloading and redistribution of sediments, assuming an upper-mantle viscosity lower than that inferred for an old craton (e.g., Fennoscandia), but higher than that for a region with recent crustal thinning (e.g., Basin and Range province).

  2. Cyclic 100-ka (glacial-interglacial) migration of subseafloor redox zonation on the Peruvian shelf

    PubMed Central

    Contreras, Sergio; Meister, Patrick; Liu, Bo; Prieto-Mollar, Xavier; Hinrichs, Kai-Uwe; Khalili, Arzhang; Ferdelman, Timothy G.; Kuypers, Marcel M. M.; Jørgensen, Bo Barker

    2013-01-01

    The coupling of subseafloor microbial life to oceanographic and atmospheric conditions is poorly understood. We examined diagenetic imprints and lipid biomarkers of past subseafloor microbial activity to evaluate its response to glacial-interglacial cycles in a sedimentary section drilled on the Peruvian shelf (Ocean Drilling Program Leg 201, Site 1229). Multiple and distinct layers of diagenetic barite and dolomite, i.e., minerals that typically form at the sulfate−methane transition (SMT), occur at much shallower burial depth than the present SMT around 30 meters below seafloor. These shallow layers co-occur with peaks of 13C-depleted archaeol, a molecular fossil of anaerobic methane-oxidizing Archaea. Present-day, non-steady state distributions of dissolved sulfate also suggest that the SMT is highly sensitive to variations in organic carbon flux to the surface shelf sediments that may lead to shoaling of the SMT. Reaction-transport modeling substantiates our hypothesis that shallow SMTs occur in response to cyclic sediment deposition with a high organic carbon flux during interglacials and a low organic carbon flux during glacial stages. Long diffusion distances expectedly dampen the response of deeply buried microbial communities to changes in sediment deposition and other oceanographic drivers over relatively short geological time scales, e.g., glacial-interglacial periods. However, our study demonstrates how dynamically sediment biogeochemistry of the Peru Margin has responded to glacial-interglacial change and how these changes are now preserved in the geological record. Such changes in subsurface biogeochemical zonation need to be taken into account to assess the role of the subseafloor biosphere in global element and redox cycling. PMID:24145422

  3. 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). Ha

  4. 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 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).

  5. Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

    PubMed

    Worni, Raphael; Huggel, Christian; Stoffel, Markus

    2013-12-01

    Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions. PMID:23218457

  6. Glacial lakes in the Indian Himalayas--from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes.

    PubMed

    Worni, Raphael; Huggel, Christian; Stoffel, Markus

    2013-12-01

    Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the world, but comparably little attention has been given to these topics in the Indian Himalayas. In this study we present a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial lakes >0.01 km(2). Lakes were detected in the five states spanning the Indian Himalayas, and lake distribution pattern and lake characteristics were found to differ significantly between regions. Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were then selected for a detailed risk assessment. Lake outburst probability, potential outburst magnitudes and associated damage were evaluated on the basis of high-resolution satellite imagery, field assessments and through the use of a dynamic model. The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to present moderate risks to downstream villages, whereas the lake in Sikkim severely threatens downstream locations. At the study site in Sikkim, a dam breach could trigger drainage of ca. 16×10(6)m(3) water and generate maximum lake discharge of nearly 7000 m(3) s(-). The identification of critical glacial lakes in the Indian Himalayas and the detailed risk assessments at three specific sites allow prioritizing further investigations and help in the definition of risk reduction actions.

  7. Range persistence during the last glacial maximum: Carex macrocephala was not restricted to glacial refugia.

    PubMed

    King, Matthew G; Horning, Matthew E; Roalson, Eric H

    2009-10-01

    The distribution of many species inhabiting northwestern North America has been heavily influenced by the climatic changes during the late Pleistocene. Several studies have suggested that species were restricted to glacial refugia north and/or south of the continental ice sheet front. It is also hypothesized that the coast of northwestern North America could have been a prime location for glacial refugia because of the lowering of the eustatic sea level and the concomitant rise of the continental shelf because of tectonic rebound. Alternatively, some coastal species distributions and demographics may have been unaffected in the long-term by the last glacial maximum (LGM). We tested the glacial refugium hypothesis on an obligate coastal plant species, Carex macrocephala by sampling 600 individuals from 41 populations with 11 nuclear microsatellite loci and the rpL16 plastid intragenic spacer region. The microsatellite data sets suggest a low level of population differentiation with a standardized G'(ST) = 0.032 and inbreeding was high with an F = 0.969. The homogenization of the populations along the coast was supported by a principal coordinate analysis, amovas and samova analyses. Analyses using the rpL16 data set support the results of the microsatellite analyses, with a low F(ST) of 0.042. Coalescent and mismatch analyses using rpL16 suggest that C. macrocephala has not gone through a significant bottleneck within the past 100,000 years, although a much earlier population expansion was indicated by the mismatch analysis. Carex macrocephala exhibits the characteristics of metapopulation dynamics and on the basis of these results, we concluded that it was not restricted to glacial refugia during the LGM, but that it existed as a large metapopulation.

  8. 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

  9. 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

  10. 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

  11. Interhemispheric correlation of late pleistocene glacial events

    SciTech Connect

    Lowell, T.V.; Heusser, C.J.; Andersen, B.G.

    1995-09-15

    A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and {ge}33,500 carbon-14 years before present ({sup 14}C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000 {sup 14}C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720 {sup 14}C yr B.P., and at the beginning of the Younger Dryas at 11,050 {sup 14}C yr B.P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges. 51 refs., 3 figs., 1 tab.

  12. 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.

  13. Arctic ocean sediment texture and the Pleistocene climate cycle

    SciTech Connect

    Clark, D.L.; Morris, T.H.

    1985-01-01

    Arctic Ocean sediment texture accurately reflects the Plio-Pleistocene climate cycle. The precision of paleoclimate interpretation is improved when deglaciation is recognized as a distinct climate stage, overlapping both glacial and interglacial stages, and for the later Pleistocene, perhaps never completed. Oxygen isotope stratigraphy and foraminifera productivity are out of phase but can be understood in the context of the transitional nature of the glacial, deglacial and interglacial climate stages of the Arctic Ocean.

  14. 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…

  15. Light attenuation characteristics of glacially-fed lakes

    NASA Astrophysics Data System (ADS)

    Rose, Kevin C.; Hamilton, David P.; Williamson, Craig E.; McBride, Chris G.; Fischer, Janet M.; Olson, Mark H.; Saros, Jasmine E.; Allan, Mathew G.; Cabrol, Nathalie

    2014-07-01

    Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400-700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

  16. A high resolution record of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the glacial inception

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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 highly resolved record of δ13Catm before, during and after the Marine Isotope Stage 5.5 (155 000 to 105 000 yr BP). 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 an 0.4‰ offset 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 MIS 5.5 (120 000 yr BP). Based on our isotopic data this lag can be explained by terrestrial carbon release and carbonate compensation.

  17. Modeling today's sea-level contribution of glacial Antarctica

    NASA Astrophysics Data System (ADS)

    Albrecht, Torsten; Levermann, Anders

    2015-04-01

    The present dynamic state of the Antarctic Ice Sheet is mainly a product of past climate evolution, namely the history of advance and retreat during the last four glacial cycles. To this end, we need to account for this internal memory in order to better understand present changes and to project future contributions to sea-level rise, particularly with regard to anthropogenic climate change. This requires a fully dynamic model including ice-shelf dynamics as well as a continental scale treatment of the transition zone and a proper coupling to oceanic and atmospheric forcing data, all of this is included in the Parallel Ice Sheet Model (PISM). Instead of aiming at a best-guess simulation, we provide an ensemble of model simulations for 15km resolution that incorporates uncertainties from climate boundary conditions, internal process-modeling and ice parameter choices. With this approach we produce a broad ensemble of model-representations of the present day Antarctic ice sheet, that is at the same time well constrained by paleoclimatic data (e.g. LGM configuation) and present-day observations.

  18. How much do carbon isotope measurements constrain glacial ocean circulation?

    NASA Astrophysics Data System (ADS)

    Schmittner, A.; Mix, A. C.

    2010-12-01

    Reconstructions of the isotopic composition of dissolved inorganic carbon in seawater (d13DIC) are often interpreted as a ventilation or circulation proxy in paleoceanography. The modern deep-sea distribution of d13C in dissolved inorganic carbon (d13DIC) is highly anti-correlated to macronutrient (PO4, NO3) and apparent oxygen utilization (AOU) patterns due to fractionation during photosynthetic carbon uptake by phytoplankton. Nutrient and AOU concentrations in freshly ventilated North Atlantic Deep Water, for example, are low (d13DIC is high), whereas older water masses contain more respired nutrients and (isotopically light) carbon and have high AOU. However, d13DIC is also influenced by fractionation during air sea gas exchange - a process that decouples d13DIC from changes in nutrients and AOU. Moreover, biological fractionation is not constant but spatially and temporally variable. Here we are using a new global three-dimensional model of stable carbon isotope cycling that includes variable biological and air-sea gas exchange fractionation effects in conjunction with modern and glacial d13C observations to reconstruct ocean circulation patterns. Model versions with different rates and patterns of ocean circulation are produced and the resulting d13C patterns are compared to a compilation of measurements from ocean sediment cores in a probabilistic approach. The method allows us to quantify the uncertainty of deep ocean mass fluxes given available d13C observations/reconstructions and provide a quantitative test of the assumption of d13C as a ventilation proxy.

  19. Volcanic forcing and climate variations during the last glacial period

    NASA Astrophysics Data System (ADS)

    Flinders, A. F.

    2012-10-01

    Measurements of δ18O in the Greenland Ice Sheet Project 2 (GISP2) ice-core from Summit, Greenland, show repeated temporal variations associated with rapid warming events throughout the last glacial period of the Pleistocene-10-110 kya. The majority of these warming events are preceded in the ice-core record by an increased concentration of insoluble micro-particulate sulfate, indicative of increases in global volcanism. Wavelet analysis of ice-core and marine-sediment records show a repeated 5000-6000 yr periodicity in both volcanic SO4 and δ18O ice records, as well as a 5000-8000 yr cycle in the lithic concentration of ice-rafted debris, atmospheric CO2 concentration, and a database of late Quaternary volcanic eruptions. Increasing concentrations in atmospheric CO2 and CH4 initiated during periods of increased volcanism, peaking during a warm transition, reflect a volcanic-atmospheric-deglaciation feedback, regulated by meridional overturning current-shutdown related cooling.

  20. 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).

  1. Glacial-Holocene Deep Atlantic Variability

    NASA Astrophysics Data System (ADS)

    Oppo, D.; Curry, W. B.; Huang, K.; Gebbie, G.; Keigwin, L. D.

    2012-12-01

    Despite decades of research on deep ocean circulation during the Last Glacial Maximum (LGM) and deglaciation, many uncertainties remain. Even first order questions such as whether Antarctic Intermediate Water (AAIW) influenced the North Atlantic in the past are unresolved. Here, we update the glacial western Atlantic benthic δ13C transect of Curry and Oppo (2005) including new data from four cores recovered between 450 and 1100 m water depth, at AAIW depths in the western tropical North Atlantic. Low glacial values are consistent with the presence of AAIW. However, in the modern ocean, remineralization of organic matter drives δ13C values at these water depths lower than expected from their end-member composition. As this may have also been the case in the past, insights from more conservative tracers like δ18O of calcite, the air-sea exchange δ13C signature (δ13Cas), and neodymium isotopes (ɛNd) are important. We evaluate new and published relevant data and present a new δ13Cas transect for the LGM (updated from Marchitto and Broecker, 2006). A preliminary inversion of LGM data using an ocean pathways model (Gebbie and Huybers, 2010) will be presented. δ13C values in these same four western tropical North Atlantic cores during the Heinrich Event are also consistent with, but may not require, a contribution of AAIW. δ13C values decrease further following the Heinrich event and remain low throughout the deglaciation, during which the records exhibit coherent millennial-scale oscillations. For much of the deglaciation, δ13C values in these cores appear to be lower than values at other sites from similar depths in the western North and South Atlantic, suggestive of non-conservative behavior. The benthic records exhibit high amplitude δ18O variability, which may reflect vertical movement of isopynals, in association with variations in geostrophic flow (e.g. Lynch-Stieglitz et al., 2011). Our new deglacial data will be discussed in the broader context of

  2. Incursions of southern-sourced water into the deep North Atlantic during late Pliocene glacial intensification

    NASA Astrophysics Data System (ADS)

    Lang, David C.; Bailey, Ian; Wilson, Paul A.; Chalk, Thomas B.; Foster, Gavin L.; Gutjahr, Marcus

    2016-05-01

    The circulation and internal structure of the oceans exert a strong influence on Earth's climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss. Circulation change, particularly in the Atlantic Ocean, is widely suggested to have been instrumental in the intensification of Northern Hemisphere glaciation when large ice sheets first developed on North America and Eurasia during the late Pliocene, approximately 2.7 million years ago. Yet the mechanistic link and cause/effect relationship between ocean circulation and glaciation are debated. Here we present new records of North Atlantic Ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the Last Glacial to Holocene (35-5 thousand years ago) and the late Pliocene to earliest Pleistocene (3.3-2.4 million years ago). Our data show no secular change. Instead we document major southern-sourced water incursions into the deep North Atlantic during prominent glacials from 2.7 million years ago. Our results suggest that Atlantic circulation acts as a positive feedback rather than as an underlying cause of late Pliocene Northern Hemisphere glaciation. We propose that, once surface Southern Ocean stratification and/or extensive sea-ice cover was established, cold-stage expansions of southern-sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean, helping to increase the amplitude of glacial cycles.

  3. 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.

  4. 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.

  5. Vegetation of the Central Beringian Lowlands: Evidence of a Glacial Refugium Found in IODP Expedition 323 Sediment

    NASA Astrophysics Data System (ADS)

    Westbrook, R.; Fowell, S. J.; Bigelow, N. H.; VanLaningham, S.

    2011-12-01

    The lowlands of central Beringia may have acted as a glacial refugium for boreal vegetation, which expanded into eastern and western Beringia as climate changed and glaciers retreated. Persistence of trees, shrubs and mesic-adapted vegetation in the vicinity of the modern Bering Strait and Bering Sea Shelf could have presented a barrier to migrating fauna during Pleistocene glacial stages. These hypotheses have been difficult to test, because sampling has been restricted to lacustrine sediment and peat deposits accessible in eastern and western Beringia. Pollen analysis of cores from IODP Expedition 323 (Bering Sea Expedition) sites U1339 and U1343, on the edge of the Bering Sea Shelf, permits reconstruction of the terrestrial vegetation of adjacent south-central Beringia. Palynological assemblages extracted from sediment that accumulated during Marine Isotope Stages 2 and 6 are dominated by grass (Poaceae ≥ 15%) and sedge (Cyperaceae ≥ 20%). Spruce (Picea ≥ 5%), birch (Betula ≥ 10%) and alder (Alnus ≥ 5%) are also consistently present throughout glacial/interglacial cycles, suggesting that small populations of trees and shrubs remained in central Beringia during glacial maxima. These results support the refugium hypothesis. Although it is possible that some of the boreal plant pollen deposited during glacial stages is derived from interglacial sediment reworked by rivers flowing across the emergent shelf, we postulate that such sources only contribute about 1-5% of the total sediment found at these Bering slope sites. Thus we consider the palynological assemblages from IODP Expedition 323 a robust proxy for the glacial vegetation of central Beringia.

  6. The influence of glacial ice sheets on Atlantic meridional overturning circulation through atmospheric circulation change under glacial climate

    NASA Astrophysics Data System (ADS)

    Sherriff-Tadano, Sam; Abe-Ouchi, Ayako; Yoshimori, Masakazu; Oka, Akira; Chan, Wing-Le

    2016-04-01

    Recent coupled modeling studies have shown that the existence of the glacial ice sheets intensifies the Atlantic meridional overturning circulation (AMOC). Since this may play an important role in maintaining a strong AMOC over the last glacial period, which is suggested by recent reconstruction study, it is very important to understand the process by which glacial ice sheets intensify the AMOC. Here, a decoupled simulation is conducted to investigate the effect of wind change due to glacial ice sheets on the AMOC, the crucial region where wind modifies the AMOC and the mechanism, which remained elusive in previous studies. First, from atmospheric general circulation model (AGCM) experiments, the effect of glacial ice sheets on the surface wind is evaluated. Second, from ocean general circulation model (OGCM) experiments, the influence of the wind stress change on the AMOC is evaluated by applying only the changes in the surface wind as a boundary condition, while leaving surface heat and freshwater fluxes unchanged. Moreover, several sensitivity experiments are conducted. Using the AGCM, glacial ice sheets are applied individually. Using the OGCM, changes in the wind are applied regionally or at different magnitudes, ranging from the full glacial to modern levels. These experiments demonstrate that glacial ice sheets intensify the AMOC through an increase in the wind stress curl mainly at the North Atlantic mid-latitudes. This intensification is caused by the increased Ekman upwelling and gyre transport of salt while the change in sea ice transport works as a negative, though minor, feedback.

