scholarly journals Siliceous subglacial deposits: archives of subglacial processes during the Last Glacial Maximum

2021 ◽  
pp. 1-8
Author(s):  
Shalev Siman-Tov ◽  
Terrence Blackburn ◽  
Bernard Hallet ◽  
Matthew A. Coble ◽  
Emily E. Brodsky
Keyword(s):  
Isotopic Analysis ◽  
Rock Fragment ◽  
Isotopic Data ◽  
Geologic Time ◽  
Rock Interface ◽  
The Last Glacial Maximum ◽  
Siliceous Deposit ◽  
Detailed Chemical ◽  
The Last Glacial

Abstract We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single, <1 μm, Si-rich layer covers the highly polished bedrock on the up-glacier (stoss) surfaces, distinct, lithified deposits commonly occur at the lee of small bedrock protuberances, on a scale <0.1 meter. The deposit is millimeters in thickness and consists of laminae tens to hundreds microns thick that differ from one another in color, rock-fragment abundance and chemical composition. Ca-rich laminae that are sufficiently enriched in uranium (~2–50 ppm) to permit U-series isotopic analysis suggest that the subglacial deposit formed 10–20 ka, much earlier than previously assumed. We conclude that (1) the siliceous deposit persisted for at least 10 000 years despite the intervening erosion and weathering, (2) distinct episodes of formation due to significant changes in hydrology and water chemistry are recorded in the deposit, and (3) a siliceous slurry may have existed at the ice-rock interface and influenced the local friction. This work reinforces earlier findings that subglacial chemical deposits can form and persist on geologic time scales and may have implications for the role of the cryosphere in the Earth's geochemical cycles and climate system.

Evolution of Scaphinotus petersi (Coleoptera: Carabidae) and the role of climate and geography in the Madrean sky islands of southeastern Arizona, USA

2013 ◽  
Vol 79 (2) ◽  
pp. 274-283 ◽  
Author(s):  
Sara Gran Mitchell ◽  
Karen A. Ober
Keyword(s):  
Population Genetic ◽  
Regional Climate ◽  
Sky Islands ◽  
Conifer Forests ◽  
Mountain Ranges ◽  
Genetic Patterns ◽  
Madrean Sky Islands ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractGeographically isolated environments such as the conifer forests atop the Madrean “sky islands” in southeastern Arizona provide natural laboratories for studying factors involved in speciation and origins of biodiversity. Using molecular and geospatial analyses, we examine beetle population phylogeny, regional climate records, and the Quaternary paleobiogeography of forests to evaluate four hypothetical scenarios regarding the current geographic and population genetic patterns of Scaphinotus petersi. Scaphinotus petersi is a large, flightless beetle that resides in the Madrean conifer forests above ~ 1900 m asl. Our results do not support the current hypothesis that S. petersi populations found on seven separate mountain ranges are genetically distinct and separated as temperatures warmed after the Last Glacial Maximum (LGM). Rather, we show that only some of the ranges hold genetically distinct populations, and the timing of separation among the populations does not appear to coincide with specific climatic events such as warming trends. In addition, we show that predicted changes to the climate of the Madrean sky islands may result in the disappearance of S. petersi from some of the lower ranges by the end of this century.

Spatial distribution of birds and terrestrial plants in Bunger Hills

2020 ◽  
Vol 32 (2) ◽  
pp. 153-166
Author(s):  
Michelle R. Leishman ◽  
John A.E. Gibson ◽  
Damian B. Gore
Keyword(s):  
Central Area ◽  
Bird Species ◽  
Terrestrial Plants ◽  
Environmental Controls ◽  
Catharacta Maccormicki ◽  
Abundance And Diversity ◽  
The Last Glacial Maximum ◽  
South Polar ◽  
The Last Glacial

AbstractIn this paper, we synthesize recorded observations of moss, lichen and bird species in Bunger Hills, East Antarctica, and assess the role of environmental controls, including sediment, salinity, moisture and geology, on species' distributions. The distribution of snow petrels (Pagodroma nivea) appears to be associated with geology; they nest by preference in crevices in bedrock outcrops around the margins of the hills or wherever jointed cliffs are found. South polar skuas (Catharacta maccormicki) are seen throughout Bunger Hills, where they nest and prey on snow petrels. Mosses and lichens were most abundant around the ice margins where fresh snow and ice meltwater are abundant. In the central area of Bunger Hills, where the highest salt concentration in sediments is found and exposure to abrasion by wind-driven mineral sand grains and ice particles is greatest, mosses and lichens are reduced in abundance and diversity. Exposure of parts of Bunger Hills from the ice sheet throughout the Last Glacial Maximum, c. 20 ka bp, means that some land and lakes could have acted as regional refugia and as a locus of recolonization of other ice-free areas.

scholarly journals Individual and combined effects of ice sheets and precession on MIS-13 climate

