720 results on '"Larter, Robert"'
Search Results
152. The periodic topography of ice stream beds: insights from the Fourier spectra of mega-scale glacial lineations
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Spagnolo, Matteo, Bartholomaus, Timothy C., Clark, Chris D., Stokes, Chris R., Atkinson, Nigel, Dowdeswell, Julian A., Ely, Jeremy C., Graham, Alistair G.C., Hogan, Kelly A., King, Edward C., Larter, Robert D., Livingstone, Stephen J., Pritchard, Hamish D., Spagnolo, Matteo, Bartholomaus, Timothy C., Clark, Chris D., Stokes, Chris R., Atkinson, Nigel, Dowdeswell, Julian A., Ely, Jeremy C., Graham, Alistair G.C., Hogan, Kelly A., King, Edward C., Larter, Robert D., Livingstone, Stephen J., and Pritchard, Hamish D.
- Abstract
Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two–dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega-scale glacial lineations (MSGLs). We find that the topography of MSGL-rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7±0.52% km-1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies, but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.
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- 2017
153. First deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf: experiences from the MARUM-MeBo70 on Polarstern-Expedition PS104
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Freudenthal, Tim, Gohl, Karsten, Klages, Johann Philipp, Hillenbrand, C.-D., Bickert, Torsten, Bohaty, Steve, Ehrmann, Werner, Esper, Oliver, Frederichs, Thomas, Gebhardt, Catalina, Kuhn, Gerhard, Larter, Robert D., Pälike, Heiko, Ronge, Thomas, Simoes Pereira, Patric, Smith, James A., Uenzelmann-Neben, Gabriele, van de Flierdt, Tina, Freudenthal, Tim, Gohl, Karsten, Klages, Johann Philipp, Hillenbrand, C.-D., Bickert, Torsten, Bohaty, Steve, Ehrmann, Werner, Esper, Oliver, Frederichs, Thomas, Gebhardt, Catalina, Kuhn, Gerhard, Larter, Robert D., Pälike, Heiko, Ronge, Thomas, Simoes Pereira, Patric, Smith, James A., Uenzelmann-Neben, Gabriele, and van de Flierdt, Tina
- Abstract
The MARUM-MeBo (abbreviation for Meeresboden-Bohrgerät, the German expression for seafloor drill rig) is a robotic drilling system that is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen in close cooperation with Bauer Maschinen GmbH and other industry partners. The MARUM-MeBo drill rigs can be deployed from multipurpose research vessel like, RV MARIA S. MERIAN, RV METEOR, RV SONNE and RV POLARSTERN and are used for getting long cores both in soft sediments as well as hard rocks in the deep sea. The first generation drill rig, the MARUM-MeBo70 is dedicated for drilling depths of more than 70 m (Freudenthal and Wefer, 2013). Between 2005 and 2017 it was deployed on 18 research expeditions and drilled more than. 3 km into different types of lithologies including carbonate and crystalline rocks, gas hydrates, sands and gravel, glacial till and hemipelagic mud with an average recovery rate of 67 %. In February and March 2017 the MeBo70 was used on the West Antarctic continental shelf in the Amundsen Sea Embayment for the first time. The goal of the deployment on RV Polarstern expedition PS104 was to recover a series of sediment cores from different ages that will provide material for investigating the glaciation history of this area known as the most dynamic drainage area of the West Antarctic Ice Sheet. In this presentation we will focus on the operational experiences of this first deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf. References: Freudenthal, T and Wefer, G (2013) Drilling cores on the sea floor with the remote-controlled sea floor drilling rig MeBo. Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-2013
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- 2017
154. MeBo70 seabed drilling on a polar continental shelf: operational report and lessons from drilling in the Amundsen Sea Embayment of West Antarctica
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Gohl, Karsten, Freudenthal, Tim, Hillenbrand, Claus-Dieter, Klages, Johann Philipp, Larter, Robert D., Bickert, Thorsten, Bohaty, Steve, Ehrmann, Werner, Esper, Oliver, Frederichs, Thomas, Gebhardt, Catalina, Küssner, Kevin, Kuhn, Gerhard, Pälike, Heiko, Ronge, Thomas, Simoes Pereira, Patric, Smith, James A., Uenzelmann-Neben, Gabriele, van der Flierdt, Christina, Gohl, Karsten, Freudenthal, Tim, Hillenbrand, Claus-Dieter, Klages, Johann Philipp, Larter, Robert D., Bickert, Thorsten, Bohaty, Steve, Ehrmann, Werner, Esper, Oliver, Frederichs, Thomas, Gebhardt, Catalina, Küssner, Kevin, Kuhn, Gerhard, Pälike, Heiko, Ronge, Thomas, Simoes Pereira, Patric, Smith, James A., Uenzelmann-Neben, Gabriele, and van der Flierdt, Christina
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- 2017
155. Recent unpinning and calving front retreat of Pine Island Glacier documented by new bathymetric and satellite data
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Arndt, Jan Erik, Larter, Robert D., Friedl, Peter, Gohl, Karsten, Höppner, Kathrin, PS104, Shipboard Scientific Party, Arndt, Jan Erik, Larter, Robert D., Friedl, Peter, Gohl, Karsten, Höppner, Kathrin, and PS104, Shipboard Scientific Party
- Abstract
Pine Island Glacier currently experiences the largest negative ice sheet mass balance in comparison to other outlet glaciers in Antarctica and hence is the largest contributor to modern sea-level rise. Ice loss of this glacial outlet and neighbouring ones has increased greatly over the recent decades through ice thinning and flow acceleration that also resulted in rapid grounding line retreat, most likely as a result of basal melting induced by the inflow of warm Circumpolar Deep Water onto the shelf. Due to the glacier’s topographic setting, a bed that deepens beyond the grounding line to the deep interior basin of the West Antarctic Ice Sheet (WAIS), it has been suggested that this increased ice loss may be a precursor of WAIS collapse. Despite the increased mass loss, however, the calving front of Pine Island Glacier remained more or less stable in a position west of a pinning point located at the northern part of the glacier and its orientation remained similar (10-30° east of north) since the earliest observations in the mid-20th century. Large icebergs where calved at intervals of a few years, e.g. the B-31 calving event (720 km²) in November 2013, but subsequently the calving front re-advanced close to or even beyond its former position. In 2015 this pattern changed with a calving event initiated by a large rift oriented 55° east of north and the calving front for the first time retreated east of the pinning point. The rifts that initiated this calving event were proposed to have formed by expansion of basal crevasses due to ocean forcing. In 2017 we were able to access the formerly ice-shelf covered area during RV Polarstern expedition PS104. Bathymetric data from this area revealed a bathymetric knoll with minimum water depth of ~375 m that was the former pinning point of the glacier. A new rift 8-9 km upstream of the calving line that may initiate the next calving event within a year was visited by helicopter. Satellite data acquired in the last decades su
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- 2017
156. MeBo70 Seabed Drilling on a Polar Continental Shelf: Operational Report and Lessons From Drilling in the Amundsen Sea Embayment of West Antarctica
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Gohl, K., Freudenthal, T., Hillenbrand, Claus-Dieter, Klages, J., Larter, Robert, Bickert, T., Bohaty, S., Ehrmann, W., Esper, O., Frederichs, T., Gebhardt, C., Küssner, K., Kuhn, G., Pälike, H., Ronge, T., Simões Pereira, P., Smith, James, Uenzelmann-Neben, G., van de Flierdt, C., Gohl, K., Freudenthal, T., Hillenbrand, Claus-Dieter, Klages, J., Larter, Robert, Bickert, T., Bohaty, S., Ehrmann, W., Esper, O., Frederichs, T., Gebhardt, C., Küssner, K., Kuhn, G., Pälike, H., Ronge, T., Simões Pereira, P., Smith, James, Uenzelmann-Neben, G., and van de Flierdt, C.
- Abstract
A multibarrel seabed drill rig was used for the first time to drill unconsolidated sediments and consolidated sedimentary rocks from an Antarctic shelf with core recoveries between 7% and 76%. We deployed the MARUM-MeBo70 drill device at nine drill sites in the Amundsen Sea Embayment. Three sites were located on the inner shelf of Pine Island Bay from which soft sediments, presumably deposited at high sedimentation rates in isolated small basins, were recovered from drill depths of up to 36 m below seafloor. Six sites were located on the middle shelf of the eastern and western embayment. Drilling at five of these sites recovered consolidated sediments and sedimentary rocks from dipping strata spanning ages from Cretaceous to Miocene. This report describes the initial coring results, the challenges posed by drifting icebergs and sea ice, and technical issues related to deployment of the MeBo70. We also present recommendations for similar future drilling campaigns on polar continental shelves.
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- 2017
157. West Antarctic Ice Sheet retreat driven by Holocene warm water incursions
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Hillenbrand, Claus-Dieter, Smith, James A., Hodell, David A., Greaves, Mervyn, Poole, Christopher R., Kender, Sev, Williams, Mark, Andersen, Thorbjørn Joest, Jernas, Patrycja E., Elderfield, Henry, Klages, Johann P., Roberts, Stephen J., Gohl, Karsten, Larter, Robert D., Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Smith, James A., Hodell, David A., Greaves, Mervyn, Poole, Christopher R., Kender, Sev, Williams, Mark, Andersen, Thorbjørn Joest, Jernas, Patrycja E., Elderfield, Henry, Klages, Johann P., Roberts, Stephen J., Gohl, Karsten, Larter, Robert D., and Kuhn, Gerhard
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Glaciological and oceanographic observations coupled with numerical models show that warm Circumpolar Deep Water (CDW) incursions onto the West Antarctic continental shelf cause melting of the undersides of floating ice shelves. Because these ice shelves buttress glaciers feeding into them, their ocean-induced thinning is driving Antarctic ice-sheet retreat today. Here we present a multi-proxy data based reconstruction of variability in CDW inflow to the Amundsen Sea sector, the most vulnerable part of the West Antarctic Ice Sheet, during the Holocene epoch (from 11.7 thousand years ago to the present). The chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced CDW upwelling, controlled by the latitudinal position of the Southern Hemisphere westerly winds, forced deglaciation of this sector from at least 10,400 years ago until 7,500 years ago—when an ice-shelf collapse may have caused rapid ice-sheet thinning further upstream—and since the 1940s. These results increase confidence in the predictive capability of current ice-sheet models.
