Subglacial sediment transport upstream of a basal channel in the ice shelf of Support Force Glacier (West Antarctica), identified by reflection seismics
Flow stripes on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the groundling line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–...
| Main Authors: | , , , , , , , , , , |
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| Format: | Text |
| Language: | English |
| Published: |
2020
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/tc-2020-54 https://tc.copernicus.org/preprints/tc-2020-54/ |
| Summary: | Flow stripes on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the groundling line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel and its upstream continuation on Support Force Glacier which feeds into the Filchner Ice Shelf, West Antarctica. We map the structure of the basal channel at the ice base in the grounded and floating part and identify the subglacial material within the grounded part of the channel and also along the seafloor. Several kilometers upstream of the grounding line we identify a landform, consisting at least in part of sediments, that forms the channel at the ice base. Immediately seaward of the grounding line, the seismic profiles show a 200 m thick partly disturbed, stratified sediment sequence at the seafloor, which we interpret as grounding line deposits. We conclude that the landform hosts the subglacial transport of sediments entering Support Force Glacier at the eastern side of the basal channel. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a very flat topography of the ice shelf base with an almost constant ice thickness gradient along flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction of grounded landforms, ice stream shear margins and subglacial hydrology to form basal channels in ice shelves. |
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