On the duration of West Antarctic Ice Sheet grounding events in Ross Sea during the Quaternary

A back-stepping succession of three seismically-defined grounding zone wedges (GZWs) in the Glomar Challenger Basin palaeo-ice-stream trough is usually assigned to the short time that elapsed since the West Antarctic Ice Sheet retreat began at 11 ka 14C BP. Recent radiocarbon dates have however suggested an alternate interpretation in which the youngest of these three GZWs, the Gray Unit GZW on the middle shelf, corresponds to deposition during the Last Glacial Maximum (LGM). If so, then the Gray Unit must represent an amalgamation of erosion and deposition spanning a much longer time interval, i.e., the 100 ky interval between the Last Interglacial and the LGM. To test these conflicting interpretations, the Gray Unit sediment volume was mapped from seismic and multibeam data. Two end-member durations were calculated because flux during ice sheet retreat is significantly higher than flux during ice sheet advance. Using the retreat-mode flux, the 1.47 ky grounding event estimate shows that the middle shelf GZW could have been deposited during the post-LGM retreat. However, the 147.34 ky grounding event estimate based on the advance-mode flux also demonstrates that the GZW might reasonably represent an amalgamation of erosion and deposition as grounded ice gradually advanced between MIS5e and MIS2, i.e., from the Last Interglacial to the Last Glacial Maximum. These data thus require that both interpretations of how the near-surface stratigraphy relates to grounding-line translations in the last glacial cycle be considered feasible working hypotheses.

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► The Glomar Challenger Basin paleo trough contains three grounding zone wedges.
► It is generally assumed that all three wedges formed since MWP1A, i.e., 11 ky BP.
► If so, the grounding event that deposited the middle shelf wedge lasted ∼1.4 ky.
► However, if the wedge formed during ice advance, the grounding event lasted ∼147 ky.
► Both hypotheses of how Ross Sea wedges formed should be considered feasible.