Preliminary reconstruction of deglacial conditions at Ross Bank following the post-LGM collapse of the Ross Bank Ice Rise

During the post-LGM, the West Antarctic Ice Sheet first retreated from deep-water troughs, followed by retreat from shallower-water banks. Deglacial succession from the troughs show a classic sequence from subglacial sediments deposited below fast-flowing ice streams, that transition upcore to sub-ice-shelf and open-marine sediments accumulated following grounding line and calving front retreat, respectively. Diatom assemblages in these sediments provide powerful evidence for making these environmental interpretations. For example, open-marine facies contain abundant Fragilariopsis curta, a sea-ice associated diatom. In comparison, deglacial successions for bank crests are poorly studied. Understanding bank stratigraphy is important because the formation of an ice rise would influence the pattern of deglaciation. Data acquired during expedition NBP2301/02 demonstrate that the Ross Ice-Shelf (RIS) was formerly pinned to Ross Bank, a broad shallow area in the central Ross Sea. Here, we evaluate the diatom assemblage data from four sediment cores from the shallow-water crest and deep-water flanks of Ross Bank. On the bank crest, the deglacial succession is a sand-rich residual glacial marine deposit. The diatom assemblage contains high to moderate percentages of sea-ice and permanently open-ocean species. These abundances suggests these winnowed products were derived from sediments that initially accumulated in distal sub-ice-shelf and/or open-marine settings. The downcore variations in diatom assemblage and abundance indicate that the intensity of winnowing on the bank was variable after the RIS unpinned. Understanding these processes is important as it can be used to constrain deglacial sequences and to identify reworked intervals in bank-crest core, which when combined with other evidence, can be used reconstruct the pattern and timing of ice shelf unpinning and other clues as to how the local deglacial conditions evolved.