Download or read book Upper Miocene History of the West Antarctic Ice Sheet Inferred from Sequence Stratigraphy Clay Mineralogy and Paleoecology of the Andrill 1B Core written by Ty M. Engler and published by . This book was released on 2018 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Late Miocene Antarctic Ice Sheet Dynamics Based on Glacial Sequence Stratigraphy of AND 1B written by Justin Andrew Rosenblume and published by . This book was released on 2016 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: Glacial sequence stratigraphic analysis provides a disconformity-bounded stratigraphic framework for Upper Miocene sediments of AND-1B ([almost equal to]758--1073 mbsf), consisting of 26 sequences, which indicate a relatively dynamic late Miocene Antarctic Ice Sheet. This study updates a glacial sequence stratigraphic model by defining base level, the correlative conformity, and within-trend surfaces to characterize ice dynamics such as: relative magnitudes of advance, relative duration at maximum extent, and relative rates of glacial retreat. In addition, genetic facies, micromorphology, and foraminifera are used to infer types of depositional systems. The Miocene glacial systems are inferred to be similar to subpolar glaciers like those in Svalbard today, which accumulate sediment at rates of [almost equal to]5 cm a-1 within [almost equal to]1 km of their grounded tidewater cliffs in water depths of 100s m. The Late Miocene represents a time when average pCO2 was lower-than-modern, whereas the depositional systems and other proxy data in this study suggest warmer-than-modern climates. Current global proxy data (d18O, pCO2) for the Late Miocene are relatively sparse, making it difficult to infer the major drivers of Antarctic Ice Sheet dynamics during this time. Although our age-model is poorly constrained, we posit that solar insolation at 75°S and climate 'noise' or aberrations may have been relatively stronger climate controls during this time than previously suggested. Further investigation and modeling is definitely warranted.
Download or read book The West Antarctic Ice Sheet written by and published by American Geophysical Union. This book was released on 1998 with total page 297 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book West Antarctic Ice Sheet Initiative Discipline reviews written by Robert A. Bindschadler and published by . This book was released on 1991 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book West Antarctic Ice Sheet Initiative Volume 2 Discipline Reviews written by Robert A. Bindschadler and published by . This book was released on 1991 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Inferring West Antarctic Subglacial Basin History and Ice Stream Processes Using Siliceous Microfossils written by Jason James Coenen and published by . This book was released on 2016 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book First Annual West Antarctic Ice Sheet WAIS Science Workshop written by Robert A. Bindschadler and published by . This book was released on 1993 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: History, current behavior, internal dynamics, and environmental interactions concerning future behavior and potential for rapid collapse of the West Antarctic Ice Sheet (WAIS).
Download or read book Dynamics of the West Antarctic Ice Sheet written by C.J. van der Veen and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: Few scientists doubt the prediction that the antropogenic release of carbon dioxide in the atmosphere will lead to some warming of the earth's climate. So there is good reason to investigate the possible effects of such a warming, in dependence of geographical and social economic setting. Many bodies, governmental or not, have organized meetings and issued reports in which the carbon dioxide problem is defined, reviewed, and possible threats assessed. The rate at which such reports are produced still increases. However, while more and more people are getting involved in the 'carbon dioxide business', the number of investigators working on the basic problems grows, in our view, too slowly. Many fundamental questions are still not answered in a satisfactory way, and the carbon dioxide building rests on a few thin pillars. One such fundamental question concerns the change in sea level associated with a climatic warming of a few degrees. A number of processes can be listed that could all lead to changes of the order of tens of centimeters (e. g. thermal expansion, change in mass balance of glaciers and ice sheets). But the picture of the carbon dioxide problem has frequently be made more dramatic by suggesting that the West Antarctic Ice Sheet is unstable, implying a certain probability of a 5 m higher sea-level stand within a few centuries.
Download or read book West Antarctic Ice Sheet Initiative Science and implementation plan written by Robert A. Bindschadler and published by . This book was released on 1991 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Miocene Fluctuations of the West Antarctic Ice Sheet and the Influence of Meltwater on the Ross Sea Outer Continental Shelf written by Sean Kerrin and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geology and Seismic Stratigraphy of the Antarctic Margin written by Alan K. Cooper and published by American Geophysical Union. This book was released on 1997-01-23 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book West Antarctic Ice Sheet Retreat During the Last Interglacial written by Gail Ruth Muldoon and published by . This book was released on 2018 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Last Interglacial (116 ka - 130 ka) is the most recent time when Earth's climate was as warm or warmer than it is today. It therefore may make a suitable proxy for understanding the impacts of modern climate change. One such impact of immediate relevance to the modern world is that of sea level rise. Global sea level is currently rising at an accelerating pace, threatening lives and economies around the world. Notably, evidence from paleoclimate data suggests global sea level during the Last Interglacial was at least 6.6 m higher than present sea level and perhaps more than 8 m higher. As the Earth adjusts to the rapid onset of modern climate change, we may expect sea level to approach that of the Last Interglacial. Noticeable changes in sea level have a number of sources, including melting glaciers, ice sheets, and ocean thermal expansion. The Antarctic Ice Sheet has been inferred to be the largest contributor to Last Interglacial sea level change, adding between 4.1 and 5.8 m to global sea level during that time. Most of this change is expected to come from the West Antarctic Ice Sheet, which is thought to be prone to marine ice sheet instability. However, uncertain basal boundary conditions and ocean forcing make it a challenge to know how the ice sheet may have lost such a large amount of mass. In this work, I seek to better constrain mass balance and sea level contributions of the Antarctic Ice Sheet during the Last Interglacial and explore evidence from inside the ice sheet itself which may reveal if and how the ice sheet sustained such a large mass balance change during the Last Interglacial. To do so, I use a transient ice sheet model to simulate reconfiguration of the Antarctic Ice Sheet under Last Interglacial conditions and find a stable configuration consistent with estimates of Antarctic contributions to Last Interglacial sea level. I then analyze englacial radar stratigraphy to study the ice dynamics by dating a series of isochronous englacial reflectors which have been mapped through the central West Antarctic Ice Sheet. For comparison to this data, I implement a steady state ice sheet model to simulate englacial isochronous surfaces with various uncertain model boundary conditions.
Download or read book Geology and Seismic Stratigraphy of the Antarctic Margin written by Alan K. Cooper and published by Wiley-AGU. This book was released on 1997-01-23 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book West Antarctic Ice Sheet Initiative Volume 1 Science and Implementation Plan written by and published by . This book was released on 1991 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Recent History of the Antarctic Ice Sheet written by Daniel Peter Zwartz and published by . This book was released on 1995 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Letter written by Timothy Naish and published by . This book was released on 2009 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (~5-3Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ~40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ~3°C warmer than today and atmospheric CO2 concentration was as high as ~400p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7m in equivalent sea level associated with the loss of the WAIS and up to +3m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO2.
Download or read book West Antarctic Ice Sheet Initiative written by Robert A. Bindschadler and published by . This book was released on 1991 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
