REFINING OUR UNDERSTANDING OF SEDIMENT RETREAT FACIES AND GEOMORPHOLOGY FOR AN ACCURATE DEGLACIAL HISTORY OF THE ROSS SEA

Recent studies of the modern grounding line and sub-ice shelf environment in Antarctica have revealed that ice margins are complex and dynamic. This understanding is not yet reflected in retreat sediment facies models for the Ross Sea, which are derived primarily from cores within deep troughs. Accurate facies interpretation is essential to constrain the timing of grounding line retreat and ice shelf collapse. Existing facies models are limited by spatial coverage and do not explain the complex retreat history inferred from glacial retreat landforms preserved on the continental shelf. It is important to consider how facies successions appear in the wide variety of glacial and glacimarine environments at the margins of a marine-based ice sheet, including banks, bank slopes, grounding zone wedge transects, and meltwater-intensive areas.

A recent cruise (NBP1502) to the Ross Sea provided us with high resolution multibeam and high frequency subbottom profiler data, as well as cores in targeted locations that are critical to enhancing our understanding of the nature, timing, and controls on ice retreat. We use a multi-proxy approach to characterize retreat facies including sedimentology, microfossil analysis, and geochemical properties. Our improved grain size techniques allow more holistic interpretations of marine influence and environments of deposition, along with fossils when present. In addition, we have determined that soft sediment clasts can be attributed to specific environmental processes. By refining sediment facies, we interpret meltwater, sediment gravity flows, and other processes as important controls on grounding line instability and ice retreat. Applying geomorphic context to our sedimentological analyses allows us to determine not only timing of retreat, but also rate and style of ice retreat from the Ross Sea.