An Empirical Estimate of Post-LGM Grounding-Event Duration in Eastern Ross Sea: Implications from a Comparison with Constraints from New Radiocarbon Dates

Abstract

The West Antarctic Ice Sheet (WAIS) advanced to the outer shelf during the Last Glacial Maximum (LGM) before beginning a rapid retreat to the inner shelf. In the Whales Deep paleo-ice-stream trough, subsurface and geomorphologic evidence shows that grounding-line retreat was interrupted by at least five pauses in the area between the shelf edge and the middle shelf. During the pauses, an overlapping cluster of backstepped grounding zone wedges (GZWs) was deposited. Each GZW represents a grounding event, i.e., a time interval during which the grounding-line position was relatively stable. Seismic correlation and isopach mapping show that the cluster has a total volume of 5.34 x 1011 m3. Based on our estimate of modern deformation-till flux at Bindschadler Ice Stream, we infer that when the WAIS was grounded at the middle shelf, the paleo-sediment flux would have been as high as ~5.36 x 108 m3a-1. Using this paleo flux, the middle-shelf grounding events would have had a duration of ~995 ± 493 years. In contrasts, radiocarbon dates show that the middle-shelf grounding events had a duration of at least 3200 years. The comparison shows that in the absence of radiocarbon control, our empirical approach provides a reasonable first-order estimate of grounding event duration.