Frozen-bed Fennoscandian and Laurentide ice sheets during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Kleman, Johan; Hättestrand, Clas

1999-11-01

The areal extents of the Laurentide and Fennoscandian ice sheets during the Last Glacial Maximum (about 20,000 years ago) are well known, but thickness estimates range widely, from high-domed to thin, with large implications for our reconstruction of the climate system regarding, for example, Northern Hemisphere atmospheric circulation and global sea levels. This uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials, a knowledge of which would better constrain reconstructions of ice-sheet thickness. Here we show that, in the absence of direct data, the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen- and thawed-bed conditions. We argue that ribbed moraines were formed by brittle fracture of subglacial sediments, induced by the excessive stress at the boundary between frozen- and thawed-bed conditions resulting from the across-boundary difference in basal ice velocity. Maps of glacial landforms from aerial photographs of Canada and Scandinavia reveal a concentration of ribbed moraines around the ice-sheet retreat centres of Quebec, Keewatin, Newfoundland and west-central Fennoscandia. Together with the evidence from relict landscapes that mark glacial areas with frozen-bed conditions, the distribution of ribbed moraines on both continents suggest that a large area of the Laurentide and Fennoscandian ice sheets was frozen-based-and therefore high-domed and stable-during the Last Glacial Maximum.

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

PubMed Central

Zecca, Giovanni; Minuto, Luigi

2016-01-01

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

Clay mineralogical record on the upper continental slope of the northwestern South China Sea since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

CHEN, Q.; Liu, Z.; Stattegger, K.

2012-12-01

Clay mineralogy of two gravity cores (18428 and 18429) on the upper continental slope of the northwestern South China Sea was investigated in order to understand terrigenous sediment sources and to evaluate the contribution from the Red River since the Late Glacial Maximum. Planktonic foraminiferal oxygen isotope and carbonate stratigraphies suggest that Core 18428 is constrained in Holocene while Core 18429 covers the period of MIS 1-2. Clay mineral assemblages of two cores are composed mainly of smectite (18-57%) and illite (21-41%), with minor chlorite (12-21%) and kaolinite (8-26%). In despite of relatively constant values of illite crystallinity, ranging among 0.14°-0.20° Δ2θ, the time series variation in clay mineral distributions indicates a strong glacial-interglacial shift. Contents of illite, chlorite, and kaolinite (Core 18429) in the Holocene are lower than in the glacial period, and vice versa for the smectite content. The provenance analysis based on clay mineralogy suggests the Red River as a predominant sedimentary source of illite, chlorite, and kaolinite during all the depositional period of MIS 1-2. The sea level change actually controlled the variations of clay mineral assemblages on the upper slope since the Last Glacial Maximum. When the sea level was low during the last glacial period, more terrigenous sediments from the Red River could reach the continental slope in the northwestern South China Sea. However, when the sea level is closed to the present situation during the Holocene, most of Red River sediments could be trapped in the Gulf of Tonkin, instead of draining in the deep South China Sea.

Environmental evolution in the Picos de Europa (Cantabrian Mountains, SW Europe) since the Last Glaciation

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesús; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Freitas, Maria da Conceição; Andrade, César; García-Hernández, Cristina; López-Sáez, José Antonio; Geraldes, Miguel

2016-04-01

The Western Massif of the Picos de Europa (latitude 43° N, longitude 4-5° W) includes some of the highest peaks in the Cantabrian Mountains. This massif was heavily glaciated during the Last Glaciation, though the post-glacial environmental evolution is still poorly understood. Using a complementary geomorphological and sedimentological approach, we have reconstructed the environmental events occurred in this massif since the last Pleistocene glaciation. The geomorphological distribution of glacial landforms suggests the occurrence of four main glacial stages: maximum glacial advance, glacial expansion after the maximum advance, Late Glacial and Little Ice Age. Moreover, a 5.4-m long sedimentary sequence was retrieved from the karstic depression of Belbín providing a continuous record of the paleoenvironmental conditions in this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, periglacial processes prevailed in the mid lands of the massif until glaciers expanded between 22.5 and 18.7 ka cal BP. Following the melting of the glaciers, a shallow lake appeared in the Belbín depression. Lake sediments do not show evidence of a cold stage during the Late Glacial, when moraine systems formed at higher locations. The terrestrification of this lake started at 8 ka cal BP and the area turned into grassland. At 4.9 ka cal BP the existence of charcoal particles in the sediments of Belbín sequence reveals the onset of human occupation in the massif through the use of fire activity for grazing purposes. Finally, the presence of moraines inside the highest northern cirques shows evidence of the last glacial phase that occurred during the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers and periglacial processes prevail in the high lands of the massif.

Central Equatorial Pacific Sea Surface Temperatures During the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Monteagudo, M. M.; Lynch-Stieglitz, J.; Schmidt, M. W.

2017-12-01

The state of the tropical Pacific ocean-atmosphere system during the Last Glacial Maximum (LGM, 19,000-23,000 years BP) remains an area of uncertainty. Spatial patterns of tropical Pacific sea surface temperature (SST) offer insight into atmospheric circulation (i.e. Walker Circulation), however, few records exist for the Central Tropical Pacific (CTP). The few existing glacial CTP SST reconstructions indicate 1-2 °C of warming based on foraminiferal transfer functions (CLIMAP Project Members, 1976). In contrast, evidence from geochemical proxies (Mg/Ca, UK'37, TEX86) show 1-3.5 °C cooling in the eastern and western tropical Pacific (e.g. MARGO Project Members, 2009). In this study we present the first Mg/Ca estimates of glacial CTP SST from a meridional sediment core transect along the Line Islands Ridge (0-7°N, 156-162 °W). We use a time slice approach to establish the magnitude of glacial-interglacial SST change between the LGM (19,000-23,0000 years BP) and the Holocene (0-10,000 years BP) using Mg/Ca in the surface-dwelling foraminifera Globigerinoides ruber. Our results indicate cooling at all latitudes, ranging between 1.2-2.7 °C (Holocene-LGM SST). Northern cores (6.83-2.77 °N) exhibit a smaller glacial-interglacial SST difference than equatorial site 20BB at 1.27 °N. The data generated thus far suggest the glacial meridional SST gradient may have been steeper, possibly as a result of increased zonal winds, equatorial upwelling, or westward expansion of the Eastern Pacific Cold Tongue.

Geomorphological and sedimentological evidences in the Western Massif of Picos de Europa since the Last Glaciation

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesus; Oliva, Marc; Cruces, Anabela; Lopes, Vera; Conceição Freitas, Maria; García-Hernández, Cristina; Nieuwendam, Alexandre; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

2015-04-01

The Western Massif of Picos de Europa includes some of the highest peaks of the Cantabrian Mountains. However, the environmental evolution in this massif since the Last Glaciation is still poorly understood. This research provides a new geochronological approach to the sequence of environmental events occurred here since the maximum expansion of glaciers during the last Pleistocene glaciation. The distribution of the glacial landforms suggests four main stages regarding the environmental evolution in the massif: maximum glacial advance, phase of second maximum glacial expansion, Late Glacial and Little Ice Age. A 5.4-m long sedimentological section retrieved from the kame terrace of Belbín, in a mid-height area of the massif, complements the geomorphological interpretation and provides a continuous paleoenvironmental sequence from this area since the Last Glaciation until nowadays. This section suggests that the maximum glacial expansion occurred at a minimum age of 37.2 ka cal BP, significantly prior to the global Last Glacial Maximum. Subsequently, a new glacial expansion occurred around 18.7-22.5 ka cal BP. The melting of the glaciers after this phase generated a shallow lake in the Belbín depression. Lake sediments do not reveal the occurrence of a cold stage during the Late Glacial, whilst, at higher locations, moraine complexes were formed suggesting a glacier readvance. The terrestrification of this lake started at 8 ka cal BP, when Belbín changed to a peaty environment. At 5 ka cal BP human occupation started at the high lands of the massif according to the existence of charcoal particles in the section. The presence of moraines in the highest northern cirques evidences the last phase with formation of small glaciers in the Western Massif of Picos de Europa, corresponding to the Little Ice Age cold event. Since then, the warming climate has led to the melting of these glaciers.

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).

Decadal-scale climate drivers for glacial dynamics in Glacier National Park, Montana, USA

USGS Publications Warehouse

Pederson, G.T.; Fagre, D.B.; Gray, S.T.; Graumlich, L.J.

2004-01-01

Little Ice Age (14th-19th centuries A.D.) glacial maxima and 20th century retreat have been well documented in Glacier National Park, Montana, USA. However, the influence of regional and Pacific Basin driven climate variability on these events is poorly understood. We use tree-ring reconstructions of North Pacific surface temperature anomalies and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, over the past three centuries. These records show that the 1850's glacial maximum was likely produced by ???70 yrs of cool/wet summers coupled with high snowpack. Post 1850, glacial retreat coincides with an extended period (>50 yr) of summer drought and low snowpack culminating in the exceptional events of 1917 to 1941 when retreat rates for some glaciers exceeded 100 m/yr. This research highlights potential local and ocean-based drivers of glacial dynamics, and difficulties in separating the effects of global climate change from regional expressions of decadal-scale climate variability. Copyright 2004 by the American Geophysical Union.

High migration rates shape the postglacial history of amphi-Atlantic bryophytes.

PubMed

Désamoré, Aurélie; Patiño, Jairo; Mardulyn, Patrick; Mcdaniel, Stuart F; Zanatta, Florian; Laenen, Benjamin; Vanderpoorten, Alain

2016-11-01

Paleontological evidence and current patterns of angiosperm species richness suggest that European biota experienced more severe bottlenecks than North American ones during the last glacial maximum. How well this pattern fits other plant species is less clear. Bryophytes offer a unique opportunity to contrast the impact of the last glacial maximum in North America and Europe because about 60% of the European bryoflora is shared with North America. Here, we use population genetic analyses based on approximate Bayesian computation on eight amphi-Atlantic species to test the hypothesis that North American populations were less impacted by the last glacial maximum, exhibiting higher levels of genetic diversity than European ones and ultimately serving as a refugium for the postglacial recolonization of Europe. In contrast with this hypothesis, the best-fit demographic model involved similar patterns of population size contractions, comparable levels of genetic diversity and balanced migration rates between European and North American populations. Our results thus suggest that bryophytes have experienced comparable demographic glacial histories on both sides of the Atlantic. Although a weak, but significant genetic structure was systematically recovered between European and North American populations, evidence for migration from and towards both continents suggests that amphi-Atlantic bryophyte population may function as a metapopulation network. Reconstructing the biogeographic history of either North American or European bryophyte populations therefore requires a large, trans-Atlantic geographic framework. © 2016 John Wiley & Sons Ltd.

Equilibrium-line altitude during the Antarctic Cold Reversal at Río Tranquilo glacier (47°S), Central Patagonia

NASA Astrophysics Data System (ADS)

Sagredo, E. A.; Ward, D.; Gonzalez, M. A.; Lowell, T. V.; Kelly, M. A.; Aravena, J. C.

2013-12-01

Documenting the magnitude of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we estimate the equilibrium line altitudes (ELA) associated with the most prominent glacial advance occurred during the Last Glacial Termination (T1) at Tranquilo glacier (47°S). Geomorphic evidence suggest that, following the Last Glacial Maximum, several small glaciers, which today occupy the headwalls of Río Tranquilo valley, expanded and coalesced, forming the extended version of the Tranquilo glacier at least three different times. 10Be ages suggest that the most prominent of these glacial advances occurred ~13 kyr BP, at the end of the Antarctic Cold Reversal (ACR). Based on glacial geomorphic mapping and the application of a glaciological model (GC2D), we reconstruct the former glacial surface at Tranquilo glacier and estimate the ELA for this major glacial advance. Preliminary data show that the equilibrium line altitude at Tranquilo glacier during the ACR could have been up to 500 m lower than the present. This study represents the first effort to quantify the ELA during the Antarctic Cold Reversal in Patagonia, and provides a baseline to decipher the climatic signals driving this glacial event.

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.

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

NASA Astrophysics Data System (ADS)

Kohfeld, Karen E.; Chase, Zanna

2017-08-01

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

Breakup of last glacial deep stratification in the South Pacific

NASA Astrophysics Data System (ADS)

Basak, Chandranath; Fröllje, Henning; Lamy, Frank; Gersonde, Rainer; Benz, Verena; Anderson, Robert F.; Molina-Kescher, Mario; Pahnke, Katharina

2018-02-01

Stratification of the deep Southern Ocean during the Last Glacial Maximum is thought to have facilitated carbon storage and subsequent release during the deglaciation as stratification broke down, contributing to atmospheric CO2 rise. Here, we present neodymium isotope evidence from deep to abyssal waters in the South Pacific that confirms stratification of the deepwater column during the Last Glacial Maximum. The results indicate a glacial northward expansion of Ross Sea Bottom Water and a Southern Hemisphere climate trigger for the deglacial breakup of deep stratification. It highlights the important role of abyssal waters in sustaining a deep glacial carbon reservoir and Southern Hemisphere climate change as a prerequisite for the destabilization of the water column and hence the deglacial release of sequestered CO2 through upwelling.

Colonization in North American Arid Lands: The Journey of Agarito (Berberis trifoliolata) Revealed by Multilocus Molecular Data and Packrat Midden Fossil Remains

PubMed Central

Angulo, Diego F.; Amarilla, Leonardo D.; Anton, Ana M.; Sosa, Victoria

2017-01-01

Here we conduct research to understand the evolutionary history of a shrubby species known as Agarito (Berberis trifoliolata), an endemic species to the Chihuahuan Desert. We identify genetic signatures based on plastid DNA and AFLP markers and perform niche modelling and spatial connectivity analyses as well as niche modelling based on records in packrats to elucidate whether orogenic events such as mountain range uplift in the Miocene or the contraction/expansion dynamics of vegetation in response to climate oscillations in the Pliocene/Pleistocene had an effect on evolutionary processes in Agarito. Our results of current niche modelling and palaeomodelling showed that the area currently occupied by Berberis trifoliolata is substantially larger than it was during the Last Interglacial period and the Last Glacial Maximum. Agarito was probably confined to small areas in the Northeastern and gradually expanded its distribution just after the Last Glacial Maximum when the weather in the Chihuahuan Desert and adjacent regions became progressively warmer and drier. The most contracted range was predicted for the Interglacial period. Populations remained in stable areas during the Last Glacial Maximum and expanded at the beginning of the Holocene. Most genetic variation occured in populations from the Sierra Madre Oriental. Two groups of haplotypes were identified: the Mexican Plateau populations and certain Northeastern populations. Haplogroups were spatially connected during the Last Glacial Maximum and separated during interglacial periods. The most important prediction of packrat middens palaeomodelling lies in the Mexican Plateau, a finding congruent with current and past niche modelling predictions for agarito and genetic results. Our results corroborate that these climate changes in the Pliocene/Pleistocene affected the evolutionary history of agarito. The journey of agarito in the Chihuahuan Desert has been dynamic, expanding and contracting its distribution range and currently occupying the largest area in its history. PMID:28146559

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.

Dominant factors controlling glacial and interglacial variations in the treeline elevation in tropical Africa

PubMed Central

Wu, Haibin; Guiot, Joël; Brewer, Simon; Guo, Zhengtang; Peng, Changhui

2007-01-01

The knowledge of tropical palaeoclimates is crucial for understanding global climate change, because it is a test bench for general circulation models that are ultimately used to predict future global warming. A longstanding issue concerning the last glacial maximum in the tropics is the discrepancy between the decrease in sea-surface temperatures reconstructed from marine proxies and the high-elevation decrease in land temperatures estimated from indicators of treeline elevation. In this study, an improved inverse vegetation modeling approach is used to quantitatively reconstruct palaeoclimate and to estimate the effects of different factors (temperature, precipitation, and atmospheric CO2 concentration) on changes in treeline elevation based on a set of pollen data covering an altitudinal range from 100 to 3,140 m above sea level in Africa. We show that lowering of the African treeline during the last glacial maximum was primarily triggered by regional drying, especially at upper elevations, and was amplified by decreases in atmospheric CO2 concentration and perhaps temperature. This contrasts with scenarios for the Holocene and future climates, in which the increase in treeline elevation will be dominated by temperature. Our results suggest that previous temperature changes inferred from tropical treeline shifts may have been overestimated for low-CO2 glacial periods, because the limiting factors that control changes in treeline elevation differ between glacial and interglacial periods. PMID:17535920

Dominant factors controlling glacial and interglacial variations in the treeline elevation in tropical Africa.

PubMed

Wu, Haibin; Guiot, Joël; Brewer, Simon; Guo, Zhengtang; Peng, Changhui

2007-06-05

The knowledge of tropical palaeoclimates is crucial for understanding global climate change, because it is a test bench for general circulation models that are ultimately used to predict future global warming. A longstanding issue concerning the last glacial maximum in the tropics is the discrepancy between the decrease in sea-surface temperatures reconstructed from marine proxies and the high-elevation decrease in land temperatures estimated from indicators of treeline elevation. In this study, an improved inverse vegetation modeling approach is used to quantitatively reconstruct palaeoclimate and to estimate the effects of different factors (temperature, precipitation, and atmospheric CO(2) concentration) on changes in treeline elevation based on a set of pollen data covering an altitudinal range from 100 to 3,140 m above sea level in Africa. We show that lowering of the African treeline during the last glacial maximum was primarily triggered by regional drying, especially at upper elevations, and was amplified by decreases in atmospheric CO(2) concentration and perhaps temperature. This contrasts with scenarios for the Holocene and future climates, in which the increase in treeline elevation will be dominated by temperature. Our results suggest that previous temperature changes inferred from tropical treeline shifts may have been overestimated for low-CO(2) glacial periods, because the limiting factors that control changes in treeline elevation differ between glacial and interglacial periods.

Chronology of the last glacial maximum in the upper Bear River Basin, Utah

USGS Publications Warehouse

Laabs, B.J.C.; Munroe, Jeffrey S.; Rosenbaum, J.G.; Refsnider, K.A.; Mickelson, D.M.; Singer, B.S.; Caffee, M.W.

2007-01-01

The headwaters of the Bear River drainage were occupied during the Last Glacial Maximum (LGM) by outlet glaciers of the Western Uinta Ice Field, an extensive ice mass (???685 km2) that covered the western slope of the Uinta Mountains. A well-preserved sequence of latero-frontal moraines in the drainage indicates that outlet glaciers advanced beyond the mountain front and coalesced on the piedmont. Glacial deposits in the Bear River drainage provide a unique setting where both 10Be cosmogenic surface-exposure dating of moraine boulders and 14C dating of sediment in Bear Lake downstream of the glaciated area set age limits on the timing of glaciation. Limiting 14C ages of glacial flour in Bear Lake (corrected to calendar years using CALIB 5.0) indicate that ice advance began at 32 ka and culminated at about 24 ka. Based on a Bayesian statistical analysis of cosmogenic surface-exposure ages from two areas on the terminal moraine complex, the Bear River glacier began its final retreat at about 18.7 to 18.1 ka, approximately coincident with the start of deglaciation elsewhere in the central Rocky Mountains and many other alpine glacial localities worldwide. Unlike valleys of the southwestern Uinta Mountains, deglaciation of the Bear River drainage began prior to the hydrologie fall of Lake Bonneville from the Provo shoreline at about 16 ka. ?? 2007 Regents of the University of Colorado.

Ice stream reorganization and glacial retreat on the northwest Greenland shelf

NASA Astrophysics Data System (ADS)

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

2017-08-01

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

Timing of maximum glacial extent and deglaciation from HualcaHualca volcano (southern Peru), obtained with cosmogenic 36Cl.

NASA Astrophysics Data System (ADS)

Alcalá, Jesus; Palacios, David; Vazquez, Lorenzo; Juan Zamorano, Jose

2015-04-01

Andean glacial deposits are key records of climate fluctuations in the southern hemisphere. During the last decades, in situ cosmogenic nuclides have provided fresh and significant dates to determine past glacier behavior in this region. But still there are many important discrepancies such as the impact of Last Glacial Maximum or the influence of Late Glacial climatic events on glacial mass balances. Furthermore, glacial chronologies from many sites are still missing, such as HualcaHualca (15° 43' S; 71° 52' W; 6,025 masl), a high volcano of the Peruvian Andes located 70 km northwest of Arequipa. The goal of this study is to establish the age of the Maximum Glacier Extent (MGE) and deglaciation at HualcaHualca volcano. To achieve this objetive, we focused in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) characterized by a well-preserved sequence of moraines and roches moutonnées. The method is based on geomorphological analysis supported by cosmogenic 36Cl surface exposure dating. 36Cl ages have been estimated with the CHLOE calculator and were compared with other central Andean glacial chronologies as well as paleoclimatological proxies. In Huayuray valley, exposure ages indicates that MGE occurred ~ 18 - 16 ka. Later, the ice mass gradually retreated but this process was interrupted by at least two readvances; the last one has been dated at ~ 12 ka. In the other hand, 36Cl result reflects a MGE age of ~ 13 ka in Mollebaya valley. Also, two samples obtained in Pujro-Huayjo and Mucurca valleys associated with MGE have an exposure age of 10-9 ka, but likely are moraine boulders affected by exhumation or erosion processes. Deglaciation in HualcaHualca volcano began abruptly ~ 11.5 ka ago according to a 36Cl age from a polished and striated bedrock in Pujro Huayjo valley, presumably as a result of reduced precipitation as well as a global increase of temperatures. The glacier evolution at HualcaHualca volcano presents a high correlation with precipitation cycles of the Altiplano (Tauca / Coipasa phases) and Heinrich 1 / Younger Dryas cold climatic events. Research funded by Cryocrisis project (CGL2012-35858), Government of Spain

Glacial stages and post-glacial environmental evolution in the Upper Garonne valley, Central Pyrenees.

PubMed

Fernandes, M; Oliva, M; Palma, P; Ruiz-Fernández, J; Lopes, L

2017-04-15

The maximum glacial extent in the Central Pyrenees during the Last Glaciation is known to have occurred before the global Last Glacial Maximum, but the succession of cold events afterwards and their impact on the landscape are still relatively unknown. This study focuses on the environmental evolution in the upper valley of the Garonne River since the Last Glaciation. Geomorphological mapping allows analysis of the spatial distribution of inherited and current processes and landforms in the study area. The distribution of glacial records (moraines, till, erratic boulders, glacial thresholds) suggests the existence of four glacial stages, from the maximum expansion to the end of the glaciation. GIS modeling allows quantification of the Equilibrium Line Altitude, extent, thickness and volume of ice in each glacial stage. During the first stage, the Garonne glacier reached 460m in the Loures-Barousse-Barbazan basin, where it formed a piedmont glacier 88km from the head and extended over 960km 2 . At a second stage of glacier stabilization during the deglaciation process, the valley glaciers were 12-23km from the head until elevations of 1000-1850m, covering an area of 157km 2 . Glaciers during stage three remained isolated in the upper parts of the valley, at heights of 2050-2200m and 2.6-4.5km from the head, with a glacial surface of 16km 2 . In stage four, cirque glaciers were formed between 2260m and 2590m, with a length of 0.4-2km and a glacial area of 5.7km 2 . Also, the wide range of periglacial, slope, nival and alluvial landforms existing in the formerly glaciated environments allows reconstruction of the post-glacial environmental dynamics in the upper Garonne basin. Today, the highest lands are organized following three elevation belts: subnival (1500-1900m), nival (1900-2300m) and periglacial/cryonival (2300-2800m). Copyright © 2017 Elsevier B.V. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2004-12-01

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

Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

NASA Astrophysics Data System (ADS)

Bromley, Gordon R. M.; Schaefer, Joerg M.; Winckler, Gisela; Hall, Brenda L.; Todd, Claire E.; Rademaker, Kurt M.

2009-11-01

Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions. Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

Tropical climate at the last glacial maximum inferred from glacier mass-balance modeling

USGS Publications Warehouse

Hostetler, S.W.; Clark, P.U.

2000-01-01

Model-derived equilibrium line altitudes (ELAs) of former tropical glaciers support arguments, based on other paleoclimate data, for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum (LGM). Relative to the present, LGM ELAs were maintained by air temperatures that were 3.5??to 6.6 ??C lower and precipitation that ranged from 63% wetter in Hawaii to 25% drier on Mt. Kenya, Africa. Our results imply the need for a ~3 ??C cooling of LGM sea surface temperatures in the western Pacific warm pool. Sensitivity tests suggest that LGM ELAs could have persisted until 16,000 years before the present in the Peruvian Andes and on Papua, New Guinea.

Tracing glacial refugia of Triturus newts based on mitochondrial DNA phylogeography and species distribution modeling

PubMed Central

2013-01-01

Introduction The major climatic oscillations during the Quaternary Ice Age heavily influenced the distribution of species and left their mark on intraspecific genetic diversity. Past range shifts can be reconstructed with the aid of species distribution modeling and phylogeographical analyses. We test the responses of the different members of the genus Triturus (i.e. the marbled and crested newts) as the climate shifted from the previous glacial period (the Last Glacial Maximum, ~21 Ka) to the current interglacial. Results We present the results of a dense mitochondrial DNA phylogeography (visualizing genetic diversity within and divergence among populations) and species distribution modeling (using two different climate simulations) for the nine Triturus species on composite maps. Conclusions The combined use of species distribution modeling and mitochondrial phylogeography provides insight in the glacial contraction and postglacial expansion of Triturus. The combined use of the two independent techniques yields a more complete understanding of the historical biogeography of Triturus than both approaches would on their own. Triturus newts generally conform to the ‘southern richness and northern purity’ paradigm, but we also find more intricate patterns, such as the absence of genetic variation and suitable area at the Last Glacial Maximum (T. dobrogicus), an ‘extra-Mediterranean’ refugium in the Carpathian Basin (T. cristatus), and areas where species displaced one another postglacially (e.g. T. macedonicus and western T. karelinii). We provide a biogeographical scenario for Triturus, showing the positions of glacial refugia, the regions that were postglacially colonized and the areas where species displaced one another as they shifted their ranges. PMID:23514662

Tracing glacial refugia of Triturus newts based on mitochondrial DNA phylogeography and species distribution modeling.

PubMed

Wielstra, Ben; Crnobrnja-Isailović, Jelka; Litvinchuk, Spartak N; Reijnen, Bastian T; Skidmore, Andrew K; Sotiropoulos, Konstantinos; Toxopeus, Albertus G; Tzankov, Nikolay; Vukov, Tanja; Arntzen, Jan W

2013-03-20

The major climatic oscillations during the Quaternary Ice Age heavily influenced the distribution of species and left their mark on intraspecific genetic diversity. Past range shifts can be reconstructed with the aid of species distribution modeling and phylogeographical analyses. We test the responses of the different members of the genus Triturus (i.e. the marbled and crested newts) as the climate shifted from the previous glacial period (the Last Glacial Maximum, ~21 Ka) to the current interglacial. We present the results of a dense mitochondrial DNA phylogeography (visualizing genetic diversity within and divergence among populations) and species distribution modeling (using two different climate simulations) for the nine Triturus species on composite maps. The combined use of species distribution modeling and mitochondrial phylogeography provides insight in the glacial contraction and postglacial expansion of Triturus. The combined use of the two independent techniques yields a more complete understanding of the historical biogeography of Triturus than both approaches would on their own. Triturus newts generally conform to the 'southern richness and northern purity' paradigm, but we also find more intricate patterns, such as the absence of genetic variation and suitable area at the Last Glacial Maximum (T. dobrogicus), an 'extra-Mediterranean' refugium in the Carpathian Basin (T. cristatus), and areas where species displaced one another postglacially (e.g. T. macedonicus and western T. karelinii). We provide a biogeographical scenario for Triturus, showing the positions of glacial refugia, the regions that were postglacially colonized and the areas where species displaced one another as they shifted their ranges.

Fingerprinting of glacial silt in lake sediments yields continuous records of alpine glaciation (35–15 ka), western USA

USGS Publications Warehouse

Rosenbaum, Joseph G.; Reynolds, Richard L.; Colman, Steven M.

2012-01-01

Fingerprinting glacial silt in last glacial-age sediments from Upper Klamath Lake (UKL) and Bear Lake (BL) provides continuous radiocarbon-dated records of glaciation for the southeastern Cascade Range and northwestern Uinta Mountains, respectively. Comparing of these records to cosmogenic exposure ages from moraines suggests that variations in glacial flour largely reflect glacial extent. The two areas are at similar latitudes and yield similar records of glacial growth and recession, even though UKL lies less than 200 km from the ocean and BL is in the continental interior. As sea level began to fall prior to the global Last Glacial Maximum (LGM), existing glaciers in the UKL area expanded. Near the beginning of the global LGM (26.5 ka), the BL record indicates onset of glaciation and UKL-area glaciers underwent further expansion. Both records indicate that local glaciers reached their maximum extents near the end of the global LGM, remained near their maxima for ~1000 yr, and underwent two stages of retreat separated by a short period of expansion.

Fingerprinting of glacial silt in lake sediments yields continuous records of alpine glaciation (35-15 ka), western USA

NASA Astrophysics Data System (ADS)

Rosenbaum, Joseph G.; Reynolds, Richard L.; Colman, Steven M.

2012-09-01

Fingerprinting glacial silt in last glacial-age sediments from Upper Klamath Lake (UKL) and Bear Lake (BL) provides continuous radiocarbon-dated records of glaciation for the southeastern Cascade Range and northwestern Uinta Mountains, respectively. Comparing of these records to cosmogenic exposure ages from moraines suggests that variations in glacial flour largely reflect glacial extent. The two areas are at similar latitudes and yield similar records of glacial growth and recession, even though UKL lies less than 200 km from the ocean and BL is in the continental interior. As sea level began to fall prior to the global Last Glacial Maximum (LGM), existing glaciers in the UKL area expanded. Near the beginning of the global LGM (26.5 ka), the BL record indicates onset of glaciation and UKL-area glaciers underwent further expansion. Both records indicate that local glaciers reached their maximum extents near the end of the global LGM, remained near their maxima for ~ 1000 yr, and underwent two stages of retreat separated by a short period of expansion.

Reconstructing spatial and temporal patterns of paleoglaciation along the Tian Shan

NASA Astrophysics Data System (ADS)

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

2012-12-01

Testing and calibrating global climate models require well-constrained information on past climates of key regions around the world. Particularly important are transitional regions that provide a sensitive record of past climate change. Central Asia is an extreme continental location with glaciers and rivers that respond sensitively to temporal variations in the dominance of several major climate systems. As an international team initiative, we are reconstructing the glacial history of the Kyrgyz and Chinese Tian Shan, based on mapping and dating of key localities along the range. Remote-sensing-based geomorphological mapping, building on previous maps produced by Kyrgyz, Russian, Chinese and German scholars, is being augmented with field observations of glacial geomorphology and the maximum distribution of erratics. We are using cosmogenic nuclide (CN) 10Be dating of moraines and other landforms that constrain the former maximum extents of glaciers. Study sites include the Ala-Archa, Ak-Shyrak and Inylchek/Sary-Dzaz areas in Kyrgyzstan and the Urumqi valley (as well as its upland and southern slopes), and the Tumur and Bogeda peak areas in China. Comparing consistently dated glacial histories along and across the range will allow us to examine potential shifts in the dominance patterns of climate systems over time in Central Asia. We are also comparing ages based on CN with optically stimulated luminescence (OSL) and electron spin resonance (ESR) dates. The final stage of this project will use intermediate complexity glacier flow models to examine paleoclimatic implications of the observed spatial and temporal patterns of glacier changes across Central Asia and eastern Tibet, focused in particular on the last glacial cycle.

The Labrador Sea during the Last Glacial Maximum: Calcite dissolution or low biogenic carbonate fluxes?

NASA Astrophysics Data System (ADS)

Marshall, Nicole; de Vernal, Anne; Mucci, Alfonso; Filippova, Alexandra; Kienast, Markus

2017-04-01

Low concentrations of biogenic carbonate characterize the sediments deposited in the Labrador Sea during the last glaciation. This may reflect poor calcite preservation and/or low biogenic carbonate productivity and fluxes. Regional bottom water ventilation was reduced during the Last Glacial Maximum (LGM), so the calcite lysocline might have been shallower than at present in the deep Labrador Sea making dissolution of calcite shells in the deep Labrador Sea possible. To address the issue, a multi-proxy approach based on micropaleontological counts (coccoliths, foraminifers, palynomorphs) and biogeochemical analyses (alkenones) was applied in the investigation of core HU2008-029-004-PC recovered in the northwestern Labrador Sea. Calcite dissolution indices based on the relative abundance benthic foraminifera shells to their organic linings as well as on fragmentation of planktonic foraminifera shells were used to evaluate changes in calcite dissolution/ preservation since the LGM. In addition, the ratio of the concentrations of coccoliths, specifically of the alkenone-producer Emiliania huxleyi, and alkenones (Emiliania huxleyi: alkenones) was explored as a potential new proxy of calcite dissolution. A sharp increase in coccoliths, foraminifers and organic linings from nearly none to substantial concentrations at 12 ka, reflect a jump to significantly greater biogenic fluxes at the glacial-interglacial transition. Furthermore, conventional dissolution indices (shells/linings of benthic foraminifera and fragmentation of planktic foraminifers) reveal that dissolution is not likely responsible for the lower glacial abundances of coccoliths and foraminifers. Only the low Emiliania huxleyi: alkenones ratios in glacial sediments could be interpreted as evidence of increased dissolution during the LGM. Given the evidence of allochthonous alkenone input into the glacial Labrador Sea, the latter observations must be treated with caution. Overall, the records indicate that low biogenic fluxes during the LGM were the most likely cause of the decreased biogenic carbonate concentrations.

Termination of the Last Glacial Maximum sea-level lowstand: The Sunda-Shelf data revisited

NASA Astrophysics Data System (ADS)

Hanebuth, T. J. J.; Stattegger, K.; Bojanowski, A.

2009-03-01

The sea-level history around the last glaciation is in the focus of recent, controversial debates. A profound understanding of sea-level changes during this time interval is, however, essential since sea level is a central parameter in the climate system as well as a major force on continental margin sedimentation. Here, we present a seismic record together with augmented data from the Sunda Shelf [Hanebuth, T.J.J., Stattegger, K., Saito, Y., 2002. The architecture of the central Sunda Shelf (SE Asia) recorded by shallow-seismic surveying. Geo-Marine Letters 22, 86-94.] and compare our results in a careful evaluation with the sparse existing data sets of global validity, i.e. the Bonaparte Gulf record [Yokoyama, Y., Lambeck, K., DeDeckker, P., Johnston, P., Fifield, L.K., 2000. Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406, 713-716.; Yokoyama, Y., De Deckker, P., Lambeck, K., Johnston, P., Fifield, L.K., 2001. Sea-level at the Last Glacial Maximum: evidence from nortwestern Australia to constrain ice volumes for oxygen isotope stage 2. Paleogeography Paleoclimatology Paleoecology 165, 281-297.], the Barbados coral record [Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea level record: influence of glacial melting dates on the Younger Dryas event and deep ocean circulation. Nature 342, 637-642.; Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23-24), 3322-3337.] and the latest numerical model of continental deglaciation [Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23-24), 3322-3337.]. Sea level seems to have been lower shortly prior to the conventional Last Glacial Maximum (LGM; 21-19 cal kyr BP). The time interval around this glacial lowstand is not covered by ages from the Sunda Shelf, but documented by an ancient barrier — tidal-flat system. These palaeo-coastal relict forms indicate such an early lowstand some 5 m deeper than sea level was during LGM times. The LGM sea level on the Sunda shelf is recalculated to - 123 ± 2 m modern water depth. This depth fits nicely with the lowstand data derived from Barbados and the Bonaparte Gulf. The recently assumed 19-kyr sea-level rise is supported by the Sunda and Bonaparte data sets combined, although it might have started already as early as at 19.6 cal kyr BP lasting for some 800 kyr with an amplitude of at least 10 m. This early pulse-like rise might have played a crucial role in the physical preservation of the high-glacial to early deglacial deposits on the Sunda Shelf. The modelled sea-level history is, thus, supported with respect to an initial high-glacial lowstand prior to the LGM, which might be in apparent contrast to observations from Bonaparte. Nevertheless, field data suggest a glacial sea-level evolution about 10 m deeper than the model. Also, the gradual rising trend from 26 to 16 cal kyr BP, as deduced from the model, can definitively not be approved by any field data. However, our knowledge is still unsatisfactory and an expansion of field data from suited areas is urgently needed.

Breakup of last glacial deep stratification in the South Pacific.

PubMed

Basak, Chandranath; Fröllje, Henning; Lamy, Frank; Gersonde, Rainer; Benz, Verena; Anderson, Robert F; Molina-Kescher, Mario; Pahnke, Katharina

2018-02-23

Stratification of the deep Southern Ocean during the Last Glacial Maximum is thought to have facilitated carbon storage and subsequent release during the deglaciation as stratification broke down, contributing to atmospheric CO 2 rise. Here, we present neodymium isotope evidence from deep to abyssal waters in the South Pacific that confirms stratification of the deepwater column during the Last Glacial Maximum. The results indicate a glacial northward expansion of Ross Sea Bottom Water and a Southern Hemisphere climate trigger for the deglacial breakup of deep stratification. It highlights the important role of abyssal waters in sustaining a deep glacial carbon reservoir and Southern Hemisphere climate change as a prerequisite for the destabilization of the water column and hence the deglacial release of sequestered CO 2 through upwelling. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Late Pleistocene oscillations of the Drau Glacier (southern Austria)

NASA Astrophysics Data System (ADS)

Karnitschar, Christina; Reitner, Jürgen; Draganits, Erich

2016-04-01

The Drau Glacier was the largest Pleistocene glacier in the southeastern part of the Alps and significantly shaped the landscape in this region. The study area is located at the termination of the Drau Glacier in the southern part of Austria (Carinthia). The investigation aims to decipher glacial dynamics during the Late Pleistocene glacial advance, stabilisation and final recession of this glacier based on geological/geomorphological mapping, interpretation of airborne laser scan (ALS) topographic data and lithostratigraphic investigations of glacial and periglacial sediments. Special emphasis is laid on the reconstruction of the maximum extent of the glaciation (LGM). Based on previous mapping by Bobek (1959) and Ucik (1996-1998) more details have been gained for the paleogeographic reconstruction based on glacial and non-glacial erosion and accumulation features. These include traces of pre-Upper Pleistocene glaciation, drumlins, terminal moraines and kettle holes. Paleogeographic reconstruction was done with correlation of different outcrops based on lithostratigraphy and ALS topography. Sequences of gravel related to glacial advance covered by till, followed by periglacial sediments allowed detailed reconstruction of the glacial sequence in this area and the complex succession of various extents of the Drau Glacier. References Bobek, Hans. 1959: Der Eisrückgang im östlichen Klagenfurter Becken. In: Mitteilungen der österreichischen geographischen Gesellschaft, Wien. Ucik, Friedrich Hans. 1996: Bericht über geologische Aufnahmen im Quartär auf Blatt 204 Völkermarkt, Jb. Geol. B.-A., 141, S. 340, Wien. Ucik, Friedrich Hans. 1997: Bericht über geologische Aufnahmen im Quartär auf Blatt 204 Völkermarkt, Jb. Geol. B.-A., 141, S. 325-326, Wien. Ucik, Friedrich Hans. 1998: Bericht über geologische Aufnahmen im Quartär auf Blatt 204 Völkermarkt, Jb. Geol. B.-A., 142, S. 333-334, Wien.

Climatic implications of correlated upper Pleistocene glacial and fluvial deposits on the Cinca and Gallego rivers, NE Spain

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

Lewis, Claudia J; Mcdonald, Eric; Sancho, Carlos

We correlate Upper Pleistocene glacial and fluvial deposits of the Cinca and Gallego River valleys (south central Pyrenees and Ebro basin, Spain) using geomorphic position, luminescence dates, and time-related trends in soil development. The ages obtained from glacial deposits indicate glacial periods at 85 {+-} 5 ka, 64 {+-} 11 ka, and 36 {+-} 3 ka (from glacial till) and 20 {+-} 3 ka (from loess). The fluvial drainage system, fed by glaciers in the headwaters, developed extensive terrace systems in the Cinca River valley at 178 {+-} 21 ka, 97 {+-} 16 ka, 61 {+-} 4 ka, 47 {+-}more » 4 ka, and 11 {+-} 1 ka, and in the Gallego River valley at 151 {+-} 11 ka, 68 {+-} 7 ka, and 45 {+-} 3 ka. The times of maximum geomorphic activity related to cold phases coincide with Late Pleistocene marine isotope stages and heinrich events. The maximum extent of glaciers during the last glacial occurred at 64 {+-} 11 ka, and the terraces correlated with this glacial phase are the most extensive in both the Cinca (61 {+-} 4 ka) and Gallego (68 {+-} 7 ka) valleys, indicating a strong increase in fluvial discharge and availability of sediments related to the transition to deglaciation. The global Last Glacial Maximum is scarcely represented in the south central Pyrenees owing to dominantly dry conditions at that time. Precipitation must be controlled by the position of the Iberian Peninsula with respect to the North Atlantic atmospheric circulation system. The glacial systems and the associated fluvial dynamic seem sensitive to (1) global climate changes controlled by insolation, (2) North Atlantic thermohaline circulation influenced by freshwater pulses into the North Atlantic, and (3) anomalies in atmospheric circulation in the North Atlantic controlling precipitation on the Iberian peninsula. The model of glacial and fluvial evolution during the Late Pleistocene in northern Spain could be extrapolated to other glaciated mountainous areas in southern Europe.« less

A fresh look at the Last Glacial Maximum using Paleoclimate Data Assimilation

NASA Astrophysics Data System (ADS)

Malevich, S. B.; Tierney, J. E.; Hakim, G. J.; Tardif, R.

2017-12-01

Quantifying climate conditions during the Last Glacial Maximum ( 21ka) can help us to understand climate responses to forcing and climate states that are poorly represented in the instrumental record. Paleoclimate proxies may be used to estimate these climate conditions, but proxies are sparsely distributed and possess uncertainties from environmental and biogeochemical processes. Alternatively, climate model simulations provide a full-field view, but may predict unrealistic climate states or states not faithful to proxy records. Here, we use data assimilation - combining climate proxy records with a theoretical understanding from climate models - to produce field reconstructions of the LGM that leverage the information from both data and models. To date, data assimilation has mainly been used to produce reconstructions of climate fields through the last millennium. We expand this approach in order to produce a climate fields for the Last Glacial Maximum using an ensemble Kalman filter assimilation. Ensemble samples were formed from output from multiple models including CCSM3, CESM2.1, and HadCM3. These model simulations are combined with marine sediment proxies for upper ocean temperature (TEX86, UK'37, Mg/Ca and δ18O of foraminifera), utilizing forward models based on a newly developed suite of Bayesian proxy system models. We also incorporate age model and radiocarbon reservoir uncertainty into our reconstructions using Bayesian age modeling software. The resulting fields show familiar patterns based on comparison with previous proxy-based reconstructions, but additionally reveal novel patterns of large-scale shifts in ocean-atmosphere dynamics, as the surface temperature data inform upon atmospheric circulation and precipitation patterns.

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.

North Pacific atmospheric rivers and their influence on western North America at the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Lora, Juan M.; Mitchell, Jonathan L.; Risi, Camille; Tripati, Aradhna E.

2017-01-01

Southwestern North America was wetter than present during the Last Glacial Maximum. The causes of increased water availability have been recently debated, and quantitative precipitation reconstructions have been underutilized in model-data comparisons. We investigate the climatological response of North Pacific atmospheric rivers to the glacial climate using model simulations and paleoclimate reconstructions. Atmospheric moisture transport due to these features shifted toward the southeast relative to modern. Enhanced southwesterly moisture delivery between Hawaii and California increased precipitation in the southwest while decreasing it in the Pacific Northwest, in agreement with reconstructions. Coupled climate models that are best able to reproduce reconstructed precipitation changes simulate decreases in sea level pressure across the eastern North Pacific and show the strongest southeastward shifts of moisture transport relative to a modern climate. Precipitation increases of ˜1 mm d-1, due largely to atmospheric rivers, are of the right magnitude to account for reconstructed pluvial conditions in parts of southwestern North America during the Last Glacial Maximum.

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. Copyright © 2012 Elsevier B.V. All rights reserved.

Hydrochemical Regions of the Glacial Aquifer System, Northern United States, and Their Environmental and Water-Quality Characteristics

USGS Publications Warehouse

Arnold, Terri L.; Warner, Kelly L.; Groschen, George E.; Caldwell, James P.; Kalkhoff, Stephen J.

2008-01-01

The glacial aquifer system in the United States is a large (953,000 square miles) regional aquifer system of heterogeneous composition. As described in this report, the glacial aquifer system includes all unconsolidated geologic material above bedrock that lies on or north of the line of maximum glacial advance within the United States. Examining ground-water quality on a regional scale indicates that variations in the concentrations of major and minor ions and some trace elements most likely are the result of natural variations in the geologic and physical environment. Study of the glacial aquifer system was designed around a regional framework based on the assumption that two primary characteristics of the aquifer system can affect water quality: intrinsic susceptibility (hydraulic properties) and vulnerability (geochemical properties). The hydrochemical regions described in this report were developed to identify and explain regional spatial variations in ground-water quality in the glacial aquifer system within the hypothetical framework context. Data analyzed for this study were collected from 1991 to 2003 at 1,716 wells open to the glacial aquifer system. Cluster analysis was used to group wells with similar ground-water concentrations of calcium, chloride, fluoride, magnesium, potassium, sodium, sulfate, and bicarbonate into five unique groups. Maximum Likelihood Classification was used to make the extrapolation from clustered groups of wells, defined by points, to areas of similar water quality (hydrochemical regions) defined in a geospatial model. Spatial data that represented average annual precipitation, average annual temperature, land use, land-surface slope, vertical soil permeability, average soil clay content, texture of surficial deposits, type of surficial deposit, and potential for ground-water recharge were used in the Maximum Likelihood Classification to classify the areas so the characteristics of the hydrochemical regions would resemble the characteristics of the clusters. The result of the Maximum Likelihood Classification is a map showing five hydrochemical regions of the glacial aquifer system. Statistical analysis of ion concentrations (calcium, chloride, fluoride, magnesium, sodium, potassium, sulfate, and bicarbonate) in samples collected from wells completed in the glacial aquifer system illustrates that variations in water quality can be explained, in part, by related environmental characteristics that control the movement of ground water through the aquifer system. A comparison of median concentrations of chemical constituents in ground water among the five hydrochemical regions indicates that ground water in the Midwestern Agricultural Region, the Urban-Influenced Region, and the Western Agriculture and Grassland Region has the highest concentrations of major and minor ions, whereas ground water in the Northern and Great Lakes Forested Region and the Mountain and Coastal Forested Region has the lowest concentrations of these ions. Median concentrations of barium, arsenic, lithium, boron, strontium, and nitrite plus nitrate as nitrogen also are significantly different among the hydrochemical regions.

Modeling the evolution of the Laurentide Ice Sheet from MIS 3 to the Last Glacial Maximum: an approach using sea level modeling and ice flow dynamics

NASA Astrophysics Data System (ADS)

Weisenberg, J.; Pico, T.; Birch, L.; Mitrovica, J. X.

2017-12-01

The history of the Laurentide Ice Sheet since the Last Glacial Maximum ( 26 ka; LGM) is constrained by geological evidence of ice margin retreat in addition to relative sea-level (RSL) records in both the near and far field. Nonetheless, few observations exist constraining the ice sheet's extent across the glacial build-up phase preceding the LGM. Recent work correcting RSL records along the U.S. mid-Atlantic dated to mid-MIS 3 (50-35 ka) for glacial-isostatic adjustment (GIA) infer that the Laurentide Ice Sheet grew by more than three-fold in the 15 ky leading into the LGM. Here we test the plausibility of a late and extremely rapid glaciation by driving a high-resolution ice sheet model, based on a nonlinear diffusion equation for the ice thickness. We initialize this model at 44 ka with the mid-MIS 3 ice sheet configuration proposed by Pico et al. (2017), GIA-corrected basal topography, and mass balance representative of mid-MIS 3 conditions. These simulations predict rapid growth of the eastern Laurentide Ice Sheet, with rates consistent with achieving LGM ice volumes within 15 ky. We use these simulations to refine the initial ice configuration and present an improved and higher resolution model for North American ice cover during mid-MIS 3. In addition we show that assumptions of ice loads during the glacial phase, and the associated reconstructions of GIA-corrected basal topography, produce a bias that can underpredict ice growth rates in the late stages of the glaciation, which has important consequences for our understanding of the speed limit for ice growth on glacial timescales.

Trans-pacific glacial response to the Antarctic Cold Reversal in the southern mid-latitudes

NASA Astrophysics Data System (ADS)

Sagredo, Esteban A.; Kaplan, Michael R.; Araya, Paola S.; Lowell, Thomas V.; Aravena, Juan C.; Moreno, Patricio I.; Kelly, Meredith A.; Schaefer, Joerg M.

2018-05-01

Elucidating the timing and regional extent of abrupt climate events during the last glacial-interglacial transition (∼18-11.5 ka) is critical for identifying spatial patterns and mechanisms responsible for large-magnitude climate events. The record of climate change in the Southern Hemisphere during this time period, however, remains scarce and unevenly distributed. We present new geomorphic, chronological, and equilibrium line altitude (ELA) data from a climatically sensitive mountain glacier at Monte San Lorenzo (47°S), Central Patagonia. Twenty-four new cosmogenic 10Be exposure ages from moraines provide a comprehensive glacial record in the mid-latitudes of South America, which constrain the timing, spatial extent and magnitude of glacial fluctuations during the Antarctic Cold Reversal (ACR, ∼14.5-12.9 ka). Río Tranquilo glacier advanced and reached a maximum extent at 13.9 ± 0.7 ka. Three additional inboard moraines afford statistically similar ages, indicating repeated glacier expansions or marginal fluctuations over the ACR. Our record represents the northernmost robust evidence of glacial fluctuations during the ACR in southern South America, documenting not only the timing of the ACR maximum, but also the sequence of glacier changes within this climate event. Based on ELA reconstructions, we estimate a cooling of >1.6-1.8 °C at the peak of the ACR. The Río Tranquilo record along with existing glacial reconstructions from New Zealand (43°S) and paleovegetation records from northwestern (41°S) and central-west (45°S) Patagonia, suggest an uniform trans-Pacific glacier-climate response to an ACR trigger across the southern mid-latitudes. We posit that the equatorial migration of the southern westerly winds provides an adequate mechanism to propagate a common ACR signal across the Southern Hemisphere.

Early warming of tropical South America at the last glacial-interglacial transition.

PubMed

Seltzer, G O; Rodbell, D T; Baker, P A; Fritz, S C; Tapia, P M; Rowe, H D; Dunbar, R B

2002-05-31

Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at Lake Titicaca, Peru/Bolivia (16 degrees S), and Lake Junin, Peru (11 degrees S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bølling-Allerød warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5 degrees to 38 degrees N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation.

Evolution of the climatic tolerance and postglacial range changes of the most primitive orchids (Apostasioideae) within Sundaland, Wallacea and Sahul.

PubMed

Kolanowska, Marta; Mystkowska, Katarzyna; Kras, Marta; Dudek, Magdalena; Konowalik, Kamil

2016-01-01

The location of possible glacial refugia of six Apostasioideae representatives is estimated based on ecological niche modeling analysis. The distribution of their suitable niches during the last glacial maximum (LGM) is compared with their current potential and documented geographical ranges. The climatic factors limiting the studied species occurrences are evaluated and the niche overlap between the studied orchids is assessed and discussed. The predicted niche occupancy profiles and reconstruction of ancestral climatic tolerances suggest high level of phylogenetic niche conservatism within Apostasioideae.

The large mean body size of mammalian herbivores explains the productivity paradox during the Last Glacial Maximum.

PubMed

Zhu, Dan; Ciais, Philippe; Chang, Jinfeng; Krinner, Gerhard; Peng, Shushi; Viovy, Nicolas; Peñuelas, Josep; Zimov, Sergey

2018-04-01

Large herbivores are a major agent in ecosystems, influencing vegetation structure, and carbon and nutrient flows. During the last glacial period, a mammoth steppe ecosystem prevailed in the unglaciated northern lands, supporting a high diversity and density of megafaunal herbivores. The apparent discrepancy between abundant megafauna and the expected low vegetation productivity under a generally harsher climate with a lower CO 2 concentration, termed the productivity paradox, requires large-scale quantitative analysis using process-based ecosystem models. However, most of the current global dynamic vegetation models (DGVMs) lack explicit representation of large herbivores. Here we incorporated a grazing module in a DGVM based on physiological and demographic equations for wild large grazers, taking into account feedbacks of large grazers on vegetation. The model was applied globally for present-day and the Last Glacial Maximum (LGM). The present-day results of potential grazer biomass, combined with an empirical land-use map, infer a reduction in wild grazer biomass by 79-93% owing to anthropogenic land replacement of natural grasslands. For the LGM, we find that the larger mean body size of mammalian herbivores than today is the crucial clue to explain the productivity paradox, due to a more efficient exploitation of grass production by grazers with a large body size.

Map showing spatial and temporal relations of mountain and continental glaciations on the Northern Plains, primarily in northern Montana and northwestern North Dakota

USGS Publications Warehouse

Fullerton, David S.; Colton, Roger B.; Bush, Charles A.; Straub, Arthur W.

2004-01-01

This report is an overview of glacial limits and glacial history on the plains in northern Montana and northeastern North Dakota (long 102?-114?W.) and also in adjacent southern Alberta and Saskatchewan, Canada. In the Rocky Mountains and on the plains adjacent to the mountains in Montana, the map also depicts spatial relations of valley glaciers and piedmont ice lobes to continental ice sheets. Glacial limits east of 102?, in the United States and also in adjacent Canada, are depicted on published maps of the U.S. Geological Survey Quaternary Geologic Atlas of the United States (I-1420) map series. The limits shown here are from data compiled for the Lethbridge, Regina, Yellowstone, and Big Horn Mountains 4? x 6? quadrangles in the Quaternary Geologic Atlas series. This geospatial database has been prepared with a degree of detail appropriate for viewing at a scale of 1:1,000,000. Because of the degree of generalization required, the map is intended for regional analysis, rather than for detailed analysis in specific areas. It depicts the geographic positions of the limits of mountain and continental glaciations and the limits of selected glacial readvances. That information provides a foundation for reconstruction of geologic history and for reconstruction. The base map is simplified. Selected hydrographic features, selected towns and cities, selected physiographic features, and a grid of 1? x 2? topographic quadrangles are included to aid the reader in location of the glacial limits and other features that are depicted here on other maps at different scales. Most of the geologic data were compiled at 1:250,000 scale. The nominal reading scale of the digitized map data is 1:1,000,000. Enlargement will not restore resolution that was lost by simplification or generalization of data. Accompanying illustrations show regional directions of ice movement from Canada into the United States during maximum Illinoian glaciation, during maximum late Wisconsin glaciation, and during a later regional glacial readvance maximum

Late Quaternary loess in northeastern Colorado: Part I - Age and paleoclimatic significance

USGS Publications Warehouse

Muhs, D.R.; Aleinikoff, J.N.; Stafford, Thomas W.; Kihl, R.; Been, J.; Mahan, S.A.; Cowherd, S.

1999-01-01

Loess in eastern Colorado covers an estimated 14000 km2, and is the westernmost part of the North American midcontinent loess province. Stratigraphic studies indicate there were two periods of loess deposition in eastern Colorado during late Quaternary time. The first period spanned ca. 20 000 to 12 000 14C yr B.P. (ca. 20-14 ka) and correlates reasonably well with the culmination and retreat of Pinedale glaciers in the Colorado Front Range during the last glacial maximum. The second period of loess deposition occurred between ca. 11 000 and 9000 14C yr B.P. This interval may be Holocene or may correlate with a hypothesized Younger Dryas glacial advance in the Colorado Front Range. Sedimentologic, mineralogic, and geochemical data indicate that as many as three sources could have supplied loess in eastern Colorado. These sources include glaciogenic silt (derived from the Colorado Front Range) and two bedrock sources, volcaniclastic silt from the White River Group, and clays from the Pierre Shale. The sediment sources imply a generally westerly paleowind during the last glacial maximum. New carbon isotope data, combined with published faunal data, indicate that the loess was probably deposited on a cool steppe, implying a last glacial maximum July temperature depression, relative to the present, of at least 5-6??C. Overall, loess deposition in eastern Colorado occurred mostly toward the end of the last glacial maximum, under cooler and drier conditions, with generally westerly winds from more than one source.

Evidence of a low-latitude glacial buzzsaw: Progressive hypsometry reveals height-limiting glacial erosion in tropical mountain belts

NASA Astrophysics Data System (ADS)

Cunningham, M.; Stark, C. P.; Kaplan, M. R.; Schaefer, J. M.; Winckler, G.

2017-12-01

It has been widely demonstrated that glacial erosion limits the height of mid-latitude mountain ranges—a phenomenon commonly referred to as the "glacial buzzsaw." The strength of the buzzsaw is thought to diminish, or die out completely, at lower latitudes, where glacial landscapes occupy only a small part of mountain belts affected by Pleistocene glaciation. Here we argue that glacial erosion has actually truncated the rise of many tropical orogens. To elicit signs of height-limiting glacial erosion in the tropics, we employ a new take on an old tool: we identify transient geomorphic features by tracking the evolution of (sub)catchment hypsometry with increasing elevation above base level, a method we term "progressive hypsometry." In several tropical mountain belts, including the Central Range of Taiwan, the Talamanca of Costa Rica, the Finisterres of Papua New Guinea, and the Rwenzoris of East Africa, progressive hypsometry reveals transient landscapes perched at various elevations, but the highest of these transient features are consistently glacial landscapes near the lower limit of late-Pleistocene glacial equilibrium line altitude (ELA) fluctuation. We attribute this pattern to an efficient glacial buzzsaw. In many cases, these glacial landscapes are undergoing contemporary destruction by headward propagating, fluvially-driven escarpments. We deduce that a duel between glacial buzzcutting and fluvially-driven scarp propagation has been ongoing throughout the Pleistocene in these places, and that the preservation potential of tropical glacial landscapes is low. To this end, we have identified possible remnants of glacial landscapes in the final stages of scarp consumption, and use 3He surface exposure age dating of boulders and bedrock surfaces in two of these landscapes to constrain major geomorphic activity to before the onset of the Last Glacial Maximum. Our work points to a profound climatic influence on the evolution of these warm, tectonically active, tropical mountain ranges and identifies glaciation as a trigger of autogenic behavior in flanking fluvial landscapes.

Pollen record from Ka'au Crater, Oahu, Hawaii: Evidence for a dry glacial maximum

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

Hotchkiss, S.C.; Juvik, J.O.

Fossil pollen from a 3.5 m-long core from Ka'au Crater, Hawaii (elev. 460 m), yields a ca. 23,000-year record of regional vegetation history. Results indicate a full-glacial period drier and possibly cooler than present, a warmer and wetter early Holocene, and a somewhat drier late Holocene; this sequence agrees with earlier work by Selling (1948) on other islands. The oldest zone is donated by pollen of Chenopodium oahuense, Acacia koa, and Dodonaea viscosa; post-glacial pollen assemblages feature high percentages of Myrsine and Coprosma, followed by increases in Lycopodium cernuum Ilex anomala. Freycinetia arborea and Pritchardia. After about 8000 years ago,more » Chenopodium, Acacia, and Dodonaea increase, suggesting a return to drier conditions. Abundant pollen of Chenopodium oahuense, a plant of dry regions, during the last glacial maximum implies that neither the trade winds nor cyclonic storms were delivering as much moisture to the regional vegetation as they presently do. This suggests that the ocean surface temperature during the last glacial maximum may have been cooler than present, a finding contradictory to the reconstructions of the CLIMAP (1981) group, which show temperatures near Hawaii equal to or even warmer than present.« less

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

NASA Astrophysics Data System (ADS)

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

1999-05-01

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

Replicate phylogenies and post-glacial range expansion of the pitcher-plant mosquito, Wyeomyia smithii, in North America.

PubMed

Merz, Clayton; Catchen, Julian M; Hanson-Smith, Victor; Emerson, Kevin J; Bradshaw, William E; Holzapfel, Christina M

2013-01-01

Herein we tested the repeatability of phylogenetic inference based on high throughput sequencing by increased taxon sampling using our previously published techniques in the pitcher-plant mosquito, Wyeomyia smithii in North America. We sampled 25 natural populations drawn from different localities nearby 21 previous collection localities and used these new data to construct a second, independent phylogeny, expressly to test the reproducibility of phylogenetic patterns. Comparison of trees between the two data sets based on both maximum parsimony and maximum likelihood with Bayesian posterior probabilities showed close correspondence in the grouping of the most southern populations into clear clades. However, discrepancies emerged, particularly in the middle of W. smithii's current range near the previous maximum extent of the Laurentide Ice Sheet, especially concerning the most recent common ancestor to mountain and northern populations. Combining all 46 populations from both studies into a single maximum parsimony tree and taking into account the post-glacial historical biogeography of associated flora provided an improved picture of W. smithii's range expansion in North America. In a more general sense, we propose that extensive taxon sampling, especially in areas of known geological disruption is key to a comprehensive approach to phylogenetics that leads to biologically meaningful phylogenetic inference.

Reversed flow of Atlantic deep water during the Last Glacial Maximum.

PubMed

Negre, César; Zahn, Rainer; Thomas, Alexander L; Masqué, Pere; Henderson, Gideon M; Martínez-Méndez, Gema; Hall, Ian R; Mas, José L

2010-11-04

The meridional overturning circulation (MOC) of the Atlantic Ocean is considered to be one of the most important components of the climate system. This is because its warm surface currents, such as the Gulf Stream, redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns, whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss, away from the atmosphere. Despite its significance for future climate, the operation of the MOC under contrasting climates of the past remains controversial. Nutrient-based proxies and recent model simulations indicate that during the Last Glacial Maximum the convective activity in the North Atlantic Ocean was much weaker than at present. In contrast, rate-sensitive radiogenic (231)Pa/(230)Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength. Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. These conclusions are based on new high-resolution data from the South Atlantic Ocean that establish the basin-scale north to south gradient in (231)Pa/(230)Th, and thus the direction of the deep ocean circulation. Our findings are consistent with nutrient-based proxies and argue that further analysis of (231)Pa/(230)Th outside the North Atlantic basin will enhance our understanding of past ocean circulation, provided that spatial gradients are carefully considered. This broader perspective suggests that the modern pattern of the Atlantic MOC-with a prominent southerly flow of deep waters originating in the North Atlantic-arose only during the Holocene epoch.

Response of the Amazon rainforest to late Pleistocene climate variability

NASA Astrophysics Data System (ADS)

Häggi, Christoph; Chiessi, Cristiano M.; Merkel, Ute; Mulitza, Stefan; Prange, Matthias; Schulz, Michael; Schefuß, Enno

2017-12-01

Variations in Amazonian hydrology and forest cover have major consequences for the global carbon and hydrological cycles as well as for biodiversity. Yet, the climate and vegetation history of the lowland Amazon basin and its effect on biogeography remain debated due to the scarcity of suitable high-resolution paleoclimate records. Here, we use the isotopic composition (δD and δ13C) of plant-waxes from a high-resolution marine sediment core collected offshore the Amazon River to reconstruct the climate and vegetation history of the integrated lowland Amazon basin for the period from 50,000 to 12,800 yr before present. Our results show that δD values from the Last Glacial Maximum were more enriched than those from Marine Isotope Stage (MIS) 3 and the present-day. We interpret this trend to reflect long-term changes in precipitation and atmospheric circulation, with overall drier conditions during the Last Glacial Maximum. Our results thus suggest a dominant glacial forcing of the climate in lowland Amazonia. In addition to previously suggested thermodynamic mechanisms of precipitation change, which are directly related to temperature, we conclude that changes in atmospheric circulation are crucial to explain the temporal evolution of Amazonian rainfall variations, as demonstrated in climate model experiments. Our vegetation reconstruction based on δ13C values shows that the Amazon rainforest was affected by intrusions of savannah or more open vegetation types in its northern sector during Heinrich Stadials, while it was resilient to glacial drying. This suggests that biogeographic patterns in tropical South America were affected by Heinrich Stadials in addition to glacial-interglacial climate variability.

Periodic Glacial Lake Outburst Floods threatening the oldest Buddhist monastery in north-west Nepal

NASA Astrophysics Data System (ADS)

Kropáček, J.; Neckel, N.; Tyrna, B.; Holzer, N.; Hovden, A.; Gourmelen, N.; Schneider, C.; Buchroithner, M.; Hochschild, V.

2014-11-01

Since 2004 Halji Village, home of the oldest Buddhist Monastery in north-west Nepal has suffered from recurrent Glacial Lake Outburst Floods (GLOFs). Studies of recent satellite images identified a supra-glacial lake, located at a distance of 6.5 km from the village, as a possible source of the flood. During a field survey in 2013, the finding was confirmed and several entrances to en-glacial conduits which are draining the lake were found. The topography of the lake basin was then mapped by combining Differential Global Positioning System (DGPS) measurements with a Structure From Motion (SFM) approach from terrestrial photographs. From this model the maximum filling capacity of the lake has been estimated as 1.06 × 106 m3 with a maximum discharge of 77.8 m3 s-1 calculated using an empirical relation. The flooded area in the valley has been estimated by employing a raster-based hydraulic model considering six scenarios of discharge volume and surface roughness. To understand the changes in glacier geometry in the last decade the thinning and retreat of Halji Glacier have been analysed by geodetic mass balance measurements and a time series of satellite images respectively. The GLOF occurrences have further been correlated with cumulative temperature and cumulative liquid precipitation calculated from the High Asia Reanalysis (HAR) dataset. Finally, effective mitigation measures and adaption strategies for Halji village have been discussed.

Excitation of the earth's rotational axis by recent glacial discharges

NASA Technical Reports Server (NTRS)

Gasperini, P.; Sabadini, R.; Yuen, D. A.

1986-01-01

The effects of present-day glacial discharges and the growth of the Antarctic ice sheet on exciting the earth's rotational axis are studied. Glacial forcing could cause a maximum change in J2 of about one-third of the observed amount, for the Maxwell rheology and for Burgers' body models with a long-term, lower-mantle viscosity greater than about 10 to the 23rd P. For transient rheologies the amount of excitation due to glacial melting decreases. Polar wander is not much excited by recent glacial melting for the various types of rheologies examined.

The narrow endemic Norwegian peat moss Sphagnum troendelagicum originated before the last glacial maximum

PubMed Central

Stenøien, H K; Shaw, A J; Stengrundet, K; Flatberg, K I

2011-01-01

It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years. PMID:20717162

High resolution analysis of northern Patagonia lake sediments

NASA Astrophysics Data System (ADS)

Jarvis, S. W.; Croudace, I. W.; Langdon, P. G.; Rindby, A.

2009-04-01

Sediment cores covering the period from the last glacial maximum through the Holocene to the present have been collected from sites in the Chacubuco valley, southern Chile (around 47°08'S, 72°25'W, to the east of the North Patagonian Icecap). Cores were taken from five lakes and one recently dried lake bed. Short cores (0.2 to 0.5m), covering approximately the last two hundred years, were taken from all the lakes. Additionally, long sequences were obtained from one of the lakes and from the dried lake bed, the latter sequence extending back to the last glacial maximum as indicated by thick clay at the base. Each of the lakes are small-medium sized and are open systems situated at 300-1000m above sea level. The shorter cores comprise predominantly clastic gyttja but show a number of distinct changes in colour and chemical composition that suggest major environmental changes over the period of sediment accumulation. This is also reflected in variations in the loss on ignition of samples from the cores and in elemental profiles produced by scanning the cores with the Itrax micro-XRF corescanner at 200μm resolution. The long sequence from the dried lake bed has very low organic content glacial clay at the base, interpreted as last glacial maximum basal clay following determination in the field that this layer exceeded 2m in thickness. Similar sediments occur within a stratigraphically discrete section of approximately 14cm and may relate to a stadial event. The latter section also shows a drop in organic content and appears to be glacial clay incorporating some coarse sandy components indicative of detrital input from the catchment. The second long sequence, from a carbonate lake, includes two mineral layers indicating increased detrital input from the catchment. The deeper and thicker of these layers appears similar to the 14cm layer in the first long sequence, while the upper layer comprises a fine grain size indicative of rock flour and hence also of glacial activity in the catchment. Variation of elemental composition of these ‘glacial' layers is also clear from the Itrax data. It therefore appears that there have been significant reglaciation events in the catchment since the last glacial maximum. Many cores contain tephra layers, identified both visually and from the Itrax scans. Some of these have been confirmed as volcanic ash from the 1991 eruption of Mt Hudson, which at 45°54'S, 72°58'W is the southern-most volcano in the Chilean Andes and only 140km from the study area. Further work is underway to confirm and identify the source and age of other suspected tephra layers. Sediment accumulation rates in the upper parts of the cores are of the order of 1mm/yr (as determined by lead-210, caesium-137 dating and the 1991 Hudson tephra). Given XRF scan resolutions of up to 200μm there is thus the potential for investigation of sub-annual variability. Funding has been obtained to determine carbon-14 dates for the lower parts of the longer cores. The reproducibility and accuracy of the Itrax data has been validated using conventional WD-XRF spectrometry and the work presented will also include geochemical interpretation of the XRF data and comparison with recorded and proxy-inferred climate data for the region.

Evolution of the climatic tolerance and postglacial range changes of the most primitive orchids (Apostasioideae) within Sundaland, Wallacea and Sahul

PubMed Central

Mystkowska, Katarzyna; Kras, Marta; Dudek, Magdalena

2016-01-01

The location of possible glacial refugia of six Apostasioideae representatives is estimated based on ecological niche modeling analysis. The distribution of their suitable niches during the last glacial maximum (LGM) is compared with their current potential and documented geographical ranges. The climatic factors limiting the studied species occurrences are evaluated and the niche overlap between the studied orchids is assessed and discussed. The predicted niche occupancy profiles and reconstruction of ancestral climatic tolerances suggest high level of phylogenetic niche conservatism within Apostasioideae. PMID:27635348

Asynchronous Glacial Chronologies in the Central Andes (15-40°S) and Paleoclimatic Implications

NASA Astrophysics Data System (ADS)

Zech, R.; Kull, C.; Kubik, P. W.; Veit, H.

2006-12-01

We have established glacial chronologies along a N-S transect over the Central Andes using 10Be surface exposure dating. Our results show that maximum glacial advances occurred asynchronously and reflect the varying influence and shifts of the major atmospheric circulation systems during the Late Quaternary: the tropical circulation in the north and the westerlies in the south. In Bolivia (three research areas in the Cordillera Real and the Cordillera Cochabamba, ~15°S) glacial advances could be dated to ~20 and 12 ka BP. This is in good agreement with published exposure age data from moraines in Bolivia and Peru (provided that all ages are calculated following the same scaling system). Accordingly, the maximum glaciation there probably occurred roughly synchronous to the temperature minimum of the global Last Glacial Maximum (LGM) and the lateglacial cold reversals. Strict correlation with neither the Younger Dryas in the northern hemisphere, nor the Antarctic Cold Reversal is possible due to the current systematic exposure age uncertainties (~10%). Glacier-Climate-Modelling corroborates the sensitivity of the reconstructed glaciers to temperature changes, rather than precipitation. On the contrary, there is good evidence for the dominant role of precipitation changes on the glacial chronologies in the lee of the Cordillera Occidental, i.e. on the Altiplano and further south. The pronounced lateglacial wet phase, which is well documented in lake transgression phases as far south as 28°S (-> tropical moisture source), seems to have caused glacial advances even at ~30°S. In two research areas in Chile at that latitude, we were able to date several lateglacial moraines. Besides, the maximum datable glaciation there occurred at ~30 ka BP. That is significantly earlier than the LGM (sensu strictu) and points to favourable climate conditions for glaciation at that time (particularly increased precipitation). We conclude that the westerlies were more intensive or shifted northward at ~30 ka BP. We have not yet been able to date LGM moraines as far south as ~40°, which would indicate the transition of precipitation- to temperature-sensitive glaciers. Instead, our preliminary exposure age chronology from Valle Rucachoroi (~39°S, Argentina) suggests that the maximum glaciation there occurred also at ~30 ka BP, but that the valleys became ice-free only by ~15 ka BP. Samples from moraines in the cirques are currently in progress and may document lateglacial re-advances.

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

NASA Astrophysics Data System (ADS)

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

2012-09-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Meltwater input to the southern ocean during the last glacial maximum

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

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

1994-12-02

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

Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica

NASA Astrophysics Data System (ADS)

Joy, Kurt; Fink, David; Storey, Bryan; De Pascale, Gregory P.; Quigley, Mark; Fujioka, Toshiyuki

2017-12-01

The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10-14 ka.

Climate change decouples oceanic primary and export productivity and organic carbon burial

PubMed Central

Lopes, Cristina; Kucera, Michal; Mix, Alan C.

2015-01-01

Understanding responses of oceanic primary productivity, carbon export, and burial to climate change is essential for model-based projection of biological feedbacks in a high-CO2 world. Here we compare estimates of productivity based on the composition of fossil diatom floras with organic carbon burial off Oregon in the Northeast Pacific across a large climatic transition at the last glacial termination. Although estimated primary productivity was highest during the Last Glacial Maximum, carbon burial was lowest, reflecting reduced preservation linked to low sedimentation rates. A diatom size index further points to a glacial decrease (and deglacial increase) in the fraction of fixed carbon that was exported, inferred to reflect expansion, and contraction, of subpolar ecosystems that today favor smaller plankton. Thus, in contrast to models that link remineralization of carbon to temperature, in the Northeast Pacific, we find dominant ecosystem and sea floor control such that intervals of warming climate had more efficient carbon export and higher carbon burial despite falling primary productivity. PMID:25453073

Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence

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

Gosse, J.C.; Klein, J.; Evenson, E.B.

Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 {+-} 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 {+-} 500 beryllium-10 years.

Timing of glacier advances and climate in the High Tatra Mountains (Western Carpathians) during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Makos, Michał; Dzierżek, Jan; Nitychoruk, Jerzy; Zreda, Marek

2014-07-01

During the Last Glacial Maximum (LGM), long valley glaciers developed on the northern and southern sides of the High Tatra Mountains, Poland and Slovakia. Chlorine-36 exposure dating of moraine boulders suggests two major phases of moraine stabilization, at 26-21 ka (LGM I - maximum) and at 18 ka (LGM II). The dates suggest a significantly earlier maximum advance on the southern side of the range. Reconstructing the geometry of four glaciers in the Sucha Woda, Pańszczyca, Mlynicka and Velicka valleys allowed determining their equilibrium-line altitudes (ELAs) at 1460, 1460, 1650 and 1700 m asl, respectively. Based on a positive degree-day model, the mass balance and climatic parameter anomaly (temperature and precipitation) has been constrained for LGM I advance. Modeling results indicate slightly different conditions between northern and southern slopes. The N-S ELA gradient finds confirmation in slightly higher temperature (at least 1 °C) or lower precipitation (15%) on the south-facing glaciers during LGM I. The precipitation distribution over the High Tatra Mountains indicates potentially different LGM atmospheric circulation than at the present day, with reduced northwesterly inflow and increased southerly and westerly inflows of moist air masses.

Changes in monsoon-driven upwelling in the South China Sea over glacial Terminations I and II: a multi-proxy record

NASA Astrophysics Data System (ADS)

Sadatzki, Henrik; Sarnthein, Michael; Andersen, Nils

2016-06-01

Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoon-driven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoon-driven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface waters (δ13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m.

