Topographic Control on Post-LGM Groundings of the West Antarctic Ice Sheet in the Whales Deep Basin, Eastern Ross Sea

Abstract

By the peak of the Last Glacial Maximum (LGM), the West Antarctic Ice Sheet (WAIS) had advanced to the outer continental shelf of eastern Ross Sea trough basins. During the post-LGM retreat, the WAIS paused several times within 75 km of the Whales Deep Basin (WDB) shelf edge. An overlapping stack of seven grounding zone wedges (GZWs) records the locations of these groundings. Here we used ~7500 km of seismic reflection data to map the subglacial unconformity that was eroded when WAIS was grounded at the shelf edge, i.e., prior to the deposition of the backstepping GZWs. With respect to the underlying subglacial topography, the first three groundings were slightly basinward of relatively low-relief knolls in the central part of the basin. The remaining four groundings were positioned above the crest of a low-elevation saddle in the center of the WDB. These latter groundings are also located at a significant convergence in the trend of the banks that bound the basin. These observations in the WDB support the general hypotheses that the locations of post-LGM groundings were at least partly controlled by antecedent topography. The results suggest that models seeking to predict ice-sheet response to climate changes should incorporate a highly detailed map of subglacial topography as an important boundary condition.