![]() ![]() These projections all rely on two tacit assumptions: firstly, that the current rapid contractions are anomalously fast and secondly, that the fast rates will be sustained for several centuries. Model simulations project that a transition to an even more rapid retreat could occur within 200–900 years 2. Recent modeling studies have projected that Pine Island Glacier losses could exceed 100 Gt/yr −1 within 20 years 3. Since 1979, discharge from fast-flowing WAIS glacial systems has contributed nearly 7 mm of sea-level equivalent volume to global sea level rise 6. These dynamics are at least partly driven by upwelled circumpolar deep water that advects onto the continental shelf and melts the ice sheet’s marine margins. In the Bellingshausen-Sea sector, 65% of WAIS grounding lines have retreated between 19 5. The term collapse is not precisely defined but is generally used to describe a significant contraction in the extent and volume of grounded ice within a relatively short time. This raises concern that an unstable collapse may be underway 2, 3, 4. Glaciers in the Amundsen Sea sector of West Antarctica are speeding up and grounding lines retreating as their ice shelves thin 1. In comparison with the modern grounding-zone dynamics, this paleo-perspective provides confidence in model projections that a large-scale sustained contraction of grounded ice is underway in several Pacific-Ocean sectors of the WAIS. The evidence favors the latter scenario because iceberg furrows that cross cut the ridges in deep water require weakly buttressed flow as the embayment opened. Grounding-line retreat is estimated to have averaged between ~ 100 ± 32 and ~ 700 ± 79 ma −1. Both scenarios require sustained rapid retreat that exceeded several centuries. The end-members fluxes correspond to deposition rates for buttressed and unbuttressed ice stream flow. We used two end-member paleo-sediment fluxes, i.e., accumulation rates, to convert the cumulative sediment volumes of the ridge field to elapsed time for measured distances of grounding-line retreat. Here, we reconstruct the pattern, duration and rate of retreat from a backstepping succession of small-scale grounding-zone ridges that formed on the embayment’s eastern flank. By ~ 11.5 ± 0.3 cal kyr BP, dynamic thinning of grounded ice triggered a retreat that opened a ~ 200-km grounding-line embayment on the Whales Deep Basin (WDB) middle continental shelf. The accelerated mass loss led to a significant negative mass balance that re-organized WAIS flow across the central and eastern Ross Sea. There, an ice shelf breakup at 12.3 ± 0.6 cal. (calibrated) kyr BP caused accelerated ice-mass loss from the Bindschadler Ice Stream (BIS). An abrupt retreat of the West Antarctic Ice Sheet (WAIS) that occurred during the early deglaciation is well recorded on the eastern Ross Sea continental shelf. Geological records of ice sheet collapse can provide perspective on the ongoing retreat of grounded and floating ice. ![]()
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