Glacial evolution in King George and Livingston Islands (Antarctica) since the Last Glacial Maximum based on cosmogenic nuclide dating and glacier surface reconstruction - CRONOANTAR project

NASA Astrophysics Data System (ADS)

Ruiz Fernández, Jesús; Oliva, Marc; Fernández Menéndez, Susana del Carmen; García Hernández, Cristina; Menéndez Duarte, Rosa Ana; Pellitero Ondicol, Ramón; Pérez Alberti, Augusto; Schimmelpfennig, Irene

2017-04-01

CRONOANTAR brings together researchers from Spain, Portugal, France and United Kingdom with the objective of spatially and temporally reconstruct the deglaciation process at the two largest islands in the South Shetlands Archipelago (Maritime Antarctica), since the Global Last Glacial Maximum. Glacier retreat in polar areas has major implications at a local, regional and even planetary scale. Global average sea level rise is the most obvious and socio-economically relevant, but there are others such as the arrival of new fauna to deglaciated areas, plant colonisation or permafrost formation and degradation. This project will study the ice-free areas in Byers and Hurd peninsulas (Livingston Island) and Fildes and Potter peninsulas (King George Island). Ice-cap glacier retreat chronology will be revealed by the use of cosmogenic isotopes (mainly 36Cl) on glacially originated sedimentary and erosive records. Cosmogenic dating will be complemented by other dating methods (C14 and OSL), which will permit the validation of these methods in regions with cold-based glaciers. Given the geomorphological evidences and the obtained ages, a deglaciation calendar will be proposed and we will use a GIS methodology to reconstruct the glacier extent and the ice thickness. The results emerging from this project will allow to assess whether the high glacier retreat rates observed during the last decades were registered in the past, or if they are conversely the consequence (and evidence) of the Global Change in Antarctica. Acknowledgements This work has been funded by the Spanish Ministry of Economy, Industry and Competitiveness (Reference: CTM2016-77878-P).

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.

Late Quaternary Glaciation of the Naches River Drainage Basin, Washington Cascades

NASA Astrophysics Data System (ADS)

Sheffer, H. B.; Goss, L.; Shimer, G.; Carson, R. J.

2014-12-01

The Naches River drainage basin east of Mount Rainer includes tributary valleys of the Little Naches, American, Bumping, and Tieton rivers. An investigation of surface boulder frequency, weathering rind thicknesses, and soil development on moraines in these valleys identified two stages of Pleistocene glaciations in the American, Bumping, and Tieton drainages, followed by Neoglaciation. These stages include a more extensive early glaciation (Hayden Creek?), and the later Evans Creek Glaciation (25-15 ka). Thick forest cover, limited road cuts, and widespread post-glacial mass wasting hamper efforts to determine the maximum extent of glaciation. However, glacial striations at Chinook Pass, moraine complexes in the vicinity of Goose Egg Mountain, ice-transported boulders and striations on Pinegrass Ridge, and a boulder field possibly derived from an Evans Creek jökulhaup in the Tieton River valley, all point to extensive Pleistocene ice in the central tributaries of the Naches River. Lowest observed ice elevations in the Tieton (780 m), Bumping (850 m), and American (920 m) drainages increase towards the north, while glacial lengths decrease from 40 to 28 km. The Little Naches is the northernmost drainage in the study, but despite a maximum elevation (1810 m) that exceeds the floor of ice caps to the south, glacially-derived sediments are not evident and the surrounding peaks lack cirques. The absence of ice in the Little Naches drainage, along with the systematic northward change in glacial length and lowest observed ice elevations in the other drainages, are likely due to a precipitation shadow northeast of Mount Rainier. In contrast, the source of glacial ice in the Tieton drainage to the southeast was the Goat Rocks peaks. Ground-based study of neoglacial moraines and analysis of 112 years of topographic maps and satellite imagery point to rapid retreat of the remaining Goat Rocks glaciers following the Little Ice Age.

Assessment of a ground water flow model of the Bangkok Basin, Thailand, using carbon-14-based ages and paleohydrology

USGS Publications Warehouse

Sanford, W.E.; Buapeng, S.

1996-01-01

A study was undertaken to understand the groundwater flow conditions in the Bangkok Basin, Thailand, by comparing 14C-based and simulated groundwater ages. 14C measurements were made on about 50 water samples taken from wells throughout the basin. Simulated ages were obtained using 1) backward-pathline tracking based on the well locations, and 2) results from a three-dimensional groundwater flow model. Comparisons of ages at these locations reveal a large difference between 14C-based ages and ages predicted by the steady-state groundwater flow model. Mainly, 14C and 13C analyses indicate that groundwater in the Bangkok area is about 20,000 years old, whereas steady-state flow and transport simulations imply that groundwater in the Bangkok area is 50,000-100,000 years old. One potential reason for the discrepancy between simulated and 14C-based ages is the assumption in the model of steady-state flow. Groundwater velocities were probably greater in the region before about 10,000 years ago, during the last glacial maximum, because of the lower position of sea level and the absence of the surficial Bangkok Clay. Paleoflow conditions were estimated and then incorporated into a second set of simulations. The new assumption was that current steady-state flow conditions existed for the last 8,000 years but were preceded by steady-state conditions representative of flow during the last glacial maximum. This "transient" paleohydrologic simulation yielded a mean simulated age that more closely agrees with the mean 14C-based age, especially if the 14C-based age is corrected for diffusion into clay layers. Although the uncertainties in both the simulated and 14C-based ages are nontrivial, the magnitude of the improved match in the mean age using a paleohydrologic simulation instead of a steady-state simulation suggests that flow conditions in the basin have changed significantly over the last 10,000-20,000 years. Given that the valid age range of 14C-dating methods and the timing of the last glacial maximum are of similar magnitude, adjustments for paleohydrologic conditions may be required for many such studies.

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

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

NASA Astrophysics Data System (ADS)

Jansen, Malte F.

2017-01-01

Earth’s climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

PubMed Central

Jansen, Malte F.

2017-01-01

Earth’s climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5–10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage. PMID:27994158

Glacial ocean circulation and stratification explained by reduced atmospheric temperature.

PubMed

Jansen, Malte F

2017-01-03

Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

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

Palaeo-ice stream pathways in the easternmost Amundsen Sea Embayment, West Antarctica

NASA Astrophysics Data System (ADS)

Klages, Johann P.; Kuhn, Gerhard; Graham, Alastair G. C.; Smith, James A.; Hillenbrand, Claus-Dieter; Nitsche, Frank O.; Larter, Rob D.; Gohl, Karsten

2015-04-01

Multibeam swath bathymetry datasets collected over the past two decades have been compiled to identify palaeo-ice stream pathways in the easternmost Amundsen Sea Embayment. We mapped 3010 glacial landforms to reconstruct palaeo-ice flow in the ~250 km-long Abbot Glacial Trough that was occupied by a large palaeo-ice stream, fed by two tributaries (Cosgrove and Abbot) that reached the continental shelf edge during the last maximum ice-sheet advance. The mapping has enabled a clear differentiation between glacial landforms interpreted as indicative of wet- (e.g. mega-scale glacial lineations) and cold-based ice (e.g. hill-hole pairs) during the last glaciation of the continental shelf. Both the regions of fast palaeo-ice flow within the palaeo-ice stream troughs, and the regions of slow palaeo-ice flow on adjacent seafloor highs (referred to as inter-ice stream ridges) additionally record glacial landforms such as grounding-zone wedges and recessional moraines that indicate grounding line stillstands of the ice sheet during the last deglaciation from the shelf. As the palaeo-ice stream flowed along a trough with variable geometry and variable subglacial substrate, it appears that trough sections characterized by constrictions and outcropping hard substrate that changes the bed gradient, led the pace of grounding-line retreat to slow and subsequently pause, resulting in the deposition of grounding-zone wedges. The stepped retreat recorded within the Abbot Glacial Trough corresponds well to post-glacial stepped retreat interpreted for the neighbouring Pine Island-Thwaites Palaeo-Ice Stream trough, thus suggesting a uniform pattern of episodic retreat across the eastern Amundsen Sea Embayment. The correlation of episodic retreat features with geological boundaries further emphasises the significance of subglacial geology in steering ice stream flow. Our new geomorphological map of the easternmost Amundsen Sea Embayment resolves the pathways of palaeo-ice streams that were probably all active during the last maximum extent of the ice sheet on this part of the shelf, and reveals the style of postglacial grounding-line retreat. Both are important input variables in ice sheet models and therefore can be used for validating the reliability of these models.

Late Wisconsinan glaciation and postglacial relative sea-level change on western Banks Island, Canadian Arctic Archipelago

NASA Astrophysics Data System (ADS)

Lakeman, Thomas R.; England, John H.

2013-07-01

The study revises the maximum extent of the northwest Laurentide Ice Sheet (LIS) in the western Canadian Arctic Archipelago (CAA) during the last glaciation and documents subsequent ice sheet retreat and glacioisostatic adjustments across western Banks Island. New geomorphological mapping and maximum-limiting radiocarbon ages indicate that the northwest LIS inundated western Banks Island after ~ 31 14C ka BP and reached a terminal ice margin west of the present coastline. The onset of deglaciation and the age of the marine limit (22-40 m asl) are unresolved. Ice sheet retreat across western Banks Island was characterized by the withdrawal of a thin, cold-based ice margin that reached the central interior of the island by ~ 14 cal ka BP. The elevation of the marine limit is greater than previously recognized and consistent with greater glacioisostatic crustal unloading by a more expansive LIS. These results complement emerging bathymetric observations from the Arctic Ocean, which indicate glacial erosion during the Last Glacial Maximum (LGM) to depths of up to 450 m.

A cosmogenic nuclide chronology of the last glacial transition in North-West Nelson, New Zealand-new insights in Southern Hemisphere climate forcing during the last deglaciation [rapid communication

NASA Astrophysics Data System (ADS)

Shulmeister, James; Fink, David; Augustinus, Paul C.

2005-05-01

We present a new glacial chronology for the last glacial interglacial transition, c. 20 to 10 ka, from the Cobb Valley, NW Nelson, New Zealand, based on a suite of 10Be and 26Al cosmogenic exposure ages. This chronology describes one of the most comprehensive deglaciation sequences from a late Quaternary valley system in the Southern Hemisphere. We chronicle the decay from the last (local) glacial maximum as follows: onset of the last deglaciation that commenced no earlier than 18-19 ka, followed by numerous short-term still-stands and/or minor re-advances over the ensuing 3-4 kyr, and complete evacuation of ice by 14 ka. We find no evidence to indicate a late glacial re-advance commensurate with the Northern Hemisphere Younger Dryas chronozone. The absence of a major glacial re-advance in this valley during the latter stages of the last glacial interglacial transition (LGIT) precludes a thermal decline in excess of about 3 °C and suggests no decline. The absence of late LGIT re-advances in the mountains of North-West Nelson, while deglacial readvances occurred in the main ranges of the Southern Alps can be best explained if westerly wind forcing rather than large-scale thermal decline is the primary control on glacier fluctuations, at least during the deglaciation. These findings challenge models of global climate change predicated on synchrony of millennial-scale glacial transitions due to thermal changes between Northern and Southern Hemispheres.

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).

Late Quaternary history of contourite drifts and variations in Labrador Current flow, Flemish Pass, offshore eastern Canada

NASA Astrophysics Data System (ADS)

Marshall, Nicole R.; Piper, David J. W.; Saint-Ange, Francky; Campbell, D. Calvin

2014-10-01

Contourite drifts of alternating sand and mud, shaped by the Labrador Current, formed during the late Quaternary in Flemish Pass seaward of the Grand Banks of Newfoundland, Canada. The drifts preserve a record of Labrador Current flow variations through the last glacial maximum. A high-resolution seismic profile and a transect of four cores were collected across Beothuk drift on the southeast side of Flemish Pass. Downcore and lateral trends in grain size and sedimentation rate provide evidence that, between 16 and 13 ka, sediment was partitioned across Beothuk drift and the adjacent Flemish Pass floor by a strong current flow but, from 29 to 16 ka, sedimentation was more of a blanketing style, represented by draped reflections interpreted as being due to a weaker current. The data poorly resolve the low sedimentation rates since 13 ka, but the modern Labrador Current in Flemish Pass is the strongest it has been in at least the past 29 ka. Pre-29 ka current flow is interpreted based on reflection architecture in seismic profiles. A prominent drift on the southwestern side of Flemish Pass formed above a mid-Miocene erosion surface, but was buried by a mass-transport deposit after the penultimate glacial maximum and after drift deposition switched to eastern Flemish Pass. These findings illustrate the temporal complexity of drift sedimentation and provide the first detailed proxy for Labrador Current flow since the last glacial maximum.

Quaternary glacial landforms and evolution in the Cantabrian Mountains (Northern Spain): a synthesis from current data

NASA Astrophysics Data System (ADS)

Serrano, Enrique; José González-Trueba, Juan; Pellitero, Ramón; González-García, María; Gómez-Lende, Manuel

2014-05-01

In Northern Iberian Peninsula are located the Cantabrian Mountains, a mountain system of 450 km length, reaching 2648 m in the Picos de Europa. It is an Atlantic mountain in the North slope, with a Atlantic Mediterranean transitional climate in the South slope.More than thirty-five massifs developed glaciers during the Pleistocene. Studies on glacial morphology are known from the XIX century and they have focused mainly on the maximum extent of glaciers. Nowadays there are detailed geomorphological maps, morphostratigraphic surveys and estimation of Equilibrium Line Altitude in different massifs and on different stages. During the last decade studies on glacial evolution and glaciation phases have been made, and the first chronological data have been published. In this work we presents the reconstruction of the glacial evolution in the Cantabrian Mountains during the Pleistocene and Holocene, based on recent chronological data (30 dates made using OSL, AMS and C14) and morphostratigraphic correlations obtained by several research groups. The number of reconstructed glacial stages varies among the different massifs, form one to four different stages. The highest massifs located in the central portion of the Cantabrian Mountains have the most complex glacial features, with at least four different moraine complexes stepped between the 400 m a.s.l in the Northern slope and 800 m a.s.l. in the Southern slope for the lowest moraine complexes, and the highest and youngest, located above 2100 m a.s.l. An ancient glacial phase has been pointed to MIS 12 -more than 400 ka-, disconnected from the present day glacial morphology. During Upper Pleistocene three main stages have been identified. The first one, the local glacial maximum, could be prior to the LGM, as all dates refer to chronologies prior to 28-38 ka. Some authors locate this stage prior to 45 and 65 ka, during the 50-70 ka cold stage. It could be a wet stage, when the main fronts reached the Iberian Peninsula from the SW. The second stage is located to around 30 ka, and point to a dryer stage when glaciers was shorter but thicker. The third stage is located at 20-18 ka, contemporary from the LGM. Glaciers are located inside of glacier-shaped mountain valleys. A few moraine complexes located in the highest massif have been related to Lateglacial, coinciding with cold phases (Dryas) recorded in the Picos de Europa lakes and paleolakes. Finally, during the Holocene only small glaciers developed in the Picos de Europa, which have been assigned to LIA. Nowadays there are still glacial ice remains in four glacial cirques of Picos de Europa, close to the LIA moraines.

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

PubMed Central

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

2017-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance

NASA Astrophysics Data System (ADS)

Rother, Henrik; Shulmeister, James; Fink, David; Alexander, David; Bell, David

2015-11-01

During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages.

Recalibration of the yellow Rhizocarpon growth curve in the Cordillera Blanca (Peru) and implications for LIA chronology

NASA Astrophysics Data System (ADS)

Jomelli, V.; Grancher, D.; Brunstein, D.; Solomina, O.

2008-01-01

A new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the Cordillera Blanca (Peru) during the Little Ice Age (LIA). Our results reveal that an early LIA glacial advance occurred around AD 1330 ± 29. However, a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers. Hence, this second glacial stage, dated from AD 1630 ± 27, is considered as the LIA maximum glacial advance in the Cordillera Blanca. During the 17th-18th centuries, at least three glacial advances were recorded synchronously for the different glaciers (AD 1670 ± 24, 1730 ± 21, and 1760 ± 19). The moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18% in the total length of the glacier. From the LIA maximum extent to the beginning of the 20th century, the 24 glaciers have retreated a distance of about 1000 m, corresponding to a reduction of 30% in their length. This rate is comparable to that observed during the 20th century. Estimates of palaeo-Equilibrium Line Altitudes show an increase in altitude of about 100 m from the LIA maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century. Because long time series are not available for precipitation and temperature, this glacial retreat is difficult to explain by past climate changes. However, there is a fair correspondence between changes in glacier length and the δ18O recorded in the Quelccaya ice core at a century timescale. Our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet LIA to the drier conditions of today. Finally, a remarkable synchronicity is observed with glacial variations in Bolivia, suggesting a common regional climatic pattern during the LIA.

Late Quaternary geomorphic history of a glacial landscape - new sedimentary and chronological data from the Cordillera de Cochabamba (Bolivia)

NASA Astrophysics Data System (ADS)

May, J.-H.; Preusser, F.; Zech, R.; Ilgner, J.; Veit, H.

2009-04-01

Throughout the Central Andes, glacial landscapes have long been used for the reconstruction of Late Quaternary glaciations and landscape evolution. Much work has focused on the Andes in Peru, Chile and the Bolivian Altiplano, whereas relatively little data has been published on glaciation history in the eastern Andean ranges and slopes. Even less is known with regard to the postglacial evolution of these glacial landscapes. In the Cordillera de Cochabamba (Bolivia), local maximum advances probably peaked around 20-25 ka BP and were followed by significant readvances between ~12-16 ka BP. This generally points to temperature controlled maximum glacial advances along the humid eastern slopes of the Central Andes, which is supported by glacier-climate-modelling studies. However, most studies include only marginal information with regard to the complex geomorphic and sedimentary situation in the Cordillera de Cochabamba. Furthermore, the chronological results are afflicted with several methodological uncertainties inherent to surface exposure dating and call for application of alternative, independent age dating methods. Therefore this study aims at i) documenting and interpreting the complex glacial geomorphology of the Huara Loma valley in the Cordillera de Cochabamba (Bolivia), ii) analyzing the involved units of glacial sediments, and iii) improving the chronological framework by applying optically stimulated luminescence (OSL) and radiocarbon dating (14C). For this purpose, geomorphic mapping was combined with field documentation of sedimentary profiles. The involved sediments were subject to geochemical and mineralogical analysis in order to deduce information on their erosional and weathering histories. In addition, the interpretation of OSL ages from glacial and proglacial sediments integrated several methodological procedures with regard to sample preparation and statistical analysis of the measurements in order to increase the degree of confidence. These combined efforts confirm two major glacial advances in the Cordillera de Cochabamba, which took place during the global LGM and during the Lateglacial. However, their relative chronologies and sedimentary interpretation indicate that the maximum extent of glaciation at Huara Loma was reached during humid Lateglacial times whereas conditions during the LGM were probably too dry.

Glacial and volcanic evolution on Nevado Coropuna (Tropical Andes) based on cosmogenic 36Cl surface exposure dating

NASA Astrophysics Data System (ADS)

Úbeda, J.; Palacios, D.; Vázquez-Selém, L.

2012-04-01

We have reconstructed the evolution of the paleo-glaciers of the volcanic complex Nevado Coropuna (15°S, 72°W; 6377 m asl) through the interpretation and dating of geomorphological evidences. Surface exposure dating (SED) based on the accumulation of 36Cl on the surface of moraine boulders, polished bedrock and lava flows allowed: 1) to confirm that the presence of ice masses in the region dates back to >80ka; 2) to produce chronologies of glacial and volcanic phases for the last ~21 ka; and 3) to obtain evidences of the reactivation of volcanic activity after the Last Glacial Maximum. Bromley et al. (2009) presented 3He SED ages of 21 ka for moraine boulders on the Mapa Mayo valley, to the North of Nevado Coropuna. Our 36Cl SED SED for moraine boulders from the valleys on the NE sector of the volcanic complex suggest a maximum initial advance between 20 and 16 ka, followed by another expansion of similar extent at 12-11 ka. On the Southern slope of Nevado Coropuna, the 36Cl ages show a maximum initial advance that reaches to the level of the Altiplano at 14 ka, and a re-advance at ~10-9 ka BP. Other data show minor re-advances at 9 ka on the Northern slope and at 6 ka to the South of the volcanic complex. These minor positive pulses interrupted a fast deglaciation process during the Holocene as shown by two series of 36Cl SED from polished rock surfaces on successively higher altitudes along the valleys of rivers Blanco and Cospanja, to the SW and SE. Despite the global warming occuring since 20 ka, deduced from the record of sea surface paleo-temperature of the Galapago Islands (Lea et al, 2006), the evolution of the fresh-water plankton from Lake Titicaca (Fritz et al, 2007) is consistent with sustained glacial conditions until 10-9 ka as suggested by the present work. Exposure ages of three lava flows indicate a reactivation of the magmatic system as the paleo-glaciers abandonned the slopes. The eruptive activity migrated from the West, where we found a lava flow of 6 ka, to the East, where we dated two units similar to the previous one at 2 and <1ka. Bromley, G.R. et al., 2009. Relative timing of last glacial maximum and late-glacial events in the central tropical Andes. Quaternary Science Reviews, 1-13. Bromley, R.M. et al., 2011. Glacier fluctuations in the southern Peruvian Andes during the late-glacial period, constrained with cosmogenic 3He. Journal of Quaternary Science, 26 (1): 37-43. Fritz, S.C. et al., 2007. Lake Titicaca 370KYr LT01-2B Sediment Database. Lake Titicaca 370KYr LT01-2B Sediment Data. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series # 92-008. NOAA/NGDC Paleoclimatology Program. Boulder (EEUU). Lea, D.W. et al., 2006. Galápagos TR163-22 Foraminiferal ^18O and Mg/Ca Data and SST Reconstruction. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2006-090. NOAA/NCDC Paleoclimatology Program, Boulder (EEUU). Research funded by CGL2009-7343 project, Government of Spain.

Intensification of the meridional temperature gradient in the Great Barrier Reef following the Last Glacial Maximum.

PubMed

Felis, Thomas; McGregor, Helen V; Linsley, Braddock K; Tudhope, Alexander W; Gagan, Michael K; Suzuki, Atsushi; Inoue, Mayuri; Thomas, Alexander L; Esat, Tezer M; Thompson, William G; Tiwari, Manish; Potts, Donald C; Mudelsee, Manfred; Yokoyama, Yusuke; Webster, Jody M

2014-06-17

Tropical south-western Pacific temperatures are of vital importance to the Great Barrier Reef (GBR), but the role of sea surface temperatures (SSTs) in the growth of the GBR since the Last Glacial Maximum remains largely unknown. Here we present records of Sr/Ca and δ(18)O for Last Glacial Maximum and deglacial corals that show a considerably steeper meridional SST gradient than the present day in the central GBR. We find a 1-2 °C larger temperature decrease between 17° and 20°S about 20,000 to 13,000 years ago. The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current. Our findings indicate that the GBR experienced substantial meridional temperature change during the last deglaciation, and serve to explain anomalous deglacial drying of northeastern Australia. Overall, the GBR developed through significant SST change and may be more resilient than previously thought.

Reply to comment received from J. Herget et al. regarding ;Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai; by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-305

NASA Astrophysics Data System (ADS)

Gribenski, Natacha; Lukas, Sven; Stroeven, Arjen P.; Jansson, Krister N.; Harbor, Jonathan M.; Blomdin, Robin; Ivanov, Mikhail N.; Heyman, Jakob; Petrakov, Dmitry A.; Rudoy, Alexei; Clifton, Tom; Lifton, Nathaniel A.; Caffee, Marc W.

2017-07-01

We thank Herget et al. (2017) for their keen interest in our study about the paleoglacial history of the Chagan Uzun Valley, in the Russian Altai (Gribenski et al., 2016). In our study, we proposed a detailed chronological and glaciodynamic reconstruction of a succession of glacial events represented by prominent moraine complexes, based on remotely-sensed data and field-geomorphological mapping, sedimentological logging, and cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. Herget et al. (2017) express skepticism about the outermost moraine complex dated in our study (CUMC 1; Gribenski et al., 2016), which slightly predates 19 thousand years (ka), during marine isotope stage (MIS) 2. To quote: "we suspect that their claim of regional climatic significance-that the ∼19 ka Chagan-Uzun moraine they dated can be used to show that the local LGM and regional LGM were the same, and occurred during MIS 2-may be premature" (Herget et al., 2017: p. 1). Their comment appears to relate to an ongoing debate regarding the timing of maximum glaciation in Central Asia during the last glacial cycle, however it is based on misinterpretations of our paper.

Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene

NASA Astrophysics Data System (ADS)

Rehfeld, Kira; Münch, Thomas; Ho, Sze Ling; Laepple, Thomas

2018-02-01

Changes in climate variability are as important for society to address as are changes in mean climate. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability. However, although glacial-interglacial changes in variability have been quantified for Greenland, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3-8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6-2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3-14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future.

Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene.

PubMed

Rehfeld, Kira; Münch, Thomas; Ho, Sze Ling; Laepple, Thomas

2018-02-15

Changes in climate variability are as important for society to address as are changes in mean climate. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability. However, although glacial-interglacial changes in variability have been quantified for Greenland, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3-8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6-2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3-14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future.

Glacial refugia and recolonization pathways in the brown seaweed Fucus serratus.

PubMed

Hoarau, G; Coyer, J A; Veldsink, J H; Stam, W T; Olsen, J L

2007-09-01

The last glacial maximum (20,000-18,000 years ago) dramatically affected extant distributions of virtually all northern European biota. Locations of refugia and postglacial recolonization pathways were examined in Fucus serratus (Heterokontophyta; Fucaceae) using a highly variable intergenic spacer developed from the complete mitochondrial genome of Fucus vesiculosus. Over 1,500 samples from the entire range of F. serratus were analysed using fluorescent single strand conformation polymorphism. A total of 28 mtDNA haplotypes was identified and sequenced. Three refugia were recognized based on high haplotype diversities and the presence of endemic haplotypes: southwest Ireland, the northern Brittany-Hurd Deep area of the English Channel, and the northwest Iberian Peninsula. The Irish refugium was the source for a recolonization sweep involving a single haplotype via northern Scotland and throughout Scandinavia, whereas recolonization from the Brittany-Hurd Deep refugium was more limited, probably because of unsuitable soft-bottom habitat in the Bay of Biscay and along the Belgian and Dutch coasts. The Iberian populations reflect a remnant refugium at the present-day southern boundary of the species range. A generalized skyline plot suggested exponential population expansion beginning in the mid-Pleistocene with maximal growth during the Eems interglacial 128,000-67,000 years ago, implying that the last glacial maximum mainly shaped population distributions rather than demography.

Large Scale Anthropogenic Reduction of Forest Cover in Last Glacial Maximum Europe

PubMed Central

Pfeiffer, Mirjam; Kolen, Jan C. A.; Davis, Basil A. S.

2016-01-01

Reconstructions of the vegetation of Europe during the Last Glacial Maximum (LGM) are an enigma. Pollen-based analyses have suggested that Europe was largely covered by steppe and tundra, and forests persisted only in small refugia. Climate-vegetation model simulations on the other hand have consistently suggested that broad areas of Europe would have been suitable for forest, even in the depths of the last glaciation. Here we reconcile models with data by demonstrating that the highly mobile groups of hunter-gatherers that inhabited Europe at the LGM could have substantially reduced forest cover through the ignition of wildfires. Similar to hunter-gatherers of the more recent past, Upper Paleolithic humans were masters of the use of fire, and preferred inhabiting semi-open landscapes to facilitate foraging, hunting and travel. Incorporating human agency into a dynamic vegetation-fire model and simulating forest cover shows that even small increases in wildfire frequency over natural background levels resulted in large changes in the forested area of Europe, in part because trees were already stressed by low atmospheric CO2 concentrations and the cold, dry, and highly variable climate. Our results suggest that the impact of humans on the glacial landscape of Europe may be one of the earliest large-scale anthropogenic modifications of the earth system. PMID:27902716

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

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

Palaeodistribution modelling of European vegetation types at the Last Glacial Maximum using modern analogues from Siberia: Prospects and limitations

NASA Astrophysics Data System (ADS)

Janská, Veronika; Jiménez-Alfaro, Borja; Chytrý, Milan; Divíšek, Jan; Anenkhonov, Oleg; Korolyuk, Andrey; Lashchinskyi, Nikolai; Culek, Martin

2017-03-01

We modelled the European distribution of vegetation types at the Last Glacial Maximum (LGM) using present-day data from Siberia, a region hypothesized to be a modern analogue of European glacial climate. Distribution models were calibrated with current climate using 6274 vegetation-plot records surveyed in Siberia. Out of 22 initially used vegetation types, good or moderately good models in terms of statistical validation and expert-based evaluation were computed for 18 types, which were then projected to European climate at the LGM. The resulting distributions were generally consistent with reconstructions based on pollen records and dynamic vegetation models. Spatial predictions were most reliable for steppe, forest-steppe, taiga, tundra, fens and bogs in eastern and central Europe, which had LGM climate more similar to present-day Siberia. The models for western and southern Europe, regions with a lower degree of climatic analogy, were only reliable for mires and steppe vegetation, respectively. Modelling LGM vegetation types for the wetter and warmer regions of Europe would therefore require gathering calibration data from outside Siberia. Our approach adds value to the reconstruction of vegetation at the LGM, which is limited by scarcity of pollen and macrofossil data, suggesting where specific habitats could have occurred. Despite the uncertainties of climatic extrapolations and the difficulty of validating the projections for vegetation types, the integration of palaeodistribution modelling with other approaches has a great potential for improving our understanding of biodiversity patterns during the LGM.

Estimating Past Temperature Change in Antarctica Based on Ice Core Stable Water Isotope Diffusion

NASA Astrophysics Data System (ADS)

Kahle, E. C.; Markle, B. R.; Holme, C.; Jones, T. R.; Steig, E. J.

2017-12-01

The magnitude of the last glacial-interglacial transition is a key target for constraining climate sensitivity on long timescales. Ice core proxy records and general circulation models (GCMs) both provide insight on the magnitude of climate change through the last glacial-interglacial transition, but appear to provide different answers. In particular, the magnitude of the glacial-interglacial temperature change reconstructed from East Antarctic ice-core water-isotope records is greater ( 9 degrees C) than that from most GCM simulations ( 6 degrees C). A possible source of this difference is error in the linear-scaling of water isotopes to temperature. We employ a novel, nonlinear temperature-reconstruction technique using the physics of water-isotope diffusion to infer past temperature. Based on new, ice-core data from the South Pole, this diffusion technique suggests East Antarctic temperature change was smaller than previously thought. We are able to confirm this result using a simple, water-isotope fractionation model to nonlinearly reconstruct temperature change at ice core locations across Antarctica based on combined oxygen and hydrogen isotope ratios. Both methods produce a temperature change of 6 degrees C for South Pole, agreeing with GCM results for East Antarctica. Furthermore, both produce much larger changes in West Antarctica, also in agreement with GCM results and independent borehole thermometry. These results support the fidelity of GCMs in simulating last glacial maximum climate, and contradict the idea, based on previous work, that the climate sensitivity of current GCMs is too low.

Contrasting scaling properties of interglacial and glacial climates

NASA Astrophysics Data System (ADS)

Ditlevsen, Peter; Shao, Zhi-Gang

2017-04-01

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

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

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

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

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

Chronology and provenance of last-glacial (Peoria) loess in western Iowa and paleoclimatic implications

USGS Publications Warehouse

Muhs, Daniel R.; Bettis, E. Arthur; Roberts, Helen M.; Harlan, Stephen S.; Paces, James B.; Reynolds, Richard L.

2013-01-01

Geologic archives show that the Earth was dustier during the last glacial period. One model suggests that increased gustiness (stronger, more frequent winds) enhanced dustiness. We tested this at Loveland, Iowa, one of the thickest deposits of last-glacial-age (Peoria) loess in the world. Based on K/Rb and Ba/Rb, loess was derived not only from glaciogenic sources of the Missouri River, but also distal loess from non-glacial sources in Nebraska. Optically stimulated luminescence (OSL) ages provide the first detailed chronology of Peoria Loess at Loveland. Deposition began after ~ 27 ka and continued until ~ 17 ka. OSL ages also indicate that mass accumulation rates (MARs) of loess were not constant. MARs were highest and grain size was coarsest during the time of middle Peoria Loess accretion, ~ 23 ka, when ~ 10 m of loess accumulated in no more than ~ 2000 yr and possibly much less. The timing of coarsest grain size and highest MAR, indicating strongest winds, coincides with a summer-insolation minimum at high latitudes in North America and the maximum southward extent of the Laurentide ice sheet. These observations suggest that increased dustiness during the last glacial period was driven largely by enhanced gustiness, forced by a steepened meridional temperature gradient.

Asymmetric Signature of Glacial Antarctic Intermediate Water in the Central South Pacific

NASA Astrophysics Data System (ADS)

Tapia, R.; Nuernberg, D.; Ho, S. L.; Lamy, F.; Ullermann, J.; Gersonde, R.; Tiedemann, R.

2017-12-01

Southern Ocean Intermediate Waters (SOIWs) play a key role in modulating the global climate on glacial-interglacial time scales as they connect the Southern Ocean and the tropics. Despite their importance, the past evolution of the SOIWs in the central South Pacific is largely unknown due to a dearth of sedimentary archives. Here we compare Mg/Ca-temperature, stable carbon and oxygen isotope records from surface-dwelling (G. bulloides) and deep-dwelling (G. inflata) planktic foraminifera at site PS75/059-2 (54°12.9' S, 125°25.53' W; recovery 13.98 m; 3.613 m water depth), located north of the modern Subantarctic Front. Our study focuses on the temperature and salinity variability controlled by SOIWs, which were subducted at the Subantarctic Front during the Last Glacial Maximum (LGM; 29-17ka BP) and the Penultimate Glacial Maximum (PGM; 180-150ka BP). During both glacial periods conditions at the subsurface ocean were colder and fresher relative to the Holocene (<10ka) suggesting an enhanced presence of SOIWs. In spite of the comparable subsurface cooling during both glacial, the subsurface ocean during the PGM was saltier and 0.35‰ more depleted in δ13C in comparison to the LGM. Interestingly, the mean δ13C value of the PGM is comparable to the Carbon Isotope Minimum Events, which might suggests a larger contribution of "old" low δ13C deep waters to the study site during the PGM. A Latitudinal comparison of subsurface proxies suggests glacial asymmetries in the advection of SOIWs into the central Pacific, plausibly related to glacial changes in the convection depth of SOIWs at the South Antarctic Front area rather than changes in production of the SOIWs.

A global perspective on Glacial- to Interglacial variability change

NASA Astrophysics Data System (ADS)

Rehfeld, Kira; Münch, Thomas; Ho, Sze Ling; Laepple, Thomas

2017-04-01

Changes in climate variability are more important for society than changes in the mean state alone. While we will be facing a large-scale shift of the mean climate in the future, its implications for climate variability are not well constrained. Here we quantify changes in temperature variability as climate shifted from the Last Glacial cold to the Holocene warm period. Greenland ice core oxygen isotope records provide evidence of this climatic shift, and are used as reference datasets in many palaeoclimate studies worldwide. A striking feature in these records is pronounced millennial variability in the Glacial, and a distinct reduction in variance in the Holocene. We present quantitative estimates of the change in variability on 500- to 1500-year timescales based on a global compilation of high-resolution proxy records for temperature which span both the Glacial and the Holocene. The estimates are derived based on power spectral analysis, and corrected using estimates of the proxy signal-to-noise ratios. We show that, on a global scale, variability at the Glacial maximum is five times higher than during the Holocene, with a possible range of 3-10 times. The spatial pattern of the variability change is latitude-dependent. While the tropics show no changes in variability, mid-latitude changes are higher. A slight overall reduction in variability in the centennial to millennial range is found in Antarctica. The variability decrease in the Greenland ice core oxygen isotope records is larger than in any other proxy dataset. These results therefore contradict the view of a globally quiescent Holocene following the instable Glacial, and imply that, in terms of centennial to millennial temperature variability, the two states may be more similar than previously thought.

Chronological and geomorphological investigation of fossil debris-covered glaciers in relation to deglaciation processes: A case study in the Sierra de La Demanda, northern Spain

NASA Astrophysics Data System (ADS)

Fernández-Fernández, José M.; Palacios, David; García-Ruiz, José M.; Andrés, Nuria; Schimmelpfennig, Irene; Gómez-Villar, Amelia; Santos-González, Javier; Álvarez-Martínez, Javier; Arnáez, José; Úbeda, José; Léanni, Laëtitia; Aumaître, Georges; Bourlès, Didier; Keddadouche, Karim; Aster Team

2017-08-01

In this study, fossil debris-covered glaciers are investigated and dated in the Sierra de la Demanda, northern Spain. They are located in glacial valleys of approximately 1 km in length, where several moraines represent distinct phases of the deglaciation period. Several boulders in the moraines and fossil debris-covered glaciers were selected for analysis of 10Be surface exposure dating. A minimum age of 17.8 ± 2.2 ka was obtained for the outermost moraine in the San Lorenzo cirque, and was attributed to the global Last Glacial Maximum (LGM) or earlier glacial stages, based on deglaciation dates determined in other mountain areas of northern Spain. The youngest moraines were dated to approximately 16.7 ± 1.4 ka, and hence correspond to the GS-2a stadial (Oldest Dryas). Given that the debris-covered glaciers fossilize intermediate moraines, it was deduced that they developed between the LGM and the Oldest Dryas, coinciding with a period of extensive deglaciation. During this deglaciation phase, the cirque headwalls likely discharged large quantities of boulders and blocks that covered the residual ice masses. The resulting debris-covered glaciers evolved slowly because the debris mantle preserved the ice core from rapid ablation, and consequently they remained active until the end of the Late Glacial or the beginning of the Holocene (for the San Lorenzo cirque) and the Holocene Thermal Maximum (for the Mencilla cirque). The north-facing part of the Mencilla cirque ensured longer preservation of the ice core.

Antarctic grounding-line migration

NASA Astrophysics Data System (ADS)

Slater, T.; Konrad, H.; Shepherd, A.; Gilbert, L.; Hogg, A.; McMillan, M.; Muir, A. S.

2017-12-01

Knowledge of grounding-line position is critical for quantifying ice discharge into the ocean, as a boundary condition for numerical models of ice flow, and as an indicator of ice sheet stability. Although geological investigations have documented extensive grounding-line retreat since the period of the Last Glacial Maximum, observations of grounding line migration during the satellite era are restricted to a handful of locations. We combine satellite altimeter observations of ice-elevation change and airborne measurements of ice geometry to track movement of the Antarctic Ice Sheet grounding line. Based on these data, we estimate that 22%, 3%, and 10% of the West Antarctic, East Antarctic, and Antarctic Peninsula ice sheet grounding lines are retreating at rates faster than the typical pace since the Last Glacial Maximum, and that the continent loses over 200 km2 of grounded-ice area per year. Although by far the fastest rates of retreat occurred in the Amundsen Sea Sector, the Pine Island Glacier grounding line has stabilized - likely as a consequence of abated ocean forcing during the survey period.

Glacier changes since Local Last Glacial Maximum in the South-West slope of Nevado Hualcán, Cordillera Blanca, Peru, deduced from moraine mapping and GIS-based analysis

NASA Astrophysics Data System (ADS)

Giráldez, Claudia; Palacios, David; Haeberli, Wilfried; Úbeda, Jose; Schauwecker, Simone; Torres, Judith

2014-05-01

Anticipating and assessing hazards and risks associated with the shrinking of surface and subsurface ice in cold mountain chains is facilitated by empirical-quantitative data on present and past rates of change, as well as by a general understanding of related landforms and landscape evolution through time. Rock/ice avalanches and devastating outburst floods from glacial lakes indeed constitute a major cause of severe damage in populated mountain areas such as the Cordillera Blanca whose combination of tectonic, topographic and glaciological characteristics make it a threatened region. This study focuses on the Río Chucchún catchment above the city of Carhuaz, which was recently affected by a flood/debris flow from a rock/ice avalanche impacting a recently grown lake (Laguna 513). Traces left by past glaciations strongly affect the current geomorphodinamic behaviour of the catchment. For instance, a prominent sediment-filled glacial overdeepening behind Younger Dryas (YD) moraines (Pampa de Shonquil) with its retention function strongly influenced the chain of processes initiated by the outburst of Laguna 513. The aim of this study is to reconstruct earlier glacial phases in the SW slope of Nevado Hualcán (Río Chucchún catchment), in order to compile quantitative information on surface areas and Equilibrium Line Altitudes (ELAs). To do so, glacier stages were assigned to five different glacial phases, through photointerpretation and moraine cartography: 2003; 1962; Hualcán-I-LIA (15th to 18th centuries); Hualcán-II-YD (~12,5 ka BP); and Hualcán-III-LLGM (~34 to 21 ka BP). Glacial stages Hualcán-I-LIA, Hualcán-II-YD and Hualcán-III-LLGM present relative dating based on previous studies from different authors in the Peruvian Andes. Once glaciers were delimited, their surface areas and Equilibrium Line Altitudes (ELAs) were calculated. For ELA estimation three different methods were used: the mid-range elevation, the Accumulation Area Ratio (AAR), and the Area x Altitude Balance Ratio (AABR). The results show a decrease in surface area with respect to Hualcán-III-LLGM of 16% for Hualcán-II-YD; 50% for Hualcán-I-LIA; and 74% for 2003. With respect to 2003, ELAs shifted ~520 m since the Local Last Glacial Maximum (LLGM), ~470 m since a marked late-glacial stage (YD?), ~130 m since the Little Ice Age (LIA) and about ~100 m since 1962. If the changes are exclusively attributed to temperature effects, warming since LLGM can be estimated at some 3°C and since the maximum glacier extent of LIA at about 0.8°C. Such values are rather close to mean global temperature change during the corresponding intervals. Most of the ELA shift since LIA appears to have taken place during recent decades characterized by very rapid glacier shrinkage, although air temperature does not seem to have risen considerably during the last 30 years. These results along with other environmental and social approaches will contribute to a better understanding of impacts from climate change and glacier shrinkage in order to develop adaptation, mitigation and disaster risk reduction strategies in the Peruvian Andes.

Glacial isostatic adjustment using GNSS permanent stations and GIA modelling tools

NASA Astrophysics Data System (ADS)

Kollo, Karin; Spada, Giorgio; Vermeer, Martin

2013-04-01

Glacial Isostatic Adjustment (GIA) affects the Earth's mantle in areas which were once ice covered and the process is still ongoing. In this contribution we focus on GIA processes in Fennoscandian and North American uplift regions. In this contribution we use horizontal and vertical uplift rates from Global Navigation Satellite System (GNSS) permanent stations. For Fennoscandia the BIFROST dataset (Lidberg, 2010) and North America the dataset from Sella, 2007 were used respectively. We perform GIA modelling with the SELEN program (Spada and Stocchi, 2007) and we vary ice model parameters in space in order to find ice model which suits best with uplift values obtained from GNSS time series analysis. In the GIA modelling, the ice models ICE-5G (Peltier, 2004) and the ice model denoted as ANU05 ((Fleming and Lambeck, 2004) and references therein) were used. As reference, the velocity field from GNSS permanent station time series was used for both target areas. Firstly the sensitivity to the harmonic degree was tested in order to reduce the computation time. In the test, nominal viscosity values and pre-defined lithosphere thicknesses models were used, varying maximum harmonic degree values. Main criteria for choosing the suitable harmonic degree was chi-square fit - if the error measure does not differ more than 10%, then one might use as well lower harmonic degree value. From this test, maximum harmonic degree of 72 was chosen to perform calculations, as the larger value did not significantly modify the results obtained, as well the computational time for observations was kept reasonable. Secondly the GIA computations were performed to find the model, which could fit with highest probability to the GNSS-based velocity field in the target areas. In order to find best fitting Earth viscosity parameters, different viscosity profiles for the Earth models were tested and their impact on horizontal and vertical velocity rates from GIA modelling was studied. For every tested model the chi-square misfit for horizontal, vertical and three-dimensional velocity rates from the reference model was found (Milne, 2001). Finally, the best fitting models from GIA modelling were compared with rates obtained from GNSS data. Keywords: Fennoscandia, North America, land uplift, glacial isostatic adjustment, visco-elastic modelling, BIFROST. References Lidberg, M., Johannson, J., Scherneck, H.-G. and Milne, G. (2010). Recent results based on continuous GPS observations of the GIA process in Fennoscandia from BIFROST. Journal of Geodynamics, 50. pp. 8-18. Sella, G. F., Stein, S., Dixon, T. H., Craymer, M., James, T. S., Mazotti, S. and Dokka, R. K. (2007). Observations of glacial isostatic adjustment in "stable" North America with GPS. Geophysical Research Letters, 34, L02306. Spada, G., Stocchi, P. (2007). SELEN: A Fortran 90 program for solving the "sea-level equation". Computers & Geosciences, 33:538-562, 2007. Peltier, W. R. (2004). Global glacial isostasy and the surface of the ice-age Earth: The Ice-5G (VM2) model and GRACE. Annu. Rev. Earth Planet. Sci., 32:111-149, 2004. Fleming, K. and Lambeck, K. (2004). Constraints on the Greenland Ice Sheet since the Last Glacial Maximum from sea-level observations and glacial-rebound models. Quaternary Science Reviews 23 (2004), pp. 1053-1077. Milne, G. A. and Davis, J. L. and Mitrovica, J. X. and Scherneck, H.-G. and Johansson, J. M. and Vermeer, M. and Koivula, H. (2001). Space-geodetic constraints on glacial isostatic adjustment in Fennoscandia. Science 291 (2001), pp. 2381-2385.

Global snowline and mountain topography: a contrasted view

NASA Astrophysics Data System (ADS)

Champagnac, Jean-Daniel; Herman, Frédéric; Valla, Pierre

2013-04-01

The examination of the relationship between Earth's topography and present and past climate (i.e., long-term elevation of glaciers Equilibrium Line Altitude) reveals that the elevation of mountain ranges may be limited or controlled by glaciations (e.g. Porter, 1989). This is of prime importance, because glacial condition would lead to a limit the mountain development, hence the accumulation of gravitational energy and prevent the development of further glacial conditions as well as setting the erosion in (peri)glacial environments. In this study, we examine the relationships between topography and the global Equilibrium Line Altitude of alpine glaciers around the world (~ long term snowline, i.e. the altitude where the ice mass balance is null). This analysis reinforce a global study previously published (Champagnac et al., 2012), and provide a much finer view of the climate-topography-tectonics relationships. Specifically, two main observations can be drawn: 1) The distance between the (averaged and maximum) topography, and the ELA decreases pole ward the poles, and even become reversed (mean elevation above to ELA) at high latitude. Correlatively, the elevation of very large portion of land at mid-latitude cannot be related to glaciations, simply because it was never glaciated (large distance between topography and long-term mean ELA). The maximum distance between the ELA and the topography is greater close to the equator and decreases poleward. In absence of glacial and periglacial erosion, this trend cannot have its origin in glacial and periglacial processes. Moreover, the ELA elevation shows a significant (1000~1500m) depression in the intertropical zone. This depression of the ELA is not reflected at all in the topography 2) The distribution of relief on Earth, if normalized by the mean elevation of mountain ranges (as a proxy for available space to create relief, see Champagnac et al., 2012 for details) shows a latitudinal band of greater relief between ~40 and ~60° (or between ELA of ~500m to ~2500m a.s.l.). This mid-latitude relatively greater relief challenges the straightforward relationship between glaciations, erosion and topography. Oppositely, it suggests that glacier may be more efficient agent in temperate area, with an important amplitude between glacial and interglacial climate. This is consistent with the view of a very variable glacier erodibility that can erode and protect the landscape, as well as with studies documenting a bimodal location of the preferred glacial erosion, at relatively high elevation (around the long-term ELA), and at much lower elevation (close to the glacial maximum lower reaches), thanks to efficient water lubrication of the glacier bases that greatly enhance the sliding velocity (Herman et al., 2011). These findings show that the relation between the mountain topography and the long term snowline is not as straightforward as previously proposed (e.g. Egholm et al., 2009) . Beside the role of tectonic forcing highlighted by several authors (e.g. Pedersen et al., 2010;Spotila and Berger, 2010),, the importance of the glacial erosion appears to be crucial at mid latitude, but more complex at both high and low latitude. Moreover, the relief at mid latitude appears to be higher, hence suggesting a positive correlation between relief and topographic control of glacier on the landscape Champagnac, J.-D., Molnar, P., Sue, C., and Herman, F.: Tectonics, Climate, and Mountain Topography, Journal of Geophysical Research B: Solid Earth, 117, doi:10.1029/2011JB008348, 2012. Egholm, D. L., Nielsen, S. B., Pedersen, V. K., and Lesemann, J. E.: Glacial effects limiting mountain height, Nature, 460, 884-888, 2009. Herman, F., Beaud, F., Champagnac, J.-D., Lemieux, J.-M., and Sternai, P.: Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys, Earth and Planetary Science Letters, 310, 498-508, 2011. Pedersen, V. K., Egholm, D. L., and Nielsen, S. B.: Alpine glacial topography and the rate of rock column uplift: a global perspective, Geomorphology, 122, 129-139, 10.1016/j.geomorph.2010.06.005, 2010. Porter, S. C.: Some geological implications of average Quaternary glacial conditions., Quaternary Research, 32, 245-261, 1989. Spotila, J. A., and Berger, A. L.: Exhumation at orogenic indentor corners under long-term glacial conditions: Example of the St. Elias orogen, Southern Alaska, Tectonophysics, 490, 241-256, doi:10.1016/j.tecto.2010.05.015, 2010.

Reconstruction of the Indian monsoon variability and its environmental impacts over the northwestern Arabian Sea and its surrounding continents since the Last Glacial Maximum: Multi-proxy study of a marine core in the Gulf of Aden

NASA Astrophysics Data System (ADS)

Wiem, F.; Bassinot, F. C.; Lézine, A. M.

2016-12-01

Core MD92-1002 retrieved from the Gulf of Aden provides a unique paleoenvironmental and paleoclimatic record to study the evolution of continental and marine environments since 20 ka. Palynological analyses (pollen grains, spores, dinoflagellate cysts) were performed and data were combined with geochemical (δ18O, X-Ray Fluorescence) and sedimentological parameters (sedimentation rates, Total Organic Carbon (TOC)). Pollen grains reveal regional hyper-arid conditions during the glacial period, characterized by sparse vegetation cover of Saharo-Sindian origin. The abundance of steppic taxa associated with charcoal fragments suggests strong wind activity. Humidity tracers increased from 14.9 ka and reached their maximum between 9 and 7.5 ka. This maximum is characterized by the development of the tropical mangrove Rhizophora in the Gulf of Aden, reflecting tropical conditions with summer monsoon rains. The timing of events deduced from palynological records and continental data such as lacustrine and palustrine deposits and speleothems from Socotra and Oman, reveals a northward and westward shift of the Inter-Tropical Convergence Zone (ITCZ) summer position at the onset of the Holocene Humid Period (HHP). Dinoflagellate cyst assemblages suggest that the glacial period was characterized by weakened upwellings and well-ventilated bottom water. Primary productivity in the Gulf of Aden increased from 14.5 ka and reached its maximum during the glacial/interglacial transition between 12.6 and 10.8 ka. It took place about 3 ka earlier than the peak intensity of upwellings off the Oman margin, which is associated with the maximum of SW monsoonal winds. This singularity could be explained by the landlocked position of the gulf, at the junction between two orthogonal wind regimes during the boreal summer season (SW monsoon winds prevailing to the East of the Gulf, while NW winds blow along the main axis of the Red Sea to the West). TOC analysis reveals a Glacial-Interglacial variability that is largely decoupled from our reconstruction of surface productivity, suggesting that organic content is mainly controlled by preservation at the sea floor.

How Many Seals Were There? The Global Shelf Loss during the Last Glacial Maximum and Its Effect on the Size and Distribution of Grey Seal Populations

PubMed Central

Boehme, Lars; Thompson, Dave; Fedak, Mike; Bowen, Don; Hammill, Mike O.; Stenson, Garry B.

2012-01-01

Predicting how marine mammal populations respond to habitat changes will be essential for developing conservation management strategies in the 21st century. Responses to previous environmental change may be informative in the development of predictive models. Here we describe the likely effects of the last ice age on grey seal population size and distribution. We use satellite telemetry data to define grey seal foraging habitat in terms of the temperature and depth ranges exploited by the contemporary populations. We estimate the available extent of such habitat in the North Atlantic at present (between 1.42·106 km2 and 2.07·106 km2) and at the last glacial maximum (between 4.74·104 km2 and 2.11·105 km2); taking account of glacial and seasonal sea-ice coverage, estimated reductions of sea-level (123 m) and sea surface temperature hind-casts. Most of the extensive continental shelf waters (North Sea, Baltic Sea and Scotian Shelf), currently supporting >95% of grey seals, were unavailable during the last glacial maximum. A combination of lower sea-level and extensive ice-sheets, massively increased seasonal sea-ice coverage and southerly extent of cold water would have pushed grey seals into areas with no significant shelf waters. The habitat during the last glacial maximum might have been as small as 3% of today's extent and grey seal populations may have fallen to similarly low numbers. An alternative scenario involving a major change to a pelagic or bathy-pelagic foraging niche cannot be discounted. However, hooded seals currently dominate that niche and may have excluded grey seals from such habitat. If as seems likely, the grey seal population fell to very low levels it would have remained low for several thousand years before expanding into current habitats over the past 12,000 years or so. PMID:23300843

Reconstructing spatial and temporal patterns of paleoglaciation across Central Asia

NASA Astrophysics Data System (ADS)

Stroeven, Arjen P.

2014-05-01

Understanding the behaviour of mountain glaciers and ice caps, the evolution of mountain landscapes, and testing global climate models all require well-constrained information on past spatial and temporal patterns of glacier change. Particularly important are transitional regions that have high spatial and temporal variation in glacier activity and that can provide a sensitive record of past climate change. Central Asia is an extreme continental location with glaciers that have responded sensitively to variations in major regional climate systems. As an international team, we are reconstructing glacial histories of several areas of the Tibetan Plateau as well as along the Tian Shan, Altai and Kunlun Mountains. Building on previous work, we are using remote sensing-based geomorphological mapping augmented with field observations to map out glacial landforms and the maximum distributions of erratics. We then use cosmogenic nuclide Be-10 and Al-26, optically stimulated luminescence, and electron spin resonance dating of moraines and other landforms to compare dating techniques and to constrain the ages of defined extents of paleo-glaciers and ice caps. Comparing consistently dated glacial histories across central Asia provides an opportunity to examine shifts in the dominance patterns of climate systems over time in the region. Results to date show significant variations in the timing and extent of glaciation, including areas in the southeast Tibetan Plateau and Tian Shan with extensive valley and small polythermal ice cap glaciation during the global last glacial maximum in contrast to areas in central and northeast Tibetan Plateau that had very limited valley glacier expansion then. Initial numerical modelling attempting to simulate mapped and dated paleoglacial extents indicates that relatively limited cooling is sufficient to produce observed past expansions of glaciers across the Tibetan Plateau, and predicts complex basal thermal regimes in some locations that match patterns of past glacial erosion inferred from landform patterns and ages. Future modelling will examine glacier behaviour along major mountain ranges across central Asia.

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 higher latitudes. The glaciated North American and European cratons show a trend of modest thinning (~3km), and glaciated western Asia minor thinning (~1.5 km). These values are at the level of model uncertainties, but we note that cratons without ice sheets during the last glacial period show substantially different patterns.

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

USGS Publications Warehouse

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

2009-01-01

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

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.

Pleistocene glacial refugia across the Appalachian Mountains and coastal plain in the millipede genus Narceus: Evidence from population genetic, phylogeographic, and paleoclimatic data

PubMed Central

Walker, Matt J; Stockman, Amy K; Marek, Paul E; Bond, Jason E

2009-01-01

Background Species that are widespread throughout historically glaciated and currently non-glaciated areas provide excellent opportunities to investigate the role of Pleistocene climatic change on the distribution of North American biodiversity. Many studies indicate that northern animal populations exhibit low levels of genetic diversity over geographically widespread areas whereas southern populations exhibit relatively high levels. Recently, paleoclimatic data have been combined with niche-based distribution modeling to locate possible refugia during the Last Glacial Maximum. Using phylogeographic, population, and paleoclimatic data, we show that the distribution and mitochondrial data for the millipede genus Narceus are consistent with classical examples of Pleistocene refugia and subsequent post-glacial population expansion seen in other organismal groups. Results The phylogeographic structure of Narceus reveals a complex evolutionary history with signatures of multiple refugia in southeastern North America followed by two major northern expansions. Evidence for refugial populations were found in the southern Appalachian Mountains and in the coastal plain. The northern expansions appear to have radiated from two separate refugia, one from the Gulf Coastal Plain area and the other from the mid-Atlantic coastal region. Distributional models of Narceus during the Last Glacial Maximum show a dramatic reduction from the current distribution, with suitable ecological zones concentrated along the Gulf and Atlantic coastal plain. We found a strong correlation between these zones of ecological suitability inferred from our paleo-model with levels of genetic diversity derived from phylogenetic and population estimates of genetic structuring. Conclusion The signature of climatic change, during and after the Pleistocene, on the distribution of the millipede genus Narceus is evident in the genetic data presented. Niche-based historical distribution modeling strengthens the conclusions drawn from the genetic data and proves useful in identifying probable refugia. Such interdisciplinary biogeographic studies provide a comprehensive approach to understanding these processes that generate and maintain biodiversity as well as the framework necessary to explore questions regarding evolutionary diversification of taxa. PMID:19183468

From valley to marginal glaciation in alpine-type relief: Lateglacial glacier advances in the Pięć Stawów Polskich/Roztoka Valley, High Tatra Mountains, Poland

NASA Astrophysics Data System (ADS)

Zasadni, Jerzy; Kłapyta, Piotr

2016-01-01

The Pięć Stawów Polskich-Roztoka Valley in the High Tatras (Western Carpathians) features typical alpine-type relief with a deeply incised glacial trough and large, compound trough head cirque. The prominent hypsographic maximum in the valley (1680-2000 m) along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms, specifically the most recent Lateglacial advances. The valley has been intensively studied before in the context of glacial chronology. In this paper, we re-establish the post-Last Glacial Maximum (LGM) glacial chronology of the valley via detailed geomorphologic mapping, equilibrium line altitude (ELA) reconstruction, and Schmidt hammer (SH) dating, along with a critical review of previously published cosmogenic exposure age data (36Cl) and lacustrine sediment chronology. Our results indicate that the first four of the five distinguished Lateglacial stages (Roztoka I-III, Pusta I) occurred before the Bølling/Allerød (B/A) interstadial; thus, virtually the entire valley became deglaciated in course of the Oldest Dryas cold phase. A distinct reorganization of deglacial patterns from valley-type to marginal-type occurred before B/A warming when the ELA increased above the valley hypsographic maximum concentrated at the cirque bottom elevation. It shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing. This points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions. We infer that glaciers vanished in the Tatra Mountains during the B/A interstadial. Later, a renewed advance during the Younger Dryas (Pusta II) formed a nearly continuous, festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls. Furthermore, we discus some paleoenvironmental significance of the geomorphological record in the valley, as well, the applicability of SH dating in constructing glacial chronology.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

New Data on Vegetation and Climate Reconstruction in the Baikal-Patom Highland (Eastern Siberia) in the Last Glacial Maximum and Early Holocene

NASA Astrophysics Data System (ADS)

Henry, A.; Bezrukova, E. V.; Teten'kin, A. V.; Kuz'min, M. I.

2018-02-01

The first results of anthracological investigation for Eastern Siberia on the carbonaceous remains of woody and shrubby plants at the archaeological sites Kovrizhka III and IV in the lower reaches of the Vitim River are presented. The results of anthracological studies enabled us to obtain new data on changes in vegetation and climate along the lower reaches of the Vitim River. As a result, new data on human habitation in the lower reaches of the Vitim River in the last glacial maximum and early Holocene were obtained.

Atlantic meridional overturning circulation during the Last Glacial Maximum.

PubMed

Lynch-Stieglitz, Jean; Adkins, Jess F; Curry, William B; Dokken, Trond; Hall, Ian R; Herguera, Juan Carlos; Hirschi, Joël J-M; Ivanova, Elena V; Kissel, Catherine; Marchal, Olivier; Marchitto, Thomas M; McCave, I Nicholas; McManus, Jerry F; Mulitza, Stefan; Ninnemann, Ulysses; Peeters, Frank; Yu, Ein-Fen; Zahn, Rainer

2007-04-06

The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the Atlantic only slightly greater than today. However, evidence from multiple water-mass tracers supports a different distribution of deep-water properties, including density, which is dynamically linked to circulation.

A long pollen record from lowland Amazonia: Forest and cooling in glacial times

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

Colinvaux, P.A.; Moreno, J.E.; Bush, M.B.

A continuous pollen history of more than 40,000 years was obtained from a lake in the lowland Amazon rain forest. Pollen spectra demonstrate that tropical rain forest occupied the region continuously and that savannas or grasslands were not present during the last glacial maximum. The data suggest that the western Amazon forest was not fragmented into refugia in glacial times and that the lowlands were not a source of dust. Glacial age forests were comparable to modern forests but also included species now restricted to higher evaluations by temperature, suggesting a cooling of the order of 5{degrees} to 6{degrees}C. 23more » refs., 22 tabs.« less

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.

Pacing the post-Last Glacial Maximum demise of the Animas Valley glacier and the San Juan Mountain ice cap, Colorado

NASA Astrophysics Data System (ADS)

Guido, Zackry S.; Ward, Dylan J.; Anderson, Robert S.

2007-08-01

During the Last Glacial Maximum (LGM), a 5000 km2 ice cap covered the San Juan Mountains of southwest Colorado. The largest valley glacier draining this ice cap occupied the Animas Valley and flowed 91 km to the south. To characterize the post-LGM demise of the Animas Valley glacier, we employ cosmogenic 10Be to date the LGM terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples. The 10Be depth profile within the terrace sediments suggests abandonment at 19.4 ± 1.5 ka. As deglaciation began, the ponding of Glacial Lake Durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment. The age of the terrace therefore records the initiation of LGM retreat. Negligible 10Be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory. Glacial polish exposure ages monotonically decrease up-valley from 17.1 to 12.3 ka, with the single exception of a sample collected from a quartzite rib, yielding an average retreat rate of 15.4 m/yr. This trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history. Retreat of the Animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes. Deglaciation lasted for ˜7.2 k.y., and was complete by 12.3 ± 1.0 ka. The retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying.

The MIS 3 maximum of the Torres del Paine and Última Esperanza ice lobes in Patagonia and the pacing of southern mountain glaciation

NASA Astrophysics Data System (ADS)

García, Juan-Luis; Hein, Andrew S.; Binnie, Steven A.; Gómez, Gabriel A.; González, Mauricio A.; Dunai, Tibor J.

2018-04-01

The timing, structure and termination of the last southern mountain glaciation and its forcing remains unclear. Most studies have focused on the global Last Glacial Maximum (LGM; 26.5-19 ka) time period, which is just part of the extensive time-frame within the last glacial period, including Marine Isotope Stages 3 and 4. Understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change. Here, we present an extensive (n = 65) cosmogenic 10Be glacier chronology derived from moraine belts marking the pre-global LGM extent of the former Patagonian Ice Sheet in southernmost South America. Our results show the mountain ice sheet reached its maximum extent at 48.0 ± 1.8 ka during the local LGM, but attained just half this extent at 21.5 ± 1.8 ka during the global LGM. This finding, supported by nearby glacier chronologies, indicates that at orbital time scales, the southern mid-latitude glaciers fluctuated out-of-phase with northern hemisphere ice sheets. At millennial time-scales, our data suggest that Patagonian and New Zealand glaciers advanced in unison with cold Antarctic stadials and reductions in Southern Ocean sea surface temperatures. This implies a southern middle latitudes-wide millennial rhythm of climate change throughout the last glacial period linked to the north Atlantic by the bipolar seesaw. We suggest that winter insolation, acting alongside other drivers such as the strength and/or position of the southern westerlies, controlled the extents of major southern mountain glaciers such as those in southernmost South America.

Congruence between distribution modelling and phylogeographical analyses reveals Quaternary survival of a toadflax species (Linaria elegans) in oceanic climate areas of a mountain ring range.

PubMed

Fernández-Mazuecos, Mario; Vargas, Pablo

2013-06-01

· The role of Quaternary climatic shifts in shaping the distribution of Linaria elegans, an Iberian annual plant, was investigated using species distribution modelling and molecular phylogeographical analyses. Three hypotheses are proposed to explain the Quaternary history of its mountain ring range. · The distribution of L. elegans was modelled using the maximum entropy method and projected to the last interglacial and to the last glacial maximum (LGM) using two different paleoclimatic models: the Community Climate System Model (CCSM) and the Model for Interdisciplinary Research on Climate (MIROC). Two nuclear and three plastid DNA regions were sequenced for 24 populations (119 individuals sampled). Bayesian phylogenetic, phylogeographical, dating and coalescent-based population genetic analyses were conducted. · Molecular analyses indicated the existence of northern and southern glacial refugia and supported two routes of post-glacial recolonization. These results were consistent with the LGM distribution as inferred under the CCSM paleoclimatic model (but not under the MIROC model). Isolation between two major refugia was dated back to the Riss or Mindel glaciations, > 100 kyr before present (bp). · The Atlantic distribution of inferred refugia suggests that the oceanic (buffered)-continental (harsh) gradient may have played a key and previously unrecognized role in determining Quaternary distribution shifts of Mediterranean plants. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

Seafloor geomorphology of western Antarctic Peninsula bays: a signature of ice flow behaviour

NASA Astrophysics Data System (ADS)

Munoz, Yuribia P.; Wellner, Julia S.

2018-01-01

Glacial geomorphology is used in Antarctica to reconstruct ice advance during the Last Glacial Maximum and subsequent retreat across the continental shelf. Analogous geomorphic assemblages are found in glaciated fjords and are used to interpret the glacial history and glacial dynamics in those areas. In addition, understanding the distribution of submarine landforms in bays and the local controls exerted on ice flow can help improve numerical models by providing constraints through these drainage areas. We present multibeam swath bathymetry from several bays in the South Shetland Islands and the western Antarctic Peninsula. The submarine landforms are described and interpreted in detail. A schematic model was developed showing the features found in the bays: from glacial lineations and moraines in the inner bay to grounding zone wedges and drumlinoid features in the middle bay and streamlined features and meltwater channels in the outer bay areas. In addition, we analysed local variables in the bays and observed the following: (1) the number of landforms found in the bays scales to the size of the bay, but the geometry of the bays dictates the types of features that form; specifically, we observe a correlation between the bay width and the number of transverse features present in the bays. (2) The smaller seafloor features are present only in the smaller glacial systems, indicating that short-lived atmospheric and oceanographic fluctuations, responsible for the formation of these landforms, are only recorded in these smaller systems. (3) Meltwater channels are abundant on the seafloor, but some are subglacial, carved in bedrock, and some are modern erosional features, carved on soft sediment. Lastly, based on geomorphological evidence, we propose the features found in some of the proximal bay areas were formed during a recent glacial advance, likely the Little Ice Age.

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.

Glacial Buzzcutting and Scarp Encroachment Limit the Height of Tropical Mountains

NASA Astrophysics Data System (ADS)

Cunningham, M.; Stark, C. P.; Kaplan, M. R.; Schaefer, J. M.; Winckler, G.

2016-12-01

In many mountain ranges hypsometric maxima occur between the glacial equilibrium line altitude (ELA) of the Last Glacial Maximum (LGM) and that of today. A common interpretation of this large-scale observation is that a "glacial buzzsaw" acting throughout the Pleistocene concentrated area within the altitudinal band of ELA fluctuation. This hypothesis remains controversial, however, as there are many examples of uplifted relict surfaces in heavily glaciated areas that occur near the ELA by coincidence. We have focused on the role of glacial erosion in the tropics, where it is spatially restricted to high elevations and temporally limited to global glacial maxima, but appears to have nevertheless truncated vertical orogen growth. Evidence of glacial buzzcutting in some of these ranges has been obscured by post-glacial destruction of glacial valleys by expanding fluvial catchments. We deduce that a duel between glacial buzzcuting and fluvially-driven scarp encroachment has proceeded throughout the Pleistocene in these places. In Costa Rica, we use 10Be and 3He surface-exposure age dating and topographic analysis to confirm that substantial glacial denudation took place at high elevations during the LGM, and employ topographic metrics there and in the Central Range of Taiwan to reveal shrinkage of glacially buzzcut surfaces driven by post-glacial scarp encroachment. These data cast new light on the buzzsaw hypothesis by showing that glacial erosion works with remarkable efficiency in the tropics, precisely where it is likely to be least effective. Our work also draws attention to landscapes with ambiguous signs of glacial erosion, as there are apparent instances of heavily modified, pre-LGM buzzcut surfaces in several tropical ranges. These perched, possibly pre-LGM landscapes may offer a window into previous phases of buzzcutting, and place speed limits on the rate of post-glacial scarp encroachment.

Allostratigraphic approach on the Alpine Lateglacial

NASA Astrophysics Data System (ADS)

Monegato, Giovanni; Reitner, Jürgen M.

2017-04-01

The reconstruction of the Alpine deglaciation after the Last Glacial Maximum is the one-of-a-kind chance of understanding glaciers dynamics in a period of climate warming. Long-lasting studies beginning in the 19th Century resulted in the definition of five major phases established on the base of Δ ELA values. However, they have been recently re-discussed on the base of dating results and field evidence. Field based reconstructions in some areas of the Alps (Tyrol, Julian Alps) utilizing allostratigraphy i.e. the use of unconformity-bounded units, provide pinpoint in total to a plausible tripartite subdivision of Lateglacial deposits (Colucci et al., 2014; Bichler et al., 2016; Reitner et al., 2016). From the chronological point no consensus on the start of the Alpine Lateglacial exists: The major Garda and Ticino glaciers persisted until about 17.5 ka (e.g. Ravazzi et al., 2014), whereas the tongue basins and, moreover, even major valleys inside the Alps where ice-free already around 18.5 ka (e.g., Schmidt et al., 2012). For the short phase of ice-decay, as the first expression of activity of rather small local glaciers in contact to dead ice, only luminescence datings are available so far centered around 19 ka. The Gschnitz stadial, at about 16-17 ka, and the Egesen stadial corresponding to the Younger Dryas, are the only two remarkable phases of advance of glacier tongues into the valleys, which stabilized for considerable time. The reconstructions suggest that more effort is needed, in term of sedimentological and (allo-)stratigraphic investigations together with geochronology to understand if this tripartite stratigraphic scheme can be exported in the whole Alpine area, or if stabilization of glacier fronts could have taken place somewhere also due to local mechanisms. References Bichler, M. G., Reindl, M., Reitner, J. M., Drescher-Schneider, R., Wirsig, C., Christl, M., Hajdas, I. & Ivy-Ochs, S., 2016: Landslide deposits as stratigraphical markers for a sequence-based glacial stratigraphy: a case study of a Younger Dryas system in the Eastern Alps. Boreas, 45: 537-551. Colucci, R. R., Monegato, G., Žebre, M. (2014). Glacial and proglacial deposits of the Resia Valley (NE Italy): New insights on the onset and decay of the last alpine glacial maximum in the Julian Alps. Alpine and Mediterranean Quaternary, 27: 85-104. Ravazzi, C., Pini, R., Badino, F., De Amicis, M., Londeix, L., Reimer, P.J. (2014). The latest LGM culmination of the Garda Glacier (Italian Alps) and the onset of glacial termination. Age of glacial collapse and vegetation chronosequence. Quaternary Science Reviews, 105: 26-47. Reitner, J.M., Ivy-Ochs, S., Drescher-Schneider, R., Hajdas, I., Linner, M. (2016). Reconsidering the current stratigraphy of the Alpine Lateglacial: Implications of the sedimentary and morphological record of the Lienz area (Tyrol/Austria). E&G Quaternary Science Journal, 65: 113-144. Schmidt, R., Weckström, K., Lauterbach, S., Tessadri, R., Huber, K. (2012). North Atlantic climate impact on early late-glacial climate oscillations in the south-eastern Alps inferred from a multi-proxy lake sediment record. Journal of Quaternary Science, 27: 40-50.

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.

Last Glacial mammals in South America: a new scenario from the Tarija Basin (Bolivia)

NASA Astrophysics Data System (ADS)

Coltorti, M.; Abbazzi, L.; Ferretti, M. P.; Iacumin, P.; Rios, F. Paredes; Pellegrini, M.; Pieruccini, P.; Rustioni, M.; Tito, G.; Rook, L.

2007-04-01

The chronology, sedimentary history, and paleoecology of the Tarija Basin (Bolivia), one of the richest Pleistocene mammalian sites in South America, are revised here based on a multidisciplinary study, including stratigraphy, sedimentology, geomorphology, paleontology, isotope geochemistry, and 14C geochronology. Previous studies have indicated a Middle Pleistocene age for this classic locality. We have been able to obtain a series of 14C dates encompassing all the fossil-bearing sequences previously studied in the Tarija Basin. The dated layers range in age from about 44,000 to 21,000 radiocarbon years before present (BP), indicating that the Tarija fauna is much younger than previously thought. Glacial advances correlated to marine isotopic stages (MIS) 4 and 2 (ca. 62 and 20 ka BP, respectively) are also documented at the base and at the very top of the Tarija Padcaya succession, respectively, indicating that the Bolivian Altiplano was not dry but sustained an ice cap during the Last Glacial Maximum. The results of this multidisciplinary study enable us to redefine the chronological limits of the Tarija sequence and of its faunal assemblage and to shift this paleontological, paleoclimatological, and paleoecological framework to the time interval from MIS 4 to MIS 2.

Using species-specific paleotemperature equations with foraminifera: A case study in the Southern California Bight

USGS Publications Warehouse

Bemis, B.E.; Spero, H.J.; Thunell, R.C.

2002-01-01

Species-specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal ??18O values over the last 25 kyr in the Southern California Bight. The equations yield similar temperatures for the ??18O values of Globigerina bulloides and Neogloboquadrina pachyderma. In contrast, applying a single paleotemperature equation to G. bulloides and N. pachyderma ??18O yields different temperatures, which has been used to suggest that these species record the surface-to-thermocline temperature gradient. In Santa Barbara Basin, an isotopically distinct morphotype of G. bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today. When a more appropriate paleotemperature equation is used for glacial G. bulloides, we obtain more realistic glacial temperatures. Glacial-interglacial temperature differences (G-I ??T) calculated in the present study indicate significant cooling (??? 8-10??C) throughout the Southern California Bight during the last glacial maximum (LGM). The magnitude of glacial cooling varies from ???8??C near the middle of the Southern California Bight (Tanner Basin and San Nicolas Basin) to ???9??C in the north (Santa Barbara Basin) and ???9.5-10??C in the south (Velero Basin and No Name Basin). Our temperature calculations agree well with previous estimates based on the modern analog technique. In contrast, studies using N. pachyderma coiling ratios, U37k??? indices, and transfer functions esfimate considerably warmer LGM temperatures and smaller G-I ??T. ?? 2002 Elsevier Science B.V. All rights reserved.

