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au=marchant

HR: 14:10h
AN: U23B-02 INVITED
TI: The Geomorphic and Potential Climatic Impact of Subglacial-Lake Outbursts
AU: * Marchant, D R
EM: marchant@bu.edu
AF: Department of Earth Sciences, Boston University, 685 Commonwealth Ave, Boston, MA 02215, United States
AB: Subglacial water flow has been linked to changes in ice-sheet elevation and enhanced ice-stream flow. In addition to these important effects, significant bedrock erosion could arise from the catastrophic release of one or more subglacial lakes. If sufficient meltwater reaches the Southern Ocean, then such outburst floods might additionally trigger ecological change at a variety of scales. In the Transantarctic Mountains, an ancient 50+ km- long network of bedrock channels, collectively termed the Labyrinth, emerges from beneath the margin of the East Antarctic Ice Sheet (Wright Upper Glacier). Three distinct surfaces are noted, with upper- and intermediate- elevation surfaces reflecting direct erosion beneath wet-based ice, and a lower-elevation surface exhibiting anastomosing channels, some as much as 600 m wide and 250 m deep, that require incision from fast-flowing subglacial meltwater. 40Ar/39Ar analyses of volcanic tephra on the Labyrinth show that the channels are relict, with the last major subglacial flood occurring sometime between 14.4 Ma and 12.4 Ma. A similar, mid- Miocene age has been assigned to buried channels observed in the central Ross Embayment. Meltwater draining through the Labyrinth ultimately flowed into the Ross Sea, a region now critical for ocean turnover and deep-water formation and one shown in modeling studies to be sensitive to freshwater influx. Given an East Antarctic Ice Sheet larger-than-present during the mid Miocene with melting margins offshore in the Ross Embayment, the Ross Sea may have been preconditioned such that a significant influx of freshwater could have exceeded threshold conditions and led to changes in sea-ice extent, near-surface ocean salinity, and regional ocean circulation. These discoveries suggest that subglacial meltwater floods likely play a major role in modifying polar landscapes and regional ocean circulation.
DE: 1621 Cryospheric change (0776)
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1637 Regional climate change
SC: Union [U]
MN: 2007 Fall Meeting


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