  7. Wind Stress Increases Glacial Atlantic Overturning

    NASA Astrophysics Data System (ADS)

    Muglia, J.; Schmittner, A.

    2015-12-01

    Previous Paleoclimate Model Intercomparison Project (PMIP) simulations of the Last Glacial Maximum (LGM) Atlantic Meridional Overturning Circulation (AMOC) showed ambiguous results on transports and structure. Here we analyze the most recent PMIP3 models, which show a consistent increase (on average by 41%) and deepening (580 m) of the AMOC for all models with respect to pre-industrial control (PIC) simulations (see Figure), in contrast to some reconstructions. Changes in wind stress alone lead to similar AMOC responses in a climate-ocean circulation model, suggesting that atmospheric circulation changes in the North Atlantic due to the presence of ice sheets are an important control in the PMIP3 models' LGM response. These results improve our understanding of the LGM AMOC's driving forces and are relevant for the evaluation of models that are used in the IPCC's Assessment Reports for future climate projections, as well as for the currently ongoing design of the next round of PMIP.

  8. Glacial terminations and the global water budget

    SciTech Connect

    Broecker, W.S. . Lamont-Doherty Geological Observatory)

    1992-01-01

    Evidence suggests that the last glacial period came to an abrupt close about 13,500 years ago. This evidence indicates: (1) that the melting of the North American ice sheet commenced abruptly at this time; (2) that surface temperatures in the northern Atlantic rose sharply at this time; (3) that surface water conditions in the Antarctic changed abruptly at this time; (4) that the salinity of the Red Sea dropped abruptly at this time; and (5) that accumulation rate of planktonic foraminifera in the South China Sea underwent an abrupt five-fold increase at this time. This project has been directed toward better developing and documenting our explanation for the abruptness of these changes. This project has supported investigation of several aspects of this hypothesis. We suggest that the Greenland climate changes are driven by oscillations in salt content which modulate the strength of the Atlantic's conveyor circulation.

  9. Characterization methods for fractured glacial tills

    USGS Publications Warehouse

    Haefner, R.J.

    2000-01-01

    This paper provides a literature review of methods successfully employed to characterize finegrained and fractured or unfractured glacial deposits. Descriptions and examples are given for four major categories of characterization methods: physical, hydraulic, chemical, and indirect. Characterization methods have evolved significantly within the past ten years; however, there still exists uncertainty about the reliability of individual characterization methods applied to till deposits. Therefore, a combination of methods is best, the choice of which depends on the objectives of the work. Sampling methods, sampling scales, and reporting methods are extremely important and should be considered when interpreting and comparing results between sites. Recognition of these issues is necessary to ensure that decisions regarding the transport of fluids in fractured tills are not based on the assumption that poorly permeable tills are always an inhibitor of subsurface flow.

  10. Understanding Antarctic Climate and Glacial History

    NASA Astrophysics Data System (ADS)

    DeConto, Rob; Escutia, Carlota

    2010-01-01

    First Antarctic Climate Evolution Symposium; Granada, Spain, 7-11 September 2009; Antarctic Climate Evolution (ACE; http://www.ace.scar.org), a scientific research project of the Scientific Committee on Antarctic Research and a core International Polar Year project, held its first international symposium in Spain in September 2009. ACE's mission is to facilitate the study of Antarctic climate and glacial history through integration of numerical modeling with geophysical and geological data. Nearly 200 international scientists from the fields of climate, ocean, and ice modeling joined geologists, geophysicists, and geochemists for 5 days of intense interaction. Oral sessions were plenary and were limited to allow time for poster viewing, discussion, and workshops (http://www.acegranada2009.com/).

  11. Dissolved organic matter export in glacial and non-glacial streams along the Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Hood, E. W.; Scott, D.; Jeffery, A.; Schreiber, S.; Heavner, M.; Edwards, R.; D'Amore, D. V.; Fellman, J.

    2009-12-01

    The Gulf of Alaska drainage basin contains more than 75,000 km2 of glaciers, many of which are rapidly thinning and receding. We are using a paired watershed approach to evaluate how changes in glacier ecosystems will impact the export dissolved organic matter (DOM) into the Gulf of Alaska. Our primary study watersheds, Lemon Creek and Montana Creek, are similar in size, bedrock lithology and elevation range and extend from near sea level to the margin or interior of the Juneau Icefield. Lemon Creek has a glacial coverage of ~60%, while Montana Creek is free of glacier ice. Our goal is to evaluate seasonal differences in the quantity, chemical character and reactivity of DOM being exported from these watersheds to downstream near-shore marine ecosystems. In addition, we are monitoring a variety of physical parameters that influence instream DOM metabolism in both watersheds. Our initial results from the 2009 runoff season indicate that concentrations of dissolved organic carbon (DOC) are substantially higher in the non-glacial watershed. However, fluorescence analyses indicate that DOM from the glacier watershed has a higher protein and lower humic material content compared to DOM from the non-glacial watershed. After the spring snowmelt season, physical parameters between the two watersheds diverged, with higher streamflow and turbidity as well as colder water temperatures in the glacial watershed. Although our previous yield calculations show significantly higher DOC fluxes from the forested watershed, our results here suggest that glacier watersheds may be an important source of labile carbon to the near shore marine ecosystem. The contrast in the physical habitat between the two rivers (e.g glacier stream = cold, low light penetration, unstable substrate) supports the hypothesis that that in-stream DOM processing is limited within glacier dominated rivers, therefore delivering a higher percentage of labile DOM downstream.

  12. Late Glacial lakes - uniform or contrasting ecosystems?

    NASA Astrophysics Data System (ADS)

    Zawiska, Izabela; Rzodkiewicz, Monika; Noryśkiewicz, Agnieszka M.; Obremska, Milena; Ott, Florian; Kramkowski, Mateusz; Słowiński, Michał; Błaszkiewicz, Mirosław; Brauer, Achim

    2015-04-01

    Climate changes are one of the most investigated topic in paleolimnology. The Late Glacial and Early Holocene time are specially interesting as than most abrupt changes happened. Lake sediments are known to be great source of information of the past environments. They are functioning as natural archives because in them preserve animal and plants remains. In this study we investigated three cores of the biogenic sediments from the lakes located in close vicinity in Tuchola Forest (Northern Poland): paleolake Trzechowskie, Lake Czechowskie-deepest part and Lake Czechowskie-bay. We made Cladocera, diatom and pollen analysis, the chronology was determined by varve counting, Laacher See Tephra (12,880 yrs BP) and 14C dating. The aim of our research was to find out the response of zooplankton, phytoplankton, lake and catchment vegetation to abrupt climate changes. We were interested in similarities and differences between those three locations in response of entire communities but also species composition. The preliminary results revealed that the Cladocera, diatoms and plants communities were sensitive to climatic shifts and it is well shown in the results of ordination method (PCA). However in the Cladocera and diatoms assemblages, which reflect well lake environment conditions, the dominant species and total number of species present, were different in all three locations. Especially great difference was noted between paleolake Trzechowskie and Lake Czechowskie (core from the deepest part). The results of our research shows that in Late Glacial time landscape in Lake Czechowskie region (Tuchola Forest, Northern Poland) had mosaic character. Local factors such as relief, edaphic conditions strongly modified type of vegetation and in close vicinity existed lakes that had very diverse environments.

  13. Numerical simulation of Glacial Isostatic Adjustment

    NASA Astrophysics Data System (ADS)

    Miglio, E.

    2015-12-01

    In the Earth's crust, stress can be subdivided into tectonic background stress, overburden pressure, and pore-fluid pressure. The superposition of the first two and the variation of the third part are key factors in controlling movement along faults. Furthermore, stresses due to sedimentation and erosion contribute to the total stress field. In deglaciated regions, an additional stress must be considered: the rebound stress, which is related to rebounding of the crust and mantle after deglaciation. During the growth of a continental ice sheet, the lithosphere under the iceload is deformed and the removal of the ice load during deglaciation initiates a rebound process. The uplift is well known in formerly glaciated areas, e.g.North America and Scandinavia, and in currently deglaciating areas, e.g.Alaska, Antarctica, and Greenland. The whole process of subsiding and uplifting during the growth and melting of an iceload and all related phenomena is known as glacial isostatic adjustment. During the process of glaciation, the surface of the lithosphere is depressed underneath the ice load and compressional flexural stresses are induced in the upper lithosphere, whereas the bottom of the lithosphere experiences extensional flexural stresses; an additional vertical stress due to the ice load is present and it decreases to zero during deglaciation. During rebound, flexural stresses relax slowly. These stresses are able to change the original stress directions and regime.In this work we aim to study the effect of the GIA process in the context of petroleum engineering. The main aspect we will focus on is the mathematical and numerical modeling of the GIA including thermal effects. We plan also to include a preliminary study of the effect of the glacial erosion. All these phenomena are of paramount importance in petroleum engineering: for example some reservoir have been depleted due to tilting caused by both GIA, erosion and thermal effects.

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

    DOE PAGES

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, Dmitry; Zhang, Kai

    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

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

    SciTech Connect

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, Dmitry; Zhang, Kai

    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, 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

  16. A simple metabolic model of glacial-interglacial energy supply to the upper ocean

    NASA Astrophysics Data System (ADS)

    Pelegrí, J. L.; Olivella, R.; García-Olivares, A.

    2011-03-01

    We use a simple two-state two-box ocean to simulate the CO2 signal during the last four glacial-interglacial transitions in the earth system. The model is inspired by the similarity in spatial organization and temporal transition patterns between the earth and other complex systems, such as mammals. The comparison identifies the earth's metabolic rate with net autotrophic primary production in the upper ocean, sustained through new inorganic carbon and nutrients advected from the deep ocean and organic matter remineralized within the upper ocean. We view the glacial-interglacial transition as a switch of the upper ocean from a basal to an enhanced metabolic state, with energy supply initially relying on the remineralization of the local organic sources and the eventual steady state resulting from the increased advective supply of inorganic deep sources. During the interglacial-glacial transition the opposite occurs, with an initial excess of advective supply and primary production that allows the replenishment of the upper-ocean organic storages. We set the relative change in energy supply from the CO2 signal and use genetic algorithms to explore the sensitivity of the model output to both the basal recirculation rate and the intensity-timing of the maximum recirculation rate. The model is capable of reproducing quite well the long-term oscillations, as shown by correlations with observations typically about 0.8. The dominant time scale for each cycle ranges between about 40 and 45 kyr, close to the 41 kyr average obliquity astronomical period, and the deep-ocean recirculation rate increases between one and two orders of magnitude from glacial to interglacial periods.

  17. 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

  18. Glacial thermohaline circulation and climate: Forcing from the north or south?

    NASA Astrophysics Data System (ADS)

    Liu, Z. Y.

    2006-03-01

    Based on the evidence available from both observations and model simulations, the author proposes a view that may provide a unified interpretation of the North Atlantic thermohaline variability. Because of the slow response time of the Southern Ocean (millennia) and the relatively faster response time of the North Atlantic (centuries), the North Atlantic thermohaline circulation is controlled predominantly by the climate forcing over the Southern Ocean at the long glacial cycle timescales, but by the North Atlantic climate forcing at the short millennial timescales.

  19. Thermochemical cycles

    NASA Technical Reports Server (NTRS)

    Funk, J. E.; Soliman, M. A.; Carty, R. H.; Conger, W. L.; Cox, K. E.; Lawson, D.

    1975-01-01

    The thermochemical production of hydrogen is described along with the HYDRGN computer program which attempts to rate the various thermochemical cycles. Specific thermochemical cycles discussed include: iron sulfur cycle; iron chloride cycle; and hybrid sulfuric acid cycle.

  20. Carbon-cycle disturbances and environmental change preceding the end-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Ruhl, M.; Ullmann, C. V.; Mette, W.; Korte, C.

    2012-04-01

    The end-Triassic mass extinction [~201.3 Ma], marked by marine and terrestrial ecosystem collapse and global marine biodiversity loss, coincides with the onset of extensive volcanic activity and emplacement of the Central Atlantic Magmatic Province (CAMP). Massive and rapid greenhouse gas release from basalts, subsurface organic rich strata and ocean-floor clathrates, had a profound impact on the global exogenic carbon cycle and caused dramatically increased atmospheric pCO2 values. A recent study however suggests global carbon cycle disturbance already (possibly ~100 kyr) before the end-Triassic mass extinction. 13C depleted atmospheric carbon injection at this event may have resulted from Late Triassic dike and sill intrusions possibly releasing thermogenic methane from subsurface organic-rich sediments. We now studied an extended, up to 1 million year long, Late Triassic marine sedimentary record from the western Tethian Eiberg basin (Northern Calcareous Alps, Austria). Sediments were deposited in the deepest part of the Eiberg basin (very close to the base Jurassic Global Stratotype Section and Point at Kuhjoch). High-resolution δ13CTOC, δ13CCARB-Bulk and δ13CCARB-Brachiopods from this record show distinct 1-2‰ δ13C negative excursions throughout the latest Triassic. This suggests disturbance of the global exogenic carbon cycle already long before the end-Triassic mass extinction. Regular alternations between (laminated) black-shales and carbonate deposition also indicate periodic changes in the palaeo-environment. Variations in the δ18OCARB record, coinciding with δ13C negative excursions, suggest climatic warming. But, distinct negative shifts may also indicate increased fresh-water input along the upper-Triassic western Tethys continental margin. Volcanic activity and palaeo-environmental change occurring already before the end-Triassic mass extinction, may have progressively weakened marine ecosystems, ultimately leading to large-scale marine

  1. High-resolution Geophysical Mapping of Submarine Glacial Landforms

    NASA Astrophysics Data System (ADS)

    Jakobsson, M.; Dowdeswell, J. A.; Canals, M.; Todd, B. J.; Dowdeswell, E. K.; Hogan, K. A.; Mayer, L. A.

    2014-12-01

    Glacial landforms are generated from the activity of glaciers and display spatial dimensions ranging from below one meter up to tens of kilometers. Glacial landforms are used as diagnostic features of past activity of ice sheets and glaciers; they are specifically important in the field of palaeoglaciology. Mapping of submarine glacial landforms is largely dependent on geophysical survey methods capable of imaging the seafloor and sub-bottom through the water column. Full "global" seafloor mapping coverage, equivalent to what exists for land elevation, is to-date only achieved by the powerful method of deriving bathymetry from altimeters on satellites like GEOSAT and ERS-1. The lateral resolution of satellite derived bathymetry is, however, limited by the footprint of the satellite and the need to average out local wave and wind effects resulting in values of around 15 km. Consequently, mapping submarine glacial landforms requires for the most part higher resolution than is achievable by satellite derived bathymetry. The most widely-used methods for mapping submarine glacial landforms are based on echo-sounding principles. This presentation shows how the evolution of marine geophysical mapping techniques, in particular the advent of side-scan and multibeam bathymetric sonars, has made it possible to study submarine glacial landforms in unprecedented detail. Examples are shown from the Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient, which will be published in late 2015 in the Memoir Series of the Geological Society of London.

  2. Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Margold, Martin; Jansen, John D.; Gurinov, Artem L.; Codilean, Alexandru T.; Fink, David; Preusser, Frank; Reznichenko, Natalya V.; Mifsud, Charles

    2016-01-01

    Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic 10Be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.

  3. Glacial and periglacial buzzsaws: fitting mechanisms to metaphors

    NASA Astrophysics Data System (ADS)

    Hall, Adrian M.; Kleman, Johan

    2014-03-01

    The buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and, on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down.

  4. 500,000 years of vegetation change in western tropical Africa

    NASA Astrophysics Data System (ADS)

    Miller, C. S.; Gosling, W. D.; Shanahan, T. M.; Coe, A. L.

    2012-12-01

    The Earth has experienced four, orbitally paced, full glacial-interglacial cycles over the last 500 kyr which have resulted in many terrestrial ecosystems experiencing significant changes in their distribution and composition. Sediment cores recovered from Lake Bosumtwi (Ghana, Africa) drilled as part of the ICDP Lake Bosumtwi Drilling Project in 2004 provide the first continental record of past environmental change in West Africa over the last 500 kyr, capturing the four glacial-interglacial cycles. Here we present a new 500 kyr pollen and δ15N isotope record from Lake Bosumtwi. Fossil pollen assemblages reveal dynamic vegetation change through the last 500 kyr, which can be broadly characterized as indicative of biome shifts between savannah and woodland. Savannah formations are heavily dominated by grass (Poaceae) pollen (>40%) typically associated with Cyperaceae and δ15N values greater than 10‰. Woodland formations are complex but fall into two main types, those associated with charcoal indicating frequent fires and those without. The woodland pollen spectra associated with high charcoal abundances are typically dominated by Celtis, Moraceae/Urticaceae and Melastomataceae/Combretaceae; while those without charcoal indicate a more diverse rainforest flora. δ15N values in all the woodland types are typically less than 7‰. Over the last 500 kyr vegetation change around Lake Bosumtwi has a positive relationship with the 100-kyr (eccentricity) and the 41-kyr (obliquity) orbital cycles. Interglacial periods are dominated by woodland systems and glacials by savannah. In addition to the glacial-interglacial cycles, periods of prolonged savannah stability occur from 113-76 kyr and extreme aridity from 76-64 kyr. The 100-kyr and 41-kyr periodicity from Lake Bosumtwi are likely to be the result of changes in glacial boundary conditions, with warmer north Atlantic SSTs occurring during interglacial periods.

