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Author: Jason James Coenen Publisher: ISBN: 9781369139457 Category : Ice sheets Languages : en Pages : 211
Book Description
In January of 2013 and 2015 the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) science team collected sediment cores from Subglacial Lake Whillans (SLW), and the Whillans Grounding Zone (WGZ) which are both part of the Whillans Ice Stream (WIS) in West Antarctica. These sediment cores along with sediment samples from the California Institute of Technology (Caltech) Glaciology group, which include sediments from Kamb Ice Stream (KIS) and Bindschadler Ice Stream (BIS) are compared with published micropaleontological data from the WIS Upstream B camp (UpB), the Crary Ice Rise (CIR) and the Ross Ice Shelf Project (RISP), using observations on preservation of microfossils in these deposits. Diatoms and other microfossils provide biostratigraphic and paleoenvironmental constraints on past marine deposition in West Antarctica interior basins, as well as inferences regarding ice stream erosion, particulate provenance and glacial mixing. Most subglacial samples contain a mixture of eroded diatoms that reflect initial deposition throughout the Cenozoic. Pleistocene diatoms are widespread but never abundant, reflecting erosion of marine sediments deposited in the West Antarctic marine basin during Quaternary ice sheet retreat events. Geologic drilling near Ross Island (the ANDRILL McMurdo Ice Shelf Project) provided abundant evidence for Pliocene and early Pleistocene retreat of the West Antarctic Ice Sheet, yet Pliocene diatoms are rare in sediments recovered from beneath grounded ice, which suggests erosion of Pliocene deposits in the Ross Embayment. Miocene age diatoms are dominant in subglacial and sub-ice shelf deposits, reflecting extensive Miocene deposition in the basin prior to entering a dominantly glacial phase. Additionally, Paleogene fossils, both marine and non-marine, occur widely, reflecting deeper erosion and providing insights into earlier basin history. SLW contains Upper Miocene fossils with a mix of younger and older taxa. These ages and taxa are consistent with previously published results from samples recovered ~200 km upstream from the UpB sites, suggesting a connection between the sites with little evidence of new subglacial erosion of material. Diatom abundance is on average lower than UpB in samples, suggesting sediments at SLW have experienced additional cumulative shearing and transport. WGZ cores exhibit stratigraphic variation in microfossil abundance as well as a transition in age dominance of taxa. Four lithostratigraphic units were observed in grounding zone cores, but a fifth unit is recognized based on microfossil data. Unit I is thought to be rain out from the base of the debris rich ice, which has a dominant Upper Miocene assemblage. Unit II is described as subglacial and is dominated by long ranging taxa, with a mix of younger material. Unit III is thought to be sub-ice shelf, which is consistent with diatomite microclasts (silt-sized aggregates) and a radiolarian that has a Late Pleistocene diatom assemblage. Unit IV is described as subglacial, based on the lithostratigraphy, however, microfossils are well-preserved, allowing definition of subunits, Unit IV-B and Unit IV-A. The stratigraphic variability at the grounding zone indicates changes in sediment provenance, indicating a variable glaciological regime, which suggesting a dynamic grounding line. Higher overall diatom abundance at WGZ indicates less cumulative glacial shear strain within the sediments than in SLW and UpB tills. KIS is one of the ice streams on the Siple Coast that has been shut down for the last 150 years. Most KIS sediments contain Upper Miocene fossils that are relatively unmixed and well-preserved, containing an order to two orders of magnitude higher diatom abundance than for all WIS samples. An exception is one sample from the KIS sticky spot (SS) that has low abundance and poor preservation indicating high cumulative shear strain. The unmixed Upper Miocene assemblage and preservation of the rest of these samples suggests close proximity to Miocene source rocks at this site. BIS is the northern-most active ice stream from this study in the Siple Coast area. These deposits contain no microfossils younger than Oligocene, suggesting tectonic processes, subglacial processes or change in source for this area. The age transition is also observed in other microfossil groups, which likely indicates a different source of sediments for BIS. Paleogene microfossils at this site are well preserved and relatively abundant. Biostratigraphic characterization of the Ross Embayment using age-specific diatoms help constrain basin scale productivity events that are linked to warm interglacial periods. Assessing when these events happened and diatom fragmentation patterns from different subglacial environments adds new insights into sediment-ice interactions and modern subglacial processes.