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- 2017
158. Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks
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Wise, Matthew G., Dowdeswell, Julian A., Jakobsson, Martin, Larter, Robert D., Wise, Matthew G., Dowdeswell, Julian A., Jakobsson, Martin, and Larter, Robert D.
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Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost1, 2. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes3, 4. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates5. It is thought1, 2 that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study1, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth6 and drift direction7. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8, 9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11, 12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI13. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers o
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- 2017
159. Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: transitions from a non-glacial, through glacially-influenced to a fully glacial state
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Hernandez-Molina, F. Javier, Larter, Robert D., Maldonado, Andres, Hernandez-Molina, F. Javier, Larter, Robert D., and Maldonado, Andres
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A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise and establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the early Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop durin
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- 2017
160. Geological Society of London Scientific Statement: what the geological record tells us about our present and future climate.
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Lear, Caroline H., Anand, Pallavi, Blenkinsop, Tom, Foster, Gavin L., Gagen, Mary, Hoogakker, Babette, Larter, Robert D., Lunt, Daniel J., McCave, I. Nicholas, McClymont, Erin, Pancost, Richard D., Rickaby, Rosalind E.M., Schultz, David M., Summerhayes, Colin, Williams, Charles J.R., and Zalasiewicz, Jan
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PHYSICAL geography ,CHEMICAL weathering ,EARTH sciences ,ENVIRONMENTAL sciences ,NATURAL disasters ,PLIOCENE Epoch ,GLACIAL landforms ,PHYSICAL sciences - Published
- 2021
- Full Text
- View/download PDF
161. Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks
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Wise, Matthew G., primary, Dowdeswell, Julian A., additional, Jakobsson, Martin, additional, and Larter, Robert D., additional
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- 2017
- Full Text
- View/download PDF
162. Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: Transitions from a non-glacial, through glacially-influenced to a fully glacial state
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Hernández-Molina, F. Javier, primary, Larter, Robert D., additional, and Maldonado, Andrés, additional
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- 2017
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163. The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations
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Spagnolo, Matteo, primary, Bartholomaus, Timothy C., additional, Clark, Chris D., additional, Stokes, Chris R., additional, Atkinson, Nigel, additional, Dowdeswell, Julian A., additional, Ely, Jeremy C., additional, Graham, Alastair G. C., additional, Hogan, Kelly A., additional, King, Edward C., additional, Larter, Robert D., additional, Livingstone, Stephen J., additional, and Pritchard, Hamish D., additional
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- 2017
- Full Text
- View/download PDF
164. West Antarctic Ice Sheet retreat driven by Holocene warm water incursions
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Hillenbrand, Claus-Dieter, primary, Smith, James A., additional, Hodell, David A., additional, Greaves, Mervyn, additional, Poole, Christopher R., additional, Kender, Sev, additional, Williams, Mark, additional, Andersen, Thorbjørn Joest, additional, Jernas, Patrycja E., additional, Elderfield, Henry, additional, Klages, Johann P., additional, Roberts, Stephen J., additional, Gohl, Karsten, additional, Larter, Robert D., additional, and Kuhn, Gerhard, additional
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- 2017
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165. Palaeo-ice stream pathways and retreat style in the easternmost Amundsen Sea Embayment, West Antarctica, revealed by combined high-resolution multibeam bathymetric and seismic data
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Klages, Johann Philipp, Kuhn, Gerhard, Graham, Alastair G. C., Smith, James A., Hillenbrand, Claus-Dieter, Nitsche, Frank O., Larter, Robert D., and Gohl, Karsten
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Multibeam swath bathymetry datasets collected over the past two decades have been compiled to identify palaeoice 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.
- Published
- 2015
166. Workshop - Amundsen Sea Embayment Tectonic and Glacial History - Programme and Abstracts
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Larter, Robert D, Gohl, Karsten, Bentley, Michael J, Anderson, John B, Larter, Robert D., Bentley, Michael J., Anderson, John B., Larter, Robert D, Gohl, Karsten, Bentley, Michael J, Anderson, John B, Larter, Robert D., Bentley, Michael J., and Anderson, John B.
- Abstract
Overall Objective: Review existing data and identify priorities for future geoscience research (terrestrial, marine and airborne) in the Amundsen Sea embayment (ASE) region required to develop a better understanding of the past, present and future behaviour of this sector of the West Antarctic Ice Sheet (WAIS). Background: The ASE is the most rapidly changing sector of the WAIS and contains enough ice to raise global sea level by 1.2 m. Over the past few years considerable efforts have been made to acquire new data to improve knowledge of the geological structure, subglacial topography, continental shelf bathymetry and glacial history of this remote region. In this workshop we aim to review the current state of knowledge on the tectonic and glacial evolution of the Amundsen Sea embayment. Particular emphasis will be placed on work that will improve boundary conditions for ice sheet models (e.g. subglacial topography, shelf bathymetry, palaeotopography, heat flow and substrate types) and provide palaeo-data against which model outputs can be compared. There will also be a focus on plans and targets for future scientific drilling that will reveal the history of this sector of the WAIS and its sensitivity to major climate changes.
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- 2011
167. A glacial landform assemblage from an inter-ice stream setting in the eastern Amundsen Sea Embayment, West Antarctica
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Dowdeswell, J. A., Canals, Miquel, Jakobsson, M., Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Klages, Johann Philipp, Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., Larter, Robert D., Gohl, Karsten, Dowdeswell, J. A., Canals, Miquel, Jakobsson, M., Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Klages, Johann Philipp, Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., Larter, Robert D., and Gohl, Karsten
- Abstract
Large ice streams that drain the West Antarctic Ice Sheet (WAIS) into the Amundsen Sea Embayment (ASE) are currently thinning, accelerating and retreating rapidly (e.g. Rignot et al. 2014). These ice streams are assumed to have reached the continental shelf edge during the Last Glacial Maximum (LGM; c. 23 – 19 cal ka BP), some 450 km north of the modern grounding line (e.g. Larter et al. 2014). Recent modelling results suggest that the expanded LGM ice sheet was characterized by fast-flowing regions across the entire ASE shelf (Golledge et al. 2013). However, the original geomorphological imprint of former fast ice-flow has usually only been preserved within deep palaeo-ice stream troughs, for example as mega-scale glacial lineations (MSGLs) (Clark 1993). In con- trast, the morphological record in inter-ice stream settings is believed to have been subsequently obliterated by ploughing iceberg keels (e.g. Dowdeswell & Bamber 2007). As a result, evi- dence for palaeo-ice sheet dynamics in these regions, which make up a substantial portion of the former ice-sheet bed, remain largely understudied (Ottesen & Dowdeswell 2009). The undisturbed geo- morphological record from a palaeo-inter-ice stream setting in the ASE, north of Burke Island, revealed an assemblage of subglacial landforms that is entirely different from those in the deep troughs (Klages et al. 2013). The geomorphological record therefore pro- vides new insights into basal conditions of the former WAIS in the Amundsen Sea sector that is also relevant to other sectors and to ice-sheet beds outside Antarctica.
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- 2016
168. Submarine glacial-landform distribution across the West Antarctic margin, from grounding line to slope: the Pine Island–Thwaites ice-stream system
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Graham, Alastair G. C., Jakobsson, Martin, Nitsche, Frank O., Larter, Robert D., Anderson, John B., Hillenbrand, Claus-Dieter, Gohl, Karsten, Klages, Johann Philipp, Smith, James A., Jenkins, Adrian, Graham, Alastair G. C., Jakobsson, Martin, Nitsche, Frank O., Larter, Robert D., Anderson, John B., Hillenbrand, Claus-Dieter, Gohl, Karsten, Klages, Johann Philipp, Smith, James A., and Jenkins, Adrian
- Published
- 2016
169. Submarine landform assemblage produced beneath the Dotson–Getz palaeo-ice stream, West Antarctica
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Graham, Alastair G. C., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, Graham, Alastair G. C., Nitsche, Frank O., Larter, Robert D., and Gohl, Karsten
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- 2016
170. Bedrock channels in Pine Island Bay, West Antarctica
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Dowdeswell, Julian A., Canals, Miquel, Jakobsson, Martin, Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, Graham, Alastair G. C., Kuhn, Gerhard, Dowdeswell, Julian A., Canals, Miquel, Jakobsson, Martin, Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, Graham, Alastair G. C., and Kuhn, Gerhard
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- 2016
171. Crag-and-tail features on the Amundsen Sea continental shelf, West Antarctica
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Dowdeswell, J. A., Canals, M., Jakobsson, M., Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, Graham, Alastair G. C., Kuhn, Gerhard, Dowdeswell, J. A., Canals, M., Jakobsson, M., Todd, B. J., Dowdeswell, E. K., Hogan, K. A., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, Graham, Alastair G. C., and Kuhn, Gerhard
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- 2016
172. Dating glacimarine sediments from the continental shelf in the Amundsen Sea using a multi-tool box: Implications for West Antarctic ice-sheet extent and retreat during the last glacial cycle
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Hillenbrand, Claus-Dieter, Smith, James A., Klages, Johann Philipp, Kuhn, Gerhard, Maher, Barbara, Moreton, Steven G., Wacker, Lukas, Frederichs, Thomas, Wiers, Steffen, Jernas, Patrycja Ewa, Anderson, John B., Ehrmann, Werner, Graham, Alastair G. C., Gohl, Karsten, Larter, Robert D., Hillenbrand, Claus-Dieter, Smith, James A., Klages, Johann Philipp, Kuhn, Gerhard, Maher, Barbara, Moreton, Steven G., Wacker, Lukas, Frederichs, Thomas, Wiers, Steffen, Jernas, Patrycja Ewa, Anderson, John B., Ehrmann, Werner, Graham, Alastair G. C., Gohl, Karsten, and Larter, Robert D.