Physical basis for a thick ice shelf in the Arctic Basin during the penultimate glacial maximum

NASA Astrophysics Data System (ADS)

Gasson, E.; DeConto, R.; Pollard, D.; Clark, C.

2017-12-01

A thick ice shelf covering the Arctic Ocean during glacial stages was discussed in a number of publications in the 1970s. Although this hypothesis has received intermittent attention, the emergence of new geophysical evidence for ice grounding in water depths of up to 1 km in the central Arctic Basin has renewed interest into the physical plausibility and significance of an Arctic ice shelf. Various ice shelf configurations have been proposed, from an ice shelf restricted to the Amerasian Basin (the `minimum model') to a complete ice shelf cover in the Arctic. Attempts to simulate an Arctic ice shelf have been limited. Here we use a hybrid ice sheet / shelf model that has been widely applied to the Antarctic ice sheet to explore the potential for thick ice shelves forming in the Arctic Basin. We use a climate forcing appropriate for MIS6, the penultimate glacial maximum. We perform a number of experiments testing different ice sheet / shelf configurations and compare the model results with ice grounding locations and inferred flow directions. Finally, we comment on the potential significance of an Arctic ice shelf to the global glacial climate system.

Late Pleistocene glacial fluctuations in Cordillera Oriental, subtropical Andes

NASA Astrophysics Data System (ADS)

Martini, Mateo A.; Kaplan, Michael R.; Strelin, Jorge A.; Astini, Ricardo A.; Schaefer, Joerg M.; Caffee, Marc W.; Schwartz, Roseanne

2017-09-01

The behavior of subtropical glaciers during Middle to Late Pleistocene global glacial maxima and abrupt climate change events, specifically in Earth's most arid low-latitude regions, remains an outstanding problem in paleoclimatology. The present-day climate of Cordillera Oriental, in arid northwestern Argentina, is influenced by shifts in subtropical climate systems, including the South American Summer Monsoon. To understand better past glacier-subtropical climates during the global Last Glacial Maximum (LGM, 26.5-19 ka) and other time periods, we combined geomorphic features with forty-two precise 10Be ages on moraine boulders and reconstructed paleo-equilibrium line altitudes (ELA) at Nevado de Chañi (24°S) in the arid subtropical Andes. We found a major glacial expansion at ∼23 ± 1.6 ka, that is, during the global LGM. Additional glacial expansions are observed before the global LGM (at ∼52-39 ka), and after, at 15 ± 0.5 and 12 ± 0.6 ka. The ∼15 ka glacial event was found on both sides of Chañi and the ∼12 ka event is only recorded on the east side. Reconstructed ELAs of the former glaciers exhibit a rise from east to west that resembles the present subtropical climate trajectory from the Atlantic side of the continent; hence, we infer that this climate pattern must have been present in the past. Based on comparison with other low-latitude paleoclimate records, such as those from lakes and caves, we infer that both temperature and precipitation influenced past glacial occurrence in this sector of the arid Andes. Our findings also imply that abrupt deglacial climate events associated with the North Atlantic, specifically curtailed meridional overturning circulation and regional cooling, may have had attendant impacts on low subtropical Southern Hemisphere latitudes, including the climate systems that affect glacial activity around Nevado de Chañi.

Record of late Pleistocene glaciation and deglaciation in the southern Cascade Range. I. Petrological evidence from lacustrine sediment in Upper Klamath Lake, southern Oregon

USGS Publications Warehouse

Reynolds, R.L.; Rosenbaum, J.G.; Rapp, J.; Kerwin, M.W.; Bradbury, J.P.; Colman, S.; Adam, D.

2004-01-01

Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37-25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter.

Climate Controls on Last Glacial Maximum to Early Holocene Glacier Extents in the Rwenzori Mountains, Uganda-Democratic Republic of Congo

NASA Astrophysics Data System (ADS)

Jackson, M. S.; Kelly, M. A.; Russell, J. M.; Baber, M.; Loomis, S. E.

2014-12-01

The climate controls on past and present tropical glacier fluctuations are unclear. Here we present a chronology of past glacial extents in the Rwenzori Mountains (~1ºN, 30ºE), on the border of Uganda and the Democratic Republic of Congo, and compare this with local and regional paleoclimate records to infer the climate controls on glaciation. The Rwenzori Mountains host the most extensive glacial system in Africa and are composed of quartz-rich bedrock lithologies, enabling 10Be dating. Our dataset includes thirty 10Be ages of boulders on moraines estimated to have been deposited between the end of the last glacial period and early Holocene time. In the Mubuku Valley, eight 10Be ages of large (~50-150 m relief) lateral moraines that extend down to ~2000 m asl indicate that deposition occurred at ~23.4 ka (n=4) and ~20.1 ka (n=4), contemporaneously with the global Last Glacial Maximum (LGM). Local and regional paleoclimate records document dry, cool conditions in East Africa during this time. Therefore, we suggest that cooler temperatures were a primary influence on the LGM glacial extents. Upvalley from these samples, six 10Be ages of boulders on moraines (between 3450 and 3720 m asl) document stillstands or readvances of glacier ice at ~14.3 ka (n=2), ~13.2 ka (n=2), and ~11.1 ka (n=2). In the nearby Nyagumasani Valley sixteen 10Be ages of boulders on moraines at similar elevations (3870-4020 m asl) indicate stillstands or readvances at ~11.5 ka (n=4), ~10.6 ka (n=4), and ~10.5 ka (n=4). Local and regional paleoclimate records indicate dry conditions during Younger Dryas time, wet conditions during early Holocene time, and no significant late-glacial temperature reversal. Thus, the relationship between glacier advance and climate conditions during late-glacial time remains enigmatic. We continue to develop the moraine chronology in order to improve our interpretations of climate controls on glacier fluctuations during late-glacial to early Holocene time.

High-elevation amplification of warming since the Last Glacial Maximum in East Africa: New perspectives from biomarker paleotemperature reconstructions

NASA Astrophysics Data System (ADS)

Loomis, S. E.; Russell, J. M.; Kelly, M. A.; Eggermont, H.; Verschuren, D.

2013-12-01

Tropical lapse rate variability on glacial/interglacial time scales has been hotly debated since the publication of CLIMAP in 1976. Low-elevation paleotemperature reconstructions from the tropics have repeatedly shown less warming from the Last Glacial Maximum (LGM) to present than reconstructions from high elevations, leading to widespread difficulty in estimating the true LGM-present temperature change in the tropics. This debate is further complicated by the fact that most paleotemperature estimates from high elevations in the tropics are derived from pollen- and moraine-based reconstructions of altitudinal shifts in vegetation belts and glacial equilibrium line altitudes (ELAs). These traditional approaches rely on the assumption that lapse rates have remained constant through time. However, this assumption is problematic in the case of the LGM, when pervasive tropical aridity most likely led to substantial changes in lapse rates. Glycerol dialkyl glycerol tetraethers (GDGTs) can be used to reconstruct paleotemperatures independent of hydrological changes, making them the ideal proxy to reconstruct high elevation temperature change and assess lapse rate variability through time. Here we present two new equatorial paleotemperature records from high elevations in East Africa (Lake Rutundu, Mt. Kenya and Lake Mahoma, Rwenzori Mountains, Uganda) based on branched GDGTs. Our record from Lake Rutundu shows deglacial warming starting near 17 ka and a mid-Holocene thermal maximum near 5 ka. The overall amplitude of warming in the Lake Rutundu record is 6.8×1.0°C from the LGM to the present, with mid-Holocene temperatures 1.6×0.9°C warmer than modern. Our record from Lake Mahoma extends back to 7 ka and shows similar temperature trends to our record from Lake Rutundu, indicating similar temporal resolution of high-elevation temperature change throughout the region. Combining these new records with three previously published GDGT temperature records from different elevations in East Africa (Sacred Lake, Lake Tanganyika, and Lake Malawi), we are able to reconstruct a continuous record of lapse rates and freezing level heights (FLHs) back to the LGM. We find that tropical lapse rates have varied widely over the last 22 ky, with the largest (lowest) lapse rate (FLH) around the LGM, while the smallest (highest) lapse rate (FLH) occurs during the mid-Holocene, confirming the amplification of warming at high altitudes between the LGM and present. These lapse rate and FLH reconstructions match records of regional hydrological variability, confirming the importance of glacial/interglacial humidity variations on altitudinal temperature gradients in the tropics. Furthermore, the FLH record largely matches records of tropical glacier ELA changes, indicating that warming from LGM-present was likely amplified at high altitudes throughout the tropics.

A Reconstruction of Temperature and δ18O Data Since the Last Glacial Maximum Using Soil and Gastropods from the Chinese Loess Plateau

NASA Astrophysics Data System (ADS)

Mitsunaga, B.; Mering, J. A.; Eagle, R.; Bricker, H. L.; Davila, N.; Trewman, S.; Burford, S.; Li, G.; Tripati, A. K.

2016-12-01

The climate of the Chinese Loess Plateau is affected by the East Asian Monsoon, an important water source for over a billion people. We are examining how temperature and hydrology on the Loess Plateau has changed since the Last Glacial Maximum (18,000 - 23,000 years before the present) in response to insolation, deglaciation, and rising levels of greenhouse gases. Specifically, we are reconstructing temperature and meteoric δ18O through paired clumped and oxygen isotope analyses performed on carbonate minerals. Clumped isotope thermometry—the use of 13C—18O bond frequency in carbonates—is a novel geochemical proxy that provides constraints on mineral formation temperatures and can be combined with carbonate δ18O to quantify meteoric δ18O. We have measured a suite of nodular loess concretions and gastropod shells from the modern as well as the Last Glacial Maximum from 15 sites across the Chinese Loess Plateau. These observations constrain spatial variations in temperature and precipitation, which in turn will provide key constraints on models that simulate changes in regional climates and monsoon intensity over the last 20,000 years.

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.

Hydroclimate changes across the Amazon lowlands over the past 45,000 years

NASA Astrophysics Data System (ADS)

Wang, Xianfeng; Edwards, R. Lawrence; Auler, Augusto S.; Cheng, Hai; Kong, Xinggong; Wang, Yongjin; Cruz, Francisco W.; Dorale, Jeffrey A.; Chiang, Hong-Wei

2017-01-01

Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin—one of Earth’s major centres of deep atmospheric convection. For example, whether the Amazon basin was substantially drier or remained wet during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting. Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide. Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the Amazon was widely drier during the last glacial period, with much less recycling of water and probably reduced plant transpiration, although the rainforest persisted throughout this time.

Hydroclimate changes across the Amazon lowlands over the past 45,000 years.

PubMed

Wang, Xianfeng; Edwards, R Lawrence; Auler, Augusto S; Cheng, Hai; Kong, Xinggong; Wang, Yongjin; Cruz, Francisco W; Dorale, Jeffrey A; Chiang, Hong-Wei

2017-01-11

Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin-one of Earth's major centres of deep atmospheric convection. For example, whether the Amazon basin was substantially drier or remained wet during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting. Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide. Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the Amazon was widely drier during the last glacial period, with much less recycling of water and probably reduced plant transpiration, although the rainforest persisted throughout this time.

A diatom record of climate and hydrology for the past 200 KA from Owens Lake, California with comparison to other Breat Basin records

USGS Publications Warehouse

Bradbury, J.P.

1997-01-01

Diatoms from lake sediments beneath Owens Lake playa, Inyo County, California, document a nearly continuous paleolimnological record of climate and hydrologic change since the penultimate glacial-interglacial cycle based on a chronology established by radiocarbon, tephrochronology, and paleomagnetic control. Freshwater planktic diatoms (especially species of Stephanodiscus), plagioclase feldspar-rich sediments with high magnetic susceptibility, and Juniperus-type pollen characterized the penultimate glaciation at Owens Lake. Saline diatoms dominated in the following interglacial period, and there are several episodes during which freshwater planktic diatoms became abundant between 100 and 50 ka that may represent interstadial climatic conditions. Saline diatoms fell to low values after 50 ka, but warm-season Aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of Owens Lake prior to the last glacial maximum. By 25 ka, glacial environments were again characterized by abundant Juniperus, plagioclase feldspar, and Stephanodiscus species. Generally and Holocene climates were recorded in Owens Lake by short-term fluctuations of saline and freshwater diatoms, desiccation, and oolitic sediments barren of diatoms. Comparison to paleoclimate records both north and south of Owens Lake suggest a southerly displacement of storm tracks originating from the Aleutian Low during glacial episodes.

Neotropical forest expansion during the last glacial period challenges refuge hypothesis.

PubMed

Leite, Yuri L R; Costa, Leonora P; Loss, Ana Carolina; Rocha, Rita G; Batalha-Filho, Henrique; Bastos, Alex C; Quaresma, Valéria S; Fagundes, Valéria; Paresque, Roberta; Passamani, Marcelo; Pardini, Renata

2016-01-26

The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods.

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).

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Anatomy of Some Non-Heinrich Events During The Last Glacial Maximum on Laurentian Fan

NASA Astrophysics Data System (ADS)

Gil, I. M.; Keigwin, L. D.

2013-12-01

High-resolution diatom assemblage analyses coupled with oxygen and carbon isotopic records from a new 28 m piston core on Laurentian Fan reveal significant sedimentological and marine productivity changes related to variability of the nearby Laurentide Ice Sheet during the Last Glacial Maximum. Between 21.0 and 19.7 ka and between 18.8 and 18.6 ka, olive-grey clays intervals interrupt the usual glacial red-clays sedimentation. The timing of these two intervals corresponds to reported occurrence of layers low in detrital carbonate (LDC, considered as non-Heinrich events) that occurred between Heinrich Event 1 and 2. Diatoms are only abundant during those LDC - olive-grey clay intervals and suggest ice retreat (allowing light penetration necessary to diatoms). The species succession reveals also different environmental conditions. The 21.0 to 19.7 ka interval is divisible to two main periods: the first was characterized by environmental conditions dominated by ice, while the second period (starting at 20.2 ka) was warmer than the first. During the shorter 18.8 to 18.6 ka interval, conditions were even warmer than during the 20.2 to 19.7 ka sub-interval. Finally, the comparison of the interpreted oceanographic conditions with changes in Ice Rafted Debris and other records from the North Atlantic will bring a new insight into those episodes that precede the transition to deglaciation beginning ~18.2 ka on Laurentian Fan (based on δ18-O in N. pachyderma (s.)).

Craniometric analysis of European Upper Palaeolithic and Mesolithic samples supports discontinuity at the Late Glacial Maximum

PubMed Central

Brewster, Ciarán; Meiklejohn, Christopher; von Cramon-Taubadel, Noreen; Pinhasi, Ron

2014-01-01

The Last Glacial Maximum (LGM) represents the most significant climatic event since the emergence of anatomically modern humans (AMH). In Europe, the LGM may have played a role in changing morphological features as a result of adaptive and stochastic processes. We use craniometric data to examine morphological diversity in pre- and post-LGM specimens. Craniometric variation is assessed across four periods—pre-LGM, late glacial, Early Holocene and Middle Holocene—using a large, well-dated, dataset. Our results show significant differences across the four periods, using a MANOVA on size-adjusted cranial measurements. A discriminant function analysis shows separation between pre-LGM and later groups. Analyses repeated on a subsample, controlled for time and location, yield similar results. The results are largely influenced by facial measurements and are most consistent with neutral demographic processes. These findings suggest that the LGM had a major impact on AMH populations in Europe prior to the Neolithic. PMID:24912847

Thermodynamic and Dynamic Causes of Pluvial Conditions During the Last Glacial Maximum in Western North America

NASA Astrophysics Data System (ADS)

Morrill, Carrie; Lowry, Daniel P.; Hoell, Andrew

2018-01-01

During the last glacial period, precipitation minus evaporation increased across the currently arid western United States. These pluvial conditions have been commonly explained for decades by a southward deflection of the jet stream by the Laurentide Ice Sheet. Here analysis of state-of-the-art coupled climate models shows that effects of the Laurentide Ice Sheet on the mean circulation were more important than storm track changes in generating wet conditions. Namely, strong cooling by the ice sheet significantly reduced humidity over land, increasing moisture advection in the westerlies due to steepened humidity gradients. Additionally, the removal of moisture from the atmosphere by mass divergence associated with the subtropical high was diminished at the Last Glacial Maximum compared to present. These same dynamic and thermodynamic factors, working in the opposite direction, are projected to cause regional drying in western North America under increased greenhouse gas concentrations, indicating continuity from past to future in the mechanisms altering hydroclimate.

Differences in ice retreat across Pine Island Bay, West Antarctica, since the Last Glacial Maximum: Indications from multichannel seismic reflection data

USGS Publications Warehouse

Uenzelmann-Neben, G.; Gohl, K.; Larter, R.D.; Schlüter, P.

2007-01-01

An understanding of the glacial history of Pine Island Bay (PIB) is essential for refining models of the future stability of the West Antarctic Ice Sheet (WAIS). New multichannel seismic reflection data from inner PIB are interpreted in context of previously published reconstructions for the retreat history in this area since the Last Glacial Maximum. Differences in the behavior of the ice sheet during deglaciation are shown to exist for the western and eastern parts of PIB. While we can identify only a thin veneer of sedimentary deposits in western PIB, eastern PIB shows sedimentary layers ≤ 400 msTWT. This is interpreted as a result of differences in ice retreat: a fast ice retreat in western PIB accompanied by rapid basal melting led to production of large meltwater streams, a slower ice retreat in eastern PIB is most probably the result of smaller drainage basins resulting in less meltwater production.

An Ocean Tale of Two Climates: Modern and Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Ferrari, R. M.

2014-12-01

In the present climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleo proxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum (LGM), resulting in an expansion of the volume occupied by Antarctic origin waters. I will argue that this rearrangement of deep water masses is dynamically connected to the expansion of summer sea ice around Antarctica. A simple theory will be introduced to suggest that these deep waters only came to the surface under summer sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. I will show that this unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass appear to be crucial in explaining the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales.

Ichnological evidence of jökulhlaup deposit recolonization from the Touchet Beds, Mabton, WA, USA

NASA Astrophysics Data System (ADS)

MacEachern, James A.; Roberts, Michael C.

2013-01-01

The late Wisconsinan Touchet Beds section at Mabton, Washington reveals at least seven stacked jökulhlaup deposits, five showing evidence of post-flood recolonization by vertebrates. Tracemakers are attributed to voles or pocket mice (1-3 cm diameter burrows) and pocket gophers or ground squirrels (3-6 cm diameter burrows). The Mount St. Helens S tephra deposited between flood beds contains the invertebrate-generated burrows Naktodemasis and Macanopsis. Estimates of times between floods are based on natal dispersal distances of the likely vertebrate tracemakers (30-50 m median distances; 127-525 m maximum distances) from upland areas containing surviving populations to the Mabton area, a distance of about 7.9 km. Tetrapods would have required at least two to three decades to recolonize these flood beds, based on maximum dispersal distances. Invertebrate recolonization was limited by secondary succession and estimated at only a few years to a decade. These ichnological data support multiple floods from failure of the ice dam at glacial Lake Missoula, separated by hiatal surfaces on the order of decades in duration. Ichnological recolonization times are consistent with published estimates of refill times for glacial Lake Missoula, and complement the other field evidence that points to repeated, autogenically induced flood discharge.

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

USGS Publications Warehouse

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

2006-01-01

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

A glacial record of the last termination in the southern tropical Andes

NASA Astrophysics Data System (ADS)

Bromley, G. R.; Schaefer, J. M.; Winckler, G.; Hall, B. L.; Todd, C. E.; Rademaker, K.

2012-12-01

The last glacial termination represents the highest-magnitude climate change of the last hundred thousand years. Accurate resolution of events during the termination is vital to our understanding of how - and why - the global climate system transitions from a full glacial to interglacial state, as well as the causes of abrupt climate change during the late-glacial period. Palaeoclimate data from low latitudes, though relatively sparse, are particularly valuable, since the tropical ocean and atmosphere likely play a crucial role in Quaternary climate variability on all timescales. We present a detailed glacier record from the Andes of southern Peru (15°S), resolved with 3He surface-exposure dating and spanning the last glacial maximum and termination. Our dataset reveals that glaciers in this part of the Southern Hemisphere maintained their Late Pleistocene maxima for several millennia and that the onset of the termination may have occurred relatively late. Deglaciation was punctuated by two major advances during the late-glacial period. Following the glacial-interglacial transition, our preliminary chronologic and morphologic data suggest that, in contrast to the Northern Hemisphere, glaciers in the southern tropical Andes have experienced overall shrinkage during the Holocene.

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.

Map of surficial deposits and materials in the eastern and central United States (east of 102 degrees West longitude)

USGS Publications Warehouse

Fullerton, David S.; Bush, Charles A.; Pennell, Jean N.

2003-01-01

This data set contains surficial geologic units in the Eastern and Central United States, as well as a glacial limit line showing the position of maximum glacial advance during various geologic time periods. The geologic units represent surficial deposits and other surface materials that accumulated or formed during the past 2+ million years, such as soils, alluvium, and glacial deposits. These surface materials are referred to collectively by many geologists as regolith, the mantle of fragmented and generally unconsolidated material that overlies the bedrock foundation of a continent. This data set and the printed map produced from it, U.S. Geological Survey (USGS) Geologic Investigation Series I-2789, were based on 31 published maps in the USGS's Quaternary Geologic Atlas of the United States map series (USGS Miscellaneous Investigations Series I-1420). The data were compiled at 1:1,000,000 scale, to be viewed as a digital map at 1:2,000,000 nominal scale and to be printed as a conventional paper map at 1:2,500,000 scale.

Killer whale nuclear genome and mtDNA reveal widespread population bottleneck during the last glacial maximum.

PubMed

Moura, Andre E; Janse van Rensburg, Charlene; Pilot, Malgorzata; Tehrani, Arman; Best, Peter B; Thornton, Meredith; Plön, Stephanie; de Bruyn, P J Nico; Worley, Kim C; Gibbs, Richard A; Dahlheim, Marilyn E; Hoelzel, Alan Rus

2014-05-01

Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline.

King penguin demography since the last glaciation inferred from genome-wide data

PubMed Central

Trucchi, Emiliano; Gratton, Paolo; Whittington, Jason D.; Cristofari, Robin; Le Maho, Yvon; Stenseth, Nils Chr; Le Bohec, Céline

2014-01-01

How natural climate cycles, such as past glacial/interglacial patterns, have shaped species distributions at the high-latitude regions of the Southern Hemisphere is still largely unclear. Here, we show how the post-glacial warming following the Last Glacial Maximum (ca 18 000 years ago), allowed the (re)colonization of the fragmented sub-Antarctic habitat by an upper-level marine predator, the king penguin Aptenodytes patagonicus. Using restriction site-associated DNA sequencing and standard mitochondrial data, we tested the behaviour of subsets of anonymous nuclear loci in inferring past demography through coalescent-based and allele frequency spectrum analyses. Our results show that the king penguin population breeding on Crozet archipelago steeply increased in size, closely following the Holocene warming recorded in the Epica Dome C ice core. The following population growth can be explained by a threshold model in which the ecological requirements of this species (year-round ice-free habitat for breeding and access to a major source of food such as the Antarctic Polar Front) were met on Crozet soon after the Pleistocene/Holocene climatic transition. PMID:24920481

Glacier fluctuations in the Rwenzori Mountains, Uganda, during the Last Glacial Maximum and Termination 1

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Jackson, M. S.; Russel, J.; Doughty, A. M.; Howley, J. A.; Cavagnaro, D. B.; Zimmerman, S. R. H.

2016-12-01

The tropics exert a profound influence on global climate; however, the role of the tropics in past climate change is uncertain. In particular, it is unclear whether the tropics may initiate abrupt climate changes or instead respond to high-latitude change. Determining the timing and spatial variability of past change in the tropics is a first step to addressing the role of the low-latitudes in both past and future climate changes. To investigate these questions, we present a cosmogenic 10Be chronology from a suite of moraines in the Rwenzori Mountains, Uganda. These results indicate that ice was most extensive early during the Last Glacial Maximum (LGM; 26.0-19.5 kyr), prior to the global sea-level lowstand at 20.5 kyr. Low-magnitude, millennial-scale glacial oscillations occurred throughout the LGM. Retreat from the LGM position was underway by 21.5 kyr, though ice remained extensive in the Rwenzori until at least 18.5 ka. Similar chronologies from elsewhere in the tropics suggest that glaciers across the low-latitudes achieved their maxima in the earliest stages of the LGM, during a period of high (mean annual) equatorial insolation and decreasing Northern Hemisphere summer insolation. In addition, the larger-scale recession that occurred subsequent to 21.5 kyr predates the post-glacial rise in atmospheric CO2 at 18.1 kyr. Therefore, we suggest that something other than Northern Hemisphere or equatorial insolation or atmospheric CO2 may have influenced the millennial-scale glacial oscillations throughout the LGM as registered by Rwenzori moraines. The chronology of glacial fluctuations in the Rwenzori Mountains is similar to other glacial chronologies located outside the tropics in both the Northern and Southern Hemispheres, suggesting that glaciers across the globe may have responded to a common forcing throughout the LGM and Termination 1.

Somma-Vesuvius ground deformation over the last glacial cycle

NASA Astrophysics Data System (ADS)

Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

2013-04-01

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

Late Pleistocene glaciation of the Mt Giluwe volcano, Papua New Guinea

USGS Publications Warehouse

Barrows, T.T.; Hope, G.S.; Prentice, M.L.; Fifield, L.K.; Tims, S.G.

2011-01-01

The Mt Giluwe shield volcano was the largest area glaciated in Papua New Guinea during the Pleistocene. Despite minimal cooling of the sea surface during the last glacial maximum, glaciers reached elevations as low as 3200 m. To investigate changes in the extent of ice through time we have re-mapped evidence for glaciation on the southwest flank of Mt Giluwe. We find that an ice cap has formed on the flanks of the mountain on at least three, and probably four, separate occasions. To constrain the ages of these glaciations we present 39 new cosmogenic 36Cl exposure ages complemented by new radiocarbon dates. Direct dating of the moraines identifies that the maximum extent of glaciation on the mountain was not during the last glacial maximum as previously thought. In conjunction with existing potassium/argon and radiocarbon dating, we recognise four distinct glacial periods between 293-306 ka (Gogon Glaciation), 136-158 ka (Mengane Glaciation), centred at 62 ka (Komia Glaciation) and from >20.3-11.5 ka (Tongo Glaciation). The temperature difference relative to the present during the Tongo Glaciation is likely to be of the order of at least 5 ??C which is a minimum difference for the previous glaciations. During the Tongo Glaciation, ice was briefly at its maximum for less than 1000 years, but stayed near maximum levels for nearly 4000 years, until about 15.4 ka. Over the next 4000 years there was more rapid retreat with ice free conditions by the early Holocene. ?? 2011 Elsevier Ltd.

Abrupt climatic changes as triggering mechanisms of massive volcanic collapses: examples from Mexico (Invited)

NASA Astrophysics Data System (ADS)

Capra, L.

2010-12-01

Climate changes have been considered to be a triggering mechanism for large magmatic eruptions. However they can also trigger volcanic collapses, phenomena that cause the destruction of the entire sector of a volcano, including its summit. During the past 30 ka, major volcanic collapses occurred just after main glacial peaks that ended with a rapid deglaciation. Glacial debuttressing, load discharge and fluid circulation coupled with the post-glacial increase of humidity and heavy rains can activate the failure of unstable edifices. Looking at the synchronicity of the maximum glaciations during the late Pleistocene and Holocene in the northern and southern hemispheres it is evident that several volcanic collapses are absent during a glacial climax, but start immediately after it during a period of rapid retreat. Several examples can be detected around the world and Mexico is not an exception. The 28 ka Nevado de Toluca volcanic collapse occurred during an intraglacial stage, under humid conditions as evidenced by paleoclimatic studies on lacustrine sediments of the area. The debris avalanche deposit associated to this event clearly shows evidence of a large amount of water into the mass previous to the failure that enhanced its mobility. It also contains peculiar, plastically deformed, m-sized fragment of lacustrine sediments eroded from glacial berms. The 17 ka BP collapse of the Colima Volcano corresponds to the initial stage of glacial retreat in Mexico after the Last Glacial Maximum (22-17.5ka). Also in this case the depositional sequence reflects high humidity conditions with voluminous debris flow containing a large amount logs left by pine trees. The occurrence of cohesive debris flows originating from the failure of a volcanic edifice can also reflect the climatic conditions, indicating important hydrothermal alteration and fluid circulation from ice-melting at an ice-capped volcano, as observed for example at the Pico de Orizaba volcano for the Tetelzingo lahar, which collapse occurred after the Terminal Glacial (15-11 ka). Furthermore, significant global warming can be responsible for the collapse of ice-capped unstable volcanoes, an unpredictable hazard that in few minutes can bury inhabited areas.

Freshwater control of ice-rafted debris in the last glacial period at Mono Lake, California, USA

NASA Astrophysics Data System (ADS)

Zimmerman, Susan R. H.; Pearl, Crystal; Hemming, Sidney R.; Tamulonis, Kathryn; Hemming, N. Gary; Searle, Stephanie Y.

2011-09-01

The type section silts of the late Pleistocene Wilson Creek Formation at Mono Lake contain outsized clasts, dominantly well-rounded pebbles and cobbles of Sierran lithologies. Lithic grains > 425 μm show a similar pattern of variability as the > 10 mm clasts visible in the type section, with decreasing absolute abundance in southern and eastern outcrops. The largest concentrations of ice-rafted debris (IRD) occur at 67-57 ka and 46-32 ka, with strong millennial-scale variability, while little IRD is found during the last glacial maximum and deglaciation. Stratigraphic evidence for high lake level during high IRD intervals, and a lack of geomorphic evidence for coincidence of lake and glaciers, strongly suggests that rafting was by shore ice rather than icebergs. Correspondence of carbonate flux and IRD implies that both were mainly controlled by freshwater input, rather than disparate non-climatic controls. Conversely, the lack of IRD during the last glacial maximum and deglacial highstands may relate to secondary controls such as perennial ice cover or sediment supply. High IRD at Mono Lake corresponds to low glacial flour flux in Owens Lake, both correlative to high warm-season insolation. High-resolution, extra-basinal correlation of the millennial peaks awaits greatly improved age models for both records.

Progressive glacial retreat in the Southern Altiplano (Uturuncu volcano, 22°S) between 65 and 14 ka constrained by cosmogenic 3He dating

NASA Astrophysics Data System (ADS)

Blard, Pierre-Henri; Lave, Jérôme; Farley, Kenneth A.; Ramirez, Victor; Jimenez, Nestor; Martin, Léo C. P.; Charreau, Julien; Tibari, Bouchaïb; Fornari, Michel

2014-07-01

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling-Allerod.

Expansion of the North Pacific subpolar gyre during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Gray, W. R.; Rae, J. W. B.; Wills, R. C.; Burke, A.; Taylor, B.

2017-12-01

Due to the opposite sign of the wind-stress forcing in the Pacific subpolar and subtropical gyres, the two gyres are characterised by vastly different nutrient and temperature regimes; the subpolar gyre is cold and nutrient-rich, whereas the subtropical gyre is warm and nutrient poor. The relative extent of the gyres therefore exerts a first order control on biogeochemistry and meridional ocean heat transport in the North Pacific Ocean. Here, by compiling all previously published planktic foraminferal d18O and sea-surface temperature data from across the North Pacific, we show a striking and hitherto unknown feature of the Glacial North Pacific; the southward expansion of the subpolar gyre by 5 degrees. We show, in the PMIP3 ensemble of state-of-the-art climate models, that this expansion is associated with a strengthening of the westerly winds. The southward expansion of the subpolar gyre would have brought nutrient-rich waters further south, providing a solution to the long-standing question of why, while productivity decreased throughout the subpolar gyre during Last Glacial Maximum, it increased in the transition zone between the gyres. The expansion and contraction of the subpolar/subtropical gyres over glacial-interglacial cycles could provide a mechanism to modulate meridional ocean heat transport.

Deglacial history of the Pensacola Mountains, Antarctica from glacial geomorphology and cosmogenic nuclide surface exposure dating

NASA Astrophysics Data System (ADS)

Bentley, M. J.; Hein, A. S.; Sugden, D. E.; Whitehouse, P. L.; Shanks, R.; Xu, S.; Freeman, S. P. H. T.

2017-02-01

The retreat history of the Antarctic Ice Sheet is important for understanding rapid deglaciation, as well as to constrain numerical ice sheet models and ice loading models required for glacial isostatic adjustment modelling. There is particular debate about the extent of grounded ice in the Weddell Sea embayment at the Last Glacial Maximum, and its subsequent deglacial history. Here we provide a new dataset of geomorphological observations and cosmogenic nuclide surface exposure ages of erratic samples that constrain the deglacial history of the Pensacola Mountains, adjacent to the present day Foundation Ice Stream and Academy Glacier in the southern Weddell Sea embayment. We show there is evidence of at least two glaciations, the first of which was relatively old and warm-based, and a more recent cold-based glaciation. During the most recent glaciation ice thickened by at least 450 m in the Williams Hills and at least 380 m on Mt Bragg. Progressive thinning from these sites was well underway by 10 ka BP and ice reached present levels by 2.5 ka BP, and is broadly similar to the relatively modest thinning histories in the southern Ellsworth Mountains. The thinning history is consistent with, but does not mandate, a Late Holocene retreat of the grounding line to a smaller-than-present configuration, as has been recently hypothesized based on ice sheet and glacial isostatic modelling. The data also show that clasts with complex exposure histories are pervasive and that clast recycling is highly site-dependent. These new data provide constraints on a reconstruction of the retreat history of the formerly-expanded Foundation Ice Stream, derived using a numerical flowband model.

Glaciation and regional groundwater flow in the Fennoscandian shield

USGS Publications Warehouse

Provost, A.M.; Voss, C.I.; Neuzil, C.E.

2012-01-01

Regional-scale groundwater flow modeling of the Fennoscandian shield suggests that groundwater flow can be strongly affected by future climate change and glaciation. We considered variable-density groundwater flow in a 1500-km-long and approximately 10-km-deep cross-section through southern Sweden. Groundwater flow and shield brine transport in the cross-sectional model were analyzed under projected surface conditions for the next 140 ka. Simulations suggest that blockage of recharge and discharge by low-permeability permafrost or cold-based ice causes sinking of brine and consequent freshening of near-surface water in areas of natural discharge. Although recharge of basal meltwater is limited by the requirement that water pressure at the base of the ice sheet not exceed the pressure exerted by the weight of the ice, warm-based ice with basal melting creates a potential for groundwater recharge rates much larger than those of present, ice-free conditions. In the simulations, regional-scale redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (approximately 10 ka). During glacial retreat, significant upward flow of groundwater may occur below the ice sheet owing to pressure release. If the mechanical loading efficiency of the rocks is high, both subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are reduced because of loading-induced pressure changes. The maximum rate of groundwater discharge in the simulations occurs at the receding ice margin, and some discharge occurs below incursive postglacial seas. Recharge of basal meltwater could decrease the concentration of dissolved solids significantly below present-day levels at depths of up to several kilometers and may bring oxygenated conditions to an otherwise reducing chemical environment for periods exceeding 10 ka.

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

North Pacific atmospheric rivers and their impact on North America since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Lora, J. M.; Mitchell, J.; Risi, C.; Tripati, A.

2017-12-01

Using climate models and reanalysis data, we investigate the climatology of North Pacific atmospheric rivers, as well as the influence of the Last Glacial Maximum conditions on the circulation and moisture budget of the eastern North Pacific and western North America. Atmospheric transport of water vapor from the North Pacific is the primary source of moisture for most of western North America. Wintertime precipitation accounts for upwards of 75% of the total along the west coast of the United States, and atmospheric rivers in particular deliver large fractions of this precipitation in high-intensity events. Proxy records from western North America indicate a much wetter environment in Nevada and southern California at the Last Glacial Maximum, which has been interpreted as evidence for a southward shift of the mid-latitude jet stream, which steers extratropical storms, in the eastern North Pacific. Our results show that a southeastward shift and intensification of the atmospheric river ``track'' into the continent, resulting from a reorganized atmospheric circulation in response to the North American ice sheets, can explain the inferred hydroclimate changes. We also examine the relative contributions of the mean flow and transient systems to these changes, and diagnose the relative importance of thermodynamic and dynamical mechanisms.

Exploring the impact of climate variability during the Last Glacial Maximum on the pattern of human occupation of Iberia.

PubMed

Burke, Ariane; Levavasseur, Guillaume; James, Patrick M A; Guiducci, Dario; Izquierdo, Manuel Arturo; Bourgeon, Lauriane; Kageyama, Masa; Ramstein, Gilles; Vrac, Mathieu

2014-08-01

The Last Glacial Maximum (LGM) was a global climate event, which had significant repercussions for the spatial distribution and demographic history of prehistoric populations. In Eurasia, the LGM coincides with a potential bottleneck for modern humans and may mark the divergence date for Asian and European populations (Keinan et al., 2007). In this research, the impact of climate variability on human populations in the Iberian Peninsula during the Last Glacial Maximum (LGM) is examined with the aid of downscaled high-resolution (16 × 16 km) numerical climate experiments. Human sensitivity to short time-scale (inter-annual) climate variability during this key time period, which follows the initial modern human colonisation of Eurasia and the extinction of the Neanderthals, is tested using the spatial distribution of archaeological sites. Results indicate that anatomically modern human populations responded to small-scale spatial patterning in climate variability, specifically inter-annual variability in precipitation levels as measured by the standard precipitation index. Climate variability at less than millennial scale, therefore, is shown to be an important component of ecological risk, one that played a role in regulating the spatial behaviour of prehistoric human populations and consequently affected their social networks. Copyright © 2014 Elsevier Ltd. All rights reserved.

Evolutionary History Underlies Plant Physiological Responses to Global Change Since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Becklin, K. M.; Medeiros, J. S.; Sale, K. R.; Ward, J. K.

2014-12-01

Assessing family and species-level variation in physiological responses to global change across geologic time is critical for understanding factors that underlie changes in species distributions and community composition. Ancient plant specimens preserved within packrat middens are invaluable in this context since they allow for comparisons between co-occurring plant lineages. Here we used modern and ancient plant specimens preserved within packrat middens from the Snake Range, NV to investigate the physiological responses of a mixed montane conifer community to global change since the last glacial maximum. We used a conceptual model to infer relative changes in stomatal conductance and maximum photosynthetic capacity from measures of leaf carbon isotopes, stomatal characteristics, and leaf nitrogen content. Our results indicate that most of the sampled taxa decreased stomatal conductance and/or photosynthetic capacity from glacial to modern times. However, plant families differed in the timing and magnitude of these physiological responses. Additionally, leaf-level responses were more similar within plant families than within co-occurring species assemblages. This suggests that adaptation at the level of leaf physiology may not be the main determinant of shifts in community composition, and that plant evolutionary history may drive physiological adaptation to global change over recent geologic time.

Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

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

Labeyrie, L.D.; Burckle, L.; Labracherie, M.

1985-01-01

Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/Smore » and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.« less

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.

Present and former equilibrium-line altitudes near Mount Everest, Nepal and Tibet

USGS Publications Warehouse

Williams, V.S.

1983-01-01

New information on equilibrium-line altitudes (ELAs) of present and former glaciers in the Mount Everest area of eastern Nepal and southern Tibet has been derived from field mapping and interpretation of topographic maps and Landsat imagery. Present ELAs rise from south to north across the Himalayan Range from 5200 to 5800 m, as indicated by the altitudes of lowest cirque glaciers and highest lateral and medial moraines on valley glaciers. In contrast, ELAs during maximum late Pleistocene glaciation rose in altitude from 4300 to 5500 m across the range, as indicated by altitudes of lowest cirque floors and maximum extent of glacial deposits. Highest ELAs occurred on previously unrecognized ice caps that formerly covered extensive highland areas in Tibet north of the range crest. During four distinct Holocene glacial advances of subequal magnitude, ELAs were depressed about 30% as much as the late Pleistocene maximum depression. Depression of ELAs during the late Pleistocene glaciation was about twice as great south of the range crest (950 m) as north of it (400 m). Although the present northward decrease in precipitation causes ELAs to rise northward for 85 km at 7.1 m km-1, the gradient during maximum late Pleistocene glaciation was 11 m km-1. Such a great contrast in glacier response to climate change over a short distance is remarkable and probably reflects increased aridity on the Tibetan Plateau and increased climatic contrast across the Himalayan Range during glacial ages.

Surface Exposure Dating of the Huancané III Moraines in Peru: A Record of Quelccaya Ice Cap's Maximum Extent during the Last Glacial Period

NASA Astrophysics Data System (ADS)

Baranes, H. E.; Kelly, M. A.; Stroup, J. S.; Howley, J. A.; Lowell, T. V.

2012-12-01

The climatic conditions that influenced the tropics during the height of the last glacial period are not well defined and controversial. There are disparities in estimates of temperature anomalies (e.g., MARGO, 2009; Rind and Peteet, 1985; CLIMAP, 1976), and critical terrestrial paleotemperature proxy records in tropical regions are poorly dated (e.g., Porter, 2001). Defining these conditions is important for understanding the mechanisms that cause major shifts in climate, as the tropics are a primary driver of atmospheric and oceanic circulation. This study aims to constrain the timing of maximum glacier extents in the Cordillera Oriental in southern Peru during the last glacial period by applying surface exposure (beryllium-10) dating to the Huancané III (Hu-III) moraines. The Hu-III moraines mark the maximum extent of Quelccaya Ice Cap (QIC) (13.93°S, 70.83°W), the largest tropical ice cap, during the last ice age. The eight beryllium-10 ages presented here yield 17,056 ± 520 yrs ago as a minimum age for the onset of recession from the ice cap advance marked by the Hu-III moraines. Comparing this age to other paleoclimate records indicates that the ice cap advance marked by the Hu-III moraines is more likely associated with a North Atlantic climate event known as Heinrich I (H1; 16,800 yrs ago, Bond et al., 1992, 1993) than with global cooling at the Last Glacial Maximum (LGM; ~21,000 yrs ago, Denton and Hughes, 1981). This result suggests that climate processes in the North Atlantic region are linked to climatic conditions in the tropical Andes. A mesoscale climate model and an ice-flow model are currently being developed for QIC. The moraine data presented in this study will be used with these two models to test response of QIC to North Atlantic and global climate events.

The deglaciation in Picos de Europa (area of Enol Glacier) based on geomorphological and sedimentological studies

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesus; Oliva, Marc; García, Cristina

2013-04-01

The chronology for the deglaciation in the Cantabrian Range is still poorly understood. Several papers have proposed a maximum advance well before the LGM (Jiménez and Farias, 2002; Moreno et al. 2010; Serrano et al. 2012). The Western massif of Picos de Europa held a ice field of 50 km2. In this communication we present two cores collected in two glacial depressions in the frontal area of Enol Glacier that allow reconstructing the environment since the deglaciation of the massif. The first core (5.6 m long) was collected in the kame terrace of Belbin. This terrace was dammed by a lateral moraine corresponding to the phase of maximum expansion of Enol Glacier. Three clear layers are observed: the basal 2.5 m consists of grey clay with small gravel limestones; the second is 2 m thick and is composed of grey clays; the upper 1.1 m shows several paleosoils with abundant organic matter and charcoals. The based was dated at 14,810 ± 70 yr BP. This age represents a minimum age for the maximum expansion of Enol Glacier. The second core was collected in the glaciokarst depression of Vega del Bricial, located within a moraine complex corresponding to LGM. The core is 8 m long and looks very homogeneous. It consists of a succession of organic layers and slope deposits. Two radiocarbon dates were performed on the sediments at 8 and 2.8 m depth, resulting in 9,690 ± 260 and 3,420 ± 95 yr BP, respectively. Based on sedimentological and geomorphological evidences, we propose a chronology for the environmental changes occurred in this massif since the last glacial period. References Jiménez, M. and Farias, P., 2002. New radiometric and geomorphologic evidences of a Last Glacial Maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains, NW Spain). Geodinamica Acta, 15, 93-101. Moreno, A., Valero, B. L., Jiménez, M., Domínguez, M. J., Mata, M. P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J. P. and Rico, M., 2010. The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Serrano, E., González-Trueba, J. J. and González-García, M., 2012. Mountain glaciation and paleoclimate reconstruction in the Picos de Europa (Iberian Peninsula, SW Europe). Quaternary Research, 78, 303-314.

Multi-scale curvature for automated identification of glaciated mountain landscapes

NASA Astrophysics Data System (ADS)

Prasicek, Günther; Otto, Jan-Christoph; Montgomery, David; Schrott, Lothar

2014-05-01

Automated morphometric interpretation of digital terrain data based on impartial rule sets holds substantial promise for large dataset processing and objective landscape classification. However, the geomorphological realm presents tremendous complexity in the translation of qualitative descriptions into geomorphometric semantics. Here, the simple, conventional distinction of V-shaped fluvial and U-shaped glacial valleys is analyzed quantitatively using the relation of multi-scale curvature and drainage area. Glacial and fluvial erosion shapes mountain landscapes in a long-recognized and characteristic way. Valleys incised by fluvial processes typically have V-shaped cross-sections with uniform and moderately steep slopes, whereas glacial valleys tend to have U-shaped profiles and topographic gradients steepening with distance from valley floor. On a DEM, thalweg cells are determined by a drainage area cutoff and multiple moving window sizes are used to derive per-cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides. The relation of the curvatures calculated for the user-defined minimum scale and the automatically detected maximum scale is presented as a novel morphometric variable termed Difference of Minimum Curvature (DMC). DMC thresholds determined from typical glacial and fluvial sample catchments are employed to identify quadrats of glaciated and non-glaciated mountain landscapes and the distinctions are validated by field-based geological and geomorphological maps. A first test of the novel algorithm at three study sites in the western United States and a subsequent application to Europe and western Asia demonstrate the transferability of the approach.

Sensitivity of Last Glacial Maximum climate to uncertainties in tropical and subtropical ocean temperatures

USGS Publications Warehouse

Hostetler, S.; Pisias, N.; Mix, A.

2006-01-01

The faunal and floral gradients that underlie the CLIMAP (1981) sea-surface temperature (SST) reconstructions for the Last Glacial Maximum (LGM) reflect ocean temperature gradients and frontal positions. The transfer functions used to reconstruct SSTs from biologic gradients are biased, however, because at the warmest sites they display inherently low sensitivity in translating fauna to SST and they underestimate SST within the euphotic zones where the pycnocline is strong. Here we assemble available data and apply a statistical approach to adjust for hypothetical biases in the faunal-based SST estimates of LGM temperature. The largest bias adjustments are distributed in the tropics (to address low sensitivity) and subtropics (to address underestimation in the euphotic zones). The resulting SSTs are generally in better agreement than CLIMAP with recent geochemical estimates of glacial-interglacial temperature changes. We conducted a series of model experiments using the GENESIS general atmospheric circulation model to assess the sensitivity of the climate system to our bias-adjusted SSTs. Globally, the new SST field results in a modeled LGM surface-air cooling relative to present of 6.4 ??C (1.9 ??C cooler than that of CLIMAP). Relative to the simulation with CLIMAP SSTs, modeled precipitation over the oceans is reduced by 0.4 mm d-1 (an anomaly -0.4 versus 0.0 mm d-1 for CLIMAP) and increased over land (an anomaly -0.2 versus -0.5 mm d-1 for CLIMAP). Regionally strong responses are induced by changes in SST gradients. Data-model comparisons indicate improvement in agreement relative to CLIMAP, but differences among terrestrial data inferences and simulated moisture and temperature remain. Our SSTs result in positive mass balance over the northern hemisphere ice sheets (primarily through reduced summer ablation), supporting the hypothesis that tropical and subtropical ocean temperatures may have played a role in triggering glacial changes at higher latitudes.

High-resolution record of the deglaciation of the British-Irish Ice Sheet from North Atlantic deep-sea sediments.

NASA Astrophysics Data System (ADS)

Tarlati, S.; Benetti, S.; Callard, L.; O'Cofaigh, C.; Dunlop, P.; Chiverrell, R. C.; Fabel, D.; Moreton, S.; Clark, C.

2016-12-01

During the last glacial maximum the British-Irish Ice Sheet (BIIS) covered the majority of Ireland and Britain. Recent studies have described the BIIS as largely marine-based and highly dynamic with several advances and retreats recorded on the continental shelf. The focus of this study is the more recent sediment record from the Donegal Barra Fan (DBF), the largest sediment depocentre formed by the ice streaming of the western BIIS onto the North Atlantic continental margin. In this project, well-preserved, glacially-derived, deep-water sediments from 3 cores, up to 6.7 m long and retrieved from the DBF, are used to investigate and chronologically constrain the pattern of deglaciation of the BIIS. Deep-water sediments can record continuous sedimentation through time, avoiding hiatuses and erosional surfaces characteristic of a glacial environment and allow a detailed reconstruction of deglacial processes. Five lithofacies have been identified using sedimentology, x-rays, physical properties and grain size analysis. They include bioturbated foraminifera-bearing muds, interpreted as hemipelagic and contouritic deposits from interglacial periods. Chaotic and laminated muds, ice-rafted debris (IRD)-rich layers and laminated mud to sand couplets are characteristic of the glacial period including ice-sheet maximum extent and the beginning of retreat. These represent downslope mass movements, plumites from meltwater alongside melting icebergs and turbidites. Radiocarbon dates from foraminifera suggest that the deglacial sedimentary sequence is up to 5m thick. The IRD concentration and abundance of the foraminifera Neogloboquadrina pachyderma sinistral indicate a minimum of 3 different calving events during deglaciation and a marked Younger Dryas cooling and ice calving period. Additionally the δ 18O record will be used to investigate the record of climatic changes in the region and x-ray fluorescence will be used to assess sediment provenance during deglaciation.

Coupled ice sheet - climate simulations of the last glacial inception and last glacial maximum with a model of intermediate complexity that includes a dynamical downscaling of heat and moisture

NASA Astrophysics Data System (ADS)

Quiquet, Aurélien; Roche, Didier M.

2017-04-01

Comprehensive fully coupled ice sheet - climate models allowing for multi-millenia transient simulations are becoming available. They represent powerful tools to investigate ice sheet - climate interactions during the repeated retreats and advances of continental ice sheets of the Pleistocene. However, in such models, most of the time, the spatial resolution of the ice sheet model is one order of magnitude lower than the one of the atmospheric model. As such, orography-induced precipitation is only poorly represented. In this work, we briefly present the most recent improvements of the ice sheet - climate coupling within the model of intermediate complexity iLOVECLIM. On the one hand, from the native atmospheric resolution (T21), we have included a dynamical downscaling of heat and moisture at the ice sheet model resolution (40 km x 40 km). This downscaling accounts for feedbacks of sub-grid precipitation on large scale energy and water budgets. From the sub-grid atmospheric variables, we compute an ice sheet surface mass balance required by the ice sheet model. On the other hand, we also explicitly use oceanic temperatures to compute sub-shelf melting at a given depth. Based on palaeo evidences for rate of change of eustatic sea level, we discuss the capability of our new model to correctly simulate the last glacial inception ( 116 kaBP) and the ice volume of the last glacial maximum ( 21 kaBP). We show that the model performs well in certain areas (e.g. Canadian archipelago) but some model biases are consistent over time periods (e.g. Kara-Barents sector). We explore various model sensitivities (e.g. initial state, vegetation, albedo) and we discuss the importance of the downscaling of precipitation for ice nucleation over elevated area and for the surface mass balance of larger ice sheets.

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

PubMed Central

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

2017-01-01

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

Last Glacial-Interglacial Transition ice dynamics in the Wicklow Mountains, Ireland

NASA Astrophysics Data System (ADS)

Knight, Lauren; Boston, Clare; Lovell, Harold; Pepin, Nick

2017-04-01

Understanding of the extent and dynamics of former ice masses in the Wicklow Mountains, Ireland, during the Last Glacial-Interglacial Transition (LGIT; 15-10 ka BP) is currently unresolved. Whilst it is acknowledged that the region hosted a local ice cap within the larger British-Irish Ice Sheet at the Last Glacial Maximum (LGM; 27 ka BP), there has been little consideration of ice cap disintegration to a topographically constrained ice mass during the LGIT. This research has produced the first regional glacial geomorphological map, through remote sensing (aerial photograph and digital terrain model interrogation) and field mapping. This has allowed both the style and extent of mountain glaciation and ice recession dynamics during the LGIT to be established. This geomorphological mapping has highlighted that evidence for local glaciation in the Wicklow Mountains is more extensive than previously recognised, and that small icefields and associated outlet valley glaciers existed during the LGIT following disintegration of the Wicklow Ice Cap. A relative chronology based on morphostratigraphic principles is developed, which indicates complex patterns of ice mass oscillation characterised by periods of both sustained retreat and minor readvance. Variations in the pattern of recession across the Wicklow Mountains are evident and appear to be influenced, in part, by topographic controls (e.g. slope, aspect, glacier hypsometry). In summary, this research establishes a relative chronology of glacial events in the region during the LGIT and presents constraints on ice mass extent, dynamics and retreat patterns, offering an insight into small ice mass behaviour in a warming climate.

Neotropical forest expansion during the last glacial period challenges refuge hypothesis

PubMed Central

Costa, Leonora P.; Loss, Ana Carolina; Rocha, Rita G.; Batalha-Filho, Henrique; Bastos, Alex C.; Quaresma, Valéria S.; Fagundes, Valéria; Paresque, Roberta; Passamani, Marcelo; Pardini, Renata

2016-01-01

The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods. PMID:26755597

Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

USGS Publications Warehouse

Levy, Joseph S.; Rittenour, Tammy M.; Fountain, Andrew G.; O'Connor, Jim E.

2017-01-01

The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

Massive Freshwater discharges: an example from Glacial Lake Missoula

NASA Astrophysics Data System (ADS)

Lopes, C.; Mix, A. C.

2016-12-01

Massive inputs of freshwater into the ocean are known to disrupt climate. This has been fairly studied in the North Atlantic with freshwater inputs from the Laurentide ice sheet and glacial Lake Agassiz. The association of these discharges with global warming has lead us to look for such prints in marine sediments. Here we show the records of Glacial Lake Missoula outbursts during the warming singe the Last Glacial Maximum in two marine cores off Oregon and California that show the presence of freshwater diatoms that are linked to massive discharges of freshwater from the glacial lake Missoula. The dynamics and timing of these north Pacific mega-flood events are fairly constrained by terrestrial records, however, the consequences of such discharges of freshwater in the northeast Pacific regional circulation remains unknown. Nevertheless we were able to estimate a salinity decrease of almost 6.0 PSU more than 400 km to the south (off northern California) during the last glacial interval (from 16-31 calendar (cal) k.y. B.P.). Anomalously high abundances of freshwater diatoms in marine sediments from the region precede generally accepted dates for the existence of glacial Lake Missoula, implying that large flooding events were also common during the advance of the Cordilleran Ice Sheet.

Source-to-sink sediment transfer in the Piave River system (North-Eastern Italy) since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Carton, Alberto; Bondesan, Aldino; Fontana, Alessandro; Meneghel, Mirco; Miola, Antonella; Mozzi, Paolo; Primon, Sandra; Surian, Nicola

2010-05-01

Aim of this study is the definition of sediment production, transfer and deposition in the Piave River system from the Last Glacial Maximum to the Present, through a basin-scale approach. The Piave River flows from North to South in the eastern sector of the Italian Alps and reaches the Adriatic Sea. Its length is 220 km and the catchment is 3899 km2. The fluvial system consists of a mountainous portion, with maximum elevation of 3343 m a.s.l., and a lower part where the river flows in the Venetian alluvial plain. Average precipitation is 1350 mm/a; the runoff coefficient is 0.63 and the mean discharge at the mouth is 60 m3/s. The highest sediment delivery to the plain was at the peak of LGM, when the Piave glacier had its maximum expansion and reached the Alpine piedmont. In this period the Piave megafan received large volumes of sediments through glaciofluvial streams and achieved its maximum expansion. LGM alluvial sediments in the distal portion of the megafan are 20-30 m thick. The last glacial advance in the Vittorio Veneto terminal moraines, at the debouch of the valley in the Venetian Plain, dates 17.6 ka 14C BP. Deglaciation started immediately afterwards and the retreat of the glacial front was rather fast, considering that at around 15.0 ka 14C BP the Prealpine tract of valley was already ice-free. Following the onset of deglaciation until about 8.0 ka 14C BP, alluvial sediments were mostly trapped in the terminal valley tracts, while the whole alluvial plain experienced a severe erosive phase, comprising the whole Lateglacial and early Holocene. At ca. 8.0 ka 14C BP, the Piave River started to downcut its Prealpine valley fill, an event which re-mobilized the alluvial sediments and contributed to delta formation on the Adriatic coast since 6.0 ka 14C BP. Post-glacial aggradation in the distal tract of the Nervesa megafan started only at about 4.0 - 3.0 ka 14C BP. In Roman times the fluvial system was rather stable, while between the 5th and 10th century AD there were several major avulsions in the distal Nervesa megafan. The last 100 years are characterized by a dramatic decrease of sediment transport due to a range of human activities (e.g. sediment mining and dams). Climate change was the main external driving factor in this fluvial system at the LGM termination, controlling both sediment production in the catchment and sea-level position. Local factors, such as the occurrence of large landslides, lake formation, post-glacial reforestation and valley topography had a major impact on sediment transfer from source to sink. Holocene millennial- and centennial-scale climatic fluctuations were able to modulate the sediment flux, increasingly intermingling with human impact during the last 6 millennia.

How well do we really know the timing and extent of glaciers during the Last Glacial Maximum in the Alps?

NASA Astrophysics Data System (ADS)

Ivy-Ochs, Susan; Braakhekke, Jochem; Monegato, Giovanni; Gianotti, Franco; Forno, Gabriella; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

2017-04-01

The Last Glacial Maximum (LGM) in the Alps saw much of the mountains inundated by ice. Several main accumulation areas comprising local ice caps and plateau icefields fit into a picture of transection glaciers flowing into huge valley glaciers. In the north the valley glaciers covered long distances (hundreds of kilometers) to reach the forelands where they spread out in fan-shaped piedmont lobes tens of kilometers across, e.g. the Rhine glacier. In the south travel distances to the mountain front were often shorter, the pathway steeper. Nevertheless, not all glaciers even reached beyond the front, as the temperatures were notably warmer in the south. For example at Orta the glacier snout remained within the mountains. Where glaciers reached the forelands they stopped abruptly and the moraine amphitheaters were constructed, e.g. at Ivrea and Rivoli-Avigliana. Sets of stacked moraines built-up as glacier advance was directly confined by the older moraines. We may temporally and spatially identify the culmination of the last glacial cycle by pinpointing the outermost moraines that date to the LGM (generally about 26-24 ka). On the other hand, the timing of abandonment of foreland positions is given by ages of the innermost, often lake-bounding, moraines (about 19-18 ka). Between the two, glacier fluctuations left the stadial moraines. In the Linth-Rhine system three stadials have been recognized: Killwangen, Schlieren and Zurich. Nevertheless, already in the Swiss sector correlation of the LGM stadials among the several foreland lobes is not unambiguous. Across the Alps, not only north to south but also west to east, how do the timing and extent of glaciers during the LGM vary? Recent glacier modelling by Seguinot et al. (2017) informs and suggests the possibility of differences in timing for reaching of the maximum extent and for the number of oscillations of individual lobes during the LGM. At present few sites in the Alps have detailed enough geomorphological constraints with well-dated ice-marginal positions for in depth discussion of outermost, innermost and in between moraines. Where locations of the LGM farthest extent are conflicting depending on author, we are trying to establish the precise location of the most extensive LGM position by directly dating moraine boulders with cosmogenic 10Be. Here we present 10Be data from the Orta and Rivoli-Avigliana amphitheatres. A key comparison is with the Tagliamento amphitheatre to the east, where dating testifies to a two-phase maximum (Monegato et al. 2007). Furthermore, comparison is made to sites north of the Alps including previously unpublished data. Monegato G. et al. 2007. Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps). Quaternary Research 68: 284-302. Seguinot J. et al. 2017. Modelling last glacial cycle ice dynamics in the Alps. EGU2017-8982

Spatial and temporal variations in high turbidity surface water off the Thule region, northwestern Greenland

NASA Astrophysics Data System (ADS)

Ohashi, Yoshihiko; Iida, Takahiro; Sugiyama, Shin; Aoki, Shigeru

2016-09-01

Glacial meltwater discharge from the Greenland ice sheet and ice caps forms high turbidity water in the proglacial ocean off the Greenland coast. Although the timing and magnitude of high turbidity water export affect the coastal marine environment, for example, through impacts on biological productivity, little is known about the characteristics of this high turbidity water. In this paper, we therefore report on the spatial and temporal variations in high turbidity water off the Thule region in northwestern Greenland, based on remote sensing reflectance data at a wavelength of 555 nm (Rrs555). The high turbidity area, identified on the basis of high reflectivity (Rrs555 ≥ 0.0070 sr-1), was generally distributed near the coast, where many outlet glaciers terminate in the ocean and on land. The extent of the high turbidity area exhibited substantial seasonal and interannual variability, and its annual maximum extent was significantly correlated with summer air temperature. Assuming a linear relationship between the high turbidity area and summer temperature, annual maximum extent increases under the influence of increasing glacial meltwater discharge, as can be inferred from present and predicted future warming trends.

On the glacial and inter-glacial thermohaline circulation and the associated transports of heat and freshwater

NASA Astrophysics Data System (ADS)

Ballarotta, M.; Falahat, S.; Brodeau, L.; Döös, K.

2014-03-01

The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, ≈ 21 kyr ago) and the present day climate are explored using an Ocean General Circulation Model and stream functions projected in various coordinates. Compared to the present day period, the LGM circulation is reorganised in the Atlantic Ocean, in the Southern Ocean and particularly in the abyssal ocean, mainly due to the different haline stratification. Due to stronger wind stress, the LGM tropical circulation is more vigorous than under modern conditions. Consequently, the maximum tropical transport of heat is slightly larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes and reorganising the freshwater transport. The LGM circulation is represented as a large intrusion of saline Antarctic Bottom Water into the Northern Hemisphere basins. As a result, the North Atlantic Deep Water is shallower in the LGM simulation. The stream functions in latitude-salinity coordinates and thermohaline coordinates point out the different haline regimes between the glacial and interglacial period, as well as a LGM Conveyor Belt circulation largely driven by enhanced salinity contrast between the Atlantic and the Pacific basin. The thermohaline structure in the LGM simulation is the result of an abyssal circulation that lifts and deviates the Conveyor Belt cell from the area of maximum volumetric distribution, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimation of the turnover times reveal a deep circulation almost sluggish during the LGM, and a Conveyor Belt cell more vigorous due to the combination of stronger wind stress and shortened circulation route.

Displaced phylogeographic signals from Gyrodactylus arcuatus, a parasite of the three-spined stickleback Gasterosteus aculeatus, suggest freshwater glacial refugia in Europe

USGS Publications Warehouse

Lumme, Jaakko; Mäkinen, Hannu; Ermolenko, Alexey V.; Gregg, Jacob L.; Ziętara, Marek S.

2016-01-01

We examined the global mitochondrial phylogeography of Gyrodactylus arcuatus, a flatworm ectoparasite of three-spined stickleback Gasterosteus aculeatus. In accordance with the suggested high divergence rate of 13%/million years, the genetic variation of the parasite was high: haplotype diversity h = 0.985 and nucleotide diversity π = 0.0161. The differentiation among the parasite populations was substantial (Φst = 0.759), with two main allopatric clades (here termed Euro and North) accounting for 54% of the total genetic variation. The diversity center of the Euro clade was in the Baltic Sea, while the North clade was spread across the Barents and White Seas. A single haplotype within the North clade was found in the western and eastern Pacific Ocean. Divergence of main clades was estimated to be circa 200 thousand years ago. Each main clade was further divided into six distinct subclades, estimated to have diverged in isolation since 135 thousand years ago. This second division corresponds approximately to the Eemian interglacial predating the last glacial maximum. A demographic expansion of the subclades is associated with colonisation of northern Europe since the last glacial maximum, circa 15–40 thousand years ago. The parasite phylogeny is most likely explained by sequential isolated bottlenecks and expansions in numerous allopatric refugia. The postglacial intermingling and high variation in the marine parasite populations, separately in the Baltic and Barents Seas, suggest low competition of divergent parasite matrilines, coupled with a large population size and high rate of dispersal of hosts. The genetic contribution of the assumed refugial fish populations maintaining the parasite during the last glacial maximum was not detected among the marine sticklebacks, which perhaps were infected after range expansion.

Displaced phylogeographic signals from Gyrodactylus arcuatus, a parasite of the three-spined stickleback Gasterosteus aculeatus, suggest freshwater glacial refugia in Europe.

PubMed

Lumme, Jaakko; Mäkinen, Hannu; Ermolenko, Alexey V; Gregg, Jacob L; Ziętara, Marek S

2016-08-01

We examined the global mitochondrial phylogeography of Gyrodactylus arcuatus, a flatworm ectoparasite of three-spined stickleback Gasterosteus aculeatus. In accordance with the suggested high divergence rate of 13%/million years, the genetic variation of the parasite was high: haplotype diversity h=0.985 and nucleotide diversity π=0.0161. The differentiation among the parasite populations was substantial (Φst=0.759), with two main allopatric clades (here termed Euro and North) accounting for 54% of the total genetic variation. The diversity center of the Euro clade was in the Baltic Sea, while the North clade was spread across the Barents and White Seas. A single haplotype within the North clade was found in the western and eastern Pacific Ocean. Divergence of main clades was estimated to be circa 200 thousand years ago. Each main clade was further divided into six distinct subclades, estimated to have diverged in isolation since 135 thousand years ago. This second division corresponds approximately to the Eemian interglacial predating the last glacial maximum. A demographic expansion of the subclades is associated with colonisation of northern Europe since the last glacial maximum, circa 15-40 thousand years ago. The parasite phylogeny is most likely explained by sequential isolated bottlenecks and expansions in numerous allopatric refugia. The postglacial intermingling and high variation in the marine parasite populations, separately in the Baltic and Barents Seas, suggest low competition of divergent parasite matrilines, coupled with a large population size and high rate of dispersal of hosts. The genetic contribution of the assumed refugial fish populations maintaining the parasite during the last glacial maximum was not detected among the marine sticklebacks, which perhaps were infected after range expansion. Copyright © 2016 Australian Society for Parasitology. All rights reserved.

20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U.S.A.

USGS Publications Warehouse

Molnia, B.F.; Post, A.; Carlson, P.R.

1996-01-01

Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacific Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake's basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of "present-day" glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake. In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year-1.

Phylogeography of the Patagonian otter Lontra provocax: adaptive divergence to marine habitat or signature of southern glacial refugia?

PubMed Central

2011-01-01

Background A number of studies have described the extension of ice cover in western Patagonia during the Last Glacial Maximum, providing evidence of a complete cover of terrestrial habitat from 41°S to 56°S and two main refugia, one in south-eastern Tierra del Fuego and the other north of the Chiloé Island. However, recent evidence of high genetic diversity in Patagonian river species suggests the existence of aquatic refugia in this region. Here, we further test this hypothesis based on phylogeographic inferences from a semi-aquatic species that is a top predator of river and marine fauna, the huillín or Southern river otter (Lontra provocax). Results We examined mtDNA sequences of the control region, ND5 and Cytochrome-b (2151 bp in total) in 75 samples of L. provocax from 21 locations in river and marine habitats. Phylogenetic analysis illustrates two main divergent clades for L. provocax in continental freshwater habitat. A highly diverse clade was represented by haplotypes from the marine habitat of the Southern Fjords and Channels (SFC) region (43°38' to 53°08'S), whereas only one of these haplotypes was paraphyletic and associated with northern river haplotypes. Conclusions Our data support the hypothesis of the persistence of L. provocax in western Patagonia, south of the ice sheet limit, during last glacial maximum (41°S latitude). This limit also corresponds to a strong environmental change, which might have spurred L. provocax differentiation between the two environments. PMID:21356052

Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.

PubMed

Khan, Shfaqat A; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L; Wahr, John; Willis, Michael; Kjær, Kurt H; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

2016-09-01

Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

Genetic analysis of potential postglacial watershed crossings in Central Europe by the bullhead (Cottus gobio L.).

PubMed

Vonlanthen, P; Excoffier, L; Bittner, D; Persat, H; Neuenschwander, S; Largiadèr, C R

2007-11-01

Natural colonizations across watersheds have been frequently proposed to explain the present distributions of many freshwater fish species. However, detailed studies of such potential watershed crossings are still missing. Here, we investigated potential postglacial watershed crossings of the widely distributed European bullhead (Cottus gobio L.) in two different areas along the Rhine-Rhône watershed using detailed genetic analysis. The main advantage of studying bullheads vs. other freshwater fish species is that their distribution has been lightly influenced by human activities and as such, interpretations of colonization history are not confounded by artificial transplantations. The genetic analyses of eight microsatellite loci revealed strong genetic similarities between populations of both sides of the Rhine-Rhône watershed in the Lake Geneva area, giving strong evidence for a natural watershed crossing of bullheads from the upper Rhine drainage into the Rhône drainage in the Lake Geneva area likely facilitated by the retreat of the glaciers after the last glacial maximum some 20,000 years ago. Populations from the Lake Geneva basin were genetically more similar to populations from across the watershed in the upper Rhine drainage than to populations further downstream in the lower Rhône. In contrast, populations from Belfort, an area, which was not covered by ice during the last glacial maximum, showed strong genetic differentiation between populations of the upper Rhine and Rhône drainages. Based on our results on the bullhead, we propose that glacial retreat may have eased the dispersal of numerous European freshwater fish species across several geological boundaries.

Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet

PubMed Central

Khan, Shfaqat A.; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L.; Wahr, John; Willis, Michael; Kjær, Kurt H.; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A.; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

2016-01-01

Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year. PMID:27679819

Timing of last deglaciation in the Cantabrian Mountains (Iberian Peninsula; North Atlantic Region) based on in situ-produced 10Be exposure dating

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María José; Rinterknecht, Vincent; Pallàs, Raimon; Aumaître, Georges; Bourlès, Didier L.; Keddadouche, Karim; Aster Team

2017-09-01

The Last Glacial Termination led to major changes in ice sheet coverage that disrupted global patterns of atmosphere and ocean circulation. Paleoclimate records from Iberia suggest that westerly episodes played a key role in driving heterogeneous climate in the North Atlantic Region. We used 10Be Cosmic Ray Exposure (CRE) dating to explore the glacier response of small mountain glaciers (ca. 5 km2) that developed on the northern slope of the Cantabrian Mountains (Iberian Peninsula), an area directly under the influence of the Atlantic westerly winds. We analyzed twenty boulders from three moraines and one rock glacier arranged as a recessional sequence preserved between 1150 and 1540 m above sea level (a.s.l.) in the Monasterio valley (Redes Natural Park). Results complement previous chronologic data based on radiocarbon and optically stimulated luminescence from the Monasterio valley, which suggest a local Glacial Maximum (local GM) prior to 33 ka BP and a long-standing glacier advance at 24 ka coeval to the global Last Glacial Maximum (LGM). Resultant 10Be CRE ages suggest a progressive retreat and thinning of the Monasterio glacier over the time interval 18.1-16.7 ka. This response is coeval with the Heinrich Stadial 1, an extremely cold and dry climate episode initiated by a weakening of the Atlantic Meridional Overturning Circulation (AMOC). Glacier recession continued through the Bølling/Allerød period as indicate the minimum exposure ages obtained from a cirque moraine and a rock glacier nested within this moraine, which yielded ages of 14.0 and 13.0 ka, respectively. Together, they suggest that the Monasterio glacier experienced a gradual transition from glacier to rock glacier activity as the AMOC started to strengthen again. Glacial evidence ascribable to the Younger Dryas cooling was not dated in the Monasterio valley, but might have occurred at higher elevations than evidence dated in this work. The evolution of former glaciers documented in the Monasterio valley seems consistent with previous 10Be chronologies reported in other mountain ranges of the Iberian Peninsula, which have been recalculated according to a common production rate and scaling scheme. However, the re-evaluation of published 10Be chronologies has highlighted the fact that glacial evidence previously ascribed to the Younger Dryas might be more limited than previously thought and the need for additional studies to characterized the extent of glaciers during the Younger Dryas cooling.

Glacial meltwater cooling of the Gulf of Mexico - GCM implications for Holocene and present-day climates

NASA Technical Reports Server (NTRS)

Oglesby, Robert J.; Maasch, Kirk A.; Saltzman, Barry

1989-01-01

The NCAR Community Climate Model GCM is presently used to investigate the possible effects on regional and hemispheric climates of reduced SSTs in the Gulf of Mexico, in view of delta-O-18 records and terrestrial evidence for at least two major glacial meltwater discharges after the last glacial maximum. Three numerical experiments have been conducted with imposed gulfwide SST coolings of 3, 6, and 12 C; in all cases, significant reductions arise in the North Atlantic storm-track intensity, together with a strong decrease in transient eddy water vapor transport out of the Gulf of Mexico. Other statistically significant changes occur across the Northern Hemisphere.

The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

NASA Astrophysics Data System (ADS)

Buchanan, Pearse J.; Matear, Richard J.; Lenton, Andrew; Phipps, Steven J.; Chase, Zanna; Etheridge, David M.

2016-12-01

The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial-interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL (Carbon-Ocean-Atmosphere-Land) earth system model to test the contribution of physical and biogeochemical processes to ocean carbon storage. For the LGM simulation, we find a significant global cooling of the surface ocean (3.2 °C) and the expansion of both minimum and maximum sea ice cover broadly consistent with proxy reconstructions. The glacial ocean stores an additional 267 Pg C in the deep ocean relative to the pre-industrial (PI) simulation due to stronger Antarctic Bottom Water formation. However, 889 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration and a global decrease in export production, causing a net loss of carbon relative to the PI ocean. The LGM deep ocean also experiences an oxygenation ( > 100 mmol O2 m-3) and deepening of the calcite saturation horizon (exceeds the ocean bottom) at odds with proxy reconstructions. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content of the glacial ocean can be sufficiently increased (317 Pg C) to explain the reduction in atmospheric and terrestrial carbon at the LGM (194 ± 2 and 330 ± 400 Pg C, respectively). Assuming an LGM-PI difference of 95 ppm pCO2, we find that 55 ppm can be attributed to the biological pump, 28 ppm to circulation changes and the remaining 12 ppm to solubility. The biogeochemical modifications also improve model-proxy agreement in export production, carbonate chemistry and dissolved oxygen fields. Thus, we find strong evidence that variations in the oceanic biological pump exert a primary control on the climate.

