Browsing by Author "Bart, Philip J."

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    A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
    (Elsevier, 2014) The RAISED Consortium; 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 D.; Mackintosh, Andrew; Smith, James A.; Verleyen, Elie; Ackert, Robert P.; Bart, Philip J.; Berg, Sonja; Brunstein, Daniel; Canals, Miquel; Colhoun, Eric A.; Crosta, Xavier; Dickens, William A.; Domack, Eugene; Dowdeswell, Julian A.; 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 M.; 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
    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
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    Characteristics of the deforming bed: till properties on the deglaciated Antarctic continental shelf
    (Cambridge University Press, 2018) Halberstadt, Anna Ruth W.; Simkins, Lauren M.; Anderson, John B.; Prothro, Lindsay O.; Bart, Philip J.
    Contemporary ice stream flow is directly linked to conditions at the ice/bed interface, yet this environment is logistically difficult to access. Instead, we investigate subglacial processes important for ice stream flow by studying tills on the deglaciated Antarctic continental shelf. We test currently-accepted hypotheses surrounding subglacial processes and till properties with a Ross Sea dataset. Till shear strengths indicate a continuum of simultaneous processes acting at the bed, rather than discrete ‘deformation’ and ‘lodgement’ end-members. We identify a threshold water content representing saturated pore spaces, leading to basal sliding and meltwater channelization. Based on observations of till properties relative to glacial landforms, we challenge the assumption that low shear strength is linked to intense deformation. Spatial variability in landform morphology reflects variability in deforming processes at the sub-ice stream scale and suggests a maximum deforming bed thickness of 2 m at the grounding line. Regional till properties generally correlate with seafloor geology and deglacial history; the western Ross Sea is characterized by higher and more variable shear strengths and water contents, while lower-shear strength till was preserved in the Eastern Basin. These observations inform till interpretation and provide context for deforming beds beneath the modern ice sheet and on glaciated continental shelves.
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    Early to middle Miocene ice sheet dynamics in the westernmost Ross Sea (Antarctica): Regional correlations
    (Elsevier, 2022) Pérez, Lara F.; McKay, Robert M.; De Santis, Laura; Larter, Robert D.; Levy, Richard H.; Naish, Timothy R.; Anderson, John B.; Bart, Philip J.; Busetti, Martina; Dunbar, Gavin; Sauli, Chiara; Sorlien, Christopher C.; Speece, Marvin
    The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma.
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    Post-LGM Grounding-Line Positions of the Bindschadler Paleo Ice Stream in the Ross Sea Embayment, Antarctica
    (Wiley, 2017) Bart, Philip J.; Anderson, John B.; Nitsche, Frank
    The West Antarctic Ice Sheet (WAIS) retreated more than 1,000 km since last grounding at the Ross Sea outer continental shelf. Here we show an interpretation of former grounding line positions from a new large-area multibeam survey and a regional grid of chirp cross-sectional data from the Whales Deep Basin in eastern Ross Sea. The basin is a paleo-glacial trough that was occupied by the Bindschadler Ice Stream when grounded ice advanced to the shelf edge during the Last Glacial Maximum. These new geophysical data provide unambiguous evidence that the WAIS occupied at least seven grounding line positions within 60 km of the shelf edge. Four of seven grounding zone wedges (GZWs) are partly exposed over large areas of the trough. The overlapping stratal arrangement created a large-volume compound GZW. Some of the groundings involved local readvance of the grounding line. Subsequent to these seven outer continental shelf groundings, the ice sheet retreated more than 200 km towards Roosevelt Island on the middle continental shelf. The major retreat across the middle continental shelf is recorded by small-scale moraine ridges that mantle the top of GZW7, and these are suggestive of relatively continuous grounding line recession. The results indicate that retreat was considerably more complex than was possible to reconstruct with reconnaissance-level data. The added details are important to climate models, which must first be able to reproduce the recent retreat pattern in all of its complexities to improve confidence in model predictions of the system's future response.
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    Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM
    (Elsevier, 2014) Anderson, John B.; Conway, Howard; Bart, Philip J.; Witus, Alexandra E.; Greenwood, Sarah L.; McKay, Robert M.; Hall, Brenda L.; Ackert, Robert P.; Licht, Kathy; Jakobsson, Martin; Stone, John O.
    Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by ∼13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by ∼11 ka BP, just north of Ross Island by ∼7.8 ka BP, and near Hatherton Glacier by ∼6.8 ka BP. Farther south, 10Be exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after ∼13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.