Exploring under the weak underbelly of the West Antarctic Ice Sheet with recent aerogeophysical data

There are growing concerns over how the West Antarctic Ice Sheet (WAIS) will respond to global warming and the major societal implications that its potential collapse would have. An area of particular concern is the Amundsen Sea Embayment (ASE), where glaciers such as Pine Island Glacier (PIG) and Thwaites Glacier (THW) have been shown to be melting, thinning, accelerating and retreating rapidly. This part of the WAIS has also been referred to as the "weak underbelly of the WAIS" where rapid deglaciation could occur. Previous aerogeophysical surveys flown over the Siple Coast (SC) ice streams have imaged subglacial geology, and have highlighted the importance of considering geology when assessing the dynamics and long-term stability of the WAIS. The SC ice streams overlie broad and narrow sediment-infilled rift basins of the West Antarctic Rift System (WARS). Subglacial sediments and Cenozoic to Recent magmatic features associated with the WARS may represent geological templates for enhanced glacial flow there. However, whether the WARS extended beneath the catchments of the dynamic ASE glaciers remained poorly constrained due to the paucity of geophysical data. Approximately 100,000 line km of new aerogeophysical data were collected over this region as part of a collaborative effort between the University and Texas and the British Antarctic Survey, comprising airborne radar, aeromagnetic and airborne gravity. The new airborne radar datasets yielded an improved picture of the deep narrow subglacial trough beneath the trunk of PIG, and the broader basin where THW flows, as well as the narrow basins where tributary flow occurs. A bedrock high was imaged on the flank of PIG, which would rise above sea-level after isostatic compensation following deglaciation, and could perhaps impede ice-sheet collapse initiated near the grounding line by preventing its progress into the deep Byrd Sublglacial Basin. The new potential field data uncovers the WARS in ASE region. Aeromagnetic patterns suggest that several rift basins were highly magmatic in the Cenozoic west of 102W, in contrast to a much more weakly magmatic area to the east. Remarkable boundaries between the Marie Byrd Land block, the WARS and the Ellsworth Mountains are imaged. Modelling of Bouguer gravity data indicates a generally higher degree of crustal thinning compared to the SC region, and low lithospheric rigidities, both of which may be indicative of a modern rift system. Rifting and magmatic processes may have induced elevated heat-flow at both local and regional scale, thereby increasing the availability of water at the base of the ice sheet. Subglacial sedimentary basins, which may further enhance fast glacial flow in the ASE are revealed by our aeromagnetic and isostatic residual gravity images.