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

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

PubMed Central

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

2017-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

From the valley floor to the peaks: Stratigraphy and landscape evolution of the Alpine Lateglacial in the Kitzbühel Alps (Tyrol, Austria)

NASA Astrophysics Data System (ADS)

Dippenaar, Elijah; Reitner, Jürgen

2017-04-01

Our understanding of Alpine landscape evolution and more specifically, chronology of glacier activity during the Alpine Lateglacial (ALG; c. 19 - 11.7 ka) i.e. the timespan between the Würmian Pleniglacial (= Alpine Last Glacial Maximum; AlpLGM) and the beginning of the Holocene, is based on the evidence of only few areas in the Alps. In order to get a better understanding of glaciation and palaeoclimate during this phase, N-S and E-W transects are needed. The Kitzbühel Alps, which are currently not glaciated, span an area of 1700km2 and have peaks that reach c. 2400m a.s.l. They lie at the center of the Eastern Alps on the northern rim, which is more humid than the relatively dry central parts. A modern geological investigation of the ALG record is missing in the Kitzbühel Alps. In order to overcome this gap of knowledge and to gain a more complete understanding of the ALG landscape development, a pioneering study has been performed in the area of Langer Grund Valley, a tributary valley of the Kelchsau Valley. This was done through detailed field mapping, thereby describing the shape and sediment composition of Quaternary morphological features, such as moraines, landslides and rock glacier deposits. Sedimentary evidence of one short glacial advance and two glacial stadials were identified. In chronological order they were named the: Frommbach advance, the Arnbach (glacier) halt and the Küharn halt. Where possible, palaeoglaciers were constructed using ArcGIS. With the palaeoglaciers, equlibrium line altitudes (ELA) were calculated and compared to ELA values of known glacial stadials in an attempt to correlate the relative local stratigraphy to the Lateglacial stratigraphy. Four methods to calculate ELAs were used; Maximum Elevation of Lateral Moraines (MELM), Toe to Headwall Altitude Ratio (THAR), Area x Altitude (AA) and Accumulation Area Ratio (AAR). Furthermore, the glacial sedimentary sequence of the study area was compared to that of the Gschnitz Valley (following the approach of Reitner et al. 2016). The result of which was that the glacial sedimentary sequences were very similar. Through the comparison of ELAs and sedimentary sequences, the Frommbach advance is correlated to the Phase of Ice-decay. Compared to the data of Reitner (2007) the Frommbach advance represents a second glacier advance in the Kelchsau Valley within this short-lasting phase around 19 ka. The Arnbach halt represents most likely the Gschnitz stadial (16-17 ka). The Küharn halt is correlated to the Younger Dryas-aged Egesen stadial (Younger Dryas; 12.8-11.7 ka). In addition, the relative timing of the activity of (nowadays relict) rock glaciers and of the onset of deep-seated gravitational slope deformations (DSGSDs) could be constrained based on the overlap of those features with the reconstructed glacial record. References: Reitner J.M., 2007: Glacial dynamics at the beginning of Termination I in the Eastern Alps and their stratigraphic implications. Quaternary International 164-165: 64-84. Reitner, J.M., Ivy-Ochs, S., Drescher-Schneider, R., Hajdas, I., Linner, M., 2016: Reconsidering the current stratigraphy of the Alpine Lateglacial: Implications of the sedimentary and morphological record of the Lienz area (Tyrol/Austria). E&G Quaternary Science Journal 65: 113-144.

Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling

NASA Astrophysics Data System (ADS)

Hopcroft, Peter O.; Valdes, Paul J.; Kaplan, Jed O.

2018-04-01

The observed rise in atmospheric methane (CH4) from 375 ppbv during the Last Glacial Maximum (LGM: 21,000 years ago) to 680 ppbv during the late preindustrial era is not well understood. Atmospheric chemistry considerations implicate an increase in CH4 sources, but process-based estimates fail to reproduce the required amplitude. CH4 stable isotopes provide complementary information that can help constrain the underlying causes of the increase. We combine Earth System model simulations of the late preindustrial and LGM CH4 cycles, including process-based estimates of the isotopic discrimination of vegetation, in a box model of atmospheric CH4 and its isotopes. Using a Bayesian approach, we show how model-based constraints and ice core observations may be combined in a consistent probabilistic framework. The resultant posterior distributions point to a strong reduction in wetland and other biogenic CH4 emissions during the LGM, with a modest increase in the geological source, or potentially natural or anthropogenic fires, accounting for the observed enrichment of δ13CH4.

Tropical Climate Variability From the Last Glacial Maximum to the Present

DTIC Science & Technology

2005-09-01

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

Are Eastern Basin (Ross Sea, Antarctica) Bathymetric Ridges Associated With the Last Glacial Maximum?

NASA Astrophysics Data System (ADS)

Chow, J. M.; Bart, P. J.

2005-05-01

Ross Sea (Antarctica) Eastern Basin bathymetric ridges have been interpreted to be ice stream divides created during the Last Glacial Maximum (LGM) advance of the Antarctic Ice Sheet based on radiocarbon dating of organic matter from near-seafloor sediments recovered in piston cores (Domack et al., 1999). Detailed seismic correlations and contour mapping show that there are at least five thick units outcropping in Eastern Basin. Four of these seismically-defined units can be correlated to age control at DSDP sites 270 and 272. In contrast to the near-seafloor sampling, the interiors of these units were initially assigned a Pliocene age based on a variety of microfossil biozones (Hayes and Frakes, 1975). Savage and Ciesielski (1983) determined that the youngest unit was deposited during the Coscinodiscus lentiginosus (since renamed Thalassiosira lentiginosa) diatom biozone (i.e., the unit formed sometime between 0.65 Ma to Recent timeframe). Thus, seafloor units in the area probably are of Quaternary age, but not necessarily LGM age. More recently, diatom biozonations for the Southern Ocean have been revised to provide more detailed biochronostratigraphic resolution (Zielinski and Gersonde, 2002; Zielinski et al., 2002). We are using the most recently-revised Southern Ocean diatom-zonation schemes to systematically evaluate ages of samples taken from the base of piston cores penetrating the five individual seismically-defined units in Eastern Basin. Using this sampling strategy, we increase the chances of penetrating through the Recent hemipelagic drape to sample the underlying seismically-defined units.

Human population dynamics in Europe over the Last Glacial Maximum.

PubMed

Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

2015-07-07

The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000-19,000 y ago (27-19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30-13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe.

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

PubMed

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

2016-02-11

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

Human population dynamics in Europe over the Last Glacial Maximum

PubMed Central

Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

2015-01-01

The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000–19,000 y ago (27–19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30–13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe. PMID:26100880

Fire and ice: volcanic and glacial impacts on the phylogeography of the New Zealand forest fern Asplenium hookerianum.

PubMed

Shepherd, Lara D; Perrie, Leon R; Brownsey, Patrick J

2007-11-01

In the Southern Hemisphere there has been little phylogeographical investigation of forest refugia sites during the last glacial. Hooker's spleenwort, Asplenium hookerianum, is a fern that is found throughout New Zealand. It is strongly associated with forest and is a proxy for the survival of woody vegetation during the last glacial maximum. DNA sequence data from the chloroplast trnL-trnF locus were obtained from 242 samples, including c. 10 individuals from each of 21 focal populations. Most populations contained multiple, and in many cases unique, haplotypes, including those neighbouring formerly glaciated areas, while the predominant inference from nested clade analysis was restricted gene flow with isolation by distance. These results suggest that A. hookerianum survived the last glacial maximum in widespread populations of sufficient size to retain the observed phylogeography, and therefore that the sheltering woody vegetation must have been similarly abundant. This is consistent with palynological interpretations for the survival in New Zealand of thermophilous forest species at considerably smaller distances from the ice sheets than recorded for the Northern Hemisphere. Eastern and central North Island populations of A. hookerianum were characterized by a different subset of haplotypes to populations from the remainder of the country. A similar east-west phylogeographical pattern has been detected in a diverse array of taxa, and has previously been attributed to recurrent vulcanism in the central North Island.

Postglacial trends of hillslope development in two glacially formed mountain valleys in western Norway

NASA Astrophysics Data System (ADS)

Laute, K.; Beylich, A. A.

2012-04-01

Although rockfall talus slopes occur in all regions where rock weathering products accumulate beneath rock faces and cliffs, they are particularly common in glacially formed mountain landscapes. The retreat of glacier ice from glaciated valleys which have probably experienced oversteepening of rock slopes by glacial erosion causes paraglacial destabilization of the valley sidewalls related to stress-relief, unloading, frost weathering and / or degradation of mountain permafrost. Large areas of the Norwegian fjord landscapes are occupied by hillslopes which are owned by the influences of the glacial inheritance of the last glacial maximum (LGM). This study focuses on Postglacial trends of hillslope development in two glacially formed mountain valleys in western Norway (Erdalen and Bødalen). The research is part of a doctoral thesis, which is integrated in the Norwegian Research Council (NFR) funded SedyMONT-Norway project within the ESF TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) Programme. The main aspects addressed in this study are: (i) the spatio-temporal variability of denudative slope processes over the Holocene and (ii) the Postglacial modification of the glacial relief. The applied process-based approach includes detailed geomorphological fieldmapping combined with terrestrial laser scans (LIDAR) of slope deposits in order to identify possible deposition processes and their spatial variability, relative dating techniques (tree rings and lichens) to analyze subrecent temporal variations, detailed surface mapping with additional geophysical subsurface investigations to estimated regolith thicknesses as well as CIR- and orthophoto delineation combined with GIS and DEM computing for calculating estimates of average valley-wide rockwall retreat rates. Results show Holocene rockwall retreat rates for the two valleys which are in a comparable range with other estimates of rockwall retreat rates in other cold mountain environments worldwide. Further on the results indicate probably higher accumulation rates of slope deposits mainly throughout an enhanced rockfall activity shortly after the glacier retreat (at about 10.000 yr BP) as compared to subrecent and contemporary rates. The overall tendency of landscape development is a Postglacial modification of the defined U-shaped valley morphometry (valley widening) throughout rockwall retreat and connected accumulation of debris material beneath these rockwalls. Active fluvial material removal at the base of slopes is almost negligible due to a very limited hillslope-channel coupling in both valleys. So far, the glacially sculptured relief has not adapted to the denudative surface processes occurring under recent environmental conditions.

Glaciation and regional ground-water flow in the Fennoscandian Shield: Site 94

USGS Publications Warehouse

Provost, Alden M.; Voss, Clifford I.; Neuzil, C.E.

1998-01-01

Results from a regional-scale ground-water flow model of the Fennoscandian shield suggest that ground-water flow is strongly affected by surface conditions associated with climatic change and glaciation. The model was used to run a series of numerical simulations of variable-density ground-water flow in a 1500-km-long and approximately 10-km-deep cross-section that passes through southern Sweden. Ground-water flow and shield brine transport in the cross-sectional model are controlled by an assumed time evolution of surface conditions over the next 140 ka. Simulations show that, under periglacial conditions, permafrost may locally or extensively impede the free recharge or discharge of ground water. Below cold-based glacial ice, no recharge or discharge of ground water occurs. Both of these conditions result in the settling of shield brine and consequent freshening of near-surface water in areas of natural discharge blocked by permafrost. The presence of warm-based ice with basal melting creates a potential for ground-water recharge rates much larger than under present, ice-free conditions. Recharging basal meltwater can reach depths of a few kilometers in a few thousand years. The vast majority of recharged water is accommodated through storage in the volume of bedrock below the local area of recharge; regional (lateral) redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (~10 ka). During glacial retreat, the weight of the ice overlying a given surface location decreases, and significant upward flow of ground water may occur below the ice sheet due to pressure release, despite the continued potential for recharge of basal meltwater. Excess meltwater must exit from below the glacier through subglacial cavities and channels. Subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are greatest if the loading efficiency of the shield rock is low. The maximum rate of ground-water discharge occurs at the receding ice margin, and some discharge occurs below incursive post-glacial seas. The simulation results suggest that vertical movement of deep shield brines induced by the next few glacial cycles should not increase the concentration of dissolved solids significantly above present-day levels. However, the concentration of dissolved solids should decrease significantly at depths of up to several kilometers during periods of glacial meltwater recharge. The meltwater may reside in the subsurface for periods exceeding 10 ka and may bring oxygenated conditions to an otherwise reducing chemical environment.

Two disjunct Pleistocene populations and anisotropic postglacial expansion shaped the current genetic structure of the relict plant Amborella trichopoda

PubMed Central

Tournebize, Rémi; Manel, Stéphanie; Vigouroux, Yves; Munoz, François; de Kochko, Alexandre

2017-01-01

Past climate fluctuations shaped the population dynamics of organisms in space and time, and have impacted their present intra-specific genetic structure. Demo-genetic modelling allows inferring the way past demographic and migration dynamics have determined this structure. Amborella trichopoda is an emblematic relict plant endemic to New Caledonia, widely distributed in the understory of non-ultramafic rainforests. We assessed the influence of the last glacial climates on the demographic history and the paleo-distribution of 12 Amborella populations covering the whole current distribution. We performed coalescent genetic modelling of these dynamics, based on both whole-genome resequencing and microsatellite genotyping data. We found that the two main genetic groups of Amborella were shaped by the divergence of two ancestral populations during the last glacial maximum. From 12,800 years BP, the South ancestral population has expanded 6.3-fold while the size of the North population has remained stable. Recent asymmetric gene flow between the groups further contributed to the phylogeographical pattern. Spatially explicit coalescent modelling allowed us to estimate the location of ancestral populations with good accuracy (< 22 km) and provided indications regarding the mid-elevation pathways that facilitated post-glacial expansion. PMID:28820899

Killer Whale Nuclear Genome and mtDNA Reveal Widespread Population Bottleneck during the Last Glacial Maximum

PubMed Central

Moura, Andre E.; Janse van Rensburg, Charlene; Pilot, Malgorzata; Tehrani, Arman; Best, Peter B.; Thornton, Meredith; Plön, Stephanie; de Bruyn, P.J. Nico; Worley, Kim C.; Gibbs, Richard A.; Dahlheim, Marilyn E.; Hoelzel, Alan Rus

2014-01-01

Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline. PMID:24497033

King penguin demography since the last glaciation inferred from genome-wide data.

PubMed

Trucchi, Emiliano; Gratton, Paolo; Whittington, Jason D; Cristofari, Robin; Le Maho, Yvon; Stenseth, Nils Chr; Le Bohec, Céline

2014-07-22

How natural climate cycles, such as past glacial/interglacial patterns, have shaped species distributions at the high-latitude regions of the Southern Hemisphere is still largely unclear. Here, we show how the post-glacial warming following the Last Glacial Maximum (ca 18 000 years ago), allowed the (re)colonization of the fragmented sub-Antarctic habitat by an upper-level marine predator, the king penguin Aptenodytes patagonicus. Using restriction site-associated DNA sequencing and standard mitochondrial data, we tested the behaviour of subsets of anonymous nuclear loci in inferring past demography through coalescent-based and allele frequency spectrum analyses. Our results show that the king penguin population breeding on Crozet archipelago steeply increased in size, closely following the Holocene warming recorded in the Epica Dome C ice core. The following population growth can be explained by a threshold model in which the ecological requirements of this species (year-round ice-free habitat for breeding and access to a major source of food such as the Antarctic Polar Front) were met on Crozet soon after the Pleistocene/Holocene climatic transition. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Integrative Taxonomy of Southeast Asian Snail-Eating Turtles (Geoemydidae: Malayemys) Reveals a New Species and Mitochondrial Introgression

PubMed Central

Ihlow, Flora; Vamberger, Melita; Flecks, Morris; Hartmann, Timo; Cota, Michael; Makchai, Sunchai; Meewattana, Pratheep; Dawson, Jeffrey E.; Kheng, Long; Rödder, Dennis; Fritz, Uwe

2016-01-01

Based on an integrative taxonomic approach, we examine the differentiation of Southeast Asian snail-eating turtles using information from 1863 bp of mitochondrial DNA, 12 microsatellite loci, morphology and a correlative species distribution model. Our analyses reveal three genetically distinct groups with limited mitochondrial introgression in one group. All three groups exhibit distinct nuclear gene pools and distinct morphology. Two of these groups correspond to the previously recognized species Malayemys macrocephala (Chao Phraya Basin) and M. subtrijuga (Lower Mekong Basin). The third and genetically most divergent group from the Khorat Basin represents a previously unrecognized species, which is described herein. Although Malayemys are extensively traded and used for religious release, only few studied turtles appear to be translocated by humans. Historic fluctuations in potential distributions were assessed using species distribution models (SDMs). The Last Glacial Maximum (LGM) projection of the predictive SDMs suggests two distinct glacial distribution ranges, implying that the divergence of M. macrocephala and M. subtrijuga occurred in allopatry and was triggered by Pleistocene climate fluctuations. Only the projection derived from the global circulation model MIROC reveals a distinct third glacial distribution range for the newly discovered Malayemys species. PMID:27050302

Aspects of late Quaternary geomorphological development in the Khangai Mountains and the Gobi Altai Mountains (Mongolia)

NASA Astrophysics Data System (ADS)

Lehmkuhl, Frank; Nottebaum, Veit; Hülle, Daniela

2018-07-01

The reconstruction of geomorphological processes as a result of environmental change is approached by investigating and dating some fluvial, aeolian and lacustrine archives at specific locations that form a N-S basin and range transect across the Khangai Mountains south to the eastern Gobi Altai mountains in Mongolia. Geomorphological processes varied a) spatially with different climatic conditions and vegetation cover in relation to different elevation and latitude and b) temporally due to climatic shifts during the late Quaternary. In total, 15 sections from three distinct sub-regions along that transect were dated by 22 OSL ages. The Khangai Mountain sub-region exhibits mainly late Glacial to Holocene aeolian silty to sandy cover sediments mainly in the upper catchment reaches (>1800 m a.s.l.). Sections in the northern and central Gobi represent river terraces and alluvial fans in basin areas as well as aeolian sediments in the mountains above 2200 m a.s.l. The oldest terrace surface found in this study (T2; NGa1) dates to the penultimate Glacial cycle. The T1 terrace surfaces, on the northern Khangai Mountain front and in the central Gobi sub-region yield a maximum accumulation during the global Last Glacial Maximum (gLGM) and late Glacial time. During the gLGM phase represents rather sheetflow dominated transport built the alluvial fans and in late Glacial times the sediments exhibit more debrisflow controlled accumulation. Incision, forming the T1-terrace edges is therefore, supposed for the Pleistocene-Holocene transition and subsequent early Holocene. The geomorphic evidence is interpreted as stronger fluvial morphodynamics induced by enhanced humidity under beginning interglacial conditions. These processes coincided with the development of aeolian mantles at higher altitudes in the Khangai and Gobi Altai mountains where higher temperatures and humidities supported the formation of a vegetation cover, that served as a dust trap at least since late Glacial times and reduced the sediment supply on the alluvial fans.

Holocene history of North Ice Cap, northwestern Greenland

NASA Astrophysics Data System (ADS)

Corbett, L. B.; Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Roy, E. P.; Thompson, J. T.

2013-12-01

Although much research has focused on the past extents of the Greenland Ice Sheet, less is known about the smaller ice caps on Greenland and how they have evolved over time. These small ice caps respond sensitively to summer temperatures and, to a lesser extent, winter precipitation, and provide valuable information about climatic conditions along the Greenland Ice Sheet margins. Here, we investigate the Holocene history of North Ice Cap (76°55'N 68°00'W), located in the Nunatarssuaq region near Thule, northwest Greenland. Our results are based on glacial geomorphic mapping, 10Be dating, and analyses of sediment cores from a glacially fed lake. Fresh, unweathered and unvegetated boulders comprise moraines and drift that mark an extent of North Ice Cap ~25 m outboard of the present ice margin. It is likely that these deposits were formed during late Holocene time and we are currently employing 10Be surface exposure dating to examine this hypothesis. Just outboard of the fresh moraines and drift, boulders and bedrock show significant weathering and are covered with lichen. Based on glacial geomorphic mapping and detailed site investigations, including stone counts, we suggest that the weathered boulders and bedrock were once covered by erosive Greenland Ice Sheet flow from southeast to northwest over the Nunatarssuaq region. Five 10Be ages from the more weathered landscape only 100-200 m outboard of the modern North Ice Cap margin are 52 and 53 ka (bedrock) and 16, 23, and 31 ka (boulders). These ages indicate that recent ice cover has likely been cold-based and non-erosive, failing to remove inherited cosmogenic nuclides from previous periods of exposure, although the youngest boulder may provide a maximum limiting deglaciation age. Sediment cores collected from Delta Sø, a glacially-fed lake ~1.5 km outside of the modern North Ice Cap margin, contain 130 cm of finely laminated sediments overlying coarse sands and glacial till. Radiocarbon ages from just above the sands are 14,940 and 14,560 cal yr BP (medians of two-sigma ranges). Our results thus far suggest that the Nunatarssuaq region preserves a long and complex glacial history, including glaciation by the Greenland Ice Sheet and potentially North Ice Cap, as well as glaciation by both erosive and non-erosive ice. Based on the basal ages from Delta Sø and the youngest boulder 10Be age, recession at the end of the most recent glacial period likely occurred by ~15 ka. This is considerably earlier than most other terrestrial margins of Greenland that did not become ice free until ~10 ka. Our ongoing research is developing proxy and further chronological data from sediment cores from Delta Sø and nearby ice-marginal lakes to constrain the Holocene fluctuations of North Ice Cap.

Interannual physiological and growth responses of glacial Juniperus to changes in atmospheric [CO2] since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Gerhart, L. M.; Harris, J. M.; Ward, J. K.

2011-12-01

During the Last Glacial Maximum, atmospheric [CO2] was as low as 180 ppm and has currently risen to a modern value of 393 ppm as a result of fossil fuel combustion and deforestation. In order to understand how changing [CO2] influenced trees over the last 50,000 years, we analyzed carbon isotope ratios and width of individual tree rings from glacial Juniperus specimens preserved in the Rancho La Brea tar pits in southern California (aged 14-49 kyr BP). Modern trees were also analyzed to compare effects of changing precipitation, temperature and atmospheric [CO2] on physiology and growth. To assess physiological responses, we calculated ci/ca (intercellular [CO2]/atmospheric [CO2]) for each annual ring of each tree. This ratio incorporates numerous aspects of plant physiology, including stomatal conductance and photosynthetic capacity. In addition, we measured ring widths for each sample, and standardized these measurements into indices in order to compare across individuals. Mean ci/ca values remained constant throughout 50,000 years despite major environmental changes, indicating a long-term physiological set point for ci/ca in this group. Constant ci/ca ratios would be maintained through offsetting changes in stomatal conductance and photosynthetic capacity. Glacial Juniperus never experienced ci values below 90 ppm, suggesting a survival compensation point for Juniperus. In addition, glacial trees showed significantly reduced interannual variation in ci/ca, even though interannual climatic variability was as high during the LGM in this region as it is today. A lack of variability in ci/ca of glacial trees suggests that tree physiology was dominated by low [CO2], which shows low interannual variation. Modern trees showed high interannual variation in ci/ca, since water availability dominates current physiological responses and varies greatly from year to year. Interestingly, interannual variation in ring width index did not show significant differences between glacial and modern trees, suggesting these trees were adapted to maintain growth under low [CO2]. These adaptations may constrain the ability of modern trees to fully utilize increases in atmospheric [CO2]. These results have significant implications for our understanding of the adaptations of trees to changing [CO2] and indicate that the environmental factors that most strongly influence plant physiology may have changed over geologic time scales.

The simulated climate of the Last Glacial Maximum and insights into the global carbon cycle.

NASA Astrophysics Data System (ADS)

Buchanan, P. J.; Matear, R.; Lenton, A.; Phipps, S. J.; Chase, Z.; Etheridge, D. M.

2016-12-01

The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial-interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL Earth System Model to test the contribution of key biogeochemical processes to ocean carbon storage. For the coupled LGM simulation, we find that significant cooling (3.2 °C), expanded minimum (Northern Hemisphere: 105 %; Southern Hemisphere: 225 %) and maximum (Northern Hemisphere: 145 %; Southern Hemisphere: 120 %) sea ice cover, and a reorganisation of the overturning circulation caused significant changes in ocean biogeochemical fields. The coupled LGM simulation stores an additional 322 Pg C in the deep ocean relative to the Pre-Industrial (PI) simulation. However, 839 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration, causing a net loss of 517 Pg C relative to the PI simulation. The LGM deep ocean also experiences an oxygenation (>100 mmol O2 m-3) and deepening of the aragonite saturation depth (> 2,000 m deeper) at odds with proxy reconstructions. Hence, these physical changes cannot in isolation produce plausible biogeochemistry nor the required drawdown of atmospheric CO2 of 80-100 ppm at the LGM. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content in the glacial oceanic reservoir can be increased (326 Pg C) to a level that is sufficient to explain the reduction in atmospheric and terrestrial carbon at the LGM (520 ± 400 Pg C). These modifications also go some way to reconcile simulated export production, aragonite saturation state and oxygen fields with those that have been reconstructed by proxy measurements, thereby implicating past changes in ocean biogeochemistry as an essential driver of the climate system.

Equilibrium line altitudes and climate during the Late Holocene glacial maximum in the Andes

NASA Astrophysics Data System (ADS)

Sagredo, E. A.; Lowell, T. V.; Kelly, M. A.; Aravena, J.

2012-12-01

Documenting the spatial and temporal pattern of climate change associated with widespread glacial fluctuations during Late Holocene time is critical for understanding the mechanisms underlying these climatic/glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) associated with the most prominent glacial advance during the last millennium for four alpine glaciers in different climatic regimes in the Andes. We reconstruct scenarios of the climatic conditions (temperature and precipitation anomalies) that accommodate the ELA depressions. The glaciers studied are an unnamed glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S) and Tranquilo glacier (47°S). Results from the combined geomorphic analysis and application of a surface energy and mass balance model suggest that there is not a unique combination of temperature and precipitation conditions that accommodates the ELA change recorded since the Late Holocene maximum at the four sites. Assuming no change in precipitation, the ELA depressions could be explained by a cooling (with respect to present-day values) of at least -0.7°C at Cordillera Vilcanota, -1.0°C at Tapado glacier, -0.5°C at Cipreses glacier and -1.3°C at Tranquilo glacier. In contrast, assuming no change in temperature, the ELA depressions could be explained by an increase in the precipitation of at least 0.51 m (63% of the annual precipitation) at Cordillera Vilcanota, 0.33 m (95%) at Tapado glacier, 0.17 m (21%) at Cipreses glacier and 0.68 m (62%) at Tranquilo glacier. Our results serve as targets to test predictions from models of global climate dynamics for the last millennium and contribute to the understanding of the mechanisms underlying the Late Holocene glacial fluctuations.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

The response of the Okhotsk Sea environment to the orbital-millennium global climate changes during the Last Glacial Maximum, deglaciation and Holocene

NASA Astrophysics Data System (ADS)

Gorbarenko, Sergey A.; Artemova, Antonina V.; Goldberg, Evgeniy L.; Vasilenko, Yuriy P.

2014-05-01

Reconstruction of regional climate and the Okhotsk Sea (OS) environment for the Last Glacial Maximum (LGM), deglaciation and Holocene was performed on the basis of high-resolution records of ice rafted debris (IRD), СаСО3, opal, total organic carbon (TOС), biogenic Ba (Ba_bio) and redox sensitive element (Mn, Mo) content, and diatom and pollen results of four cores that form a north-southern transect. Age models of the studied cores were earlier established by AMS 14C data, oxygen-isotope chronostratigraphy and tephrochronology. According to received results, since 25 ka the regional climate and OS environmental conditions have changed synchronously with LGM condition, cold Heinrich event 1, Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Pre-Boreal (PB) warming recorded in the Greenland ice core, North Atlantic sediment, and China cave stalagmites. Calculation of IRD MAR in sediment of north-south transect cores indicates an increase of sea ice formation several times in the glacial OS as compared to the Late Holocene. Accompanying ice formation, increased brine rejection and the larger potential density of surface water at the north shelf due to a drop of glacial East Asia summer monsoon precipitation and Amur River run off, led to strong enhancement of the role of the OS in glacial North Pacific Intermediate Water (NPIW) formation. The remarkable increase in OS productivity during BA and PB warming was probably related with significant reorganisation of the North Pacific deep water ventilation and nutrient input into the NPIW and OS Intermediate Water (OSIW). Seven Holocene OS millennial cold events based on the elevated values of the detrended IRD stack record over the IRD broad trend in the sediments of the studied cores have occurred synchronously with cold events recorded in the North Atlantic, Greenland ice cores and China cave stalagmites after 9 ka. Diatom production in the OS was mostly controlled by sea ice cover changes and surface water stratification induced by sea-ice melting; therefore significant opal accumulation in sediments of this basin begin from 4 to 6 ka ago simultaneously with a remarkable decrease of sea ice cover.

The Carbon Isotopic Record of The C37:2 Alkenone In Sediments From The Equatorial and South Atlantic: Last Glacial Maximum (lgm) Vs. Holocene

NASA Astrophysics Data System (ADS)

Benthien, A.; Schulte, S.; Andersen, N.; Müller, P. J.; Schneider, R. R.

The carbon isotopic signal of the C37-alkenone, a taxon-specific biomarker for hap- tophyte algae, has been used in various paleoceanographic studies as a proxy for an- cient surface water CO2 concentration ([CO2aq]). However, a number of recent cul- ture, field and sediment studies imply that the carbon isotopic fractionation (ep) of alkenones is controlled predominantly by physiological processes and environmental factors other than the ambient CO2 concentration (i.e., growth rate, nutrient availabil- ity, light intensity, active carbon uptake, bicarbonate utilisation). The environmental conditions controlling phytoplankton growth are likely to vary strongly with oceano- graphic setting. Culture experiments can not perfectly recreate natural growth con- ditions and physical processes which affect the carbon isotopic signal in the field and its preservation in the sediment. Consequently, the use of the carbon isotopic record of alkenones as a reliable paleoceonographic proxy also requires sediment- based studies covering a broad range of different oceanic regimes for the past and modern ocean. Here, we present the first basin-wide comparison of alkenone ep val- ues from sediments of the Last Glacial Maximum (LGM) and the latest Holocene. Different oceanographic regions from the equatorial and South Atlantic Ocean were examined. Generally, alkenone ep is lower during the LGM compared to the Holocene. Considering present understanding of LGM-Holocene changes in surface water condi- tions, the observed glacial/interglacial difference in ep indicates that different effects controlled the isotopic fractionation in alkenone-producing algae depending on the regional setting. In upwelling regions, the variations in ep probably reflect a glacial increase in haptophyte productivity controlled by the availability of surface water nu- trient concentrations. By contrast, in oligotrophic areas slightly lower nutrient content was available during LGM. Here, the observed ep difference can be explained partly with an assumed glacial decrease in surface water [CO2aq]. However, it can not be ruled out that changes in haptophyte productivity also affected the ep signal to some extent. This study clearly demonstrates that a reliable reconstruction of [CO2aq] on the basis of the isotopic composition of alkenones is not feasible without a detailed 1 knowledge of ancient haptophyte growth conditions. 2

Does Temperature (Rather than Precipitation) Dictate the Geomorphic Legacy of Glacial Intervals in Unglaciated Mid-Latitude Terrains?

NASA Astrophysics Data System (ADS)

Marshall, J. A.; Roering, J. J.; Bartlein, P. J.; Praskievicz, S. J.; Gavin, D. G.; Hales, T. C.; Granger, D. E.

2014-12-01

Whereas glaciated landscapes record increased erosional efficiency through moraines and U-shaped valleys, unglaciated hillslopes and rivers lack a mechanistic theory for climate controls on their dynamics and form. Changes in precipitation and associated aggradation due to vegetation loss or incision due to increased river discharge are commonly invoked when considering the effect of glacial intervals on unglaciated terrains, but there is scant evidence supporting or discounting these hypotheses. Surprisingly, there is little consideration that temperature, rather than precipitation, may dictate the frequency, magnitude, or style of erosion in unglaciated landscapes during glacial intervals. Here, we present results combining a mechanistic frost-cracking model with downscaled general circulation model output to predict the extent and intensity of sediment production via frost processes across the unglaciated Oregon Coast Range (OCR) during the Last Glacial Maximum (LGM). Our results show that in this mid-latitude region, well south of the Cordilleran ice sheet, frost-driven processes likely shaped 90% of the present-day landmass during the LGM. A suite of geomorphic and vegetation data from a 50-ky sediment core from a paleo landslide-dammed lake in the OCR support our model results. Our study site, Little Lake, is located in the central portion of the OCR, over 400 m south of the maximum extent of the Cordilleran ice sheet. Based on 10Be-derived erosion rates, present-day catchment erosion rates average 0.07 ± 0.03 mm/yr (mean ± sd), while LGM erosion rates remained constant around 0.19 ± 0.01 mm/yr. These LGM values are nearly 3X greater than present-day erosion rates and coincide with high frost cracking intensity predicted by our model. We also observe a transition from finely laminated lacustrine clays and sands to coarse lacustrine blue-grey sands at ~ 28 ka, during the transition to the LGM. The presence of Picea sitchensis (Sitka spruce) and Abies lasiocarpa (subalpine fir) in the core during the LGM imply mean annual temperatures of ~ 1 °C and January mean temperatures of ~ -7 °C. Our results suggest that broad swaths of continental landscapes likely experienced accelerated sediment production via frost processes rather than via changes in precipitation during glacial intervals.

Atlantic Ocean Circulation at the Last Glacial Maximum: Inferences from Data and Models

DTIC Science & Technology

2012-09-01

available. Uncertainties in proxies themselves, and in the dating of the proxy records, are generally lower for the LGM than for periods further back...proven useful in understanding new aspects of the modern ocean circulation. Due to the poor dating resolution of sediment cores from the LGM period, and...Environmental Processes of the Ice Age: Land, Oceans, Glaciers (EPI- LOG) project was an effort to reconstruct the state of the Earth in glacial states; a

Investigating Long-term Behavior of Outlet Glaciers in Greenland

NASA Technical Reports Server (NTRS)

Csatho, Beata; vanderVeen, Kees; Schenk, Toni

2005-01-01

Repeat surveys by airborne laser altimetry in the 1990s have revealed significant thinning of outlet glaciers draining the interior of the Greenland Ice Sheet, with thinning rates up to several meters per year. To fully appreciate the significance of these recent glacier changes, the magnitude of retreat and surface lowering must be placed within the broader context of the retreat since the Last Glacial Maximum and, more significantly, of the retreat following the temporary glacier advance during the Little Ice Age (LIA). The LIA maximum stand is marked by trimlines, sharp boundaries between recently deglacifated unvegetated rocks, and vegetated surfaces at higher elevations. The objective of this project was to demonstrate the use of remote sensing data to map these trimlines and other glacial geomorphologic features.

­Chronology of the Last Termination of Tsagaan Gol-Potanin Glacier Valley, Altai Mountains, Mongolia using 10Be surface-exposure dating

NASA Astrophysics Data System (ADS)

Radue, M. J.; Putnam, A. E.; Strand, P.; Norris, N. R.

2017-12-01

The last termination ( 19-11 ka) marks the end of the last ice age and the transition to modern interglacial conditions. Increasing Northern Hemisphere summer insolation alone cannot account for the rapid global warming during the termination and the mechanisms that triggered the dramatic deglaciation are unresolved. Various hypotheses for deglacial warming include an increase in atmospheric CO­2, changes in ocean circulation, shifting wind belts, and water vapor. Here, we investigate the last termination in the Mongolian Altai (49°N, 88°E), a mountain range in the heart of Asia, to constrain the nature of the termination in the center of Earth's largest continent. We present a 10Be surface-exposure chronology for a system of glacial landforms in the Tsagaan Gol- Potanin Glacier Valley. Our chronology is underpinned by detailed glacial geomorphic maps made using satellite and unmanned aerial vehicle (UAV) imagery. Based on our glacial reconstruction, we estimate changes in atmospheric temperature from the Last Glacial Maximum to the Late Holocene using snowline reconstruction techniques. Mongolia is an ideal location to document past climate because it is isolated from oceanic influences; therefore, our record should provide insight into the roles of local radiation forcing from changes in Earth's orbital configuration, greenhouse gases, and atmospheric heat transfer in Asian climate dynamics. With a high-resolution chronology and detailed glacial geomorphic maps of the Potanin-Tsagaan Gol Valley in the Mongolian Altai, we compare the timing of deglaciation in interior Asia with records of climate drivers, such as CO­2­­, to understand what caused this major global warming event.

Ice thickness and topographic relief in glaciated landscapes of the western USA

NASA Astrophysics Data System (ADS)

Brocklehurst, Simon H.; Whipple, Kelin X.; Foster, David

2008-05-01

The development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes. In particular, glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes. Previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice. Here we summarise a field-based test of this hypothesis in two mountain ranges in the western United States, the Sierra Nevada, California, and the Sangre de Cristo Range, Colorado. These areas exhibit a range of degrees of glacial occupation during the Quaternary, including some drainage basins essentially unoccupied by ice, allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification. We mapped last glacial maximum (LGM) trimlines to estimate the ice thickness at the equilibrium line altitude during the LGM, and determined several metrics of relief for drainage basins across the full spectrum of LGM ice extents. Comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area. We extended our study to the Bitterroot Range in Idaho/Montana, and the Teton Range in Wyoming, for a more comprehensive understanding of sub-ridgeline relief, or 'missing mass'. This measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers, but appears to be influenced by the more active tectonics of the Teton Range. While the effects of glacial modification on the landscape are clear (valley widening, hanging valley formation), the overall change in the relief structure of the mountain ranges studied here is surprisingly modest.

Submarine glacial landforms and interactions with volcanism around Sub-Antarctic Heard and McDonald Islands

NASA Astrophysics Data System (ADS)

Picard, K.; Watson, S. J.; Fox, J. M.; Post, A.; Whittaker, J. M.; Lucieer, V.; Carey, R.; Coffin, M. F.; Hodgson, D.; Hogan, K.; Graham, A. G. C.

2017-12-01

Unravelling the glacial history of Sub-Antarctic islands can provide clues to past climate and Antarctic ice sheet stability. The glacial history of many sub-Antarctic islands is poorly understood, including the Heard and McDonald Islands (HIMI) located on the Kerguelen Plateau in the southern Indian Ocean. The geomorphologic development of HIMI has involved a combination of construction via hotspot volcanism and mechanical erosion caused by waves, weather, and glaciers. Today, the 2.5 km2 McDonald Islands are not glacierised; in contrast, the 368 km2 Heard Island has 12 major glaciers, some extending from the summit of 2813 m to sea level. Historical accounts from Heard Island suggest that the glaciers were more extensive in the 1850s to 1870s, and have retreated at least 12% (33.89 km2) since 1997. However, surrounding bathymetry suggests a much more extensive previous glaciation of the HIMI region that encompassed 9,585 km2, likely dating back at least to the Last Glacial Maximum (LGM) ca. 26.5 -19 ka. We present analyses of multibeam bathymetry and backscatter data, acquired aboard RV Investigator in early 2016, that support the previous existence of an extensive icecap. These data reveal widespread ice-marginal and subglacial features including moraines, over-deepened troughs, drumlins and crag-and-tails. Glacial landforms suggest paleo-ice flow directions and a glacial extent that are consistent with previously documented broad scale morphological features. We identify >660 iceberg keel scours in water depths ranging from 150 - 530 m. The orientations of the iceberg keel scours reflect the predominantly east-flowing Antarctic Circumpolar Current and westerly winds in the region. 40Ar/39Ar dating of volcanic rocks from submarine volcanoes around McDonald Islands suggests that volcanism and glaciation coincided. The flat-topped morphology of these volcanoes may result from lava-ice interaction or erosion by glaciers post eruption during a time of extensive ice-sheet cover and/or wave base erosion during sea level low stands. The prevalence and range of glacial landforms around HIMI suggest extensive past glaciation, and that glaciers have exerted a major influence on submarine geomorphology.

The sedimentary evolution of the Celtic Sea during Marine Isotope Stages 1 and 2

NASA Astrophysics Data System (ADS)

Lockhart, Edward; Scourse, James; Van Landeghem, Katrien; Praeg, Daniel; Mellett, Claire; Huws, Dei; Saher, Margot; Benetti, Sara

2017-04-01

During the Last Glacial Maximum (LGM), the Celtic Sea was partially glaciated by the Irish Sea Ice Stream and is considered to have subsequently experienced a high-energy post-glacial transgression. The combination of these events resulted in the deposition, reworking and erosion of a wide range of sediment types to produce the upper stratigraphy of the shelf, including the world's largest submarine elongated ridges. These geomorphic features dominate the shelf and have been previously interpreted to have formed as a result of the tidal reworking of shelf deposits during transgression, despite not having been directly dated. Shelf-wide high-resolution geophysical data, and vibrocores, collected as part of the BRITICE-CHRONO Project, provide new information on relationships between seismic and shallow sedimentary units. A regionally extensive near-surface reflector, cored in several locations, correlates to a gravel/shell layer with an erosive base, unconformably overlying fine-grained LGM glacial sediments with undrained shear strengths in excess of 120 kPa, and in places exhibiting visibly deformed laminations. Geotechnical tests suggest these sediments to be over-consolidated, and we propose that these properties and the observed deformation can only be explained by subglacial reworking under a re-advancing Irish Sea Ice Stream, a scenario never before evidenced in reconstructions of Celtic Sea glaciation. Previous reconstructions propose a single advance-retreat cycle; therefore, a re-advance during a time of inferred retreat would represent a significant change in glacial dynamics. Seismic reflection profiles show that the regionally continuous gravel/shell layer appears to form an undulating palaeo-topography, possibly influenced by the geotechnical properties of the deposits below, on which the large surface ridges are formed. The presence of a regionally continuous reflection surface truncating LGM glacial sediments would suggest a significant erosion event after glacial deposition occurred, possibly representing transgression. This suggests that the large surface ridges may be of post-glacial tidal origin, but with significant sediment supply and morphological control influenced by the glaciation of the Celtic Sea.

The rare peat moss Sphagnum wulfianum (Sphagnaceae) did not survive the last glacial period in northern European refugia.

PubMed

Kyrkjeeide, Magni Olsen; Hassel, Kristian; Flatberg, Kjell I; Stenøien, Hans K

2012-04-01

Organisms may survive unfavorable conditions either by moving to more favorable areas by means of dispersal or by adapting to stressful environments. Pleistocene glacial periods represent extremely unfavorable conditions for the majority of life forms, especially sessile organisms. Many studies have revealed placements of refugial areas and postglacial colonization patterns of seed plants, but little is still known about areas of long-term survival and historical migration routes of bryophytes. Given overall differences in stress tolerance between seed plants and bryophytes, it is of interest to know whether bryophytes have survived periods of extreme climatic conditions better then seed plants in northern areas. The haploid and rarely spore-producing peat moss Sphagnum wulfianum is mostly found in areas that were covered by ice during the last glacial maximum. Twelve microsatellite markers were amplified from 43 populations (367 shoots) of this species, and data were analyzed using population genetic diversity statistics, Bayesian clustering methods, and coalescence-based inference tools to estimate historical and demographic parameters. Genetic diversity within populations was low, but populations were highly differentiated, with two main genetic clusters being recognized. The two main genetic groups have diverged quite recently in the Holocene, and the pattern of genetic variability and structuring gives no support for survival in Scandinavian refugia during the last glacial period in this species. The dispersal ability of this plant thus seems surprisingly high despite its infrequent spore production.

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

NASA Astrophysics Data System (ADS)

Opazo, N. E.; Lambert, F.

2017-12-01

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

A Bi-hemispheric perspective on the last glacial termination from the Southern Alps of New Zealand and the Altai Mountains of western Mongolia

NASA Astrophysics Data System (ADS)

Strand, P.; Putnam, A. E.; Schaefer, J. M.; Denton, G.; Putnam, D.; Barrell, D.; Schwartz, R.; Sambuu, O.

2016-12-01

The last glacial termination ( 18,000 - 11,000 yrs ago) represents the last great global warming and the last time CO2 rose by a substantial amount before the industrial period. Understanding the processes that drove this glacial to interglacial transition will help refine the global climate system sensitivity to CO2 and will place ongoing global warming into a paleoclimatic context. Here, we test possible drivers of the last glacial termination by comparing chronologies of mountain glacier recession in the middle latitudes of both polar hemispheres. Extra-polar mountain glaciers are highly sensitive to changes in atmospheric temperature. Thus glacier landforms, such as moraine ridges constructed along glacier margins, afford quantitative insight into past climate conditions. We present 10Be surface-exposure chronologies and glacial geomorphologic maps of mountain glacier recession since the Last Glacial Maximum in the Southern Alps of New Zealand (44°S, 170°E) and in the Altai Mountains of western Mongolia (49°N, 88°E). On the basis of these chronologies from opposing hemispheres, we will evaluate the relative roles of rising atmospheric CO2, local insolation forcing, and ocean-atmosphere reorganizations in driving the warming that ended the last ice age.

Changes in North Atlantic deep-sea temperature during climatic fluctuations of the last 25,000 years based on ostracode Mg/Ca ratios

USGS Publications Warehouse

Dwyer, Gary S.; Cronin, Thomas M.; Baker, Paul A.; Rodriguez-Lazaro, Julio

2000-01-01

We reconstructed three time series of last glacial-to-present deep-sea temperature from deep and intermediate water sediment cores from the western North Atlantic using Mg/Ca ratios of benthic ostracode shells. Although the Mg/Ca data show considerable variability (“scatter”) that is common to single-shell chemical analyses, comparisons between cores, between core top shells and modern bottom water temperatures (BWT), and comparison to other paleo-BWT proxies, among other factors, suggest that multiple-shell average Mg/Ca ratios provide reliable estimates of BWT history at these sites. The BWT records show not only glacial-to-interglacial variations but also indicate BWT changes during the deglacial and within the Holocene interglacial stage. At the deeper sites (4500- and 3400-m water depth), BWT decreased during the last glacial maximum (LGM), the late Holocene, and possibly during the Younger Dryas. Maximum deep-sea warming occurred during the latest deglacial and early Holocene, when BWT exceeded modern values by as much as 2.5°C. This warming was apparently most intense around 3000 m, the depth of the modern-day core of North Atlantic deep water (NADW). The BWT variations at the deeper water sites are consistent with changes in thermohaline circulation: warmer BWT signifies enhanced NADW influence relative to Antarctic bottom water (AABW). Thus maximum NADW production and associated heat flux likely occurred during the early Holocene and decreased abruptly around 6500 years B.P., a finding that is largely consistent with paleonutrient studies in the deep North Atlantic. BWT changes in intermediate waters (1000-m water depth) of the subtropical gyre roughly parallel the deep BWT variations including dramatic mid-Holocene cooling of around 4°C. Joint consideration of the Mg/Ca-based BWT estimates and benthic oxygen isotopes suggests that the cooling was accompanied by a decrease in salinity at this site. Subsequently, intermediate waters warmed to modern values that match those of the early Holocene maximum of ∼7°C. Intermediate water BWT changes must also be driven by changes in ocean circulation. These results thus provide independent evidence that supports the hypothesis that deep-ocean circulation is closely linked to climate change over a range of timescales regardless of the mean climate state. More generally, the results further demonstrate the potential of benthic Mg/Ca ratios as a tool for reconstructing past ocean and climate conditions.

Asynchronous glaciations in arid continental climate

NASA Astrophysics Data System (ADS)

Batbaatar, Jigjidsurengiin; Gillespie, Alan R.; Fink, David; Matmon, Ari; Fujioka, Toshiyuki

2018-02-01

Mountain glaciers at ∼26-19 ka, during the global Last Glacial Maximum near the end of the last 105 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8-7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for glaciation in arid conditions only at high altitudes of sub-freezing temperatures, where the melt fraction in ablation is low. We expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions; an individual glacier advance should not be necessarily interpreted as evidence of cooling climate.

Reliable radiocarbon evidence for the maximum extent of the West Antarctic Ice Sheet in the easternmost Amundsen Sea Embayment during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hillenbrand, C. D.; Klages, J. P.; Kuhn, G.; Smith, J.; Graham, A. G. C.; Gohl, K.; Wacker, L.

2016-02-01

We present the first age control and sedimentological data for the upper part of a stratified seismic unit that is unusually thick ( 6-9 m) for the outer shelf of the ASE and overlies an acoustically transparent unit. The transparent unit probably consists of soft till deposited during the last advance of grounded ice onto the outer shelf. We mapped subtle mega-scale glacial lineations (MSGL) on the seafloor and suggest that these are probably the expressions of bedforms originally moulded into the surface of the underlying till layer. We note that the lineations are less distinct when compared to MSGLs recorded in bathymetric data collected further upstream and suggest that this is because of the blanketing influence of the thick overlying drape. The uppermost part (≤ 3 m) of the stratified drape was sampled by two of our sediment cores and contains sufficient amounts of calcareous foraminifera throughout to establish reliable age models by radiocarbon dating. In combination with facies analysis of the recovered sediments the obtained radiocarbon dates suggest deposition of the draping unit in a sub-ice shelf/sub-sea ice to seasonal-open marine environment that existed on the outer shelf from well before (>45 ka BP) the Last Glacial Maximum until today. This indicates the maximum extent of grounded ice at the LGM must have been situated south of the two core locations, where a well-defined grounding-zone wedge (`GZWa') was deposited. The third sediment core was recovered from the toe of this wedge and retrieved grounding-line proximal glaciogenic debris flow sediments that were deposited by 14 cal. ka BP. Our new data therefore provide direct evidence for 1) the maximum extent of grounded ice in the easternmost ASE at the LGM (=GZWa), 2) the existence of a large shelf area seawards the wedge that was not covered by grounded ice during that time, and 3) landward grounding line retreat from GZWa prior to 14 cal. ka BP. This knowledge will help to improve LGM ice sheet reconstructions and to quantify precisely the volume of LGM ice-sheet build-up in Antarctica. Our study also alludes to the possibility that refugia for Antarctic shelf benthos may have existed in the ASE during the last glacial period.

The relationship between mammal faunas and climatic instability since the Last Glacial Maximum: A Nearctic vs. Western Palearctic comparison

NASA Astrophysics Data System (ADS)

Torres-Romero, Erik Joaquín; Varela, Sara; Fisher, Jason T.; Olalla-Tárraga, Miguel Á.

2017-07-01

Climate has played a key role in shaping the geographic patterns of biodiversity. The imprint of Quaternary climatic fluctuations is particularly evident on the geographic distribution of Holarctic faunas, which dramatically shifted their ranges following the alternation of glacial-interglacial cycles during the Pleistocene. Here, we evaluate the existence of differences between climatically stable and unstable regions - defined on the basis of climatic change velocity since the Last Glacial Maximum - in the geographic distribution of several biological attributes of extant terrestrial mammals of the Nearctic and Western Palearctic regions. Specifically, we use a macroecological approach to assess the dissimilarities in species richness, range size, body size, longevity and litter size of species that inhabit regions with contrasting histories of climatic stability. While several studies have documented how the distributional ranges of animals can be affected by long-term historic climatic fluctuations, there is less evidence on the species-specific traits that determine their responsiveness under such climatic instability. We find that climatically unstable areas have more widespread species and lower mammal richness than stable regions in both continents. We detected stronger signatures of historical climatic instability on the geographic distribution of body size in the Nearctic region, possibly reflecting lagged responses to recolonize deglaciated regions. However, the way that animals respond to climatic fluctuations varies widely among species and we were unable to find a relationship between climatic instability and other mammal life-history traits (longevity and litter size) in any of the two biogeographic regions. We, therefore, conclude that beyond some biological traits typical of macroecological analyses such as geographic range size and body size, it is difficult to infer the responsiveness of species distributions to climate change solely based on particular life-history traits.

Sedimentology and lithostratigraphy of a late Wisconsinan outer shelf delta, research consortium boring in Main Pass Block 303, Mississippi delta area

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

Roberts, H.H.; Bouma, A.H.; Coleman, J.M.

A 92 m continuous boring was collected in Main Pass Area, Block 303, to better understand deltaic sedimentation and facies architecture in relationship to glacio eustatic cycles. The boring was also used to calibrate sequence stratigraphy with lithology and chronostratigraphy. The boring spans six isotope stages, covering parts of the last three sea-level cycles. The basal part (92-81 m; glacial isotope Stage 6) is interpreted as a mudflow composed of a rapidly deposited shale with distorted bedding, gas-related structures, and C-13 depleted diagenetic carbonates. This glacial stage is overlain by transgressive systems tract shelf shales capped by a 4-m thickmore » nodular calcareous shale/shelly limestone, representing the interglacial isotope Stage 5 condensed section as well as part of an outer shelf high stand systems tract. Isotope Stage 4 (60-55 m), a lowstand, appears to be condensed or missing, according to benthic foraminifera and oxygen isotope data, possibly constituting a parasequence boundary. The ensuing early Stage 3 transgression (53-45 m) and maximum flooding surface at 43 m precede a distinct progradational deltaic event (43-18 m). There is no clear sedimentary record of the latter part of Stage 3. This midshelf delta has a fauna-poor, rapidly deposited prodelta shale at the base overlain by alternating thin clays, silts, and sands of the distal bar facies and topped by a thick distributary mouth bar sand with numerous layers of redistributed organics. The Stage 2 glacial maximum appears represented by an erosional contact between the fine deltaic sands and the coarse sandy and fine gravelly transgressive system tract channel deposits. There are about 3 m of Stage 1 bioturbated silts and shelly sands capping the section.« less

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

PubMed

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

2010-10-13

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

Grounded meets floating

NASA Astrophysics Data System (ADS)

Walker, Ryan T.

2018-04-01

A comprehensive assessment of grounding-line migration rates around Antarctica, covering a third of the coast, suggests retreat in considerable portions of the continent, beyond the rates expected from adjustment following the Last Glacial Maximum.

Spiroides shrubs on Qinghai-Tibetan Plateau: Multilocus phylogeography and palaeodistributional reconstruction of Spiraea alpina and S. Mongolica (Rosaceae).

PubMed

Khan, Gulzar; Zhang, Faqi; Gao, Qingbo; Fu, Pengcheng; Zhang, Yu; Chen, Shilong

2018-06-01

A common hypothesis for the rich biodiversity found in mountains is uplift-driven diversification. Using a multilocus approach, here we assessed the influence of Qinghai-Tibetan Plateau (QTP) uplift and fluctuating regional climate on genetic diversity of two sister spiroides shrubs, Spiraea alpina and S. mongolica. Combined with palaeodistributional reconstruction modelling, we investigated the current and past-predicted distribution of these species under different climatic episodes. The study demonstrated that continuous pulses of retreat and expansion during last glacial-interglacial episodes, combined with the uplifting of QTP shaped the current distribution of these species. All the populations showed high level of genetic diversity based on both cpDNA and SSR markers. The average gene diversity within populations based on cpDNA markers was 0.383 ± 0.052 for S. alpina and 0.477 ± 0.048 for S. mongolica. The observed and expected heterozygosities based on SSR for both Spiraea alpina and S. mongolicawere H E (0.72-0.90)/H O (0.35-0.78) and H E (0.77-0.92)/H O (0.47-0.77) respectively. Palaeodistributional reconstruction indicated species' preferences at southeastern edge of the plateau during last glacial maximum, at higher altitude areas of QTP and range expansion to central plateau during the interglacial episodes. Assignment tests in STRUCTURE, discriminant analysis of principal coordinates and Immigrants analysis in GENECLASS based on nuclear SSR markers did not support the hypothesis of gene flow between both the species. However, maximum likelihood approach based on cpDNA showed sharing of haplotypes between both species. Copyright © 2018 Elsevier Inc. All rights reserved.

New Zealand supereruption provides time marker for the Last Glacial Maximum in Antarctica

USGS Publications Warehouse

Dunbar, Nelia W.; Iverson, Nels A.; Van Eaton, Alexa R.; Sigl, Michael; Alloway, Brent V.; Kurbatov, Andrei V.; Mastin, Larry G.; McConnell, Joseph R.; Wilson, Colin J. N.

2017-01-01

Multiple, independent time markers are essential to correlate sediment and ice cores from the terrestrial, marine and glacial realms. These records constrain global paleoclimate reconstructions and inform future climate change scenarios. In the Northern Hemisphere, sub-visible layers of volcanic ash (cryptotephra) are valuable time markers due to their widespread dispersal and unique geochemical fingerprints. However, cryptotephra are not as widely identified in the Southern Hemisphere, leaving a gap in the climate record, particularly during the Last Glacial Maximum (LGM). Here we report the first identification of New Zealand volcanic ash in Antarctic ice. The Oruanui supereruption from Taupo volcano (25,580  ±  258 cal. a BP) provides a key time marker for the LGM in the New Zealand sector of the SW Pacific. This finding provides a high-precision chronological link to mid-latitude terrestrial and marine sites, and sheds light on the long-distance transport of tephra in the Southern Hemisphere. As occurred after identification of the Alaskan White River Ash in northern Europe, recognition of ash from the Oruanui eruption in Antarctica dramatically increases the reach and value of tephrochronology, providing links among climate records in widely different geographic areas and depositional environments.

Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?

PubMed Central

Leonard, Saoirse A.; Risley, Claire L.; Turvey, Samuel T.

2013-01-01

Brown bears are recorded from Ireland during both the Late Pleistocene and early–mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British–Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear–polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions. PMID:23676655

Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?

PubMed

Leonard, Saoirse A; Risley, Claire L; Turvey, Samuel T

2013-08-23

Brown bears are recorded from Ireland during both the Late Pleistocene and early-mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British-Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear-polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions.

Late Quaternary megafloods from Glacial Lake Atna, Southcentral Alaska, U.S.A.

NASA Astrophysics Data System (ADS)

Wiedmer, Michael; Montgomery, David R.; Gillespie, Alan R.; Greenberg, Harvey

2010-05-01

Geomorphic, stratigraphic, geotechnical, and biogeographic evidence indicate that failure of a Pleistocene ice dam between 15.5 and 26 ka generated a megaflood from Glacial Lake Atna down the Matanuska Valley. While it has long been recognized that Lake Atna occupied ≥ 9000 km 2 of south-central Alaska's Copper River Basin, little attention has focused on the lake's discharge locations and behaviors. Digital elevation model and geomorphic analyses suggest that progressive lowering of the lake level by decanting over spillways exposed during glacial retreat led to sequential discharges down the Matanuska, Susitna, Tok, and Copper river valleys. Lake Atna's size, ˜ 50 ka duration, and sequential connection to four major drainages likely made it a regionally important late Pleistocene freshwater refugium. We estimate a catastrophic Matanuska megaflood would have released 500-1400 km 3 at a maximum rate of ≥ 3 × 10 6 m 3 s - 1 . Volumes for the other outlets ranged from 200 to 2600 km 3 and estimated maximum discharges ranged from 0.8 to 11.3 × 10 6 m 3 s - 1 , making Lake Atna a serial generator of some of the largest known freshwater megafloods.

Relative sea-level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Shennan, Ian; Bradley, Sarah L.; Edwards, Robin

2018-05-01

The new sea-level database for Britain and Ireland contains >2100 data points from 86 regions and records relative sea-level (RSL) changes over the last 20 ka and across elevations ranging from ∼+40 to -55 m. It reveals radically different patterns of RSL as we move from regions near the centre of the Celtic ice sheet at the last glacial maximum to regions near and beyond the ice limits. Validated sea-level index points and limiting data show good agreement with the broad patterns of RSL change predicted by current glacial isostatic adjustment (GIA) models. The index points show no consistent pattern of synchronous coastal advance and retreat across different regions, ∼100-500 km scale, indicating that within-estuary processes, rather than decimetre- and centennial-scale oscillations in sea level, produce major controls on the temporal pattern of horizontal shifts in coastal sedimentary environments. Comparisons between the database and GIA model predictions for multiple regions provide potentially powerful constraints on various characteristics of global GIA models, including the magnitude of MWP1A, the final deglaciation of the Laurentide ice sheet and the continued melting of Antarctica after 7 ka BP.

Atmospheric Rivers Enhanced Water Delivery to Southwestern North America at the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Lora, J. M.; Mitchell, J.; Risi, C. M.; Tripati, A. K.

2015-12-01

Proxy reconstructions of the late Pleistocene paleoclimate indicate that southwestern North America was significantly more wet at the Last Glacial Maximum (LGM; ~21 ka) than in the present. Pluvial paleolakes were abundant throughout the Great Basin and as far south as the modern Mojave Desert. The source of precipitation that fed these lakes and the role of evaporation in the hydrologic balance are debated. A leading hypothesis is increased Pacific winter storm frequency as a result of the jet stream being split or shifted south by the North American ice sheets. Alternative hypotheses include enhanced monsoonal precipitation, a re-routing of the storm track across the continent, and/or reduced evaporation. Using LGM simulations from the PMIP3 ensemble and the LMDZ general circulation model, and comparing to proxy records of LGM precipitation in the region, we find that atmospheric rivers, narrow filaments of humid tropical air, were strengthened over the eastern Pacific during glacial intervals and directed into southern California. A strengthened Aleutian Low and a weakened North Pacific High produced a mean state conducive to this strong, south-shifted atmospheric river system, which enhanced moisture delivery into the southwestern part of the Great Basin.

Southern Hemisphere climate variability forced by Northern Hemisphere ice-sheet topography

NASA Astrophysics Data System (ADS)

Jones, T. R.; Roberts, W. H. G.; Steig, E. J.; Cuffey, K. M.; Markle, B. R.; White, J. W. C.

2018-02-01

The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean-atmosphere climate dynamics. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Niño-Southern Oscillation, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.

Gradual demise of a thin southern Laurentide ice sheet recorded by Mississippi drainage.

PubMed

Wickert, Andrew D; Mitrovica, Jerry X; Williams, Carlie; Anderson, Robert S

2013-10-31

At the Last Glacial Maximum (LGM), about 21,000 years before present, land-based ice sheets held enough water to reduce global mean sea level by 130 metres. Yet after decades of study, major uncertainties remain as to the distribution of that ice. Here we test four reconstructions of North American deglacial ice-sheet history by quantitatively connecting them to high-resolution oxygen isotope (δ(18)O) records from the Gulf of Mexico using a water mixing model. For each reconstruction, we route meltwater and seasonal runoff through the time-evolving Mississippi drainage basin, which co-evolves with ice geometry and changing topography as ice loads deform the solid Earth and produce spatially variable sea level in a process known as glacial isostatic adjustment. The δ(18)O records show that the Mississippi-drained southern Laurentide ice sheet contributed only 5.4 ± 2.1 metres to global sea level rise, of which 0.66 ± 0.07 metres were released during the meltwater pulse 1A event 14,650-14,310 years before present, far less water than previously thought. In contrast, the three reconstructions based on glacial isostatic adjustment overpredict the δ(18)O-based post-LGM meltwater volume by a factor of 1.6 to 3.6. The fourth reconstruction, which is based on ice physics, has a low enough Mississippi-routed meltwater discharge to be consistent with δ(18)O constraints, but also contains the largest LGM North American ice volume. This suggests that modelling based on ice physics may be the best way of matching isotopic records while also sequestering enough water in the North American ice sheets to match the observed LGM sea level fall.

Ice-age survival of Atlantic cod: agreement between palaeoecology models and genetics

PubMed Central

Bigg, Grant R; Cunningham, Clifford W; Ottersen, Geir; Pogson, Grant H; Wadley, Martin R; Williamson, Phillip

2007-01-01

Scant scientific attention has been given to the abundance and distribution of marine biota in the face of the lower sea level, and steeper latitudinal gradient in climate, during the ice-age conditions that have dominated the past million years. Here we examine the glacial persistence of Atlantic cod (Gadus morhua) populations using two ecological-niche-models (ENM) and the first broad synthesis of multi-locus gene sequence data for this species. One ENM uses a maximum entropy approach (Maxent); the other is a new ENM for Atlantic cod, using ecophysiological parameters based on observed reproductive events rather than adult distribution. Both the ENMs were tested for present-day conditions, then used to hindcast ranges at the last glacial maximum (LGM) ca 21 kyr ago, employing climate model data. Although the LGM range of Atlantic cod was much smaller, and fragmented, both the ENMs agreed that populations should have been able to persist in suitable habitat on both sides of the Atlantic. The genetic results showed a degree of trans-Atlantic divergence consistent with genealogically continuous populations on both sides of the North Atlantic since long before the LGM, confirming the ENM results. In contrast, both the ENMs and the genetic data suggest that the Greenland G. morhua population post-dates the LGM. PMID:17999951

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

USGS Publications Warehouse

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

2006-01-01

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

Initial Results from the Deep Drilling of Lake Junin, Perú

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

A modeling approach to investigate the sensitivity of plankton phenology to global change since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Kretschmer, K.; Kucera, M.; Schulz, M.

2016-02-01

Plankton phenology is a key aspect of ecosystem dynamics. Up to now, it is not known how sensitive this parameter is to environmental perturbations and what magnitude of change is conceivable under extreme climate change scenarios. For example, one could argue that the phenology of the dominant Arctic planktonic foraminifera species Neogloboquadrina pachyderma will only shift slightly recording the more or less delayed onset of spring ocean warming. This assumption can be tested by examining the likely phenology of this species in the fossil record. Although phenology is difficult to derive directly from proxies, it can be estimated for past periods by models. Here we use an ecosystem modeling approach to investigate seasonal variations of N. pachyderma since the Last Glacial Maximum (LGM) in the North Atlantic. The model implies that the phenology of N. pachyderma during the LGM and the ensuing Heinrich Event 1 shifted by several months from the modern situation with a maximum seasonal production occurring later in the year (i.e. boreal summer). In comparison with the fossil records our model performs well in reproducing the observed abundance patterns and range shifts in the studied species during the last glacial period. Hence, the predicted large (and partly no-analog) shifts in the phenology of N. pachyderma are a plausible scenario. For instance, its maximum growth during Heinrich Event 1 in a region northeast of Newfoundland occurred during a part of the season where this species never peaks anywhere in the North Atlantic at present. Understanding the drivers of this change and knowing the potential adaptive space of phenology shifts are essential in predictions of plankton response to future global change scenarios.

A new concept for glacial geological investigations of surges, based on High-Arctic examples (Svalbard)

NASA Astrophysics Data System (ADS)

Lønne, Ida

2016-01-01

Svalbard is a key area for the investigation of glacial surges, and almost two centuries worth of field observations exists from this region. Studies have shown that the course of a surge and the associated formation of landforms are strongly influenced by basinal factors, and that the broad range of variables involved can hamper interpretations and comparisons. Based on a review of surges in Svalbard, a new concept for glacial geological investigations has been developed that combines ice-flows, ice-front movements, and morphostratigraphy. The concept is comprised of the following four elements: 1) classification based on the configuration and characteristics of the receiving basin, 2) division of the surge cycle into six stages, 3) guidelines for morphological mapping, and 4) use of an allostratigraphic approach for interpreting ice-front movements. In this context, delineation of the active phase is critical, which include the history of terminus movements, and four main categories of receiving basins are recognized. These are (A) terrestrial basins with deformable substrates, (B) terrestrial basins with poorly deformable substrates, (C) shallow water basins, and (D) deep water basins. The ice-front movement history is reconstructed by coupling information from the proglacial moraines (syn-surge), the supraglacial moraines (post-surge), and the associated traces of meltwater to the surge stages (I-VI). This approach has revealed a critical relationship between the termination of the active phase and three morphological elements, namely, the maximum ice-front position, the maximum moraine extent and the youngest proglacial moraine, which are unique for each of the basins A-D. The concept is thus a novel and more precise approach for mapping the active phase and the active phase duration, as shown by the ∼12-year long surge of Fridtjovbreen, where stage I was 30 months (inception), stage II was 54 months (ice-front advance), stage III was 12 months (stillstand), and stage IV was 48 months (retreat during active flow). The glacier has been in quiescent phase (stages V/VI) since 2002.

Reduced El Niño-Southern Oscillation during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Ford, Heather L.; Ravelo, A. Christina; Polissar, Pratigya J.

2015-01-01

El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate.

Stable water isotope behavior during the last glacial maximum: A general circulation model analysis

NASA Technical Reports Server (NTRS)

Jouzel, Jean; Koster, Randal D.; Suozzo, Robert J.; Russell, Gary L.

1994-01-01

Global water isotope geochemisty during the last glacial maximum (LGM) is simulated with an 8 deg x 10 deg atmospheric general circulation model (GCM). The simulation results suggest that the spatial delta O-18/temperature relationships observed for the present day and LGM climates are very similar. Furthermore, the temporal delta O-18/temperature relationship is similar to the present-day spatial relationship in regions for which the LGM/present-day temperature change is significant. This helps justify the standard practice of applying the latter to the interpretation of paleodata, despite the possible influence of other factors, such as changes in the evaportive sources of precipitation or in the seasonality of precipitation. The model suggests, for example, that temperature shifts inferred from ice core data may differ from the true shifts by only about 30%.

Assessing the proposed pre-last glacial maximum human occupation of North America at Coats-Hines-Litchy, Tennessee, and other sites

NASA Astrophysics Data System (ADS)

Tune, Jesse W.; Waters, Michael R.; Schmalle, Kayla A.; DeSantis, Larisa R. G.; Kamenov, George D.

2018-04-01

Genomic studies indicate that the first Pleistocene foragers who entered North America diverged from ancestral populations in Beringia sometime after the Last Glacial Maximum (LGM); however, several archaeological sites in North America have been proposed to predate the LGM. We present the results of our excavation and analysis of one such site, Coats-Hines-Litchy, Tennessee, which show that this site is a paleontological locality containing a geofact assemblage that pre-dates the LGM. Other sites in North America that purportedly predate the LGM occur in geomorphic contexts that are also conducive to the formation of geofact assemblages. As such, we propose that the reported artifacts from these sites were created by natural processes. No sites in North America currently provide credible evidence of a pre-LGM occupation.

Eocene to mid-Pliocene landscape evolution in Scandinavia inferred from offshore sediment volumes and pre-glacial topography using inverse modelling

NASA Astrophysics Data System (ADS)

Pedersen, Vivi K.; Braun, Jean; Huismans, Ritske S.

2018-02-01

The origin of high topography in Scandinavia is highly debated, both in terms of its age and the underlying mechanism for its formation. Traditionally, the current high topography is assumed to have formed by several Cenozoic (mainly Neogene) phases of surface uplift and dissection of an old peneplain surface. These same surface uplift events are suggested to explain the increased deposition observed in adjacent offshore basins on the Norwegian shelf and in the North Sea. However, more recently it has been suggested that erosion and isostatic rock uplift of existing topography may also explain the recent evolution of topography in Scandinavia. For this latter view, the increased sedimentation towards the present is assumed to be a consequence of a climate related increase in erosion. In this study we explore whether inverse modelling of landscape evolution can give new insight into Eocene to mid-Pliocene (54-4 Ma) landscape evolution in the Scandinavian region. We do this by combining a highly efficient forward-in-time landscape evolution model (FastScape) with an optimization scheme suitable for non-linear inverse problems (the neighbourhood algorithm - NA). To limit our approach to the fluvial regime, we exclude the most recent mid-Pliocene-Quaternary time period where glacial erosion processes are expected to dominate landscape evolution. The "goodness" of our landscape evolution models is evaluated using i) sediment fluxes based on decompacted offshore sediment volumes and ii) maximum pre-glacial topography from a mid-Pliocene landscape, reconstructed using geophysical relief and offshore sediment volumes from the mid-Pliocene-Quaternary. We find several tested scenarios consistent with the offshore sediment record and the maximum elevation for our reconstructed pre-glacial (mid-Pliocene) landscape reconstruction, including: I) substantial initial topography ( 2 km) at 54 Ma and no induced tectonic rock uplift, II) the combination of some initial topography ( 1.1 km) at 54 Ma and minor continued rock uplift (< 0.04 mm/yr) until 4 Ma, and III) a two-phased tectonic rock uplift of an initially low topography ( 0.1 km). However, out of these, only scenario I (no tectonic rock uplift) matches large-scale characteristics of our reconstructed pre-glacial (mid-Pliocene) topography well. Our preferred model for Eocene to mid-Pliocene landscape evolution in Scandinavia is therefore one where high topography ( 2 km) has existed throughout the time interval from 54 to 4 Ma. We do not find several phases of peneplain surface uplift necessary to explain offshore sediment volumes and large-scale topographic patterns. On the contrary, extensive peneplain dissection seems inconsistent with the low rates of erosion we infer based on the offshore sediment volumes.

Timing of lake-level changes for a deep last-glacial Lake Missoula: optical dating of the Garden Gulch area, Montana, USA

NASA Astrophysics Data System (ADS)

Smith, Larry N.; Sohbati, Reza; Buylaert, Jan-Pieter; Lian, Olav B.; Murray, Andrew; Jain, Mayank

2018-03-01

Glaciolacustrine sediments in the Clark Fork River valley at Garden Gulch, near Drummond, Montana, USA record highstand positions of the ice-dammed glacial Lake Missoula and repeated subaerial exposure. During these highstands the lake was at greater than 65% of its recognized maximum capacity. The initial lake transgression deposited a basal sand unit. Subsequent cycles of lake-level fluctuations are recorded by sequences of laminated and cross laminated silt, sand, and clay deformed by periglacial processes during intervening periods of lower lake levels. Optically stimulated luminescence (OSL) dating of quartz sand grains, using single-aliquot regenerative-dose procedures, was carried out on 17 samples. Comparison of infrared stimulated luminescence (IRSL) from K-rich feldspar to OSL from quartz for all the samples suggests that they were well bleached prior to deposition and burial. Ages for the basal sand and overlying glaciolacustrine exposure surfaces are indistinguishable within one standard deviation, and give a weighted mean age of 20.9 ± 1.3 ka (n = 11). Based on sedimentological and stratigraphic analysis we infer that the initial transgression, and at least six cycles of lake-level fluctuation, occurred over time scales of decades to ∼2 ka. Bioturbated sandy slopewash dated at 10.6 ± 0.9 ka and 11.9 ± 1.2 ka unconformably overlies the upper glaciolacustrine deposits. The uppermost sediments, above the glaciolacustrine section, are younger than the Glacier Peak tephra (13.7-13.4 cal ka B.P.), which was deposited across parts of the drained lake basin, but has not been found at Garden Gulch. Our study indicates that glacial Lake Missoula reached >65 percent of maximum capacity by about 20.9 ± 1.3 ka and either partially or completely drained twelve times from this position. Rapid lowering from the lake's highstand position due to ice-dam failure likely led to scour in the downstream portions of the glacial Lake Missoula basin and megafloods in the Channeled Scabland.

Ocean (de)oxygenation from the Last Glacial Maximum to the twenty-first century: insights from Earth System models.

PubMed

Bopp, L; Resplandy, L; Untersee, A; Le Mezo, P; Kageyama, M

2017-09-13

All Earth System models project a consistent decrease in the oxygen content of oceans for the coming decades because of ocean warming, reduced ventilation and increased stratification. But large uncertainties for these future projections of ocean deoxygenation remain for the subsurface tropical oceans where the major oxygen minimum zones are located. Here, we combine global warming projections, model-based estimates of natural short-term variability, as well as data and model estimates of the Last Glacial Maximum (LGM) ocean oxygenation to gain some insights into the major mechanisms of oxygenation changes across these different time scales. We show that the primary uncertainty on future ocean deoxygenation in the subsurface tropical oceans is in fact controlled by a robust compensation between decreasing oxygen saturation (O 2sat ) due to warming and decreasing apparent oxygen utilization (AOU) due to increased ventilation of the corresponding water masses. Modelled short-term natural variability in subsurface oxygen levels also reveals a compensation between O 2sat and AOU, controlled by the latter. Finally, using a model simulation of the LGM, reproducing data-based reconstructions of past ocean (de)oxygenation, we show that the deoxygenation trend of the subsurface ocean during deglaciation was controlled by a combination of warming-induced decreasing O 2sat and increasing AOU driven by a reduced ventilation of tropical subsurface waters.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Author(s).

Ocean (de)oxygenation from the Last Glacial Maximum to the twenty-first century: insights from Earth System models

NASA Astrophysics Data System (ADS)

Bopp, L.; Resplandy, L.; Untersee, A.; Le Mezo, P.; Kageyama, M.