2009 ◽  
Vol 5 (2) ◽  
pp. 229-243 ◽  
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
M. Crucifix
Keyword(s):  
Global Climate ◽  
Wave Train ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Summer Precipitation ◽  
East China ◽  
Thermal Contrast ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. An Earth System Model of Intermediate Complexity is used to investigate the role of insolation and of the size of ice sheets on the regional and global climate of marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when northern hemisphere (NH) summer occurs at perihelion (at 506 ka (1 ka=1000 years) BP), and the other when it occurs at aphelion (at 495 ka BP). Five different volumes of the Eurasian ice sheet (EA) and North American ice sheet (NA), ranging from 0 to the Last Glacial Maximum (LGM) one, are used. The global cooling due to the ice sheets is mainly related to their area, little to their height. The regional cooling and warming anomalies caused by the ice sheets intensify with increasing size. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa and India, precipitation decreases with increasing ice sheet size due to the southward shift of the Intertropical Convergence Zone (ITCZ), whatever the astronomical configuration is. However, the situation is more complicated over East Asia. The ice sheets play a role through both reducing the land/ocean thermal contrast and generating a wave train which is topographically induced by the EA ice sheet. This wave train contributes to amplify the Asian land/ocean pressure gradient in summer and finally reinforces the precipitation. The presence of this wave train depends on the combined effect of the ice sheet size and insolation. When NH summer occurs at perihelion, the EA is able to induce this wave train whatever its size is, and this wave train plays a more important role than the reduction of the land/ocean thermal contrast. Therefore, the ice sheets reinforce the summer precipitation over East China whatever their sizes are. However, when NH summer occurs at aphelion, there is a threshold in the ice volume beyond which the wave train is not induced anymore. Therefore, below this threshold, the wave train effect is dominant and the ice sheets reinforce precipitation over East China. Beyond this threshold, the ice sheets reduce the precipitation mainly through reducing the land/ocean thermal contrast.

scholarly journals A new perspective on permafrost boundaries in France during the Last Glacial Maximum

2021 ◽  
Vol 17 (6) ◽  
pp. 2559-2576
Author(s):  
Kim H. Stadelmaier ◽  
Patrick Ludwig ◽  
Pascal Bertran ◽  
Pierre Antoine ◽  
Xiaoxu Shi ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Last Glacial Maximum ◽  
Climate Model ◽  
Regional Climate ◽  
Thermal Contraction ◽  
Model Data ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. During the Last Glacial Maximum (LGM), a very cold and dry period around 26.5–19 kyr BP, permafrost was widespread across Europe. In this work, we explore the possible benefit of using regional climate model data to improve the permafrost representation in France, decipher how the atmospheric circulation affects the permafrost boundaries in the models, and test the role of ground thermal contraction cracking in wedge development during the LGM. With these aims, criteria for possible thermal contraction cracking of the ground are applied to climate model data for the first time. Our results show that the permafrost extent and ground cracking regions deviate from proxy evidence when the simulated large-scale circulation in both global and regional climate models favours prevailing westerly winds. A colder and, with regard to proxy data, more realistic version of the LGM climate is achieved given more frequent easterly winds conditions. Given the appropriate forcing, an added value of the regional climate model simulation can be achieved in representing permafrost and ground thermal contraction cracking. Furthermore, the model data provide evidence that thermal contraction cracking occurred in Europe during the LGM in a wide latitudinal band south of the probable permafrost border, in agreement with field data analysis. This enables the reconsideration of the role of sand-wedge casts to identify past permafrost regions.

The role of dust in climate changes today, at the last glacial maximum and in the future

2001 ◽  
Vol 54 (1-3) ◽  
pp. 43-80 ◽  
Author(s):  
Sandy P. Harrison ◽  
Karen E. Kohfeld ◽  
Caroline Roelandt ◽  
Tanguy Claquin
Keyword(s):  
Last Glacial Maximum ◽  
Climate Changes ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Future ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals The role of basal hydrology in the surging of the Laurentide Ice Sheet

2016 ◽  
Vol 12 (8) ◽  
pp. 1601-1617 ◽  
Author(s):  
William H. G. Roberts ◽  
Antony J. Payne ◽  
Paul J. Valdes
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Water Drainage ◽  
Heinrich Events ◽  
Sensitivity Tests ◽  
Wide Range ◽  
Switch Mechanism ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use the Glimmer ice sheet model to simulate periodic surges over the Laurentide Ice Sheet during the Last Glacial Maximum. In contrast to previous studies we use the depth of water at the base of the ice sheet as the switch for these surges. We find that the surges are supported within the model and are quite robust across a very wide range of parameter choices, in contrast to many previous studies where surges only occur for rather specific cases. The robustness of the surges is likely due to the use of water as the switch mechanism for sliding. The statistics of the binge–purge cycles resemble observed Heinrich events. The events have a period of between 10 and 15 thousand years and can produce fluxes of ice from the mouth of Hudson Strait of 0.05 Sv – a maximum flux of 0.06 Sv is possible. The events produce an ice volume of 2.50  ×  106 km3, with a range of 4.30  ×  106–1.90  ×  106 km3 possible. We undertake a suite of sensitivity tests varying the sliding parameter, the water drainage scheme, the sliding versus water depth parameterisation and the resolution, all of which support the ice sheet surges. This suggests that internally triggered ice sheet surges were a robust feature of the Laurentide Ice Sheet and are a possible explanation for the observed Heinrich events.

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