  5. Glacial Erosion Rates from Bayesian Inversion of Cosmogenic Nuclide Concentrations in a Bedrock Core, Streaked Mtn., ME

    NASA Astrophysics Data System (ADS)

    Ploskey, Z. T.; Stone, J. O.

    2014-12-01

    Glacial erosion is an important source of sediment and could be an important coupling to glacier and ice sheet models that track sediment. However, glacial erosion is difficult to quantify, and models of glacial erosion can benefit from independent erosion rate estimates. Here we present the results of a Bayesian Markov chain Monte Carlo (MCMC) inversion of a cosmogenic nuclide (CN) geomorphic model for glacial erosion rates on a bedrock landform formerly eroded beneath the Laurentide ice sheet. The CN 10Be was measured in quartz to 8 m depth in a bedrock core from the summit of Streaked Mountain, ME. The accumulation of 10Be was modeled over multiple glacial cycles of alternating exposure and glacial erosion. This model was invertedfor glacial erosion rates and burial history using MCMC algorithms implemented in PyMC (Patil et al., 2010). This Bayesian approach allows us to incorporate prior constraints on ice cover history, including oxygen isotope records and radiometric dates, which is otherwise difficult to differentiate from erosion in rapidly eroding areas. We compare these results to depth profile and surface CN measurements elsewhere in Maine (Ploskey and Stone, 2013).The forward model of CN production used in the inversion is part of Cosmogenic (github.com/cosmolab/cosmogenic), an open-source Python-based software library we developed for modeling the growth and decay of in-situ CN inventories in rock during geomorphic evolution. It includes calibrated production rates for 10Be and 26Al in quartz and 36Cl in K-feldspar by both neutrons and muons, with more isotopic production pathways and material targets to be added in the future. Production rates are scaled to the site altitude and latitude using modular scaling schemes. Cosmogenic includes a variety of functions representing common geomorphic histories, and can be used to model any arbitrary exposure, erosion and burial history that can be defined as Python function.ReferencesPatil, A., D. Huard and C

  6. Late Ordovician (Ashgillian) glacial deposits in southern Jordan

    NASA Astrophysics Data System (ADS)

    Turner, Brian R.; Makhlouf, Issa M.; Armstrong, Howard A.

    2005-11-01

    The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near the top of this palaeovalley-fill contains intersecting glacial striations aligned E-W and NW-SE. The upper palaeovalley-fill comprises glaciofluvial and marine sandstones, incised into the lower palaeovalley or, where this is absent, into the Tubeiliyat Formation. Southern Jordan lay close to the margin of a Late Ordovician terrestrial ice sheet in Northwest Saudi Arabia, characterised by two major ice advances. These are correlated with the lower and upper palaeovalleys in southern Jordan, interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest. Thus, four ice advances are now recorded from the Late Ordovician glacial record of southern Jordan. Disturbed and deformed green sandstones beneath the upper palaeovalley-fill in the Jebel Ammar area, are confined to the margins of the Hutayya graben, and have been interpreted as structureless glacial loessite or glacial rock flour. Petrographic and textural analyses of the deformed sandstones, their mapped lateral transition into undeformed Tubeiliyat marine sandstones away from the fault zone, and the presence of similar sedimentary structures to those in the pre-glacial marine Tubeiliyat Formation suggest that they are a locally deformed facies equivalent of the Tubeiliyat, not part of the younger glacial deposits. Deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre-existing faults, previously weakened by epeirogenesis, triggering sediment

  7. Probability of moraine survival in a succession of glacial advances.

    USGS Publications Warehouse

    Gibbons, A.B.; Megeath, J.D.; Pierce, K.L.

    1984-01-01

    Emplacement of glacial moraines normally results in obliteration of older moraines deposited by less extensive glacial advances, a process we call 'obliterative overlap'. Assuming randomness and obliterative overlap, after 10 glacial episodes the most likely number of surviving moraines is only three. The record of the Pleistocene is in agreement with the probability analysis: the 10 glaciations during the past 0.9 Myr inferred from the deep-sea record resulted in moraine sequences in which only two or three different-aged moraine belts can generally be distinguished. -from Authors

  8. Isotopic evidence for reduced productivity in the glacial Southern Ocean

    SciTech Connect

    Shemesh, A. ); Macko, S.A. ); Charles, C.D. ); Rau, G.H. )

    1993-10-15

    Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.

  9. 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.

  10. 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, Rob; Schuster, Paul F.; Raymond, Peter A.

    2016-01-01

    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.

  11. Far-flung moraines: Exploring the feedback of glacial erosion on the evolution of glacier length

    NASA Astrophysics Data System (ADS)

    Anderson, Robert S.; Dühnforth, Miriam; Colgan, William; Anderson, Leif

    2012-12-01

    Over many glacial cycles, the glacial erosion of alpine valleys can be sufficient to reduce the length of glaciers in the most recent cycles. We document field cases illustrative of this erosional feedback and model the long-term evolution of glacier lengths analytically and numerically. The general feature we target is a moraine deposited well beyond the last glacial maximum (LGM) limit, which we refer to as a "far-flung" moraine. Firstly, we assemble published observations to illustrate that far-flung moraines are documented around the world. The observations suggest that the downvalley distance to such far-flung moraines can exceed the distance to LGM moraines by up to twofold. Secondly, we address the problem analytically, making several simplifying assumptions, to demonstrate that glacier length scales linearly with erosion depth. Finally, we employ a numerical model to test the analytical solution. This 1D (depth-integrated) flowline model includes: (i) a depth-averaged longitudinal coupling stress approximation, (ii) prescribed winter and summer surface mass balance profiles, (iii) evolving ice temperature calculated via the conventional heat equation, and (iv) glacier sliding velocity parameterized as a function of basal ice temperature and spatially and temporally variable prescribed flotation fraction. The simulated alpine landscape is modified through the competing processes of glacier erosion, which is dependent on glacier sliding velocity and prescribed bedrock erodibility, and prescribed uplift rate. The climate controlling surface mass balance is prescribed by time series of air temperature and snowfall approximated by the sum of two sinusoidal cycles. The recurrence statistics of these prescribed climate drivers closely match those of the marine isotopic record; hence the prescribed climate drivers faithfully mimic observed long-term climate drivers. Consistent with earlier landscape evolution studies, we find that the primary effect of repeated

  12. What happened to the coal forests during Pennsylvanian glacial phases?

    SciTech Connect

    Falcon-Lang, H.J.; Dimichele, W.A.

    2010-09-15

    Sequence stratigraphic analysis of Pennsylvanian coal-bearing strata suggests that glacial-interglacial fluctuations at high latitudes drove cyclic changes in tropical biomes. A literature review of plant assemblages in this paleoclimatic context suggests that coal forests dominated during humid interglacial phases, but were replaced by seasonally dry vegetation during glacial phases. After each glacial event, coal forests reassembled with largely the same species composition. This remarkable stasis implies that coal-forest refugia existed across the equatorial landscape during glacial phases, expanding to repopulate lowlands during and following deglaciation. One possibility is that refugia comprised small pockets of wetland forest strung out along valleys at some sites, but data are currently insufficient to test this hypothesis. The model presented here, if accepted, dramatically alters our understanding of the coal forests and helps explain aspects of their dynamics.

  13. The taphonomy of human remains in a glacial environment.

    PubMed

    Pilloud, Marin A; Megyesi, Mary S; Truffer, Martin; Congram, Derek

    2016-04-01

    A glacial environment is a unique setting that can alter human remains in characteristic ways. This study describes glacial dynamics and how glaciers can be understood as taphonomic agents. Using a case study of human remains recovered from Colony Glacier, Alaska, a glacial taphonomic signature is outlined that includes: (1) movement of remains, (2) dispersal of remains, (3) altered bone margins, (4) splitting of skeletal elements, and (5) extensive soft tissue preservation and adipocere formation. As global glacier area is declining in the current climate, there is the potential for more materials of archaeological and medicolegal significance to be exposed. It is therefore important for the forensic anthropologist to have an idea of the taphonomy in this setting and to be able to differentiate glacial effects from other taphonomic agents. PMID:26917542

  14. 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

  15. Enigmatic sediment ridges in the German Bight - glacial vs post-glacial morphologies?

    NASA Astrophysics Data System (ADS)

    Unnithan, Vikram; Pio Rossi, Angelo; Praeg, Daniel

    2014-05-01

    The German Wadden Sea extends over 1000 km from the Dutch coast to that of Sweden and consists of a long chain of barrier islands and ephemeral sand banks punctuated by estuaries and rivers. The sedimentary environment is currently shaped and characterised by storm surges, high tidal and wave energy levels. However, this part of the North Sea has been repeatedly covered by continental ice sheets, and it remains unclear how glacial to interglacial sedimentary processes may have influenced seabed morphology in the region. The study area is situated approximately 70 km north of Cuxhaven, and 5 km due east of the islands of Helgoland and Dune. It covers an approximate area of 5 km square with water depths ranging from 50 m in the south to about 20 m in the north. High resolution multibeam (Simrad EM710) and parametric echosounder (Innomar SES2000) data were acquired during graduate and undergraduate teaching excursions on the RV Heincke in Spring 2010 (HE-324) and 2011 (HE-349). The seabed swath bathymetric data reveal distinctive linear seabed ridges. The ridges trend NNW-SSE, are 1-5 m in height, have wavelengths on the order of 100 m and crest lengths ranging from 100-2500 m. The ridge crests are broadly anastomosing. They bifurcate towards the north to form more subdued structures, while they converge and disappear to the south. Profiles across the ridges show an asymmetric structure, with steeper slopes trending west in the western part of the study area but trending east in the eastern part. These enigmatic sedimentary structures have not been previously mapped in the Wadden Sea, and their origin remains uncertain. Possible interpretations to be tested include sub-crop structural control on seabed morphology, relict glacial or glaciofluvial landforms and post-glacial marine bedforms linked to processes of sediment redistribution.

  16. Greenland ice cores constrain glacial atmospheric fluxes of phosphorus

    NASA Astrophysics Data System (ADS)

    Kjær, Helle Astrid; Dallmayr, Remi; Gabrieli, Jacopo; Goto-Azuma, Kumiko; Hirabayashi, Motohiro; Svensson, Anders; Vallelonga, Paul

    2015-10-01

    Phosphorus is a limiting nutrient for primary productivity, but little is known about past atmospheric fluxes to the open ocean. In this study, phosphate and phosphorus concentrations have been determined in the North Greenland Eemian Ice Drilling Project ice core for selected periods during the last glacial. Phosphate was determined continuously by using a molybdenum blue spectroscopic absorption method and discretely using an ion chromatograph. Total P was determined discretely using an inductively coupled plasma sector field mass spectrometer. For the last glacial period, we found concentrations of between 3 and 62 nM PO43- and 7 and 929 nM P. We find glacial atmospheric fluxes of phosphorus to Greenland were 4 to 11 times higher than in the past century, with the highest input during the cold glacial stadials (GS). Changes in P and PO43- fluxes between mild glacial interstadials (GI) and GS correlate positively with dust variability. The soluble fraction of P is larger in the mild GIs as compared to the dust-rich GSs. For the very high phosphate and phosphorus loads during the Last Glacial Maximum, the relationship between phosphate and dust is weaker than in GIs and milder GSs, suggesting either secondary phosphate sources or multiple dust sources. Based on crustal abundances, we find that dust inputs are sufficient to account for all P deposited during all periods investigated except the Last Glacial Maximum. During the glacial, sea salts contributed 10-3 nM P, while land biogenic emissions were a minor source of P.

  17. Oceanographic gradients and seabird prey community dynamics in glacial fjords

    USGS Publications Warehouse

    Arimitsu, Mayumi L.; Piatt, John F.; Madison, Erica N.; Conaway, Jeff; Hillgruber, N.

    2012-01-01

    Glacial fjord habitats are undergoing rapid change as a result of contemporary global warming, yet little is known about how glaciers influence marine ecosystems. These ecosystems provide important feeding, breeding and rearing grounds for a wide variety of marine organisms, including seabirds of management concern. To characterize ocean conditions and marine food webs near tidewater glaciers, we conducted monthly surveys of oceanographic variables, plankton, fish and seabirds in Kenai Fjords, Alaska, from June to August of 2007 and 2008. We also measured tidal current velocities near glacial features. We found high sediment load from glacial river runoff played a major role in structuring the fjord marine ecosystem. Submerged moraines (sills) isolated cool, fresh, stratified and silt-laden inner fjord habitats from oceanic influence. Near tidewater glaciers, surface layers of turbid glacial runoff limited availability of light to phytoplankton, but macrozooplankton were abundant in surface waters, perhaps due to the absence of a photic cue for diel migration. Fish and zooplankton community structure varied along an increasing temperature gradient throughout the summer. Acoustic measurements indicated that low density patches of fish and zooplankton were available in the surface waters near glacial river outflows. This is the foraging habitat occupied most by Kittlitz's murrelet (Brachyramphus brevirostris), a rare seabird that appears to be specialized for life in glacially influenced environments. Kittlitz's murrelets were associated with floating glacial ice, and they were more likely to occur near glaciers, in deeper water, and in areas with high acoustic backscatter. Kittlitz's murrelet at-sea distribution was limited to areas influenced by turbid glacial outflows, and where prey was concentrated near the surface in waters with low light penetration. Tidewater glaciers impart unique hydrographic characteristics that influence marine plankton and fish

  18. 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

  19. Rapid loss of glacial ice reveals stream community assembly processes

    PubMed Central

    Brown, Lee E; Milner, Alexander M

    2012-01-01

    Glacial retreat creates new habitat which is colonized and developed by plants and animals during the process of primary succession. While there has been much debate about the relative role of deterministic and stochastic processes during terrestrial succession, evidence from freshwater ecosystems remains minimal and a general consensus is lacking. Using a unique 27 years record of community assembly following glacial recession in southeast Alaska, we demonstrate significant change in the trait composition of stream invertebrate communities as catchment glacial cover decreased from ∼70% to zero. Functional diversity increased significantly as glacier cover decreased and taxonomic richness increased. Null modelling approaches led to a key finding that niche filtering processes were dominant when glacial cover was extensive, reflecting water temperature and dispersal constraints. Thereafter the community shifted towards co-occurrence of stochastic and deterministic assembly processes. A further novel discovery was that intrinsic functional redundancy developed throughout the study, particularly because new colonizers possessed similar traits to taxa already present. Rapid glacial retreat is occurring in Arctic and alpine environments worldwide and the assembly processes observed in this study provide new fundamental insights into how glacially influenced stream ecosystems will respond. The findings support tolerance as a key primary successional mechanism in this system, and have broader value for developing our understanding of how biological communities in river ecosystems assemble or restructure in response to environmental change.

  20. Deglaciation of the James Bay Lowlands and Northern Abitibi: Insights on Late-Glacial Ice Readvances and Drainage of Glacial Lake Ojibway

    NASA Astrophysics Data System (ADS)

    Roy, M.; Veillette, J. J.; Dell'Oste, F.

    2008-12-01

    Deglaciation in the James Bay region was marked by the scission of the Laurentide ice sheet margin into the Hudson dome to the west and the New-Quebec dome to the east, which subsequently retreated northward, in contact with the waters of glacial Lake Ojibway. Previous work based on air photo-interpretation and field observations indicate that ice retreat in the region was highly dynamic, with the occurrence of at least three ice readvances into the basin of Lake Objiway prior to the final deglaciation, and the incursion of the post- glacial Tyrrell Sea at ~8 ka (Hardy, 1976). Our investigations of stratigraphic sections exposed along the Harricana, Nottaway, Broadback, and Rupert rivers in the lowlands of Quebec indicate that only part of these events are preserved in these sedimentary sequences. The base of the late-glacial sequence generally consists of a carbonate-bearing clayey readvance till that lies on older tills of the last glacial cycle, or truncate Lake Ojibway glaciolacustrine sediments. None of the sections showed more than one till of the three (Cochrane I, Rupert, Cochrane II) readvances documented in the region. Nonetheless, an extensive Ojibway sequence located just south from the lowlands shows three intervals with significant increases in detrital carbonate and coarsening of the varve sequence that can be linked with these late-glacial surges. In the lowlands, the readvance till is commonly capped by a thick sequence of Ojibway varves. The contact between the glaciolacustrine sediments and the overlying Tyrrell Sea marine deposits is marked by a ~50 cm-thick horizon composed at the bottom of thinly laminated reddish and grey silt beds containing abundant rounded clay balls, overlain by coarser silts and fine sands with disseminated clasts. This horizon is here interpreted to reflect the abrupt drainage of Lake Ojibway. Recent radiocarbon dating of mollusks and foraminifers from the uppermost part of this horizon yielded ages of ~7.7 ka and ~8

  1. Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate.

