A Holocene Collapse of a Ross Ice Shelf Ice Rise

Ice rises and rumples are common features of the Antarctica ice sheet margin that appear where thick ice shelves are grounded to an underlying shallow submarine bank.  The ice rises buttress ice flow, partly controlling the extent of both grounded and floating ice. Here we reconstruct the unpinning of the Ross Ice Shelf (RIS) from Ross Bank, a broad, shallow submarine bank located approximately 100 km north of the current RIS calving front in the central Ross Sea.  The Ross Bank Ice Rise formed after the retreat of grounded ice from the adjacent deep-water Glomar Challenger and Pennell troughs following the Last Glacial Maximum.  High resolution seafloor bathymetry reveals small-scale, concentric backstepping moraines marking the progressive contraction of the edges of the ice rise toward the shallow bank crest.  Kasten and piston cores from the crest recovered clay-poor, winnowed glacimarine sediment rich in carbonate macrofossils, with radiocarbon ages indicating that the unpinning proceeded over several thousand years.  The long-lived pinning point eventually failed, with the RIS fully unpinning from the shallowest crest by 4160 ± 20 ¹⁴C year BP (uncorrected). This ultimately led to the shift of the RIS calving front to its current location.  Our reconstructions validate concerns that destabilizing ice rises could lead to significant reorganization of grounded and floating ice.