Subglacial Water Flow Over an Antarctic Palaeo‐Ice Stream Bed. Issue 2 (18th February 2022)

• Record Type: Journal Article
• Authors: Hogan, K. A.; Arnold, N. S.; Larter, R. D.; Kirkham, J. D.; Noormets, R.; Ó Cofaigh, C.; Golledge, N. R.; Dowdeswell, J. A.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-18
• Subjects: palaeo‐ice stream -- subglacial hydrology -- bedrock channels -- Antarctica -- subglacial lakes -- marine geophysics; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2021JF006442
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: The subglacial hydrological system exerts a critical control on the dynamic behavior of the overlying ice because its configuration affects the degree of basal lubrication between the ice and the bed. Yet, this component of the glaciological system is notoriously hard to access and observe, particularly over timescales longer than the satellite era. In Antarctica, abundant evidence for past subglacial water flow over former ice‐sheet beds exists around the peripheries of the ice sheet including networks of huge channels carved into bedrock (now submarine) on the Pacific margin of West Antarctica. Here, we combine detailed bathymetric investigations of a channel system in Marguerite Trough, a major palaeo‐ice stream bed, with numerical hydrological modeling to explore subglacial water accumulation, routing and potential for erosion over decadal‐centennial timescales. Detailed channel morphologies from remotely operated vehicle surveys indicate multiple stages of localized incision, and the occurrence of potholes, some gigantic in scale, suggests incision by turbulent water carrying a significant bedload. Further, the modeling indicates that subglacial water is available during deglaciation and was likely released in episodic drainage events, from subglacial lakes, varying in magnitude over time. Our observations support previous assertions that these huge bedrock channel systems were incised over multiple glacial cycles through episodic subglacial lake drainage events; however, here we present a viable pattern for subglacial drainage at times when the ice sheet existed over the continental shelf and was capable of continuing to erode the bedrock substrate. Plain Language Summary: Some 20, 000 years ago, during the Last Glacial Maximum, Marguerite Trough on the continental shelf of West Antarctica, was occupied by a major fast‐flowing ice stream. Now the seafloor of the trough is incised by a series of interlinked channels cut into the bedrock. These huge channels are similar to others found offshore Antarctica, for example, in Pine Island Bay, and were formed by pressurized water flowing underneath past ice sheets. Still, very little is known about the exact timing or mechanisms of channel formation. In this study, we present a combination of seafloor observations and numerical modeling of water flow under the ice to investigate processes of channel erosion, and whether incision occurs during all stages of a glacial cycle. Detailed seafloor morphology and imagery from a remotely operated vehicle, show that incision processes include the formation of circular potholes by swirling water, as well as the formation of smaller channels, within much larger channel tracts that were probably mostly filled with ice widening their upper parts. Interestingly, our model results suggest that water under the retreating ice stream may have been trapped in seafloor depressions, as subglacial lakes, and was then released periodically every few tens to hundreds of years. Key Points: Seafloor observations and hydrological modeling are used to investigate bedrock channels on a major Antarctic palaeo‐ice stream bed Episodic releases from subglacial lakes modulated water availability under an expanded ice sheet driving channel incision in multiple stages Recharge and drainage of subglacial lakes are predicted to occur on timescales of tens to hundreds of years