Drivers of abrupt Holocene shifts in West Antarctic ice stream direction determined from combined ice sheet modelling and geologic signatures

Abstract

Determining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here highresolution ice sheet modelling was combined with new terrestrial geological constraints (in situ 14 C and 10 Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.

Ice‐flow reorganization in West Antarctica 2.5 kyr ago dated using radar‐derived englacial flow velocities

“…The divide could have formed due to the grounding line of the main ice sheet retreating past this location or as regional flow reorganization ceased, perhaps after a grounding of the ice shelf and grounding line advance. Regional ice‐flow modeling [e.g., Fogwill et al , ; Wright and ohters , ; Thoma et al , ] and geophysical surveys of other ice rises in the region could be used to test these contrasting ice‐flow histories and investigate the connection between the reorganization we have dated and the undated switches in flow of the Institute and Möller Ice Streams (Figure ) inferred from airborne radar data [ Siegert et al , ; Bingham et al , ; Winter et al , ].…”

“…[ Clark et al , ] have occurred in the Weddell and Ross Seas [e.g., Bentley et al , ; Golledge et al , ; Whitehouse et al , ; Anderson et al , ; Hillenbrand et al , ]. In both regions deglacial ages from marine radiocarbon and cosmogenic exposure dating [e.g., Conway et al , , ; Bentley et al , ; Anderson et al , ; Fogwill et al , ], as well as observations of glacio‐isostatic adjustment [ Bradley et al , ], ice surface lineations [e.g., Fahnestock et al , ; Hulbe and Fahnestock , ; Siegert et al , ], and ice‐sheet internal structure [e.g., Conway et al , ; Catania et al , ; Siegert et al , ; Bingham et al , ; Winter et al , ] indicate ice‐sheet retreat since the LGM and flow reorganization during the last few thousand years.…”

Airborne radar evidence for tributary flow switching in Institute Ice Stream, West Antarctica: Implications for ice sheet configuration and dynamics

“…Surface flow stripes on Bungenstock Ice Rise (Figure b) have led to the suggestion that an adjustment to the flow path of IIS could have occurred during a phase of ice sheet retreat or by an advance of the grounding line from an already retreated situation that existed approximately 400–4000 years ago. Modeling studies have suggested that a migration of IIS occurred during the last deglaciation [ Fogwill et al ., ] and that future changes in mass balance may lead to rapid grounding line retreat [ Wright et al ., ].…”

Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination

“…Secondly, it is possible under a scenario of dynamic deglaciation during the LGT that rapid regional bedrock isostatic variations may have effectively masked rapid ice-sheet elevation changes that have occurred during deglaciation and subsequently during the Holocene (Supplementary Information). Therefore, terrestrial cosmogenic isotope reconstructions from mountains and nunataks across the WSE are only likely to robustly reconstruct ice-sheet surface elevation changes during Holocene deglaciation252930. This is an issue which requires future detailed analysis, with multiple lines of evidence pointing towards a dynamic history of ice-sheet change across the WSE during the Holocene293031, with significant implications for defining the pre-Holocene history of this sector of the AIS.…”

“…Therefore, terrestrial cosmogenic isotope reconstructions from mountains and nunataks across the WSE are only likely to robustly reconstruct ice-sheet surface elevation changes during Holocene deglaciation252930. This is an issue which requires future detailed analysis, with multiple lines of evidence pointing towards a dynamic history of ice-sheet change across the WSE during the Holocene293031, with significant implications for defining the pre-Holocene history of this sector of the AIS. Innovative reconstructions, such as that provided by the Patriot Hills BIA, are urgently required to define in detail dynamic Antarctic ice-climate feedbacks and better constrain the ice sheets contribution to global sea level rise during periods of rapid climate transition such as the LGT.…”