- Abstract
Satellite data and in-situ measurements show that today considerable mass loss is occurring from the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS). The observational record only spans the past four decades, and until recently the long-term context of the current deglaciation was poorly constrained. This information is, however, crucial for understanding WAIS dynamics, evaluating the role of forcing mechanisms for ice-sheet melting, and testing and calibrating ice-sheet models that attempt to predict future WAIS behavior and its impact on global sea level. Over the past decade several multinational marine expeditions and terrestrial fieldwork campaigns have targeted the Amundsen Sea shelf and its hinterland to reconstruct the WAIS configuration during the Last Glacial Maximum (LGM) and its subsequent deglacial history. The resulting studies succeeded in shedding light on the maximum WAIS extent at the LGM and the style, pattern and speed of its retreat and thinning thereafter. Despite this progress, however, significant uncertainties and discrepancies between marine and terrestrial reconstructions remain, which may arise from difficulties in dating sediment cores from the Antarctic shelf, especially their deglacial sections. Resolving these issues is crucial for understanding the WAIS’ contribution to post-LGM sea-level rise, its sensitivity to different forcing mechanisms and its future evolution. Here we present chronological constraints on WAIS advance in the Amundsen Sea and its retreat from ~20 ka BP into the Holocene that were obtained by various techniques, such as 14C dating of large (~10 mg) and small (<<1 mg) sample aliquots of calcareous microfossils, 14C dating of acid-insoluble organic matter combusted at low (300 °C) and high (800 °C) temperatures and dating of sediment cores by using geomagnetic paleointensity. We will compare the different age constraints and discuss their reliability, applicability and implications for WAIS history.
- Published
- 2016
173. Bathymetry and geological setting of the South Sandwich Islands volcanic arc
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Leat, Philip T., Fretwell, Peter T., Tate, Alex J., Larter, Robert D., Martin, Tara J., Smellie, John L., Jokat, Wilfred, Bohrmann, Gerhard, Leat, Philip T., Fretwell, Peter T., Tate, Alex J., Larter, Robert D., Martin, Tara J., Smellie, John L., Jokat, Wilfred, and Bohrmann, Gerhard
- Abstract
The South Sandwich Islands and associated seamounts constitute the volcanic arc of an active subduction system situated in the South Atlantic. We introduce a map of the bathymetry and geological setting of the South Sandwich Islands and the associated East Scotia Ridge back-arc spreading centre that consists of two sides: side 1, a regional overview of the volcanic arc, trench and back-arc, and side 2, detailed maps of the individual islands. Side 1 displays the bathymetry at scale 1:750 000 of the intra-oceanic, largely submarine South Sandwich arc, the back-arc system and other tectonic boundaries of the subduction system. Satellite images of the islands on side 2 are at scales of 1:50 000 and 1:25 000 with contours and main volcanological features indicated. These maps are the first detailed topological and bathymetric maps of the area. The islands are entirely volcanic in origin, and most have been volcanically or fumarolically active in historic times. Many of the islands are ice-covered, and the map forms a baseline for future glaciological changes caused by volcanic activities and climate change. The back-arc spreading centre consists of nine segments, most of which have rift-like morphologies
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- 2016
174. Antarctica's Cenozoic ice and climate history: new science and new challenges of drilling in Antarctic waters
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Williams, Trevor, McKay, Robert, Gohl, Karsten, Channell, James E. T., De Santis, Laura, Larter, Robert D., Kulhanek, Denise, Shevenell, Amelia, Harwood, David, Gulick, Sean, Williams, Trevor, McKay, Robert, Gohl, Karsten, Channell, James E. T., De Santis, Laura, Larter, Robert D., Kulhanek, Denise, Shevenell, Amelia, Harwood, David, and Gulick, Sean
- Abstract
Scientific drilling continues to advance knowledge of Antarctica’s role in the climate system and the evolution of its ice sheets. Since 1972, seven DSDP, ODP, and IODP expeditions to Antarctic waters have documented cooling of Antarctic climate since the early Eocene; inception of large-scale glaciation at the start of the Oligocene; ice-sheet expansion and relative stabilization in the middle Miocene; fluctuations of the ice margins in the Pliocene; and high-resolution details of Holocene climate. Geological drilling by land- and ice-based projects such as ANDRILL has provided shoreward evidence of ice and climate behaviour complimentary to the ship-based drilling. The scientific significance of the sediment cores collected on these expeditions has grown as the problem of global warming has become more apparent, and the cores continue to be analysed with the development of new techniques, such as biomarker temperature estimates and geochemical sediment provenance. However, these existing sedimentary records do not cover all of the Cenozoic and the core locations are geographically restricted. Antarctic marine sediments hold further records of ice sheet dynamics and warm climates of the past that form analogues for high-CO2 greenhouse scenarios of the next centuries. Several proposals to collect these records are in the IODP review system, for regions where the ice sheets are sensitive to warming and for time periods when the ice response to warm climates is not well known. A workshop is being held at IODP in College Station, Texas, in May 2016 to: (1) Produce an integrated overview of how IODP drilling can advance understanding of Antarctic ice sheet retreat (and hence sea level rise) under warm climates; (2) Examine existing sediment cores that revealed Antarctica’s past marine glaciological history; and (3) Establish best practices for assessing ice and weather to conduct safe drilling operations in Antarctic waters. Here we review the highlights and outcomes of
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- 2016
175. Searching for the most detailed, continuous, late Miocene to Quaternary records of Antarctic Peninsula and West Antarctic Ice Sheet dynamics
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Larter, Robert D., Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Channell, James E. T., Hernández-Molina, F. J., Hodell, David A., Hogan, Kelly, Xuan, C., Gohl, Karsten, Rebesco, Michele, Uenzelmann-Neben, Gabriele, Crowhurst, S., Williams, M., Larter, Robert D., Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Channell, James E. T., Hernández-Molina, F. J., Hodell, David A., Hogan, Kelly, Xuan, C., Gohl, Karsten, Rebesco, Michele, Uenzelmann-Neben, Gabriele, Crowhurst, S., and Williams, M.
