Browsing by Author "Schroeder, Dustin M."

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    A subglacial hydrologic drainage hypothesis for silt sorting and deposition during retreat in Pine Island Bay
    (Cambridge University Press, 2019) Schroeder, Dustin M.; MacKie, Emma J.; Creyts, Timothy T.; Anderson, John B.
    Late Holocene sediment deposits in Pine Island Bay, West Antarctica, are hypothesized to be linked to intensive meltwater drainage during the retreat of the paleo-Pine Island Ice Stream after the Last Glacial Maximum. The uppermost sediment units show an abrupt transition from ice-proximal debris to a draped silt during the late Holocene, which is interpreted to coincide with rapid deglaciation. The small scale and fine sorting of the upper unit could be attributed to origins in subglacial meltwater; however the thickness and deposition rate for this unit imply punctuated- rather than continuous-deposition. This, combined with the deposit's location seaward of large, bedrock basins, has led to the interpretation of this unit as the result of subglacial lake outbursts in these basins. However, the fine-scale sorting of the silt unit is problematic for this energetic interpretation, which should mobilize and deposit a wider range of sediment sizes. To resolve this discrepancy, we present an alternative mechanism in which the silt was sorted by a distributed subglacial water system, stored in bedrock basins far inland of the grounding line, and subsequently eroded at higher flow speeds during retreat. We demonstrate that this mechanism is physically plausible given the subglacial conditions during the late Holocene. We hypothesize that similar silt units observed elsewhere in Antarctica downstream of bedrock basins could be the result of the same mechanism.
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    Airborne radar sounding evidence for deformable sediments and outcropping bedrock beneath Thwaites Glacier, West Antarctica
    (Wiley, 2014) Schroeder, Dustin M.; Blankenship, Donald D.; Young, Duncan A.; Witus, Alexandra E.; Anderson, John B.
    The geologic and morphologic records of prior ice sheet configurations show evidence of rapid, back-stepping, meltwater intensive retreats. However, the potential for such a retreat in a contemporary glacier depends on the lithology of the current ice sheet bed, which lies beneath kilometers of ice, making its physical properties difficult to constrain. We use radar sounding and marine bathymetry data to compare the bed configuration of Thwaites Glacier to the bed of paleo-Pine Island Glacier. Using observed and modeled radar scattering, we show that the tributaries and upper trunk of Thwaites Glacier are underlain by ice flow-aligned bedforms consistent with deformable sediment and that the lower trunk is grounded on a region of high bed roughness consistent with outcropping bedrock. This is the same configuration as paleo-Pine Island Glacier during its retreat across the inner continental shelf.