HR: 09:30h
AN: C11B-07    [Abstracts]
TI: Response of the Antarctic Ice Sheet Periphery to Late Pleistocene MWP-1a Event: Sedimentologic, Geomorphologic, and Chronologic Evidence
AU: * Domack, E W
EM: edomack!@hamilton.edu
AF: Hamilton College, 198 College Hill Road, Clinton, NY 13323 United States
AU: Leventer, A
EM: aleventer@mail.colgate.edu
AF: Colgate University, 13 Oak Drive, Hamilton, NY 13346 United States
AB: Nowhere were ice sheets grounded to such depth and were exposed to such rapid increases in sea level as they were around the periphery of the Antarctic Ice Sheet during Termination 1, a unique period in the last 100,000 years. We document the conditions within nine ice drainage systems including the NW Weddell Sea, Palmer Deep, western Ross Sea, Mertz Trough, Mertz-Ninnis Trough, Svenner Channel, Prydz Channel, Nielsen Basin, and Iceberg Alley. In so doing we demonstrate that recession of these systems was a response to, not a cause of, the global MWP-1a event. Explicit in our model for deglaciation is the pattern of recession (exclusive of the Ross and NW Weddell seas), which we demonstrate involved the development of distinctive calving bay re-entrants within the troughs occupied by former ice streams. This pattern and style of deglaciation is consistent with early conceptual models of calving bays which developed in association with linear zones of convergent flow constrained by surrounding banks or pinning points. Our conceptual model is supported by observed seafloor morphology, sediment lithofacies, and constrains of glacial meltwater and bed softening (deformation). The initiation of calving bay conditions we believe was a response to a rapid rise in sea level in combination with a lowering of ice thickness, due to enhanced ice flow within confining troughs. The rapid encroachment of a dynamic calving line into the interior of the ice sheet margin means that subglacial conditions of meltwater drainage were suddenly enhanced, due to reduced ice overburden pressure and a lower hydrostatic (seawater) pressure at the grounding line. Evidence for energetic meltwater discharge at grounding lines comes from the observation of channels cut into and sediment fans on top of recessional (back-stepping) morainal banks. These features are unambiguously indicative of subglacial meltwater discharge at the grounding line of a receding ice margin. In support of the timing of recession we review over 300 radiocarbon ages we have published in the last 6 years and discuss the critical constraints that must be placed upon the interpretation of radiocarbon ages from Antarctic marine and glacial sediments, including uncertain but assumed correction and calibration routines. Consideration of this evidence indicates that the source for MWP-1a was not the Antarctic Ice Sheet. The former may have in-fact, responded to but was not responsible for the short lived rise in sea level observed in regions far-field from the Antarctic margin. Rather the peripheral recession of the Antarctic Ice Sheet was more likely contemporaneous with the well known Younger Dryas and we briefly discuss the implications for this apparent coincidence.
DE: 1105 Quaternary geochronology
DE: 1621 Cryospheric change (0776)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 1724 Ocean sciences
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: Fall Meeting 2005