2017-08-01

All Earth System models project a consistent decrease in the oxygen content of oceans for the coming decades because of ocean warming, reduced ventilation and increased stratification. But large uncertainties for these future projections of ocean deoxygenation remain for the subsurface tropical oceans where the major oxygen minimum zones are located. Here, we combine global warming projections, model-based estimates of natural short-term variability, as well as data and model estimates of the Last Glacial Maximum (LGM) ocean oxygenation to gain some insights into the major mechanisms of oxygenation changes across these different time scales. We show that the primary uncertainty on future ocean deoxygenation in the subsurface tropical oceans is in fact controlled by a robust compensation between decreasing oxygen saturation (O2sat) due to warming and decreasing apparent oxygen utilization (AOU) due to increased ventilation of the corresponding water masses. Modelled short-term natural variability in subsurface oxygen levels also reveals a compensation between O2sat and AOU, controlled by the latter. Finally, using a model simulation of the LGM, reproducing data-based reconstructions of past ocean (de)oxygenation, we show that the deoxygenation trend of the subsurface ocean during deglaciation was controlled by a combination of warming-induced decreasing O2sat and increasing AOU driven by a reduced ventilation of tropical subsurface waters. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

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.

Post-Glacial and Paleo-Environmental History of the West Coast of Vancouver Island

NASA Astrophysics Data System (ADS)

Dallimore, A.; Enkin, R. J.

2005-12-01

Annually laminated sediments in anoxic fjords are potentially ideal paleoclimate recorders, particularly once proxy measurements for atmospheric, oceanographic and sedimentological conditions have been calibrated. On the west coast of Canada, these sediments also record the changing environment as glaciers retreated from this area about 12 ka y BP. In Effingham Inlet, a 40 m core taken from the French ship the Marion Dufresne as part of the international IMAGES/PAGES program, gives evidence of an isolation basin at maximum glacial isostatic rebound and lowest paleo-sea level followed by eustatic sea level rise about 10 ka y BP. The Late Pleistocene record also marks dramatic changes in glacial sedimentary source and transport. Excellent chronological control is provided by complementary yet independent dating methods including radiocarbon dates on both plants and shells, identification of the Mazama Ash, varve counting and paleomagnetic, paleosecular variation correlations in the lower, pro-glacial section of the core which does not contain organic material. Paleoenvironmental evidence from this core provides information on immediate post-glacial conditions along the coast and rapid climatic changes throughout the Holocene, with implications for the possibility of early human migration routes and refugia.

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

NASA Astrophysics Data System (ADS)

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

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

Hypsometry and the distribution of high-alpine lakes in the European Alps

NASA Astrophysics Data System (ADS)

Prasicek, Günther; Otto, Jan-Christoph; Buckel, Johannes; Keuschnig, Markus

2017-04-01

Climate change strongly affects alpine landscapes. Cold-climate processes shape the terrain in a typical way and ice-free overdeepenings in cirques and glacial valleys as well as different types of moraines favor the formation of lakes. These water bodies act as sediment sinks and high-alpine water storage but may also favor outburst and flooding events. Glacier retreat worldwide is associated with an increasing number and size of high-alpine lakes which implies a concurrent expansion of sediment retention and natural hazard potential. Rising temperatures are regarded to be the major cause for this development, but other factors such as the distribution of area over elevation and glacier erosional and depositional dynamics may play an important role as well. While models of ice flow and glacial erosion are employed to understand the impact of glaciers on mountain landscapes, comprehensive datasets and analyses on the distribution of existing high-alpine lakes are lacking. In this study we present an exhaustive database of natural lakes in the European Alps and analyze lake distribution with respect to hypsometry. We find that the distribution of lake number and lake area over elevation only weakly coincides with hypsometry. Unsurprisingly, largest lakes are often tectonically influenced and located at the fringe of the mountain range and in prominent inter-montane basins. With increasing elevation, however, the number of lakes, lake area and total area decrease until a local minimum is reached around the equilibrium line latitude (ELA) of the last glacial maximum (LGM). Above the LGM ELA, total area further decreases, but lake number and area increase again. A local maximum in lake area coincides with an absolute maximum in lake number between the ELAs of the LGM and the little ice age around 2500 m. We conclude that glacial erosional and depositional dynamics control the distribution and size of high-alpine lakes and thus demand for exceptional attention when predicting future lake development.

The role of historical and contemporary processes on phylogeographic structure and genetic diversity in the Northern Cardinal, Cardinalis cardinalis

PubMed Central

2011-01-01

Background Earth history events such as climate change are believed to have played a major role in shaping patterns of genetic structure and diversity in species. However, there is a lag between the time of historical events and the collection of present-day samples that are used to infer contemporary population structure. During this lag phase contemporary processes such as dispersal or non-random mating can erase or reinforce population differences generated by historical events. In this study we evaluate the role of both historical and contemporary processes on the phylogeography of a widespread North American songbird, the Northern Cardinal, Cardinalis cardinalis. Results Phylogenetic analysis revealed deep mtDNA structure with six lineages across the species' range. Ecological niche models supported the same geographic breaks revealed by the mtDNA. A paleoecological niche model for the Last Glacial Maximum indicated that cardinals underwent a dramatic range reduction in eastern North America, whereas their ranges were more stable in México. In eastern North America cardinals expanded out of glacial refugia, but we found no signature of decreased genetic diversity in areas colonized after the Last Glacial Maximum. Present-day demographic data suggested that population growth across the expansion cline is positively correlated with latitude. We propose that there was no loss of genetic diversity in areas colonized after the Last Glacial Maximum because recent high-levels of gene flow across the region have homogenized genetic diversity in eastern North America. Conclusion We show that both deep historical events as well as demographic processes that occurred following these events are critical in shaping genetic pattern and diversity in C. cardinalis. The general implication of our results is that patterns of genetic diversity are best understood when information on species history, ecology, and demography are considered simultaneously. PMID:21599972

Glacial Extent During the Late Early Miocene (18-16 Ma): Results from the ANDRILL AND-2A Drillcore, Southern McMurdo Sound Project, Antarctica

NASA Astrophysics Data System (ADS)

Pekar, Stephen; Koss, Howard; Passchier, Sandra

2010-05-01

Litho- and sequence stratigraphic results from the ANtarctic Geological DRILLing Program (ANDRILL) Southern McMurdo Sound (SMS) AND-2A drill hole indicate that glacial conditions varied widely in the western Ross Sea between the two isotopic Mi events (i.e., inferred glacioeustasy) Mi1b (17.7 Ma) and Mi2 (16.2 Ma). Most of this interval had not been previously recovered from the Antarctic continental margin providing the first opportunity to use direct evidence in understanding the evolution of the ice sheet during this time. During the 2007 austral spring/summer, the SMS drill hole cored 1138 meters of sediments, with ~98% recovery. The section between 700 and 400 mbsf has high sedimentation rates (180 m/ my) and excellent age control, based on radiometric ages and magnetostratigraphy, providing an exceptional record of glacial advances and retreats deposited in a shallow water environment in Antarctica between 18 and 16 Ma. Approximately twenty sequences within this interval were identified. Each sequence is bounded by distinct surfaces characterized by a pronounced shift in lithofacies, with typically more ice distal facies below (e.g., characteristic of open marine to iceberg influenced depositional environments), and more proximal facies above (e.g., sandy massive diamictites and conglomerates). Lithofacies and grain size analysis suggest that these cycles are controlled by a combination of water depth and ice proximity. A surface at 648.74 mbsf contains a hiatus that spans 18.0-17.6 Ma and correlates to the isotopic event Mi1b. This surface separates a prolonged interval of glacial advance over this site below, based on extensive sediment deformation and more ice distal environments above. A sharp surface at 436.13 mbsf (~16.3 Ma), interpreted to represent glacial maximum extent, contains a possible short hiatus and is correlated to the Mi2 event. In contrast, although the lithofacies indicates a glacial advance, evidence of ice grounding at 436 mbsf is equivocal, suggesting a smaller advance than for the one at the Mi1b event. Between these two ice advances, the lithofacies indicates generally more distal ice environments and therefore less ice volume and correlates to the early Miocene Climatic Optimum (17.2-16.4 Ma).

Quaternary glacial, lacustrine, and fluvial interactions in the western Noatak basin, Northwest Alaska

USGS Publications Warehouse

Hamilton, T.D.

2001-01-01

The 130 km long Noatak basin is surrounded by mountains of the western Brooks Range. Middle and late Pleistocene glaciers flowing southeast into the basin dammed a succession of proglacial lakes defined by shorelines, outlet channels and upper limits of wave erosion. More than 60 bluffs along the Noatak River and its principal tributaries expose glacial and glaciolacustrine sediments that exhibit cut-and-fill relationships with interglacial and interstadial river-channel and floodplain deposits. This report focuses on the western Noatak basin, where high bluffs created by deep postglacial erosion record four major glacial advances. During the Cutler advance, a floating ice tongue terminated in a large proglacial lake that filled the Noatak basin. The retreating glacier abandoned a trough along the valley center that subsequently filled with about 40m of sediment during several younger glaciations and probably two major interglacial episodes. Alluvium that formed near the beginning of the younger interglaciation contains the 140,000 yr old Old Crow tephra. The subsequent closely spaced Okak and Makpik advances are clearly younger than the maximum of the last interglaciation, but they preceded a middle Wisconsin (36-30 ka) nonglacial interval in the Noatak basin. The Okak advance terminated in an extensive lake, whereas glaciers of the Makpik and the subsequent Anisak advances flowed into much narrower lakes that filled only the basin center. The Anisak advance, bracketed by radiocarbon ages of about 35 and 13.6 ka, represents the Last Glacial Maximum (LGM) in the western Noatak basin. Correlations with the oldest and youngest glacial deposits of the central Brooks Range are clear, but relationships to events of intermediate age are more tenuous. Early Pleistocene and older glacial advances from the central Brooks Range must have filled the Noatak basin and overflowed northward through Howard Pass. A younger glacial advance, of inferred middle Pleistoscene (Sagavanirktok River) age, extended down the Noatak valley into the basin center, but its deposits are deeply buried beneath the basin floor and must be older than the Cutler moraine. The Cutler advance may have been synchronous with the older of two advances of Itkillik I age in the Atongarak Creek area, but other evidence indicates that the Okak-Makpik moraine succession more likely was synchronous with the two Atongarak Creek moraines. Radiocarbon ages, surface morphology, soil and weathering profiles, and lake-level history all support correlation of the last (Anisak) major glacial advance in the western basin with the Douglas Creek moraine farther east and with Itkillik II (late Wisconsin) glaciation of the central Brooks Range. ?? 2000 Elsevier Science Ltd.

Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hu, Rong; Piotrowski, Alexander M.; Bostock, Helen C.; Crowhurst, Simon; Rennie, Victoria

2016-08-01

The deep Pacific Ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales. The circulation of the deep Pacific during the Last Glacial Maximum (LGM), however, is not well understood. Neodymium (Nd) isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography. In this study, we present Nd isotope compositions (εNd) of planktonic foraminifera for the Holocene and the LGM obtained from 55 new sites widely distributed in the Pacific Ocean. The Holocene planktonic foraminiferal εNd results agree with the proximal seawater data, indicating that they provide a reliable record of modern bottom water Nd isotopes in the deep Pacific. There is a good correlation between foraminiferal εNd and seawater phosphate concentrations (R2 = 0.80), but poorer correlation with silicate (R2 = 0.37). Our interpretation is that the radiogenic Nd isotope is added to the deep open Pacific through particle release from the upper ocean during deep water mass advection and aging. The data thus also imply the Nd isotopes in the Pacific are not likely to be controlled by silicate cycling. In the North Pacific, the glacial Nd isotopic compositions are similar to the Holocene values, indicating that the Nd isotope composition of North Pacific Deep Water (NPDW) remained constant (-3.5 to -4). During the LGM, the southwest Pacific cores throughout the water column show higher εNd corroborating previous studies which suggested a reduced inflow of North Atlantic Deep Water to the Pacific. However, the western equatorial Pacific deep water does not record a corresponding radiogenic excursion, implying reduced radiogenic boundary inputs during the LGM probably due to a shorter duration of seawater-particle interaction in a stronger glacial deep boundary current. A significant negative glacial εNd excursion is evident in mid-depth (1-2 km) cores of the eastern equatorial Pacific (EEP) which may suggest a stronger influence of NPDW return flow to the core sites and decreased local input in the EEP. Taken together, our Nd records do not support a dynamically slower glacial Pacific overturning circulation, and imply that the increased carbon inventory of Pacific deep water might be due to poor high latitude air-sea exchange and increased biological pump efficiency in glacial times.

Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

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

Kokorowski, H D; Anderson, P M; Sletten, R S

Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicatesmore » no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.« less

Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska

USGS Publications Warehouse

Zander, Paul D.; Kaufman, Darrell S.; Kuehn, Stephen C.; Wallace, Kristi L.; Anderson, R. Scott

2013-01-01

Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin. Three intervals of an advanced Sheridan Glacier are recorded in the Cabin Lake sediments during the late Holocene: 1110–1180, 1260–1540 and 1610–1780 CE. The sedimentary sequence also contains the first five reported tephra deposits from the Copper River delta region, and their geochemical signatures suggest that the sources are the Cook Inlet volcanoes Redoubt, Augustine and Crater Peak, and possibly Mt Churchill in the Wrangell Volcanic field.

A Chronologic Dual-Hemisphere Approach to the Last Glacial Termination from the Southern Alps of New Zealand and the Altai Mountains of Western Mongolia

NASA Astrophysics Data System (ADS)

Strand, P.; Putnam, A. E.; Schaefer, J. M.; Denton, G.; Barrell, D.; Putnam, D.; Schwartz, R.; Sambuu, O.; Radue, M. J.; Lindsay, B. J.; Stevens, J.

2017-12-01

Understanding the processes that drove the last glacial termination in the tropics and mid-latitudes is a major unresolved problem in paleoclimate. The most recent glacial to interglacial transition represents the last great global warming and the last time CO2 rose by a substantial amount before the industrial period. Determining the speed of this warming will help refine the global climate system sensitivity to CO2 and will place ongoing global warming into a paleoclimatic context. Here, we test possible drivers of the last glacial termination by comparing chronologies of mountain glaciers, which are highly sensitive to changes in atmospheric temperature, in the middle latitudes of both polar hemispheres. The dating of glacier landforms, such as moraine ridges constructed along glacier margins, affords quantitative insight into past climate conditions. We present 10Be surface-exposure chronologies and glacial geomorphologic maps of mountain glacier recession since the Last Glacial Maximum in the Southern Alps of New Zealand (44°S, 170°E) and in the Altai Mountains of western Mongolia (49°N, 88°E). On the basis of these chronologies from opposing hemispheres, we evaluate the relative roles of rising atmospheric CO2, local insolation forcing, and ocean-atmosphere reorganizations in driving the global warming that ended the last ice age.

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

NASA Astrophysics Data System (ADS)

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

2010-10-01

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

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

PubMed

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

2016-01-01

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

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

PubMed Central

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

2016-01-01

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

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

DOE PAGES

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

2015-05-19

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

Cosmogenic exposure-age chronologies of Pinedale and Bull Lake glaciations in greater Yellowstone and the Teton Range, USA

USGS Publications Warehouse

Licciardi, J.M.; Pierce, K.L.

2008-01-01

We have obtained 69 new cosmogenic 10Be surface exposure ages from boulders on moraines deposited by glaciers of the greater Yellowstone glacial system and Teton Range during the middle and late Pleistocene. These new data, combined with 43 previously obtained 3He and 10Be ages from deposits of the northern Yellowstone outlet glacier, establish a high-resolution chronology for the Yellowstone-Teton mountain glacier complexes. Boulders deposited at the southern limit of the penultimate ice advance of the Yellowstone glacial system yield a mean age of 136??13 10Be ka and oldest ages of ???151-157 10Be ka. These ages support a correlation with the Bull Lake of West Yellowstone, with the type Bull Lake of the Wind River Range, and with Marine Isotope Stage (MIS) 6. End moraines marking the maximum Pinedale positions of outlet glaciers around the periphery of the Yellowstone glacial system range in age from 18.8??0.9 to 16.5??1.4 10Be ka, and possibly as young as 14.6??0.7 10Be ka, suggesting differences in response times of the various ice-cap source regions. Moreover, all dated Pinedale terminal moraines in the greater Yellowstone glacial system post-date the Pinedale maximum in the Wind River Range by ???4-6 kyr, indicating a significant phase relationship between glacial maxima in these adjacent ranges. Boulders on the outermost set and an inner set of Pinedale end moraines enclosing Jenny Lake on the eastern Teton front yield mean ages of 14.6??0.7 and 13.5??1.1 10Be ka, respectively. The outer Jenny Lake moraines are partially buried by outwash from ice on the Yellowstone Plateau, hence their age indicates a major standstill of an expanded valley glacier in the Teton Range prior to the Younger Dryas, followed closely by deglaciation of the Yellowstone Plateau. These new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the Rocky Mountains during the Pleistocene. ?? 2008 Elsevier Ltd. All rights reserved.

Seasonality in the Western Mediterranean During the Last Glacial From Paired Oxygen Isotopes and Mg/Ca in Limpet Shells

NASA Astrophysics Data System (ADS)

Ferguson, J. E.; Henderson, G. M.; Fa, D.; Finlayson, C.

2008-12-01

Molluscs have shown great potential to act as seasonal-resolution archives of sea-surface temperatures (SST) at mid to high latitudes, outside the range of tropical surface corals. Seasonal resolution climate records from higher latitudes are important to allow investigation of the role of seasonality in controlling mean climate on diverse timescales, and of the evolution of climate systems such as the North Atlantic Oscillation. Long sequences of intertidal mollusc shells are difficult to find due to sea level fluctuations over glacial- interglacial periods. This study makes use of Patella shells collected by Neanderthals and humans and transported inland to caves on Gibraltar over at least the last 120 kyrs. Some 30 fossil Patella shells were selected from several hundred excavated from Gorham's and Vanguard Caves at Gibraltar. Oxygen isotope analysis of micromilled samples of modern Patella shells from the Gibraltar coastline demonstrate that the shells accurately record absolute SSTs and capture more than 80% of the full seasonal range. Analysis of fossil Patella shells, dated using 14C, provides records of the change in absolute SST and seasonality during the last glacial. Paired Mg/Ca ratios of micromilled samples in modern Patella shells follow a consistent positive relationship with SST providing an independent paleothermometer, analogous with coral Sr/Ca. Applying this Mg/Ca-SST relationship to fossil Patella shells allows the independent reconstruction of the absolute values and range of SSTs and the reconstruction of seawater δ18O for the western Mediterranean. Results show a cooling of glacial summer SSTs from 36 kyr BP to the LGM with maximum cooling of glacial summer SSTs of 7.5 °C relative to modern. In contrast, winter SSTs show greater variability on millennial timescales with a maximum cooling of up to 10 °C. SST seasonality is therefore extended due to greater winter cooling but SST seasonality is highly variable as a result of large fluctuation in the extent of winter cooling. These results contrast with GCM model estimates of SST values and seasonality during the glacial.

Seasonally Distinct Reconstructions of Northern Alaskan Temperature Variability Since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Longo, W. M.; Crowther, J.; Daniels, W.; Russell, J. M.; Giblin, A. E.; Morrill, C.; Zhang, X.; Wang, X.; Huang, Y.

2015-12-01

Paleoclimate reconstructions have provided little consensus on how continental temperatures in Eastern Beringia changed from the Last Glacial Maximum (LGM) to the present. Reconstructions show regional differences in LGM severity, the timing of deglacial warming, and Holocene temperature variability. Currently, arctic temperatures are increasing at the fastest rates on the planet, highlighting the need to identify the sensitivities of arctic systems to various climate forcings. This cannot be done without resolving the complex climate history of Eastern Beringia. Here, we present two new organic geochemical temperature reconstructions from Lake E5, north central Alaska that span the LGM, last glacial termination and Holocene. The proxies (alkenones and brGDGTs) record seasonally distinct temperatures, allowing for the attribution of different forcings to each proxy. The alkenone-based UK37 reconstruction records spring/early summer lake temperatures and indicates a 4 oC abrupt warming at 13.1 ka and a relatively warm late Holocene, which peaks at 2.4 ka and exhibits a cooling trend from 2.4 to 0.1 ka. The brGDGT reconstruction is calibrated to mean annual air temperature and interpreted here as exhibiting a strong warm season bias. BrGDGTs show an abrupt 4.5 oC warming at 14 ka, and show evidence for an early Holocene Thermal Maximum (HTM), which cools by 3 oC after 8.4 ka. Because UK37 temperatures do not exhibit an early HTM, we hypothesize that summer insolation had a minimal effect on spring/early summer lake temperatures. Instead, the UK37 reconstruction agrees with sea ice and sea surface temperature reconstructions from the Beaufort and Chukchi Seas and northeast Pacific Ocean. We hypothesize that forcings associated with sea ice concentration and changes in atmospheric circulation had stronger affects on spring/early summer lake temperatures and we present modern observational data in support of this hypothesis. By contrast, the summer-biased brGDGT reconstruction suggests a strong and relatively direct temperature response to summer insolation forcing. Together, these records suggest that both internal and external forcings significantly affected LGM to present temperature variability in Eastern Beringia, with different seasonal biases.

Repeated megafloods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000 years

NASA Astrophysics Data System (ADS)

Margold, Martin; Jansen, John D.; Codilean, Alexandru T.; Preusser, Frank; Gurinov, Artem L.; Fujioka, Toshiyuki; Fink, David

2018-05-01

Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km3 megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0-6.5 million m3s-1, mean flow depths of 120-150 m, and average flow velocities up to 21 m s-1.

Population demographic history of a temperate shrub, Rhododendron weyrichii (Ericaceae), on continental islands of Japan and South Korea.

PubMed

Yoichi, Watanabe; Tamaki, Ichiro; Sakaguchi, Shota; Song, Jong-Suk; Yamamoto, Shin-Ichi; Tomaru, Nobuhiro

2016-12-01

Continental islands provide opportunities for testing the effects of isolation and migration on genetic variation in plant populations. In characteristic of continental islands is that the geographic connections between these islands, which are currently distinguished by seaways, have experienced fluctuations caused by sea-level changes due to climate oscillations during the Quaternary. Plant populations on the islands have migrated between these islands via the exposed seafloors or been isolated. Here, we examined the demographic history of a temperate shrub, Rhododendron weyrichii , which is distributed in the southwestern parts of the Japanese archipelago and on an island of South Korea, using statistical phylogeographic approaches based on the DNA sequences of two chloroplast and eight nuclear loci in samples analyzed from 18 populations on eight continental islands, and palaeodistribution modeling. Time estimates for four island populations indicate that the durations of vicariance history are different between these populations, and these events have continued since the last glacial or may have predated the last glacial. The constancy or expansion of population sizes on the Japanese islands, and in contrast a bottleneck in population size on the Korean island Jeju, suggests that these islands may have provided different conditions for sustaining populations. The result of palaeodistribution modeling indicates that the longitudinal range of the species as a whole has not changed greatly since the last glacial maximum. These results indicate that exposed seafloors during the glacial period formed both effective and ineffective migration corridors. These findings may shed light on the effects of seafloor exposure on the migration of plants distributed across continental islands.

Rethinking refugia: Tree topology, divergence dates, and demographic history trace the distribution of the endangered Plymouth gentian (Sabatia kennedyana) from the Pleistocene glaciation to present day.

PubMed

Suarez-Gonzalez, Adriana; Sutton, Jolene T; Trant, Andrew J; Zamlynny, Elena; Good, Sara V

2015-04-01

Molecular population genetics is a powerful tool to infer how species responded to past environmental change. In the northern hemisphere, interest is increasing in how species responded to changes in ice coverage and temperature during the last glaciation maximum (LGM, between 18000-21000 yr ago) with a common assumption that glacial refugia were located at the southern edge of a species range. We reconstructed the glacial and postglacial phylogeography of Sabatia kennedyana, a member of the Atlantic Coastal Plains Flora with a current distribution from Nova Scotia (NS) to South Carolina, using both cpDNA and nuclear markers. We also examined clinal variation in morphological traits, in particular relative investment in asexual vs sexual growth. We find strong evidence that the species did not reside in southern glacial refugia, but rather in primary glacial refugia off the exposed continental shelf extending from Cape Cod and that this area was responsible for the founding of modern populations across the range from Nova Scotia (NS) to the United States. Additionally, based on the finding of higher cpDNA diversity and older cpDNA lineages in NS, we propose that multiple founder events occurred in NS, while only a single lineage gave rise to current populations in the United States. By understanding how S. kennedyana responded to past shifts in climate and by identifying areas of high genetic diversity in the northern range edge, we discuss the potential response of the species to future climate change scenarios. © 2015 Botanical Society of America, Inc.

Little Ice Age mapping as a tool for identifying hazard in the paraglacial environment: The case study of Trentino (Eastern Italian Alps)

NASA Astrophysics Data System (ADS)

Zanoner, Thomas; Carton, Alberto; Seppi, Roberto; Carturan, Luca; Baroni, Carlo; Salvatore, Maria Cristina; Zumiani, Matteo

2017-10-01

The Little Ice Age (LIA) is a well-recognized climatic event during which the glaciers in the Alps advanced and reached their maximum Holocene extent. During their retreat following the LIA, the glaciers left large areas of loose or poorly consolidated glacial deposits in their forelands, which are subject to paraglacial reworking and may represent potential hazards for human infrastructures. In this study, we present a regional scale mapping of the LIA and post-LIA glacial deposits and a reconstruction of the maximum LIA extents of glaciers in the same area. This work is motivated by a local law requiring the classification of areas subject to natural hazards in Trentino (Italian Alps). Results highlight that glaciers shrunk by 63% from the LIA maximum, leaving 30 km2 of unconsolidated deposits, which are subject to geomorphic paraglacial processes. Potentially hazardous consequences can occur, in particular, during high-magnitude instantaneous events, causing debris and mud flows, mass wasting from debris-covered ice, and floods from small moraine-dammed lakes.

Reconstructing temperatures in the Maritime Alps, Italy, since the Last Glacial Maximum using cosmogenic noble gas paleothermometry

NASA Astrophysics Data System (ADS)

Tremblay, Marissa; Spagnolo, Matteo; Ribolini, Adriano; Shuster, David

2016-04-01

The Gesso Valley, located in the southwestern-most, Maritime portion of the European Alps, contains an exceptionally well-preserved record of glacial advances during the late Pleistocene and Holocene. Detailed geomorphic mapping, geochronology of glacial deposits, and glacier reconstructions indicate that glaciers in this Mediterranean region responded to millennial scale climate variability differently than glaciers in the interior of the European Alps. This suggests that the Mediterranean Sea somehow modulated the climate of this region. However, since glaciers respond to changes in temperature and precipitation, both variables were potentially influenced by proximity to the Sea. To disentangle the competing effects of temperature and precipitation changes on glacier size, we are constraining past temperature variations in the Gesso Valley since the Last Glacial Maximum (LGM) using cosmogenic noble gas paleothermometry. The cosmogenic noble gases 3He and 21Ne experience diffusive loss from common minerals like quartz and feldspars at Earth surface temperatures. Cosmogenic noble gas paleothermometry utilizes this open-system behavior to quantitatively constrain thermal histories of rocks during exposure to cosmic ray particles at the Earth's surface. We will present measurements of cosmogenic 3He in quartz sampled from moraines in the Gesso Valley with LGM, Bühl stadial, and Younger Dryas ages. With these 3He measurements and experimental data quantifying the diffusion kinetics of 3He in quartz, we will provide a preliminary temperature reconstruction for the Gesso Valley since the LGM. Future work on samples from younger moraines in the valley system will be used to fill in details of the more recent temperature history.

Mitogenomes from Two Uncommon Haplogroups Mark Late Glacial/Postglacial Expansions from the Near East and Neolithic Dispersals within Europe

PubMed Central

Olivieri, Anna; Pala, Maria; Gandini, Francesca; Kashani, Baharak Hooshiar; Perego, Ugo A.; Woodward, Scott R.; Grugni, Viola; Battaglia, Vincenza; Semino, Ornella; Achilli, Alessandro; Richards, Martin B.; Torroni, Antonio

2013-01-01

The current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ∼19 ky ago, and the beginning of the first main warming phase, ∼15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe. PMID:23936216

The impact of Pleistocene climate change on an ancient arctic–alpine plant: multiple lineages of disparate history in Oxyria digyna

PubMed Central

Allen, Geraldine A; Marr, Kendrick L; McCormick, Laurie J; Hebda, Richard J

2012-01-01

The ranges of arctic–alpine species have shifted extensively with Pleistocene climate changes and glaciations. Using sequence data from the trnH-psbA and trnT-trnL chloroplast DNA spacer regions, we investigated the phylogeography of the widespread, ancient (>3 million years) arctic–alpine plant Oxyria digyna (Polygonaceae). We identified 45 haplotypes and six highly divergent major lineages; estimated ages of these lineages (time to most recent common ancestor, TMRCA) ranged from ∼0.5 to 2.5 million years. One lineage is widespread in the arctic, a second is restricted to the southern Rocky Mountains of the western United States, and a third was found only in the Himalayan and Altai regions of Asia. Three other lineages are widespread in western North America, where they overlap extensively. The high genetic diversity and the presence of divergent major cpDNA lineages within Oxyria digyna reflect its age and suggest that it was widespread during much of its history. The distributions of individual lineages indicate repeated spread of Oxyria digyna through North America over multiple glacial cycles. During the Last Glacial Maximum it persisted in multiple refugia in western North America, including Beringia, south of the continental ice, and within the northern limits of the Cordilleran ice sheet. Our data contribute to a growing body of evidence that arctic–alpine species have migrated from different source regions over multiple glacial cycles and that cryptic refugia contributed to persistence through the Last Glacial Maximum. PMID:22822441

Geology and hydrology of the Elk River, Minnesota, nuclear-reactor site

USGS Publications Warehouse

Norvitch, Ralph F.; Schneider, Robert; Godfrey, Richard G.

1963-01-01

The Elk River, Minn., nuclear-reactor site is on the east bluff of the Mississippi River about 35 miles northwest of Minneapolis and St. Paul. The area is underlain by about 70 to 180 feet of glacial drift, including at the top as much as 120 feet of outwash deposits (valley train) of the glacial Mississippi River. The underlying Cambrian bedrock consists of marine sedimentary formations including artesian sandstone aquifers. A hypothetically spilled liquid at the reactor site could follow one or both of two courses, thus: (1) It could flow over the land surface and through an artificial drainage system to the river in a matter of minutes; (2) part or nearly all of it could seep downward to the water table and then move laterally to the river. The time required might range from a few weeks to a year, or perhaps more. The St. Paul and Minneapolis water-supply intakes, 21 and 25 miles downstream, respectively, are the most critical points to be considered in the event of an accidental spill. Based on streamflow and velocity data for the Mississippi River near Anoka, the time required for the maximum concentration of a contaminant to travel from the reactor site to the St. Paul intake was computed to be about 8 hours, at the median annual maximum daily discharge. For this discharge, the maximum concentration at the intake would be about 0.0026 microcurie per cubic foot for the release of 1 curie of activity into the river near the reactor site.

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

NASA Astrophysics Data System (ADS)

Slee, Adrian; Shulmeister, James; Clark, Doug

2014-05-01

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

Differences in Bacterial Diversity and Communities Between Glacial Snow and Glacial Soil on the Chongce Ice Cap, West Kunlun Mountains.

PubMed

Yang, Guang Li; Hou, Shu Gui; Le Baoge, Ri; Li, Zhi Guo; Xu, Hao; Liu, Ya Ping; Du, Wen Tao; Liu, Yong Qin

2016-11-04

A detailed understanding of microbial ecology in different supraglacial habitats is important due to the unprecedented speed of glacier retreat. Differences in bacterial diversity and community structure between glacial snow and glacial soil on the Chongce Ice Cap were assessed using 454 pyrosequencing. Based on rarefaction curves, Chao1, ACE, and Shannon indices, we found that bacterial diversity in glacial snow was lower than that in glacial soil. Principal coordinate analysis (PCoA) and heatmap analysis indicated that there were major differences in bacterial communities between glacial snow and glacial soil. Most bacteria were different between the two habitats; however, there were some common bacteria shared between glacial snow and glacial soil. Some rare or functional bacterial resources were also present in the Chongce Ice Cap. These findings provide a preliminary understanding of the shifts in bacterial diversity and communities from glacial snow to glacial soil after the melting and inflow of glacial snow into glacial soil.

The influence of climate on peatland extent in Western Siberia since the Last Glacial Maximum

PubMed Central

Alexandrov, G. A.; Brovkin, V. A.; Kleinen, T.

2016-01-01

Boreal and subarctic peatlands are an important dynamical component of the earth system. They are sensitive to climate change, and could either continue to serve as a carbon sink or become a carbon source. Climatic thresholds for switching peatlands from sink to source are not well defined, and therefore, incorporating peatlands into Earth system models is a challenging task. Here we introduce a climatic index, warm precipitation excess, to delineate the potential geographic distribution of boreal peatlands for a given climate and landscape morphology. This allows us to explain the present-day distribution of peatlands in Western Siberia, their absence during the Last Glacial Maximum, their expansion during the mid-Holocene, and to form a working hypothesis about the trend to peatland degradation in the southern taiga belt of Western Siberia under an RCP 8.5 scenario for the projected climate in year 2100. PMID:27095029

The influence of climate on peatland extent in Western Siberia since the Last Glacial Maximum.

PubMed

Alexandrov, G A; Brovkin, V A; Kleinen, T

2016-04-20

Boreal and subarctic peatlands are an important dynamical component of the earth system. They are sensitive to climate change, and could either continue to serve as a carbon sink or become a carbon source. Climatic thresholds for switching peatlands from sink to source are not well defined, and therefore, incorporating peatlands into Earth system models is a challenging task. Here we introduce a climatic index, warm precipitation excess, to delineate the potential geographic distribution of boreal peatlands for a given climate and landscape morphology. This allows us to explain the present-day distribution of peatlands in Western Siberia, their absence during the Last Glacial Maximum, their expansion during the mid-Holocene, and to form a working hypothesis about the trend to peatland degradation in the southern taiga belt of Western Siberia under an RCP 8.5 scenario for the projected climate in year 2100.

Reply to comment received from J. C. Knight regarding "Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet" by Barth et al. (2016), Quaternary Science Reviews 141, 85-93

NASA Astrophysics Data System (ADS)

Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

2016-10-01

We concluded that our new 10Be chronology records onset of retreat of a cirque glacier within the Alohart basin of southwestern Ireland 24.5 ± 1.4 ka, placing limiting constraints on reconstructions of the Irish Ice Sheet (IIS) and Kerry-Cork Ice Cap (KCIC) during the Last Glacial Maximum (LGM) (Barth et al., 2016). Knight (2016) raises two main arguments against our interpretation: (1) the glacier in the Alohart basin was not a cirque glacier, but instead a southern-sourced ice tongue from the KCIC overtopping the MacGillycuddy's Reeks, and (2) that the boulders we sampled for 10Be exposure dating were derived from supraglacial rockfall rather than transported subglacially, experienced nuclide inheritance, and are thus too old. In the following, we address both of these arguments.

Fossils reject climate change as the cause of extinction of Caribbean bats

PubMed Central

Soto-Centeno, J. Angel; Steadman, David W.

2015-01-01

We combined novel radiocarbon dates of bat fossils with time-scaled ecological niche models (ENM) to study bat extinctions in the Caribbean. Radiocarbon-dated fossils show that late Quaternary losses of bat populations took place during the late Holocene (<4 ka) rather than late Pleistocene (>10 ka). All bat radiocarbon dates from Abaco (Bahamas) that represent extirpated populations are younger than 4 ka. We include data on six bat species, three of which are Caribbean endemics, and include nectarivores as well as insectivores. Climate-based ENMs from the Last Glacial Maximum to the present reflect overall stability in distributions, with suitable climatic habitat being present over time. In the absence of radiocarbon dates, bat extinctions had been presumed to take place during the last glacial-interglacial transition (ca. 10 ka). Now we see that extirpation of bats on these tropical islands is more complex than previously thought and primarily postdates the major climate changes that took place during the late Pleistocene-Holocene transition. PMID:25610991

Fossils reject climate change as the cause of extinction of Caribbean bats.

PubMed

Soto-Centeno, J Angel; Steadman, David W

2015-01-22

We combined novel radiocarbon dates of bat fossils with time-scaled ecological niche models (ENM) to study bat extinctions in the Caribbean. Radiocarbon-dated fossils show that late Quaternary losses of bat populations took place during the late Holocene (<4 ka) rather than late Pleistocene (>10 ka). All bat radiocarbon dates from Abaco (Bahamas) that represent extirpated populations are younger than 4 ka. We include data on six bat species, three of which are Caribbean endemics, and include nectarivores as well as insectivores. Climate-based ENMs from the Last Glacial Maximum to the present reflect overall stability in distributions, with suitable climatic habitat being present over time. In the absence of radiocarbon dates, bat extinctions had been presumed to take place during the last glacial-interglacial transition (ca. 10 ka). Now we see that extirpation of bats on these tropical islands is more complex than previously thought and primarily postdates the major climate changes that took place during the late Pleistocene-Holocene transition.

Post-glacial redistribution and shifts in productivity of giant kelp forests

PubMed Central

Graham, Michael H.; Kinlan, Brian P.; Grosberg, Richard K.

2010-01-01

Quaternary glacial–interglacial cycles create lasting biogeographic, demographic and genetic effects on ecosystems, yet the ecological effects of ice ages on benthic marine communities are unknown. We analysed long-term datasets to develop a niche-based model of southern Californian giant kelp (Macrocystis pyrifera) forest distribution as a function of oceanography and geomorphology, and synthesized palaeo-oceanographic records to show that late Quaternary climate change probably drove high millennial variability in the distribution and productivity of this foundation species. Our predictions suggest that kelp forest biomass increased up to threefold from the glacial maximum to the mid-Holocene, then rapidly declined by 40–70 per cent to present levels. The peak in kelp forest productivity would have coincided with the earliest coastal archaeological sites in the New World. Similar late Quaternary changes in kelp forest distribution and productivity probably occurred in coastal upwelling systems along active continental margins worldwide, which would have resulted in complex shifts in the relative productivity of terrestrial and marine components of coastal ecosystems. PMID:19846450

The vegetation cover of New Zealand at the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Newnham, Rewi; McGlone, Matt; Moar, Neville; Wilmshurst, Janet; Vandergoes, Marcus

2013-08-01

A new reconstruction of the vegetation cover for New Zealand at the Last Glacial Maximum (LGM) is presented, based primarily on a database of 66 pollen site records and a more limited range of plant macrofossil and coleopteran records. Extensive forest is evident only from Auckland northwards. Conifer-broadleaf forest similar to that in the region today, but with Agathis australis scarce, persisted in the far north, whilst Nothofagus trees and a range of shrub taxa characterised the more open forests elsewhere in Northland. Survival of Nothofagus-dominated forest in coastal and exposed continental shelf locations to the southwest of Auckland and northwestern South Island is also indicated. Beyond these regions, vegetation cover comprised shrubland- and grassland-dominant communities, with the latter more prominent in eastern areas, to the south and presumably at higher altitudes. Nevertheless the survival of forest trees is indicated unambiguously in most regions apart from the eastern South Island. Thus the concept of 'micro glacial forest refugia' in New Zealand remains supported by this latest glacial vegetation reconstruction and we draw possible parallels with the developing but contentious concept of 'northern cryptic refugia' in Europe. Recent assertions that pollen and beetle reconstructions of the New Zealand LGM vegetation patterns diverge significantly are not supported by this analysis. Rather, the two proxies are readily reconciled if the term 'woody' as indicated by coleoptera is not restricted to tall forest trees but extended to the widespread woody shrub and small tree elements of the New Zealand flora. Regional distinctions in the LGM vegetation reconstruction concur broadly with the contemporary vegetation pattern, suggesting that, along with temperature depression and likely drier growing conditions, a zonal circulation regime with prominent southern westerly winds was important at 21 ka, as it is today. Pollen-climate modelling of the extent of temperature change is limited by the lack of LGM analogues and the relatively small number of cool climate indicator taxa in the modern (predeforestation) pollen training set. Nevertheless, a group of 17 sites which display a >90% match with the modern training set, and therefore should provide more reliable estimates, give an average reconstructed mean annual temperature depression of -6.01 ± 1.91 °C using the partial least squares method. This value, towards the upper end of the range of most independently derived estimates, accords with recent reconstructions of LGM temperature depression derived from glacial modelling.

Influence of glacial ice sheets on the Atlantic meridional overturning circulation through surface wind change

NASA Astrophysics Data System (ADS)

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

2018-04-01

Coupled modeling studies have recently shown that the existence of the glacial ice sheets intensifies the Atlantic meridional overturning circulation (AMOC). However, most models show a strong AMOC in their simulations of the Last Glacial Maximum (LGM), which is biased compared to reconstructions that indicate both a weaker and stronger AMOC during the LGM. Therefore, a detailed investigation of the mechanism behind this intensification of the AMOC is important for a better understanding of the glacial climate and the LGM AMOC. Here, various numerical simulations are conducted to focus on the effect of wind changes due to glacial ice sheets on the AMOC and the crucial region where the wind modifies the AMOC. First, from atmospheric general circulation model experiments, the effect of glacial ice sheets on the surface wind is evaluated. Second, from ocean general circulation model experiments, the influence of the wind stress change on the AMOC is evaluated by applying wind stress anomalies regionally or at different magnitudes as a boundary condition. These experiments demonstrate that glacial ice sheets intensify the AMOC through an increase in the wind stress at the North Atlantic mid-latitudes, which is induced by the North American ice sheet. This intensification of the AMOC is caused by the increased oceanic horizontal and vertical transport of salt, while the change in sea ice transport has an opposite, though minor, effect. Experiments further show that the Eurasian ice sheet intensifies the AMOC by directly affecting the deep-water formation in the Norwegian Sea.

Late Pleistocene glacial chronology of the Retezat Mts, Southern Carpathians, using 10Be exposure ages

NASA Astrophysics Data System (ADS)

Ruszkiczay-Rüdiger, Zsófia; Kern, Zoltán; Urdea, Petru; Braucher, Régis; Madarász, Balázs; Schimmelpfennig, Irene

2015-04-01

Our knowledge on the timing of glacial advances in the Southern Carpathians is limited. Recently, some attempts have been made to develop an improved temporal framework for the glaciations of the region using cosmogenic 10Be exposure dating. However, glacial chronology of the Romanian Carpathians remains contradictory. E.g. the timing of the maximum ice advance appears to be asynchronous within the area and also with other dated glacial events in Europe. Main objective of our study is to utilize cosmogenic in situ produced 10Be dating to disentangle the contradictions of the Southern Carpathian Late Pleistocene glacial chronology. Firstly, previously published 10Be data are recalculated in accordance with the new half-life, standardization and production rate of 10Be. The recalculated 10Be exposure ages of the second largest (M2) moraines in the Retezat Mts. appear to be ca. 19-24% older than exposure ages calculated by Reuther et al. (2007, Quat. Int. 164-165, 151-169). This contradicts the earlier conclusions suggesting post LGM age of M2 glacial advance and suggests that M2 moraines can be connected to the end of the LGM with final stabilization possibly at the beginning of the Late Glacial. We emphasize that it is ambiguous to correlate directly the exposure-dated glacier chronologies with millennial scale climate changes due to uncertainties in sample collection and in computation of exposure ages from measured nuclide concentrations. New 10Be samples were collected in order to determine the 10Be exposure age of moraines outside the most prominent generation (M2) including the largest and oldest moraine (M1) and the landforms connected to the smallest ice advances (M4), which remained undated so far. The new exposure ages of M2 moraines are well in harmony with the recalculated ages of Reuther at al. (2007). 10Be exposure age of boulders on the smallest moraine suggest that the last glaciers disappeared in the area during the Late Glacial, indicating no glaciation during the Younger Dryas and Holocene. Previous works, based on geomorphologic analogies and pedological properties suggested that the M1 ice advance was older than LGM, and possibly occurred during the MIS4. Our 10Be exposure dating provided LGM ages for boulders on the M1 side moraine. It is question of further research whether these ages show the time when the glacier abandoned the moraine or they only indicate an LGM erosional event affecting an older moraine. If we accept the LGM age of maximum ice extent (M1), our 10Be exposure age data enables the calculation of a mean glacier retreat rate of 1.3 m/a for the period between M1 and M4 (21.4 to 13.6ka). Alternatively, considering only the oldest 10Be exposure age of the M2 moraine, the M2 to M4 (20.2-13.6ka) glacier retreat rate was slightly lower: 1.1 m/a. Our research was supported by the OTKA PD83610, by the MTA-CNRS cooperation (NKM-96/2014), by the Bolyai Scholarship, and by the 'Lendület' program of the HAS (LP2012-27/2012). The 10Be measurements were performed at the ASTER AMS national facility (CEREGE, Aix en Provence, France).

Flowline Modeling of the Quelccaya Icecap to Constrain Tropical Climate Fluctuations During the Holocene

NASA Astrophysics Data System (ADS)

Malone, A.; Pierrehumbert, R.; Insel, N.; Lowell, T. V.; Kelly, M. A.

2012-12-01

The response of the tropics to climate forcing mechanisms is poorly understood, and there is limited data regarding past tropical climate fluctuations. Past climate fluctuations often leave a detectable record of glacial response in the location of moraines. Computer reconstructions of glacial length variations can thus help constrain past climate fluctuations. Chronology and position data for Holocene moraines are available for the Quelccaya Ice Cap in the Peruvian Andes. The Quelccaya Ice Cap is the equatorial region's largest glaciated area, and given its size and the available data, it is an ideal location at which to use a computer glacier model to reconstruct past glacial extents and constrain past tropical climate fluctuations. We can reproduce the current length and shape of the glacier in the Huancane Valley of the Quelccaya Ice Cap using a 1-D mountain glacier flowline model with an orographic precipitation scheme, an energy balance model for the ablation scheme, and reasonable modern climate conditions. We conduct two experiments. First, we determine the amount of cooling necessary to reproduce the observed Holocene moraine locations by holding the precipitation profile constant and varying the mean sea surface temperature (SST) values. Second, we determine the amount of precipitation increase necessary to reproduce the observed moraine locations by holding the mean SST value constant and varying the maximum precipitation values. We find that the glacier's length is highly sensitive to changes in temperature while only weakly sensitive to changes in precipitation. In the constant precipitation experiment, a decrease in the mean SST of only 0.35 °C can reproduce the nearest Holocene moraine downslope from the current glacier terminus and a decrease in the mean SST of only 1.43 °C can reproduce the furthest Holocene moraine downslope from the current terminus. In the experiment with constant SST, the necessary increase in maximum precipitation is much greater. An increase in the maximum precipitation of 30% is necessary to reproduce the nearest Holocene moraine and an increase in the maximum precipitation of 130% is necessary to reproduce the furthest Holocene moraine. Our results provide a range of values for the mean SST and maximum precipitation that can reproduce the location of Holocene glacial moraines, constraining some of the climate fluctuations in the tropics during the Holocene. These constraints can be used to test hypotheses for climate forcing mechanisms during Holocene events such as the Little Ice Age and possibly provide insight into future tropical climate fluctuations given current and future forcing mechanisms.

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

NASA Astrophysics Data System (ADS)

Lucchi, M. Ricci

2008-12-01

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

The salinity, temperature, and delta18O of the glacial deep ocean.

PubMed

Adkins, Jess F; McIntyre, Katherine; Schrag, Daniel P

2002-11-29

We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level.

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.

Fire and vegetation shifts in the Americas at the vanguard of Paleoindian migration

NASA Astrophysics Data System (ADS)

Pinter, Nicholas; Fiedel, Stuart; Keeley, Jon E.

2011-02-01

Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.

Extra-Mediterranean refugia: The rule and not the exception?

PubMed Central

2012-01-01

Some decades ago, biogeographers distinguished three major faunal types of high importance for Europe: (i) Mediterranean elements with exclusive glacial survival in the Mediterranean refugia, (ii) Siberian elements with glacial refugia in the eastern Palearctic and only postglacial expansion to Europe and (iii) arctic and/or alpine elements with large zonal distributions in the periglacial areas and postglacial retreat to the North and/or into the high mountain systems. Genetic analyses have unravelled numerous additional refugia both of continental and Mediterranean species, thus strongly modifying the biogeographical view of Europe. This modified notion is particularly true for the so-called Siberian species, which in many cases have not immigrated into Europe during the postglacial period, but most likely have survived the last, or even several glacial phases, in extra-Mediterranean refugia in some climatically favourable but geographically limited areas of southern Central and Eastern Europe. Recently, genetic analyses revealed that typical Mediterranean species have also survived the Last Glacial Maximum in cryptic northern refugia (e.g. in the Carpathians or even north of the Alps) in addition to their Mediterranean refuge areas. PMID:22953783

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

NASA Astrophysics Data System (ADS)

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

2005-12-01

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

Impact of climate changes during the last 5 million years on groundwater in basement aquifers.

PubMed

Aquilina, Luc; Vergnaud-Ayraud, Virginie; Les Landes, Antoine Armandine; Pauwels, Hélène; Davy, Philippe; Pételet-Giraud, Emmanuelle; Labasque, Thierry; Roques, Clément; Chatton, Eliot; Bour, Olivier; Ben Maamar, Sarah; Dufresne, Alexis; Khaska, Mahmoud; Le Gal La Salle, Corinne; Barbecot, Florent

2015-09-22

Climate change is thought to have major effects on groundwater resources. There is however a limited knowledge of the impacts of past climate changes such as warm or glacial periods on groundwater although marine or glacial fluids may have circulated in basements during these periods. Geochemical investigations of groundwater at shallow depth (80-400 m) in the Armorican basement (western France) revealed three major phases of evolution: (1) Mio-Pliocene transgressions led to marine water introduction in the whole rock porosity through density and then diffusion processes, (2) intensive and rapid recharge after the glacial maximum down to several hundred meters depths, (3) a present-day regime of groundwater circulation limited to shallow depth. This work identifies important constraints regarding the mechanisms responsible for both marine and glacial fluid migrations and their preservation within a basement. It defines the first clear time scales of these processes and thus provides a unique case for understanding the effects of climate changes on hydrogeology in basements. It reveals that glacial water is supplied in significant amounts to deep aquifers even in permafrosted zones. It also emphasizes the vulnerability of modern groundwater hydrosystems to climate change as groundwater active aquifers is restricted to shallow depths.

Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean

PubMed Central

Glasser, Neil F.; Jansson, Krister N.; Duller, Geoffrey A. T.; Singarayer, Joy; Holloway, Max; Harrison, Stephan

2016-01-01

Large freshwater lakes formed in North America and Europe during deglaciation following the Last Glacial Maximum. Rapid drainage of these lakes into the Oceans resulted in abrupt perturbations in climate, including the Younger Dryas and 8.2 kyr cooling events. In the mid-latitudes of the Southern Hemisphere major glacial lakes also formed and drained during deglaciation but little is known about the magnitude, organization and timing of these drainage events and their effect on regional climate. We use 16 new single-grain optically stimulated luminescence (OSL) dates to define three stages of rapid glacial lake drainage in the Lago General Carrera/Lago Buenos Aires and Lago Cohrane/Pueyrredón basins of Patagonia and provide the first assessment of the effects of lake drainage on the Pacific Ocean. Lake drainage occurred between 13 and 8 kyr ago and was initially gradual eastward into the Atlantic, then subsequently reorganized westward into the Pacific as new drainage routes opened up during Patagonian Ice Sheet deglaciation. Coupled ocean-atmosphere model experiments using HadCM3 with an imposed freshwater surface “hosing” to simulate glacial lake drainage suggest that a negative salinity anomaly was advected south around Cape Horn, resulting in brief but significant impacts on coastal ocean vertical mixing and regional climate. PMID:26869235

Glacial changes in warm pool climate dominated by shelf exposure and ice sheet albedo

NASA Astrophysics Data System (ADS)

Di Nezio, P. N.; Tierney, J. E.; Otto-Bliesner, B. L.; Timmermann, A.; Bhattacharya, T.; Brady, E. C.; Rosenbloom, N. A.

2017-12-01

The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool (IPWP) are unclear. We addressed this issue combining model simulations and paleoclimate reconstructions of the Last Glacial Maximum (LGM). Two drivers - the exposure of tropical shelves due to lower sea level and a monsoonal response to ice sheet albedo - explain the proxy-inferred patterns of hydroclimate change. Shelf exposure influences IPWP climate by weakening the ascending branch of the Walker circulation. This response is amplified by coupled interactions akin to the Bjerknes feedback involving a stronger sea-surface temperature (SST) gradient along the equatorial Indian Ocean (IO). Ice sheet albedo enhances the import of cold, dry air into the tropics, weakening the Afro-Asian monsoon system. This "ventilation" mechanism alters temperature contrasts between the Arabian Sea and surrounding land leading to further monsoon weakening. Additional simulations show that the altered SST patterns associated with these responses are essential for explaining the proxy-inferred changes. Together our results show that ice sheets are a first order driver of tropical climate on glacial-interglacial timescales. While glacial climates are not a straightforward analogue for the future, our finding of an active Bjerknes feedback deserves further attention in the context of future climate projections.

Extent and timing of paleoglaciation in the Kanas Valley, Altai Mountains, China, based on remote sensing, field investigations and multiple dating methods

NASA Astrophysics Data System (ADS)

Zhang, Wei; Harbor, Jon; Cui, Zhijiu; Liu, Liang; Liu, Beibei; Fu, Yanjing; Shi, Yuanhuang; Gribenski, Natacha; Blomdin, Robin; Stroeven, Arjen; Caffee, Marc; Jansson, Krister

2014-05-01

Reconstructions of the timing and extent of past glaciation provide key constraints for paleoclimate and numerical modeling of past glacier behavior. As part of the multinational Central Asian Paleoglaciology Project we are reconstructing the timing and extent of past glaciation along and across a series of mountain ranges in central Asia using consistent methods for mapping, field investigations and numerical dating. Here we report on new findings for the Kanas Valley in northwest China, a large glaciated valley system on the south side of the Altai Mountains. Previous studies have concluded that the Kanas Valley has been shaped by a series of major glacial advances that produced overdeepened basins, a U-shaped valley cross profile, and extensive glacial and glaciofluvial deposits. Existing Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) dating results suggest major glaciation in the Kanas Valley during Marine Oxygen Isotope Stages (MIS) 3, 5, and 6, but very limited MIS 2 glaciation. Limited MIS 2 glaciation has also been suggested for other parts of central Asia, and this contrasts with extensive MIS 2 glaciation in Europe and North America. Field studies in 2013 provided new evidence for the highest elevation extent of glaciation in the Kanas Valley in the vicinity of the 20-km long Lake Kanas, with the upper limit of distinct erratics on the valley sidewalls indicating past ice thicknesses here up to 1000 m. Upper limits of erratics extending from Lake Kanas to the mapped maximum down-valley extent of glaciation suggest an ice surface slope of 1.8 degrees for the lower half of the paleoglacier in the Kanas Valley, assuming that all the erratics were deposited at the same time. Systematic sampling of glacial erratics, basal till, terminal moraines, glacially eroded bedrock, and glaciofluvial deposits provided material that is being used for cosmogenic radionuclide, OSL and ESR dating of the glacial chronology, and for dating intercomparisons.

Flow cytometry, microsatellites and niche models reveal the origins and geographical structure of Alnus glutinosa populations in Europe

PubMed Central

Mandák, Bohumil; Vít, Petr; Krak, Karol; Trávníček, Pavel; Havrdová, Alena; Hadincová, Věroslava; Zákravský, Petr; Jarolímová, Vlasta; Bacles, Cecile Fanny Emilie; Douda, Jan

2016-01-01

Background and Aims Polyploidy in plants has been studied extensively. In many groups, two or more cytotypes represent separate biological entities with distinct distributions, histories and ecology. This study examines the distribution and origins of cytotypes of Alnus glutinosa in Europe, North Africa and western Asia. Methods A combined approach was used involving flow cytometry and microsatellite analysis of 12 loci in 2200 plants from 209 populations combined with species distribution modelling using MIROC and CCSM climatic models, in order to analyse (1) ploidy and genetic variation, (2) the origin of tetraploid A. glutinosa, considering A. incana as a putative parent, and (3) past distributions of the species. Key Results The occurrence of tetraploid populations of A. glutinosa in Europe is determined for the first time. The distribution of tetraploids is far from random, forming two geographically well-delimited clusters located in the Iberian Peninsula and the Dinaric Alps. Based on microsatellite analysis, both tetraploid clusters are probably of autopolyploid origin, with no indication that A. incana was involved in their evolutionary history. A projection of the MIROC distribution model into the Last Glacial Maximum (LGM) showed that (1) populations occurring in the Iberian Peninsula and North Africa were probably interconnected during the LGM and (2) populations occurring in the Dinaric Alps did not exist throughout the last glacial periods, having retreated southwards into lowland areas of the Balkan Peninsula. Conclusions Newly discovered tetraploid populations are situated in the putative main glacial refugia, and neither of them was likely to have been involved in the colonization of central and northern Europe after glacial withdrawal. This could mean that neither the Iberian Peninsula nor the western part of the Balkan Peninsula served as effective refugial areas for northward post-glacial expansion of A. glutinosa. PMID:26467247

Tracking Extra Tropical Cyclones to Explore how the Jet Stream Shifted During The Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Garrett, H.

2016-12-01

The behavior of the jet stream during the last glacial maximum (LGM 21ka) has been the focus of multiple studies but remains highly debated. Proxy data shows that during this time in the United States, the northwest was drier than modern conditions and the southwest was wetter than modern conditions. To explain this there are two competing hypothesis, one which suggests that the jet stream shifted uniformly south and the other which suggests a stronger jet that split shifting both north and south. For this study we used TECA, to reanalyze model out-put, looking at the frequency and patterns of Extra Tropical Cyclones (ETC's), which have been found to be steered by the jet stream. We used the CCSM4 model based on its agreement with proxy data, and compared data from both the LGM and pre-industrial time periods. Initial results show a dramatic shift of ETC's north by about 10º-15º degrees and a decrease in frequency compared to pre-industrial conditions, coupled with a less pronounced southward shift of 5º-10º degrees.This evidence supports the idea that the jet stream split during the LGM. A stronger understanding of jet stream behavior will help to improve future models and prediction capabilities to prepare for hydro-climate change in drought sensitive areas.

The Bossons glacier protects Europe's summit from erosion

NASA Astrophysics Data System (ADS)

Godon, C.; Mugnier, J. L.; Fallourd, R.; Paquette, J. L.; Pohl, A.; Buoncristiani, J. F.

2013-08-01

The contrasting efficiency of erosion beneath cold glacier ice, beneath temperate glacier ice, and on ice-free mountain slopes is one of the key parameters in the development of relief during glacial periods. Detrital geochronology has been applied to the subglacial streams of the north face of the Mont-Blanc massif in order to estimate the efficiency of erosional processes there. Lithologically this area is composed of granite intruded at ~303 Ma within an older polymetamorphic complex. We use macroscopic features (on ~10,000 clasts) and U-Pb dating of zircon (~500 grains) to establish the provenance of the sediment transported by the glacier and its subglacial streams. The lithology of sediment collected from the surface and the base of the glacier is compared with the distribution of bedrock sources. The analysis of this distribution takes into account the glacier's surface flow lines, the surface areas beneath temperate and cold ice above and below the Equilibrium Line Altitude (ELA), and the extent of the watersheds of the three subglacial meltwater stream outlets located at altitudes of 2300 m, 1760 m and 1450 m. Comparison of the proportions of granite and metamorphics in these samples indicates that (1) glacial transport does not mix the clasts derived from subglacial erosion with the clasts derived from supraglacial deposition, except in the lower part of the ice tongue where supraglacial streams and moulins transfer the supraglacial load to the base of the glacier; (2) the glacial erosion rate beneath the tongue is lower than the erosion rate in adjacent non-glaciated areas; and (3) glacial erosion beneath cold ice is at least 16 times less efficient than erosion beneath temperate ice. The low rates of subglacial erosion on the north face of the Mont-Blanc massif mean that its glaciers are protecting "the roof of Europe" from erosion. A long-term effect of this might be a rise in the maximum altitude of the Alps.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Phylogenetic assemblage structure of North American trees is more strongly shaped by glacial-interglacial climate variability in gymnosperms than in angiosperms.

PubMed

Ma, Ziyu; Sandel, Brody; Svenning, Jens-Christian

2016-05-01

How fast does biodiversity respond to climate change? The relationship of past and current climate with phylogenetic assemblage structure helps us to understand this question. Studies of angiosperm tree diversity in North America have already suggested effects of current water-energy balance and tropical niche conservatism. However, the role of glacial-interglacial climate variability remains to be determined, and little is known about any of these relationships for gymnosperms. Moreover, phylogenetic endemism, the concentration of unique lineages in restricted ranges, may also be related to glacial-interglacial climate variability and needs more attention. We used a refined phylogeny of both angiosperms and gymnosperms to map phylogenetic diversity, clustering and endemism of North American trees in 100-km grid cells, and climate change velocity since Last Glacial Maximum together with postglacial accessibility to recolonization to quantify glacial-interglacial climate variability. We found: (1) Current climate is the dominant factor explaining the overall patterns, with more clustered angiosperm assemblages toward lower temperature, consistent with tropical niche conservatism. (2) Long-term climate stability is associated with higher angiosperm endemism, while higher postglacial accessibility is linked to to more phylogenetic clustering and endemism in gymnosperms. (3) Factors linked to glacial-interglacial climate change have stronger effects on gymnosperms than on angiosperms. These results suggest that paleoclimate legacies supplement current climate in shaping phylogenetic patterns in North American trees, and especially so for gymnosperms.

Proglacial hydrology in the tropical Andes: lessons from the Cordillera Blanca, Peru (Invited)

NASA Astrophysics Data System (ADS)

McKenzie, J. M.; Mark, B. G.; Baraer, M.

2009-12-01

Understanding the complexities of tropical Andean hydrology is critical for managing modern water resources and interpreting paleohydrologic records. Glaciers are the most visible component of these systems, responding to global climate change and acting as critical hydrologic reservoirs. Tropical Andean glaciers are undergoing rapid retreat with complex impacts on the downstream hydrology. Groundwater is also an important component of the Andean regional hydrologic system, but its contribution is difficult to assess due to remote site access, minimal baseline data, and lack of continuous historical discharge and precipitation measurements. We have synthesized hydrochemical data from synoptically sampled glacial melt water, groundwater, precipitation, and stream discharge collected intermittently between 1998 and July 2008 throughout the Callejon de Huaylas, a 5000 km2 watershed that drains the western side of the Cordillera Blanca in northern Perú. Our data from 2004 to 2006 show systematic annual shifts in the isotopic ratios (δ18O and δ2H) of river water, indicating an increase in glacial melt water input, and we are able to use these changes across the Cordillera Blanca to estimate an average increase of 1.6 (± 1.1) % in the specific discharge of the glacierized basins. Enhanced total stream discharge in more glacierized catchments (>20% glacier area) is demonstrated by a significant positive trend in a 43-year discharge anomaly record. Our hydrochemical basin characterization method (HBCM) uses chemical mass balance mixing to quantify the contribution of glacial melt water, groundwater, and surface runoff to streams for different valleys and nested watersheds in the Callejon de Huaylas. The Yanamarey basin (7% glaciated) has been observed since 1998 and the HBCM results show good agreement with measured stream discharge (maximum R2 of 0.99) for monthly cumulative values. These results suggest that for most of the studied years groundwater is the main contributor (median value = 59%) to basin outflow during the dry season and also that it is subject to large flux variations. The groundwater system appears to have two flow components with 3- and 18-to-36- month residence times. The pro-glacial area in the Callejon de Huaylas has extensive long, relatively low-relief valleys that connect to the main Rio Santa Valley. We have assessed groundwater contributions to river outflow using HBCM from four of these valleys with differing geomorphic features (e.g., lakes, wetlands, glacial cover) and bedrock lithology, and find that there is a connection between increasing glacial cover and decreasing relative groundwater contributions. The groundwater is stored and flows through the heterogeneous unconsolidated valley fill materials (e.g., glacial-lacustrine and landslide deposits) deposited since the local last glacial maximum. The results from this study have important implications for interpreting high resolution paleohydrologic records from Andean glacial valleys. Groundwater is a critical component of the hydrologic system, in particular for high elevation watersheds, and the resulting outflow from these basins is already partially time-integrated due to groundwater mixing and storage.

Response of spatial vegetation distribution in China to climate changes since the Last Glacial Maximum (LGM)

PubMed Central

Wang, Siyang; Xu, Xiaoting; Shrestha, Nawal; Zimmermann, Niklaus E.; Tang, Zhiyao; Wang, Zhiheng

2017-01-01

Analyzing how climate change affects vegetation distribution is one of the central issues of global change ecology as this has important implications for the carbon budget of terrestrial vegetation. Mapping vegetation distribution under historical climate scenarios is essential for understanding the response of vegetation distribution to future climatic changes. The reconstructions of palaeovegetation based on pollen data provide a useful method to understand the relationship between climate and vegetation distribution. However, this method is limited in time and space. Here, using species distribution model (SDM) approaches, we explored the climatic determinants of contemporary vegetation distribution and reconstructed the distribution of Chinese vegetation during the Last Glacial Maximum (LGM, 18,000 14C yr BP) and Middle-Holocene (MH, 6000 14C yr BP). The dynamics of vegetation distribution since the LGM reconstructed by SDMs were largely consistent with those based on pollen data, suggesting that the SDM approach is a useful tool for studying historical vegetation dynamics and its response to climate change across time and space. Comparison between the modeled contemporary potential natural vegetation distribution and the observed contemporary distribution suggests that temperate deciduous forests, subtropical evergreen broadleaf forests, temperate deciduous shrublands and temperate steppe have low range fillings and are strongly influenced by human activities. In general, the Tibetan Plateau, North and Northeast China, and the areas near the 30°N in Central and Southeast China appeared to have experienced the highest turnover in vegetation due to climate change from the LGM to the present. PMID:28426780

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Paleoceanographic conditions at approximately 20 and 70 ka recorded in Kikaithyris hanzawai (Brachiopoda) shells

NASA Astrophysics Data System (ADS)

Takizawa, Mamoru; Takayanagi, Hideko; Yamamoto, Koshi; Abe, Osamu; Sasaki, Keiichi; Iryu, Yasufumi

2017-10-01

The δ13C and δ18O values of fossil brachiopod shells have been widely used as paleoenvironmental proxies. In this study, we investigated intrashell and intraspecific variations in the isotopic and minor element concentrations of well-preserved shells of the brachiopod Kikaithyris hanzawai (Yabe) from the last glacial period (∼20 ka [Last Glacial Maximum; LGM] and ∼70 ka [Marine Isotope Stage 4; MIS4]), collected in the Central Ryukyus, and used these data to estimate the paleoceanographic conditions (seawater temperature, concentration of dissolved inorganic carbon [DIC], and δ13C value of DIC [δ13CDIC]). The δ13C and δ18O profiles along the maximum growth axis, obtained from the inner shell surface, show three distinct intervals, corresponding to changes in shell morphology. These results suggest that the bulk isotopic compositions of brachiopods with complex shell morphologies are unsuitable for paleoenvironmental reconstructions. Nevertheless, there exists a specific shell portion with relatively small intrashell and intraspecific variations. The past seawater temperatures derived from the δ18O values of this portion are consistent with the alkenone- and planktic foraminiferal Mg/Ca-based past seawater temperatures reported in previous studies. The past δ13CDIC values estimated from the δ13C values of the specific shell portion are within the range of the past δ13CDIC values calculated from known atmospheric and oceanographic parameters. The past DIC concentrations reconstructed from the brachiopod-based δ13CDIC values are lower than the present concentrations in the East China Sea, which can be explained by low partial pressure of CO2 during the last glacial period. These results indicate that the δ13C and δ18O values obtained from K. hanzawai shells are potential paleoenvironmental indicators. The intrashell and intraspecific variations in the K. hanzawai shells are different for each minor element. Some anomalously high Mn and Fe concentrations in the shells are probably caused by metabolic factor(s), not by meteoric diagenesis. This suggests that the minor element concentrations are useful but not perfect for distinguishing diagenetically altered and unaltered portions of the shells of K. hanzawai in the studied succession.

Marine record of late quaternary glacial-interglacial fluctuations in the Ross Sea and evidence for rapid, episodic sea level change due to marine ice sheet collapse

NASA Technical Reports Server (NTRS)

Anderson, John B.

1991-01-01

Some of the questions to be addressed by SeaRISE include: (1) what was the configuration of the West Antarctic ice sheet during the last glacial maximum; (2) What is its configuration during a glacial minimum; and (3) has it, or any marine ice sheet, undergone episodic rapid mass wasting. These questions are addressed in terms of what is known about the history of the marine ice sheet, specifically in Ross Sea, and what further studies are required to resolve these problems. A second question concerns the extent to which disintegration of marine ice sheets may result in rises in sea level that are episodic in nature and extremely rapid, as suggested by several glaciologists. Evidence that rapid, episodic sea level changes have occurred during the Holocene is also reviewed.

Forest contraction in north equatorial Southeast Asia during the Last Glacial Period

PubMed Central

Wurster, Christopher M.; Bird, Michael I.; Bull, Ian D.; Creed, Frances; Bryant, Charlotte; Dungait, Jennifer A. J.; Paz, Victor

2010-01-01

Today, insular Southeast Asia is important for both its remarkably rich biodiversity and globally significant roles in atmospheric and oceanic circulation. Despite the fundamental importance of environmental history for diversity and conservation, there is little primary evidence concerning the nature of vegetation in north equatorial Southeast Asia during the Last Glacial Period (LGP). As a result, even the general distribution of vegetation during the Last Glacial Maximum is debated. Here we show, using the stable carbon isotope composition of ancient cave guano profiles, that there was a substantial forest contraction during the LGP on both peninsular Malaysia and Palawan, while rainforest was maintained in northern Borneo. These results directly support rainforest “refugia” hypotheses and provide evidence that environmental barriers likely reduced genetic mixing between Borneo and Sumatra flora and fauna. Moreover, it sheds light on possible early human dispersal events. PMID:20660748

Pollen-based continental climate reconstructions at 6 and 21 ka: a global synthesis

USGS Publications Warehouse

Bartlein, P.J.; Harrison, S.P.; Brewer, Sandra; Connor, S.; Davis, B.A.S.; Gajewski, K.; Guiot, J.; Harrison-Prentice, T. I.; Henderson, A.; Peyron, O.; Prentice, I.C.; Scholze, M.; Seppa, H.; Shuman, B.; Sugita, S.; Thompson, R.S.; Viau, A.E.; Williams, J.; Wu, H.

2010-01-01

Subfossil pollen and plant macrofossil data derived from 14C-dated sediment profiles can provide quantitative information on glacial and interglacial climates. The data allow climate variables related to growing-season warmth, winter cold, and plant-available moisture to be reconstructed. Continental-scale reconstructions have been made for the mid-Holocene (MH, around 6 ka) and Last Glacial Maximum (LGM, around 21 ka), allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change. The synthesis of the available MH and LGM climate reconstructions and their uncertainties, obtained using modern-analogue, regression and model-inversion techniques, is presented for four temperature variables and two moisture variables. Reconstructions of the same variables based on surface-pollen assemblages are shown to be accurate and unbiased. Reconstructed LGM and MH climate anomaly patterns are coherent, consistent between variables, and robust with respect to the choice of technique. They support a conceptual model of the controls of Late Quaternary climate change whereby the first-order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance.

Influence of external forcings on abrupt millennial-scale climate changes: a statistical modelling study

NASA Astrophysics Data System (ADS)

Mitsui, Takahito; Crucifix, Michel

2017-04-01

The last glacial period was punctuated by a series of abrupt climate shifts, the so-called Dansgaard-Oeschger (DO) events. The frequency of DO events varied in time, supposedly because of changes in background climate conditions. Here, the influence of external forcings on DO events is investigated with statistical modelling. We assume two types of simple stochastic dynamical systems models (double-well potential-type and oscillator-type), forced by the northern hemisphere summer insolation change and/or the global ice volume change. The model parameters are estimated by using the maximum likelihood method with the NGRIP Ca^{2+} record. The stochastic oscillator model with at least the ice volume forcing reproduces well the sample autocorrelation function of the record and the frequency changes of warming transitions in the last glacial period across MISs 2, 3, and 4. The model performance is improved with the additional insolation forcing. The BIC scores also suggest that the ice volume forcing is relatively more important than the insolation forcing, though the strength of evidence depends on the model assumption. Finally, we simulate the average number of warming transitions in the past four glacial periods, assuming the model can be extended beyond the last glacial, and compare the result with an Iberian margin sea-surface temperature (SST) record (Martrat et al. in Science 317(5837): 502-507, 2007). The simulation result supports the previous observation that abrupt millennial-scale climate changes in the penultimate glacial (MIS 6) are less frequent than in the last glacial (MISs 2-4). On the other hand, it suggests that the number of abrupt millennial-scale climate changes in older glacial periods (MISs 6, 8, and 10) might be larger than inferred from the SST record.

Glacial conditions in the Red Sea

NASA Astrophysics Data System (ADS)

Rohling, Eelco J.

1994-10-01

In this paper, results from previous studies on planktonic foraminifera, δ18O, and global sea level are combined to discuss climatic conditions in the Red Sea during the last glacial maximum (18,000 B.P.). First, the influence of 120-m sea level lowering on the exchange transport through the strait of Bab-el-Mandab is considered. This strait is the only natural connection of the Red Sea to the open ocean. Next, glacial Red Sea outflow salinity is estimated (about 48 parts per thousand) from the foraminiferal record. Combined, these results yield an estimate of the glacial net water deficit, which appears to have been quite similar to the present (about 2 m yr-1). Finally, budget calculation of δ18O fluxes suggests that the glacial δ18O value of evaporation was about 50% of the present value. This is considered to have resulted from substantially increased mean wind speeds over the glacial Red Sea, which would have caused a rapid drop in the kinematic fractionation factor for 18O. The sensitivity of the calculated values for water deficit and isotopic fractionation to the various assumptions and estimates is evaluated in the discussion. Improvents are to be expected especially through research on the glacial salinity contrast between the Red Sea and Gulf of Aden. It is argued, however, that such future improvement will likely result in a worsening of the isotopic discrepancy, thus increasing the need for an additional mechanism that influenced fractionation (such as mean wind speed). This study demonstrates the need for caution when calculating paleosalinities from δ18O records under the assumption that the modern S∶δ18O relation has remained constant through time. Previously overlooked factors, such as mean wind speed, may have significantly altered that relation in the past.

Seasonal variations in aridity and temperature characterize changing climate during the last deglaciation in New Zealand

NASA Astrophysics Data System (ADS)

Sikes, Elisabeth L.; Medeiros, Patricia M.; Augustinus, Paul; Wilmshurst, Janet M.; Freeman, Katherine R.

2013-08-01

New multiproxy records of aridity from northern New Zealand assess the seasonality and overall pattern of wetness through the Last Glacial Coldest Period (LGCP) to the early Holocene in the subtropical Southwest Pacific. Biomass burning indicators based on terrestrial biomarkers and δ13C of individual plant leaf wax carbon compounds (n-alkanoic acids) from a maar lake were used to track aridity. In combination with published sea surface temperatures and new pollen-based temperature estimates from the same core, seasonal climatological changes in the Auckland area were determined from 27 to 9 cal. ka BP. These proxies document a shift from cold and dry conditions in the Last Glacial Maximum to seasonally wetter conditions through the deglaciation. Spring became warmer first and possibly wetter while summers remained drier and initially cooler. The progression from cold-dry to warm-wet was punctuated by the Antarctic Cold Reversal (ACR) which stands out as having wetter conditions in both spring and summer and mild cooling largely concentrated in spring. The seasonal climate trends observed here can be plausibly explained by a rapid change from a subpolar climate to one with subtropical control in this region of the southwest Pacific across the Last Glacial to Interglacial transition. A southerly shift and decreasing intensity of the westerly wind belt after the LGCP is considered to have driven the early deglacial warming and pulse of wetness whereas a northward shift without a commensurate increase in intensity of the westerlies may explain conditions in the ACR.