- Abstract
Changes observed in the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS) over recent decades include thinning and break up of ice shelves, glacier flow acceleration and grounding line retreat. How rapidly and how far these ice sheets will retreat in a warmer climate, however, remains uncertain. For example, it remains unclear whether or not the marine-based WAIS “collapsed” during Quaternary interglacial periods, including the last one, contributing more than 3 m to global sea-level rise. Continuous long-term records of ice sheet change with precise chronology are needed in order to answer these questions. On the Antarctic continental shelf, sedimentary records are interrupted by numerous unconformities resulting from glacial erosion, good core recovery has only been achieved from platforms sited on sea ice or ice shelves, and establishing reliable chronologies has proved challenging. In contrast, sediment drifts on the upper continental rise around Antarctica contain expanded, continuous successions dominated by muddy lithologies from which good recovery can be achieved using standard scientific ocean drilling methods. Ocean Drilling Program (ODP) Leg 178 demonstrated that sediment drifts west of the Antarctic Peninsula contain a rich high-resolution archive of Southern Ocean paleoceanography and APIS history that extends back to at least the late Miocene. The potential of existing ODP cores from the drifts is, however, compromised by incomplete composite sections and lack of precise chronological control. An International Ocean Discovery Program proposal (732-Full2) for future drilling on these drifts has been scientifically approved and is with the JOIDES Resolution Facilities Board for scheduling. The main aims of the proposal are to obtain continuous, high-resolution records from sites on sediment drifts off both the Antarctic Peninsula and West Antarctica (southern Bellingshausen Sea). The challenges will then be achieving good chronolo
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- 2016
176. Documenting past retreats of the West Antarctic Ice Sheet – Drilling targets in the Amundsen Sea Embayment
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Gohl, Karsten, Kuhn, Gerhard, Uenzelmann-Neben, Gabriele, Hillenbrand, Claus-Dieter, Larter, Robert D., Bickert, Thorsten, Gohl, Karsten, Kuhn, Gerhard, Uenzelmann-Neben, Gabriele, Hillenbrand, Claus-Dieter, Larter, Robert D., and Bickert, Thorsten
- Abstract
The West Antarctic Ice-Sheet (WAIS) is likely to have been subject to very dynamic changes during its history as most of its base is grounded below modern sea-level, making it particularly sensitive to climate changes. Its collapse would result in global sea-level rise of 3-5 m. The reconstruction and quantification of possible partial or full collapses of the WAIS in the past can provide important constraints for ice-sheet models, used for projecting its future behaviour and resulting sea-level rise. Large uncertainties exist regarding the chronology, extent, rates as well as spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves. By using the seafloor drilling device MeBo during an RV Polarstern cruise scheduled for early 2017, a series of sediment cores will be drilled on the Amundsen Sea Embayment (ASE) shelf, where seismic data show glacially-derived sequences covered by only a thin veneer of postglacial deposits in some areas. From analyses of seismic data, we infer that interglacial sediments can be sampled which may have been deposited under seasonally open water conditions and thus contain datable microfossil-bearing material. A shallow basin near the Pine Island Glacier front will be one of the prime targets for the drilling. The near-horizontal seismic reflection horizons may represent a sequence of continuously deposited, mainly terrigenous material, including ice-rafted debris, meltwater deposits and hemipelagic sediments deposited rapidly during the last deglaciation and Holocene or a series of unconformities caused by erosion resulting from grounding line oscillations through numerous glacial cycles. Subglacial bedforms imaged in multibeam bathymetric data indicate fast glacial flow over some shelf areas of the ASE, where seismic profiles show acoustic basement near the seafloor. It is unknown, whether fast ice-flow in these areas was facilitated by water-lubricated sliding over bedrock or presence of
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- 2016
177. Paleo-Ice Sheet/Stream Flow Directions of the Northern Antarctic Peninsula Ice Sheet Based Upon New Synthesis of Multibeam Seabed Imagery
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Lavoie, Caroline, Domack, Eugene, Scambos, Theodore, Pettit, Erin, Schenke, Hans-Werner, Yoo, Kyu-Cheul, Larter, Robert, Gutt, Julian, Wellner, Julia, Canals, Miquel, Anderson, John, and Amblas, David
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- 2014
178. A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
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Bentley, Michael J., Ó Cofaigh, Colm, Anderson, John B., Conway, Howard, Davies, Bethan, Graham, Alastair G.C., Hillenbrand, Claus-Dieter, Hodgson, Dominic A., Jamieson, Stewart S.R., Larter, Robert, Mackintosh, Andrew N., Smith, James A., Verleyen, Elie, Ackert, Robert, Bart, Philip J., Berg, Sonja, Brunstein, Daniel, Canals, Miquel, Colhoun, Eric A., Crosta, Xavier, Dickens, William A., Domack, Eugene, Dowdeswell, Julia, Dunbar, Robert, Ehrmann, Werner, Evans, Jeffrey, Favier, Vincent, Fink, David, Fogwill, Christopher J., Glasser, Neil F., Gohl, Karsten, Golledge, Nicholas R., Goodwin, Ian, Gore, Damian B., Greenwood, Sarah L., Hall, Brenda L., Hall, Kevin, Hedding, David W., Hein, Andrew S., Hocking, Emma P., Jakobsson, Martin, Johnson, Joanne S., Jomelli, Vincent, Jones, R. Selwyn, Klages, Johann P., Kristoffersen, Yngve, Kuhn, Gerhard, Leventer, Amy, Licht, Kathy, Lilly, Katherine, Lindow, Julia, Livingstone, Stephen J., Massé, Guillaume, Mcglone, Matt S., Mckay, Robert, Melles, Martin, Miura, Hideki, Mulvaney, Robert, Nel, Werner, Nitsche, Frank O., O'Brien, Philip E., Post, Alexandra L., Roberts, Stephen J., Saunders, Krystyna M., Selkirk, Patricia M., Simms, Alexander R., Spiegel, Cornelia, Stolldorf, Travis D., Sugden, David E., van Der Putten, Nathalie, van Ommen, Tas, Verfaillie, Deborah, Vyverman, Wim, Wagner, Bernd, White, Duanne A., Witus, Alexandra E., Zwartz, Dan, Department of Geography, Durham University, School of Oceanography [Seattle], University of Washington [Seattle], Biological and Biomedical Sciences, Glasgow Caledonian University (GCU), British Antarctic Survey (BAS), Natural Environment Research Council (NERC), Universiteit Gent = Ghent University (UGENT), Laboratoire de géographie physique : Environnements Quaternaires et Actuels (LGP), Université Paris 1 Panthéon-Sorbonne (UP1)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), GRC Geociencies Marines, GRC, School of Environmental and Life Sciences, The University of Newcastle, Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Space Research Institute of Austrian Academy of Sciences (IWF), Austrian Academy of Sciences (OeAW), College of Marine Science [St Petersburg, FL], University of South Florida [Tampa] (USF), Scott Polar Research Institute, University of Cambridge [UK] (CAM), Stanford University, Centre for glaciology, Department of Geography and Earth Sciences (DGES), Aberystwyth University-Aberystwyth University, Department of biomedical sciences, University of Prince Edward Island, University of Calgary, Department of Evolutionary Biology, Uppsala University, Institute for Biomechanics, Colgate University, Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Takuvik Joint International Laboratory ULAVAL-CNRS, Université Laval [Québec] (ULaval)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institute of integrative biology (Liverpool), University of Liverpool, Paul Scherrer Institute (PSI), NIFS, National Institute for Fusion Science (NIFS), Gent University, Department of Biology, Lamont-Doherty Earth Observatory (LDEO), Columbia University [New York], University of West London, Dpt Biological Sciences, Macquarie University, Macquarie University, Division of Migratory Birds - Northeast Region, US Fish and Wildlife Service, Lund University [Lund], UMR 5805 Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Department of Geology and Geochemistry [Stockholm], Stockholm University, Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Panthéon-Sorbonne (UP1), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Protistology and Aquatic Ecology, Ghent University, Universiteit Gent = Ghent University [Belgium] (UGENT), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Laval [Québec] (ULaval)-Centre National de la Recherche Scientifique (CNRS), and Earth and Climate
- Subjects
Matematikk og naturvitenskap: 400::Geofag: 450::Kvartærgeologi, glasiologi: 465 [VDP] ,[PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] ,Modelling ,Mathematics and natural scienses: 400::Geosciences: 450::Quaternary geology, glaciology: 465 [VDP] ,Quaternary ,HISTORY ,MASS-BALANCE ,COLLAPSE ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,Ecology, Evolution, Behavior and Systematics ,ComputingMilieux_MISCELLANEOUS ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,Global and Planetary Change ,WEDDELL SEA EMBAYMENT ,CONSTRAINTS ,LEVEL CHANGE ,Geology ,RETREAT ,Antarctic Ice Sheet ,STREAM STABILITY ,Glacial geology ,ISOSTATIC-ADJUSTMENT ,[SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology ,Earth and Environmental Sciences ,PENINSULA - Abstract
The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica’s continental ice volume. Over the last few decades, studies on glacialegeological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23e19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on theWeddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different icesheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sealevel low-stand of w130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past icesheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post- LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim of our study is to provide two alternative interpretations of glacialegeological datasets on Antarctic Ice- Sheet History for the Weddell Sea sector, which can be utilised to test and improve numerical icesheet models
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- 2014
- Full Text
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179. Assessing the extent of the West Antarctic Ice Sheet on the eastern Amundsen Sea shelf during the last glacial period
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Klages, Johann Philipp, Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., Nitsche, Frank O., Larter, Robert D., Gohl, Karsten, and Wacker, Lukas
- Abstract
High-resolution swath bathymetry data collected during several research cruises over the past two decades reveal a palaeo-ice stream trough (Abbot Glacial Trough) crossing the middle and outer shelf of the easternmost Amundsen Sea Embayment, east of the main Pine Island Trough. Regions of both fast palaeo-ice flow (within the central trough) and slow palaeo-ice flow (on adjacent seafloor highs referred to as inter-ice stream ridges) bear glacial landforms indicative of phases of grounding-line stabilization of the ice sheet. We associate a grounding-zone wedge situated within the outer Abbot Glacial Trough with a grounding-zone wedge in outer Pine Island Trough and suggest a synchronous grounding-line halt in both troughs. New sediment echosounder and sediment core data collected from outer Abbot Glacial Trough, between the seaward limit of the grounding-zone wedge and the shelf edge, reveal an up to 6 m-thick well stratified drape that is composed of unconsolidated glaciomarine sediments occasionally bearing calcareous microfossils. In order to decipher whether this unusually thick sediment drape might indicate sub-ice shelf and/or seasonal-open marine deposition throughout or since the Last Glacial Maximum, we used a multi-proxy approach to characterize its lithofacies and applied radiocarbon dating of calcareous microfossils. Here we present our initial results and discuss since when the outer shelf in the eastern Amundsen Sea has been free of grounded-ice. Such information will 1) improve ice sheet models that aim to reconstruct the flow and extent of the West Antarctic Ice Sheet during the Last Glacial Maximum, 2) help to quantify the ice volume of the West Antarctic Ice Sheet during this time, and 3) prove or reject the possibility that Antarctic benthic biota endured glacial periods in outer shelf refugia.