    PubMed

    Frank, David C; Esper, Jan; Raible, Christoph C; Büntgen, Ulf; Trouet, Valerie; Stocker, Benjamin; Joos, Fortunat

    2010-01-28

    The processes controlling the carbon flux and carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive and are likely to provide a positive feedback leading to amplified anthropogenic warming. Owing to this feedback, at timescales ranging from interannual to the 20-100-kyr cycles of Earth's orbital variations, warming of the climate system causes a net release of CO(2) into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the global carbon cycle (termed gamma), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in global warming projections. Here we quantify the median gamma as 7.7 p.p.m.v. CO(2) per degrees C warming, with a likely range of 1.7-21.4 p.p.m.v. CO(2) per degrees C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO(2) data from three ice cores, provide robust constraints for gamma on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of gamma is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of gamma calculated from any of ten coupled carbon-climate models, we find that gamma is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of approximately 40 p.p.m.v. CO(2) per degrees C (refs 6, 7), and correspondingly suggest approximately 80% less potential amplification of ongoing global warming.

  2. Status of glacial Lake Columbia during the last floods from glacial Lake Missoula

    USGS Publications Warehouse

    Atwater, B.F.

    1987-01-01

    The last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia's Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200-400 successive varves conformably overlie the highest flood bed. This sequence suggests that jo??kulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia's late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200-400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia's Okanogan-lobe dam. ?? 1987.

  3. Glacial History of a Modern Invader: Phylogeography and Species Distribution Modelling of the Asian Tiger Mosquito Aedes albopictus

    PubMed Central

    Porretta, Daniele; Mastrantonio, Valentina; Bellini, Romeo; Somboon, Pradya; Urbanelli, Sandra

    2012-01-01

    Background The tiger mosquito, Aedes albopictus, is one of the 100 most invasive species in the world and a vector of human diseases. In the last 30 years, it has spread from its native range in East Asia to Africa, Europe, and the Americas. Although this modern invasion has been the focus of many studies, the history of the species’ native populations remains poorly understood. Here, we aimed to assess the role of Pleistocene climatic changes in shaping the current distribution of the species in its native range. Methodology/Principal Findings We investigated the phylogeography, historical demography, and species distribution of Ae. albopictus native populations at the Last Glacial Maximum (LGM). Individuals from 16 localities from East Asia were analyzed for sequence variation at two mitochondrial genes. No phylogeographic structure was observed across the study area. Demographic analyses showed a signature of population expansion that started roughly 70,000 years BP. The occurrence of a continuous and climatically suitable area comprising Southeast China, Indochinese Peninsula, and Sundaland during LGM was indicated by species distribution modelling. Conclusions/Significance Our results suggest an evolutionary scenario in which, during the last glacial phase, Ae. albopictus did not experience a fragmentation phase but rather persisted in interconnected populations and experienced demographic growth. The wide ecological flexibility of the species probably played a crucial role in its response to glacial-induced environmental changes. Currently, there is little information on the impact of Pleistocene climatic changes on animal species in East Asia. Most of the studies focused on forest-associated species and suggested cycles of glacial fragmentation and post-glacial expansion. The case of Ae. albopictus, which exhibits a pattern not previously observed in the study area, adds an important piece to our understanding of the Pleistocene history of East Asian biota

  4. Should precise numerical dating overrule glacial geomorphology?

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan

    2016-04-01

    Numerical age dating techniques, namely different types of terrestrial cosmogenic nuclide dating (TCND), have achieved an impressive progress in both laboratory precision and regional calibration models during the past few decades. It is now possible to apply precise TCND even to young landforms like Late Holocene moraines, a task seemed hardly achievable just about 15 years ago. An increasing number of studies provide very precise TCND ages for boulders from Late Holocene moraines enabling related reconstruction of glacier chronologies and the interpretation of these glacial landforms in a palaeoclimatological context. These studies may also solve previous controversies about different ages assigned to moraines obtained by different dating techniques, for example relative-age dating techniques or techniques combining relative-age dating with few fixed points derived from numerical age dating. There are a few cases, for example Mueller Glacier and nearby long debris-covered valley glacier in Aoraki/Mt.Cook National Park (Southern Alps, New Zealand), where the apparent "supremacy" of TCND-ages seem to overrule glacial geomorphological principles. Enabled by a comparatively high number of individual boulders precisely dated by TCND, moraine ridges on those glacier forelands have been primarily clustered on basis of these boulder ages rather than on their corresponding morphological position. To the extreme, segments of a particular moraine complex morphologically and sedimentologically proven to be formed during one event have become split and classified as two separate "moraines" on different parts of the glacier foreland. One ledge of another moraine complex contains 2 TCND-sampled boulders apparently representing two separate "moraines"-clusters of an age difference in the order of 1,500 years. Although recently criticism has been raised regarding the non-contested application of the arithmetic mean for calculation of TCND-ages for individual moraines, this

  5. Preformed Nitrate in the Glacial North Atlantic

    NASA Astrophysics Data System (ADS)

    Homola, K.; Spivack, A. J.; D'Hondt, S.; Estes, E. R.; Insua, T. L.; McKinley, C. C.; Murray, R. W.; Pockalny, R. A.; Robinson, R. S.; Sauvage, J.

    2015-12-01

    Atmospheric CO2 abundances are highly correlated with global temperature variations over the past 800,000 years. Consequently, understanding the feedbacks between climate and CO2 is important for predictions of future climate. Leading hypotheses to explain this feedback invoke changes in ocean biology, circulation, chemistry, and/or gas exchange rates to trap CO2 in the deep ocean, thereby reducing the greenhouse effect of CO2 in the atmosphere. To test these hypotheses, we use sediment pore water profiles of dissolved nitrate and oxygen to reconstruct paleo-preformed nitrate concentrations at two deep-water sites in the western North Atlantic (23°N 57°W, 5557 m water depth; 30°N 58°W, 5367 m water depth). Preformed nitrate increases down-core to 22.7 μM (25.6 m core depth) at the northern site, and to 28.5 μM (27.8 m core depth) at the southern site. The large preformed nitrate gradient between these sites reveals a paleo-boundary between a southern water source high in preformed nitrate and a northern water source with lower concentrations, similar to today's ocean. However, the boundary between these water masses occurs north of where their modern counterparts meet, indicating that Antarctic Bottom Water (AABW) extended farther north during the Last Glacial Maximum (LGM). In addition, the southern source had a higher preformed nitrate concentration than today's AABW (25 μM), contradicting hypotheses that nutrient utilization was more efficient in the Southern Ocean deep-water formation regions during the LGM. Comparison to our previous Pacific data reveals that the average preformed nitrate concentration of the deep ocean was slightly higher during the LGM than today. This result implies that the CO2-climate feedback was not principally due to more efficient nitrate utilization.

  6. 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.

  7. Aspects of conducting site investigations in glacial terrain

    SciTech Connect

    Schilling, K.E. )

    1993-03-01

    Much of northern US is mantled by Pleistocene glacial drift consisting of heterogeneous deposits of fine to coarse-textured sediments. Hazardous waste site investigations in glacial settings can often present unique design and implementation considerations. Complex glacial stratigraphy encountered during drilling activities demands flexibility built into work plans to allow for field decisions based on field conditions. Continuous cores should be collected from boreholes on a routine basis for stratigraphic purposes with particular importance assigned to field identification of relative permeabilities of stratigraphic units. Selection of appropriate field screening methodology should be based on site conditions. Utilization of open borehole groundwater sampling is recommended for fine-textured glacial settings where soil gas and well point sampling are ineffective. Installation of boreholes allows for collection of stratigraphic information and enables more surface area exposed beneath the water table for groundwater recharge and sampling. Water level determinations can be made on open boreholes for an initial assessment of the horizontal direction of groundwater flow. Placement of screens for monitoring wells should be based on field determination of likely groundwater flow paths. Nested wells are necessary to define the vertical groundwater flow system at most sites. Evaluation of the vertical flow system can often dominate site investigations in fine-textured glacial terrain. Two case studies from Iowa illustrate the usefulness of incorporating the above considerations in planning and implementing in fine-textured glacial sediments. Field investigations utilizing open borehole groundwater sampling successfully delineated site glacial geology and hydrogeology for determination of the nature and extent of groundwater contamination and better located the horizontal and vertical placement of monitoring wells.

  8. On the issue of equifinality in glacial geomorphology

    NASA Astrophysics Data System (ADS)

    Möller, Per; Dowling, Thomas; Cleland, Carol; Johnson, Mark

    2016-04-01

    A contemporary trend in glacial geomorphology is the quest for some form of unifying theory for drumlin and/or ribbed moraine formation: there MUST be ONE explanation. The result of this is attempts to apply 'instability theory' to the formation of all drumlinoid and ribbed moraine formation or, as an alternative to this, the 'erodent layer hypothesis' for single processes driven formation. However, based on field geology evidence on internal composition and architecture and the internals relation to the exterior, i.e. the shape of drumlins or ribbed moraine, many glacial sedimentologists would argue that it is instead different processes in their own or in combination that lead to similar form, i.e. look-alike geomorphologic expression or equifinality in spite of different process background for their formation. As expressed by Cleland (2013) from a philosophical point of view of a 'common cause explanation', as exemplified with mass extinctions through geologic time, there is probably a 'common cause explanation' for the K/T boundary extinction (massive meteorite impact on Earth), but this is not a common explanation for every other mass extinction. The parallel to our Quaternary enigma is that there can of course be a single common cause for explaining a specific drumlinoid flow set (a particular case), but that does not have to be the explanation of another flow set showing other sedimentological/structural attributes, in turn suggesting that the particular case cause cannot be used for explaining the general case, i.e. all drumlins over glaciated terrain on the globe. We argue in the case of streamlined terrain, which often have considerable morphologic difference between features at local landscape scale whilst still remaining part of the drumlinoid continuum on regional scale, is a product of different processes or process combinations (erosion/deformation/accumulation) in the subglacial system, tending towards the most efficient obstacle shape and thus

  9. Paleoclimatic significance of Middle Pleistocene glacial deposits in the Kotzebue Sound region, northwest coastal Alaska

    SciTech Connect

    Roof, S.R.; Brigham-Grette, J. )

    1992-01-01

    During Middle Pleistocene time, glaciers extended from the western Brooks Range in NW Alaska to the coast at Kotzebue Sound, forming Baldwin Peninsula, a 120 km-long terminal moraine. Marine, glacigenic, and fluvial facies exposed along coastal bluffs surrounding Kotzebue Sound and Hotham Inlet indicate that at least the initial stages of the glacial advance occurred while sea level was high enough to cover the shallow Bering Shelf. Although it is presently uncertain if the ice actually reached tidewater before extensive middle-latitude ice-sheet formation, the marine and glacigenic facies clearly indicate that this advance must have occurred significantly out-of-phase with lower latitude glaciation. The authors believe an ice-free Bering Sea provided the moisture for glacier growth during the waning phases of a global interglacial climate. Although the magnitude of the Baldwin Peninsula advance was large compared to late Pleistocene advances, the timing with respect to sea level is consistent with observations by Miller and de Vernal that late Pleistocene polar glaciations also occurred near the end of interglacial periods, when global sea level was high, high-latitude oceans were relatively warm, and summer insolation was decreasing. An important implication of this out-of-phase glaciation hypothesis is that the critical transition point between climate states may be earlier in the interglacial-glacial cycle than previously thought. Because it appears that climate change is initiated in polar regions while the rest of Earth is experiencing an interglacial climate, many of their climate models must be revised. The glacial record at Baldwin Peninsula provides an opportunity to test, revise, and perhaps extend this out-of-phase glaciation hypothesis to the middle Pleistocene interval.

  10. 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. PMID:23927498

  11. Ocean - ice sheet interaction along the NW European margin during the last glacial phases

    NASA Astrophysics Data System (ADS)

    Becker, L. W. M.; Sejrup, H. P.; Haflidason, H.; Hjelstuen, B. O. B.

    2015-12-01

    The NW European continental margin was repeatedly covered by shelf edge glaciations during the last glacial cycles. Here, we present a compilation of new and previously published data from a SW to NE transect of 8 sediment cores raised along the upper continental slope. This study aims to investigate the interaction between sea surface conditions and the variability seen in the British Irish Ice Sheet (BIIS) and the Fennoscandian Ice Sheet (FIS) during the last 13-40 ka BP. Ice Rafted Debris (IRD) counts, IRD flux data, grain size data, the content of the polar planktonic foraminifera Neogloboquadrina pachyderma (sin) and ∂18O measurements were compiled and combined with new Bayesian age models. From 40-24.5 ka BP the build up and consecutive confluence of the BIIS and the FIS are reflected in sediment composition and flux data. Pulses of large quantities of fine material to the southern part of the transect suggest riverine BIIS related influx. The sediment composition in cores close to the Norwegian channel indicates that the Norwegian Channel Ice Stream (NCIS) was only active between 24.5-18.5 ka BP during the last glacial stage. The planktonic foraminifera data during this period strongly suggests a dependence of NCIS extent variability and pulses in warm Atlantic water entering the Nordic Seas. In the northernmost cores rapidly deposited, laminated sediments and ∂18O spikes in planktonic foraminifera dated to 18.5 ka BP were interpreted as meltwater plume deposits. This may reflect NCIS retreat allowing BIIS and FIS to unzip and route ice dammed lake- and meltwater to the margin. In conclusion, the investigation suggests a close co-variation in extent of marine based parts of the BIIS, the FIS and ocean circulation while demonstrating the strong influence of the local glacial history on standard open marine proxies. This suggests that tuning chronologies of single marine records to ice cores in some regions might be more challenging than previously

  12. Crevassing and calving of glacial ice

    NASA Astrophysics Data System (ADS)

    Kenneally, James Patrick

    Calving of ice is a relatively new area of research in the still young field of glaciology. In the short time that calving has been studied, it has been mainly treated as an afterthought, with the predominant mode of thinking being that it will happen so to concern oneself with why is not important. Many studies dealt with observations of calving front positions over time vs. ice velocity in an attempt to quantify the calving rate as the difference between the two, while others have attempted to deduce some empirical relationship between calving rate and variables such as water depth or temperature. This study instead addresses the question of why, where, and when ice will first become crevassed, which is an obviously necessary condition for a later calving event to occur. Previous work examining the causes of calving used ideas put forth from a variety of fields, including civil engineering, materials science, and results from basic physics and mechanics. These theories are re-examined here and presented as part of a larger whole. Important results from the field of fracture mechanics are utilized frequently, and these results can be used as a predictor of ice behavior and intrinsic properties of ice, as well as properties like back stresses induced by local pinning points and resistive shears along glacial ice boundaries. A theory of fracture for a material experiencing creep is also presented with applications to ice shelves and crevasse penetration. Finally, a speculative theory regarding large scale iceberg formation is presented. It is meant mainly as an impetus to further discussion on the topic, with the hope that a model relating crevasse geometries to flow parameters can result in crevasse spacings that could produce the tabular icebergs which are so newsworthy. The primary focus of this thesis is to move away from the "after the fact" studies that are so common in calving research, and instead devote energy to determining what creates the conditions that

  13. Bering Sea Porewaters and Late Glacial Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Mix, A. C.; McKay, J. L.; Ross, A.; Okazaki, Y.; Scientific Team of IODP Expedition 323

    2011-12-01

    The combination of high-resolution porewater d18O and chlorinity, benthic and planktonic foraminiferal d18O in IODP Sites U1339 (1870 m depth) and U1344 (3172 m depth) constrain late glacial circulation in the Bering Sea. During the Last Glacial Interval, the water column below 1800 m approached the freezing point, and upper ocean stratification was lower than today. Both scenarios point to likely local ventilation, associated with brine formation, during glacial time. An additional deep ventilation event may have occurred during late Holocene (Neoglacial?) time, evidenced by relatively low d18O and high chlorinity porewaters. Intervals of high biological productivity appear to be associated with relatively high upper-ocean stratification, perhaps implying a role for nutrients or micronutrients sourced from the continents.

  14. Tectonic control on the persistence of glacially sculpted topography.

    PubMed

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

    2015-08-14

    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 10(4) 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.