Using environmental isotopes along with major hydro-geochemical compositions to assess deep groundwater formation and evolution in eastern coastal China

NASA Astrophysics Data System (ADS)

Xu, Naizheng; Gong, Jianshi; Yang, Guoqiang

2018-01-01

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3- is the dominant anion in the freshwater samples, whereas Na+ and Cl- are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.

Salt exchange in the Indian-Atlantic Ocean Gateway since the Last Glacial Maximum: A compensating effect between Agulhas Current changes and salinity variations?

NASA Astrophysics Data System (ADS)

Simon, Margit H.; Gong, Xun; Hall, Ian R.; Ziegler, Martin; Barker, Stephen; Knorr, Gregor; van der Meer, Marcel T. J.; Kasper, Sebastian; Schouten, Stefan

2015-10-01

The import of relatively salty water masses from the Indian Ocean to the Atlantic is considered to be important for the operational mode of the Atlantic Meridional Overturning Circulation (AMOC). However, the occurrence and the origin of changes in this import behavior on millennial and glacial/interglacial timescales remains equivocal. Here we reconstruct multiproxy paleosalinity changes in the Agulhas Current since the Last Glacial Maximum and compare the salinity pattern with records from the Indian-Atlantic Ocean Gateway (I-AOG) and model simulations using a fully coupled atmosphere-ocean general circulation model. The reconstructed paleosalinity pattern in the Agulhas Current displays coherent variability with changes recorded in the wider I-AOG region over the last glacial termination. We infer that salinities simultaneously increased in both areas consistent with a quasi interhemispheric salt-seesaw response, analogous to the thermal bipolar seesaw in response to a reduced cross-hemispheric heat and salt exchange during times of weakened AMOC. Interestingly, these hydrographic shifts can also be recognized in the wider Southern Hemisphere, which indicates that salinity anomalies are not purely restricted to the Agulhas Current System itself. More saline upstream Agulhas waters were propagated to the I-AOG during Heinrich Stadial 1 (HS1). However, the salt flux into the South Atlantic might have been reduced due to a decreased volume transport through the I-AOG during the AMOC slowdown associated with HS1. Hence, our combined data-model interpretation suggests that intervals with higher salinity in the Agulhas Current source region are not necessarily an indicator for an increased salt import via the I-AOG into the South Atlantic.

Export production in the New-Zealand region since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Durand, Axel; Chase, Zanna; Noble, Taryn L.; Bostock, Helen; Jaccard, Samuel L.; Kitchener, Priya; Townsend, Ashley T.; Jansen, Nils; Kinsley, Les; Jacobsen, Geraldine; Johnson, Sean; Neil, Helen

2017-07-01

Increased export production (EP) in the Subantarctic Zone (SAZ) of the Southern Ocean due to iron fertilisation has been proposed as a key mechanism for explaining carbon drawdown during the last glacial maximum (LGM). This work reconstructs marine EP since the LGM at four sites around New Zealand. For the first time in this region, 230-Thorium-normalised fluxes of biogenic opal, carbonate, excess barium, and organic carbon are presented. In Subtropical Waters and the SAZ, these flux variations show that EP has not changed markedly since the LGM. The only exception is a site currently north of the subtropical front. Here we suggest the subtropical front shifted over the core site between 18 and 12 ka, driving increased EP. To understand why EP remained mostly low and constant elsewhere, lithogenic fluxes at the four sites were measured to investigate changes in dust deposition. At all sites, lithogenic fluxes were greater during the LGM compared to the Holocene. The positive temporal correlation between the Antarctic dust record and lithogenic flux at a site in the Tasman Sea shows that regionally, increased dust deposition contributed to the high glacial lithogenic fluxes. Additionally, it is inferred that lithogenic material from erosion and glacier melting deposited on the Campbell Plateau during the deglaciation (18-12 ka). From these observations, it is proposed that even though increased glacial dust deposition may have relieved iron limitation within the SAZ around New Zealand, the availability of silicic acid limited diatom growth and thus any resultant increase in carbon export during the LGM. Therefore, silicic acid concentrations have remained low since the LGM. This result suggests that both silicic acid and iron co-limit EP in the SAZ around New Zealand, consistent with modern process studies.

Using environmental isotopes along with major hydro-geochemical compositions to assess deep groundwater formation and evolution in eastern coastal China.

PubMed

Xu, Naizheng; Gong, Jianshi; Yang, Guoqiang

2018-01-01

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO 3 - is the dominant anion in the freshwater samples, whereas Na + and Cl - are the dominant major ions in the saline samples. According to δ 18 O, δ 2 H and 14 C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ 18 O, δ 2 H and 3 H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points. Copyright © 2017 Elsevier B.V. All rights reserved.

Geomorphic investigation of the Late-Quaternary landforms in the southern Zanskar Valley, NW Himalaya

NASA Astrophysics Data System (ADS)

Sharma, Shubhra; Hussain, Aadil; Mishra, Amit K.; Lone, Aasif; Solanki, Tarun; Khan, Mohammad Khatib

2018-02-01

The Suru, Doda and Zanskar river valleys in the semi-arid region of Southern Zanskar Ranges (SZR) preserve a rich repository of the glacial and fluvial landforms, alluvial fans, and lacustrine deposits. Based on detailed field observations, geomorphic mapping and limited optical ages, we suggest four glaciations of decreasing magnitude in the SZR. The oldest Southern Zanskar Glaciation Stage (SZS-4) is inferred from glacially polished bedrock and tillite pinnacles. The SZS-4 is ascribed to the Marine Isotopic Stage (MIS)-4/3. The subsequent SZS-3 is represented by obliterated and dissected moraines, and is assigned to MIS-2/Last Glacial Maximum. The multiple recessional moraines of SZS-2 glaciation are assigned the early to mid Holocene age whereas, the youngest SZS-1 moraines were deposited during the Little Ice Age. We suggest that during the SZS-2 glaciation, the Drang-Drung glacier shifted its course from Suru Valley (west) to the Doda Valley (east). The study area has preserved three generations of outwash gravel terraces, which broadly correlate with the phases of deglaciation associated with SZS-3, 2, and 1. The alluvial fan aggradation, lacustrine sedimentation, and loess deposition occurred during the mid-to-late Holocene. We suggest that glaciation was driven by a combination of the mid-latitude westerlies and the Indian Summer Monsoon during periods of cooler temperature, while phases of deglaciation occurred during enhanced temperature.

Long-term record of Barents Sea Ice Sheet advance to the shelf edge from a 140,000 year record

NASA Astrophysics Data System (ADS)

Pope, Ed L.; Talling, Peter J.; Hunt, James E.; Dowdeswell, Julian A.; Allin, Joshua R.; Cartigny, Matthieu J. B.; Long, David; Mozzato, Alessandro; Stanford, Jennifer D.; Tappin, David R.; Watts, Millie

2016-10-01

The full-glacial extent and deglacial behaviour of marine-based ice sheets, such as the Barents Sea Ice Sheet, is well documented since the Last Glacial Maximum about 20,000 years ago. However, reworking of older sea-floor sediments and landforms during repeated Quaternary advances across the shelf typically obscures their longer-term behaviour, which hampers our understanding. Here, we provide the first detailed long-term record of Barents Sea Ice Sheet advances, using the timing of debris-flows on the Bear Island Trough-Mouth Fan. Ice advanced to the shelf edge during four distinct periods over the last 140,000 years. By far the largest sediment volumes were delivered during the oldest advance more than 128,000 years ago. Later advances occurred from 68,000 to 60,000, 39,400 to 36,000 and 26,000 to 20,900 years before present. The debris-flows indicate that the dynamics of the Saalian and the Weichselian Barents Sea Ice Sheet were very different. The repeated ice advance and retreat cycles during the Weichselian were shorter lived than those seen in the Saalian. Sediment composition shows the configuration of the ice sheet was also different between the two glacial periods, implying that the ice feeding the Bear Island Ice stream came predominantly from Scandinavia during the Saalian, whilst it drained more ice from east of Svalbard during the Weichselian.

Comparison of clast and matrix dispersal in till: Charlo-Atholville area, north-central New Brunswick

USGS Publications Warehouse

Dickson, M.L.; Broster, B.E.; Parkhill, M.A.

2004-01-01

Striations and dispersal patterns for till clasts and matrix geochemistry are used to define flow directions of glacial transport across an area of about 800km2 in the Charlo-Atholville area of north-central New Brunswick. A total of 170 clast samples and 328 till matrix samples collected for geochemical analysis across the region, were analyzed for a total of 39 elements. Major lithologic contacts used here to delineate till clast provenance were based on recent bedrock mapping. Eleven known mineral occurrences and a gossan are used to define point source targets for matrix geochemical dispersal trains and to estimate probable distance and direction of transport from unknown sources. Clast trains are traceable for distances of approximately 10 km, whereas till geochemical dispersal patterns are commonly lost within 5 km of transport. Most dispersal patterns reflect more than a single direction of glacial transport. These data indicate that a single till sheet, 1-4 m thick, was deposited as the dominant ice-flow direction fluctuated between southeastward, eastward, and northward over the study area. Directions of early flow represent changes in ice sheet dominance, first from the northwest and then from the west. Locally, eastward and northward flow represent the maximum erosive phases. The last directions of flow are likely due to late glacial ice sheet drawdown towards the valley outlet at Baie des Chaleurs.

Correcting Borehole Temperture Profiles for the Effects of Postglacial Warming

NASA Astrophysics Data System (ADS)

Rath, V.; Gonzalez-Rouco, J. F.

2010-09-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the signifcance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature proiles. It also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climatology. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, in particular with deeper boreholes, where the warming signal in heat flow can no longer be approximated linearly. We will show examples from North America and Eurasia, comparing temperatures reduced the proposed algoritm with AOGCM modeling results.

An 80 kyr-long continuous speleothem record from Dim Cave, SW Turkey with paleoclimatic implications for the Eastern Mediterranean

PubMed Central

Ünal-İmer, Ezgi; Shulmeister, James; Zhao, Jian-Xin; Tonguç Uysal, I.; Feng, Yue-Xing; Duc Nguyen, Ai; Yüce, Galip

2015-01-01

Speleothem-based stable isotope records are valuable in sub-humid and semi-arid settings where many other terrestrial climate proxies are fragmentary. The Eastern Mediterranean is one such region. Here we present an 80-kyr-long precisely-dated (by U-series) and high-resolution oxygen (δ18O) and carbon (δ13C) records from Dim Cave (~36°N) in SW Turkey. The glacial-interglacial δ18O variations in the Dim Cave speleothem are best explained in terms of changes in the trajectories of winter westerly air masses. These are along a northerly (European) track (isotopically less depleted) during the early last glaciation but are gradually depressed southward closer to the modern westerly track along the North African coast (more depleted) after c.50 kyr and remain in the southern track through the Last Glacial Maximum. The southward displacement of the westerly track reflects growth of the Fennoscandian ice sheet and its impact on westerly wind fields. Changes in δ13C are interpreted as reflecting soil organic matter composition and/or thickness. δ13C values are significantly more negative in interglacials reflecting active carbonic acid production in the soil and less negative in glacial times reflecting carbonate rock values. Several Heinrich events are recorded in the Dim record indicating intensification of westerly flow across this part of the EM. PMID:26337921

Lithologic influences on groundwater recharge through incised glacial till from profile to regional scales: Evidence from glaciated Eastern Nebraska

USGS Publications Warehouse

Gates, John B.; Steele, Gregory V.; Nasta, Paolo; Szilagyi, Jozsef

2014-01-01

Variability in sediment hydraulic properties associated with landscape depositional and erosional features can influence groundwater recharge processes by affecting soil-water storage and transmission. This study considers recharge to aquifers underlying river-incised glaciated terrain where the distribution of clay-rich till is largely intact in upland locations but has been removed by alluvial erosion in stream valleys. In a stream-dissected glacial region in eastern Nebraska (Great Plains region of the United States), recharge estimates were developed for nested profile, aquifer, and regional scales using unsaturated zone profile measurements (matric potentials, Cl- and 3H), groundwater tracers (CFC-12 and SF6), and a remote sensing-assisted water balance model. Results show a consistent influence of till lithology on recharge rates across nested spatial scales despite substantial uncertainty in all recharge estimation methods, suggesting that minimal diffuse recharge occurs through upland glacial till lithology whereas diffuse recharge occurs in river valleys where till is locally absent. Diffuse recharge is estimated to account for a maximum of 61% of total recharge based on comparison of diffuse recharge estimated from the unsaturated zone (0-43 mm yr-1) and total recharge estimated from groundwater tracers (median 58 mm yr-1) and water balance modeling (median 56 mm yr-1). The results underscore the importance of lithologic controls on the distributions of both recharge rates and mechanisms.

A multi-proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits, western Tennessee, USA

USGS Publications Warehouse

Grimley, D.A.; Daniel, L.; Kaplan, S.W.; Yansa, C.H.; Curry, B. Brandon; Oches, E.A.

2009-01-01

The Fulton Section, along the Mississippi River in western Tennessee, USA, is a 1km continuous exposure (~20m vertically) of Quaternary fluvial and lacustrine deposits, inset within Eocene sediments and buried by thick loess. Fossiliferous slackwater lake sediments record maximum aggradation during the last two major glaciations, with deposition between ca. 190-140 ka and 24-1814C ka BP, based on amino acid and radiocarbon chronology, respectively. During the onset of full glacial conditions (ca. 24-22 14C ka BP), a relatively permanent shallow lake environment is indicated by ostracods, aquatic molluscs, and both pollen and macrofossils of aquatic plants. By 21.8 14C ka BP, increasing emergent plants, amphibious gastropods (Pomatiopsis) and heavier ??18O compositions suggest marsh-like conditions in a periodically drying lake. The surrounding uplands consisted of Picea-Pinus woodlands mixed with cool-temperate hardwoods (e.g. Quercus, Populus, Carya), grasses and herbs. More open conditions ensued ca. 20 14C ka BP, with loess and slopewash gradually infilling the former lake by 18 14C ka BP. Modern analogue analyses of ostracods and palaeontological evidence imply a full glacial climate similar to today's mixed-boreal zone in central Minnesota, USA, about 98C cooler in mean annual temperature than present-day western Tennessee. Copyright ?? 2009 John Wiley & Sons, Ltd.

Glaciolacustrine deposits formed in an ice-dammed tributary valley in the south-central Pyrenees: New evidence for late Pleistocene climate

NASA Astrophysics Data System (ADS)

Sancho, Carlos; Arenas, Concha; Pardo, Gonzalo; Peña-Monné, José Luis; Rhodes, Edward J.; Bartolomé, Miguel; García-Ruiz, José M.; Martí-Bono, Carlos

2018-04-01

Combined geomorphic features, stratigraphic characteristics and sedimentologic interpretation, coupled with optically stimulated luminescence (OSL) dates, of a glacio-fluvio-lacustrine sequence (Linás de Broto, northern Spain) provide new information to understand the palaeoenvironmental significance of dynamics of glacier systems in the south-central Pyrenees during the Last Glacial Cycle (≈130 ka to 14 ka). The Linás de Broto depositional system consisted of a proglacial lake fed primarily by meltwater streams emanating from the small Sorrosal glacier and dammed by a lateral moraine of the Ara trunk glacier. The resulting glacio-fluvio-lacustrine sequence, around 55 m thick, is divided into five lithological units consisting of braided fluvial (gravel deposits), lake margin (gravel and sand deltaic deposits) and distal lake (silt and clay laminites) facies associations. Evolution of the depositional environment reflects three phases of progradation of a high-energy braided fluvial system separated by two phases of rapid expansion of the lake. Fluvial progradation occurred during short periods of ice melting. Lake expansion concurred with ice-dam growth of the trunk glacier. The first lake expansion occurred over a time range between 55 ± 9 ka and 49 ± 11 ka, and is consistent with the age of the Viu lateral moraine (49 ± 8 ka), which marks the maximum areal extent of the Ara glacier during the Last Glacial Cycle. These dates confirm that the maximum areal extent of the glacier occurred during Marine Isotope Stages 4 and 3 in the south-central Pyrenees, thus before the Last Glacial Maximum. The evolution of the Linás de Broto depositional system during this maximum glacier extent was modulated by climate oscillations in the northern Iberian Peninsula, probably related to latitudinal shifts of the atmospheric circulation in the southern North-Atlantic Ocean, and variations in summer insolation intensity.

Climate sensitivity of Tibetan Plateau glaciers - past and future implications

NASA Astrophysics Data System (ADS)

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

2013-04-01

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

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.

Demographic Divergence History of Pied Flycatcher and Collared Flycatcher Inferred from Whole-Genome Re-sequencing Data

PubMed Central

Nadachowska-Brzyska, Krystyna; Burri, Reto; Olason, Pall I.; Kawakami, Takeshi; Smeds, Linnéa; Ellegren, Hans

2013-01-01

Profound knowledge of demographic history is a prerequisite for the understanding and inference of processes involved in the evolution of population differentiation and speciation. Together with new coalescent-based methods, the recent availability of genome-wide data enables investigation of differentiation and divergence processes at unprecedented depth. We combined two powerful approaches, full Approximate Bayesian Computation analysis (ABC) and pairwise sequentially Markovian coalescent modeling (PSMC), to reconstruct the demographic history of the split between two avian speciation model species, the pied flycatcher and collared flycatcher. Using whole-genome re-sequencing data from 20 individuals, we investigated 15 demographic models including different levels and patterns of gene flow, and changes in effective population size over time. ABC provided high support for recent (mode 0.3 my, range <0.7 my) species divergence, declines in effective population size of both species since their initial divergence, and unidirectional recent gene flow from pied flycatcher into collared flycatcher. The estimated divergence time and population size changes, supported by PSMC results, suggest that the ancestral species persisted through one of the glacial periods of middle Pleistocene and then split into two large populations that first increased in size before going through severe bottlenecks and expanding into their current ranges. Secondary contact appears to have been established after the last glacial maximum. The severity of the bottlenecks at the last glacial maximum is indicated by the discrepancy between current effective population sizes (20,000–80,000) and census sizes (5–50 million birds) of the two species. The recent divergence time challenges the supposition that avian speciation is a relatively slow process with extended times for intrinsic postzygotic reproductive barriers to evolve. Our study emphasizes the importance of using genome-wide data to unravel tangled demographic histories. Moreover, it constitutes one of the first examples of the inference of divergence history from genome-wide data in non-model species. PMID:24244198

Demographic divergence history of pied flycatcher and collared flycatcher inferred from whole-genome re-sequencing data.

PubMed

Nadachowska-Brzyska, Krystyna; Burri, Reto; Olason, Pall I; Kawakami, Takeshi; Smeds, Linnéa; Ellegren, Hans

2013-11-01

Profound knowledge of demographic history is a prerequisite for the understanding and inference of processes involved in the evolution of population differentiation and speciation. Together with new coalescent-based methods, the recent availability of genome-wide data enables investigation of differentiation and divergence processes at unprecedented depth. We combined two powerful approaches, full Approximate Bayesian Computation analysis (ABC) and pairwise sequentially Markovian coalescent modeling (PSMC), to reconstruct the demographic history of the split between two avian speciation model species, the pied flycatcher and collared flycatcher. Using whole-genome re-sequencing data from 20 individuals, we investigated 15 demographic models including different levels and patterns of gene flow, and changes in effective population size over time. ABC provided high support for recent (mode 0.3 my, range <0.7 my) species divergence, declines in effective population size of both species since their initial divergence, and unidirectional recent gene flow from pied flycatcher into collared flycatcher. The estimated divergence time and population size changes, supported by PSMC results, suggest that the ancestral species persisted through one of the glacial periods of middle Pleistocene and then split into two large populations that first increased in size before going through severe bottlenecks and expanding into their current ranges. Secondary contact appears to have been established after the last glacial maximum. The severity of the bottlenecks at the last glacial maximum is indicated by the discrepancy between current effective population sizes (20,000-80,000) and census sizes (5-50 million birds) of the two species. The recent divergence time challenges the supposition that avian speciation is a relatively slow process with extended times for intrinsic postzygotic reproductive barriers to evolve. Our study emphasizes the importance of using genome-wide data to unravel tangled demographic histories. Moreover, it constitutes one of the first examples of the inference of divergence history from genome-wide data in non-model species.

Genetic and palaeo-climatic evidence for widespread persistence of the coastal tree species Eucalyptus gomphocephala (Myrtaceae) during the Last Glacial Maximum.

PubMed

Nevill, Paul G; Bradbury, Donna; Williams, Anna; Tomlinson, Sean; Krauss, Siegfried L

2014-01-01

Few phylogeographic studies have been undertaken of species confined to narrow, linear coastal systems where past sea level and geomorphological changes may have had a profound effect on species population sizes and distributions. In this study, a phylogeographic analysis was conducted of Eucalyptus gomphocephala (tuart), a tree species restricted to a 400 × 10 km band of coastal sand-plain in south west Australia. Here, there is little known about the response of coastal vegetation to glacial/interglacial climate change, and a test was made as to whether this species was likely to have persisted widely through the Last Glacial Maximum (LGM), or conforms to a post-LGM dispersal model of recovery from few refugia. The genetic structure over the entire range of tuart was assessed using seven nuclear (21 populations; n = 595) and four chloroplast (24 populations; n = 238) microsatellite markers designed for eucalypt species. Correlative palaeodistribution modelling was also conducted based on five climatic variables, within two LGM models. The chloroplast markers generated six haplotypes, which were strongly geographically structured (GST = 0·86 and RST = 0·75). Nuclear microsatellite diversity was high (overall mean HE 0·75) and uniformly distributed (FST = 0·05), with a strong pattern of isolation by distance (r(2) = 0·362, P = 0·001). Distribution models of E. gomphocephala during the LGM showed a wide distribution that extended at least 30 km westward from the current distribution to the palaeo-coastline. The chloroplast and nuclear data suggest wide persistence of E. gomphocephala during the LGM. Palaeodistribution modelling supports the conclusions drawn from genetic data and indicates a widespread westward shift of E. gomphocephala onto the exposed continental shelf during the LGM. This study highlights the importance of the inclusion of complementary, non-genetic data (information on geomorphology and palaeoclimate) to interpret phylogeographic patterns.

Genetic and palaeo-climatic evidence for widespread persistence of the coastal tree species Eucalyptus gomphocephala (Myrtaceae) during the Last Glacial Maximum

PubMed Central

Nevill, Paul G.; Bradbury, Donna; Williams, Anna; Tomlinson, Sean; Krauss, Siegfried L.

2014-01-01

Background and Aims Few phylogeographic studies have been undertaken of species confined to narrow, linear coastal systems where past sea level and geomorphological changes may have had a profound effect on species population sizes and distributions. In this study, a phylogeographic analysis was conducted of Eucalyptus gomphocephala (tuart), a tree species restricted to a 400 × 10 km band of coastal sand-plain in south west Australia. Here, there is little known about the response of coastal vegetation to glacial/interglacial climate change, and a test was made as to whether this species was likely to have persisted widely through the Last Glacial Maximum (LGM), or conforms to a post-LGM dispersal model of recovery from few refugia. Methods The genetic structure over the entire range of tuart was assessed using seven nuclear (21 populations; n = 595) and four chloroplast (24 populations; n = 238) microsatellite markers designed for eucalypt species. Correlative palaeodistribution modelling was also conducted based on five climatic variables, within two LGM models. Key Results The chloroplast markers generated six haplotypes, which were strongly geographically structured (GST = 0·86 and RST = 0·75). Nuclear microsatellite diversity was high (overall mean HE 0·75) and uniformly distributed (FST = 0·05), with a strong pattern of isolation by distance (r2 = 0·362, P = 0·001). Distribution models of E. gomphocephala during the LGM showed a wide distribution that extended at least 30 km westward from the current distribution to the palaeo-coastline. Conclusions The chloroplast and nuclear data suggest wide persistence of E. gomphocephala during the LGM. Palaeodistribution modelling supports the conclusions drawn from genetic data and indicates a widespread westward shift of E. gomphocephala onto the exposed continental shelf during the LGM. This study highlights the importance of the inclusion of complementary, non-genetic data (information on geomorphology and palaeoclimate) to interpret phylogeographic patterns. PMID:24284819

The Near East as a cradle of biodiversity: A phylogeography of banded newts (genus Ommatotriton) reveals extensive inter- and intraspecific genetic differentiation.

PubMed

van Riemsdijk, Isolde; Arntzen, Jan W; Bogaerts, Sergé; Franzen, Michael; Litvinchuk, Spartak N; Olgun, Kurtuluş; Wielstra, Ben

2017-09-01

The banded newt (genus Ommatotriton) is widely distributed in the Near East (Anatolia, Caucasus and the Levant) - an understudied region from the perspective of phylogeography. The genus is polytypic, but the number of species included and the phylogenetic relationships between them are not settled. We sequenced two mitochondrial and two nuclear DNA markers throughout the range of Ommatotriton. For mtDNA we constructed phylogenetic trees, estimated divergence times using fossil calibration, and investigated changes in effective population size with Bayesian skyline plots and mismatch analyses. For nuDNA we constructed phylogenetic trees and haplotype networks. Species trees were constructed for all markers and nuDNA only. Species distribution models were projected on current and Last Glacial Maximum climate layers. We confirm the presence of three Ommatotriton species: O. nesterovi, O. ophryticus and O. vittatus. These species are genetically distinct and their most recent common ancestor was dated at ∼25Ma (Oligocene). No evidence of recent gene flow between species was found. The species show deep intraspecific genetic divergence, represented by geographically structured clades, with crown nodes of species dated ∼8-13Ma (Miocene to Early Quaternary); evidence of long-term in situ evolution and survival in multiple glacial refugia. While a species tree based on nuDNA suggested a sister species relationship between O. vittatus and O. ophryticus, when mtDNA was included, phylogenetic relationships were unresolved, and we refrain from accepting a particular phylogenetic hypothesis at this stage. While species distribution models suggest reduced and fragmented ranges during the Last Glacial Maximum, we found no evidence for strong population bottlenecks. We discuss our results in the light of other phylogeographic studies from the Near East. Our study underlines the important role of the Near East in generating and sustaining biodiversity. Copyright © 2017 Elsevier Inc. All rights reserved.

Reconstruction of past equilibrium line altitude using ice extent data

NASA Astrophysics Data System (ADS)

Visnjevic, Vjeran; Herman, Frederic; Podladchikov, Yuri

2017-04-01

With the end of the Last Glacial Maximum (LGM), about 20 000 years ago, ended the most recent long-lasting cold phase in Earth's history. This last glacial advance left a strong observable imprint on the landscape, such as abandoned moraines, trimlines and other glacial geomorphic features. These features provide a valuable record of past continental climate. In particular, terminal moraines reflect the extent of glaciers and ice-caps, which itself reflects past temperature and precipitation conditions. Here we present an inverse approach, based on a Tikhonov regularization, we have recently developed to reconstruct the LGM mass balance from observed ice extent data. The ice flow model is developed using the shallow ice approximation and solved explicitly using Graphical Processing Units (GPU). The mass balance field, b, is the constrained variable defined by the ice surface S, balance rate β and the spatially variable equilibrium line altitude field (ELA): b = min (β ṡ(S(x,y)- ELA (x,y)),c). (1) where c is a maximum accumulation rate. We show that such a mass balance, and thus the spatially variable ELA field, can be inferred from the observed past ice extent and ice thickness at high resolution and very efficiently. The GPU implementation allows us solve one 1024x1024 grid points forward model run under 0.5s, which significantly reduces the time needed for our inverse method to converge. We start with synthetic test to demonstrate the method. We then apply the method to LGM ice extents of South Island of New Zealand, the Patagonian Andes, where we can see a clear influence of Westerlies on the ELA, and the European Alps. These examples show that the method is capable of constraining spatial variations in mass balance at the scale of a mountain range, and provide us with information on past continental climate.

The disjunct pattern of the Neotropical harvestman Discocyrtus dilatatus (Gonyleptidae) explained by climate-driven range shifts in the Quaternary: Paleodistributional and molecular evidence

PubMed Central

Vergara, Julia; González-Ittig, Raúl E.; Vaschetto, Luis M.; Gardenal, Cristina N.

2017-01-01

The disjunct distribution of the harvestman Discocyrtus dilatatus (Opiliones, Gonyleptidae) is used as a case study to test the hypothesis of a trans-Chaco Pleistocene paleobridge during range expansion stages. This would have temporarily connected humid regions (‘Mesopotamia’ in northeastern Argentina, and the ‘Yungas’ in the northwest, NWA) in the subtropical and temperate South American lowlands. The present study combines two independent approaches: paleodistributional reconstruction, using the Species Distribution Modeling method MaxEnt and projection onto Quaternary paleoclimates (6 kya, 21 kya, 130 kya), and phylogeographic analyses based on the cytochrome oxidase subunit I molecular marker. Models predict a maximal shrinkage during the warm Last Interglacial (130 kya), and the rise of the hypothesized paleobridge in the Last Glacial Maximum (21 kya), revealing that cold-dry stages (not warm-humid ones, as supposed) enabled the range expansion of this species. The disjunction was formed in the mid-Holocene (6 kya) and is intensified under current conditions. The median-joining network shows that NWA haplotypes are peripherally related to different Mesopotamian lineages; haplotypes from Santa Fe and Córdoba Provinces consistently occupy central positions in the network. According to the dated phylogeny, Mesopotamia-NWA expansion events would have occurred in the last glacial period, in many cases closely associated to the Last Glacial Maximum, with most divergence events occurring shortly thereafter. Only two (out of nine) NWA haplotypes are shared with Mesopotamian localities. A single, presumably relictual NWA haplotype was found to have diverged much earlier, suggesting an ancient expansion event not recoverable by the paleodistributional models. Different measures of sequence statistics, genetic diversity, population structure and history of demographic changes are provided. This research offers the first available evidence for the historical origin of NWA disjunct populations of a Mesopotamian harvestman. PMID:29141036

Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

NASA Astrophysics Data System (ADS)

Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko

2016-04-01

Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-ice controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last interglacial ESL.

δ18O and salinity variability from the Last Glacial Maximum to Recent in the Bay of Bengal and Andaman Sea

NASA Astrophysics Data System (ADS)

Sijinkumar, A. V.; Clemens, Steven; Nath, B. Nagender; Prell, Warren; Benshila, Rachid; Lengaigne, Matthieu

2016-03-01

Oxygen isotopes of surface, thermocline and bottom dwelling foraminifera were analysed from two well-dated Andaman Sea cores and combined with nine previously published records from the Bay of Bengal (BoB) and Andaman Sea to create a transect spanning 20°N to 5°N. Combined with temperature estimates and the observed seawater δ18O-salinity relationship, these data are used to estimate past changes in BoB salinity structure. Compared to modern, mid-Holocene (9-6 cal ka BP) surface waters in the northern BoB were 2.5 psμ (8%) fresher, Andaman Sea were 3.8 psμ (12%) fresher, and southern BoB were 1.2 psμ (3.5%) fresher. Conversely, during the last glacial maximum (LGM), surface waters in the northern BoB were 2.9 psμ (9%) more saline while Andaman Sea were essentially unchanged and southern BoB were 1.7 psμ (4.9%) more saline compared to modern. The relative freshness of the Andaman during the last glacial maximum is likely the result of basin morphology during sea level low stand, resulting in reduced surface water mixing with the open BoB as well as shelf emergence, causing increased proximity of the core locations to river outflow. Sensitivity experiments using a regional ocean model indicate that the increased mid-Holocene north to south (20°N to 5°N) salinity gradient can be achieved with a ∼50% increase in precipitation/runoff while the decreased glacial age gradient can be achieved with a ∼50% reduction in precipitation/runoff. During the deglaciation, both surface and thermocline-dwelling species in the Andaman and northern BoB exhibit depleted δ18O within the Younger Dryas (YD), indicating colder and/or more saline conditions. None of the records from the southern BoB site have clear YD structure, possibly due to the combined effects of bioturbation and low sedimentation rates.

Geochronology of Quaternary glaciations from the tropical Cordillera Huayhuash, Peru

NASA Astrophysics Data System (ADS)

Hall, Sarah R.; Farber, Daniel L.; Ramage, Joan M.; Rodbell, Donald T.; Finkel, Robert C.; Smith, Jacqueline A.; Mark, Bryan G.; Kassel, Christopher

2009-12-01

The Cordillera Huayhuash in the central Peruvian Andes (10.3°S, 76.9°W) is an ideal mountain range in which to study regional climate through variations in paleoglacier extents. The range trends nearly north-south with modern glaciers confined to peaks >4800 m a.s.l. Geomorphology and geochronology in the nearby Cordillera Blanca and Junin Plain reveal that the Peruvian Andes preserve a detailed record of tropical glaciation. Here, we use ASTER imagery, aerial photographs, and GPS to map and date glacial features in both the western and eastern drainages of the Cordillera Huayhuash. We have used in situ produced cosmogenic 10Be concentrations in quartz bearing erratics on moraine crests and ice-polished bedrock surfaces to develop an exposure age chronology for Pleistocene glaciation within the range. We have also collected sediment cores from moraine-dammed lakes and bogs to provide limiting 14C ages for glacial deposits. In contrast to the ranges to the north and south, most glacial features within the Cordillera Huayhuash are Lateglacial in age, however we have identified features with ages that span ˜0.2 to ˜38 ka with moraine sets marking the onset of glacier retreat at ˜0.3 ka, ˜9-10 ka, ˜13-14 ka, ˜20-22 ka, and >26 ka. The range displays a pronounced east-west variation in maximum down-valley distance from the headwall of moraine crests with considerably longer paleoglaciers in the eastern drainages. Importantly, Lateglacial paleoglaciers reached a terminal elevation of ˜4000 m a.s.l. on both sides of the Cordillera Huayhuash; suggesting that temperature may have been a dominant factor in controlling the maximum glacier extent. We suggest that valley morphology, specifically valley slope, strongly influences down-valley distance to the maximum glacier extent and potential for moraine preservation. While regionally there is an extensive record of older (>50 ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the apparent lack of old moraines in this locality may be explained by the confined morphology of the Cordillera Huayhuash valleys that has inhibited the preservation of older glacial geomorphic features.

Gypsophila bermejoi G. López: A possible case of speciation repressed by bioclimatic factors.

PubMed

de Luis, Miguel; Bartolomé, Carmen; García Cardo, Óscar; Álvarez-Jiménez, Julio

2018-01-01

Gypsophila bermejoi G. López is an allopolyploid species derived from the parental G. struthium L. subsp. struthium and G. tomentosa L. All these plants are gypsophytes endemic to the Iberian Peninsula of particular ecological, evolutionary and biochemical interest. In this study, we present evidence of a possible repression on the process of G. bermejoi speciation by climatic factors. We modelled the ecological niches of the three taxa considered here using a maximum entropy approach and employing a series of bioclimatic variables. Subsequently, we projected these models onto the geographical space of the Iberian Peninsula in the present age and at two past ages: the Last Glacial Maximum and the mid-Holocene period. Furthermore, we compared these niches using the statistical method devised by Warren to calculate their degree of overlap. We also evaluated the evolution of the bioclimatic habitat suitability at those sites were the soil favors the growth of these species. Both the maximum entropy model and the degree of overlap indicated that the ecological behavior of the hybrid differs notably from that of the parental species. During the Last Glacial Maximum, the two parental species appear to take refuge in the western coastal strip of the Peninsula, a region in which there are virtually no sites where G. bermejoi could potentially be found. However, in the mid-Holocene period the suitability of G. bermejoi to sites with favorable soils shifts from almost null to a strong adaptation, a clear change in this tendency. These results suggest that the ecological niches of hybrid allopolyploids can be considerably different to those of their parental species, which may have evolutionary and ecologically relevant consequences. The data obtained indicate that certain bioclimatic variables may possibly repress the processes by which new species are formed. The difference in the ecological niche of G. bermejoi with respect to its parental species prevented it from prospering during the Last Glacial Maximum. However, the climatic change in the mid-Holocene period released this block and as such, it permitted the new species to establish itself. Accordingly, we favor a recent origin of the current populations of G. bermejoi.

Gypsophila bermejoi G. López: A possible case of speciation repressed by bioclimatic factors

PubMed Central

de Luis, Miguel; García Cardo, Óscar; Álvarez-Jiménez, Julio

2018-01-01

Gypsophila bermejoi G. López is an allopolyploid species derived from the parental G. struthium L. subsp. struthium and G. tomentosa L. All these plants are gypsophytes endemic to the Iberian Peninsula of particular ecological, evolutionary and biochemical interest. In this study, we present evidence of a possible repression on the process of G. bermejoi speciation by climatic factors. We modelled the ecological niches of the three taxa considered here using a maximum entropy approach and employing a series of bioclimatic variables. Subsequently, we projected these models onto the geographical space of the Iberian Peninsula in the present age and at two past ages: the Last Glacial Maximum and the mid-Holocene period. Furthermore, we compared these niches using the statistical method devised by Warren to calculate their degree of overlap. We also evaluated the evolution of the bioclimatic habitat suitability at those sites were the soil favors the growth of these species. Both the maximum entropy model and the degree of overlap indicated that the ecological behavior of the hybrid differs notably from that of the parental species. During the Last Glacial Maximum, the two parental species appear to take refuge in the western coastal strip of the Peninsula, a region in which there are virtually no sites where G. bermejoi could potentially be found. However, in the mid-Holocene period the suitability of G. bermejoi to sites with favorable soils shifts from almost null to a strong adaptation, a clear change in this tendency. These results suggest that the ecological niches of hybrid allopolyploids can be considerably different to those of their parental species, which may have evolutionary and ecologically relevant consequences. The data obtained indicate that certain bioclimatic variables may possibly repress the processes by which new species are formed. The difference in the ecological niche of G. bermejoi with respect to its parental species prevented it from prospering during the Last Glacial Maximum. However, the climatic change in the mid-Holocene period released this block and as such, it permitted the new species to establish itself. Accordingly, we favor a recent origin of the current populations of G. bermejoi. PMID:29338010

Occurrence of Uranium and 222Radon in Glacial and Bedrock Aquifers in the Northern United States, 1993-2003

USGS Publications Warehouse

Ayotte, Joseph D.; Flanagan, Sarah M.; Morrow, William S.

2007-01-01

Water-quality data collected from 1,426 wells during 1993-2003 as part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) program were evaluated to characterize the water quality in glacial and bedrock aquifers of the northern United States. One of the goals of the NAWQA program is to synthesize data from individual studies across the United States to gain regional- and national-scale information about the behavior of contaminants. This study focused on the regional occurrence and distribution of uranium and 222radon in ground water in the glacial aquifer system of the United States as well as in the Cambrian-Ordovician and the New York and New England crystalline aquifer systems that underlie the glacial aquifer system. The occurrence of uranium and 222radon in ground water has long been a concern throughout the United States. In the glacial aquifers, as well as the Cambrian-Ordovician and the New York and New England crystalline aquifer systems of the United States, concentrations of uranium and 222radon were highly variable. High concentrations of uranium and 222radon affect ground water used for drinking water and for agriculture. A combination of information or data on (1) national-scale ground-water regions, (2) regional-scale glacial depositional models, (3) regional-scale geology, and (4) national-scale terrestrial gamma-ray emissions were used to confirm and(or) refine the regions used in the analysis of the water-chemistry data. Significant differences in the occurrence of uranium and 222radon, based primarily on geologic information were observed and used in this report. In general, uranium was highest in the Columbia Plateau glacial, West-Central glacial, and the New York and New England crystalline aquifer groups (75th percentile concentrations of 22.3, 7.7, and 2.9 micrograms per liter (ug/L), respectively). In the Columbia Plateau glacial and the West-Central glacial aquifer groups, more than 10 percent of wells sampled had concentrations of uranium that exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level of 30 ug/L; in the New York and New England crystalline aquifer group, 4 percent exceeded 30 ug/L. Ground-water samples with high concentrations of uranium were commonly linked to geologic sources rich in uranium. In eight of nine aquifer groups defined for this study, concentrations of uranium correlated significantly with concentrations of sulfate in ground water (Spearman's rho = 0.20 to 0.56; p < 0.05). In the Columbia Plateau, glacial aquifers were derived in part from basaltic lava flows, some felsic volcanic rocks, and some paleo-lake bed materials that may be rich in uranium. In the Columbia Plateau and West-Central glacial aquifer groups, uranium correlated with total dissolved solids, bicarbonate, boron, lithium, selenium, and strontium. In the West-Central glacial aquifer group, rocks such as Cretaceous marine shales, which are abundant in uranium, probably contribute to the high concentrations in ground water; in the southern part of this group, which extends into Nebraska, the glacial or glacial-related sediment may be interbedded with uranium-rich materials that originated to the north and west and in the Rocky Mountains. In New England, crystalline bedrock that is granitic, such as two-mica granites, as well as other high-grade metamorphic rocks, has abundant uranium that is soluble in the predominantly oxic to sub-oxic geochemical conditions. This appears to contribute to high uranium concentrations in ground water. The highest 222radon concentrations were present in samples from wells completed in the New York and New England crystalline aquifer group; the median value (2,122 picocurries per liter (pCi/L)) was about 10 times the median values of all other aquifer groups. More than 25 percent of the samples from the New York and New England crystalline aquifer group wells had 222radon concentrations that exceeded the USEPA Alternative

Simulations of cataclysmic outburst floods from Pleistocene Glacial Lake Missoula

USGS Publications Warehouse

Denlinger, Roger P.; O'Connell, D. R. H.

2009-01-01

Using a flow domain that we constructed from 30 m digital-elevation model data of western United States and Canada and a two-dimensional numerical model for shallow-water flow over rugged terrain, we simulated outburst floods from Pleistocene Glacial Lake Missoula. We modeled a large, but not the largest, flood, using initial lake elevation at 1250 m instead of 1285 m. Rupture of the ice dam, centered on modern Lake Pend Oreille, catastrophically floods eastern Washington and rapidly fills the broad Pasco, Yakima, and Umatilla Basins. Maximum flood stage is reached in Pasco and Yakima Basins 38 h after the dam break, whereas maximum flood stage in Umatilla Basin occurs 17 h later. Drainage of these basins through narrow Columbia gorge takes an additional 445 h. For this modeled flood, peak discharges in eastern Washington range from 10 to 20 × 106 m3/s. However, constrictions in Columbia gorge limit peak discharges to 6 m3/s and greatly extend the duration of flooding. We compare these model results with field observations of scabland distribution and high-water indicators. Our model predictions of the locations of maximum scour (product of bed shear stress and average flow velocity) match the distribution of existing scablands. We compare model peak stages to high-water indicators from the Rathdrum-Spokane valley, Walulla Gap, and along Columbia gorge. Though peak stages from this less-than-maximal flood model attain or exceed peak-stage indicators along Rathdrum-Spokane valley and along Columbia gorge, simulated peak stages near Walulla Gap are 10–40 m below observed peak-stage indicators. Despite this discrepancy, our match to field observations in most of the region indicates that additional sources of water other than Glacial Lake Missoula are not required to explain the Missoula floods.

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

Bennett, Katrina E.; Cannon, Alex J.; Hinzman, Larry

Climate change will shift the frequency, intensity, duration and persistence of extreme hydroclimate events and have particularly disastrous consequences in vulnerable systems such as the warm permafrost-dominated Interior region of boreal Alaska. This work focuses on recent research results from nonparametric trends and nonstationary generalized extreme value (GEV) analyses at eight Interior Alaskan river basins for the past 50/60 years (1954/64–2013). Trends analysis of maximum and minimum streamflow indicates a strong (>+50%) and statistically significant increase in 11-day flow events during the late fall/winter and during the snowmelt period (late April/mid-May), followed by a significant decrease in the 11-day flowmore » events during the post-snowmelt period (late May and into the summer). The April–May–June seasonal trends show significant decreases in maximum streamflow for snowmelt dominated systems (<–50%) and glacially influenced basins (–24% to –33%). Annual maximum streamflow trends indicate that most systems are experiencing declines, while minimum flow trends are largely increasing. Nonstationary GEV analysis identifies time-dependent changes in the distribution of spring extremes for snowmelt dominated and glacially dominated systems. Temperature in spring influences the glacial and high elevation snowmelt systems and winter precipitation drives changes in the snowmelt dominated basins. The Pacific Decadal Oscillation was associated with changes occurring in snowmelt dominated systems, and the Arctic Oscillation was linked to one lake dominated basin, with half of the basins exhibiting no change in response to climate variability. The paper indicates that broad scale studies examining trend and direction of change should employ multiple methods across various scales and consider regime dependent shifts to identify and understand changes in extreme streamflow within boreal forested watersheds of Alaska.« less

Historical trends and extremes in boreal Alaska river basins

DOE PAGES

Bennett, Katrina E.; Cannon, Alex J.; Hinzman, Larry

2015-05-12

Climate change will shift the frequency, intensity, duration and persistence of extreme hydroclimate events and have particularly disastrous consequences in vulnerable systems such as the warm permafrost-dominated Interior region of boreal Alaska. This work focuses on recent research results from nonparametric trends and nonstationary generalized extreme value (GEV) analyses at eight Interior Alaskan river basins for the past 50/60 years (1954/64–2013). Trends analysis of maximum and minimum streamflow indicates a strong (>+50%) and statistically significant increase in 11-day flow events during the late fall/winter and during the snowmelt period (late April/mid-May), followed by a significant decrease in the 11-day flowmore » events during the post-snowmelt period (late May and into the summer). The April–May–June seasonal trends show significant decreases in maximum streamflow for snowmelt dominated systems (<–50%) and glacially influenced basins (–24% to –33%). Annual maximum streamflow trends indicate that most systems are experiencing declines, while minimum flow trends are largely increasing. Nonstationary GEV analysis identifies time-dependent changes in the distribution of spring extremes for snowmelt dominated and glacially dominated systems. Temperature in spring influences the glacial and high elevation snowmelt systems and winter precipitation drives changes in the snowmelt dominated basins. The Pacific Decadal Oscillation was associated with changes occurring in snowmelt dominated systems, and the Arctic Oscillation was linked to one lake dominated basin, with half of the basins exhibiting no change in response to climate variability. The paper indicates that broad scale studies examining trend and direction of change should employ multiple methods across various scales and consider regime dependent shifts to identify and understand changes in extreme streamflow within boreal forested watersheds of Alaska.« less

Area and Carbon Content of Sphagnum Since Last Glacial Maximum

DOE Data Explorer

Gajewski, K. [University of Ottawa, Ottawa, Ontario (Canada); Viau, A. [University of Ottawa, Ottawa, Ontario (Canada); Sawada, M. [University of Ottawa, Ottawa, Ontario (Canada); Atkinson, D. [University of Ottawa, Ottawa, Ontario (Canada); Wilson, S. [University of Ottawa, Ottawa, Ontario (Canada)

2002-01-01

The distribution and abundance of Sphagnum spores in North America and Eurasia are mapped for the past 21ka, as described in Gajewski et al. (2002). In summary, spore data were taken from existing pollen data bases, as were radiocarbon chronologies. The abundance of Sphagnum spores was mapped at 2000-year intervals beginning 21000 years BP (before present). The present-day distribution of abundant Sphagnum spores corresponds closely to areas with peatland development, with maximum Sphagnum abundance between 630 and 1300 mm annual precipitation and between -2° and 60°C mean annual air temperature. Carbon content of peatlands was generated from estimated peatland area, calculated values of peat thickness, and specified values of bulk density (112 × 10³ g m^-3) and fraction of carbon (51.7%).

Geology, hydrology, and water quality of the glacial drift aquifer in the vicinity of the Nelson landfill near Yorkville, Illinois

USGS Publications Warehouse

Kay, Robert T.

2006-01-01

The geologic and hydrologic characteristics of the sand-and-gravel deposits that compose the glacial drift aquifer in the vicinity of the Nelson Landfill site in Yor-kville, Illinois indicate that the aquifer could be devel-oped as a source of public water supply. The geology of these deposits within the Newark Bedrock Valley is com-plex, however, and a detailed investigation of their water bearing and transmitting properties will be required to successfully locate high-capacity wells. Volatile organic compounds, pesticides, and cyanide were not detected in ground water during this investiga-tion. Metals and nitrogen compounds were not detected at concentrations above their Maximum Contaminant Level. Iron, manganese, and aluminum were detected at concentrations above their Secondary Maximum Con-taminant Level and various constituents were detected at concentrations above background levels downgradi-ent of the landfill. Nitrate and ammonia, presumably derived from agricultural practices, also were detected in samples from locations hydraulically upgradient of the landfill. Oxidation-reduction conditions in the aquifer become more reducing with depth. This change is reflected by a change in the type of nitrogen compound detected and the concentration of dissolved oxygen and iron in the glacial drift aquifer. Concentrations of some of the major ions and metals may be affected by disso-lution of carbonate minerals in the aquifer and perhaps road salts.

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

NASA Astrophysics Data System (ADS)

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

2003-04-01

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

Glacial landform assemblages in the catchment area of the upper Quitarasca valley (Cordillera Blanca, Perú)

NASA Astrophysics Data System (ADS)

Iturrizaga, L.

2012-04-01

The research project focuses on the glacial landform sequences in the upper Quitarasca valley (8°51´S/77°36´W) with particular consideration of the Pucahirca glacier. The study area is located at the eastern side of the Cordillera Blanca, about almost 40 km valley upstream of the confluence with the Rio Santa valley. The highest catchment area is the Pucahirca Massif (6020 m a.s.l.). The present glacier tongue terminates at an elevation of 4500 m a.s.l.. The investigations analyzed the extent of the glaciations from the Last Glacial Maximum to modern times in regard to the transition of the moraine types during the course of deglaciation. The distinct moraine stages were correlated with existent glacial chronologies of adjacent valleys. Due to the hazard potential of the Laguna Safuna Alta, which developed in the late 1940s at the terminus of the Pucahirca glacier, detailed studies have been carried out by various research groups in regard to the composition of the historical / Neoglacial moraine composition providing at the same time valuable material for multi-temporal comparison of the recent development of the glacier tongue. The investigations presented here are part of a project on the glacial geomorphology in the Tropical Andes, financed by the Alexander von Humboldt Foundation.

Late Pleistocene glaciations of the arid subtropical Andes and new results from the Chajnantor Plateau, northern Chile

NASA Astrophysics Data System (ADS)

Ward, Dylan J.; Cesta, Jason M.; Galewsky, Joseph; Sagredo, Esteban

2015-11-01

The spatiotemporal pattern of glaciation along the Andes Mountains is an important proxy record reflecting the varying influence of global and regional circulation features on South American climate. However, the timing and extent of glaciation in key parts of the orogen, particularly the deglaciated arid Andes, are poorly constrained. We present new cosmogenic 10Be and 36Cl exposure ages for glacial features on and near the Chajnantor Plateau (23 °S). The new dates, although scattered due to cosmogenic inheritance, imply that the most recent extensive glacial occupation ended before or during the global Last Glacial Maximum (LGM). We discuss this new record in the context of published glacial chronologies from glacial features in Peru, Bolivia, and northern Chile rescaled using the latest cosmogenic 10Be production rate calibration for the tropical Andes. The results imply regionally synchronous moraine stabilization ca. 25-40 ka, 15-17 ka, and 12-14 ka, with the youngest of these moraines absent in records south of ∼20 °S, including in our new Chajnantor area chronology. This spatial pattern implicates easterly moisture in generating sufficient snowfall to glaciate the driest parts of the Andes, while allowing a role for westerly moisture, possibly modulated by the migration of the Southern Westerly Wind belt, in the regions near and south of the Atacama Desert.

Influential aspects of glacial resource for establishing Kuhl system (gravity flow irrigation) in the Hindu Kush, Karakoram and Himalaya ranges.

PubMed

Ashraf, Arshad; Iqbal, Ayesha

2018-04-27

The meltwater components play an important role in the hydrological regime of the Hindu Kush, Karakorum and Himalaya (HKH) region, in terms of high demand of water for food and fiber from snow and glacial resource. The communities of Himalayan mountains are facing challenges of food security owing to lack of the resource information for meeting their water requirements. In this study, suitability index approach was adopted to assess glacier resource potential for establishing kuhl irrigation system in HKH ranges of Pakistan. The basis of indexing is glacier accessibility and water yield potential of the glacial resource for irrigation estimated in terms of number and ice reserve of the glaciers. The suitability index was found good for about 1.4% glaciers constituting about 80% of the total ice reserves of the HKH region. Medium suitability constitutes about 36.1% glaciers with 12.6% of the total ice reserves, while low suitability was assessed for about 60% glaciers containing 1.5% ice reserves only. Maximum unit glacial reserve was estimated for Shigar basin, i.e., 1.44 km 3 , and among HKH ranges, 0.46 km 3 for the Karakoram range. A regular monitoring of the glacial resource would prove helpful in assessing vulnerability of this resource to climate change in the high Himalayan region in future. Copyright © 2018. Published by Elsevier B.V.

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

Risky business: The impact of climate and climate variability on human population dynamics in Western Europe during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Burke, Ariane; Kageyama, Masa; Latombe, Guilllaume; Fasel, Marc; Vrac, Mathieu; Ramstein, Gilles; James, Patrick M. A.

2017-05-01

The extent to which climate change has affected the course of human evolution is an enduring question. The ability to maintain spatially extensive social networks and a fluid social structure allows human foragers to ;map onto; the landscape, mitigating the impact of ecological risk and conferring resilience. But what are the limits of resilience and to which environmental variables are foraging populations sensitive? We address this question by testing the impact of a suite of environmental variables, including climate variability, on the distribution of human populations in Western Europe during the Last Glacial Maximum (LGM). Climate variability affects the distribution of plant and animal resources unpredictably, creating an element of risk for foragers for whom mobility comes at a cost. We produce a model of habitat suitability that allows us to generate predictions about the probable distribution of human populations and discuss the implications of these predictions for the structure of human populations and their social and cultural evolution during the LGM.

On the differences between Last Glacial Maximum and Mid-Holocene climates in southern South America simulated by PMIP3 models

NASA Astrophysics Data System (ADS)

Berman, Ana Laura; Silvestri, Gabriel E.; Tonello, Marcela S.

2018-04-01

Differences between climate conditions during the Last Glacial Maximum (LGM) and the Mid-Holocene (MH) in southern South America inferred from the state-of-the-art PMIP3 paleoclimatic simulations are described for the first time in this paper. The aim is to expose characteristics of past climate changes occurred without human influence. In this context, numerical simulations are an indispensable tool for inferring changes in near-surface air temperature and precipitation in regions where proxy information is scarce or absent. The analyzed PMIP3 models describe MH temperatures significantly warmer than those of LGM with magnitudes of change depending on the season and the specific geographic region. In addition, models indicate that seasonal mean precipitation during MH increased with respect to LGM values in wide southern continental areas to the east of the Andes Cordillera whereas seasonal precipitation developed in areas to the west of Patagonian Andes reduced from LGM to MH.

Paleolithic human exploitation of plant foods during the last glacial maximum in North China

PubMed Central

Liu, Li; Bestel, Sheahan; Shi, Jinming; Song, Yanhua; Chen, Xingcan

2013-01-01

Three grinding stones from Shizitan Locality 14 (ca. 23,000–19,500 calendar years before present) in the middle Yellow River region were subjected to usewear and residue analyses to investigate human adaptation during the last glacial maximum (LGM) period, when resources were generally scarce and plant foods may have become increasingly important in the human diet. The results show that these tools were used to process various plants, including Triticeae and Paniceae grasses, Vigna beans, Dioscorea opposita yam, and Trichosanthes kirilowii snakegourd roots. Tubers were important food resources for Paleolithic hunter–gatherers, and Paniceae grasses were exploited about 12,000 y before their domestication. The long tradition of intensive exploitation of certain types of flora helped Paleolithic people understand the properties of these plants, including their medicinal uses, and eventually led to the plants' domestication. This study sheds light on the deep history of the broad spectrum subsistence strategy characteristic of late Pleistocene north China before the origins of agriculture in this region. PMID:23509257

The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum

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

Liu, Wei; Lu, Jian; Leung, Lai-Yung R.

2015-02-22

This paper investigates the changes of the Southern Westerly Winds (SWW) and Southern Ocean (SO) upwelling between the Last Glacial Maximum (LGM) and preindustrial (PI) in the PMIP3/CMIP5 simulations, highlighting the role of the Antarctic sea ice in modulating the wind stress effect on the ocean. Particularly, a discrepancy may occur between the changes in SWW and westerly wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the wind stress in driving the liquid ocean. Such discrepancy may reflect the LGM condition in reality, in view of that the model simulates this condition hasmore » most credible simulation of modern SWW and Antarctic sea ice. The effect of wind stress on the SO upwelling is further explored via the wind-induced Ekman pumping, which is reduced under the LGM condition in all models, in part by the sea-ice “capping” effect present in the models.« less

Paleolithic human exploitation of plant foods during the last glacial maximum in North China.

PubMed

Liu, Li; Bestel, Sheahan; Shi, Jinming; Song, Yanhua; Chen, Xingcan

2013-04-02

Three grinding stones from Shizitan Locality 14 (ca. 23,000-19,500 calendar years before present) in the middle Yellow River region were subjected to usewear and residue analyses to investigate human adaptation during the last glacial maximum (LGM) period, when resources were generally scarce and plant foods may have become increasingly important in the human diet. The results show that these tools were used to process various plants, including Triticeae and Paniceae grasses, Vigna beans, Dioscorea opposita yam, and Trichosanthes kirilowii snakegourd roots. Tubers were important food resources for Paleolithic hunter-gatherers, and Paniceae grasses were exploited about 12,000 y before their domestication. The long tradition of intensive exploitation of certain types of flora helped Paleolithic people understand the properties of these plants, including their medicinal uses, and eventually led to the plants' domestication. This study sheds light on the deep history of the broad spectrum subsistence strategy characteristic of late Pleistocene north China before the origins of agriculture in this region.

Stable isotopes of fossil teeth corroborate key general circulation model predictions for the Last Glacial Maximum in North America

NASA Astrophysics Data System (ADS)

Kohn, Matthew J.; McKay, Moriah

2010-11-01

Oxygen isotope data provide a key test of general circulation models (GCMs) for the Last Glacial Maximum (LGM) in North America, which have otherwise proved difficult to validate. High δ18O pedogenic carbonates in central Wyoming have been interpreted to indicate increased summer precipitation sourced from the Gulf of Mexico. Here we show that tooth enamel δ18O of large mammals, which is strongly correlated with local water and precipitation δ18O, is lower during the LGM in Wyoming, not higher. Similar data from Texas, California, Florida and Arizona indicate higher δ18O values than in the Holocene, which is also predicted by GCMs. Tooth enamel data closely validate some recent models of atmospheric circulation and precipitation δ18O, including an increase in the proportion of winter precipitation for central North America, and summer precipitation in the southern US, but suggest aridity can bias pedogenic carbonate δ18O values significantly.

Wet-based glaciation in Phlegra Montes, Mars.

NASA Astrophysics Data System (ADS)

Gallagher, Colman; Balme, Matt

2016-04-01

Eskers are sinuous landforms composed of sediments deposited from meltwaters in ice-contact glacial conduits. This presentation describes the first definitive identification of eskers on Mars still physically linked with their parent system (1), a Late Amazonian-age glacier (~150 Ma) in Phlegra Montes. Previously described Amazonian-age glaciers on Mars are generally considered to have been dry based, having moved by creep in the absence of subglacial water required for sliding, but our observations indicate significant sub-glacial meltwater routing. The confinement of the Phlegra Montes glacial system to a regionally extensive graben is evidence that the esker formed due to sub-glacial melting in response to an elevated, but spatially restricted, geothermal heat flux rather than climate-induced warming. Now, however, new observations reveal the presence of many assemblages of glacial abrasion forms and associated channels that could be evidence of more widespread wet-based glaciation in Phlegra Montes, including the collapse of several distinct ice domes. This landform assemblage has not been described in other glaciated, mid-latitude regions of the martian northern hemisphere. Moreover, Phlegra Montes are flanked by lowlands displaying evidence of extensive volcanism, including contact between plains lava and piedmont glacial ice. These observations provide a rationale for investigating non-climatic forcing of glacial melting and associated landscape development on Mars, and can build on insights from Earth into the importance of geothermally-induced destabilisation of glaciers as a key amplifier of climate change. (1) Gallagher, C. and Balme, M. (2015). Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars, Earth and Planetary Science Letters, 431, 96-109.

Reconstructing the migration patterns of late Pleistocene mammals from northern Florida, USA

NASA Astrophysics Data System (ADS)

Hoppe, Kathryn A.; Koch, Paul L.

2007-11-01

We used analyses of the strontium isotope ( 87Sr/ 86Sr) ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the Aucilla River in northern Florida. Specimens date to the late-glacial period and before the last glacial maximum (pre-LGM). Deer and tapir displayed low 87Sr/ 86Sr ratios that were similar to the ratios of Florida environments, which suggest that these taxa did not migrate long distance outside of the Florida region. Mastodons, mammoths, and equids all displayed a wide range of 87Sr/ 86Sr ratios. Some individuals in each taxon displayed low 87Sr/ 86Sr ratios that suggest they ranged locally, while other animals had high 87Sr/ 86Sr ratios that suggest they migrated long distances (> 150 km) outside of the Florida region. Mastodons were the only taxa from this region that provided enough well-dated specimens to compare changes in migration patterns over time. Pre-LGM mastodons displayed significantly lower 87Sr/ 86Sr ratios than late-glacial mastodons, which suggests that late-glacial mastodons from Florida migrated longer distances than their earlier counterparts. This change in movement patterns reflects temporal changes in regional vegetation patterns.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Sea-level records from the U.S. mid-Atlantic constrain Laurentide Ice Sheet extent during Marine Isotope Stage 3

PubMed Central

Pico, T; Creveling, J. R.; Mitrovica, J. X.

2017-01-01

The U.S. mid-Atlantic sea-level record is sensitive to the history of the Laurentide Ice Sheet as the coastline lies along the ice sheet's peripheral bulge. However, paleo sea-level markers on the present-day shoreline of Virginia and North Carolina dated to Marine Isotope Stage (MIS) 3, from 50 to 35 ka, are surprisingly high for this glacial interval, and remain unexplained by previous models of ice age adjustment or other local (for example, tectonic) effects. Here, we reconcile this sea-level record using a revised model of glacial isostatic adjustment characterized by a peak global mean sea level during MIS 3 of approximately −40 m, and far less ice volume within the eastern sector of the Laurentide Ice Sheet than traditional reconstructions for this interval. We conclude that the Laurentide Ice Sheet experienced a phase of very rapid growth in the 15 kyr leading into the Last Glacial Maximum, thus highlighting the potential of mid-field sea-level records to constrain areal extent of ice cover during glacial intervals with sparse geological observables. PMID:28555637

The Influence of the East Asian Winter Monsoon on Indonesian Rainfall During the Past 60,000 Years

NASA Astrophysics Data System (ADS)

Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

2013-12-01

The Indo-Pacific Warm Pool (IPWP) invigorates the oceanic-atmospheric circulation in the tropics, with far-reaching climate impacts that extend into the high latitudes. A growing number of deglacial proxy reconstructions from the Maritime Continent and its surrounding seas have revealed the importance of both high- and low-latitude climate processes to IPWP rainfall during the deglaciation and the Holocene. However, few records extend beyond the Last Glacial Maximum (LGM), making it difficult to assess regional rainfall characteristics and monsoon interactions under the glacial/interglacial boundary conditions of the Pleistocene. Proxy reconstructions of the oxygen and hydrogen isotopic composition of rainfall (δ18O/δDprecip) have proven useful in understanding millennial to orbital scale changes in the climate of the Maritime Continent, but the tendency for δ18O/δDprecip in this region to reflect regional and/or remote climate processes has highlighted the need to reconstruct δ18O/δDprecip alongside independent proxies for continental rainfall amount. Here we present a reconstruction of δDprecip using leaf wax compounds preserved in the sediments of Lake Towuti, Central Sulawesi, from 60,000 years before present (kyr BP) to today. Our δDprecip reconstruction provides a precipitation isotopic counterpart to multi-proxy geochemical reconstructions of surface hydrology and vegetation characteristics from the same sediment cores, enabling for the first time an independent assessment of both continental rainfall intensity and δDprecip from this region on glacial/interglacial timescales. We find that orbital-scale variations in δDprecip and rainfall intensity are strongly tied to the East Asian Winter Monsoon (EAWM), which is an important contributor to the band of convection over the Maritime Continent during austral summer. Unlike today, however, severely dry conditions in Central Sulawesi during the Last Glacial Maximum were accompanied by a strengthened EAWM and D-depleted precipitation. In contrast, wet conditions in Central Sulawesi during Marine Isotope Stage 3 (MIS3) and during the early Holocene occurred when the EAWM was weakened. These findings support previous inferences based on Australian data that glacial boundary conditions modified the relationship between the EAWM and the Australian-Indonesian Summer Monsoon (AISM). However, previously proposed mechanisms for this modified EAWM/AISM relationship are not sufficient to explain our observations in Indonesia, and must be expanded. We propose revisions to these mechanisms in order to explain observations of Indonesian rainfall and δDprecip. Our findings provide important context for the circulation patterns that drove rainfall variations in Central Sulawesi during the past 60 kyr, and help to reconcile some of the disagreements among late Pleistocene records of surface runoff and δ18O/δDprecip from the IPWP region.

Impact of Anthropogenic CO2 on the Next Glacial Cycle

NASA Astrophysics Data System (ADS)

Herrero, C.; García-Olivares, A.; Pelegrí, J. L.

2014-12-01

A simple relaxation-type model (García-Olivares and Herrero, 2013) based on an optimization of Paillard and Parrenin (2004), has been used to predict the future evolution of atmospheric CO2, global ice volume and Antarctic ice cover during the next 300 kyr, with and without the atmospheric CO2 perturbation caused by anthropogenic emissions.The initial atmospheric CO2 condition is obtained after a critical data analysis that sets 1300 Gt as the most realistic carbon Ultimate Recoverable Resources, with the help of a global compartmental model to determine the carbon transfer function to the atmosphere. This analysis sets a peak of emissions on year 2037 AD and a maximum CO2 concentration of 519 ppmv in 2300 AD, leading to 20 kyr of abnormally high greenhouse effect. Weathering compensation and emission of methane from clathrates have also been considered as they have relevant effects on the dynamics of the system after the perturbation.The anthropogenic CO2 pulse clearly perturbs the natural cycle for all model variables during the forthcoming 300 kyr. The present interglacial will be lengthen by 25 kyr, as the anthropogenic perturbation will lead to a delay in the future advance of the ice sheet on the Antarctic shelf and a consequent perturbation of the deep ocean stratification, so the relative maximum of boreal insolation 65 kyr AP will not affect the developing glaciation. Instead, it will be the following insolation peak, about 110 kyr AP, which will find an appropriate climatic state to trigger the next deglaciation. The next glacial maximum will take place about 105 kyr AP and the following interglacial will be delayed forward in time by 44 kyr in relation to unperturbed conditions.This study endorses the idea that relaxation type coupled models, despite their simple structure, may retain the principal Earth's climatic interactions, being capable of accounting for the natural evolution of an externally imposed atmospheric CO2 pulse. - Garcia-Olivares, A. and Herrero, C. (2013) "Simulation of glacial-interglacial cycles by simple relaxation models: consistency with observational results" Clim. Dyn., 41:1307-1331- Paillard, D. and Parrenin, F. (2004) "The Antarctic ice sheet and the triggering of deglaciations" Earth. Planet. Sci. Lett., 227, 263 - 271

Glacial vicariance in Eurasia: mitochondrial DNA evidence from Scots pine for a complex heritage involving genetically distinct refugia at mid-northern latitudes and in Asia Minor

PubMed Central

Naydenov, Krassimir; Senneville, Sauphie; Beaulieu, Jean; Tremblay, Francine; Bousquet, Jean

2007-01-01

Background At the last glacial maximum, Fennoscandia was covered by an ice sheet while the tundra occupied most of the rest of northern Eurasia. More or less disjunct refugial populations of plants were dispersed in southern Europe, often trapped between mountain ranges and seas. Genetic and paleobotanical evidences indicate that these populations have contributed much to Holocene recolonization of more northern latitudes. Less supportive evidence has been found for the existence of glacial populations located closer to the ice margin. Scots pine (Pinus sylvestris L.) is a nordic conifer with a wide natural range covering much of Eurasia. Fractures in its extant genetic structure might be indicative of glacial vicariance and how different refugia contributed to the current distribution at the continental level. The population structure of Scots pine was investigated on much of its Eurasian natural range using maternally inherited mitochondrial DNA polymorphisms. Results A novel polymorphic region of the Scots pine mitochondrial genome has been identified, the intron 1 of nad7, with three variants caused by insertions-deletions. From 986 trees distributed among 54 populations, four distinct multi-locus mitochondrial haplotypes (mitotypes) were detected based on the three nad7 intron 1 haplotypes and two previously reported size variants for nad1 intron B/C. Population differentiation was high (GST = 0.657) and the distribution of the mitotypes was geographically highly structured, suggesting at least four genetically distinct ancestral lineages. A cosmopolitan lineage was widely distributed in much of Europe throughout eastern Asia. A previously reported lineage limited to the Iberian Peninsula was confirmed. A new geographically restricted lineage was found confined to Asia Minor. A new lineage was restricted to more northern latitudes in northeastern Europe and the Baltic region. Conclusion The contribution of the various ancestral lineages to the current distribution of Scots pine was asymmetric and extant endemism reflected the presence of large geographic barriers to migration. The results suggest a complex biogeographical history with glacial refugia shared with temperate plant species in southern European Peninsulas and Asia Minor, and a genetically distinct glacial population located more North. These results confirm recent observations for cold tolerant species about the possible existence of refugial populations at mid-northern latitudes contributing significantly to the recolonization of northern Europe. Thus, Eurasian populations of nordic plant species might not be as genetically homogenous as assumed by simply considering them as offsets of glacial populations located in southern peninsulas. As such, they might have evolved distinctive genetic adaptations during glacial vicariance, worth evaluating and considering for conservation. PMID:18034901

Changing Dust Provenance to the South Atlantic Since the Last Glacial Maximum and Implications for the Southern Hemisphere Wind Belts

NASA Astrophysics Data System (ADS)

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

2017-12-01

The Southern Hemisphere Westerly Winds are known to be important for climate due to their effects on the global carbon cycle and on the global thermohaline circulation (THC). Numerous proxy records have been interpreted to indicate significant glacial to interglacial changes in the SHWW. There is no clear consensus regarding their strength and position during the Last Glacial Maximum (LGM), though most observations are consistent with an equatorward displacement of the glacial wind belts. We test this hypothesis using geochemical provenance measurements of deep-sea sediments deposited along the Mid-Atlantic Ridge between 24°S and 37°S. In the central South Atlantic, dust can be delivered from South America via the Westerlies, or from Africa via the Trade Winds. The dust sources on South America and Africa have very different geochemical signatures, making it possible to distinguish between eolian transport via the Westerlies vs. the Trade Winds. Any northward shift in the Southern Hemisphere Westerlies should increase the northward extent of a South American provenance in sediments dominated by eolian sources. We measured major and trace element concentrations, and radiogenic isotopes of Ar, Sr, Nd, and Pb on the <5 μm lithogenic sediments from a latitudinal transect of cores along the flanks of the Mid-Atlantic Ridge. In general, the data point to an older continental provenance for the northernmost sites, and a much younger provenance for the southernmost sites, consistent with western Africa as the primary source of sediment in the north, and South American sediments being delivered to the south. Glacial sediments display a clear compositional boundary near 30°S, which likely reflects the boundary between the Westerlies and the Trade Winds. The data are therefore not consistent with northward shifted wind belts at the LGM. The observed variations in terrigenous sediment composition at these sites may, however, be consistent with an equatorward displacement of the SHWW through the deglaciation. The results may also point to changes in the continental source regions supplying dust to the atmosphere as the glaciers retreated.

Deep circulation changes in the South Atlantic since the Last Glacial Maximum from Nd isotope and multi-proxy records

NASA Astrophysics Data System (ADS)

Wei, R.; Abouchami, W.; Zahn, R.; Masque, P.

2016-01-01

We report down-core sedimentary Nd isotope (εNd) records from two South Atlantic sediment cores, MD02-2594 and GeoB3603-2, located on the western South African continental margin. The core sites are positioned downstream of the present-day flow path of North Atlantic Deep Water (NADW) and close to the Southern Ocean, which makes them suitable for reconstructing past variability in NADW circulation over the last glacial cycle. The Fe-Mn leachates εNd records show a coherent decreasing trend from glacial radiogenic values towards less radiogenic values during the Holocene. This trend is confirmed by εNd in fish debris and mixed planktonic foraminifera, albeit with an offset during the Holocene to lower values relative to the leachates, matching the present-day composition of NADW in the Cape Basin. We interpret the εNd changes as reflecting the glacial shoaling of Southern Ocean waters to shallower depths combined with the admixing of southward flowing Northern Component Water (NCW). A compilation of Atlantic εNd records reveals increasing radiogenic isotope signatures towards the south and with increasing depth. This signal is most prominent during the Last Glacial Maximum (LGM) and of similar amplitude across the Atlantic basin, suggesting continuous deep water production in the North Atlantic and export to the South Atlantic and the Southern Ocean. The amplitude of the εNd change from the LGM to Holocene is largest in the southernmost cores, implying a greater sensitivity to the deglacial strengthening of NADW at these sites. This signal impacted most prominently the South Atlantic deep and bottom water layers that were particularly deprived of NCW during the LGM. The εNd variations correlate with changes in 231Pa/230Th ratios and benthic δ13C across the deglacial transition. Together with the contrasting 231Pa/230Th: εNd pattern of the North and South Atlantic, this indicates a progressive reorganization of the AMOC to full strength during the Holocene.

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

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

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

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 line. During the Holocene no increased anthropogenic impact around the Maundi crater can be observed, since neither higher fire activity nor a spread of hemerophilic plants is recorded. This pollen archive reveals shifts in the upper vegetation zones (ericaceous zone and montane forest zone) of at least 1100 m but underlines the role of Mt Kilimanjaro as a glacial refuge for montane forest species similar to that of the Eastern Arc Mountains.

Quantifying the resolution level where the GRACE satellites can separate Greenland's glacial mass balance from surface mass balance

NASA Astrophysics Data System (ADS)

Bonin, J. A.; Chambers, D. P.

2015-02-01

Mass change over Greenland can be caused by either changes in the glacial mass balance (GMB) or the precipitation-based surface mass balance (SMB). The GRACE satellite gravity mission cannot directly separate the two physical causes because it measures the sum of the entire mass column with limited spatial resolution. We demonstrate one theoretical way to indirectly separate SMB from GMB with GRACE, using a least squares inversion technique with knowledge of the location of the glacier. However, we find that the limited 60 × 60 spherical harmonic representation of current GRACE data does not provide sufficient resolution to adequately accomplish the task. We determine that at a maximum degree/order of 90 × 90 or above, a noise-free gravity measurement could theoretically separate the SMB from GMB signals. However, current GRACE satellite errors are too large at present to separate the signals. A noise reduction of a factor of 9 at a resolution of 90 × 90 would provide the accuracy needed for the interannual SMB and GMB to be accurately separated.

