Geologic evidence of a leaky Antarctic Ice Sheet: Tracking meltwater influence on ice-sheet retreat in the Ross Sea, Antarctica since the Last Glacial Maximum

Abstract:

Meltwater at the base of an ice sheet has a significant influence on the flow dynamics and stability. Processes that lead to ice-sheet instability are at the forefront of research addressing uncertainty in the fate of modern ice sheets. A better understanding of subglacial meltwater is needed to assess the role of meltwater on ice-sheet instability and place modern observations of meltwater drainage into a longer-term context. Observations of subglacial channels and evidence of meltwater influence on ice-sheet dynamics are sparse in the geologic record around Antarctica. We present subglacial meltwater channels incised into the post-LGM sea scape of the Ross Sea continental shelf with clear relationships to glacial retreat landforms. We combine geomorphic and stratigraphic evidence to test the influence of meltwater on ice-sheet retreat during the last deglaciation. The channel systems are associated with small, closely-spaced ice-marginal landforms suggestive of rapid grounding line retreat. The channels were active during the late stages of retreat based on their positions in the southernmost portions of the troughs and cross-cutting relationships with glacial retreat landforms. Although channelized meltwater appears to be spatially limited, we have identified meltwater deposits within proximal grounding line facies from cores across the continental shelf in the western Ross Sea. Therefore, not only do we observe clear evidence of meltwater under the dwindling ice sheet, but basal meltwater in the Ross Sea is a pervasive feature and associated with geomorphic and sedimentologic expressions of rapid ice-sheet retreat. Ongoing work focuses on quantifying channel flow properties and reasonable meltwater production rates as well as further constraining evidence of meltwater in the Ross Sea and elsewhere around Antarctica.