SEDIMENTARY PROCESSES AT PALEO-GROUNDING LINES: GLACIAL AND OCEANOGRAPHIC INTERACTIONS DURING ICE-SHEET RETREAT

Grounding lines of marine-based ice sheets are a potential point of vulnerability for ice sheets due to their direct contact with the changing ocean. The geologic record of deglaciated continental shelves provides an opportunity to study multiple grounding lines in a state of retreat. Grounding line conditions are documented in sediment cores collected from the Ross Sea, Antarctica, which reveal a range of sedimentary processes that were active during the most recent deglaciation of the continental shelf. We collected the cores within a geomorphic framework, specifically targeting paleo-grounding line positions as expressed by grounding line landforms. By coupling geomorphic and sedimentary analyses, we show that marine-based grounding lines of the East Antarctic and West Antarctic ice sheets experienced sediment accumulation by debris flows and meltout of basal debris and were influenced by episodic subglacial meltwater expulsion. While debris flows and meltout of basal debris serve as grounding-line stabilizers by facilitating grounding line landform growth, channelized subglacial meltwater expulsion appears to act as a hindrance to landform growth. We also demonstrate that the distribution and thickness of basal meltout deposits differentiates episodic and continuous ice sheet retreat styles, which is useful for interpreting ice-sheet behavior from stratigraphic data with less geomorphic context. We have constrained the lateral extent of meltout of basal debris to within 1.2 km of paleo-grounding lines, which is consistent with observations of the modern grounding line inland of the Ross Sea Embayment. Grain size data show little to no reworking near grounding lines, indicating marine currents are sluggish near the ice margin. Open marine sediments and biogenic components do not indicate any drastic changes in marine currents from the most recent glacial maximum to present. Laterally, however, open marine deposits show sedimentological variability, with outer continental shelf and banktop regions consistently displaying more evidence of strong impinging currents than deep inner troughs. Understanding the interactions between glacial and marine processes at paleo-grounding lines during deglaciation give insights into retreat forcings as well as meaning to radiocarbon dates.