  15. EDITORIAL: Cryospheric ecosystems: a synthesis of snowpack and glacial research

    NASA Astrophysics Data System (ADS)

    Hodson, Andy; Brock, Ben; Pearce, David; Laybourn-Parry, Johanna; Tranter, Martyn

    2015-11-01

    The fourteen letters that contributed to this focus issue on cryospheric ecosytems provide an excellent basis for considering the state of the science following a marked increase in research attention since the new millennium. Research letters from the focus issue provide significant insights into the biogeochemical and biological processes associated with snow, glacier ice and glacial sediments. This has been achieved via a significant, empirical effort that has given particular emphasis to glacier surface habitats. However, far less is known about aerobiology, glacial snow covers, supraglacial lakes and sub-ice sedimentary habitats, whose access for sampling and in-situ monitoring remains a great challenge to scientists. Furthermore, the use of models to explore key fluxes, processes and impacts of a changing glacial cryosphere are conspicuous by their absence. As a result, a range of process investigations and modelling studies are required to address the increasing urgency and uncertainty that is associated with understanding the response of cryospheric ecosystems to global change.

  16. Glacial geology of the Hellas region on Mars

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.; Strom, Robert G.; Johnson, Natasha

    1991-01-01

    A glacial geologic interpretation was recently presented for Argyre, which is herein extended to Hellas. This glacial event is believed to constitute an important link in a global cryohydric epoch of Middle Amazonian age. At glacial maximum, ice apparently extended far beyond the regions of Argyre and Hellas, and formed what is termed as the Austral Ice Sheet, an agglomeration of several ice domes and lobes including the Hellas Lobe. It is concluded that Hellas was apparently heavily glaciated. Also glaciation was young by Martian standards (Middle Amazonian), and ancient by terrestrial standards. Glaciation appears to have occurred during the same period that other areas on Mars were experiencing glaciation and periglacial activity. Glaciation seems to have occurred as a geological brief epoch of intense geomorphic activity in an era characterized by long periods of relative inactivity.

  17. 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

  18. Tectonic control on the persistence of glacially sculpted topography.

    PubMed

    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 10(4) 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

  19. 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

  20. Giant glacial cirques of non-mountainous terrains

    NASA Astrophysics Data System (ADS)

    Amantov, A.; Amantova, M.

    2012-04-01

    Cirques are usually considered as specific landforms of hill and mountain terrains produced by alpine glaciers, and/or slope failures (landslides). However, glacial cirques seem to be present also in non-mountainous terrains that underwent extensive Pleistocene ice-sheet glaciations and strong glacial and fluvio-glacial erosion. The largest form in the Baltic region is Severoladozhsky (North Lake Ladoga) cirque, probably the world's largest representative, with the length and width close to 100 km. Another example is the deepest Landsort basin of the Baltic Sea. In those cases Meso-Neoproterozoic sediments were subject to selected erosion, with evident overdeepening of the bedrock surface in comparison with surrounding crystalline frame. The bowl headwall shape of the cirque-like landforms was determined by the outline of the margin of exhumed basin. The origin of the major basins of margins of the Baltic and Canadian shields are similar. However, direct analogues of giant cirques are not well developed in this part of North America due to geological deviations and dominant directions of ice movement. Comparable landforms (like the South Chippewa basin of the Lake Michigan) are therefore less mature. We define glacial cirque as an amphitheatre-shape depression with comparable values of length and width, steep headwall with adjacent side slopes and gentle lip with commonly increased glacial accumulation. They are usually located within an ice stream that created typical relief profile with normal horseshoe overdeepening, and in areas predefined by geological and geomorphological peculiarities. This definition likely fits both classic mountain cirques, and giant ones created in favorable conditions in domains that underwent extensive glaciations and relevant selective glacial erosion. Length/width ratio typical for giant cirques group is close to 1:1, being comparable with classical alpine ones. Major differences (like length/height ratio of other order and possible

  1. Is rate of glacial retreat accelerated in Indian Himalaya? (Invited)

    NASA Astrophysics Data System (ADS)

    Kulkarni, A. V.

    2013-12-01

    The Himalaya has one of the largest concentration of glaciers and rivers like Indus, Ganga and Bramhputra originate from this region. The snow and glacier melt is an important source of water for these rivers. However, this source of water may get affected in the near future due to changes in the cryosphere. Therefore, retreat of Himalayan glaciers are discussed extensively in scientific and public forums in India. Conventionally health of glaciers is assessed using changes in glacial length, as it is widely measured. However changes in glacial length and loss in areal extent near terminus needs to be interpreted carefully, as these changes can be influenced by numerous terrain and climatically sensitive parameters. The terrain parameters which can influence glacial retreat are slope, area altitude distribution, debris cover and orientation. In addition, climatically sensitive parameters like mass balance, glacial lakes and black carbon can also influence glacier retreat. These multiple influences can produce a complex pattern of glacial retreat. In this paper long-term glacier retreat in three river basins in the Indian Himalaya as Tista, Baspa and Parbati will be discussed. These basins are located in different climatically sensitive regions and each basin has unique dominant process of mass wasting. In addition to terrain parameters, influence of process like formation and expansion of moraine dammed lakes in Tista basin, deposition of black carbon on accumulation area in Baspa basin and debris cover in Parbati basin will also be discussed. This will provide understanding on varying influence of different mass wasting processes on glacial retreat during last five decades in the Indian Himalaya.

  2. Magmatic cycles pace tectonic and morphological expression of rifting (Afar depression, Ethiopia)

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Pik, R.; Burnard, P.; Dumont, S.; Grandin, R.; Williams, A.; Blard, P.-H.; Schimmelpfennig, I.; Vye-Brown, C.; France, L.; Ayalew, D.; Benedetti, L.; Yirgu, G.

    2016-07-01

    The existence of narrow axial volcanic zones of mid-oceanic ridges testifies of the underlying concentration of both melt distribution and tectonic strain. As a result of repeated diking and faulting, axial volcanic zones therefore represent a spectacular topographic expression of plate divergence. However, the submarine location of oceanic ridges makes it difficult to constrain the interplay between tectonic and magmatic processes in time and space. In this study, we use the Dabbahu-Manda Hararo (DMH) magmatic rift segment (Afar, Ethiopia) to provide quantitative constraints on the response of tectonic processes to variations in magma supply at divergent plate boundaries. The DMH magmatic rift segment is considered an analogue of an oceanic ridge, exhibiting a fault pattern, extension rate and topographic relief comparable to intermediate- to slow-spreading ridges. Here, we focus on the northern and central parts of DMH rift, where we present quantitative slip rates for the past 40 kyr for major and minor normal fault scarps in the vicinity of a recent (September 2005) dike intrusion. The data obtained show that the axial valley topography has been created by enhanced slip rates that occurred during periods of limited volcanism, suggestive of reduced magmatic activity, probably in association with changes in strain distribution in the crust. Our results indicate that the development of the axial valley topography has been regulated by the lifetimes of the magma reservoirs and their spatial distribution along the segment, and thus to the magmatic cycles of replenishment/differentiation (<100 kyr). Our findings are also consistent with magma-induced deformation in magma-rich rift segments. The record of two tectonic events of metric vertical amplitude on the fault that accommodated the most part of surface displacement during the 2005 dike intrusion suggests that the latter type of intrusion occurs roughly every 10 kyr in the northern part of the DMH segment.

  3. 20 Myr of eccentricity paced lacustrine cycles in the Cenozoic Ebro Basin

    NASA Astrophysics Data System (ADS)

    Valero, Luis; Garcés, Miguel; Cabrera, Lluís; Costa, Elisenda; Sáez, Alberto

    2014-12-01

    Long-period orbital forcing is a crucial component of the major global climate shifts during the Cenozoic as revealed in marine pelagic records. A complementary regional perspective of climate change can be assessed from internally drained lake basins, which are directly affected by insolation and precipitation balance. The Ebro Basin in northeastern Iberia embraces a 20 Myr long continuous sedimentary record where recurrent expansions and retractions of the central lacustrine system suggest periodic shifts of water balance due to orbital oscillations. In order to test climatic (orbital) forcing a key-piece of the basin, the Los Monegros lacustrine system, has been analyzed in detail. The cyclostratigraphic analysis points to orbital eccentricity as pacemaker of short to long-term lacustrine sequences, and reveals a correlation of maxima of the 100-kyr, 400-kyr and 2.4-Myr eccentricity cycles with periods of lake expansion. A magnetostratigraphy-based chronostratigraphy of the complete continental record allows further assessing long-period orbital forcing at basin scale, a view that challenges alternate scenarios where the stratigraphic architecture in foreland systems is preferably associated to tectonic processes. We conclude that while the location of lacustrine depocenters reacted to the long-term tectonic-driven accommodation changes, shorter wavelenght oscillations of lake environments, still million-year scale, claims for a dominance of orbital forcing. We suggest a decoupling between (tectonic) supply-driven clastic sequences fed from basin margins and (climatic) base level-driven lacustrine sequences in active settings with medium to large sediment transfer systems.

  4. Erosion of the Laurentide region of North America by glacial and glaciofluvial processes

    USGS Publications Warehouse

    Bell, M.; Laine, E.P.

    1985-01-01

    Collection of seismic reflection data from continental margins and ocean basins surrounding North America makes it possible to estimate the amount of material eroded from the area formerly covered by Laurentide ice sheets since major glaciation began in North America. A minimum estimate is made of 1.62 ?? 106 km3, or an average 120 m of rock physically eroded from the Laurentide region. This figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift, Cenozoic marine sediments, and modern sediment loads of rivers. Most of the sediment produced during Laurentide glaciation has already been transported to the oceans. The importance of continental glaciation as a geomorphic agency in North America may have to be reevaluated. Evidence from sedimentation rates in ocean basins surrounding Greenland and Antarctica suggests that sediment production, sediment transport, and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps, such as the Laurentide. Low rates of sediment survival from the time of the Permo-Carboniferous and Precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust. ?? 1985.

  5. 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

  6. Tropical-Subpolar Linkages in the North Atlantic during the last Glacial Period

    NASA Astrophysics Data System (ADS)

    Vautravers, M. J.; Hodell, D. A.

    2010-12-01

    We studied millennial-scale changes in planktonic foraminifera assemblages from the last glacial period in a high-resolution core (KN166-14-JPC13) recovered from the southern part of the Gardar Drift in the subpolar North Atlantic. Similar to recent findings reported by Jonkers et al. (2010), we also found that the sub-polar North Atlantic Ocean experienced some seasonal warming during each of the Heinrich Events (HEs). In addition, increasing abundances of tropical species are found just prior to the IRD event marking the end of each Bond cycle, suggesting that summer warming may have been involved in triggering Heinrich events. We suggest that tropical-subtropical water transported via the Gulf Stream and North Atlantic Drift may have triggered the collapse of large NH ice-shelves. Sharp decreases in polar species are tied to abrupt warming following Heinrich Events as documented in Greenland Ice cores and other marine records in the North Atlantic. The record bears a strong resemblance to the tropical record of Cariaco basin (Peterson et al., 2000), suggesting strong tropical-subpolar linkages in the glacial North Atlantic. Enhanced spring productivity, possibly related to eddy activity along the Subpolar Front, is recorded by increased shell size, high δ13C in G. bulloides and other biological indices early during the transition from HE stadials to the following interstadial.

  7. Antarctic density stratification and the strength of the circumpolar current during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, Jean; Ito, Takamitsu; Michel, Elisabeth

    2016-05-01

    The interaction between ocean circulation and biological processes in the Southern Ocean is thought to be a major control on atmospheric carbon dioxide content over glacial cycles. A better understanding of stratification and circulation in the Southern Ocean during the Last Glacial Maximum (LGM) provides information that will help us to assess these scenarios. First, we evaluate the link between Southern Ocean stratification and circulation states in a suite of climate model simulations. While simulated Antarctic Circumpolar Current (ACC) transport varies widely (80-350 Sverdrup (Sv)), it co-varies with horizontal and vertical stratification and the formation of the southern deep water. We then test the LGM simulations against available data from paleoceanographic proxies, which can be used to assess the density stratification and ACC transport south of Australia. The paleoceanographic data suggest a moderate increase in the Southern Ocean stratification and the ACC strength during the LGM. Even with the relatively large uncertainty in the proxy-based estimates, extreme scenarios exhibited by some climate models with ACC transports of greater than 250 Sv and highly saline Antarctic Bottom Water are highly unlikely.

  8. 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

  9. The Southern Ocean's biological pump during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Anderson, Robert F.; Chase, Zanna; Fleisher, Martin Q.; Sachs, Julian

    Ice core records from Antarctica show large (˜80 ppm) and regular climate-related changes in atmospheric CO 2, with minimum values during glacial periods and maximum values during peak interglacials. The suggested role of the Southern Ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times. Several recent studies have invoked increased stratification of the Southern Ocean to explain lower glacial atmospheric CO 2 levels in terms of reduced exchange of CO 2 between the deep sea and the atmosphere. A northward displacement and/or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification. However, both circulation models and proxy results argue against a weakening of the westerlies. In fact, the mean flow of the Antarctic Circumpolar Current and wind-driven upwelling during the Last Glacial Maximum (LGM) are thought to be at least as vigorous as those which exist today. Given these boundary conditions, we offer two (competing) scenarios for ecosystem structure and export production of the glacial Southern Ocean. The first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate, and requires increased (relative to today) nitrate utilization south of the Antarctic Polar Front (APF) by phytoplankton other than diatoms, together with a shift in the zone of maximum diatom growth from south (interglacials) to north (glacials) of the APF. The second scenario has reduced growth of all phytoplankton species south of the APF during glacials, and a shift in the zone of maximum export production to the north of the Polar Front. The principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south

  10. Glacial modification of granite tors in the Cairngorms, Scotland

    USGS Publications Warehouse

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

    2006-01-01

    A range of evidence indicates that many granite tors in the Cairngorms have been modified by the flow of glacier ice during the Pleistocene. Comparisons with SW England and the use of a space-time transformation across 38 tor groups in the Cairngorms allow a model to be developed for progressive glacial modification. Tors with deeply etched surfaces and no, or limited, block removal imply an absence of significant glacial modification. The removal of superstructure and blocks, locally forming boulder trains, and the progressive reduction of tors to stumps and basal slabs represent the more advanced stages of modification. Recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be reconstructed for large areas of the Cairngorms. Unmodified tors require covers of non-erosive, cold-based ice during all of the cold stages of the Middle and Late Pleistocene. Deformation beneath cold-based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet-based glacier ice. The depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form. Cosmogenic nuclide exposure ages (Phillips et al., 2006) together with data from weathering pit depths (Hall and Phillips, 2006), from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in Marine Isotope Stages (MIS) 4-2, 6 and, probably, at least one earlier phase. The occurrence of glacially modified tors on or close to, the main summits of the Cairngorms requires full ice cover over the mountains during these Stages. Evidence from the Cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas, particularly where other evidence of ice cover is sparse. Recognition of the glacial modification of tors is important

  11. Glacial-interglacial variations of microbial communities in permafrost and lake deposits in the Siberian Arctic

    NASA Astrophysics Data System (ADS)

    Mangelsdorf, Kai; Bischoff, Juliane; Gattinger, Andreas; Wagner, Dirk

    2013-04-01

    The Artic regions are expected to be very sensitive to the currently observed climate change. When permafrost is thawing, the stored carbon becomes available again for microbial degradation, forming a potential source for the generation of carbon dioxide and methane with their positive feedback effect on the climate warming. For the prediction of future climate evolution it is, therefore, important to improve our knowledge about the microbial-driven greenhouse gas dynamics in the Siberian Arctic and their response to glacial-interglacial changes in the past. Sample material was drilled on Kurungnahk Island (Russian-German LENA expedition) located in the southern part of the Lena delta and in lake El'gygytgyn (ICDP-project) in the eastern part of Siberia. The Kurungnahk samples comprise Late Pleistocene to Holocene deposits, whereas the lake El'gygytgyn samples cover Middle to Late Pleistocene sediments. Samples were investigated applying a combined biogeochemical and microbiological approach. The methane profile of the Kurungnahk core reveals highest methane contents in the warm and wet Holocene and Late Pleistocene (LP) deposits and correlates largly to the organic carbon (TOC) contents. Archaeol concentrations, being a biomarker for past methanogenic archaea, are also high during the warm and wet Holocene and LP intervals and low during the cold and dry LP periods. This indicates that part of the methane might be produced and trapped in the past. However, biomarkers for living microorganisms (bacteria and archaea) and microbial activity measurements of methanogens point, especially, for the Holocene to a viable archaeal community, indicating a possible in-situ methane production. Furthermore, warm/wet-cold/dry climate cycles are recorded in the archaeal diversity as revealed by genetic fingerprint analysis. Although the overlying lake water buffers the temperature effect on the lake sediments, which never became permafrost, the bacterial and archaeal biomarker

