We present marine geological and geophysical data for the Antarctic Peninsula that call for a larger ice-sheet reconstruction during the Last Glacial Maximum (LGM) than suggested by previous studies. Such glacial reconstructions are important for quantifying post-LGM sea-level rise and providing boundary conditions for general circulation models.
Megascale glacial lineations on the continental shelf surrounding Antarctica provide documentation for grounded ice that was streaming. Swath bathymetry data (NBP02-01) reveal lineations in each of the major glacial troughs, except for Smith Trough, which features grooves and bedrock drumlins (0.5–3 km spacing, 1:20 elongation ratios) on crystalline bedrock. We place the maximum extent of ice at the seaward limit of the lineations, at or near (<10 km landward of) the shelf break. The occurrence of line-sourced gullies at the mouth of each glacial trough (except Vega Trough, Weddell Sea) supports the interpretation of ice grounded at the shelf break.
Megascale glacial lineations imaged in this study and other areas surrounding Antarctica (including the Ross Sea, Pine Island Bay) have a consistent morphology, with elongation ratios of >80:1 and spacings of 200–600 m (mode of 300 m). In contrast, lineations (“bundles”; Canals et al., 2000) in the Gerlache-Boyd Trough exhibit larger spacing (1–5 km), and the upstream portions (∼7 km) are carved directly into bedrock rather than till, as suggested by previously unpublished air gun (∼120 Hz) seismic data. These features have yet to be dated; however, they are believed to have been active during the LGM.
Radiocarbon dates in glaciomarine sediments (foraminifera and organic matter) from seven glacial troughs indicate that megascale glacial lineations were formed during the LGM. Other geomorphic features, such as the grounding zone wedge in the northwestern Weddell Sea, formed when the ice sheet was retreating. The initial retreat of the grounded ice from the outer shelf occurred by 18,500 cal yr B.P. The inner shelf was mostly ice free by 13,000 cal yr B.P. This is significantly earlier than numerical models, which suggest Antarctic deglaciation began at 12,000 cal yr B.P. This also suggests the peninsula area contributed to global sea-level rise associated with meltwater pulse (MWP) 1a.