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- 2014
180. Bathymetry and geological setting of the South Sandwich Islands volcanic arc
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Leat, Philip T., primary, Fretwell, Peter T., additional, Tate, Alex J., additional, Larter, Robert D., additional, Martin, Tara J., additional, Smellie, John L., additional, Jokat, Wilfried, additional, and Bohrmann, Gerhard, additional
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- 2016
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181. A Submarine Landform Continuum across Marine Ice-Stream Margins
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Graham, Alastair G. C., Klages, Johann Philipp, Larter, Robert D., Smith, James A., Hillenbrand, Claus-Dieter, Kuhn, Gerhard, Graham, Alastair G. C., Klages, Johann Philipp, Larter, Robert D., Smith, James A., Hillenbrand, Claus-Dieter, and Kuhn, Gerhard
- Abstract
The interface between grounded ice and the open ocean is one of the most critical for resolving processes of change in Earth‘s ice sheets. However, this environment remains one of the least explored on the planet and is poorly understood as a result. While the sedimentological facies succession of the transition from grounded ice to (seasonal) open marine conditions is relatively well known from sediment cores recovered from the continental shelf around Antarctica, the corresponding geomorphological signature has been less well studied. Here we analyse high-resolution marine geophysical surveys from palaeo-ice stream troughs on Antarctica‘s continental shelf, including bathymetry from sub-ice shelf settings, that allow for the geological imprint of the transition between grounded and floating ice to be fully explored. We document six styles of landform assemblage from Antarctic palaeo-ice stream beds, which we further interpret as diagnostic of particular stages in the transition of a marine ice-stream margin from a fully grounded state to an open water setting. Descriptively, the six types comprise of (i) Mega-scale glacial lineations, evolving into (ii) Elongate lineations with corrugated ridges, (iii) Sub-parallel elongate keel-marks, (iv) Broadly-spaced elongate furrows, (v) Elongate furrows with sinuous or ridged termini, and (vi) Curvi-linear, randomly-oriented ploughmarks. Whilst several of these landform types have been described in isolation in previous bathymetric studies, rarely have they been considered in the context of such assemblage groupings and have not been viewed together as a continuum. In drawing together observations, these landform types, exposed by past ice-margin fluctuations across the sea bed, demonstrate a close similarity to one another but significant differences in their extremes. We thus argue that they form a recognisable continuum (evolution) of forms within fully grounded, through ice-plain, sub-ice shelf, pro-marginal, distal mar
- Published
- 2015
182. Testing the Extent and Timing of Past Glaciations Offshore of the Sub-Antarctic Island of South Georgia
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Graham, Alastair G. C., Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Hodgson, Dominic A., Ehrmann, Werner U, Meisel, Ove, Larter, Robert D., Cofaigh, Colm Ó, Graham, Alastair G. C., Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Hodgson, Dominic A., Ehrmann, Werner U, Meisel, Ove, Larter, Robert D., and Cofaigh, Colm Ó
- Abstract
There has been a long history of debate over the extent and timing of past glaciations on the small but climatically-sensitive islands of the sub-Antarctic. The largest of these islands, South Georgia, has been the focus of contention with two conflicting models proposed for the peak of the last glaciation (the Last Glacial Maximum, c. 21 k yrs B.P.): one suggesting an ice cap of restricted extent that saw tidewater outlets limited to the coastal basins of radial fjords; the other proposing an extensive shelf-wide ice cap based on well-preserved though as yet un-dated or un-sampled sea-bed geomorphology. It has been suggested that these two models form comparative end-members of 'South American‘ (restricted) and 'Antarctic‘ (extensive) modes of glaciation, and thus establishing whether the pattern of glaciation on sub- Antarctic islands follows one of these modes, or is in itself entirely different, can provide potentially important insight into past climate forcing of an otherwise poorly-constrained Southern Ocean region. The extent of island glaciation can also provide valuable far-field constraint for Antarctic ice sheet models, and forms vital information for biologists seeking to understand benthic marine communities around South Georgia, whose evolution and structure are intimately linked to the long-term history of ice advance and retreat. Here we investigate the geological record offshore of South Georgia to improve understanding of the extent and timing of past glaciation. Marine geophysical data from new and previous research cruises have been compiled and analysed to advance knowledge of palaeo-ice cap dynamics on the island‘s submerged sea bed and subsurface. We have also sought an independent verification of the glacial history of the island by linking new geomorphological analyses with dated marine sedimentary records recovered by coring, for the first time, on the continental shelf. We present results of new landform mapping on the sea-bed of the Sout
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- 2015
183. Multichannel Seismic Investigations of Sediment Drifts on the west Antarctic Peninsula Pacific Margin: Preliminary Results from Research Cruise JR298
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Graham, Alastair G. C., Larter, Robert D., Channell, James E. T., Hillenbrand, Claus-Dieter, Hodell, David A., Hernández-Molina, F. J., Gohl, Karsten, Uenzelmann-Neben, Gabriele, Rebesco, Michele, Hogan, Kelly, JR298 Shipboard Party, Graham, Alastair G. C., Larter, Robert D., Channell, James E. T., Hillenbrand, Claus-Dieter, Hodell, David A., Hernández-Molina, F. J., Gohl, Karsten, Uenzelmann-Neben, Gabriele, Rebesco, Michele, Hogan, Kelly, and JR298 Shipboard Party
- Abstract
Observations across both the West Antarctic and Antarctic Peninsula ice sheets over recent decades have confirmed that the region is warming and undergoing major and potentially rapid changes as a result. These changes have manifest in the form of significant ice-sheet thinning and retreat, and in dramatic short-lived events such as ice-shelf collapses. The longer-term backdrop to this recent change is vital information for our understanding of future ice and climate evolution, and for wider knowledge of ice-sheet function and sensitivity. Providing context on geological timescales, such records can be obtained from two main sources: (1) from ice cores extracted from the ice sheet interiors and (2) from continuous marine sedimentary sequences recovered from the sea floor surrounding the Antarctic continent. Whilst ice cores provide a very high-resolution archive of palaeo-climate, they offer data over only a relatively short window of time (<1 million years) and provide little information on how the ice and oceans were changing at the ice sheet periphery. By contrast, sediments derived from the Antarctic continent have discharged continuously to the continental slope and deeper ocean over millions of years, and are sensitive recorders of both ice sheet an oceanographic variability. Repeated continental margin-derived turbidity currents, in combination with the activity of along-slope currents, have led to the accumulation of large hemi-pelagic depositional bodies, termed sediment drifts that are, today, oriented orthogonal to the continental margin and record continuous sedimentation on the continental rise since at least the Miocene. Along the Antarctic Peninsula Pacific margin, a chain of twelve large sediment drifts separated out by channels eroded by turbidity currents provide unique archives of environmental changes in Antarctica‘s ice sheets and the Southern Ocean. IODP proposal 732FULL2 aims to recover drill cores extending back into the Pliocene from the cre
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- 2015
184. Sea-bed corrugations beneath an Antarctic ice shelf revealed by autonomous underwater vehicle survey: Origin and implications for the history of Pine Island Glacier
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Graham, Alastair, Dutrieux, Pierre, Vaughan, David G., Nitsche, Frank O., Gyllencreutz, Richard, Greenwood, Sarah L., Larter, Robert D., and Jenkins, Adrian
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Glaciology ,F700 ,F800 - Abstract
Ice shelves are critical features in the debate about West Antarctic ice sheet change and sea level rise, both because they limit ice discharge and because they are sensitive to change in the surrounding ocean. The Pine Island Glacier ice shelf has been thinning rapidly since at least the early 1990s, which has caused its trunk to accelerate and retreat. Although the ice shelf front has remained stable for the past six decades, past periods of ice shelf collapse have been inferred from relict seabed "corrugations" (corrugated ridges), preserved 340 km from the glacier in Pine Island Trough. Here we present high-resolution bathymetry gathered by an autonomous underwater vehicle operating beneath an Antarctic ice shelf, which provides evidence of long-term change in Pine Island Glacier. Corrugations and ploughmarks on a sub-ice shelf ridge that was a former grounding line closely resemble those observed offshore, interpreted previously as the result of iceberg grounding. The same interpretation here would indicate a significantly reduced ice shelf extent within the last 11 kyr, implying Holocene glacier retreat beyond present limits, or a past tidewater glacier regime different from today. The alternative, that corrugations were not formed in open water, would question ice shelf collapse events interpreted from the geological record, revealing detail of another bed-shaping process occurring at glacier margins. We assess hypotheses for corrugation formation and suggest periodic grounding of ice shelf keels during glacier unpinning as a viable origin. This interpretation requires neither loss of the ice shelf nor glacier retreat and is consistent with a "stable" grounding-line configuration throughout the Holocene.
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- 2013
185. Deglaciation of the West Antarctic continental shelf in the Amundsen Sea sector since the Last Glacial Maximum
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Hillenbrand, Claus-Dieter, Smith, James A., Kuhn, Gerhard, Poole, Chris, Hodell, David A., Elderfield, H., Kender, Sev, Williams, Mark, Peck, Viktoria, Larter, Robert D., Klages, Johann Philipp, Graham, Alastair G. C., Forwick, Matthias, and Gohl, Karsten