Influence of Physiochemical and watershed characteristics on mercury concentration in walleye, Sander vitreus, M.

USGS Publications Warehouse

Hayer, Cari-Ann; Chipps, Steven R.; Stone, James J.

2011-01-01

Elevated mercury concentration has been documented in a variety of fish and is a growing concern for human consumption. Here, we explore the influence of physiochemical and watershed attributes on mercury concentration in walleye (Sander vitreus, M.) from natural, glacial lakes in South Dakota. Regression analysis showed that water quality attributes were poor predictors of walleye mercury concentration (R2 = 0.57, p = 0.13). In contrast, models based on watershed features (e.g., lake level changes, watershed slope, agricultural land, wetlands) and local habitat features (i.e., substrate composition, maximum lake depth) explained 81% (p = 0.001) and 80% (p = 0.002) of the variation in walleye mercury concentration. Using an information theoretic approach we evaluated hypotheses related to water quality, physical habitat and watershed features. The best model explaining variation in walleye mercury concentration included local habitat features (Wi = 0.991). These results show that physical habitat and watershed features were better predictors of walleye mercury concentration than water chemistry in glacial lakes of the Northern Great Plains.

Genetic structure of faucet snail, Bithynia tentaculata populations in North Americal based on microsattelite markers

USGS Publications Warehouse

Perez, Kathryn E.; Werren, Rebecca L.; Lynum, Christopher A.; Hartman, Levi A.; Majoros, Gabor; Cole, Rebecca A.

2016-01-01

Bithynia tentaculata is believed to have been extirpated from North America during the last glacial maximum. It was reintroduced into North America via the Great Lakes basin in the 1800’s and has recently been expanding its geographic range. This snail serves as intermediate host for three trematodes that cause extensive recurring morbidity and mortality events in migratory water birds along the Mississippi River. Using twelve microsatellite loci for ~200 individual snails from 11 populations in North America and Europe, we examined one of the three major geographic regions from which founding populations into the Great Lakes typically originate. Our data supports a single recolonization of North America into the Great Lakes Basin followed by subsequent introduction events from the Great Lakes to other large watersheds in North America. However, additional watersheds in Europe require sampling to confirm this result. No populations with genetic signatures indicative of North American glacial relics were found. The initial invasion of North America was likely not from the Ponto-Caspian basin, the usual source of freshwater invasive species to the Laurentian Great Lakes.

Calcareous microfossil-based orbital cyclostratigraphy in the Arctic Ocean

USGS Publications Warehouse

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

2016-01-01

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

Run-off regime of the small rivers in mountain landscapes (on an example of the mountain "Mongun-taiga

NASA Astrophysics Data System (ADS)

Pryahina, G.; Zelepukina, E.; Guzel, N.

2012-04-01

Hydrological characteristics calculations of the small mountain rivers in the basins with glaciers frequently cause complexity in connection with absence of standard hydrological supervision within remote mountain territories. The unique way of the actual information reception on a water mode of such rivers is field work. The rivers of the mountain Mongun-taiga located on a joint of Altai and Sayan mountains became hydrological researches objects of Russian geographical society complex expeditions in 2010-2011. The Mongun-taiga cluster of international biosphere reserve "Ubsunurskaya hollow" causes heightened interest of researchers — geographers for many years. The original landscape map in scale 1:100000 has been made, hydrological supervision on the rivers East Mugur and ugur, belonging inland basin of Internal Asia are lead. Supervision over the river drain East Mugur runoff were spent in profile of glacier tongue (the freezing area - 22 % (3.2 km2) from the reception basin) and in the closing alignment of the river located on distance of 3,4 km below tongue of glacier. During researches following results have been received. During the ablation period diurnal fluctuations with a strongly shown maximum and minimum of water discharges are typically for the small rivers with considerable share of a glacial food. The run-off maximum from the glacier takes place from 2 to 7 p.m., the run-off minimum is observed early in the morning. High speed of thawed snow running-off from glacier tongue and rather small volume of dynamic stocks water on an ice surface lead to growth of water discharge. In the bottom profile the time of maximum and minimum of water discharge is displaced on the average 2 hours, it depends of the water travel time. Maximum glacial run-off discharge (1.12 m3/s) in the upper profile was registered on July 16 (it was not rain). Volumes of daily runoff in the upper and bottom profiles were 60700-67600 m3 that day. The run-off from nonglacial part of the basin is formed by underground waters and melting snowfields, during the absence of rainfall period the part of one amounted to 10% of the run-off in the lower profile. We suggest that this water discharge corresponds to base flow value in the lower profile because the area of snowfields of the basin was < 0.1 km2 that year. Run-off monitoring has showed that rivers with a small glacial food are characterized by absence of diurnal balance of runoff. During rainfall the water content of river has being increased due to substantial derivation of basin and, as a result, fast flowing rain water into bed of river. The sharp decrease in water content of river during periods of rainfall absence indicates low inventory of soil and groundwater and the low rate of glacial. Thus, glaciers and character of the relief influence the formation of run-off small mountain rivers. Results of researches will be used for mathematical modeling mountain rivers run-off.

Overdeeping and stratigraphy of a typical Alpine foreland glacier

NASA Astrophysics Data System (ADS)

Salcher, Bernhard; Reinhard, Starnberger; Götz, Joachim

2015-04-01

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

INTERACTION OF CLIMATE AND LAND USE IN FUTURE TERRESTRIAL CARBON STORAGE AND RELEASE

EPA Science Inventory

The processes controlling total carbon (C) storage and release from the terrestrial biosphere are still poorly quantified. e conclude from analysis of paleodata and climate biome model output that terrestrial C exchanges since the last glacial maximum (LGM) were dominated by slow...

Noble Gas Proxy Evidence Of Holocene Climate Fluctuations In The Elwha Watershed, Olympic Mountains, Washington

EPA Science Inventory

Paleotempertures retrieved from the groundwater archives in the largest watershed (≈800 km2) in the Olympic Mountains suggest asynchronous Olympic Peninsula climate responses during the Everson interstade period after the last continental glacial maximum. Dissolved noble gases fr...

Deglaciation and post-glacial environmental evolution in the Western Massif of Picos de Europa

NASA Astrophysics Data System (ADS)

Ruiz-Fernández, Jesús; Oliva, Marc; García, Cristina; López-Sáez, José Antonio; Gallinar, David; Geraldes, Miguel

2014-05-01

This study examines the process of deglaciation of the Western Massif of Picos de Europa through field work, geomorphological mapping, sedimentary records and absolute datings of 14C. This massif has several peaks over 2,400 m a.s.l. (Peña Santa de Castilla, 2,596 m; Torre Santa María, 2,486 m; Torre del Mediu, 2,467 m). It is composed mainly by Carboniferous limestones. This area has been intensively affected by karstic dissolution, Quaternary glaciers and fluvio-torrential processes (Miotke, 1968; Moreno et al, 2010; Ruiz-Fernández et al, 2009; Ruiz-Fernández, 2013). At present day, periglacial processes are active at the highest elevations (Ruiz-Fernández, 2013). We have identified four main glacial stages regarding the deglaciation of the massif: (i) maximum advance corresponding to the Last Glaciation, (ii) retreat and stabilization after the maximum advance, (iii) Late Glacial, and (iv) Little Ice Age. Sedimentological studies also contribute data to the understanding of the chronological framework of these environmental changes. The datings of the bottom sediments in two long sequences (8 and 5.4 m) provided a minimum age of 18,075 ± 425 cal BP for the maximum advance stage and 11,150 ± 900 cal BP for retreat and stabilization in the phase following the maximum advance. The ongoing analyses of these sequences at very high resolution will provide new knowledge about the environmental conditions prevailing since the deglaciation of the massif. References Miotke, F.D. (1968). Karstmorphologische studien in der glazial-überformten Höhenstufe der Picos de Europa, Nordspanien. Hannover, Selbtverlag der Geografischen Gessellschaft, 161 pp. Moreno, A., Valero, B.L., Jiménez, M., Domínguez, M.J., Mata, M.P., Navas, A., González, P., Stoll, H., Farias, P., Morellón, M., Corella, J.P. & Rico, M. (2010). The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains, Northern Spain). Journal of Quaternary Science, 25 (7), 1076-1091. Ruiz-Fernández, J. (2013). Las formas de modelado glaciar, periglaciar y fluviotorrencial del Macizo Occidental de los Picos de Europa (Cordillera Cantábrica). Unpublished PhD Thesis, University of Oviedo, 314 pp. Ruiz-Fernández, J., Poblete. M.A., Serrano, P., Martí, C. & García-Ruiz, J.M. (2009). Morphometry of glacial cirques in the Cantabrian Range (Northwest Spain). Zeitschrift für Geomorphologie N. F., 53, 47-68.

Origin and depositional environment of fine-grained sediments since the last glacial maximum in the southeastern Yellow Sea: evidence from rare earth elements

NASA Astrophysics Data System (ADS)

Um, In Kwon; Choi, Man Sik; Lee, Gwang Soo; Chang, Tae Soo

2015-12-01

Despite the well-reconstructed seismic stratigraphy of the Holocene mud deposit in the southeastern Yellow Sea, known as the Heuksan mud belt (HMB), the provenances of these sediments and their depositional environments are unclear, especially for the fine-grained sediments. According to seismic data (extracted from another article in this special issue), the HMB comprises several sedimentary units deposited since the last glacial maximum. Based on analytical results on rare earth elements, fine-grained sediments in all sedimentary units can be interpreted as mixtures of sediments discharged from Chinese and Korean rivers. The proportions of fine-grained sediments from Chinese rivers (74.5 to 80.0%) were constant and higher than those from Korean rivers in all units. This fact demonstrates that all units have the same fine-grained sediment provenance: units III-b and III-a, located in the middle and northern parts of the HMB and directly deposited from Chinese rivers during the sea-level lowstand, could be the sediment source for units II-b and II-a. Unit I, while ambiguous, is of mixed origin combining reworked sediments from nearby mud deposits and Changjiang River-borne material with those of the Keum River. The results of this study indicate that at least 18.6% of bulk sediments in the HMB clearly originate from Chinese rivers, despite its location close to the southwestern coast of Korea.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Ferraro, Serena; Sulli, Attilio; Di Stefano, Enrico; Giaramita, Luigi; Incarbona, Alessandro; Graham Mortyn, P.; Sprovieri, Mario; Sprovieri, Rodolfo; Tonielli, Renato; Vallefuoco, Mattia; Zizzo, Elisabetta; Tranchida, Giorgio

2018-06-01

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW-SE normal faults and filled by thick Pliocene-Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

Vegetative Succession in Recently Deglaciated Land in Kenai Fjords National Park

NASA Astrophysics Data System (ADS)

Green, C.; Klein, A. G.; Cairns, D. M.

2017-12-01

Poleward vegetation expansion has affected Alaska for decades and due to recently increased rates of warming, the expansion will accelerate. Glacial recession in Kenai Fjords National Park has exposed previously ice-covered land with vegetation succession occurring just a few years following glacial retreat. Land cover changes in recently deglaciated areas are affected by surface-air interactions, temperature gradients, and ecosystem development. Using satellite images from Landsat 5, 7, and 8 and the previous extents of four retreating glaciers from 1985 to 2015 within Kenai Fjords National Park, this study examines the relationship between deglaciation rates and vegetation greening. The glaciers, Exit (-15.04 m/yr), Petrof (-31.12 m/yr), Lowell (-33.14 m/yr), and Yalik (-51.32 m/yr) were selected based on their location, whether they were land or lake terminating, and their average retreat rate measured between 1985 and 2015. These glaciers have also been extensively studied. Combining historic glacier extents with 371 summer (JJA) Landsat images gathered from Google's Earth Engine platform we identified annual summer changes in NDVI of locations that were deglaciated between 1985, 1995, 2005, and 2015. Summer temperature maximums were determined to be more correlated with deglaciation, as measured using NDSI, than mean summer temperatures. Using NDVI, heightened deglaciation rates were found to be reasonably correlated with vegetation succession. The faster retreating glaciers, Lowell and Yalik, exhibited higher mean and maximum rates of increase of NDVI in their terminus areas than Exit and Petrof, the two slower retreating glaciers.

Late Quaternary palaeoenvironmental reconstruction of sediment drift accumulation in the Malta Graben (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Ferraro, Serena; Sulli, Attilio; Di Stefano, Enrico; Giaramita, Luigi; Incarbona, Alessandro; Graham Mortyn, P.; Sprovieri, Mario; Sprovieri, Rodolfo; Tonielli, Renato; Vallefuoco, Mattia; Zizzo, Elisabetta; Tranchida, Giorgio

2018-03-01

The Malta Graben is a deep tectonic depression in the Sicily Channel, bounded by NW-SE normal faults and filled by thick Pliocene-Quaternary deposits. A previous analysis of a giant piston core (LC09) from the Malta Graben had revealed a wide range of sedimentary features (carbonate turbidites, bioturbated mud and scours), although the chronostratigraphic constraint of the stacking pattern has remained elusive. After establishing a reliable chronological framework based on seven radiocarbon dates for a shorter core from the Malta Graben (ANSIC03-735), a down-core analysis of planktonic foraminifer and coccolith abundance, stable isotopes and sediment grain size was carried out. Since the last glacial maximum, palaeoenvironmental conditions (surface fertility and deep chlorophyll maximum during the last glacial and the Younger Dryas; warm and oligotrophic water masses, with a deep nutricline and intense winter mixing during the Holocene) as well as selected calcareous plankton taxa trends and peaks seem to be similar to those reported for other central and western Mediterranean sites, possibly in spite of a unique response of these areas to late Quaternary climatic fluctuations. Four distinct layers, each tens of centimetres thick, are barren of foraminifers but not of coccoliths. Morphobathymetric data as well as new high-resolution and high-penetration seismic profiles show that prolonged contouritic activity has persisted on the western side of the Malta Graben. It is thus likely that layers barren of foraminifers are due to the overflow of fine-grained (clayey) material beyond drift channel dikes.

BMPix and PEAK tools: New methods for automated laminae recognition and counting—Application to glacial varves from Antarctic marine sediment

NASA Astrophysics Data System (ADS)

Weber, M. E.; Reichelt, L.; Kuhn, G.; Pfeiffer, M.; Korff, B.; Thurow, J.; Ricken, W.

2010-03-01

We present tools for rapid and quantitative detection of sediment lamination. The BMPix tool extracts color and gray scale curves from images at pixel resolution. The PEAK tool uses the gray scale curve and performs, for the first time, fully automated counting of laminae based on three methods. The maximum count algorithm counts every bright peak of a couplet of two laminae (annual resolution) in a smoothed curve. The zero-crossing algorithm counts every positive and negative halfway passage of the curve through a wide moving average, separating the record into bright and dark intervals (seasonal resolution). The same is true for the frequency truncation method, which uses Fourier transformation to decompose the curve into its frequency components before counting positive and negative passages. The algorithms are available at doi:10.1594/PANGAEA.729700. We applied the new methods successfully to tree rings, to well-dated and already manually counted marine varves from Saanich Inlet, and to marine laminae from the Antarctic continental margin. In combination with AMS14C dating, we found convincing evidence that laminations in Weddell Sea sites represent varves, deposited continuously over several millennia during the last glacial maximum. The new tools offer several advantages over previous methods. The counting procedures are based on a moving average generated from gray scale curves instead of manual counting. Hence, results are highly objective and rely on reproducible mathematical criteria. Also, the PEAK tool measures the thickness of each year or season. Since all information required is displayed graphically, interactive optimization of the counting algorithms can be achieved quickly and conveniently.

The Red Sea during the Last Glacial Maximum: implications for sea level reconstructions

NASA Astrophysics Data System (ADS)

Gildor, H.; Biton, E.; Peltier, W. R.

2006-12-01

The Red Sea (RS) is a semi-enclosed basin connected to the Indian Ocean via a narrow and shallow strait, and surrounded by arid areas which exhibits high sensitivity to atmospheric changes and sea level reduction. We have used the MIT GCM to investigate the changes in the hydrography and circulation in the RS in response to reduced sea level, variability in the Indian monsoons, and changes in atmospheric temperature and humidity that occurred during the Last Glacial Maximum (LGM). The model results show high sensitivity to sea level reduction especially in the salinity field (increasing with the reduction in sea level) together with a mild atmospheric impact. Sea level reduction decreases the stratification, increases subsurface temperatures, and alters the circulation pattern at the Strait of Bab el Mandab, which experiences a transition from submaximal flow to maximal flow. The reduction in sea level at LGM alters the location of deep water formation which shifts to an open sea convective site in the northern part of the RS compared to present day situation in which deep water is formed from the Gulf of Suez outflow. Our main result based on both the GCM and on a simple hydraulic control model which takes into account mixing process at the Strait of Bab El Mandeb, is that sea level was reduced by only ~100 m in the Bab El Mandeb region during the LGM, i.e. the water depth at the Hanish sill (the shallowest part in the Strait Bab el Mandab) was around 34 m. This result agrees with the recent reconstruction of the LGM low stand of the sea in this region based upon the ICE-5G (VM2) model of Peltier (2004).

Long-Term Vegetation Dynamics in a Megadiverse Hotspot: The Ice-Age Record of a Pre-montane Forest of Central Ecuador.

PubMed

Montoya, Encarni; Keen, Hayley F; Luzuriaga, Carmen X; Gosling, William D

2018-01-01

Tropical ecosystems play a key role in many aspects of Earth system dynamics currently of global concern, including carbon sequestration and biodiversity. To accurately understand complex tropical systems it is necessary to parameterise key ecological aspects, such as rates of change (RoC), species turnover, dynamism, resilience, or stability. To obtain a long-term (>50 years) perspective on these ecological aspects we must turn to the fossil record. However, compared to temperate zones, collecting continuous sedimentary archives in the lowland tropics is often difficult due to the active landscape processes, with potentially frequent volcanic, tectonic, and/or fluvial events confounding sediment deposition, preservation, and recovery. Consequently, the nature, and drivers, of vegetation dynamics during the last glacial are barely known from many non-montane tropical landscapes. One of the first lowland Amazonian locations from which palaeoecological data were obtained was an outcrop near Mera (Ecuador). Mera was discovered, and analysed, by Paul Colinvaux in the 1980s, but his interpretation of the data as indicative of a forested glacial period were criticised based on the ecology and age control. Here we present new palaeoecological data from a lake located less than 10 km away from Mera. Sediment cores raised from Laguna Pindo (1250 masl; 1°27'S, 78°05'W) have been shown to span the late last glacial period [50-13 cal kyr BP (calibrated kiloyears before present)]. The palaeoecological information obtained from Laguna Pindo indicate that the region was characterised by a relatively stable plant community, formed by taxa nowadays common at both mid and high elevations. Miconia was the dominant taxon until around 30 cal kyr BP, when it was replaced by Hedyosmum , Asteraceae and Ilex among other taxa. Heat intolerant taxa including Podocarpus , Alnus , and Myrica peaked around the onset of the Last Glacial Maximum (c. 21 cal kyr BP). The results obtained from Laguna Pindo support Colinvaux's hypothesis that glacial cooling resulted in a reshuffling of taxa in the region but did not lead to a loss of the forest structure. Wide tolerances of the plant species occurring to glacial temperature range and cloud formation have been suggested to explain Pindo forest stability. This scenario is radically different than the present situation, so vulnerability of the tropical pre-montane forest is highlighted to be increased in the next decades.

Late-Quaternary glaciation and postglacial emergence, southern Eureka Sound, high-Arctic Canada

NASA Astrophysics Data System (ADS)

O Cofaigh, Colm Seamus

Eureka Sound is the inter-island channel separating Ellesmere and Axel Heiberg islands, High Arctic Canada. This thesis reconstructs the glacial and sea level history of southern Eureka Sound through surficial geological mapping, studies of glacial sedimentology and geomorphology, surveying of raised marine shorelines, radiocarbon dating of marine shells and driftwood and surface exposure dating of erratics and bedrock. Granite dispersal trains, shelly till and ice-moulded bedrock record westerly-flow of warm-based, regional ice into Eureka Sound from a source on southeastern Ellesmere Island during the late Wisconsinan. Regional ice was coalescent with local ice domes over Raanes and northern Svendsen peninsulas. Marine limit (dating <=9.2 ka BP; <=9.9 ka cal BP) is inset into the dispersal trains and records early Holocene deglaciation of regional ice. Collectively these data indicate an extensive ice-cover in southern Eureka Sound during the Last Glacial Maximum. Ice-divides were located along the highlands of central Ellesmere and Axel Heiberg islands, from which ice converged on Eureka Sound, and subsequently flowed north and south along the channel. Deglaciation was characterised by a two-step retreat pattern, likely triggered by eustatic sea level rise and abrupt early Holocene warming. Initial break-up and radial retreat of ice in Eureka Sound and the larger fiords, preceded terrestrial stabilisation along coastlines and inner fiords. Location of deglacial depocentres was predominantly controlled by fiord bathymetry. Regionally, two-step deglaciation is reflected by prominent contrasts in glacial geomorphology between the inner and outer parts of many fiords. Glacial sedimentological and geomorphological evidence indicates spatial variation in basal thermal regime between retreating trunk glaciers. Holocene emergence of up to 150 m asl along southern Eureka Sound is recorded by raised marine deltas, beaches and washing limits. Emergence curves exhibit marked contrasts in the form and rate of initial unloading. Isobases drawn on the 8.5 ka shoreline for greater Eureka Sound demonstrate that a cell of highest emergence extends along the length of the channel, and closes in the vicinity of the entrance to Norwegian Bay. The isobase pattern indicates a distinct loading centre over the sound, and in conjunction with glacial geological evidence, suggests that the thickest late Wisconsinan ice lay over the channel.

Past ice-sheet behaviour: retreat scenarios and changing controls in the Ross Sea, Antarctica

NASA Astrophysics Data System (ADS)

Halberstadt, Anna Ruth W.; Simkins, Lauren M.; Greenwood, Sarah L.; Anderson, John B.

2016-05-01

Studying the history of ice-sheet behaviour in the Ross Sea, Antarctica's largest drainage basin can improve our understanding of patterns and controls on marine-based ice-sheet dynamics and provide constraints for numerical ice-sheet models. Newly collected high-resolution multibeam bathymetry data, combined with two decades of legacy multibeam and seismic data, are used to map glacial landforms and reconstruct palaeo ice-sheet drainage. During the Last Glacial Maximum, grounded ice reached the continental shelf edge in the eastern but not western Ross Sea. Recessional geomorphic features in the western Ross Sea indicate virtually continuous back-stepping of the ice-sheet grounding line. In the eastern Ross Sea, well-preserved linear features and a lack of small-scale recessional landforms signify rapid lift-off of grounded ice from the bed. Physiography exerted a first-order control on regional ice behaviour, while sea floor geology played an important subsidiary role. Previously published deglacial scenarios for Ross Sea are based on low-spatial-resolution marine data or terrestrial observations; however, this study uses high-resolution basin-wide geomorphology to constrain grounding-line retreat on the continental shelf. Our analysis of retreat patterns suggests that (1) retreat from the western Ross Sea was complex due to strong physiographic controls on ice-sheet drainage; (2) retreat was asynchronous across the Ross Sea and between troughs; (3) the eastern Ross Sea largely deglaciated prior to the western Ross Sea following the formation of a large grounding-line embayment over Whales Deep; and (4) our glacial geomorphic reconstruction converges with recent numerical models that call for significant and complex East Antarctic ice sheet and West Antarctic ice sheet contributions to the ice flow in the Ross Sea.

Glacial Lake Expansion in the Central Himalayas by Landsat Images, 1990–2010

PubMed Central

Nie, Yong; Liu, Qiao; Liu, Shiyin

2013-01-01

Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed. PMID:24376778

Glacial lake expansion in the central Himalayas by Landsat images, 1990-2010.

PubMed

Nie, Yong; Liu, Qiao; Liu, Shiyin

2013-01-01

Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed.

Glacial Lake Expansion in the Central Himalayas By Landsat Images, 1990-2010

NASA Astrophysics Data System (ADS)

Nie, Y.; Liu, Q.; Liu, S.

2014-12-01

Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed.

Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

NASA Astrophysics Data System (ADS)

Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

2013-12-01

Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid records therefore provide opportunities to compare climate inferences based upon ice core data and reconstructed ice margin histories with independent, biologically based estimates of air temperatures for the Holocene and possibly the Last Interglacial. Briner, J.P., Axford, Y., Forman, S.L., Miller, G.H., and Wolfe, A.P. 2007. Multiple generations of interglacial lake sediment preserved beneath the Laurentide Ice Sheet. Geology 35, 887-890. Levy, L.B., Kelly, M.A., Lowell, T.V., Hall, B.L., Hempel, L.A., Honsaker, W.M., Lusas, A.R., Howley, J.A., Axford, Y.L., 2013. Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate along the Greenland Ice Sheet margin. In press, Quaternary Science Reviews.

Insect-Based Holocene (and Last Interglacial?) Paleothermometry from the E and NW Greenland Ice Sheet Margins: A Fly's-Eye View of Warmth on Greenland

NASA Astrophysics Data System (ADS)

Axford, Y.; Bigl, M.; Carrio, C.; Corbett, L. B.; Francis, D. R.; Hall, B. L.; Kelly, M. A.; Levy, L.; Lowell, T. V.; Osterberg, E. C.; Richter, N.; Roy, E.; Schellinger, G. C.

2011-12-01

Here we present new paleotemperature reconstructions based upon insect (Chironomidae) assemblages and other proxies from lake sediment cores recovered in east Greenland at ~71° N near Scoresby Sund and in northwest Greenland at ~77° N near Thule/Qaanaaq. In east Greenland, Last Chance Lake (informal name) is a small, non-glacial lake situated ~90 km east of the Greenland Ice Sheet margin. The lake preserves a sedimentary record of the entire Holocene (Levy et al. 2013). Chironomids from Last Chance Lake record cold summer temperatures (and establishment of a cold-climate fauna including abundant Oliveridia and Pseudodiamesa) during the late Holocene, preceded by summer temperatures estimated to have been 3 to 6°C warmer during the first half of the Holocene (when summer insolation forcing was greater than today). In northwest Greenland, Delta Sø and Wax Lips Lake (informal name) both preserve Holocene sediments. Here we discuss the late Holocene chironomid record from Delta Sø, whereas from Wax Lips Lake (a small, non-glacial lake situated ~2 km west of the ice sheet margin) we present a longer sedimentary and biostratigraphic record. The deeper portions of cores from Wax Lips Lake yield pre-Holocene and nonfinite radiocarbon ages, suggesting that this lake preserves sediments predating the Last Glacial Maximum. Abundant chironomids in the pre-glacial sediments appear to record interglacial conditions, and we infer that these sediments may date to the Last Interglacial (Eemian). The preservation of in situ Last Interglacial lacustrine sediments so close to the modern ice sheet margin suggests a minimally erosive glacierization style throughout the last glacial period, like that inferred for other Arctic locales such as on Baffin Island (Briner et al. 2007), ~750 km southwest of our study site. Our study sites are situated nearby key ice core sites (including NEEM, Camp Century, Agassiz and Renland) and very close to the ice sheet margin. These chironomid records therefore provide opportunities to compare climate inferences based upon ice core data and reconstructed ice margin histories with independent, biologically based estimates of air temperatures for the Holocene and possibly the Last Interglacial. Briner, J.P., Axford, Y., Forman, S.L., Miller, G.H., and Wolfe, A.P. 2007. Multiple generations of interglacial lake sediment preserved beneath the Laurentide Ice Sheet. Geology 35, 887-890. Levy, L.B., Kelly, M.A., Lowell, T.V., Hall, B.L., Hempel, L.A., Honsaker, W.M., Lusas, A.R., Howley, J.A., Axford, Y.L., 2013. Holocene fluctuations of Bregne ice cap, Scoresby Sund, east Greenland: a proxy for climate along the Greenland Ice Sheet margin. In press, Quaternary Science Reviews.

Fire and vegetation shifts in the Americas at the vanguard of Paleoindian migration

USGS Publications Warehouse

Pinter, N.; Fiedel, S.; Keeley, J.E.

2011-01-01

Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt postglacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.

Major advance of South Georgia glaciers during the Antarctic Cold Reversal following extensive sub-Antarctic glaciation

PubMed Central

Graham, Alastair G. C.; Kuhn, Gerhard; Meisel, Ove; Hillenbrand, Claus-Dieter; Hodgson, Dominic A.; Ehrmann, Werner; Wacker, Lukas; Wintersteller, Paul; dos Santos Ferreira, Christian; Römer, Miriam; White, Duanne; Bohrmann, Gerhard

2017-01-01

The history of glaciations on Southern Hemisphere sub-polar islands is unclear. Debate surrounds the extent and timing of the last glacial advance and termination on sub-Antarctic South Georgia in particular. Here, using sea-floor geophysical data and marine sediment cores, we resolve the record of glaciation offshore of South Georgia through the transition from the Last Glacial Maximum to Holocene. We show a sea-bed landform imprint of a shelf-wide last glacial advance and progressive deglaciation. Renewed glacier resurgence in the fjords between c. 15,170 and 13,340 yr ago coincided with a period of cooler, wetter climate known as the Antarctic Cold Reversal, revealing a cryospheric response to an Antarctic climate pattern extending into the Atlantic sector of the Southern Ocean. We conclude that the last glaciation of South Georgia was extensive, and the sensitivity of its glaciers to climate variability during the last termination more significant than implied by previous studies. PMID:28303885

Ground-water quality in the Red River of the North Basin, Minnesota and North Dakota, 1991-95

USGS Publications Warehouse

Cowdery, T.K.

1998-01-01

Agricultural land use and soil texture can explain pesticide distributions; soil texture best explains nutrient distributions in waters in surficial aquifers. Confining beds protect waters in buried glacial aquifers from land use effects, resulting in no or low concentrations of nutrients and pesticides. Upward movement of bedrock waters high in dissolved solids concentration can increase concentrations in waters in buried glacial and, to a lesser degree, waters in surficial aquifers in the Lake Plain and Drift Prairie areas. Waters in surficial aquifers exceeded the U.S. Environmental Protection Agency (USEPA) maximum contaminant level in drinking water for nitrate in the Drift Prairie (27 percent) and Moraine (8 percent) areas. Their limited areal extent and susceptibility to contamination restrict the usefulness of surficial aquifers as a drinking water source. Waters in buried glacial aquifers exceeded USEPA health advisories for dissolved solids, sodium, and manganese. Sixty-six percent of waters in surficial aquifers also exceeded the Health Advisory for manganese.

Fine Dissection of Human Mitochondrial DNA Haplogroup HV Lineages Reveals Paleolithic Signatures from European Glacial Refugia

PubMed Central

Sarno, Stefania; Sevini, Federica; Vianello, Dario; Tamm, Erika; Metspalu, Ene; van Oven, Mannis; Hübner, Alexander; Sazzini, Marco; Franceschi, Claudio; Pettener, Davide; Luiselli, Donata

2015-01-01

Genetic signatures from the Paleolithic inhabitants of Eurasia can be traced from the early divergent mitochondrial DNA lineages still present in contemporary human populations. Previous studies already suggested a pre-Neolithic diffusion of mitochondrial haplogroup HV*(xH,V) lineages, a relatively rare class of mtDNA types that includes parallel branches mainly distributed across Europe and West Asia with a certain degree of structure. Up till now, variation within haplogroup HV was addressed mainly by analyzing sequence data from the mtDNA control region, except for specific sub-branches, such as HV4 or the widely distributed haplogroups H and V. In this study, we present a revised HV topology based on full mtDNA genome data, and we include a comprehensive dataset consisting of 316 complete mtDNA sequences including 60 new samples from the Italian peninsula, a previously underrepresented geographic area. We highlight points of instability in the particular topology of this haplogroup, reconstructed with BEAST-generated trees and networks. We also confirm a major lineage expansion that probably followed the Late Glacial Maximum and preceded Neolithic population movements. We finally observe that Italy harbors a reservoir of mtDNA diversity, with deep-rooting HV lineages often related to sequences present in the Caucasus and the Middle East. The resulting hypothesis of a glacial refugium in Southern Italy has implications for the understanding of late Paleolithic population movements and is discussed within the archaeological cultural shifts occurred over the entire continent. PMID:26640946

Extensive Quaternary glaciations in eastern Turkey

NASA Astrophysics Data System (ADS)

Yeşilyurt, Serdar; Akçar, Naki; Doǧan, Uǧur; Yavuz, Vural; Ivy-Ochs, Susan; Vockenhuber, Christof; Schlunegger, Fritz; Schlüchter, Christian

2016-04-01

During cold periods in the Quaternary, global ice volume increased and as a result valley glaciers advanced and the vice versa occurred during the warm periods. Quaternary glacier fluctuations had been also recorded in the Turkish mountains. Recently, the chronology of Late Quaternary advances in the northern and western Turkish mountains was reconstructed by surface exposure dating. However, these advances in the eastern Turkey are not dated yet. In this study, we investigated paleoglaciations in Kavuşşahap Mountains, which is located to the south of Lake Van in eastern Turkey. These mountains are one of the extensively glaciated areas in Turkey. Glacial activity is evidenced by more than 20 U-shaped valleys. For instance, one of the prominent and well-preserved glacial landscapes of Turkey is situated in the Narlıca valley system. Lateral and terminal moraines in the valley system indicate more than 10 glacial advances. To build their chronology, 39 erratic carbonaceous boulders were sampled for surface exposure dating with cosmogenic 36Cl. We also reconstructed the ice margin reconstruction of the Narlıca paleoglacier using the accumulation area ratio and area-altitude balance ratio approaches. We estimated an equilibrium line altitude (ELA) of ca. 2900 m above sea level based on the maximum ice extend, which implied ca. 800 m decrease in the ELA during the Late Quaternary in comparison to the lower bound of the modern ELA estimate. The first results of the surface exposure dating will be presented.

Palaeocirculation across New Zealand during the last glacial maximum at ˜21 ka

NASA Astrophysics Data System (ADS)

Lorrey, Andrew M.; Vandergoes, Marcus; Almond, Peter; Renwick, James; Stephens, Tom; Bostock, Helen; Mackintosh, Andrew; Newnham, Rewi; Williams, Paul W.; Ackerley, Duncan; Neil, Helen; Fowler, Anthony M.

2012-03-01

What circulation pattern drove Southern Alps glacial advances at ˜21 ka? Late 20th century glacial advances in New Zealand are commonly attributed to a dual precipitation increase and cooler than normal temperatures associated with enhanced westerly flow that occur under synoptic pressure patterns termed 'zonal' regimes (Kidson, 2000). But was the circulation pattern that supported major Southern Alps glacial advances during the global LGM similar to the modern analog? Here, a Regional Climate Regime Classification (RCRC) time slice was used to infer past circulation for New Zealand during the LGM at ˜21 ka. Palaeoclimate information that supported the construction of the ˜21 ka time slice was derived from the NZ-INTIMATE Climate Event Stratigraphy (CES), one new Auckland maar proxy record, and additional low-resolution data sourced from the literature. The terrestrial evidence at ˜21 ka implicates several possibilities for past circulation, depending on how interpretations for some proxies are made. The interpretation considered most tenable for the LGM, based on the agreement between terrestrial evidence, marine reconstructions and palaeoclimate model results is an 'anticyclonic/zonal' circulation regime characterized by increased influences from blocking 'highs' over the South Island during winter and an increase in zonal and trough synoptic types (with southerly to westerly quarter wind flow) during summer. These seasonal circulation traits would have generated lower mean annual temperatures, cooler than normal summer temperatures, and overall lower mean annual precipitation for New Zealand (particularly in the western South Island) at ˜21 ka. The anticyclonic/zonal time slice reconstruction presented in this study has different spatial traits than the late 20th Century and the early Little Ice Age signatures, suggesting more than one type of regional circulation pattern can drive Southern Alps glacial activity. This finding lends support to the hypothesis that temperature over precipitation change is more important as the primary modulator of Southern Alps ice advances. The RCRC approach also demonstrates some subtle advantages of integrating multi-proxy data within a palaeocirculation context for New Zealand, notably because this reconstruction technique enables direct comparisons to coarsely resolved palaeoclimate model outputs that do not have downscaled information.

Impact of the Agulhas Return Current on the glacial Subantarctic region in the South Indian Ocean

NASA Astrophysics Data System (ADS)

Ikehara, M.; Crosta, X.; Manoj, M. C.

2017-12-01

The Southern Ocean has played an important role in the evolution of the global climate system. The Southern Ocean circulation is dominated by the Antarctic Circumpolar Current (ACC), the world's longest and largest current system. Sea ice coverage on sea surface strongly affects the climate of the Southern Hemisphere through its impacts on the energy and gas budget, on the atmospheric circulation, on the hydrological cycle, and on the biological productivity. The Agulhas Return Current (ARC) originates from the Agulhas Current, the major western boundary current in the Indian Ocean, and transports heat from subtropical to subantarctic region. It's thought that the Agulhas leakage from the Indian Ocean to the Atlantic was reduced for the last glacial due to a northward shift of the westerlies and ACC, however, there are still unknown yet how the ARC was responded to the reduced Agulhas leakage. A piston core DCR-1PC was collected from the Del Caño Rise (46°S, 44°E, 2632m), Indian sector of the Southern Ocean. Core site located in the Subantarctic region between the Subtropical Front (STF) and Subantarctic Front (SAF). Age model of the core was established by radiocarbon dating of planktic foraminifer Globorotalia bulloides and oxygen isotope stratigraphy of benthic foraminifers Cibicidoides wuellerstorfi and Melonis bareelanus. Sediment of DCR-1PC show the cyclic changes of diatom/carbonate ooze sedimentation corresponding to Southern Ocean fronts' migrations on glacial-interglacial timescales. Records of ice-rafted debris (IRD) and oxygen isotope in planktic foraminfer G. bulloides suggest that the melting of sea ice was significantly increased during the last glacial maximum (LGM) in the Subantarctic surface water. Diatom assemblage based summer SST also shows the relative warmer condition in the Subantarctic during the LGM. These results might be explained by the strong influence of the Agulhas Return Current during the LGM in the Subantarctic. The reduced Agulhas leakage due to a northward shift of the westerlies and ACC impacted significantly on sea ice melting in the glacial Subantarctic region in the South Indian Ocean.

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2015-11-01

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

Changes in sea ice cover and ice sheet extent at the Yermak Plateau during the last 160 ka - Reconstructions from biomarker records

NASA Astrophysics Data System (ADS)

Kremer, A.; Stein, R.; Fahl, K.; Ji, Z.; Yang, Z.; Wiers, S.; Matthiessen, J.; Forwick, M.; Löwemark, L.; O'Regan, M.; Chen, J.; Snowball, I.

2018-02-01

The Yermak Plateau is located north of Svalbard at the entrance to the Arctic Ocean, i.e. in an area highly sensitive to climate change. A multi proxy approach was carried out on Core PS92/039-2 to study glacial-interglacial environmental changes at the northern Barents Sea margin during the last 160 ka. The main emphasis was on the reconstruction of sea ice cover, based on the sea ice proxy IP25 and the related phytoplankton - sea ice index PIP25. Sea ice was present most of the time but showed significant temporal variability decisively affected by movements of the Svalbard Barents Sea Ice Sheet. For the first time, we prove the occurrence of seasonal sea ice at the eastern Yermak Plateau during glacial intervals, probably steered by a major northward advance of the ice sheet and the formation of a coastal polynya in front of it. Maximum accumulation of terrigenous organic carbon, IP25 and the phytoplankton biomarkers (brassicasterol, dinosterol, HBI III) can be correlated to distinct deglaciation events. More severe, but variable sea ice cover prevailed at the Yermak Plateau during interglacials. The general proximity to the sea ice margin is further indicated by biomarker (GDGT) - based sea surface temperatures below 2.5 °C.

Pollen-based continental climate reconstructions at 6 and 21 ka: A global synthesis

USGS Publications Warehouse

Bartlein, P.J.; Harrison, S.P.; Brewer, Sandra; Connor, S.; Davis, B.A.S.; Gajewski, K.; Guiot, J.; Harrison-Prentice, T. I.; Henderson, A.; Peyron, O.; Prentice, I.C.; Scholze, M.; Seppa, H.; Shuman, B.; Sugita, S.; Thompson, R.S.; Viau, A.E.; Williams, J.; Wu, H.

2011-01-01

Subfossil pollen and plant macrofossil data derived from 14C-dated sediment profiles can provide quantitative information on glacial and interglacial climates. The data allow climate variables related to growing-season warmth, winter cold, and plant-available moisture to be reconstructed. Continental-scale reconstructions have been made for the mid-Holocene (MH, around 6 ka) and Last Glacial Maximum (LGM, around 21 ka), allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change. The synthesis of the available MH and LGM climate reconstructions and their uncertainties, obtained using modern-analogue, regression and model-inversion techniques, is presented for four temperature variables and two moisture variables. Reconstructions of the same variables based on surface-pollen assemblages are shown to be accurate and unbiased. Reconstructed LGM and MH climate anomaly patterns are coherent, consistent between variables, and robust with respect to the choice of technique. They support a conceptual model of the controls of Late Quaternary climate change whereby the first-order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance. ?? 2010 The Author(s).

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

PubMed

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

2016-06-01

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

Late Quaternary deglacial history of the Mérida Andes, Venezuela

NASA Astrophysics Data System (ADS)

Stansell, Nathan D.; Abbott, Mark B.; Polissar, Pratigya J.; Wolfe, Alexander P.; Bezada, Maximiliano; Rull, Valentí

2005-10-01

Radiocarbon-dated sediment cores from seven lakes and two bogs spanning the Cordillera de Mérida in the Venezuelan Andes were used to identify and date the regional history of late Pleistocene and Holocene glacial activity. Coring sites were selected at different elevations across a pronounced rain shadow from southeast (wet) to northwest (dry). Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation. The local expression of the Last Glacial Maximum occurred between 22 750 and 19 960 cal. yr BP. On the wetter southeastern side of the Cordillera de Mérida, glaciers had significantly retreated by 15 700 cal. yr BP, followed by several minor glacial advances and retreats between 14 850 and 13 830 cal. yr BP. At least one major glacial readvance occurred between 13 830 and 10 000 cal. yrBP in the wetter southeastern sector of the region. The drier northwest side of the Cordillera de Mérida records initial glacial retreat by 14240cal.yrBP. Multiple sites on both sides of the Mérida Andes record a further phase of extensive deglaciation approximately 10000cal.yrBP. However, the north-northwest facing Mucubají catchment remained partially glaciated until ca. 6000cal.yrBP. Deglacial ages from the Venezuelan Andes are consistently younger than those reported from the Southern Hemisphere Andes, suggesting an inter-hemispheric deglacial lag in the northern tropics of the order of two thousand years.

Microrefugia and Shifts of Hippophae tibetana (Elaeagnaceae) on the north side of Mt. Qomolangma (Mt. Everest) during the last 25000 years.

PubMed

Xu, Lu; Wang, Hao; La, Qiong; Lu, Fan; Sun, Kun; Fang, Yang; Yang, Mei; Zhong, Yang; Wu, Qianhong; Chen, Jiakuan; Birks, H John B; Zhang, Wenju

2014-01-01

Microrefugia at high altitudes or high latitudes are thought to play an important role in the post-glacial colonization of species. However, how populations in such microrefugia have responded to climate changes in alternating cold glacial and warm interglacial stages remain unclear. Here we present evidence to indicate the Rongbuk Valley of the Mt. Qomolangma (Mt. Everest) area, the highest region on earth, had microrefugia for Hippophae tibetana and discuss how this low shrub was adapted to the extreme climate fluctuations of the last 25,000 years by shifts. By integrating geological, glaciological, meteorological, and genetic information, we found that the Rongbuk Valley was not only a glacial microrefugium but also an interglacial microrefugium for H. tibetana: the former was located on the riverbank below 4800 m above sea level (asl) or lower area and the latter at ∼ 5000 m asl. Our results show that after the Last Glacial Maximum (LGM), H. tibetana in the valley has undergone upward and downward migrations around ∼ 5000 m driven by climate fluctuations and the population in the glacial microrefugium has suffered extinction or extreme contraction. Moreover, with the rise of temperature in the last four decades, the upper limit of H. tibetana has shifted at least 30 m upward. Combining population history and recent range shift of this species is important in predicting the fate of this endemic species to future climate changes.

Microrefugia and Shifts of Hippophae tibetana (Elaeagnaceae) on the North Side of Mt. Qomolangma (Mt. Everest) during the Last 25000 Years

PubMed Central

Lu, Fan; Sun, Kun; Fang, Yang; Yang, Mei; Zhong, Yang; Wu, Qianhong; Chen, Jiakuan; Birks, H. John B.; Zhang, Wenju

2014-01-01

Microrefugia at high altitudes or high latitudes are thought to play an important role in the post-glacial colonization of species. However, how populations in such microrefugia have responded to climate changes in alternating cold glacial and warm interglacial stages remain unclear. Here we present evidence to indicate the Rongbuk Valley of the Mt. Qomolangma (Mt. Everest) area, the highest region on earth, had microrefugia for Hippophae tibetana and discuss how this low shrub was adapted to the extreme climate fluctuations of the last 25,000 years by shifts. By integrating geological, glaciological, meteorological, and genetic information, we found that the Rongbuk Valley was not only a glacial microrefugium but also an interglacial microrefugium for H. tibetana: the former was located on the riverbank below 4800 m above sea level (asl) or lower area and the latter at ∼5000 m asl. Our results show that after the Last Glacial Maximum (LGM), H. tibetana in the valley has undergone upward and downward migrations around ∼5000 m driven by climate fluctuations and the population in the glacial microrefugium has suffered extinction or extreme contraction. Moreover, with the rise of temperature in the last four decades, the upper limit of H. tibetana has shifted at least 30 m upward. Combining population history and recent range shift of this species is important in predicting the fate of this endemic species to future climate changes. PMID:24841004

Indonesian vegetation response to changes in rainfall seasonality over the past 25,000 years

NASA Astrophysics Data System (ADS)

Dubois, Nathalie; Oppo, Delia W.; Galy, Valier V.; Mohtadi, Mahyar; van der Kaars, Sander; Tierney, Jessica E.; Rosenthal, Yair; Eglinton, Timothy I.; Lückge, Andreas; Linsley, Braddock K.

2014-07-01

The hydrologic response to climate forcing in the Indo-Pacific warm pool region has varied spatially over the past 25,000 years. For example, drier conditions are inferred on Java and Borneo for the period following the end of the Last Glacial Maximum, whereas wetter conditions are reconstructed for northwest Australia. The response of vegetation to these past rainfall variations is poorly constrained. Using a suite of 30 surface marine sediment samples from throughout the Indo-Pacific warm pool, we demonstrate that today the stable isotopic composition of vascular plant fatty acids (δ13CFA) reflects the regional vegetation composition. This in turn is controlled by the seasonality of rainfall consistent with dry season water stress. Applying this proxy in a sediment core from offshore northeast Borneo, we show broadly similar vegetation cover during the Last Glacial Maximum and the Holocene, suggesting that, despite generally drier glacial conditions, there was no pronounced dry season. In contrast, δ13CFA and pollen data from a core off the coast of Sumba indicate an expansion of C4 herbs during the most recent glaciation, implying enhanced aridity and water stress during the dry season. Holocene vegetation trends are also consistent with a response to dry season water stress. We therefore conclude that vegetation in tropical monsoon regions is susceptible to increases in water stress arising from an enhanced seasonality of rainfall, as has occurred in past decades.

Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions

NASA Astrophysics Data System (ADS)

Hendry, Katharine R.; Georg, R. Bastian; Rickaby, Rosalind E. M.; Robinson, Laura F.; Halliday, Alex N.

2010-04-01

The relative importance of biological and physical processes within the Southern Ocean for the storage of carbon and atmospheric pCO 2 on glacial-interglacial timescales remains uncertain. Understanding the impact of surface biological production on carbon export in the past relies on the reconstruction of the nutrient supply from upwelling deep waters. In particular, the upwelling of silicic acid (Si(OH) 4) is tightly coupled to carbon export in the Southern Ocean via diatom productivity. Here, we address how changes in deep water Si(OH) 4 concentrations can be reconstructed using the silicon isotopic composition of deep-sea sponges. We report δ30Si of modern deep-sea sponge spicules and show that they reflect seawater Si(OH) 4 concentration. The fractionation factor of sponge δ30Si compared to seawater δ30Si shows a positive relationship with Si(OH) 4, which may be a growth rate effect. Application of this proxy in two down-core records from the Scotia Sea reveals that Si(OH) 4 concentrations in the deep Southern Ocean during the Last Glacial Maximum (LGM) were no different than today. Our result does not support a coupling of carbon and nutrient build up in an isolated deep ocean reservoir during the LGM. Our data, combined with records of stable isotopes from diatoms, are only consistent with enhanced LGM Southern Ocean nutrient utilization if there was also a concurrent reduction in diatom silicification or a shift from siliceous to organic-walled phytoplankton.

Arctic Dinoflagellate Migration Marks the Oligocene Glacial Maximum: Implications for the Rupelian-Chattian Boundary

NASA Astrophysics Data System (ADS)

van Simaeys, S.; Brinkhuis, H.; Pross, J.; Williams, G. L.; Zachos, J. C.

2004-12-01

Various geochemical and biotic climate proxies, and notably deep-sea benthic foraminiferal δ 18O records indicate that the Eocene 'greenhouse' state of the Earth gradually evolved towards an earliest Oligocene 'icehouse' state, eventually triggering the abrupt appearance of large continental ice-sheets on Antarctic at ˜33.3 Ma (Oi-1 event). This, however, was only the first of two major glacial events in the Oligocene. Benthic foraminiferal δ 18O records show a second positive excursion in the mid Oligocene, consistent with a significant ice-sheet expansion and/or cooling at 27.1 Ma (Oi-2b) coincident with magnetosubchron C9n. Here, we report on a mid Oligocene, globally synchronous, Arctic dinoflagellate migration event, calibrated against the upper half of C9n. A sudden appearance, and abundance increases of the Arctic taxon Svalbardella at lower-middle latitudes coincides with the so-called Oi-2b benthic δ 18O event, dated at ˜27.1 Ma. This phenomenon is taken to indicate significant high-latitude surface water cooling, concomitant Antarctic ice-sheet growth, and sea level lowering. The duration of the Svalbardella migrations, and the episode of profound cooling is estimated as ˜500 ka, and is here termed the Oligocene Glacial Maximum (OGM). Our records suggest a close link between the OGM, sea-level fall, and the classic Rupelian-Chattian boundary, magnetostratigraphically dating this boundary as ˜27.1 Ma.

Trends in the Diversity, Distribution and Life History Strategy of Arctic Hydrozoa (Cnidaria)

PubMed Central

Ronowicz, Marta; Kukliński, Piotr; Mapstone, Gillian M.

2015-01-01

This is the first attempt to compile a comprehensive and updated species list for Hydrozoa in the Arctic, encompassing both hydroid and medusa stages and including Siphonophorae. We address the hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic by Hydrozoa after the Last Glacial Maximum. Presence-absence data of Hydrozoa in the Arctic were prepared on the basis of historical and present-day literature. The Arctic was divided into ecoregions. Species were grouped into distributional categories according to their worldwide occurrences. Each species was classified according to life history strategy. The similarity of species composition among regions was calculated with the Bray-Curtis index. Average and variation in taxonomic distinctness were used to measure diversity at the taxonomic level. A total of 268 species were recorded. Arctic-boreal species were the most common and dominated each studied region. Nineteen percent of species were restricted to the Arctic. There was a predominance of benthic species over holo- and meroplanktonic species. Arctic, Arctic-Boreal and Boreal species were mostly benthic, while widely distributed species more frequently possessed a pelagic stage. Our results support hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic. The predominance of benthic Hydrozoa suggests that the Arctic could have been colonised after the Last Glacial Maximum by hydroids rafting on floating substrata or recolonising from glacial refugia. PMID:25793294

Trends in the diversity, distribution and life history strategy of Arctic Hydrozoa (Cnidaria).

PubMed

Ronowicz, Marta; Kukliński, Piotr; Mapstone, Gillian M

2015-01-01

This is the first attempt to compile a comprehensive and updated species list for Hydrozoa in the Arctic, encompassing both hydroid and medusa stages and including Siphonophorae. We address the hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic by Hydrozoa after the Last Glacial Maximum. Presence-absence data of Hydrozoa in the Arctic were prepared on the basis of historical and present-day literature. The Arctic was divided into ecoregions. Species were grouped into distributional categories according to their worldwide occurrences. Each species was classified according to life history strategy. The similarity of species composition among regions was calculated with the Bray-Curtis index. Average and variation in taxonomic distinctness were used to measure diversity at the taxonomic level. A total of 268 species were recorded. Arctic-boreal species were the most common and dominated each studied region. Nineteen percent of species were restricted to the Arctic. There was a predominance of benthic species over holo- and meroplanktonic species. Arctic, Arctic-Boreal and Boreal species were mostly benthic, while widely distributed species more frequently possessed a pelagic stage. Our results support hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic. The predominance of benthic Hydrozoa suggests that the Arctic could have been colonised after the Last Glacial Maximum by hydroids rafting on floating substrata or recolonising from glacial refugia.

Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

NASA Astrophysics Data System (ADS)

Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

2018-05-01

Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations, controlled by the sub-ice-shelf melting which was dictated by the RSL forcing and the glacial history of the IIS and LIS. In contrast, the southwestern part of the ice sheet was insensitive to these forcings, with a uniform response in all simulations controlled by the surface air temperature, derived from ice cores.

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Detection of Supra-Glacial Lakes on the Greenland Ice Sheet Using MODIS Images

NASA Astrophysics Data System (ADS)

Verin, Gauthier; Picard, Ghislain; Libois, Quentin; Gillet-Chaulet, Fabien; Roux, Antoine

2015-04-01

During melt season, supra-glacial lakes form on the margins of the Greenland ice sheet. Because of their size exceeding several kilometers, and their concentration, they affect surface albedo leading to an amplification of the regional melt. Furthermore, they foster hydro-fracturing that propagate liquid water to the bedrock and therefore enhance the basal lubrication which may affect the ice motion. It is known that Greenland ice sheet has strongly responded to recent global warming. As air temperature increases, melt duration and melt intensity increase and surface melt area extends further inland. These recent changes may play an important role in the mass balance of the Greenland ice sheet. In this context, it is essential to better monitor and understand supra-glacial spatio-temporal dynamics in order to better assess future sea level rise. In this study MODIS (Moderate Resolution Imaging Spectroradiometer) images have been used to detect supra-glacial lakes. The observation site is located on the West margin of the ice sheet, between 65°N and 70°N where the concentration of lake is maximum. The detection is performed by a fully automatic algorithm using images processing techniques introduced by Liang et al. (2012) which can be summarized in three steps: the selection of usable MODIS images, mainly we exclude images with too many clouds. The detection of lake and the automatic correction of false detections. This algorithm is capable to tag each individual lake allowing a survey of all lake geometrical properties over the entire melt season. We observed a large population of supra-glacial lakes over 14 melt seasons, from 2000 to 2013 on an extended area of 70.000 km2. In average, lakes are observed from June 9 ± 8.7 days to September 13 ± 13.9 days, and reach a maximum total area of 699 km2 ± 146 km2. As the melt season progresses, lakes form higher in altitude up to 1800 m above sea level. Results show a very strong inter-annual variability in term of date of melt and freeze up onset, melt season duration, maximum total surface area and number of lakes. As it has already been noticed, we observed a strong spatial persistence. Lakes tend to form at the same place for several years, probably because of the ice sheet surface topography. In order to investigate possible links with climatic parameters we calculated positive degree day (PDD). The main result of this comparison is a strong correlation between melt intensity and the altitude of lakes. During warmer summer, lakes form higher in altitude and consequently the extent of melting increase. Recent studies showed this trend is likely to continue and to increase in the years to come.

The glacial/deglacial history of sedimentation in Bear Lake, Utah and Idaho

USGS Publications Warehouse

Rosenbaum, J.G.; Heil, C.W.

2009-01-01

Bear Lake, in northeastern Utah and southern Idaho, lies in a large valley formed by an active half-graben. Bear River, the largest river in the Great Basin, enters Bear Lake Valley ???15 km north of the lake. Two 4-m-long cores provide a lake sediment record extending back ???26 cal k.y. The penetrated section can be divided into a lower unit composed of quartz-rich clastic sediments and an upper unit composed largely of endogenic carbonate. Data from modern fluvial sediments provide the basis for interpreting changes in provenance of detrital material in the lake cores. Sediments from small streams draining elevated topography on the east and west sides of the lake are characterized by abundant dolomite, high magnetic susceptibility (MS) related to eolian magnetite, and low values of hard isothermal remanent magnetization (HIRM, indicative of hematite content). In contrast, sediments from the headwaters of the Bear River in the Uinta Mountains lack carbonate and have high HIRM and low MS. Sediments from lower reaches of the Bear River contain calcite but little dolomite and have low values of MS and HIRM. These contrasts in catchment properties allow interpretation of the following sequence from variations in properties of the lake sediment: (1) ca. 26 cal ka-onset of glaciation; (2) ca. 26-20 cal ka-quasicyclical, millennial-scale variations in the concentrations of hematite-rich glacial fl our derived from the Uinta Mountains, and dolomite- and magnetite-rich material derived from the local Bear Lake catchment (reflecting variations in glacial extent); (3) ca. 20-19 cal ka-maximum content of glacial fl our; (4) ca. 19-17 cal ka-constant content of Bear River sediment but declining content of glacial fl our from the Uinta Mountains; (5) ca. 17-15.5 cal ka-decline in Bear River sediment and increase in content of sediment from the local catchment; and (6) ca. 15.5-14.5 cal ka-increase in content of endogenic calcite at the expense of detrital material. The onset of glaciation indicated in the Bear Lake record postdates the initial rise of Lake Bonneville and roughly corresponds to the Stansbury shoreline. The lake record indicates that maximum glaciation occurred as Lake Bonneville reached its maximum extent ca. 20 cal ka and that deglaciation was under way while Lake Bonneville remained at its peak. The transition from siliciclastic to carbonate sedimentation probably indicates increasingly evaporative conditions and may coincide with the climatically driven fall of Lake Bonneville from the Provo shoreline. Although lake levels fluctuated during the Younger Dryas, the Bear Lake record for this period is more consistent with drier conditions, rather than cooler, moister conditions interpreted from many studies from western North America. Copyright ?? 2009 The Geological Society of America.

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

NASA Astrophysics Data System (ADS)

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

2014-09-01

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

Hydrological and climate changes in southeast Siberia over the last 33 kyr

NASA Astrophysics Data System (ADS)

Katsuta, Nagayoshi; Ikeda, Hisashi; Shibata, Kenji; Saito-Kokubu, Yoko; Murakami, Takuma; Tani, Yukinori; Takano, Masao; Nakamura, Toshio; Tanaka, Atsushi; Naito, Sayuri; Ochiai, Shinya; Shichi, Koji; Kawakami, Shin-ichi; Kawai, Takayoshi

2018-05-01

Paleoenvironmental and paleoclimate changes in intracontinental Siberia were reconstructed by continuous, high-resolution records (biogenic silica, U, total organic carbon and N, total S, and grain size) from a sediment core retrieved from the Buguldeika Saddle, Lake Baikal, dating back to the last 33 cal. ka BP. The Holocene climate was wet relative to the last glacial period. The climate became gradually warm and wet from the early to middle Holocene, followed by a shift at ca. 6.5 cal. ka BP toward warm and dry, possibly because of evapotranspiration. This suggests that the climate system transition from the glacial to interglacial state occurred at that time. In the last glacial, the deposition of carbonate mud from the Primorsky Range was associated with Heinrich events (H3 and H1) and the Selenga River inflow during the Last Glacial Maximum was caused by meltwater of mountain glaciers in the Khamar-Daban Range. The anoxic bottom-water during the Allerød-Younger Dryas was probably a result of weakened ventilation associated with reduced Selenga River inflow and microbial decomposition of organic matters originating from moderate input of nutrients from the Primorsky Range. The rapid decline in precipitation during the early Holocene may have been a response to the 8.2 ka cooling event.

Mitochondrial DNA signals of late glacial recolonization of Europe from near eastern refugia.

PubMed

Pala, Maria; Olivieri, Anna; Achilli, Alessandro; Accetturo, Matteo; Metspalu, Ene; Reidla, Maere; Tamm, Erika; Karmin, Monika; Reisberg, Tuuli; Hooshiar Kashani, Baharak; Perego, Ugo A; Carossa, Valeria; Gandini, Francesca; Pereira, Joana B; Soares, Pedro; Angerhofer, Norman; Rychkov, Sergei; Al-Zahery, Nadia; Carelli, Valerio; Sanati, Mohammad Hossein; Houshmand, Massoud; Hatina, Jiři; Macaulay, Vincent; Pereira, Luísa; Woodward, Scott R; Davies, William; Gamble, Clive; Baird, Douglas; Semino, Ornella; Villems, Richard; Torroni, Antonio; Richards, Martin B

2012-05-04

Human populations, along with those of many other species, are thought to have contracted into a number of refuge areas at the height of the last Ice Age. European populations are believed to be, to a large extent, the descendants of the inhabitants of these refugia, and some extant mtDNA lineages can be traced to refugia in Franco-Cantabria (haplogroups H1, H3, V, and U5b1), the Italian Peninsula (U5b3), and the East European Plain (U4 and U5a). Parts of the Near East, such as the Levant, were also continuously inhabited throughout the Last Glacial Maximum, but unlike western and eastern Europe, no archaeological or genetic evidence for Late Glacial expansions into Europe from the Near East has hitherto been discovered. Here we report, on the basis of an enlarged whole-genome mitochondrial database, that a substantial, perhaps predominant, signal from mitochondrial haplogroups J and T, previously thought to have spread primarily from the Near East into Europe with the Neolithic population, may in fact reflect dispersals during the Late Glacial period, ∼19-12 thousand years (ka) ago. Copyright © 2012 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

Pennsylvanian tropical rain forests responded to glacial-interglacial rhythms

NASA Astrophysics Data System (ADS)

Falcon-Lang, Howard J.

2004-08-01

Pennsylvanian tropical rain forests flourished during an icehouse climate mode. Although it is well established that Milankovitch-band glacial-interglacial rhythms caused marked synchronous changes in Pennsylvanian tropical climate and sea level, little is known of vegetation response to orbital forcing. This knowledge gap has now been addressed through sequence- stratigraphic analysis of megafloral and palynofloral assemblages within the Westphalian D Cantabrian Sydney Mines Formation of eastern Canada. This succession was deposited in a low- accommodation setting where sequences can be attributed confidently to glacio-eustasy. Results show that long-lived, low-diversity peat mires dominated by lycopsids were initiated during deglaciation events, but were mostly drowned by rising sea level at maximum interglacial conditions. Only upland coniferopsid forests survived flooding without significant disturbance. Mid- to late interglacial phases witnessed delta-plain progradation and establishment of high-diversity, mineral-substrate rain forests containing lycopsids, sphenopsids, pteridosperms, cordaites, and tree ferns. Renewed glaciation resulted in sea-level fall, paleovalley incision, and the onset of climatic aridity. Glacial vegetation was dominated by cordaites, pteridosperms, and tree ferns; hydrophilic lycopsids and sphenopsids survived in paleovalley refugia. Findings clearly demonstrate the dynamic nature of Pennsylvanian tropical ecosystems and are timely given current debates about the impact of Quaternary glacial-interglacial rhythms on the biogeography of tropical rain forest.

A 33,000-year-old incipient dog from the Altai Mountains of Siberia: evidence of the earliest domestication disrupted by the Last Glacial Maximum.

PubMed

Ovodov, Nikolai D; Crockford, Susan J; Kuzmin, Yaroslav V; Higham, Thomas F G; Hodgins, Gregory W L; van der Plicht, Johannes

2011-01-01

Virtually all well-documented remains of early domestic dog (Canis familiaris) come from the late Glacial and early Holocene periods (ca. 14,000-9000 calendar years ago, cal BP), with few putative dogs found prior to the Last Glacial Maximum (LGM, ca. 26,500-19,000 cal BP). The dearth of pre-LGM dog-like canids and incomplete state of their preservation has until now prevented an understanding of the morphological features of transitional forms between wild wolves and domesticated dogs in temporal perspective. We describe the well-preserved remains of a dog-like canid from the Razboinichya Cave (Altai Mountains of southern Siberia). Because of the extraordinary preservation of the material, including skull, mandibles (both sides) and teeth, it was possible to conduct a complete morphological description and comparison with representative examples of pre-LGM wild wolves, modern wolves, prehistoric domesticated dogs, and early dog-like canids, using morphological criteria to distinguish between wolves and dogs. It was found that the Razboinichya Cave individual is most similar to fully domesticated dogs from Greenland (about 1000 years old), and unlike ancient and modern wolves, and putative dogs from Eliseevichi I site in central Russia. Direct AMS radiocarbon dating of the skull and mandible of the Razboinichya canid conducted in three independent laboratories resulted in highly compatible ages, with average value of ca. 33,000 cal BP. The Razboinichya Cave specimen appears to be an incipient dog that did not give rise to late Glacial-early Holocene lineages and probably represents wolf domestication disrupted by the climatic and cultural changes associated with the LGM. The two earliest incipient dogs from Western Europe (Goyet, Belguim) and Siberia (Razboinichya), separated by thousands of kilometers, show that dog domestication was multiregional, and thus had no single place of origin (as some DNA data have suggested) and subsequent spread.

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

USGS Publications Warehouse

Hunter, K.L.; Betancourt, J.L.; Riddle, B.R.; Van Devender, T. R.; Cole, K.L.; Geoffrey, Spaulding W.

2000-01-01

1 A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26-10 14C kyr BP or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ???4.0 14C kyr BP. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr BP. Hexaploids appeared by 8.5 14C kyr BP in the lower Colorado River Basin, reaching their northernmost limits (???37??N) in the Mohave Desert between 5.6 and 3.9 14C kyr BP. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture. ?? 2001 Blackwell Science Ltd.

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larea tridentata

USGS Publications Warehouse

Hunter, Kimberly L.; Betancourt, Julio L.; Riddle, Brett R.; Van Devender, Thomas R.; Cole, K.L.; Spaulding, W.G.

2001-01-01

1. A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26a??10 14C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14C kyr bp. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr bp. Hexaploids appeared by 8.5 14C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37A?N) in the Mohave Desert between 5.6 and 3.9 14C kyr bp. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

Multilocus phylogeography and population structure of common eiders breeding in North America and Scandinavia

USGS Publications Warehouse

Sonsthagen, Sarah A.; Talbot, Sandra L.; Scribner, Kim T.; McCracken, Kevin G.

2011-01-01

Aim  Glacial refugia during the Pleistocene had major impacts on the levels and spatial apportionment of genetic diversity of species in northern latitude ecosystems. We characterized patterns of population subdivision, and tested hypotheses associated with locations of potential Pleistocene refugia and the relative contribution of these refugia to the post-glacial colonization of North America and Scandinavia by common eiders (Somateria mollissima). Specifically, we evaluated localities hypothesized as ice-free areas or glacial refugia for other Arctic vertebrates, including Beringia, the High Arctic Canadian Archipelago, Newfoundland Bank, Spitsbergen Bank and north-west Norway.Location  Alaska, Canada, Norway and Sweden.Methods  Molecular data from 12 microsatellite loci, the mitochondrial DNA (mtDNA) control region, and two nuclear introns were collected and analysed for 15 populations of common eiders (n = 716) breeding throughout North America and Scandinavia. Population genetic structure, historical population fluctuations and gene flow were inferred using F-statistics, analyses of molecular variance, and multilocus coalescent analyses.Results  Significant inter-population variation in allelic and haplotypic frequencies were observed (nuclear DNA FST = 0.004–0.290; mtDNA ΦST = 0.051–0.927). Whereas spatial differentiation in nuclear genes was concordant with subspecific designations, geographic proximity was more predictive of inter-population variance in mitochondrial DNA haplotype frequency. Inferences of historical population demography were consistent with restriction of common eiders to four geographic areas during the Last Glacial Maximum: Belcher Islands, Newfoundland Bank, northern Alaska and Svalbard. Three of these areas coincide with previously identified glacial refugia: Newfoundland Bank, Beringia and Spitsbergen Bank. Gene-flow and clustering analyses indicated that the Beringian refugium contributed little to common eider post-glacial colonization of North America, whereas Canadian, Scandinavian and southern Alaskan post-glacial colonization is likely to have occurred in a stepwise fashion from the same glacial refugium.Main conclusions  Concordance of proposed glacial refugia used by common eiders and other Arctic species indicates that Arctic and subarctic refugia were important reservoirs of genetic diversity during the Pleistocene. Furthermore, suture zones identified at MacKenzie River, western Alaska/Aleutians and Scandinavia coincide with those identified for other Arctic vertebrates, suggesting that these regions were strong geographic barriers limiting dispersal from Pleistocene refugia.

The BMPix and PEAK Tools: New Methods for Automated Laminae Recognition and Counting - Application to Glacial Varves From Antarctic Marine Sediment

NASA Astrophysics Data System (ADS)

Weber, M. E.; Reichelt, L.; Kuhn, G.; Thurow, J. W.; Ricken, W.

2009-12-01

We present software-based tools for rapid and quantitative detection of sediment lamination. The BMPix tool extracts color and gray-scale curves from images at ultrahigh (pixel) resolution. The PEAK tool uses the gray-scale curve and performs, for the first time, fully automated counting of laminae based on three methods. The maximum count algorithm counts every bright peak of a couplet of two laminae (annual resolution) in a Gaussian smoothed gray-scale curve. The zero-crossing algorithm counts every positive and negative halfway-passage of the gray-scale curve through a wide moving average. Hence, the record is separated into bright and dark intervals (seasonal resolution). The same is true for the frequency truncation method, which uses Fourier transformation to decompose the gray-scale curve into its frequency components, before positive and negative passages are count. We applied the new methods successfully to tree rings and to well-dated and already manually counted marine varves from Saanich Inlet before we adopted the tools to rather complex marine laminae from the Antarctic continental margin. In combination with AMS14C dating, we found convincing evidence that the laminations from three Weddell Sea sites represent true varves that were deposited on sediment ridges over several millennia during the last glacial maximum (LGM). There are apparently two seasonal layers of terrigenous composition, a coarser-grained bright layer, and a finer-grained dark layer. The new tools offer several advantages over previous tools. The counting procedures are based on a moving average generated from gray-scale curves instead of manual counting. Hence, results are highly objective and rely on reproducible mathematical criteria. Since PEAK associates counts with a specific depth, the thickness of each year or each season is also measured which is an important prerequisite for later spectral analysis. Since all information required to conduct the analysis is displayed graphically, interactive optimization of the counting algorithms can be achieved quickly and conveniently.

Early warning method of Glacial Lake Outburst Floods based on temperature and rainfall

NASA Astrophysics Data System (ADS)

Liu, Jingjing; Su, Pengcheng; Cheng, Zunlan

2017-04-01

Glacial lake outburst floods (GLOFs) are serious disasters in glacial areas. At present, glaciers are retreating while glacial lake area and the outburst risk increases due to the global warming. Therefore, the research of early warning method of GLOFs is important to prevent and reduce the disasters. This paper provides an early warning method using the temperature and rainfall as indices. The daily growth rate of positive antecedent accumulative temperature and the antecedent thirty days accumulative precipitation are calculated for 21 events of GLOF before 2010, based on data from the 21 meteorological stations nearby. The result shows that all the events are above the curve, TV = -0.0193RDC + 3.0018, which can be taken as the early warning threshold curve. This has been verified by the GLOF events in the Ranzeaco glacial lake on 2013-07-05.

The influence of high viscosity slabs on post-glacial sea-level change: the case of Barbados

NASA Astrophysics Data System (ADS)

Austermann, Jacqueline; Mitrovica, Jerry X.; Latychev, Konstantin

2013-04-01

The coral record at Barbados is one of the best available measures of relative sea level during the last glacial cycle and has been widely used to reconstruct ice volume (or, equivalently, eustatic sea-level, ESL) changes during the last deglaciation phase of the ice age. However, to estimate ESL variations from the local relative sea level (RSL) history at Barbados, one has to account for the contaminating effect of glacial isostatic adjustment (GIA). In previous work, the GIA signal at this site has been corrected for by assuming a spherically symmetric (i.e., 1-D) viscoelastic Earth. Since Barbados is located at the margin of the South American - Caribbean subduction zone, this assumption may introduce a significant error in inferences of ice volumes. To address this issue, we use a finite-volume numerical code to model GIA in the Caribbean region including the effects of a lithosphere with variable elastic thickness, plate boundaries, lateral variations in lower mantle viscosity, and a high viscosity slab within the upper mantle. The geometry of the subducted slab is inferred from local seismicity. We find that predictions of relative sea-level change since the Last Glacial Maximum (LGM) in the Caribbean region are diminished by ~10 m, relative to 1-D calculations, which suggests that previous studies have underestimated post-LGM ESL change by the same amount. This perturbation, which largely reflects the impact of the high viscosity slab, is nearly twice the total GIA-induced departure from eustasy predicted at Barbados using the 1-D Earth model. Our calculations imply an excess ice-volume equivalent to ~130 m ESL at the LGM, which brings the Barbados-based estimate into agreement with inferences based on other far-field RSL histories, such as at Bonaparte Gulf. This inference, together with recent studies that have substantially lowered estimates of Antarctic Ice Sheet mass at LGM, suggest that a significant amount of ice remains unaccounted for in sea-level based ice sheet reconstructions. In addition, we conclude that inference of ice age ice volumes derived from RSL histories at sites in proximity to subduction zones must incorporate slab structure into the numerical predictions of the GIA process.

Comparing a thermo-mechanical Weichselian Ice Sheet reconstruction to reconstructions based on the sea level equation: aspects of ice configurations and glacial isostatic adjustment

NASA Astrophysics Data System (ADS)

Schmidt, P.; Lund, B.; Näslund, J.-O.; Fastook, J.

2014-05-01

In this study we compare a recent reconstruction of the Weichselian Ice Sheet as simulated by the University of Maine ice sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modelling: ICE-5G and ANU (Australian National University, also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling, whereas ANU and ICE-5G are global models based on the sea level equation. The three models of the Weichselian Ice Sheet are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. Whereas UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), the thickness and areal extent of the ICE-5G ice sheet is more or less constant up until the LGM. During the post-LGM deglaciation phase ANU and ICE-5G melt relatively uniformly over the entire ice sheet in contrast to UMISM, which melts preferentially from the edges, thus reflecting the fundamental difference in the reconstruction scheme. We find that all three reconstructions fit the present-day uplift rates over Fennoscandia equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present-day uplift rates, and ANU the slowest. Moreover, only for ANU can a unique best-fit model be determined. For UMISM and ICE-5G there is a range of earth models that can reproduce the present-day uplift rates equally well. This is understood from the higher present-day uplift rates predicted by ICE-5G and UMISM, which result in bifurcations in the best-fit upper- and lower-mantle viscosities. We study the areal distributions of present-day residual surface velocities in Fennoscandia and show that all three reconstructions generally over-predict velocities in southwestern Fennoscandia and that there are large differences in the fit to the observational data in Finland and northernmost Sweden and Norway. These difference may provide input to further enhancements of the ice sheet reconstructions.