Author: Jason James Coenen Publisher: ISBN: 9781369139457 Category : Ice sheets Languages : en Pages : 211
Book Description
In January of 2013 and 2015 the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) science team collected sediment cores from Subglacial Lake Whillans (SLW), and the Whillans Grounding Zone (WGZ) which are both part of the Whillans Ice Stream (WIS) in West Antarctica. These sediment cores along with sediment samples from the California Institute of Technology (Caltech) Glaciology group, which include sediments from Kamb Ice Stream (KIS) and Bindschadler Ice Stream (BIS) are compared with published micropaleontological data from the WIS Upstream B camp (UpB), the Crary Ice Rise (CIR) and the Ross Ice Shelf Project (RISP), using observations on preservation of microfossils in these deposits. Diatoms and other microfossils provide biostratigraphic and paleoenvironmental constraints on past marine deposition in West Antarctica interior basins, as well as inferences regarding ice stream erosion, particulate provenance and glacial mixing. Most subglacial samples contain a mixture of eroded diatoms that reflect initial deposition throughout the Cenozoic. Pleistocene diatoms are widespread but never abundant, reflecting erosion of marine sediments deposited in the West Antarctic marine basin during Quaternary ice sheet retreat events. Geologic drilling near Ross Island (the ANDRILL McMurdo Ice Shelf Project) provided abundant evidence for Pliocene and early Pleistocene retreat of the West Antarctic Ice Sheet, yet Pliocene diatoms are rare in sediments recovered from beneath grounded ice, which suggests erosion of Pliocene deposits in the Ross Embayment. Miocene age diatoms are dominant in subglacial and sub-ice shelf deposits, reflecting extensive Miocene deposition in the basin prior to entering a dominantly glacial phase. Additionally, Paleogene fossils, both marine and non-marine, occur widely, reflecting deeper erosion and providing insights into earlier basin history. SLW contains Upper Miocene fossils with a mix of younger and older taxa. These ages and taxa are consistent with previously published results from samples recovered ~200 km upstream from the UpB sites, suggesting a connection between the sites with little evidence of new subglacial erosion of material. Diatom abundance is on average lower than UpB in samples, suggesting sediments at SLW have experienced additional cumulative shearing and transport. WGZ cores exhibit stratigraphic variation in microfossil abundance as well as a transition in age dominance of taxa. Four lithostratigraphic units were observed in grounding zone cores, but a fifth unit is recognized based on microfossil data. Unit I is thought to be rain out from the base of the debris rich ice, which has a dominant Upper Miocene assemblage. Unit II is described as subglacial and is dominated by long ranging taxa, with a mix of younger material. Unit III is thought to be sub-ice shelf, which is consistent with diatomite microclasts (silt-sized aggregates) and a radiolarian that has a Late Pleistocene diatom assemblage. Unit IV is described as subglacial, based on the lithostratigraphy, however, microfossils are well-preserved, allowing definition of subunits, Unit IV-B and Unit IV-A. The stratigraphic variability at the grounding zone indicates changes in sediment provenance, indicating a variable glaciological regime, which suggesting a dynamic grounding line. Higher overall diatom abundance at WGZ indicates less cumulative glacial shear strain within the sediments than in SLW and UpB tills. KIS is one of the ice streams on the Siple Coast that has been shut down for the last 150 years. Most KIS sediments contain Upper Miocene fossils that are relatively unmixed and well-preserved, containing an order to two orders of magnitude higher diatom abundance than for all WIS samples. An exception is one sample from the KIS sticky spot (SS) that has low abundance and poor preservation indicating high cumulative shear strain. The unmixed Upper Miocene assemblage and preservation of the rest of these samples suggests close proximity to Miocene source rocks at this site. BIS is the northern-most active ice stream from this study in the Siple Coast area. These deposits contain no microfossils younger than Oligocene, suggesting tectonic processes, subglacial processes or change in source for this area. The age transition is also observed in other microfossil groups, which likely indicates a different source of sediments for BIS. Paleogene microfossils at this site are well preserved and relatively abundant. Biostratigraphic characterization of the Ross Embayment using age-specific diatoms help constrain basin scale productivity events that are linked to warm interglacial periods. Assessing when these events happened and diatom fragmentation patterns from different subglacial environments adds new insights into sediment-ice interactions and modern subglacial processes.
Author: Martin J. Siegert Publisher: John Wiley & Sons ISBN: 1118671481 Category : Science Languages : en Pages : 642
Book Description
Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 192. Antarctic Subglacial Aquatic Environments is the first volume on this important and fascinating subject. With its underlying theme of bridging existing knowledge to future research, it is a benchmark in the history of subglacial lake exploration and study, containing up-to-date discussions about the history and background of subglacial aquatic environments and future exploration. The main topics addressed are identification, location, physiography, and hydrology of 387 subglacial lakes; protocols for environmental stewardship and protection of subglacial lake environments; details of three programs aiming to explore Vostok Subglacial Lake, Ellsworth Subglacial Lake, and Whillans Subglacial Lake over the next 3–5 years; assessment of technological requirements for exploration programs based on best practices for environmental stewardship and scientific success; and knowledge of subglacial lakes as habitats for microbial life and as recorders of past climate and ice sheet change. Its uniqueness, breadth, and inclusiveness will appeal to microbiologists and those interested in life in extreme environments, paleoclimatologists and those interested in sedimentary records of past changes, glaciologists striving to understand how water beneath glaciers affects their flow, and those engaged in developing technology to undertake direct measurement and sampling of extreme environments on Earth and in the solar system.