  12. Simulating the last glacial-interglacial transition with a coupled atmosphere-ocean-ice sheet model

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe; Ziemen, Florian

    2015-04-01

    One of the major challenges in climate modeling is the simulation of glacial-interglacial transitions. A few models of intermediate complexity have been successful in simulating the last termination. Complex atmosphere-ocean general circulation models have been shown to be able to yield realistic climate changes with prescribed ice sheets. Here we presents results from a first attempt to simulate a substantial part of the last glacial cycle with an AOGCM coupled interactively with a state-of-the-art ice sheet model. The ECHAM5/MPIOM AOGCM has been interactively coupled to the dynamical ice sheet model PISM. The latter is run for most of the northern hemisphere with a horizontal resolution of 20 km. An earlier version of this model ( Ziemen et al. 2014) has been applied to a steady state simulation of the last glacial maximum (LGM). The model was integrated from the late Glacial into the Holocene using insolation and greenhouse gas concentrations as transient forcing. Land sea mask and ocean topography are fixed at LGM conditions, river routing and surface elevation for the atmospheric model component are calculated interactively depending on the simulated ice sheets. To make these long simulations feasible, the atmosphere is accelerated by a factor of 10 relative to the other model components using a periodically-synchronous coupling technique. A mini-ensemble with different initial conditions has been run. In all simulation the northern hemispheric deglaciation starts between 18 and 17 kyr BP, consistent with the onset of global warming. The model produces Heinrich event like variability as part of its internal variability. These rapid ice discharge events have a strong impact on the North Atlantic meridional overturning circulation (NAMOC). During the peak deglaciation the NAMOC is collapsed (with a few short interruptions) for several thousand years, which is longer than the estimates from reconstructions. This seems to be an artifact due to keeping ocean

  13. Glacial landforms of the southern Ungava Bay region (Canada): implications for the late-glacial dynamics and the damming of glacial Lake Naskaupi

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin

    2014-05-01

    The Laurentide ice sheet played an important role in the late Pleistocene climate, notably through discharges of icebergs and meltwater. In this context, the Ungava Bay region in northern Quebec-Labrador appears particularly important, especially during the last deglaciation when the retreating ice margin dammed major river valleys, creating large proglacial lakes (e.g., McLean, aux Feuilles). The history of these lakes is closely related to the temporal evolution of the Labrador-Quebec ice dome. There are, however, large uncertainties regarding the position of its ice divide system through time, thereby limiting our understanding of the history of these glacial lakes. Here we focus on glacial and deglacial landforms present in the George River valley, south of Ungava Bay, in order to bring additional constraints on the late-glacial ice dynamics of this region, which also comprised glacial Lake Naskaupi. This work is based on surficial mapping using aerial photos and satellite imagery, combined with extensive fieldwork and sediment sampling. Our investigation showed significant differences in the distribution of glacial landforms across the region. The area east of the George River is characterized by well-developed Naskaupi shorelines while the elevated terrains show a succession of geomorphological features indicative of cold-based ice or ice with low basal velocities. In the easternmost part of this sector, ice flow directional data indicate that the ice was flowing towards ENE, against the regional slope. Eskers show paleocurrent directions indicating a general ice retreat from east to west. In the western part of this sector, near the George River valley, eskers are absent and the region is covered by felsenmeer and ground moraine that likely reflect the presence of a residual ice mass that was no longer dynamic. The presence of a stagnant ice represents the best mechanism to explain the formation of glacial lakes in the George River valley and its main

  14. Morphologic Map of Glacial and Periglacial Features in the Northwestern Argyre Basin, Mars

    NASA Astrophysics Data System (ADS)

    Raack, J.; Hiesinger, H.; Reiss, D.

    2010-03-01

    We produced a morphological map of the northwestern rim of the Argyre Basin with focus on glacial and periglacial features. We report on features such as gullies, pingo-like forms and glacial remnants which are observed.

  15. The Influence of Glacial Ice Sheets on Atlantic Meridional Overturning Circulation Through Atmospheric Circulation Change under Glacial Climate

    NASA Astrophysics Data System (ADS)

    Sherriff-Tadano, S.; Abe-Ouchi, A.; Yoshimori, M.; Oka, A.; Chan, W. L.

    2014-12-01

    It is well known that glacial ice sheets (Laurentide, Fennoscandian and Antarctic ice sheets) exert a large influence on the climate including the atmospheric circulation. Moreover, recent climate modeling studies suggest that glacial ice sheets have a large impact on the Atlantic meridional overturning circulation (AMOC). However, the process by which the ice sheets impact on the AMOC is not yet fully understood. On the other hand, recent studies showed that surface wind changes play a crucial role on changes to the AMOC under glacial climate. Therefore, in this study, we investigate in detail, the process by which the ice sheet modifies the AMOC through surface wind change. Here we conduct numerical experiments using an atmospheric general circulation model (AGCM) and an ocean general circulation model (OGCM) separately. Our method consists of 2 steps. First, from AGCM experiments, we evaluate the effect of glacial ice sheets on the surface wind. Second, from OGCM experiments, we evaluate the influence of the wind stress change on the AMOC by applying the surface wind change as a boundary condition, while leaving other boundary conditions (surface heat and water fluxes) unchanged. In addition, we conduct several sensitivity experiments. Using the AGCM, we explore individual ice sheet effect, ice sheet topography effect and albedo effect on surface wind change. Moreover, using the OGCM, we change the surface wind gradually or apply the surface wind change only at a specific region in order to explore the wind change effect in detail. We find that glacial ice sheets largely intensify the AMOC by surface wind change under glacial climate. Compare to other regions, it reveals that the wind change at the North Atlantic (NA) is a key region. There, the northern glacial ice sheet topography intensifies the Icelandic Low and anti-cyclonic circulation over the Laurentide ice sheet. However, this wind effect is effective only when the NA is not widely covered by sea ice

  16. 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

  17. 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

  18. Glacial erosion, deep exhumation and the development of high topography along the Kongur detachment, Pamir Mountains, Western China

    NASA Astrophysics Data System (ADS)

    Schoenbohm, L.; Chen, J.; Sobel, E.; Thiede, R.; Strecker, M.

    2006-12-01

    moraine volume for correlative moraines along the length of the detachment. Age data will also be used to evaluate the variability of glacial erosion on both short term (single glacial cycle) and long term (onset of northern hemisphere glaciation ca. 2.75 Ma) time scales.

  19. Stratigraphy and reservoir potential of glacial deposits of the Itarare Group (Carboniferous-Permian), Parana basin, Brazil

    SciTech Connect

    Franca, A.B. ); Potter, P.E. )

    1991-01-01

    Drilling in the Parana basin of Brazil in the mid-1980s discovered gas and condensate in the Itarare Group, and showed that glacial deposits in Brazil can contain hydrocarbons. The reservoir potential of the Carboniferous-Permian Itarare Group of the basin is analyzed using new subsurface data from 20 deep wells drilled in the early to middle 1980s. Central to the analysis was the construction of over 3000 km of cross sections based on more than 100 wells, the description of more than 400 m of core, and study of 95 thin sections. Subsurface exploration and mapping of the Itarare are greatly aided by the recognition of three recently defined and described formations and four members, which are traceable for hundreds of kilometers. These units belong to three major glacial cycles in which the pebbly mudstones and shales are seals and glacially related sandstones are reservoirs. The best sandstone reservoirs in the deep subsurface belong to the Rio Segredo Member, the upper-most sandy unit of the Itarare. The Rio Segredo Member is the best petroleum target because it is overlain by thick seals and massive pebbly mudstones and shales, and because it is shallower and less compacted than underlying, more deeply buried sandstones. This member has little detrital matrix and much of its porosity is secondary, developed by carboxylic acid and CO{sub 2} generated when Jurassic-Cretaceous basalts, sills, and dikes were intruded into the Parana basin as Gondwana broke up.

  20. Reduced admixture of North Atlantic Deep Water to the deep central South Pacific during the last two glacial periods

    NASA Astrophysics Data System (ADS)

    Molina-Kescher, Mario; Frank, Martin; Tapia, Raúl; Ronge, Thomas A.; Nürnberg, Dirk; Tiedemann, Ralf

    2016-06-01

    The South Pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the Atlantic Ocean, the Southern Ocean, and the Pacific Basin are exchanged. Here we reconstruct the deep water circulation of the central South Pacific for the last two glacial cycles (from 240,000 years ago to the Holocene) based on radiogenic neodymium (Nd) and lead (Pb) isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the East Pacific Rise. The records show small but consistent glacial/interglacial changes in all three isotopic systems with interglacial average values of -5.8 and 18.757 for ɛNd and 206Pb/204Pb, respectively, whereas glacial averages are -5.3 and 18.744. Comparison of this variability of Circumpolar Deep Water (CDW) to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of North Atlantic Deep Water to CDW during cold stages. The absolute values and amplitudes of the benthic δ13C variations are essentially indistinguishable from other records of the Southern Hemisphere and confirm that the low central South Pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies. In addition, the combined detrital Nd and strontium (87Sr/86Sr) isotope signatures imply that Australian and New Zealand dust has remained the principal contributor of lithogenic material to the central South Pacific.

  1. 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. PMID:26811782

  2. On the Syn-glacial Sedimentary Record of Snowball Earth: Tales of Three Ice-mass Types

    NASA Astrophysics Data System (ADS)

    Hoffman, P. F.; Maloof, A. C.; Halverson, G. P.

    2004-05-01

    We sketch a conceptual model of the glacial history of a snowball Earth, based on new field studies of Marinoan (c640 Ma), Sturtian (c710 Ma) and Huronian (c2.4 Ga) syn-glacial deposits, and informed by sea-ice dynamics modeling. If the oceans froze over from pole to pole, sea ice would thicken and flow glacially towards the Equator, maintained in dynamic steady state by sublimation-precipitation and melting-freezing (Goodman & Pierrehumbert, 2003). Flowage thickens tropical sea ice (and thins extratropical sea ice) relative to adjacent landfast sea ice, where ice thickness is set by one-dimensional thermal diffusion. The latter, called 'sikussak' on Greenland fjords, would occur on rimmed shelves, silled basins and inland seas that are physically protected from invasion by sea glaciers. Such areas have high preservation potential in the geological record and their stratigraphic development through a snowball cycle (CO2 hysteresis loop) ought to reflect an interplay between three distinct ice-mass types: (1) sea glaciers, (2) sikussak, and (3) grounded ice domes. The snowball stage begins when sea glaciers invade the tropics and sikussak prevents calving from outlet glaciers and associated shelf ice. The snowball onset might easily be mistaken for a glacial termination in the sedimentary record. Suspended sediment discharged from wet-base grounded ice may accumulate beneath the sikussak, producing deposits previously interpreted as interstadial or non-glacial. Despite tropical sea ice c450 m thick (GP2003), sea glacier movement ensures a perpetual habitat for photoautotrophy in grounding-line crack systems. After greenhouse forcing raises tropical sea-surface temperature to the melting point, sikussak is replaced by 'oases' of open water, but the tropical ocean remains ice covered due to sea glacial inflow from higher latitudes. If evolved snowball seawater is anoxic and charged with dissolved iron, banded iron-formation will precipitate in snowball oases due to

  3. Glacial/interglacial climate controls on east African interannual rainfall variability

    NASA Astrophysics Data System (ADS)

    Timmermann, A.; Wolff, C.; Haug, G. H.; Sinninghe Damsté, J. S.; Brauer, A.; Sigman, D. M.; Cane, M. A.; Verschuren, D.

    2011-12-01

    Interannual rainfall variations in equatorial East Africa are tightly linked to the El Niño Southern Oscillation (ENSO), with more rain and flooding during El Niño and droughts in La Niña years, both having severe impacts on water stress and food security. Here we report evidence from an annually laminated lake-sediment record from southeastern Kenya for inter-annual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia, abrupt changes in variability between the Medieval Climate Anomaly and the Little Ice Age, and an overall reduction in East African rainfall and its variability during the Last Glacial period. A suite of CCSM3 climate model experiments for LGM, present-day and future CO2-doubling conditions supports forward extrapolations from these lake-sediment data that future Indian Ocean warming will intensify East Africa's hydrological cycle during the short rainy season in September to November.

  4. Ecology of invasive Melilotus alba on Alaskan glacial river floodplains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    White sweetclover has recently invaded glacial river floodplains in Alaska. We sampled vegetation and measured environmental variables along transects located along the Nenana, Matanuska, and Stikine Rivers to describe plant communities and to determine the effects of white sweetclover on other plan...

  5. Terrestrial glacial eskers: Analogs for Martian sinuous ridges

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.; Strom, Roger G.

    1991-01-01

    A glacial model was introduced last year for the Argyre region, a concept which is now extended, and which was recently integrated with a Global Hydrologic Model incorporating many other aspects of Martian geology. Despite wide agreement that the Martian ridges strongly resemble glacial eskers, this hypothesis has been presented with great equivocation due to a perceived lack of other glacial landforms. Quite to the contrary, it is shown that the Martian ridges actually do occur in logical ordered sequences with many other types of characteristically glacial appearing landforms. Herein, the esker hypothesis is further supported in isolation from considerations of regional landform assemblages. It is concluded that Martian sinuous ridges are similar in every respect to terrestrial eskers: scale, morphology, planimetric pattern, and associations with other probable glaciogenic landforms. It is found that the esker hypothesis is well supported. Eskers are glaciofluvial structures, and owe their existence to large scale melting of stagnant temporate glaciers. Thus, eskers are indicators of an ameliorating climatic regime after a protracted episode of cold, humid conditions.

  6. Glacial melting: an overlooked threat to Antarctic krill

    PubMed Central

    Fuentes, Verónica; Alurralde, Gastón; Meyer, Bettina; Aguirre, Gastón E.; Canepa, Antonio; Wölfl, Anne-Cathrin; Hass, H. Christian; Williams, Gabriela N.; Schloss, Irene R.

    2016-01-01

    Strandings of marine animals are relatively common in marine systems. However, the underlying mechanisms are poorly understood. We observed mass strandings of krill in Antarctica that appeared to be linked to the presence of glacial meltwater. Climate-induced glacial meltwater leads to an increased occurrence of suspended particles in the sea, which is known to affect the physiology of aquatic organisms. Here, we study the effect of suspended inorganic particles on krill in relation to krill mortality events observed in Potter Cove, Antarctica, between 2003 and 2012. The experimental results showed that large quantities of lithogenic particles affected krill feeding, absorption capacity and performance after only 24 h of exposure. Negative effects were related to both the threshold concentrations and the size of the suspended particles. Analysis of the stomach contents of stranded krill showed large quantities of large particles ( > 106 μm3), which were most likely mobilized by glacial meltwater. Ongoing climate-induced glacial melting may impact the coastal ecosystems of Antarctica that rely on krill. PMID:27250339

  7. Glacial Influences on Solar Radiation in a Subarctic Sea.

    EPA Science Inventory

    Understanding macroscale processes controlling solar radia­tion in marine systems will be important in interpreting the potential effects of global change from increasing ultraviolet radiation (UV) and glacial retreat. This study provides the first quantitative assessment of UV i...

  8. Alaskan mountain glacial melting observed by satellite gravimetry

    NASA Astrophysics Data System (ADS)

    Chen, J. L.; Tapley, B. D.; Wilson, C. R.

    2006-08-01

    We use satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) as an indication of mass change to study potential long-term mountain glacial melting in southern Alaska and West Canada. The first 3.5 yr of GRACE monthly gravity data, spanning April 2002-November 2005, show a prominent glacial melting trend in the mountain regions around the Gulf of Alaska (GOA). GRACE-observed surface mass changes correlate remarkably well with available mass balance data at Gulkana and Wolverine, two benchmark glaciers of the U.S. Geological Survey (USGS), although the GRACE signals are smaller in magnitude. In addition, terrestrial water storage (TWS) changes estimated from an advanced land surface model show significant mass loss in this region during the same period. After correcting for the leakage errors and removing TWS contributions using model estimates, we conclude that GRACE-observed glacial melting in the GOA mountain region is equivalent to ˜ - 101 ± 22 km 3/yr, which agrees quite well with the assessment of ˜ - 96 ± 35 km 3/yr based on airborne laser altimetry data, and is consistent with an earlier estimate based on the first 2 yr of GRACE data. This study demonstrates the significant potentials of satellite gravity measurements for monitoring mountain glacial melting and regional climate change.

  9. Sulfur/Carbonate Springs and Life in Glacial Ice

    NASA Technical Reports Server (NTRS)

    Allen, C. C.; Grasby, S.; Longazo, T.

    2001-01-01

    Glacial springs are useful analogs to channels and seeps issuing from frozen strata on Mars. Mineralized water can move through, and discharge from, solid ice. This water, even near freezing, can support microbial life and bring it to the surface. Additional information is contained in the original extended abstract.

  10. Oxygen-isotope variations in post-glacial Lake Ontario

    NASA Astrophysics Data System (ADS)

    Hladyniuk, Ryan; Longstaffe, Fred J.

