TIMING AND SEA LEVEL CONTRIBUTIONS OF THE DECONVOLVING ANTARCTIC ICE SHEET DURING POST-LGM RETREAT OF THE ROSS SEA SECTOR

Perhaps the most concerning possible climate scenario to ice sheet and sea level modelers is large-scale mass wasting of Antarctica’s ice sheets, the largest reservoirs of ice on Earth. In such a scenario, the volume of future ice loss is less important than the rate of change, which will determine how quickly coastal communities will be impacted by rising sea levels. Future projections are difficult to create without observational data to inform models, so evidence of ice loss in the paleo-record is used for model testing and tuning. However, much is still unknown or disputed about past ice-sheet extent and timing of retreat, due largely to difficulties in obtaining accurate radiocarbon dates as a result of a poorly constrained marine reservoir effect, bias from glacially-reworked carbon, and uncertainty in glacial-retreat sediment facies. We have taken steps to minimize these effects by using detailed sediment facies interpretation within a well-resolved geomorphic context and, based on these interpretations, selected appropriate radiocarbon dating methods to eliminate reworked carbon bias. Using high-resolution multibeam swath bathymetric data and cores from the Ross Sea, we have identified grounding zone deposits suitable for accelerator mass spectrometry radiocarbon dating of in-situ carbonate material, as well as compound-specific methods to accurately constrain grounding line retreat. Diatomaceous open marine deposits are relatively unbiased by relict carbon; therefore, the timing of floating ice loss and onset of open marine conditions is primarily determined using acid insoluble organic (AIO) bulk radiocarbon dating. We supplement constraints on open marine onset with previously published AIO dates from legacy cores that have been reinterpreted according to our sediment facies model. Using this information and estimates of grounding line position throughout retreat, we have calculated the volume of ice loss and associated sea level contributions throughout the deglaciation of one of the largest drainage basins for the East and West Antarctic ice sheets.