Author: Ty M. Engler Publisher: ISBN: 9780438391598 Category : Geology Languages : en Pages : 195
Book Description
The Upper Miocene succession (Motif 3, ~758-1073 meters below sea floor) of the ANDRILL 1B core was recovered from below the McMurdo Ice Shelf, in the flexural moat around the volcanic Ross Island, Antarctica. Clay mineral assemblages and microfossils of the succession have the potential to be used as paleoenvironmental and provenance indicators, which when placed in a glacial sequence stratigraphic framework, may be used to help constrain past dynamics of the West Antarctic Ice Sheet (WAIS) under warm paleoclimatic conditions. Smectite and illite clay mineral assemblages dominate Motif 3 and chlorite (+kaolinite) is a minor component. High relative smectite percentages may be directly related to volcanic units of the McMurdo Volcanic Complex, located locally to the drill site. Higher relative percentages of illite, combined with lower smectite proportions, may be sourced from weathered schists, amphibolites and gneisses of the Koettlitz Group, granitoids of the Granite Harbor Intrusives, and other basement rocks along the coast to the south and west of the drill site within the Transantarctic Mountains. That clay assemblage is considered an indicator of transport by the WAIS from the south and that assemblage was then mixed with reworked, locally derived sediment (the volcaniclastic smectite clays). Clays of the mudstones showed little excess Si, which is used to infer that low numbers of diatoms were present during deposition, even in open-water settings. A paucity of diatoms in this interval had been attributed to either loss by diagenesis or a lack of productivity in brackish surface waters rich in suspended muds coming from temperate-polythermal ice. Data presented here indicate the latter option is most likely, and agree with other facies indicators. Diagenesis and authigenesis may also be expressed in the recorded clay signatures. Post-depositional alteration can occur within sedimentary successions and it is often difficult to discriminate between smectites occurring from primary detrital volcanic grains, and those grown in situ either by authigenic growth from hydrothermal fluids, or by alteration during diagenetic reactions within the original parent sedimentary rock. Understanding the sediment provenance established using clay mineralogy in the Upper Miocene may provide a better understanding of ice dynamics by helping constrain the inferred glacial sequences that are used to interpret past WAIS dynamics. This pilot study has shown the way forward, but more detailed sampling and more advanced analytical techniques should be performed in the future to fully develop the concept. These data along with more detailed microfossil analyses should allow for the development of an enhanced and perhaps more reliable sequence stratigraphic model, which could lead to better-constrained interpretations of WAIS dynamics under warmer climatic conditions. Understanding how the ice reacted to past major cooling and warming events will allow for better model predictions for the future.
Author: Alan K. Cooper Publisher: American Geophysical Union ISBN: 9780875908847 Category : Science Languages : en Pages : 220
Book Description
Published by the American Geophysical Union as part of the Antarctic Research Series, Volume 71. The Antarctic Ice Sheet has greatly affected global climate, sea level, ocean circulation, and southern hemisphere biota during Cenozoic times. Much of our understanding of the evolution of the ice sheet has been inferred from isotopic studies on distant deep-ocean sediments, because few Cenozoic rocks are exposed on the Antarctic continent. Yet, large differences occur between past ice volumes inferred from isotopic studies and those inferred from low-latitude sea-level variation. The massive quantities of glacially transported terrigenous sediments that lie beneath the Antarctic continental margin provide an additional, more direct record of the inferred ice sheet fluctuations. Volume 68 addresses the history of ice sheet fluctuations as recorded by geological and geophysical investigations of selected areas of the Antarctic continental margin. As described below, the volume gives data and results from on-going research by a major multinational project directed toward better understanding the impact of Antarctic Ice Sheet fluctuations on global sea levels and climates.