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- 2013
186. Bathymetric controls on calving processes at Pine Island Glacier.
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Arndt, Jan Erik, Larter, Robert D., Friedl, Peter, Gohl, Karsten, Höppner, Kathrin, and the Science Team of Expedition PS104
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CATTLE parturition , *SEA level , *ICE shelves , *BATHYMETRY , *FLUCTUATIONS (Physics) - Abstract
Pine Island Glacier is the largest current Antarctic contributor to sea-level rise. Its ice loss has substantially increased over the last 25 years through thinning, acceleration and grounding line retreat. However, the calving line positions of the stabilising ice shelf did not show any trend within the observational record (last 70 years) until calving in 2015 led to unprecedented retreat and changed the alignment of the calving front. Bathymetric surveying revealed a ridge below the former ice shelf and two shallower highs to the north. Satellite imagery shows that ice contact on the ridge was likely lost in 2006 but was followed by intermittent contact resulting in back stress fluctuations on the ice shelf. Continuing ice-shelf flow also led to occasional ice-shelf contact with the northern bathymetric highs, which initiated rift formation that led to calving. The observations show that bathymetry is an important factor in initiating calving events. [ABSTRACT FROM AUTHOR]
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- 2018
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187. Pre-Holocene to recent deglaciation of the Amundsen Sea Embayment, West Antarctica
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Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Klages, Johann Philipp, Smith, James A., Graham, Alastair G. C., Larter, Robert D., and Gohl, Karsten
- Abstract
Ice loss from the marine-based, inherently unstable West Antarctic Ice Sheet (WAIS) contributes to the currently observed rise in sea-level and may raise it by up to 3.3-5 metres in the future. Over the last few decades, glaciers draining the WAIS into the Amundsen Sea Embayment (ASE), in particular into Pine Island Bay, have shown thinning, grounding-line retreat and ice-flow acceleration at dramatic rates. These changes are mainly attributed to significant ice-shelf melting by upwelling warm deep water. A critical unknown, limiting our ability to accurately predict future WAIS behaviour, is the poorly constrained long-term context of ice-sheet retreat in the ASE. Here we present a new pre-Holocene to present chronology for WAIS retreat in Pine Island Bay (PIB) based on radiocarbon dating of marine sediment cores. The dates give evidence that grounded ice had retreated close to its modern-day position by ~10 ka BP. Maximum average retreat rates calculated from the deglaciation ages suggest, that the current rapid WAIS retreat in Pine Island Bay is unprecedented over the last ~10 ka and originates in recent changes in regional climate, ocean circulation or ice-sheet dynamics. However, our data and previously published ages for grounding-line retreat from the wider ASE further demonstrate, that, other than in the Ross Sea, the WAIS did not retreat continuously since the LGM. A unique assemblage of glacial morphological features mapped on the eastern ASE shelf suggest a more complex deglacial history, with ice masses slowly flowing and/or stagnating on topographic highs (’Inter-ice stream ridges’) adjacent to main palaeo-ice stream troughs. The incorporation of our results into ice-sheet models will improve predictions of future sea-level rise.
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- 2012
188. Insights into post-LGM deglaciation at the margins of the Pine Island-Thwaites Palaeo-Ice Stream in the Amundsen Sea Embayment, West Antarctica
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Klages, Johann Philipp, Kuhn, Gerhard, Gohl, Karsten, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., and Larter, Robert D.
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During recent years interest in the West Antarctic Ice Sheet (WAIS) increased among the geoscientific community because: (1) its bed is located mainly below sea level and drops towards the interior of the Antarctic continent, making the WAIS inherently unstable in a future warming world, (2) extensive thinning and associated grounding-line retreat of the Pine Island and Thwaites glaciers draining into the Amundsen Sea Embayment (ASE) have suggested major changes are underway in the sector, increasing contributions to current sea level rise, (3) a complete collapse of the WAIS in the future would raise global eustatic sea level by 3.4-5 m, while melting of the ASE drainiage basin alone would raise sea level by 1.2-1.5 m. A sea level rise of that magnitude would cause major global socio-economical and ecological problems. Detailed knowledge of the long-term behaviour of the WAIS in the ASE during the recent geological past (Last Glacial Maximum [LGM] to present) will contribute to a better understanding of current glacier dynamics and help to improve numerical ice-sheet models, which aim to predict future sea-level rise. Previous marine geoscientific studies in the ASE focused on the main palaeo-ice stream troughs to reconstruct the LGM extent of the WAIS on the continental shelf and its subsequent retreat history. However, little is known about elevated marinal areas of the palaeo-ice streams in the ASE, where ice retreat most likely lagged behind that in the troughs. Here we present results from multibeam swath bathymetry surveys, high-resolution seismic and sedimentological investigations from the former bed in an inter-ice stream area between the Pine Island-Thwaites palaeo-ice stream and a fast-flow tributary emanating from the area now occupied by the Cosgrove Ice Shelf. The data show an unusual assemblage of glacial morphological features including crevasse-squeeze ridges, large-scale hummocks perpendicular to the palaeo-ice flow, associated recessional moraines, and hill-hole pairs. This combination of bedforms has not been described before from the Antarctic shelf and indicates a more complex ice flow behaviour for the eastern ASE than suggested by the pattern of bedforms in the palaeo-ice stream troughs alone. Our data indicate that slow flowing ice masses covered the topographical highs adjacent to the Pine Island-Thwaites palaeo-ice stream (PITPIS) during the LGM. These ice masses most likely stagnated during a phase of general stillstand of the PITPIS. Here we introduce a six-phase formation model based on these interpretations. New radiocarbon ages indicate a pre-Holocene deglaciation of the inter-ice stream ridge between ~11.6 and 16 ka BP. This new information can be used as a reference dataset for interpreting more inter-ice stream areas in future studies, since they are key areas for stabilising ice streams, and form a large part of the ice sheet in general. New insights into ice dynamics here may help improve ice flow models.
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- 2012
189. The Discovery of New Deep-Sea Hydrothermal Vent Communities in the Southern Ocean and Implications for Biogeography
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Eisen, Jonathan, Rogers, Alex, Tyler, Paul, Connelly, Douglas, Copley, Jon, James, Rachael, Larter, Robert, Linse, Katrin, Mills, Rachel, Garabato, Alfredo Naveira, Pancost, Richard, Pearce, David, Polunin, Nicholas, German, Christopher, Shank, Timothy, Boersch-Supan, Philipp, Alker, Belinda, Aquilina, Alfred, Bennett, Sarah, Clarke, Andrew, Dinley, Robert, Graham, Alastair, Green, Darryl, Hawkes, Jeffrey, Hepburn, Laura, Hilario, Ana, Huvenne, Veerle, Marsh, Leigh, Ramirez-Llodra, Eva, Reid, William, Roterman, Christopher, Sweeting, Christopher, Thatje, Sven, Zwirglmaier, Katrin, University of St Andrews. School of Biology, and University of St Andrews. Scottish Oceans Institute
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0106 biological sciences ,Ecophysiology ,Gastropoda ,Mid-Atlantic Ridge ,Molecular phylogeny ,Animal Phylogenetics ,01 natural sciences ,Kiwaidae ,Crustacea ,Decapoda ,RNA, Ribosomal, 16S ,Oceans ,RNA, Ribosomal, 28S ,QE ,Morphological evidence ,Community Assembly ,Hydrogen Sulfide ,Biology (General) ,Phylogeny ,Chemosynthesis ,0303 health sciences ,biology ,Ecology ,Geography ,General Neuroscience ,Marine Ecology ,Temperature ,Geology ,Biodiversity ,Marine Technology ,Biogeochemistry ,Hydrogen-Ion Concentration ,C700 ,Biota ,Plate Tectonics ,Antarctic Ocean ,Community Ecology ,Biogeography ,Spreading Centers ,Ocean Ridges ,General Agricultural and Biological Sciences ,Marine Geology ,Hydrothermal vent ,Mid-atlantic ridge ,Research Article ,QH301-705.5 ,Siboglinidae ,Evolution ,Oceans and Seas ,Molecular Sequence Data ,Sequence data ,Antarctic Regions ,Marine Biology ,010603 evolutionary biology ,Deep sea ,Microbiology ,General Biochemistry, Genetics and Molecular Biology ,West Pacific ,Microbial Ecology ,Electron Transport Complex IV ,03 medical and health sciences ,Bransfield Strait ,Extremophiles ,Hydrothermal Vents ,Species Specificity ,RNA, Ribosomal, 18S ,Animal Physiology ,Animals ,Seawater ,14. Life underwater ,SDG 14 - Life Below Water ,Biology ,Ecosystem ,030304 developmental biology ,Polychaete ,General Immunology and Microbiology ,East scotia ridge ,Marine ,Bacteria ,Sodium ,Sequence Analysis, DNA ,biology.organism_classification ,Astrobiology ,Invertebrates ,Marine and aquatic sciences ,Marine Sciences ,QE Geology ,Earth sciences ,Geochemistry ,13. Climate action ,Evolutionary Ecology ,Zoology - Abstract
Rogers, Alex D. ... et. al.-- 17 pages, 6 figures, 2 tables, supporting information in https://doi.org/10.1371/journal.pbio.1001234, Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised. © 2012 Rogers et al., The ChEsSo research programme was funded by a NERC Consortium Grant (NE/DO1249X/1) and supported by the Census of Marine Life and the Sloan Foundation, and the Total Foundation for Biodiversity (Abyss 2100)(SVTH) all of which are gratefully acknowledged. We also acknowledge NSF grant ANT-0739675 (CG and TS), NERC PhD studentships NE/D01429X/1(LH, LM, CNR), NE/H524922/1(JH) and NE/F010664/1 (WDKR), a Cusanuswerk doctoral fellowship, and a Lesley & Charles Hilton-Brown Scholarship, University of St. Andrews (PHBS)
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- 2012
190. Reconstruction of changes in the Weddell Sea sector of the Antarctic Ice Sheet since the Last Glacial Maximum
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Hillenbrand, Claus-Dieter, Bentley, Michael J., Stolldorf, Travis D., Hein, Andrew S., Kuhn, Gerhard, Graham, Alastair G. C., Fogwill, Christopher J., Kristoffersen, Yngve, Smith, James A., Anderson, John B., Larter, Robert D., Melles, Martin, Hodgson, Dominic A., Mulvaney, Robert, Sugden, David E., Hillenbrand, Claus-Dieter, Bentley, Michael J., Stolldorf, Travis D., Hein, Andrew S., Kuhn, Gerhard, Graham, Alastair G. C., Fogwill, Christopher J., Kristoffersen, Yngve, Smith, James A., Anderson, John B., Larter, Robert D., Melles, Martin, Hodgson, Dominic A., Mulvaney, Robert, and Sugden, David E.
