Antarctic Ice Sheet retreat in the western Ross Embayment since the Last Glacial Maximum constrained by geochronology and ice flow modeling

Glacial geologic evidence from the Transantarctic Mountains (TAM) shows that much of the western Ross Embayment deglaciated within a few thousand years in the early Holocene. We present detailed chronologies of fluctuations of Darwin and Hatherton Glaciers based on surface exposure ages of glacial erratics and bedrock and radiocarbon ages of ancient algae, which constrain changes in the western Ross Embayment since the Last Glacial Maximum. Darwin and Hatherton Glaciers thinned to their modern configurations later and more slowly than other TAM outlet glaciers, from 8 to ≤3 kyr BP. Two mechanisms may have been responsible for this delayed retreat: (1) dynamic thickening due to the convergence of Darwin Glacier with the much larger Byrd and Mulock glaciers, and (2) ice shelf pinning on currently undetected topographic highs on the seafloor. To test this, we use an ensemble of high-resolution (5 km), three-dimensional ice sheet model simulations over the Ross Embayment to examine possible patterns of grounding-line retreat during the last deglaciation. These simulations establish time-varying boundary conditions for a glacier flow-band model, which we use to determine the fit of the ice sheet model runs to our geochronologic data along the glacier profiles. Simulations using reasonable ranges of model parameter values and BEDMAP2 bed topography for the Ross Embayment show rapid, early Holocene grounding-line retreat to the mouth of Darwin Glacier, and do not readily fit our glacial chronology. An idealized case with slow and smooth thinning at the mouth of Darwin Glacier yields the best fit to the data. Therefore, our modeling shows that the dynamic thickening caused by the convergence of Darwin, Byrd, and Mulock glaciers was not sufficient to delay grounding-line retreat by thousands of years. We suggest that unresolved pinning points could have controlled ice dynamics over 100-km spatial scales.