    2016-02-01

    The role of glacial meltwater input to the Atlantic Ocean in triggering the Younger Dryas (YD) cooling event has been the subject of controversy in recent literature. Lake Ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the Laurentide Ice Sheet (LIS) to the Atlantic Ocean via the lower Great Lakes. Here, we use the oxygen-isotope compositions of ostracode valves and clam shells from three Lake Ontario sediment cores to identify glacial meltwater contributions to ancient Lake Ontario since the retreat of the LIS (∼16,500 cal [13,300 14C] BP). Differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime. The average lakewater δ18O of -17.5‰ (determined from ostracode compositions) indicates a significant contribution from glacial meltwater. Upon LIS retreat from the St. Lawrence lowlands, ancient Lake Ontario (glacial Lake Iroquois) lakewater δ18O increased to -12‰ largely because of the loss of low-18O glacial meltwater input. A subsequent decrease in lakewater δ18O (from -12 to -14‰), accompanied by a median sediment grain size increase to 9 μm, indicates that post-glacial Lake Ontario received a final pulse of meltwater (∼13,000-12,500 cal [11,100-10,500 14C] BP) before the onset of hydrologic closure. This meltwater pulse, which is also recorded in a previously reported brief freshening of the neighbouring Champlain Valley (Cronin et al., 2012), may have contributed to a weakening of thermohaline circulation in the Atlantic Ocean. After 12,900 cal [11,020 14C] BP, the meltwater presence in the Ontario basin continued to inhibit entry of Champlain seawater into early Lake Ontario. Opening of the North Bay outlet diverted upper Great Lakes water from the lower Great Lakes causing a period (12,300-8300 cal [10,400-7500 14C] BP) of hydrologic closure in Lake Ontario (Anderson and Lewis, 2012). This change is demarcated by a shift to higher δ18Olakewater

  11. Glacial geology, glacial recession, proglacial lakes, and postglacial environments, Fishers Island, New York

    SciTech Connect

    Sirkin, L. ); Funk, R.E. . Anthropological Survey)

    1993-03-01

    The Fishers Island Moraine, a complex of three parallel ice margin depositional trends, forms the west-central segment of a major recessional moraine of the Connecticut-Rhode Island Lobe of the late Wisconsinan glacier. As such, the moraine links the Orient Point Moraine of eastern Long Island and the Charlestown Moraine of western Rhode Island and marks a prominent recessional ice margin. The moraine is correlative with the Roanoke Point Moraine of the Connecticut Lobe of northeastern Long Island. Pollen stratigraphy of >13,180 ka bog sediments begins early in the spruce (A) pollen zone with evidence of a cold, late-glacial climate. The pine (B) pollen zone, beginning prior to 11,145 ka, and the oak (C) pollen zone, dating from about 9,000 ka with hickory and hemlock subzones, are well represented. However, after about 2,000 ka, the stratigraphic record in the bog sections is missing in most cases due to peat harvesting. Pollen spectra from several archeological sites fall within the late oak pollen zone, well within the land clearing interval with evidence of hardwood forests and locally holly and cedar. Evidence of cultigens in the pollen record is sparse. Marine deposits over fresh water bog and proglacial lake sediments show that some coastal bogs were drowned by sea level rise.

  12. 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".

  13. Debris flow sensitivity to glacial-interglacial climate change - supply vs transport

    NASA Astrophysics Data System (ADS)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.

    2016-04-01

    Numerical models suggest that small mountain catchment-alluvial fan systems might be sensitive to climate changes over glacial-interglacial cycles, and record these palaeoclimate signals in the sedimentology of their deposits. However, these models are still largely untested, and the propagation of climate signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological records from 8 debris flow fan systems in Owens Valley, California, that capture the past ~ 120 ka of deposition. We identify a strong and sustained relationship between deposit grain size and palaeoclimate records over a full glacial-interglacial cycle, with significantly coarser-grained deposits found in warm and dry periods. Our data show that these systems are highly sensitive to climate with a rapid response timescale of < 10ka, which we attribute to rapid transfer from source to sink. This sensitive record might be explained by changes in sediment supply and/or changes in sediment mobilisation, and we evaluate these mechanisms quantitatively. We find little evidence that changes in catchment hypsometry, weathering patterns, past glaciation or sediment production can explain the grain size changes we observe on the fans. However we do find that grain size has increased exponentially with rising temperatures, at a rate that matches the intensification of storms with warming. As these debris flows are triggered by surface runoff during intense storms, we interpret that enhanced runoff rates in warm and stormy conditions are responsible for entraining larger clasts during debris flow initiation. This implies that debris flow fans might record signals of past storm intensity. Our study utilises field sedimentology and focuses on short transport distances (~ 10 km) and climate changes over ~ 1-100 ka timespans, but could additionally have important implications for how eroding landscapes might respond to future warming scenarios. We address the

  14. On the role of thermohaline advection and sea ice in glacial transitions

    NASA Astrophysics Data System (ADS)

    Kravtsov, S.; Dewar, W. K.

    2003-06-01

    A two-dimensional, one-basin thermohaline oceanic circulation (THC) model coupled to an atmospheric energy balance model (EBM) with land ice albedo effect and a thermodynamic sea ice model is used to study global climate on centennial, and longer, timescales. The model is interpreted to represent the effect of the global ocean, rather than the Atlantic, as is commonly done. It is forced by symmetric insolation and includes a diagnostic parameterization of the hydrologic cycle. Here the strength of the ocean's haline forcing is controlled by a parameter, which reflects the effect of river runoff. This parameter is varied in a set of experiments, which also differ by the magnitude of solar insolation. In wide ranges of the hydrologic cycle, multiple climatic equilibria exist, consisting of circulations with different degrees of asymmetry. More symmetric states have a higher global atmospheric temperature, characteristic of modern climate, whereas less symmetric states are colder and resemble glacial conditions. The maximum global atmospheric temperature difference between such states is consistent with proxy-data-derived temperature drop of about 4°C during the glacial, in contrast to EBM-only sensitivity of about 0.4°C. The mechanics of climate transitions in the model are due to amplification of the orbitally induced global heat budget changes by a major reorganization of the oceanic heat transport. In our model this reorganization is caused by the nonlinear dynamics of the ocean's THC, whose stability regime shifts subject to variable external forcing. Sea ice enhances model climate sensitivity by anchoring deep-ocean temperature to be near freezing [, 2000] and by affecting atmospheric temperature and land ice extent near the poles because of sea ice insulating properties.

  15. Multiple glacial refugia for cool-temperate deciduous trees in northern East Asia: the Mongolian oak as a case study.

    PubMed

    Zeng, Yan-Fei; Wang, Wen-Ting; Liao, Wan-Jin; Wang, Hong-Fang; Zhang, Da-Yong

    2015-11-01

    In East Asia, temperate forests are predicted to have retracted southward to c. 30° N during the last glacial maximum (LGM) based on fossil pollen data, whereas phylogeographic studies have often suggested glacial in situ survival of cool-temperate deciduous trees in their modern northern ranges. Here we report a study of the genetic diversity and structure of 29 natural Mongolian oak (Quercus mongolica) populations using 19 nuclear simple sequence repeat (nSSR) loci and four chloroplast DNA fragments. Bayesian clustering analysis with nSSRs revealed five groups, which were inferred by approximate Bayesian computation (ABC) to have diverged in multiple refugia through multiple glacial-interglacial cycles. Analysis of chloroplast DNA variation revealed four lineages that were largely but incompletely geographically disjunct. Ecological niche modelling (ENMs) indicated a southward range shift of the oak's distribution at the LGM, although high suitability scores were also evident in the Changbai Mts. (Northeast China), the Korean Peninsula, areas surrounding the Bohai Sea, and along the coast of the Russian Far East. In addition, endemic chloroplast DNA haplotypes and nuclear lineages occurred in high-latitude northern areas where the ENM predicted no suitable habitat. The combined evidence from nuclear and chloroplast DNA, and the results of the ENM clearly demonstrate that multiple northern refugia, including cryptic ones, were maintained across the current distributional range of the Mongolian oak during the LGM or earlier glacial periods. Though spatially limited, postglacial expansions from these refugia have led to a pattern of decreased genetic diversity with increasing latitude. PMID:26439083

  16. Multiple glacial refugia for cool-temperate deciduous trees in northern East Asia: the Mongolian oak as a case study.

    PubMed

    Zeng, Yan-Fei; Wang, Wen-Ting; Liao, Wan-Jin; Wang, Hong-Fang; Zhang, Da-Yong

    2015-11-01

    In East Asia, temperate forests are predicted to have retracted southward to c. 30° N during the last glacial maximum (LGM) based on fossil pollen data, whereas phylogeographic studies have often suggested glacial in situ survival of cool-temperate deciduous trees in their modern northern ranges. Here we report a study of the genetic diversity and structure of 29 natural Mongolian oak (Quercus mongolica) populations using 19 nuclear simple sequence repeat (nSSR) loci and four chloroplast DNA fragments. Bayesian clustering analysis with nSSRs revealed five groups, which were inferred by approximate Bayesian computation (ABC) to have diverged in multiple refugia through multiple glacial-interglacial cycles. Analysis of chloroplast DNA variation revealed four lineages that were largely but incompletely geographically disjunct. Ecological niche modelling (ENMs) indicated a southward range shift of the oak's distribution at the LGM, although high suitability scores were also evident in the Changbai Mts. (Northeast China), the Korean Peninsula, areas surrounding the Bohai Sea, and along the coast of the Russian Far East. In addition, endemic chloroplast DNA haplotypes and nuclear lineages occurred in high-latitude northern areas where the ENM predicted no suitable habitat. The combined evidence from nuclear and chloroplast DNA, and the results of the ENM clearly demonstrate that multiple northern refugia, including cryptic ones, were maintained across the current distributional range of the Mongolian oak during the LGM or earlier glacial periods. Though spatially limited, postglacial expansions from these refugia have led to a pattern of decreased genetic diversity with increasing latitude.

  17. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  18. Abrupt glacial climate shifts controlled by ice sheet changes

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-01

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  19. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials. PMID:25119027

  20. Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum: Paleo-data Synthesis

    NASA Astrophysics Data System (ADS)

    Kohfeld, Karen; Graham, Robert; De Boer, Agatha; Sime, Louise; Wolff, Eric; Le Quéré, Corinne; Bopp, Laurent

    2013-04-01

    Changes in the strength and position of Southern Hemisphere westerly winds during the last glacial cycle have been invoked to explain glacial-interglacial climate fluctuations. However, neither paleo models nor paleodata agree on the magnitude, or even the sign, of the change in wind strength and latitude during the Last Glacial Maximum (LGM), compared to the recent past. This study synthesizes paleo-environmental data that have been used to infer changes in winds during the LGM compared with the late Holocene. These compilations include changes in terrestrial moisture, dust deposition, and ocean productivity, along with summaries of previously published information on sea surface temperatures (SSTs) and ocean dynamics in the Southern Hemisphere. Our compilations of terrestrial moisture from 94 sites and dust deposition from 87 sites show generally drier conditions for the LGM between 0 and 40°S, with wetter conditions along the west coasts and drying along the east coasts of continents. LGM dust deposition rates ranged from 2 to 4.5 times higher over the Southern Ocean and about 13 times higher over the Antarctic continent. For the oceans, reconstructed changes in SSTs show maximum cooling (>4°C) in the modern-day Subantarctic Zone, coincident with a region of enhanced export production during the LGM compared with today. We find that any hypothesis of LGM wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents, cooler temperatures and higher productivity in the Subantarctic Zone, and reductions in Agulhas leakage around southern Africa. Our comparison suggests that an overall strengthening, an equatorward displacement, or no change at all in winds could all be interpreted as consistent with observations. If a single cause related to the southern westerlies is sought for all the evidence presented, then an equatorward displacement or strengthening of the winds would be consistent with the largest

  1. Numerical model of the glacially-induced intraplate earthquakes and faults formation

    NASA Astrophysics Data System (ADS)

    Petrunin, Alexey; Schmeling, Harro

    2016-04-01

    According to the plate tectonics, main earthquakes are caused by moving lithospheric plates and are located mainly at plate boundaries. However, some of significant seismic events may be located far away from these active areas. The nature of the intraplate earthquakes remains unclear. It is assumed, that the triggering of seismicity in the eastern Canada and northern Europe might be a result of the glacier retreat during a glacial-interglacial cycle (GIC). Previous numerical models show that the impact of the glacial loading and following isostatic adjustment is able to trigger seismicity in pre-existing faults, especially during deglaciation stage. However this models do not explain strong glaciation-induced historical earthquakes (M5-M7). Moreover, numerous studies report connection of the location and age of major faults in the regions undergone by glaciation during last glacial maximum with the glacier dynamics. This probably imply that the GIC might be a reason for the fault system formation. Our numerical model provides analysis of the strain-stress evolution during the GIC using the finite volume approach realised in the numerical code Lapex 2.5D which is able to operate with large strains and visco-elasto-plastic rheology. To simulate self-organizing faults, the damage rheology model is implemented within the code that makes possible not only visualize faulting but also estimate energy release during the seismic cycle. The modeling domain includes two-layered crust, lithospheric mantle and the asthenosphere that makes possible simulating elasto-plastic response of the lithosphere to the glaciation-induced loading (unloading) and viscous isostatic adjustment. We have considered three scenarios for the model: horizontal extension, compression and fixed boundary conditions. Modeling results generally confirm suppressing seismic activity during glaciation phases whereas retreat of a glacier triggers earthquakes for several thousand years. Tip of the glacier

  2. 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.

  3. 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

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

    PubMed

    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.

  5. Dust in High Latitudes in the Community Earth System Model since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Albani, S.; Mahowald, N. M.

    2015-12-01

    Earth System Models are one of the main tools in modern climate research, and they provide the means to produce future climate projections. Modeling experiments of past climates is one of the pillars of the Coupled Modelling Inter-comparison Project (CMIP) / Paleoclimate Modelling Inter-comparison Project (PMIP) general strategy, aimed at understanding the climate sensitivity to varying forcings. Physical models are useful tools for studying dust transport patterns, as they allow representing the full dust cycle from sources to sinks with an internally consistent approach. Combining information from paleodust records and climate models in coherent studies can be a fruitful approach from different points of view. Based on a new quality-controlled, size- and temporally-resolved data compilation, we used the Community Earth System Model to estimate the mass balance of and variability in the global dust cycle since the Last Glacial Maximum and throughout the Holocene. We analyze the variability of the reconstructed global dust cycle at different climate equilibrium conditions since the LGM until the pre-industrial climate, and compare with palodust records, focusing on the high latitudes, and discuss the uncertainties and the implications for dust and iron deposition to the oceans.

  6. Quaternary glacial and post-glacial depositional history associated with the Green Bay lobe, east-central Wisconsin

    SciTech Connect

    Thieme, L.D.; Smith, G.L. . Dept. of Geology)

    1993-03-01

    Multiple layers of peat and wood fragments indicate that Quaternary glaciation of the east-central region of Wisconsin was punctuated by at least two interglacial periods. Till, outwash, and glaciolacustrine deposits suggest that deposition took place in alternating glacial and non-glacial environments due to oscillations in the position of the Green Bay Lobe terminus. The data for this study consists of 36 auger borings, 70 geologic logs and 100 well-construction reports from water wells. Nine vibracores were taken at the northern margin of Lake Winnebago in order to document in detail the post-glacial history of Glacial Lake Oshkosh/Lake Winnebago. Local bedrock consists of limestones and dolomites of the Middle Ordovician Sinnipee Group. Bedrock elevations range from 211--237 m; bedding dips regionally to the southeast at 1--2 degrees. Bedrock is overlain by a 3--13 m-thick layer of alternating red clay and gray silty-clay (basal Kewaunee Formation ) perhaps deposited in a proglacial lake. These sediments are overlain by apeat/wood layer indicating marsh deposition. This peat/wood layer is overlain by more proglacial lake sediment, 3--10 m of gray brown clay to silty-clay. A second peat/wood layer overlies the gray/brown sediment and may correlate with the Two Creeks buried forest bed. The uppermost unit consists of 2--3 m red silty-clay till (Middle Inlet Member of the Kewaunee Formation). Along the northern margin of present-day Lake Winnebago, red silty-clay is overlain by silty-sand deposited by Glacial Lake Oshkosh. Future work includes obtaining radiocarbon dates from buried peat/wood layers to verify these tentative correlations between east-central Wisconsin and the Lake Michigan Basin.

  7. The Post-Glacial Species Velocity of Picea glauca following the Last Glacial Maximum in Alaska.

    NASA Astrophysics Data System (ADS)

    Morrison, B. D.; Napier, J.; Kelly, R.; Li, B.; Heath, K.; Hug, B.; Hu, F.; Greenberg, J. A.