- Abstract
The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica's continental ice volume. Over the last few decades, studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23-19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on the Weddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different ice-sheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sea-level low-stand of similar to 130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past ice-sheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post-LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. T
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- 2014
191. Bathymetry and geological setting of the South Sandwich Islands Volcanic Arc
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Leat, Philip T., Fretwell, Peter T., Tate, Alex J., Larter, Robert D., Martin, T.J., Smellie, J.K., Jokat, W., Bohrmann, G., Leat, Philip T., Fretwell, Peter T., Tate, Alex J., Larter, Robert D., Martin, T.J., Smellie, J.K., Jokat, W., and Bohrmann, G.
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- 2014
192. Reconstruction of ice-sheet changes in the Antarctic Peninsula since the Last Glacial Maximum
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Ó Cofaigh, Colm, Davies, Bethan J., Livingstone, Stephen J., Smith, James A., Johnson, Joanne S., Hocking, Emma P., Hodgson, Dominic A., Anderson, John B., Bentley, Michael J., Canals, Miquel, Domack, Eugene, Dowdeswell, Julian A., Evans, Jeffrey, Glasser, Neil F., Hillenbrand, Claus-Dieter, Larter, Robert D., Roberts, Stephen J., Simms, Alexander R., Ó Cofaigh, Colm, Davies, Bethan J., Livingstone, Stephen J., Smith, James A., Johnson, Joanne S., Hocking, Emma P., Hodgson, Dominic A., Anderson, John B., Bentley, Michael J., Canals, Miquel, Domack, Eugene, Dowdeswell, Julian A., Evans, Jeffrey, Glasser, Neil F., Hillenbrand, Claus-Dieter, Larter, Robert D., Roberts, Stephen J., and Simms, Alexander R.
- Abstract
This paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the Antarctic Peninsula Ice Sheet (APIS) from the Last Glacial Maximum (LGM) through deglaciation to the present day. These data are used to reconstruct grounding-line retreat in 5 ka time-steps from 25 ka BP to present. Glacial landforms and subglacial tills on the eastern and western Antarctic Peninsula (AP) shelf indicate that the APIS was grounded to the outer shelf/shelf edge at the LGM and contained a series of fast-flowing ice streams that drained along cross-shelf bathymetric troughs. The ice sheet was grounded at the shelf edge until ∼20 cal ka BP. Chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains, as well as cosmogenic nuclide dates on erratics and ice moulded bedrock. Retreat in the east was underway by about 18 cal ka BP. The earliest dates on recession in the west are from Bransfield Basin where recession was underway by 17.5 cal ka BP. Ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid-shelf. The timing of initial retreat decreased progressively southwards along the western AP shelf; the large ice stream in Marguerite Trough may have remained grounded at the shelf edge until about 14 cal ka BP, although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka BP. Between 15 and 10 cal ka BP the APIS underwent significant recession along the western AP margin, although retreat between individual troughs was asynchronous. Ice in Marguerite Trough may have still been grounded on the mid-shelf at 10 cal ka BP. In the Larsen-A region the transition from grounded to floating ice was established by 10.7–10.6 cal ka BP. The APIS had retreated towards its present configuration in the western AP by the mid-Holocene but on the eastern peninsula may have approached its pre
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- 2014
193. New constraints on the timing of West Antarctic ice sheet retreat in the eastern Amundsen Sea since the Last Glacial Maximum
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Smith, James A., Hillenbrand, Claus-Dieter, Kuhn, Gerard, Klages, Johann Phillip, Graham, Alastair C.G., Larter, Robert D., Ehrmann, Werner, Moreton, Steven G., Wiers, Steffen, Smith, James A., Hillenbrand, Claus-Dieter, Kuhn, Gerard, Klages, Johann Phillip, Graham, Alastair C.G., Larter, Robert D., Ehrmann, Werner, Moreton, Steven G., and Wiers, Steffen
- Abstract
Glaciers flowing into the Amundsen Sea Embayment (ASE) account for > 35% of the total discharge of the West Antarctic Ice Sheet (WAIS) and have thinned and retreated dramatically over the past two decades. Here we present detailed marine geological data and an extensive new radiocarbon dataset from the eastern ASE in order to constrain the retreat of the WAIS since the Last Glacial Maximum (LGM) and assess the significance of these recent changes. Our dating approach, relying mainly on the acid insoluble organic (AIO) fraction, utilises multi-proxy analyses of the sediments to characterise their lithofacies and determine the horizon in each core that would yield the most reliable age for deglaciation. In total, we dated 69 samples and show that deglaciation of the outer shelf was underway before 20,600 calibrated years before present (cal yr BP), reaching the mid-shelf by 13,575 cal yr BP and the inner shelf to within ca. 150 km of the present grounding line by 10,615 cal yr BP. The timing of retreat is broadly consistent with previously published radiocarbon dates on biogenic carbonate from the eastern ASE as well as AIO 14C ages from the western ASE and provides new constraints for ice sheet models. The overall retreat trajectory – slow on the outer shelf, more rapid from the middle to inner shelf – clearly highlights the importance of reverse bedslopes in controlling phases of accelerated groundling line retreat. Despite revealing these broad scale trends, the current dataset does not capture detailed changes in ice flow, such as stillstands during grounding line retreat (i.e., deposition of grounding zone wedges) and possible readvances as depicted in the geomorphological record.
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- 2014
194. A new bathymetric compilation for the South Orkney Islands, Antarctic Peninsula (49°-39°W to 64°-59°S): insights into the glacial development of the continental shelf
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Dickens, William A., Graham, Alastair G. C., Smith, James A., Dowdeswell, Julian A., Larter, Robert D., Hillenbrand, Claus-Dieter, Trathan, Phil N., Arndt, Jan Erik, Kuhn, Gerard, Dickens, William A., Graham, Alastair G. C., Smith, James A., Dowdeswell, Julian A., Larter, Robert D., Hillenbrand, Claus-Dieter, Trathan, Phil N., Arndt, Jan Erik, and Kuhn, Gerard
- Abstract
We present a new, high resolution (300 m) bathymetric grid of the continental shelf surrounding the South Orkney Islands, northeast of the Antarctic Peninsula. The new grid, derived from a compilation of marine echo-sounding data, improves previous regional bathymetric representations and helps to visualize the morphology of the shelf in unrivalled detail. The compilation forms important baseline information for a range of scientific applications and end users including oceanographers, glacial modelers, biologists, and geologists. In particular, due to the limited understanding of glacial history in this region, the bathymetry provides the first detailed insights into past glacial regimes. The continental shelf is dominated by seven glacially eroded troughs, marking the pathways of glacial outlets that once drained a former ice cap centered on the South Orkney Islands. During previous glacial periods, grounded ice extended to the shelf edge north of the islands. A large, ∼250 km long sediment depocenter, interpreted as a maximum former ice limit of one or more Cenozoic glaciations, suggests that ice was only grounded to the ∼300–350 m contour in the south. Hypsometric analyses support this interpretation, indicating that a significant proportion of the shelf has been unaffected by glacial erosion. Using these observations, we propose a preliminary ice cap reconstruction for maximum glaciation of the South Orkney plateau, suggesting an ice coverage of about ∼19,000 km2. The timing of maximum ice extent, number of past advances and pattern of subsequent deglaciation(s) remain uncertain and will require further targeted marine geological and geophysical investigations to resolve.
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- 2014
195. Reconstruction of changes in the Amundsen Sea and Bellingshausen Sea sector of the West Antarctic Ice Sheet since the Last Glacial Maximum
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Larter, Robert D., Anderson, John B., Graham, Alastair G.C., Gohl, Karsten, Hillenbrand, Claus-Dieter, Jakobsson, Martin, Johnson, Joanne S., Kuhn, Gerhard, Nitsche, Frank O., Smith, James A., Witus, Alexandra E., Bentley, Michael J., Dowdeswell, Julian A., Ehrmann, Werner, Klages, Johann P., Lindow, Julia, Cofaigh, Colm Ó, Spiegel, Cornelia, Larter, Robert D., Anderson, John B., Graham, Alastair G.C., Gohl, Karsten, Hillenbrand, Claus-Dieter, Jakobsson, Martin, Johnson, Joanne S., Kuhn, Gerhard, Nitsche, Frank O., Smith, James A., Witus, Alexandra E., Bentley, Michael J., Dowdeswell, Julian A., Ehrmann, Werner, Klages, Johann P., Lindow, Julia, Cofaigh, Colm Ó, and Spiegel, Cornelia
- Abstract
Marine and terrestrial geological and marine geophysical data that constrain deglaciation since the Last Glacial Maximum (LGM) of the sector of the West Antarctic Ice Sheet (WAIS) draining into the Amundsen Sea and Bellingshausen Sea have been collated and used as the basis for a set of time-slice reconstructions. The drainage basins in these sectors constitute a little more than one-quarter of the area of the WAIS, but account for about one-third of its surface accumulation. Their mass balance is becoming increasingly negative, and therefore they account for an even larger fraction of current WAIS discharge. If all of the ice in these sectors of the WAIS were discharged to the ocean, global sea level would rise by ca 2 m. There is compelling evidence that grounding lines of palaeo-ice streams were at, or close to, the continental shelf edge along the Amundsen Sea and Bellingshausen Sea margins during the last glacial period. However, the few cosmogenic surface exposure ages and ice core data available from the interior of West Antarctica indicate that ice surface elevations there have changed little since the LGM. In the few areas from which cosmogenic surface exposure ages have been determined near the margin of the ice sheet, they generally suggest that there has been a gradual decrease in ice surface elevation since pre-Holocene times. Radiocarbon dates from glacimarine and the earliest seasonally open marine sediments in continental shelf cores that have been interpreted as providing approximate ages for post-LGM grounding-line retreat indicate different trajectories of palaeo-ice stream recession in the Amundsen Sea and Bellingshausen Sea embayments. The areas were probably subject to similar oceanic, atmospheric and eustatic forcing, in which case the differences are probably largely a consequence of how topographic and geological factors have affected ice flow, and of topographic influences on snow accumulation and warm water inflow across the continental sh
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- 2014
196. A new bathymetric compilation for the South Orkney Islands region, Antarctic Peninsula (49°–39°W to 64°–59°S): Insights into the glacial development of the continental shelf
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Dickens, William A., Graham, Alastair G. C., Smith, James A., Dowdeswell, Julian A., Larter, Robert D., Hillenbrand, Claus-Dieter, Trathan, Phil N., Arndt, Jan Erik, Kuhn, Gerhard, Dickens, William A., Graham, Alastair G. C., Smith, James A., Dowdeswell, Julian A., Larter, Robert D., Hillenbrand, Claus-Dieter, Trathan, Phil N., Arndt, Jan Erik, and Kuhn, Gerhard
- Abstract
We present a new, high resolution (300 m) bathymetric grid of the continental shelf surrounding the South Orkney Islands, northeast of the Antarctic Peninsula. The new grid, derived from a compilation of marine echo-sounding data, improves previous regional bathymetric representations and helps to visualize the morphology of the shelf in unrivalled detail. The compilation forms important baseline information for a range of scientific applications and end users including oceanographers, glacial modelers, biologists, and geologists. In particular, due to the limited understanding of glacial history in this region, the bathymetry provides the first detailed insights into past glacial regimes. The continental shelf is dominated by seven glacially eroded troughs, marking the pathways of glacial outlets that once drained a former ice cap centered on the South Orkney Islands. During previous glacial periods, grounded ice extended to the shelf edge north of the islands. A large, ∼250 km long sediment depocenter, interpreted as a maximum former ice limit of one or more Cenozoic glaciations, suggests that ice was only grounded to the ∼300–350 m contour in the south. Hypsometric analyses support this interpretation, indicating that a significant proportion of the shelf has been unaffected by glacial erosion. Using these observations, we propose a preliminary ice cap reconstruction for maximum glaciation of the South Orkney plateau, suggesting an ice coverage of about ∼19,000 km2. The timing of maximum ice extent, number of past advances and pattern of subsequent deglaciation(s) remain uncertain and will require further targeted marine geological and geophysical investigations to resolve.