An improved active contour model for glacial lake extraction

NASA Astrophysics Data System (ADS)

Zhao, H.; Chen, F.; Zhang, M.

2017-12-01

Active contour model is a widely used method in visual tracking and image segmentation. Under the driven of objective function, the initial curve defined in active contour model will evolve to a stable condition - a desired result in given image. As a typical region-based active contour model, C-V model has a good effect on weak boundaries detection and anti noise ability which shows great potential in glacial lake extraction. Glacial lake is a sensitive indicator for reflecting global climate change, therefore accurate delineate glacial lake boundaries is essential to evaluate hydrologic environment and living environment. However, the current method in glacial lake extraction mainly contains water index method and recognition classification method are diffcult to directly applied in large scale glacial lake extraction due to the diversity of glacial lakes and masses impacted factors in the image, such as image noise, shadows, snow and ice, etc. Regarding the abovementioned advantanges of C-V model and diffcults in glacial lake extraction, we introduce the signed pressure force function to improve the C-V model for adapting to processing of glacial lake extraction. To inspect the effect of glacial lake extraction results, three typical glacial lake development sites were selected, include Altai mountains, Centre Himalayas, South-eastern Tibet, and Landsat8 OLI imagery was conducted as experiment data source, Google earth imagery as reference data for varifying the results. The experiment consequence suggests that improved active contour model we proposed can effectively discriminate the glacial lakes from complex backgound with a higher Kappa Coefficient - 0.895, especially in some small glacial lakes which belongs to weak information in the image. Our finding provide a new approach to improved accuracy under the condition of large proportion of small glacial lakes and the possibility for automated glacial lake mapping in large-scale area.

Ancient humans influenced the current spatial genetic structure of common walnut populations in Asia

Treesearch

Paola Pollegioni; Keith E. Woeste; Francesca Chiocchini; Stefano Del Lungo; Irene Olimpieri; Virginia Tortolano; Jo Clark; Gabriel E. Hemery; Sergio Mapelli; Maria Emilia Malvolti; Gyaneshwer Chaubey

2015-01-01

Common walnut (Juglans regia L) is an economically important species cultivated worldwide for its wood and nuts. It is generally accepted that J. regia survived and grew spontaneously in almost completely isolated stands in its Asian native range after the Last Glacial Maximum. Despite its natural geographic isolation, J....

A database of biological and geomorphological sea-level markers from the Last Glacial Maximum to present

PubMed Central

Hibbert, F.D.; Williams, F.H.; Fallon, S.J.; Rohling, E.J.

2018-01-01

The last deglacial was an interval of rapid climate and sea-level change, including the collapse of large continental ice sheets. This database collates carefully assessed sea-level data from peer-reviewed sources for the interval 0 to 25 thousand years ago (ka), from the Last Glacial Maximum to the present interglacial. In addition to facilitating site-specific reconstructions of past sea levels, the database provides a suite of data beyond the range of modern/instrumental variability that may help hone future sea-level projections. The database is global in scope, internally consistent, and contains U-series and radiocarbon dated indicators from both biological and geomorpohological archives. We focus on far-field data (i.e., away from the sites of the former continental ice sheets), but some key intermediate (i.e., from the Caribbean) data are also included. All primary fields (i.e., sample location, elevation, age and context) possess quantified uncertainties, which—in conjunction with available metadata—allows the reconstructed sea levels to be interpreted within both their uncertainties and geological context. PMID:29809175

Ground movement at Somma-Vesuvius from Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Marturano, Aldo; Aiello, Giuseppe; Barra, Diana; Fedele, Lorenzo; Morra, Vincenzo

2012-01-01

Detailed micropalaeontological and petrochemical analyses of rock samples from two boreholes drilled at the archaeological excavations of Herculaneum, ~ 7 km west of the Somma -Vesuvius crater, allowed reconstruction of the Late Quaternary palaeoenvironmental evolution of the site. The data provide clear evidence for ground uplift movements involving the studied area. The Holocenic sedimentary sequence on which the archaeological remains of Herculaneum rest has risen several meters at an average rate of ~ 4 mm/yr. The uplift has involved the western apron of the volcano and the Sebeto-Volla Plain, a populous area including the eastern suburbs of Naples. This is consistent with earlier evidence for similar uplift for the areas of Pompeii and Sarno valley (SE of the volcano) and the Somma -Vesuvius eastern apron. An axisimmetric deep source of strain is considered responsible for the long-term uplift affecting the whole Somma -Vesuvius edifice. The deformation pattern can be modeled as a single pressure source, sited in the lower crust and surrounded by a shell of Maxwell viscoelastic medium, which experienced a pressure pulse that began at the Last Glacial Maximum.

Last Glacial Maximum to Holocene climate evolution controlled by sea-level change, Leeuwin Current, and Australian Monsoon in the Northwestern Australia

NASA Astrophysics Data System (ADS)

Ishiwa, T.; Yokoyama, Y.; McHugh, C.; Reuning, L.; Gallagher, S. J.

2017-12-01

The transition from cold to warm conditions during the last deglaciation influenced climate variability in the Indian Ocean and Pacific as a result of submerge of continental shelf and variations in the Indonesian Throughflow and Australian Monsoon. The shallow continental shelf (< 200 m water depth) developed along the northwestern Australian margin is influenced by the Australian Monsoon and Leeuwin Current (one of branch of the Indonesian Throughflow). The International Ocean Discovery Program Expedition 356 Indonesian Throughflow drilled in the northwestern Australian shallow continental shelf and recovered an interval from the Last Glacial Maximum to Holocene in Site U1461. Radiocarbon dating on macrofossils, foraminifera, and bulk organic matter provided a precise age-depth model, leading to high-resolved paleoclimate reconstruction. X-ray elemental analysis results are interpreted as an indicator of sedimentary environmental changes. The upper 20-m part of Site U1461 apparently records the climate transition from the LGM to Holocene in the northwestern Australia, which could be associated with sea-level change, Leeuwin Current activity, and the Australian Monsoon.

Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet

USGS Publications Warehouse

Brigham-Grette, J.; Gualtieri, L.M.; Glushkova, O.Y.; Hamilton, T.D.; Mostoller, D.; Kotov, A.

2003-01-01

The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

Complementary constraints from carbon (13C) and nitrogen (15N) isotopes on the glacial ocean's soft-tissue biological pump

NASA Astrophysics Data System (ADS)

Schmittner, A.; Somes, C. J.

2016-06-01

A three-dimensional, process-based model of the ocean's carbon and nitrogen cycles, including 13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results are presented from one preindustrial control run (piCtrl) and six simulations of the Last Glacial Maximum (LGM) with increasing values of the spatially constant maximum phytoplankton growth rate μmax, which accelerates biological nutrient utilization mimicking iron fertilization. The default LGM simulation, without increasing μmax and with a shallower and weaker Atlantic Meridional Overturning Circulation and increased sea ice cover, leads to 280 Pg more respired organic carbon (Corg) storage in the deep ocean with respect to piCtrl. Dissolved oxygen concentrations in the colder glacial thermocline increase, which reduces water column denitrification and, with delay, nitrogen fixation, thus increasing the ocean's fixed nitrogen inventory and decreasing δ15NNO3 almost everywhere. This simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well, but it overestimates deep ocean δ13CDIC and underestimates δ15NNO3 at high latitudes. Increasing μmax enhances Corg and lowers deep ocean δ13CDIC, improving the agreement with sediment data. In the model's Antarctic and North Pacific Oceans modest increases in μmax result in higher δ15NNO3 due to enhanced local nutrient utilization, improving the agreement with reconstructions there. Models with moderately increased μmax fit both isotope data best, whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well. The best fitting models reproduce major features of the glacial δ13CDIC, δ15N, and oxygen reconstructions while simulating increased Corg by 510-670 Pg compared with the preindustrial ocean. These results are consistent with the idea that the soft-tissue pump was more efficient during the LGM. Both circulation and biological nutrient utilization could contribute. However, these conclusions are preliminary given our idealized experiments, which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes. The analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes. Whereas carbon isotopes are sensitive to circulation changes and indicate well the three-dimensional Corg distribution, nitrogen isotopes are more sensitive to biological nutrient utilization.

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 for debates about the former existence of nunataks and refugia. Copyright ?? 2006 John Wiley & Sons, Ltd.

Geochronology and Equilibrium Line Altitudes of LLGM through Holocene Glaciations from the Tropical Cordillera Huayhuash, Peru

NASA Astrophysics Data System (ADS)

Hall, S. R.; Ramage, J. M.; Rodbell, D. T.; Finkel, R. C.; Smith, J. A.; Mark, B. G.; Farber, D. L.

2006-12-01

Geomorphologic relationships and cosmogenic 10Be ages from the Central Peruvian Andes reveal a rich record of glaciations from at least the late Holocene, Late Glacial, Last Local Glacial Maximum (LLGM), and older more extensive glaciations - dated between 50ka and 440ka in both the Cordillera Blanca, to the north and the Junin Region to the south. The Cordillera Huayhuash (10.3°S, 76.9°W) is located between these two well-studied regions. The spine of the range trends nearly north-south and contains a substantial east-west spur which together can be used to evaluate the spatial variation in paleo-ELAs. The range is thus a key location to study changes in ice extent and equilibrium line altitudes (ELAs) between the LLGM and modern periods. Modern glaciers are confined to altitudes >4800 m and the present (1997) ELA is 4800- 5100m. In order to determine the paleo-ice positions of glaciers in different valleys we have developed a new chronology from cosmogenic 10Be ages of moraine boulder and 14C basal bog core ages. Through field mapping of glacial features, analysis of satellite imagery, digital elevation models (DEMs), and geochronology, we have delineated the ice limits associated with the LLGM, Late Glacial, and Late Holocene advances. Ages in the three valleys we have studied cluster at ~29ka, ~13ka, and ~9ka and overall we have identified surfaces with ages that range from 39.9±1.4ka to 0.2ka±0.05ka. Based on these data, we have mapped the extent of the correlative paleo-glaciers in these three drainages and extracted the modern hypsometry for each paleo-glacier from the DEMs. From this data set, we have generated paleo- ELAs using a range of methods: Toe-to-Headwall-Altitude Ratio (THAR), the Accumulation Area Ratio (AAR), and Accumulation Area Balance Ratio (AABR). For each of the LLGM, Late Glacial and Holocene stages, we have calculated both: (1) the temperature depression assuming no moisture variations, and (2) the potential relative moisture gradients assuming a constant temperature depression. Our results suggest that variations in glacial extent (and therefore paleo-ELAs) are strongly correlated with differences in valley orientation and morphology as eastern drainages receive more moisture and have shallower topographic gradients than western drainages. Additionally, while there is an extensive record of older (>39.9±1.4ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the confined morphology of the Cordillera Huayhaush valleys may have inhibited the preservation of older glacial geomorphologic features, thereby explaining the apparent lack of old moraines in this range.

Controls on bedrock bedform development at the base of the Uummannaq Ice Stream System, West Greenland

NASA Astrophysics Data System (ADS)

Lane, Tim; Roberts, David; Rea, Brice; Cofaigh, Colm Ó.

2014-05-01

This research investigates the glacial and non-glacial controls on glacially eroded bedrock bedforms beneath the topographically confined upstream fjord region of the Uummannaq Ice Stream (UIS), West Greenland. The UIS was a cross-shelf ice stream system that operated during the Last Glacial Maximum (LGM), formed of 10 coalescent outlet glaciers. Reconstructions suggest that palaeo-glaciological conditions were similar for all sites in the study, characterised by thick, fast flowing ice moving over a rigid bedrock bed. Areally scoured terrain were mapped using remotely sensed imagery to assess regional-scale patterns of glacial erosion and to select suitable field locations. In the field, bedform measurements were taken from four discrete areas within two neighbouring fjords in the northern Uummannaq region (Rink-Karrat and Ingia). Classic bedrock bedforms indicative of glacially eroded terrain were mapped, including p-forms, roche moutonnées, and whalebacks. Bedform long axes and plucked face orientations display close correlation with palaeo-ice flow directions inferred from striae measurements. Across all sites, elongation ratios (length to width) varied by an order of magnitude between 0.8:1 and 8.4:1. Bedform properties (length, height, width, and long axis orientation) from the four sample areas form individual morphometrically distinct populations. However, bedform populations display high inter-area variability despite their close proximity, and hypothesised similarity in palaeo-glaciological conditions. The relationship of bedforms to palaeo-glaciological conditions in this study is not simple, having been complicated by bedrock properties. Geological structures including: joint frequency; joint dip; joint orientation; bedding plane thickness; and bedding plane dip have provided lines of geological weakness along which glacial erosion has been able to focus, controlling bedform length and width. Lateral plucking, a mechanism previously described for the development of megagroove features, is invoked here for the formation of whaleback-type bedforms in Ingia Fjord. Bedding plane thickness and bedding plane dip relative to palaeo-ice flow direction and is shown to a key control on bedform morphology and ELR. Consequently, a knowledge of bedding plane dip relative to palaeo-ice flow can allow predictions to be made about likely bedform shape, relative length, amplitude, and wavelength. These predictions have important ramifications for understanding subglacial bed roughness, cavity formation, and likely ice-bed erosion processes. These observations demonstrate the direct link between bedrock bedform properties and underlying geological structure. This supports evidence which suggests that the use of bedrock bedform characteristics to directly infer palaeo-glaciological conditions must be approached with caution. In order to robustly understand bedform morphology, a full appreciation of local geological structure is necessary.

Postglacial species displacement in Triturus newts deduced from asymmetrically introgressed mitochondrial DNA and ecological niche models

PubMed Central

2012-01-01

Background If the geographical displacement of one species by another is accompanied by hybridization, mitochondrial DNA can introgress asymmetrically, from the outcompeted species into the invading species, over a large area. We explore this phenomenon using the two parapatric crested newt species, Triturus macedonicus and T. karelinii, distributed on the Balkan Peninsula in south-eastern Europe, as a model. Results We first delimit a ca. 54,000 km2 area in which T. macedonicus contains T. karelinii mitochondrial DNA. This introgression zone bisects the range of T. karelinii, cutting off a T. karelinii enclave. The high similarity of introgressed mitochondrial DNA haplotypes with those found in T. karelinii suggests a recent transfer across the species boundary. We then use ecological niche modeling to explore habitat suitability of the location of the present day introgression zone under current, mid-Holocene and Last Glacial Maximum conditions. This area was inhospitable during the Last Glacial Maximum for both species, but would have been habitable at the mid-Holocene. Since the mid-Holocene, habitat suitability generally increased for T. macedonicus, whereas it decreased for T. karelinii. Conclusion The presence of a T. karelinii enclave suggests that T. karelinii was the first to colonize the area where the present day introgression zone is positioned after the Last Glacial Maximum. Subsequently, we propose T. karelinii was outcompeted by T. macedonicus, which captured T. karelinii mitochondrial DNA via introgressive hybridization in the process. Ecological niche modeling suggests that this replacement was likely facilitated by a shift in climate since the mid-Holocene. We suggest that the northwestern part of the current introgression zone was probably never inhabited by T. karelinii itself, and that T. karelinii mitochondrial DNA spread there through T. macedonicus exclusively. Considering the spatial distribution of the introgressed mitochondrial DNA and the signal derived from ecological niche modeling, we do not favor the hypothesis that foreign mitochondrial DNA was pulled into the T. macedonicus range by natural selection. PMID:22935041

Postglacial species displacement in Triturus newts deduced from asymmetrically introgressed mitochondrial DNA and ecological niche models.

PubMed

Wielstra, Ben; Arntzen, Jan W

2012-08-30

If the geographical displacement of one species by another is accompanied by hybridization, mitochondrial DNA can introgress asymmetrically, from the outcompeted species into the invading species, over a large area. We explore this phenomenon using the two parapatric crested newt species, Triturus macedonicus and T. karelinii, distributed on the Balkan Peninsula in south-eastern Europe, as a model. We first delimit a ca. 54,000 km(2) area in which T. macedonicus contains T. karelinii mitochondrial DNA. This introgression zone bisects the range of T. karelinii, cutting off a T. karelinii enclave. The high similarity of introgressed mitochondrial DNA haplotypes with those found in T. karelinii suggests a recent transfer across the species boundary. We then use ecological niche modeling to explore habitat suitability of the location of the present day introgression zone under current, mid-Holocene and Last Glacial Maximum conditions. This area was inhospitable during the Last Glacial Maximum for both species, but would have been habitable at the mid-Holocene. Since the mid-Holocene, habitat suitability generally increased for T. macedonicus, whereas it decreased for T. karelinii. The presence of a T. karelinii enclave suggests that T. karelinii was the first to colonize the area where the present day introgression zone is positioned after the Last Glacial Maximum. Subsequently, we propose T. karelinii was outcompeted by T. macedonicus, which captured T. karelinii mitochondrial DNA via introgressive hybridization in the process. Ecological niche modeling suggests that this replacement was likely facilitated by a shift in climate since the mid-Holocene. We suggest that the northwestern part of the current introgression zone was probably never inhabited by T. karelinii itself, and that T. karelinii mitochondrial DNA spread there through T. macedonicus exclusively. Considering the spatial distribution of the introgressed mitochondrial DNA and the signal derived from ecological niche modeling, we do not favor the hypothesis that foreign mitochondrial DNA was pulled into the T. macedonicus range by natural selection.

A cosmogenic 10Be chronology for the local last glacial maximum and termination in the Cordillera Oriental, southern Peruvian Andes: Implications for the tropical role in global climate

NASA Astrophysics Data System (ADS)

Bromley, Gordon R. M.; Schaefer, Joerg M.; Hall, Brenda L.; Rademaker, Kurt M.; Putnam, Aaron E.; Todd, Claire E.; Hegland, Matthew; Winckler, Gisela; Jackson, Margaret S.; Strand, Peter D.

2016-09-01

Resolving patterns of tropical climate variability during and since the last glacial maximum (LGM) is fundamental to assessing the role of the tropics in global change, both on ice-age and sub-millennial timescales. Here, we present a10Be moraine chronology from the Cordillera Carabaya (14.3°S), a sub-range of the Cordillera Oriental in southern Peru, covering the LGM and the first half of the last glacial termination. Additionally, we recalculate existing 10Be ages using a new tropical high-altitude production rate in order to put our record into broader spatial context. Our results indicate that glaciers deposited a series of moraines during marine isotope stage 2, broadly synchronous with global glacier maxima, but that maximum glacier extent may have occurred prior to stage 2. Thereafter, atmospheric warming drove widespread deglaciation of the Cordillera Carabaya. A subsequent glacier resurgence culminated at ∼16,100 yrs, followed by a second period of glacier recession. Together, the observed deglaciation corresponds to Heinrich Stadial 1 (HS1: ∼18,000-14,600 yrs), during which pluvial lakes on the adjacent Peruvian-Bolivian altiplano rose to their highest levels of the late Pleistocene as a consequence of southward displacement of the inter-tropical convergence zone and intensification of the South American summer monsoon. Deglaciation in the Cordillera Carabaya also coincided with the retreat of higher-latitude mountain glaciers in the Southern Hemisphere. Our findings suggest that HS1 was characterised by atmospheric warming and indicate that deglaciation of the southern Peruvian Andes was driven by rising temperatures, despite increased precipitation. Recalculated 10Be data from other tropical Andean sites support this model. Finally, we suggest that the broadly uniform response during the LGM and termination of the glaciers examined here involved equatorial Pacific sea-surface temperature anomalies and propose a framework for testing the viability of this conceptual model.

Reaching and abandoning the furthest ice extent during the Last Glacial Maximum in the Alps

NASA Astrophysics Data System (ADS)

Ivy-Ochs, Susan; Wirsig, Christian; Zasadni, Jerzy; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

2016-04-01

During the Last Glacial Maximum (LGM) in the European Alps (late Würm) local ice caps and extensive ice fields in the high Alps fed huge outlet glaciers that occupied the main valleys and extended onto the forelands as piedmont lobes. Records from numerous sites suggest advance of glaciers beyond the mountain front by around 30 ka (Ivy-Ochs 2015 and references therein). Reaching of the maximum extent occurred by about 27-26 ka, as exemplified by dates from the Rhein glacier area (Keller and Krayss, 2005). Abandonment of the outermost moraines at sites north and south of the Alps was underway by about 24 ka. In the high Alps, systems of transection glaciers with transfluences over many of the Alpine passes dominated, for example, at Grimsel Pass in the Central Alps (Switzerland). 10Be exposure ages of 23 ± 1 ka for glacially sculpted bedrock located just a few meters below the LGM trimline in the Haslital near Grimsel Pass suggest a pulse of ice surface lowering at about the same time that the foreland moraines were being abandoned (Wirsig et al., 2016). Widespread ice surface lowering in the high Alps was underway by no later than 18 ka. Thereafter, glaciers oscillated at stillstand and minor re-advance positions on the northern forelands for several thousand years forming the LGM stadial moraines. Final recession back within the mountain front took place by 19-18 ka. Recalculation to a common basis of all published 10Be exposure dates for boulders situated on LGM moraines suggests a strong degree of synchrony for the timing of onset of ice decay both north and south of the Alps. Ivy-Ochs, S., 2015, Cuadernos de investigación geográfica 41: 295-315. Keller, O., Krayss, E., 2005, Vierteljahrschr. Naturforsch. Gesell. Zürich 150: 69-85. Wirsig, C. et al., 2016, J. Quat. Sci. 31: 46-59.

Lateglacial temperature reconstruction in the Eastern Tropical Andes (Bolivia) inferred from paleoglaciers and paleolakes

NASA Astrophysics Data System (ADS)

Martin, L.; Blard, P. H.; Lave, J.; Prémaillon, M.; Jomelli, V.; Brunstein, D.; Lupker, M.; Charreau, J.; Mariotti, V.; Condom, T.; Bourles, D. L.

2015-12-01

Recent insights shed light on the global mechanisms involved in the abrupt oscillations of the Earth climate for the Late Glacial Maximum (LGM) to Holocene period (Zhang et al., 2014; Banderas et al., 2015). Yet the concomitant patterns of regional climate reorganization on continental areas are for now poorly documented. Particularly, few attempts have been made to propose temporal reconstructions of the regional climate variables in the High Tropical Andes, a region under the direct influence of the upper part of the troposphere. We present new glacial chronologies from the Zongo (16.3°S - 68.1°W, Bolivia) and Wara-Wara (17.3°S - 66.1°W, Bolivia) valleys based on Cosmic Ray Exposure dating (CRE) from an exceptional suite of recessive moraines. These new data permitted to refine existing chronologies (Smith et al., 2005 ; Zech et al., 2010): the Zongo valley is characterized by an older local last glacial maximum than the Wara Wara valley. Both sites however exhibit similar glacier behaviours, with a progressive regression between 18 ka and the Holocene. In both sites, glaciers recorded stillstand episodes synchronous with the cold events of the Norther Hemisphere (Henrich 1 event, Younger Dryas). Since the nearby Altiplano basin registered lake level variations over the same period, we were able to apply a joint modelling of glaciers Equilibrium Line Altitude (ELA) and lake budget. This permits to derive a temporal evolution of temperature and precipitation for both sites. These new reconstructions show for both sites that glaciers of the Eastern Tropical Andes were both influenced by the major climatic events of the Northern and Southern Hemispheres. However, precipitation variability is more influenced by the Northern Atlantic events. This observation is in good agreement with the theories suggesting that North Hemisphere cold events are coeval with an important southward deflexion of the Intertropical Convergence Zone (ITCZ) due to the inter-hemispheric temperature gradient (Schneider et al., 2014). Such a southward shift would lead to an increased moist supply of the subequatorial Amazonian basin (Montade et al., 2015) and thus an increased easterly driven moist transport over the Altiplano.

Regional assessment of concentrations and sources of pharmaceutically active compounds, pesticides, nitrate, and E. coli in post-glacial aquifer environments (Canada).

PubMed

Saby, Marion; Larocque, Marie; Pinti, Daniele L; Barbecot, Florent; Gagné, Sylvain; Barnetche, Diogo; Cabana, Hubert

2017-02-01

There is growing concern worldwide about the exposure of groundwater resources to pharmaceutically active compounds (PhACs) and agricultural contaminants, such as pesticides, nitrate, and Escherichia coli. For regions with a low population density and an abundance of water, regional contamination assessments are not carried out systematically due to the typically low concentrations and high costs of analyses. The objectives of this study were to evaluate regional-scale contaminant distributions in untreated groundwater in a rural region of Quebec (Canada). The geological and hydrogeological settings of this region are typical of post-glacial regions around the world, where groundwater flow can be complex due to heterogeneous geological conditions. A new spatially distributed Anthropogenic Footprint Index (AFI), based on land use data, was developed to assess surface pollution risks. The Hydrogeochemical Vulnerability Index (HVI) was computed to estimate aquifer vulnerability. Nine wells had detectable concentrations of one to four of the 13 tested PhACs, with a maximum concentration of 116ng·L -1 for benzafibrate. A total of 34 of the 47 tested pesticides were detected in concentrations equal to or greater than the detection limit, with a maximum total pesticide concentration of 692ng·L -1 . Nitrate concentrations exceeded 1mg·L -1 N-NO 3 in 15.3% of the wells, and the Canadian drinking water standard was exceeded in one well. Overall, 13.5% of the samples had detectable E. coli. Including regional-scale sources of pollutants to the assessment of aquifer vulnerability with the AFI did not lead to the identification of contaminated wells, due to the short groundwater flow paths between recharge and the sampled wells. Given the occurrence of contaminants, the public health concerns stemming from these new data on regional-scale PhAC and pesticide concentrations, and the local flow conditions observed in post-glacial terrains, there is a clear need to investigate the sources and behaviours of local-scale pollutants. Copyright © 2016 Elsevier B.V. All rights reserved.

Mediterranean fire histories since the Last Glacial Maximum from lake sedimentary micro- charcoals

NASA Astrophysics Data System (ADS)

Roberts, C.; Turner, R.

2006-12-01

Microscopic charcoal analysis has been used to reconstruct past fire activity over a range of spatial and temporal scales in Europe, the Americas and Australasia. By contrast, and despite the importance of fire in its modern landscape ecology, few systematic attempts have been made in the circum-Mediterranean region to reconstruct long-term fire histories using micro-charcoals or other methods of analysis. This study has used non-destructive methods of charcoal extraction based on sieving plus heavy-liquid separation (Turner et al in press In: Charcoal from the past: cultural and palaeoenvironmental implications. BAR International Series, Archaeopress, Oxford) along with contiguous core sampling of sedimentary core sequences from a number of East Mediterranean lakes that span the last glacial-interglacial climatic transition. At Eski Acýgöl, central Turkey (Roberts et al. Holocene, 2001, 11, 719-734), then a deepwater crater lake, overall micro-charcoal concentrations in sediments are low and were dominated by influx from regional-landscape rather than local- scale fire events. This record therefore provides a good proxy for overall fire frequency/intensity across the central Anatolia plateau, whose (hypothetical) modern "natural" vegetation is predominantly open oak-grass- Artemisia parkland. Shallow water sites such as Akgöl typically record much higher overall micro-charcoal abundance as a result of local-scale burning of the marsh surface at times of lowered water table, and thus received episodic local charcoal influx superimposed on background regional airborne sources. These results indicate that site type / catchment area and sampling / analytic methodology can critically influence reconstructed fire histories. We have correlated our charcoal records with existing multi-proxy data from the same cores (stable isotopes and pollen). This shows that climatic variations and biomass availability were the main factors controlling the timing of regional fire activity from the Last Glacial Maximum through to the Early Holocene. The Holocene portion of the Eski Acýgöl record contains a significant cyclicity with a periodicity of 1400 to 1500 years which may be linked with external (e.g. solar) forcing.

Complementary Constraints from Carbon (13C) and Nitrogen (15N) Isotopes on the Efficiency of the Glacial Ocean's Soft-Tissue Biological Pump

NASA Astrophysics Data System (ADS)

Schmittner, A.; Somes, C. J.

2016-12-01

A three-dimensional, process-based model of the ocean's carbon and nitrogen cycles, including 13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results are presented from one preindustrial control run and six simulations of the Last Glacial Maximum (LGM) with increasing values of the spatially constant maximum phytoplankton growth rate μmax, which mimicks iron fertilization. The default LGM simulation, without increasing μmax and with a shallower and weaker Atlantic Meridional Overturning Circulation and increased sea ice cover, leads to 280 Pg more respired organic carbon (Corg) than the pre-industrial control. Dissolved oxygen in the thermocline increase, which reduces water column denitrification and nitrogen fixation, thus increasing the ocean's fixed nitrogen inventory and decreasing δ15NNO3. This simulation already fits observed carbon and nitrogen isotopes relatively well, but it overestimates deep ocean δ13CDIC and underestimates δ15NNO3 at high latitudes. Increasing μmax enhances Corg and lowers deep ocean δ13CDIC, improving the fit. Modest increases in μmax result in higher subpolar δ15NNO3 due to enhanced local nutrient utilization, and better agreement with reconstructions. Large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well. The best fitting models with modest increases in μmax reproduce major features of the glacial δ13CDIC, δ15N, and oxygen reconstructions while simulating increased Corg by 510-670 Pg. These results are consistent with the idea that the soft-tissue pump was more efficient during the LGM. Both circulation and biological nutrient utilization contribute. However, these conclusions are preliminary given our idealized experiments, which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes. The analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes. Whereas carbon isotopes are sensitive to circulation changes and indicate well the three-dimensional Corg distribution, nitrogen isotopes are more sensitive to biological nutrient utilization.

Geochemical Weathering in Glacial and Proglacial Environments

NASA Astrophysics Data System (ADS)

Tranter, M.

2003-12-01

It seems counterintuitive that chemical erosion in glaciated regions proceeds at rates comparable to those of temperate catchments with comparable specific runoff (Anderson et al., 1997). All the usual factors that are associated with elevated rates of chemical weathering ( Drever, 1988, 1994), such as water, soil, and vegetation, are either entirely absent or absent for much of the year. For example, glaciated regions are largely frozen for significant periods each year, the residence time of liquid water in the catchment is low ( Knight, 1999), there are thin, skeletal soils at best, and vegetation is either absent or limited ( French, 1997). Other chapters in this volume have highlighted how these factors are important in other, more temperate and tropical environments. Even so, chemical erosion rates in glaciated terrain are usually near to or greater than the continental average ( Sharp et al., 1995; Wadham et al., 1997; Hodson et al., 2000). This is because glaciated catchments usually have high specific runoff, there are high concentrations of freshly comminuted rock flour, which is typically silt sized and coated with microparticles, and adsorbed organic matter or surface precipitates that may hinder water-rock interactions are largely absent ( Tranter, 1982). In short, the rapid flow of water over fine-grained, recently crushed, reactive mineral surfaces maximizes both the potential rates of chemical weathering and chemical erosion.A range of both lab- and field-based studies of glacial chemical weathering have been undertaken, mainly on the smaller glaciers of Continental Europe (e.g., Brown et al., 1993a, b), Svalbard (e.g., Hodson et al., 2002), and North America (e.g., Anderson et al., 2000). The field-based studies typically generate hydrographs of glacier runoff, which show a characteristic diurnal cycle during summer in low latitudes ( Figure 1), and more subdued diurnal cycles at high latitudes (Figure 2 and Figure 3). The concentration of ions in solution, typically monitored by electrical conductivity, is often inverse with discharge on both a diurnal and a seasonal basis at lower latitudes, but ismore complex at higher latitudes (Figure 1, Figure 2 and Figure 3). Figure 1, Figure 2 and Figure 3 also show that the total flux of glacial solutes is usually dominated by fluxes associated with high discharge, dilute waters. The chemical weathering reactions that are inferred to occur from the field studies have been supported, in part, by controlled laboratory studies (e.g., Brown et al., 1993a). Recent stable-isotope studies have reported the key involvement of microbial processes in certain regions of the glacier bed ( Bottrell and Tranter, 2002), and these processes are yet to be incorporated in lab-based chemical weathering studies. (14K)Figure 1. (a) The temporal variation of discharge and in non-sea-salt calcium (*Ca2+) concentration in runoff from Haut Glacier d'Arolla, a small, warm-based, valley glacier in the Swiss Alps, during 1989 (Brown et al., 1993a). (b) The temporal variation in *Ca2+ flux from Haut Glacier d'Arolla during 1989. Maximum fluxes are associated with higher discharge waters. (9K)Figure 2. (a) The temporal variation of discharge (Q) and non-sea-salt *Ca2+ concentration in runoff from Manitsoq Glacier, a small outlet glacier on the SW margin of the Greenland Ice Sheet, during 1999. The glacier is warm based, but has a cold-based margin during the winter and early ablation season, so displays polythermal-based hydrological features (Skidmore et al., in preparation). (b) The temporal variation in *Ca2+ flux from Manitsoq Glacier during 1999. Maximum flux is associated with an early season "outburst" event, where longer stored subglacial water first exits the glacier. Otherwise, maximum fluxes are associated with higher discharge waters. (10K)Figure 3. (a) The temporal variation of discharge and *Ca2+ concentration in runoff from Scott Turnerbreen, a small, cold-based, valley glacier on Svalbard, during 1994 (after Hodgkins et al., 1997). (b) The temporal variation in *Ca2+ flux from Scott Turnerbreen during 1994. Maximum fluxes are associated with higher discharge waters, although the precise associations are complex. This chapter will expand on these themes, and endeavor to integrate ongoing research into a state-of-the-science review, as well as indicating the areas into which the next generation of studies are likely to proceed. It is first necessary to understand a little basic glaciology and glacier hydrology to appreciate the principal features of the different chemical weathering environments that will be described below. The following sections summarize the types of glacial environments in which water flows, their typical debris content, the relative residence time of water, and the typical reactions that occur within them.

Long-term changes in composition and distribution patterns in the Iberian herpetofaunal communities since the latest Pleistocene

NASA Astrophysics Data System (ADS)

Bisbal-Chinesta, Josep Francesc; Blain, Hugues-Alexandre

2018-03-01

The climate has undergone significant changes since the end of the Last Glacial Maximum and in the course of the Holocene, parallel to important cultural transformations and migrations in the human communities. The faunal record has also suffered the effects of climate change. Amphibians and reptiles in particular have been shown to be highly sensitive because they are very susceptible to temperature alterations due to their ectothermy. This research presents the first approach to the Iberian paleobiogeography of the different species of amphibians and reptiles from the Late Pleistocene (MIS3) to present times, based on a comparative synthesis of the latest research published in recent years and the fossil record of the 58 archaeo-paleontological sites with significant assemblages. The paleoherpetofaunal associations make it possible to establish two major biotic regions during the Late Pleistocene. The first biotic region was located in the center and south of the Iberian Peninsula, with thermophilic species as the most representative taxa. The second biotic region was formed by the Atlantic-Cantabrian facade and the northeast Iberian area, dominated by hygrophilous and Euro-Siberian species, with an absence of Mediterranean species. After the Last Glacial Maximum there was an unprecedented concurrence in the northern Iberian Peninsula of autochthonous taxa from that area with thermophilic species. In the early Holocene, new species with no previous record in the Iberian Peninsula entered northern Iberia from eastern Mediterranean refugia. Finally, the introduction of North African species was the last significant biogeographical change during the Middle-Late Holocene.

Glacial Refugia and Future Habitat Coverage of Selected Dactylorhiza Representatives (Orchidaceae)

PubMed Central

2015-01-01

The intensively discussed taxonomic complexity of the Dactylorhiza genus is probably correlated with its migration history during glaciations and interglacial periods. Previous studies on past processes affecting the current distribution of Dactylorhiza species as well as the history of the polyploid complex formation were based only on molecular data. In the present study the ecological niche modeling (ENM) technique was applied in order to describe the distribution of potential refugia for the selected Dactylorhiza representatives during the Last Glacial Maximum. Additionally, future changes in their potential habitat coverage were measured with regard to three various climatic change scenarios. The maximum entropy method was used to create models of suitable niche distribution. A database of Dactylorhiza localities was prepared on the grounds of information collected from literature and data gathered during field works. Our research indicated that the habitats of majority of the studied taxa will decrease by 2080, except for D. incarnata var. incarnata, for which suitable habitats will increase almost two-fold in the global scale. Moreover, the potential habitats of some taxa are located outside their currently known geographical ranges, e.g. the Aleutian Islands, the western slopes of the Rocky Mountains, Newfoundland, southern Greenland and Iceland. ENM analysis did not confirm that the Balkans, central Europe or central Russia served as the most important refugia for individual representatives of the Dactylorhiza incarnata/maculata complex. Our study rather indicated that the Black Sea coast, southern Apennines and Corsica were the main areas characterized by habitats suitable for most of the taxa. PMID:26599630

Evidence for Multiple Late Quaternary Glaciations in the Southernmost Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Smith, J. A.; Rodbell, D. T.; Ramage, J. M.

2007-12-01

Surface-exposure dating with in-situ-produced cosmogenic isotopes has provided the basis for a growing framework of glacial chronologies in the tropical Andes. In the Peruvian Andes, long chronologies (>400 ka) with relatively small local last glacial maximum (LLGM) advances have been reported for the central Cordillera Blanca (ca. 9°30'S) and Junin Plain (11°00'S), whereas preliminary data suggest a shorter record (<40 ka) in the intervening Cordillera Huayhuash (10°15'S). These seemingly contradictory findings raise several questions: Was the LLGM a relatively minor event in the Peruvian Andes, far exceeded by bigger, older advances? Which combination of geographic and geomorphic factors increases the likelihood that evidence of older advances will be preserved? With these questions in mind, we sought a site with both high peaks and a high-altitude plateau. The glaciated Nevado Jeulla Rajo massif (10°00'S, 77°16'W, peaks ca. 5600 masl) marks the southern end of the Cordillera Blanca and the Callejon de Huaylas valley in the central Peruvian Andes. The Conococha Plain (ca. 4050 masl) borders the western side of the massif. Large lateral moraines extend onto the Conococha Plain from the west-facing valleys and multiple moraine loops lie upvalley, closer to active ice margins. Surface-exposure dating (10Be) indicates that the largest lateral moraines from Jeullesh Valley are compound features deposited during the LLGM (ca. 30 ka) and a late-glacial readvance (ca. 16 ka). The LLGM/late-glacial moraines cross-cut an older pair of lateral moraines (ca. 70 ka) that may provide evidence for a smaller advance during marine isotope stage 4. Although the LLGM/late-glacial moraines are impressively large (ca. 150 m high), they do not represent the maximum ice extent in the region. Fluvial outwash deposits beyond the termini of the moraines on the Conococha Plain are underlain by lodgement till that is up to 20 m thick and extends ca. 6 km across the width of the Plain to the Rió Santa. The wide distribution of the till suggests that at least one older glaciation was far more extensive than any of the late Quaternary advances that we have dated by 10Be. The combination of high peaks, a high-altitude plateau, and an active fault may be ideal for enhancing preservation of older moraines and till deposits.

A Glacial Perspective on the Impact of Heinrich Stadials on North Atlantic Climate

NASA Astrophysics Data System (ADS)

Bromley, G. R.; Putnam, A. E.; Rademaker, K. M.; Balter, A.; Hall, B. L.

2017-12-01

The British Isles contain a rich geologic record of Late Pleistocene ice sheet behaviour in the NE North Atlantic basin. We are using cosmogenic 10Be surface-exposure dating, in conjunction with detailed glacial-geomorphic mapping, to reconstruct the timing and nature of cryospheric change - and thus climate variability - in northern Scotland since the Last Glacial Maximum. Our specific focus is Heinrich Stadial 1 (18,300-14,700 years ago), arguably the most significant abrupt climate event of the last glacial cycle and a major feature in global palaeoclimate records. Such constraint is needed because of currently conflicting models of how these events impact terrestrial environments and a recent hypothesis attributing this disparity to enhanced seasonality in the North Atlantic basin. To date, we have measured 10Be in > 30 samples from glacial erratics located on moraines deposited by the British Ice Sheet as it retreated from the continental shelf to its highland source regions. Our preliminary results indicate that the stadial was characterised by widespread deglaciation driven by atmospheric warming, a pattern that is suggestive of pronounced seasonality. Additionally, we report new exposure ages from moraines deposited during a subsequent phase of alpine glaciation (known locally as the Loch Lomond Readvance) that has long been attributed to the Younger Dryas stadial. With the growing focus on the full expression of stadials, and the inherent vulnerability of Europe to shifts in North Atlantic climate, developing the extant record of terrestrial glaciation and comparing these data to marine records is a critical step towards understanding the drivers of abrupt climate change.

Late Quaternary glaciation history of monsoon-dominated Dingad basin, central Himalaya, India

NASA Astrophysics Data System (ADS)

Shukla, Tanuj; Mehta, Manish; Jaiswal, Manoj K.; Srivastava, Pradeep; Dobhal, D. P.; Nainwal, H. C.; Singh, Atul K.

2018-02-01

The study presents the Late Quaternary glaciation history of monsoon-dominated Dokriani Glacier valley, Dingad basin, central Himalaya, India. The basin is tested for the mechanism of landforms preservation in high relief and abundant precipitation regimes of the Higher Himalaya. Field geomorphology and remote sensing data, supported by Optical Stimulated Luminescence (OSL) dating enabled identification of five major glacial events of decreasing magnitude. The oldest glacial stage, Dokriani Glacial Stage I (DGS-I), extended down to ∼8 km (2883 m asl) from present-day snout (3965 m asl) followed by other four glaciations events viz. DGS-II, DGS-III, DGS-IV and DGS-V terminating at ∼3211, 3445, 3648 and ∼3733 m asl respectively. The DGS-I glaciation (∼25-∼22 ka BP) occurred during early Marine Isotope Stage (MIS) -2, characterized as Last Glacial Maximum (LGM) extension of the valley. Similarly, DGS-II stage (∼14-∼11 ka BP) represents the global cool and dry Older Dryas and Younger Dryas event glaciation. The DGS-III glaciation (∼8 ka BP) coincides with early Holocene 8.2 ka cooling event, the DGS-IV glaciations (∼4-3.7 ka BP) corresponds to 4.2 ka cool and drier event, DGS-V (∼2.7-∼1 ka BP) represents the cool and moist late Holocene glacial advancement of the valley. This study suggests that the Dokriani Glacier valley responded to the global lowering of temperature and variable precipitation conditions. This study also highlights the close correlation between the monsoon-dominated valley glaciations and Northern Hemisphere cooling events influenced by North Atlantic climate.

Glacial origin for cave rhythmite during MIS 5d-c in a glaciokarst landscape, Picos de Europa (Spain)

NASA Astrophysics Data System (ADS)

Ballesteros, Daniel; Jiménez-Sánchez, Montserrat; Giralt, Santiago; DeFelipe, Irene; García-Sansegundo, Joaquín

2017-06-01

Laminated slackwater deposits have been identified in many karst caves related to fluvial and lacustrine sedimentation. However, sedimentological evidence rarely supports a glacial origin for these deposits, which was proposed by previous studies. The Torca La Texa shaft is located in a glaciokarst area that comprises numerous slackwater-type deposits, piled up in fining-upward sequences. A basal sandy erosive layer and millimeter-sized laminated rhythmite with interbedded flowstone characterize these sequences. Fining-upward layers of carbonate silt, clay, and minor quartz sand deposited in flooded conduits define the rhythmite lamination. The presence of allochthonous minerals indicates that the rhythmite sediment comes from the glacial erosion of nearby carbonate mountains. Two 234U/230Th radiometric ages dated the rhythmite deposits around 109 and 95 ka, coinciding with relative cold periods included in the MIS 5d-c. These cold periods were marked by a high annual seasonality, immediately after the glacial local maximum extension, in agreement with a varve-type deposit. The combination of these sedimentological mineralogical, geomorphological and paleoclimate information indicates that the rhythmite should be introduced into the studied cave during the summer melting of the glaciers, which produced the recharge of the karst aquifer, triggering cave floods. In addition, punctual glacier collapses would also have their imprint in the slackwater sequences with thicker, coarser and erosive sand deposits and the spring blocking by glaciers may have promoted floods inside the cave. Therefore, the studied rhythmite can be interpreted as glacial varves decanted during the relatively cold climate conditions.

A rapid, ideal, and eco-friendlier protocol for quantifying proline.

PubMed

Shabnam, Nisha; Tripathi, Indu; Sharmila, P; Pardha-Saradhi, P

2016-11-01

Proline, a stress marker, is routinely quantified by a protocol that essentially uses hazardous toluene. Negative impacts of toluene on human health prompted us to develop a reliable alternate protocol for proline quantification. Absorbance of the proline-ninhydrin condensation product formed by reaction of proline with ninhydrin at 100 °C in the reaction mixture was significantly higher than that recorded after its transfer to toluene, revealing that toluene lowers sensitivity of this assay. λ max of the proline-ninhydrin complex in the reaction mixture and toluene were 508 and 513 nm, respectively. Ninhydrin in glacial acetic acid yielded higher quantity of the proline-ninhydrin condensation product compared to ninhydrin in mixture of glacial acetic acid and H 3 PO 4 , indicating negative impact of H 3 PO 4 on proline quantification. Further, maximum yield of the proline-ninhydrin complex with ninhydrin in glacial acetic acid and ninhydrin in mixture of glacial acetic acid and H 3 PO 4 was achieved within 30 and 60 min, respectively. This revealed that H 3 PO 4 has negative impact on the reaction rate and quantity of the proline-ninhydrin complex formed. In brief, our proline quantification protocol involves reaction of a 1-ml proline sample with 2 ml of 1.25 % ninhydrin in glacial acetic acid at 100 °C for 30 min, followed by recording absorbance of the proline-ninhydrin condensation product in the reaction mixture itself at 508 nm. Amongst proline quantification protocols known till date, our protocol is the most simple, rapid, reliable, cost-effective, and eco-friendlier.

Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Weber, M. E.; Clark, P. U.; Ricken, W.; Mitrovica, J. X.; Hostetler, S. W.; Kuhn, G.

2012-04-01

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood because only a few findings with robust chronologies exist for Antarctic ice sheets. We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates the advance to their maximum extent at 29 -28 ka, and retreat from their maximum extent at 19 ka was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. - Science, 334, 1265-1269, doi: 10.1126:science.1209299). As for the deglaciation, modeling studies suggest a late ice-sheet retreat starting around 14 ka BP and ending around 7 ka BP with a large impact of an unstable West Antarctic Ice Sheet (WAIS) and a small impact of a stable East Antarctic Ice Sheet (EAIS). However, the Weddell Sea sites studied here, as well as sites from the Scotia Sea, provide evidence that specifically the EAIS responded much earlier, possibly provided a significant contribution to the last sea-level rise, and was much more dynamic than previously thought. Using the results of an atmospheric general circulation we conclude that surface climate forcing of Antarctic ice mass balance would likely cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling. Also, changes in North Atlantic Deepwater formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.

Water resources of the Keweenaw Bay Indian Community, Baraga County, Michigan

USGS Publications Warehouse

Sweat, M.J.; Rheaume, S.J.

1998-01-01

The Keweenaw Bay Indian Community (KBIC) in Baraga County uses ground water for most domestic, commercial, and industrial supplies. An industrial park within KBIC could adversely affect some ground-water supplies should contaminants be spilled at the park. Additional development of the park is being planned. Information on water supply potential and aquifer vulnerability to contamination is needed to make sound decisions about future activities at the industrial park. Unconsolidated glacial deposits overlie bedrock within the Keweenaw Bay Indian Community. Usable amounts of ground water are withdrawn from the glacial deposits only in isolated areas. Principal aquifers are the Jacobsville Sandstone and the Michigamme Slate. Aquifer test and water level data from these principal aquifers indicate that they are confined and hydraulically connected throughout most of KBIC. Ground water generally flows toward Keweenaw and Huron Bays and the Silver River. Between the industrial park and Keweenaw Bay, ground water flows to the southeast, toward the Bay. Along this flow path in the bedrock, glacial deposits are generally thicker than 25 meters, and contain thick lenses of clay and clay mixed with sand. The average depth to ground water along this flow path is greater than 25 meters, indicating unconfined conditions. Near the shore of Keweenaw and Huron Bays, however, and at isolated areas throughout KBIC, water levels in wells are above land surface. Analyses of water samples collected in 1991 and 1997 indicate that the quality of ground water and surface water is suitable for most domestic, commercial, and industrial uses. However, U.S. Environmental Protection Agency secondary maximum contaminant limits for dissolved iron and manganese were exceeded in 4 and 5 wells, respectively, which may make the water from these wells unsuitable for some uses. Concentrations of lead in water from one well was above the maximum contaminant limit. Concentrations of tritium in ground water downgradient from the industrial park indicate that at least some recharge to the Jacobsville Sandstone has taken place within the last 45 years. Where clay lenses greater than 1 meter thick overlie the glacial aquifer or the Jacobsville Sandstone, however, recharge may take longer than 45 years. A contaminant spill at the industrial park would likely move laterally, toward Keweenaw Bay, in the glacial aquifer. Some infiltration does occur through the glacial aquifer to the bedrock aquifers. No information is available concerning the rate of movement of water within this aquifer, so it is not possible to determine the rate at which a spill would move either vertically or laterally within the glacial aquifer toward either Keweenaw Bay or the Jacobsville Sandstone. Increased pumping from the existing well at the industrial park, or the development of additional wells, could potentially lower water levels in the Jacobsville Sandstone in the area of the park. Sufficient lowering of water levels could create unconfined conditions in the Jacobsville Sandstone, thereby increasing the susceptability of the aquifer to contamination.

Short-term expansion of glacial lakes in the Himalayas

NASA Astrophysics Data System (ADS)

Nagai, H.; Tadono, T.

2017-12-01

A glacial lake outburst flood (GLOF) is a serious mountainous hazard that is related to glacial shrinkage. Despite technical developments in satellite-based lake expansion monitoring, small glacial lakes were collapsed in Bhutan in June 2015 and in Nepal in May 2017. Relatively heavy rainfall was reported downstream just before the floods. Does a large amount of short-term precipitation have a possibility of triggering a GLOF? To answer this question, the temporal change in the glacial lake area is assessed by means of satellite-based synthetic aperture radar, coupled with satellite-derived spatial and temporal distribution of precipitation to evaluate the contribution of rainfall in glacial lake expansion. The Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) observed the Mande Chu river basin in central Bhutan on Aug 11, 2016. Glacial lakes were manually delineated from the orthorectified backscatter amplitude image. They were compared with those delineated from the old satellite images of ALOS ( 2011), PALSAR-2 (2014-2016), and Landsat-8 (2016). The temporal and spatial distributions of precipitation (2010-2016) are obtained from the Global Satellite Mapping of Precipitation (GSMaP) data (10-km spatial / 60-min. temporal resolutions), calibrated by in situ rain gauges (GSMap_RNL/MVL). The outlines of 11 glacial lakes in the study site were successfully traced from 2011 to 2016; rapid expansion was recorded especially in the period between March and July 2016. In this period, exceeding 500 mm of the total amount of precipitation is recorded by GSMaP, whereas the mean precipitation amount is 300-400 mm in the previous years. This implies that relatively larger precipitation occurred in 2016, which is related to the short-term expansion of the glacial lakes. The rapid expansion of smaller lakes can be explained by their relatively shallow depths, which is sensitive to the increase in inflow water volume. This study highlights the importance of high-resolution, frequent observation of small glacial lakes that can expand, possibly corresponding to heavy rainfall, whereas most previous studies focused on large glacial lakes expanding at annual scales. Extreme precipitation should be considered as one of the factors responsible for glacial lake expansion as well as glacier melt.

A Sulfur-based Glacial Ecosystem as a Model for the Habitability of Europa and Mars

NASA Astrophysics Data System (ADS)

Wright, K. E.; Gleeson, D. F.; Williamson, C.; Grasby, S. E.; Spear, J.; Pappalardo, R. T.; Templeton, A. S.

2010-04-01

Identifying the sulfur redox reactions and dominant microbial organisms in a sulfur-based glacial microbial ecosystem provides insights into the type of metabolisms that might exist on other planetary bodies, and the biosignatures they may present.

Geographic and temporal dynamics of a global radiation and diversification in the killer whale.

PubMed

Morin, Phillip A; Parsons, Kim M; Archer, Frederick I; Ávila-Arcos, María C; Barrett-Lennard, Lance G; Dalla Rosa, Luciano; Duchêne, Sebastián; Durban, John W; Ellis, Graeme M; Ferguson, Steven H; Ford, John K; Ford, Michael J; Garilao, Cristina; Gilbert, M Thomas P; Kaschner, Kristin; Matkin, Craig O; Petersen, Stephen D; Robertson, Kelly M; Visser, Ingrid N; Wade, Paul R; Ho, Simon Y W; Foote, Andrew D

2015-08-01

Global climate change during the Late Pleistocene periodically encroached and then released habitat during the glacial cycles, causing range expansions and contractions in some species. These dynamics have played a major role in geographic radiations, diversification and speciation. We investigate these dynamics in the most widely distributed of marine mammals, the killer whale (Orcinus orca), using a global data set of over 450 samples. This marine top predator inhabits coastal and pelagic ecosystems ranging from the ice edge to the tropics, often exhibiting ecological, behavioural and morphological variation suggestive of local adaptation accompanied by reproductive isolation. Results suggest a rapid global radiation occurred over the last 350 000 years. Based on habitat models, we estimated there was only a 15% global contraction of core suitable habitat during the last glacial maximum, and the resources appeared to sustain a constant global effective female population size throughout the Late Pleistocene. Reconstruction of the ancestral phylogeography highlighted the high mobility of this species, identifying 22 strongly supported long-range dispersal events including interoceanic and interhemispheric movement. Despite this propensity for geographic dispersal, the increased sampling of this study uncovered very few potential examples of ancestral dispersal among ecotypes. Concordance of nuclear and mitochondrial data further confirms genetic cohesiveness, with little or no current gene flow among sympatric ecotypes. Taken as a whole, our data suggest that the glacial cycles influenced local populations in different ways, with no clear global pattern, but with secondary contact among lineages following long-range dispersal as a potential mechanism driving ecological diversification. © 2015 John Wiley & Sons Ltd.

Good News for Borehole Climatology

NASA Astrophysics Data System (ADS)

Rath, Volker; Fidel Gonzalez-Rouco, J.; Goosse, Hugues

2010-05-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature profiles. It influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climate, but implies that the geological heat flow values have to be interpreted accordingly. Borehole climate reconstructions from these shallow are most probably underestimating past variability due to the diffusive character of the heat conduction process, and the smoothness constraints necessary for obtaining stable solutions of this ill-posed inverse problem. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, also with deeper boreholes, where the heat flow signal can not be approximated linearly, and improves the comparisons with AOGCM modeling results.

Terrestrial biosphere changes over the last 120 kyr and their impact on ocean δ 13C

NASA Astrophysics Data System (ADS)

Hoogakker, B. A. A.; Smith, R. S.; Singarayer, J. S.; Marchant, R.; Prentice, I. C.; Allen, J. R. M.; Anderson, R. S.; Bhagwat, S. A.; Behling, H.; Borisova, O.; Bush, M.; Correa-Metrio, A.; de Vernal, A.; Finch, J. M.; Fréchette, B.; Lozano-Garcia, S.; Gosling, W. D.; Granoszewski, W.; Grimm, E. C.; Grüger, E.; Hanselman, J.; Harrison, S. P.; Hill, T. R.; Huntley, B.; Jiménez-Moreno, G.; Kershaw, P.; Ledru, M.-P.; Magri, D.; McKenzie, M.; Müller, U.; Nakagawa, T.; Novenko, E.; Penny, D.; Sadori, L.; Scott, L.; Stevenson, J.; Valdes, P. J.; Vandergoes, M.; Velichko, A.; Whitlock, C.; Tzedakis, C.

2015-03-01

A new global synthesis and biomization of long (>40 kyr) pollen-data records is presented, and used with simulations from the HadCM3 and FAMOUS climate models to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial-interglacial cycle. Global modelled (BIOME4) biome distributions over time generally agree well with those inferred from pollen data. The two climate models show good agreement in global net primary productivity (NPP). NPP is strongly influenced by atmospheric carbon dioxide (CO2) concentrations through CO2 fertilization. The combined effects of modelled changes in vegetation and (via a simple model) soil carbon result in a global terrestrial carbon storage at the Last Glacial Maximum that is 210-470 Pg C less than in pre-industrial time. Without the contribution from exposed glacial continental shelves the reduction would be larger, 330-960 Pg C. Other intervals of low terrestrial carbon storage include stadial intervals at 108 and 85 ka BP, and between 60 and 65 ka BP during Marine Isotope Stage 4. Terrestrial carbon storage, determined by the balance of global NPP and decomposition, influences the stable carbon isotope composition (δ13C) of seawater because terrestrial organic carbon is depleted in 13C. Using a simple carbon-isotope mass balance equation we find agreement in trends between modelled ocean δ13C based on modelled land carbon storage, and palaeo-archives of ocean δ13C, confirming that terrestrial carbon storage variations may be important drivers of ocean δ13C changes.

Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles

NASA Astrophysics Data System (ADS)

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

2008-12-01

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

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean

USGS Publications Warehouse

Polyak, L.; Bischof, J.; Ortiz, J.D.; Darby, D.A.; Channell, J.E.T.; Xuan, C.; Kaufman, D.S.; Lovlie, R.; Schneider, D.A.; Eberl, D.D.; Adler, R.E.; Council, E.A.

2009-01-01

Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX and some earlier expeditions have been analyzed to develop a stratigraphic correlation from the Alaskan Chukchi margin to the Northwind and Mendeleev-Alpha ridges. The correlation was primarily based on terrigenous sediment composition that is not affected by diagenetic processes as strongly as the biogenic component, and paleomagnetic inclination records. Chronostratigraphic control was provided by 14C dating and amino-acid racemization ages, as well as correlation to earlier established Arctic Ocean stratigraphies. Distribution of sedimentary units across the western Arctic indicates that sedimentation rates decrease from tens of centimeters per kyr on the Alaskan margin to a few centimeters on the southern ends of Northwind and Mendeleev ridges and just a few millimeters on the ridges in the interior of the Amerasia basin. This sedimentation pattern suggests that Late Quaternary sediment transport and deposition, except for turbidites at the basin bottom, were generally controlled by ice concentration (and thus melt-out rate) and transportation distance from sources, with local variances related to subsurface currents. In the long term, most sediment was probably delivered to the core sites by icebergs during glacial periods, with a significant contribution from sea ice. During glacial maxima very fine-grained sediment was deposited with sedimentation rates greatly reduced away from the margins to a hiatus of several kyr duration as shown for the Last Glacial Maximum. This sedimentary environment was possibly related to a very solid ice cover and reduced melt-out over a large part of the western Arctic Ocean.

Long-Term Vegetation Dynamics in a Megadiverse Hotspot: The Ice-Age Record of a Pre-montane Forest of Central Ecuador

PubMed Central

Montoya, Encarni; Keen, Hayley F.; Luzuriaga, Carmen X.; Gosling, William D.

2018-01-01

Tropical ecosystems play a key role in many aspects of Earth system dynamics currently of global concern, including carbon sequestration and biodiversity. To accurately understand complex tropical systems it is necessary to parameterise key ecological aspects, such as rates of change (RoC), species turnover, dynamism, resilience, or stability. To obtain a long-term (>50 years) perspective on these ecological aspects we must turn to the fossil record. However, compared to temperate zones, collecting continuous sedimentary archives in the lowland tropics is often difficult due to the active landscape processes, with potentially frequent volcanic, tectonic, and/or fluvial events confounding sediment deposition, preservation, and recovery. Consequently, the nature, and drivers, of vegetation dynamics during the last glacial are barely known from many non-montane tropical landscapes. One of the first lowland Amazonian locations from which palaeoecological data were obtained was an outcrop near Mera (Ecuador). Mera was discovered, and analysed, by Paul Colinvaux in the 1980s, but his interpretation of the data as indicative of a forested glacial period were criticised based on the ecology and age control. Here we present new palaeoecological data from a lake located less than 10 km away from Mera. Sediment cores raised from Laguna Pindo (1250 masl; 1°27′S, 78°05′W) have been shown to span the late last glacial period [50–13 cal kyr BP (calibrated kiloyears before present)]. The palaeoecological information obtained from Laguna Pindo indicate that the region was characterised by a relatively stable plant community, formed by taxa nowadays common at both mid and high elevations. Miconia was the dominant taxon until around 30 cal kyr BP, when it was replaced by Hedyosmum, Asteraceae and Ilex among other taxa. Heat intolerant taxa including Podocarpus, Alnus, and Myrica peaked around the onset of the Last Glacial Maximum (c. 21 cal kyr BP). The results obtained from Laguna Pindo support Colinvaux’s hypothesis that glacial cooling resulted in a reshuffling of taxa in the region but did not lead to a loss of the forest structure. Wide tolerances of the plant species occurring to glacial temperature range and cloud formation have been suggested to explain Pindo forest stability. This scenario is radically different than the present situation, so vulnerability of the tropical pre-montane forest is highlighted to be increased in the next decades. PMID:29515609

Quantifying Regional Vegetation Changes in China During Three Contrasting Warming Intervals since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Li, Q.; Wu, H.; Yu, Y.; Sun, A.; Luo, Y.

2017-12-01

Reconstructing patterns of past vegetation change on a large-scale facilitates a better understanding of the interactions and feedbacks between climate change and the terrestrial biosphere. In addition, reducing the uncertainty in predictions of vegetation change under global warming highlights the importance of reconstructing vegetation patterns during past warming intervals. Here, we present a quantitative regional vegetation reconstruction for China during three intervals: Last Glacial Maximum (LGM, 18±2 14C kyr B.P.), early Holocene (8.5±0.5 14C kyr B.P.), and mid-Holocene (6±0.5 14C kyr B.P.). The biomization method, based on 249 pollen records, was used for the reconstructions. The results demonstrate that during the LGM, steppe and desert expanded eastwards and southwards, reaching the present-day temperate deciduous forest (TEDE) zone, and dominated northern China. In contrast, the forest in Eastern China underwent a substantial southwards retreat and the percentage of forest-type sites was at a minimum. In addition, the warm mixed forest (WAMF) and TEDE shifted southwards of 10° N relative to the present-day, and tropical seasonal rain forest (TSFO) was almost absent. At the same time, the forest-steppe boundary shifted southwards to near the middle and lower reaches of Yangtze River. For the early Holocene and mid-Holocene, the TSFO, WAMF, and TEDE shifted northwards by 2-5° relative to today, and the percentage of forest sites increased and reached a maximum in the mid-Holocene. The slight expansion of forest from the early Holocene to the mid-Holocene caused the forest-steppe boundary to shift northwestwards to near the present-day 300 mm isohyet by the mid-Holocene. Our results also indicate that climatic warming since the LGM, which strengthened the East Asian summer monsoon, favored the development of forest in China. This is potentially an important finding for evaluating the possible response of forest in China to future global warming.

Linking microbial assemblages to paleoenvironmental conditions from the Holocene and Last Glacial Maximum times in Laguna Potrok Aike sediments, Argentina

NASA Astrophysics Data System (ADS)

Vuillemin, Aurele; Ariztegui, Daniel; Leavitt, Peter R.; Bunting, Lynda

2014-05-01

Laguna Potrok Aike is a closed basin located in the southern hemisphere's mid-latitudes (52°S) where paleoenvironmental conditions were recorded as temporal sedimentary sequences resulting from variations in the regional hydrological regime and geology of the catchment. The interpretation of the limnogeological multiproxy record developed during the ICDP-PASADO project allowed the identification of contrasting time windows associated with the fluctuations of Southern Westerly Winds. In the framework of this project, a 100-m-long core was also dedicated to a detailed geomicrobiological study which aimed at a thorough investigation of the lacustrine subsurface biosphere. Indeed, aquatic sediments do not only record past climatic conditions, but also provide a wide range of ecological niches for microbes. In this context, the influence of environmental features upon microbial development and survival remained still unexplored for the deep lacustrine realm. Therefore, we investigated living microbes throughout the sedimentary sequence using in situ ATP assays and DAPI cell count. These results, compiled with pore water analysis, SEM microscopy of authigenic concretions and methane and fatty acid biogeochemistry, provided evidence for a sustained microbial activity in deep sediments and pinpointed the substantial role of microbial processes in modifying initial organic and mineral fractions. Finally, because the genetic material associated with microorganisms can be preserved in sediments over millennia, we extracted environmental DNA from Laguna Potrok Aike sediments and established 16S rRNA bacterial and archaeal clone libraries to better define the use of DNA-based techniques in reconstructing past environments. We focused on two sedimentary horizons both displaying in situ microbial activity, respectively corresponding to the Holocene and Last Glacial Maximum periods. Sequences recovered from the productive Holocene record revealed a microbial community adapted to subsaline conditions producing methane with a high potential of organic matter degradation. In contrast, sediments rich in volcanic detritus from the Last Glacial Maximum showed a substantial presence of lithotrophic microorganisms and sulphate-reducing bacteria mediating authigenic minerals. Together, these features suggested that microbial communities developed in response to climatic control of lake and catchment productivity at the time of sediment deposition. Prevailing climatic conditions exerted a hierarchical control on the microbial composition of lake sediments by regulating the influx of organic and inorganic material to the lake basin, which in turn determined water column chemistry, production and sedimentation of particulate material, resulting in the different niches sheltering these microbial assemblages. Moreover, it demonstrated that environmental DNA can constitute sedimentary archives of phylogenetic diversity and diagenetic processes over tens of millennia.

Gridded climate data from 5 GCMs of the Last Glacial Maximum downscaled to 30 arc s for Europe

NASA Astrophysics Data System (ADS)

Schmatz, D. R.; Luterbacher, J.; Zimmermann, N. E.; Pearman, P. B.

2015-06-01

Studies of the impacts of historical, current and future global change require very high-resolution climate data (≤ 1 km) as a basis for modelled responses, meaning that data from digital climate models generally require substantial rescaling. Another shortcoming of available datasets on past climate is that the effects of sea level rise and fall are not considered. Without such information, the study of glacial refugia or early Holocene plant and animal migration are incomplete if not impossible. Sea level at the last glacial maximum (LGM) was approximately 125 m lower, creating substantial additional terrestrial area for which no current baseline data exist. Here, we introduce the development of a novel, gridded climate dataset for LGM that is both very high resolution (1 km) and extends to the LGM sea and land mask. We developed two methods to extend current terrestrial precipitation and temperature data to areas between the current and LGM coastlines. The absolute interpolation error is less than 1 and 0.5 °C for 98.9 and 87.8 %, respectively, of all pixels within two arc degrees of the current coastline. We use the change factor method with these newly assembled baseline data to downscale five global circulation models of LGM climate to a resolution of 1 km for Europe. As additional variables we calculate 19 "bioclimatic" variables, which are often used in climate change impact studies on biological diversity. The new LGM climate maps are well suited for analysing refugia and migration during Holocene warming following the LGM.

Radiocarbon constraints on the extent and evolution of the South Pacific glacial carbon pool

PubMed Central

Ronge, T. A.; Tiedemann, R.; Lamy, F.; Köhler, P.; Alloway, B. V.; De Pol-Holz, R.; Pahnke, K.; Southon, J.; Wacker, L.

2016-01-01

During the last deglaciation, the opposing patterns of atmospheric CO2 and radiocarbon activities (Δ14C) suggest the release of 14C-depleted CO2 from old carbon reservoirs. Although evidences point to the deep Pacific as a major reservoir of this 14C-depleted carbon, its extent and evolution still need to be constrained. Here we use sediment cores retrieved along a South Pacific transect to reconstruct the spatio-temporal evolution of Δ14C over the last 30,000 years. In ∼2,500–3,600 m water depth, we find 14C-depleted deep waters with a maximum glacial offset to atmospheric 14C (ΔΔ14C=−1,000‰). Using a box model, we test the hypothesis that these low values might have been caused by an interaction of aging and hydrothermal CO2 influx. We observe a rejuvenation of circumpolar deep waters synchronous and potentially contributing to the initial deglacial rise in atmospheric CO2. These findings constrain parts of the glacial carbon pool to the deep South Pacific. PMID:27157845

231Pa/230Th evidence for a weakened but persistent Atlantic meridional overturning circulation during Heinrich Stadial 1.

PubMed

Bradtmiller, Louisa I; McManus, Jerry F; Robinson, Laura F

2014-12-18

The strength of Atlantic meridional overturning circulation is believed to affect the climate over glacial-interglacial and millennial timescales. The marine sedimentary (231)Pa/(230)Th ratio is a promising paleocirculation proxy, but local particle effects may bias individual reconstructions. Here we present new Atlantic sedimentary (231)Pa/(230)Th data from the Holocene, the last glacial maximum and Heinrich Stadial 1, a period of abrupt cooling ca. 17,500 years ago. We combine our results with published data from these intervals to create a spatially distributed sedimentary (231)Pa/(230)Th database. The data reveal a net (231)Pa deficit during each period, consistent with persistent (231)Pa export. In highly resolved cores, Heinrich (231)Pa/(230)Th ratios exceed glacial ratios at nearly all depths, indicating a significant reduction, although not cessation, of overturning during Heinrich Stadial 1. These results support the inference that weakened overturning was a driver of Heinrich cooling, while suggesting that abrupt climate oscillations do not necessarily require a complete shutdown of overturning.

Responses of high-elevation herbaceous plant assemblages to low glacial CO₂ concentrations revealed by fossil marmot (Marmota) teeth.

PubMed

McLean, Bryan S; Ward, Joy K; Polito, Michael J; Emslie, Steven D

2014-08-01

Atmospheric CO2 cycles of the Quaternary likely imposed major constraints on the physiology and growth of C3 plants worldwide. However, the measured record of this remains both geographically and taxonomically sparse. We present the first reconstruction of physiological responses in a late Quaternary high-elevation herbaceous plant community from the Southern Rocky Mountains, USA. We used a novel proxy-fossilized tooth enamel of yellow-bellied marmots (Marmota flaviventris)-which we developed using detailed isotopic analysis of modern individuals. Calculated C isotopic discrimination (Δ) of alpine plants was nearly 2 ‰ lower prior to the Last Glacial Maximum than at present, a response almost identical to that of nonherbaceous taxa from lower elevations. However, initial shifts in Δ aligned most closely with the onset of the late Pleistocene bipolar temperature "seesaw" rather than CO2 increase, indicating unique limitations on glacial-age high-elevation plants may have existed due to both low temperatures and low CO2. Further development of system-specific faunal proxies can help to clarify this and other plant- and ecosystem-level responses to past environmental change.

Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group

NASA Astrophysics Data System (ADS)

Turney, C. S. M.; Haberle, S.; Fink, D.; Kershaw, A. P.; Barbetti, M.; Barrows, T. T.; Black, M.; Cohen, T. J.; Corrège, T.; Hesse, P. P.; Hua, Q.; Johnston, R.; Morgan, V.; Moss, P.; Nanson, G.; van Ommen, T.; Rule, S.; Williams, N. J.; Zhao, J.-X.; D'Costa, D.; Feng, Y.-X.; Gagan, M.; Mooney, S.; Xia, Q.

2006-10-01

The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric teleconnection and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. Copyright

In Review (Geology): Alpine Landscape Evolution Dominated by Cirque Retreat

NASA Technical Reports Server (NTRS)

Oskin, Michael; Burbank, Doug

2005-01-01

Despite the abundance in alpine terrain of glacially dissected landscapes, the magnitude and geometry of glacial erosion can rarely be defined. In the eastern Kyrgyz Range, a widespread unconformity exhumed as a geomorphic surface provides a regional datum with which to calibrate erosion. As tectonically driven surface uplift has progressively pushed this surface into the zone of ice accumulation, glacial erosion has overprinted the landscape. With as little as 500 m of incision into rocks underlying the unconformity, distinctive glacial valleys display their deepest incision adjacent to cirque headwalls. The expansion of north-facing glacial cirques at the expense of south-facing valleys has driven the drainage divide southwards at rates up to 2 to 3 times the rate of valley incision. Existing ice-flux-based glacial erosion rules incompletely model expansion of glacial valleys via cirque retreat into the low-gradient unconformity remnants. Local processes that either directly sap cirque headwalls or inhibit erosion down-glacier appear to control, at least initially, alpine landscape evolution.

Polyploidisation and Geographic Differentiation Drive Diversification in a European High Mountain Plant Group (Doronicum clusii Aggregate, Asteraceae)

PubMed Central

Pachschwöll, Clemens; Escobar García, Pedro; Winkler, Manuela; Schneeweiss, Gerald M.; Schönswetter, Peter

2015-01-01

Range shifts (especially during the Pleistocene), polyploidisation and hybridization are major factors affecting high-mountain biodiversity. A good system to study their role in the European high mountains is the Doronicum clusii aggregate (Asteraceae), whose four taxa (D. clusii s.s., D. stiriacum, D. glaciale subsp. glaciale and D. glaciale subsp. calcareum) are differentiated geographically, ecologically (basiphilous versus silicicolous) and/or via their ploidy levels (diploid versus tetraploid). Here, we use DNA sequences (three plastid and one nuclear spacer) and AFLP fingerprinting data generated for 58 populations to infer phylogenetic relationships, origin of polyploids—whose ploidy level was confirmed by chromosomally calibrated DNA ploidy level estimates—and phylogeographic history. Taxonomic conclusions were informed, among others, by a Gaussian clustering method for species delimitation using dominant multilocus data. Based on molecular data we identified three lineages: (i) silicicolous diploid D. clusii s.s. in the Alps, (ii) silicicolous tetraploid D. stiriacum in the eastern Alps (outside the range of D. clusii s.s.) and the Carpathians and (iii) the basiphilous diploids D. glaciale subsp. glaciale (eastern Alps) and D. glaciale subsp. calcareum (northeastern Alps); each taxon was identified as distinct by the Gaussian clustering, but the separation of D. glaciale subsp. calcareum and D. glaciale subsp. glaciale was not stable, supporting their taxonomic treatment as subspecies. Carpathian and Alpine populations of D. stiriacum were genetically differentiated suggesting phases of vicariance, probably during the Pleistocene. The origin (autopolyploid versus allopolyploid) of D. stiriacum remained unclear. Doronicum glaciale subsp. calcareum was genetically and morphologically weakly separated from D. glaciale subsp. glaciale but exhibited significantly higher genetic diversity and rarity. This suggests that the more widespread D. glaciale subsp. glaciale originated from D. glaciale subsp. calcareum, which is restricted to a prominent Pleistocene refugium previously identified in other alpine plant species. PMID:25749621

The role of geophysical modeling of glacio-isostasy in paleohydrological reconstructions of the glacial Great Lakes

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

Clark, J.A.; Ehlers, T.A.

The volume and chronology of late-glacial and postglacial lakes of the Great Lakes region were controlled by the elevation of their outlets which moved vertically relative to the geoid because of glacial isostasy. The shorelines of these lakes and their drainages are now tilted and deformed so that correlation of these discontinuous features usually requires an estimate of the amount of vertical movement throughout the region. The authors approach is to use a computer model of a spherical viscoelastic and self-gravitating earth to simulate earth deformation as the Laurentide ice sheet advanced into its glacial maximum and subsequently retreated. Becausemore » neither the earth's viscosity structure nor the ice sheet thickness are well known, they have used a range of likely ice/earth models each resulting in predicted shoreline deformation that can be compared directly to observations. Results indicate that many of the shorelines as well as present rates of tilt determined from lake-level gauges can be understood through the modeling. The chronology of the various lakes is also explained through predictions of the time-dependent changes in the elevation of the various outlets relative to each other. In contrast to common interpretations none of their results indicate that the southern part of the Great Lakes region is now or ever has been geodynamically stable''.« less