    2015-12-01

    Anthropogenic climate change is leading to dramatic fluctuations to Earth's biodiversity that has not been observed since past interglacial periods. There is rising concern that Earth's warming climate will have significant impacts to current species ranges and the ability of a species to persist in a rapidly changing environment. The paleorecord provides information on past species distributions in relation to climate change, which can illuminate the patterns of potential future distributions of species. Particularly in areas where there are multiple potential limiting factors on a species' range, e.g. temperature, radiation, and evaporative demand, the spatial patterns of species migrations may be particularly complex. In this study, we assessed the change in the distributions of white spruce (Picea glauca) from the Last Glacial Maxima (LGM) to present-day for the entire state of Alaska. To accomplish this, we created species distribution models (SDMs) calibrated from modern vegetation data and high-resolution, downscaled climate surfaces at 60m. These SDMs were applied to downscaled modern and paleoclimate surfaces to produce estimated ranges of white spruce during the LGM and today. From this, we assessed the "species velocity", the rate at which white spruce would need to migrate to keep pace with climate change, with the goal of determining whether the expansion from the LGM to today originated from microclimate refugia. Higher species velocities indicate locations where climate changed drastically and white spruce would have needed to migrate rapidly to persist and avoid local extinction. Conversely, lower species velocities indicated locations where the local climate was changing less rapidly or was within the center of the range of white spruce, and indicated locations where white spruce distributions were unlikely to have changed significantly. Our results indicate the importance of topographic complexity in buffering the effects of climate change

  8. Menstrual Cycle

    MedlinePlus

    ... Pregnancy This information in Spanish ( en español ) The menstrual cycle Day 1 starts with the first day of ... drop around Day 25 . This signals the next menstrual cycle to begin. The egg will break apart and ...

  9. Biogeochemical Cycling

    NASA Technical Reports Server (NTRS)

    Bebout, Brad; Fonda, Mark (Technical Monitor)

    2002-01-01

    This lecture will introduce the concept of biogeochemical cycling. The roles of microbes in the cycling of nutrients, production and consumption of trace gases, and mineralization will be briefly introduced.

  10. Late Neogene evolution of the East Asian monsoon revealed by terrestrial mollusk record in Western Chinese Loess Plateau: From winter to summer dominated sub-regime

    NASA Astrophysics Data System (ADS)

    Li, Fengjiang; Rousseau, Denis-Didier; Wu, Naiqin; Hao, Qingzhen; Pei, Yunpeng

    2008-10-01

    More and more evidence indicates that the onset of the East Asian (EA) monsoon can be traced back to the Oligocene-Miocene boundary (at about 23 Ma). However, the process of its evolution is still less well-known until now. Here we investigate its late Neogene evolution by analyzing a terrestrial mollusk sequence, from the Chinese Loess Plateau (CLP), covering the period between 7.1 and 3.5 Ma. Considering the modern ecological requirements of these organisms, we were able to define two groups of cold-aridiphilous (CA) and thermo-humidiphilous (TH) species, representing the EA winter and summer monsoon variations, respectively, as previously defined in the Quaternary glacial-interglacial cycles. Variations in these two groups indicate two different monsoon dominated periods during 7.1-3.5 Ma. First, between 7.1 and 5.5 Ma, the EA winter monsoon, with a 100-kyr periodicity, was dominant. Second, between 5.1 and 4 Ma, the EA summer monsoon dominated, with a 41-kyr periodicity. Furthermore, our mollusk record yields valuable evidence for a late Miocene-Pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated, associated with a periodicity transition from weak 100 kyr to 41 kyr. The strengthened winter monsoon interval, with a 100-kyr periodicity, is coeval with orbital-scale global ice-volume changes, in conjunction with the uplift of the Tibetan Plateau which probably reinforced the winter monsoon sub-regime. Conversely, closures of the Panama and Indonesian seaways, associated with changes in obliquity between 5.1 and 4 Ma, are probably major forcing factors for the observed dominant summer monsoon with 41-kyr frequency, favoring heat and moisture transports between low and high latitudes to allow TH mollusks to grow and develop in the CLP.

  11. The Glacial BuzzSaw, Isostasy, and Global Crustal Models

    NASA Astrophysics Data System (ADS)

    Levander, A.; Oncken, O.; Niu, F.

    2015-12-01

    The glacial buzzsaw hypothesis predicts that maximum elevations in orogens at high latitudes are depressed relative to temperate latitudes, as maximum elevation and hypsography of glaciated orogens are functions of the glacial equilibrium line altitude (ELA) and the modern and last glacial maximum (LGM) snowlines. As a consequence crustal thickness, density, or both must change with increasing latitude to maintain isostatic balance. For Airy compensation crustal thickness should decrease toward polar latitudes, whereas for Pratt compensation crustal densities should increase. For similar convergence rates, higher latitude orogens should have higher grade, and presumably higher density rocks in the crustal column due to more efficient glacial erosion. We have examined a number of global and regional crustal models to see if these predictions appear in the models. Crustal thickness is straightforward to examine, crustal density less so. The different crustal models generally agree with one another, but do show some major differences. We used a standard tectonic classification scheme of the crust for data selection. The globally averaged orogens show crustal thicknesses that decrease toward high latitudes, almost reflecting topography, in both the individual crustal models and the models averaged together. The most convincing is the western hemisphere cordillera, where elevations and crustal thicknesses decrease toward the poles, and also toward lower latitudes (the equatorial minimum is at ~12oN). The elevation differences and Airy prediction of crustal thickness changes are in reasonable agreement in the North American Cordillera, but in South America the observed crustal thickness change is larger than the Airy prediction. The Alpine-Himalayan chain shows similar trends, however the strike of the chain makes interpretation ambiguous. We also examined cratons with ice sheets during the last glacial period to see if continental glaciation also thins the crust toward

  12. Glacially induced stresses in sedimentary rocks of northern Poland

    NASA Astrophysics Data System (ADS)

    Trzeciak, Maciej; Dąbrowski, Marcin

    2016-04-01

    During the Pleistocene large continental ice sheets developed in Scandinavia and North America. Ice-loading caused bending of the lithosphere and outward flow in the mantle. Glacial loading is one of the most prominent tectono-mechanical event in the geological history of northern Poland. The Pomeranian region was subjected several times to a load equivalent of more than 1 km of rocks, which led to severe increase in both vertical and horizontal stresses in the upper crustal rocks. During deglaciation a rapid decrease in vertical stress is observed, which leads to destabilization of the crust - most recent postglacial faults scarps in northern Sweden indicate glacially induced earthquakes of magnitude ~Mw8. The presence of the ice-sheet altered as well the near-surface thermal structure - thermal gradient inversion is still observable in NW Poland. The glacially related processes might have left an important mark in the sedimentary cover of northern Poland, especially with regard to fracture reopening, changes in stress state, and damage development. In the present study, we model lithospheric bending caused by glacial load, but our point of interest lies in the overlying sediments. Typical glacial isostatic studies model the response of (visco-) elastic lithosphere over viscoelastic or viscous asthenosphere subjected to external loads. In our model, we introduce viscoelastic sedimentary layers at the top of this stack and examine the stress relaxation patterns therein. As a case study for our modelling, we used geological profiles from northern Poland, near locality of Wejherowo, which are considered to have unconventional gas potential. The Paleozoic profile of this area is dominated by almost 1 km thick Silurian-Ordovician shale deposits, which are interbedded with thin and strong limestone layers. This sequence is underlain by Cambrian shales and sandstones, and finally at ~3 km depth - Precambrian crystalline rocks. Above the Silurian there are approximately

  13. Pleistocene glacial evolution of Fuentes Carrionas (Cantabrian Range, NW Spain)

    NASA Astrophysics Data System (ADS)

    Pellitero, Ramon

    2014-05-01

    Fuentes Carrionas is a massif situated at the N of Spain, between Castilla y Leon and Cantabria regions. It is the second highest mountain massif of the Cantabrian Range after Picos de Europa, with peaks over 2500 m.a.s.l. and valleys well over 1000 m.a.s.l. Fuentes Carrionas was glaciated during Quaternary, and even during the Holocene and as far as Little Ice Age the presence of glaciers, or at least permafrost is controversial. Results from glacial geomorphology analysis of Fuentes Carrionas Massif are presented. Based on the interpretation of glacial landforms, glacial evolution since the Last Glacial Maximum until Pleistocene deglaciation is described. Four different glacial equilibrium phases are identified, the last one divided into two pulsations. Deglaciation process took place between 36 ka BP and 11 ka BP. Local Last Glacial Maximum is dated back to 36-38 ka. BP, therefore earlier than LGM. Glaciers reached 15 km. long and occupied valleys down to 1250 m.a.s.l. during this phase. By European LGM (20-18 ka.BP) glaciers had substantially retreated to fronts about 1700 m.a.s.l. A final stage with two marked pulsations shows only small glaciers located at cirques above 2000 m.a.s.l. and, finally, only small cirque glaciers at North and Northeast orientation above 2200 m.a.s.l. Both these phases have been correlated to Oldest and Younger Dryas, although no dates have been done yet. A palaeoenvironmental reconstruction is proposed, based on ELA (Equilibrium Line Altitude) rise. ELA has been calculated with the AAR method and 0.67 ratio. This reconstruction shows that temperatures ranged between 9°C and 10°C lower than present ones at the end of Pleistocene, depending on a precipitations variation between 30% higher and 20% lower than current ones. Further research will focus on these retreat phases, especially on Younger Dryas identification and reconstruction for this site and the rest of Cantabrian Range.

  14. Glacial landscape evolution on Hall Peninsula, Baffin Island, since the Last Glacial Maximum: insights into switching glacial dynamics and thermo-mechanical conditions

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Ross, M.

    2012-12-01

    Ice cover in north central Hall Peninsula, Baffin Island has evolved from full Laurentide Ice Sheet (LIS) cover during the Last Glacial Maximum (LGM) to a thin ice cap that now covers about 800 km2 in the northeast sector. The exposed subglacial landscape consists of contrasting geomorphological zones which allude to complex spatial and temporal changes in basal ice dynamics and thermal regime since LGM. We used satellite imagery, field observations, a large till geochemical database, and terrestrial cosmogenic isotopes to get new insights into subglacial erosion intensity, ice flow dynamics, and glacial history. Fields of streamlined bedrock-cored ridges (e.g. drumlins) have been mapped and their elongation ratios calculated. The density of bedrock-controlled lakes, which has traditionally been used as a proxy for subglacial erosion intensity on Baffin Island, has been re-examined using modern GIS techniques. This work has revealed a mosaic of glacial terrain zones each consisting of characteristics that are distinct from the other zones. Five glacial terrain zones (GTZ) have been recognized. One zone (GTZ 1) is characterized by a broad flowset of northeast trending streamlined hills and parallel paleo-flow indicators. It also has the highest streamlined hill density, longest elongation ratios, and the highest lake density of the study area. This northeast flowset is crosscut locally by ice flow indicators that converge into troughs that now form a series of fjords. Landforms and ice flow indicators of this younger system (GTZ 2) are traced inland showing propagation of the channelized system into this portion of the LIS. The central area of the peninsula contains a zone of thicker till and rolling topography (GTZ 3) as well as a zone consisting of southeast trending features and associated perpendicular moraines (GTZ 4). The modern ice cap and its past extension form the last zone (GTZ 5). The preservation of the northeast system (GTZ 1) outside of the

  15. Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2016-09-01

    The historical view of a uniformly warm Cretaceous is being increasingly challenged by the accumulation of new data hinting at the possibility of glacial events, even during the Cenomanian-Turonian (~95 Myr ago), the warmest interval of the Cretaceous. Here we show that the palaeogeography typifying the Cenomanian-Turonian renders the Earth System resilient to glaciation with no perennial ice accumulation occurring under prescribed CO2 levels as low as 420 p.p.m. Conversely, late Aptian (~115 Myr ago) and Maastrichtian (~70 Myr ago) continental configurations set the stage for cooler climatic conditions, favouring possible inception of Antarctic ice sheets under CO2 concentrations, respectively, about 400 and 300 p.p.m. higher than for the Cenomanian-Turonian. Our simulations notably emphasize that palaeogeography can crucially impact global climate by modulating the CO2 threshold for ice sheet inception and make the possibility of glacial events during the Cenomanian-Turonian unlikely.

  16. Glacial geomorphic evidence for a late climatic change on Mars

    NASA Technical Reports Server (NTRS)

    Kargel, J. S.; Strom, R. G.

    1992-01-01

    In a series of preliminary reports, we documented evidence of former glacial epochs on Mars. Apparent glacial landforms seemed to be concentrated primarily at middle to high southern latitudes. We now have additional evidence supporting the view that Martian glaciation appears to have been more extensive than previously recognized. The growth and collapse of ice sheets on Mars seems closely analogous to the growth and decline of Earth's great Pleistocene ice sheets. This implies that climate change was probably somewhat comparable on the two planets, although in the case of Mars the entire planet seems to have changed rapidly to a cold, dry present-day environment after the collapse of the ice sheets.

  17. Climate model benchmarking with glacial and mid-Holocene climates

    NASA Astrophysics Data System (ADS)

    Harrison, S. P.; Bartlein, P. J.; Brewer, S.; Prentice, I. C.; Boyd, M.; Hessler, I.; Holmgren, K.; Izumi, K.; Willis, K.

    2014-08-01

    Past climates provide a test of models' ability to predict climate change. We present a comprehensive evaluation of state-of-the-art models against Last Glacial Maximum and mid-Holocene climates, using reconstructions of land and ocean climates and simulations from the Palaeoclimate Modelling and Coupled Modelling Intercomparison Projects. Newer models do not perform better than earlier versions despite higher resolution and complexity. Differences in climate sensitivity only weakly account for differences in model performance. In the glacial, models consistently underestimate land cooling (especially in winter) and overestimate ocean surface cooling (especially in the tropics). In the mid-Holocene, models generally underestimate the precipitation increase in the northern monsoon regions, and overestimate summer warming in central Eurasia. Models generally capture large-scale gradients of climate change but have more limited ability to reproduce spatial patterns. Despite these common biases, some models perform better than others.

  18. Pre-glacial, Early Glacial, and Ice Sheet Stratigraphy Cored During NBP1402, Sabrina Coast, East Antarctic Margin

    NASA Astrophysics Data System (ADS)

    Domack, E. W.; Gulick, S. P. S.; Fernandez-Vasquez, R. A.; Frederick, B.; Lavoie, C.; Leventer, A.; Shevenell, A.; Saustrup, S., Sr.; Bohaty, S. M.; Sangiorgi, F.

    2014-12-01

    Western Wilkes Land provides an unusual setting with regard to passive margin subsidence and exposure of Cenozoic sedimentary units across the continental shelf, due to the unique rift to drift history off of the Australian-Antarctic Discordance and subsequent deep glacial erosion of the evolved continental shelf. The first factor has provided extensive accommodation space for the preservation of stratigraphic sequences that in turn represent critical periods in the climate evolution of Antarctica. Glacial erosion has then provided access to this stratigraphy that is usually inaccessible to all but deep drilling programs. Such stratigraphies are well exposed to within cm of the seafloor off the Sabrina Coast. Cruise NBP1402 investigated this region via a combination of multi-channel seismic imaging and innovative, strategic coring. The geophysical data imaged the geologic evolution of the margin, which exhibits a continuum from non-glacial, partly glaciated, to fully glaciated depo- and erosional systems. Based on the seismic stratigraphy, we collected dredges and one barrel Jumbo Piston Cores (JPCs) across areas of outcropping strata imaged seismically, a unique strategy that allowed us to identify and sample specific reflectors. The stratigraphically deepest coring targeted sections for which the seismic character suggested a pre-glacial context, with non-glaciated continental margin sequences including deltas. Coring recovered dark organic rich siltstones and sandy mudstones, and a large concretion whose center contained a cm-sized plant fossil. In addition, the sediments contain a fossil snail. These fossils provide a glimpse into the pre-glacial terrestrial environment in Antarctica. Overlying this section, coring recovered similar dark siltstones with a 20 cm thick horizon with abundant large angular clasts of variable lithology, interpreted to be ice-rafted debris and indicative of early glacial ice in Antarctica. Finally, JPCs targeting a younger part of

  19. Mercury fluxes out of glacial and non-glacial streams, as determined by continuous measurements of turbidity and CDOM

    NASA Astrophysics Data System (ADS)

    Vermilyea, A.; Nagorski, S. A.; Lamborg, C. H.; Scott, D.; Hood, E. W.

    2011-12-01

    Glaciers and icefields along the Alaskan coast contribute nearly half of the freshwater discharge to the Gulf of Alaska and can play an important role in near-shore marine ecosystems. In southeastern Alaska, glaciers are rapidly thinning and retreating and are being replaced by temperate forests and wetlands. This ongoing landscape evolution is altering the sensitivity of coastal watersheds to atmospheric Hg inputs. The influence of glacial runoff with high suspended sediment loads on in-stream mercury fluxes and dynamics is poorly understood. In contrast, numerous studies have shown that streams with large contributions from wetlands typically carry high dissolved organic matter (DOM) and filtered methylmercury (FMHg) loads. This study compares and contrasts the mercury concentrations, fluxes, partitioning, and speciation in two coastal watersheds in southeastern Alaska. The two watersheds are separated by only 23 km and are relatively similar in area, however one is heavily glaciated (Lemon Creek) and one is dominated by temperate forest and wetlands (Peterson Creek). Grab samples for unfiltered total mercury (UTHg), particulate total mercury (PTHg), filtered total mercury (