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- 2014
197. Revealing potential past collapses of the West Antarctic Ice Sheet - Upcoming drilling in the Amundsen Sea Embayment
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Kuhn, Gerhard, Gohl, Karsten, Uenzelmann-Neben, Gabriele, Bickert, Thorsten, Schulz, Michael, Larter, Robert D., Hillenbrand, Claus-Dieter, Kuhn, Gerhard, Gohl, Karsten, Uenzelmann-Neben, Gabriele, Bickert, Thorsten, Schulz, Michael, Larter, Robert D., and Hillenbrand, Claus-Dieter
- Abstract
The West Antarctic Ice-Sheet (WAIS) is likely to have been subject to very dynamic changes during its history as most of its base is grounded below modern sea-level, making it particularly sensitive to climate changes. Its collapse would result in global sea-level rise of 3-5 m. The reconstruction and quantification of possible partial or full collapses of the WAIS in the past can provide important constraints for ice-sheet models, used for projecting its future behaviour and resulting sea-level rise. Large uncertainties exist regarding the chronology, extent, rates as well as spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves. By using the seafloor drilling device MeBo during an RV Polarstern cruise scheduled for early 2015, a series of sediment cores will be drilled on the Amundsen Sea Embayment (ASE) shelf, where seismic data show glacially-derived sequences covered by only a thin veneer of postglacial deposits in some areas. From analyses of seismic data, we infer that interglacial sediments can be sampled which may have been deposited under seasonally open water conditions and thus contain datable microfossil-bearing material. A shallow basin near the Pine Island Glacier front will be one of the prime targets for the drilling. The near-horizontal seismic reflection horizons may represent a sequence of continuously deposited, mainly terrigenous material, including ice-rafted debris, meltwater deposits and hemipelagic sediments deposited rapidly during the Holocene or a series of unconformities caused by erosion resulting from grounding line oscillations through many glacial cycles. Subglacial bedforms imaged in multibeam bathymetric data indicate fast glacial flow over some shelf areas of the ASE, where seismic profiles show acoustic basement near the seafloor. It is unknown, whether fast ice-flow in these areas was facilitated by water-lubricated sliding over bedrock or presence of a thin layer of deformabl
- Published
- 2014
198. Retreat of the West Antarctic Ice Sheet from the western Amundsen Sea shelf at a pre- or early LGM stage
- Author
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Klages, Johann Philipp, Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., Larter, Robert D., Gohl, Karsten, Wacker, Lukas, Klages, Johann Philipp, Kuhn, Gerhard, Hillenbrand, Claus-Dieter, Graham, Alastair G. C., Smith, James A., Larter, Robert D., Gohl, Karsten, and Wacker, Lukas
- Abstract
Recent palaeoglaciological studies on the West Antarctic shelf have mainly focused on the wide embayments of the Ross and Amundsen seas in order to reconstruct the extent and subsequent retreat of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum (LGM). However, the narrower shelf sectors between these two major embayments have remained largely unstudied in previous geological investigations despite them covering extensive areas of the West Antarctic shelf. Here, we present the first systematic marine geological and geophysical survey of a shelf sector offshore from the Hobbs Coast. It is dominated by a large grounding zone wedge (GZW), which fills the base of a palaeo-ice stream trough on the inner shelf and marks a phase of stabilization of the grounding line during general WAIS retreat following the last maximum ice-sheet extent in this particular area (referred to as the Local Last Glacial Maximum, ‘LLGM’). Reliable age determination on calcareous microfossils from the infill of a subglacial meltwater channel eroded into the GZW reveals that grounded ice had retreated landward of the GZW before ∼20.88 cal. ka BP, with deglaciation of the innermost shelf occurring prior to ∼12.97 cal. ka BP. Geophysical sub-bottom information from the inner-, mid- and outer shelf indicates grounded ice extended to the shelf edge prior to the formation of the GZW. Assuming the wedge was deposited during deglaciation, we infer the timing of maximum grounded ice extent occurred before ∼20.88 cal. ka BP. This could suggest that the WAIS retreat from the outer shelf was already underway during or even prior to the global LGM (∼23–19 cal. ka BP). Our new findings give insights into the regional deglacial behaviour of this understudied part of the West Antarctic shelf and at the same time support early deglaciation ages recently presented for adjacent drainage sectors of the WAIS. If correct, these findings contrast with the hypothesis that initial deglaciation of Antar
- Published
- 2014
199. Rapid thinning of Pine Island Glacier in the early Holocene
- Author
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Johnson, Joanne S., Bentley, Michael J., Smith, James A., Finkel, R. C., Rood, D. H., Gohl, Karsten, Balco, G., Larter, Robert D., Schaefer, J. M., Johnson, Joanne S., Bentley, Michael J., Smith, James A., Finkel, R. C., Rood, D. H., Gohl, Karsten, Balco, G., Larter, Robert D., and Schaefer, J. M.
- Abstract
Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet, has been undergoing rapid thinning and retreat for the past two decades. We demonstrate, using glacial-geological and geochronological data, that Pine Island Glacier (PIG) also experienced rapid thinning during the early Holocene, around 8000 years ago. Cosmogenic 10Be concentrations in glacially transported rocks show that this thinning was sustained for decades to centuries at an average rate of more than 100 centimeters per year, which is comparable with contemporary thinning rates. The most likely mechanism was a reduction in ice shelf buttressing. Our findings reveal that PIG has experienced rapid thinning at least once in the past and that, once set in motion, rapid ice sheet changes in this region can persist for centuries.
- Published
- 2014
200. A new bathymetric compilation highlighting extensive paleo-ice sheet drainage on the continental shelf, South Georgia, sub-Antarctica
- Author
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Graham, Alastair G.C., Fretwell, Peter T., Larter, Robert D., Hodgson, Dominic A., Wilson, Christian K., Tate, Alexander James, and Morris, Peter
- Subjects
Glaciology ,Earth Sciences - Abstract
A grid derived from a new compilation of marine echo-sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around South Georgia at an unprecedented level of detail. The grid is the first continuous bathymetric data set covering South Georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution. Large and previously undescribed glacially eroded troughs, linked to South Georgia's modern-day fjords, radiate from the island, marking the former pathways of large outlet glaciers and ice streams. A tectonic or geological influence is apparent for the major troughs, where glaciers have exploited structural weaknesses on the continental block. Bed forms lining the troughs give some first insights into glacial dynamics within the troughs, suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates. On the outer shelf and within the troughs, large ridges and banks are also common, interpreted as terminal, lateral, and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation. A small trough mouth fan has developed at the mouth of at least one of the cross-shelf troughs, demonstrating a focused sediment delivery to the margin. Slides and slide scars are also present on parts of the margin, showing that margin stability, perhaps also related to glaciation, has been an important factor in depositional processes on the continental slope. Implications of the new observations are that ice sheets have been more extensive on South Georgia than any previous studies have reported. Their age may date back to late Miocene times, and evolution of the shelf system has probably involved numerous late Cenozoic glacial episodes. However, relatively fresh seafloor geomorphology coupled with evidence from other maritime-Antarctic islands (Heard Island and Kerguelen Island) indicating extensive glaciation at the Last Glacial Maximum raises the possibility that the extent of sub-Antarctic glaciation for the Last Glacial period has, until now, been underestimated.
- Published
- 2008
- Full Text
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