Author: Zachary E. Mason Publisher: ISBN: 9780438630161 Category : Languages : en Pages :
Book Description
The marine-based West Antarctic Ice Sheet (WAIS) is susceptible to collapse during periods of warming. During the warm Pliocene (5.33 – 2.58 Ma) and especially the Mid-Pliocene Warm Period (3.3 – 3 Ma), temperatures were roughly 3̊C higher than the preindustrial average, and atmospheric CO2 concentrations were comparable to today’s levels. Sediments taken on the ocean floor beneath Ross Ice Shelf show open ocean conditions, during the warm Pliocene, yet it is uncertain whether the WAIS collapsed during this interval. Ice sheet models (Pollard and DeConto, 2009, 2012a, 2012b) point to a thinner Pliocene WAIS, but lack supporting data from the interior of the ice sheet. To test the predictions of the ice sheet, we obtained the first subglacial rock samples from under the WAIS by drilling from the Ohio Range, an interior location in the WAIS along the Transantarctic Mountains. Rock cores were recovered from 10-30 m under the present-day ice levels for measurements of cosmogenic 10Be, 26Al, and 21Ne. High measured nuclide concentrations and spallation-like depth profiles in the rock cores indicate extensive periods of ice-free exposure to cosmic irradiation during the last 2 Ma. The cosmogenic nuclides show complex exposure history for the bedrock. Assuming a simple two-stage scenario of exposure followed by burial reveals that subglacial bedrock surfaces experienced more exposure (250 kyr – 2 Myr) than ice cover (100 – 200 kyr), especially in the Pleistocene. An ice sheet model prediction for the Ohio Range subglacial sample sites significantly underestimates exposure in the last 5 Ma, and overpredicts ice cover in the Pleistocene. Ice sheet model simulations require more frequent and longer-lasting WAIS drawdowns to adjust for higher exposure. Our observations indicate that Pollard and DeConto’s ice sheet model needs to be adjusted to allow for more bedrock exposure. A more accurate model will improve our ability to investigate long-term WAIS stability.
Author: Perry Spector Publisher: ISBN: Category : Languages : en Pages : 118
Book Description
This dissertation describes three research projects on the glacial history of Antarctica using measurements of cosmogenic-nuclides in glacial deposits and bedrock surfaces. The first chapter investigates the deglaciation chronology of the Ross Sea following the last ice age. Abrupt thinning of glaciers in the southern Transantarctic Mountains occurred [approximately]9-8 kyr B.P. This coincided with deglaciation of the Scott Coast, [approximately]800 km to the north. At the end of this period the grounding line was located near Shackleton Glacier, indicating that most of the central and western Ross Sea deglaciated in less than 2 kyr. The rapidity of this event appears to have been influenced by unstable grounding-line retreat into deep marine basins and, potentially, enhanced melting at the marine margin. Because the majority of the deglaciation occurred during the early Holocene, the Ross Sea sector could not have significantly contributed or responded to rapid sea-level rise during Meltwater Pulse 1A. The second chapter discusses sites in West Antarctica for subglacial drilling to test for past ice-sheet collapse. It has been hypothesized that marine-based portions of the WAIS deglaciated during warm interglacial periods. Measurements of cosmogenic nuclides in subglacial bedrock surfaces therefore have the potential to establish whether and when this occurred. However, because most of the bedrock revealed by ice-sheet collapse would remain below sea level, shielded from the cosmic-ray flux, drill sites for subglacial sampling must be located in areas where thinning of the residue ice sheet would expose presently subglacial bedrock surfaces. In this chapter I discuss the criteria and considerations for choosing drill sites where subglacial samples will provide maximum information about WAIS extent during past interglacial periods. I evaluate candidate sites in West Antarctica and find that sites located adjacent to the large marine basins of West Antarctica will be most diagnostic of past ice-sheet collapse. There are important considerations for drill-site selection on the kilometer scale that can only be assessed by field reconnaissance. As a case study of these considerations, I describe reconnaissance at sites in West Antarctica, focusing on the Pirrit Hills, where in the summer of 2016-2017, an 8 m bedrock core was retrieved from below 150 m of ice. The third chapter investigates the glacial history of three isolated groups of nunataks in West Antarctica. The objectives of this chapter are to examine (i) the development and preservation of alpine landscapes, and (ii) past variations in ice thickness on timescales ranging from thousands to millions of years. Alpine landscapes were carved during the mid-Miocene and have since remained exceptionally well preserved. A trimline at the Pirrit Hills is an extension of a prominent trimline that occurs throughout the Ellsworth Mountains to the north. At the divide, ice levels have rarely, if ever, been higher than present, but they appear to have been lower for prolonged periods in the past. Midway between the divide and the grounding line, ice levels have repeatedly been [approximately]300-400 m higher than present, as occurred during the last ice age. Ice levels here also appear to have been lower than present during past interglacial periods.
Author: Jason James Coenen
Author: Jason James Coenen
Author: Martin J. Siegert
Author: Ty M. Engler
Author: S. TULACZYK
Author: Sean T. Rooney
Author: Alan K. Cooper
Author: R.E. BELL
Author: Zachary E. Mason
Author: S. ANANDAKRISHNAN
Author: Perry Spector