Reconstruction of the Ross Ice Drainage System, Antarctica, at the Last Glacial Maximum

We present here a revised reconstruction of the Ross ice drainage system of Antarctica at the last glacial maximum (LGM) based on a recent convergence of terrestrial and marine data. The Ross drainage system includes all ice flowlines that enter the marine Ross Embayment. Today, it encompasses one-fourth of the ice-sheet surface, extending far inland into both East and West Antarctica. Grounding lines now situated in the inner Ross Embayment advanced seaward at the LGM (radiocarbon chronology in Denton and Marchant 2000 and in Hall and Denton 2000a, b), resulting in a thick grounded ice sheet across the Ross continental shelf. In response to this grounding in the Ross (and Weddell) Embayment, ice-surface elevations of the marine-based West Antarctic Ice Sheet were somewhat higher at the LGM than at present (Steig and White 1997; Borns et al. 1998; Ackert et al. 1999). At the same time, surface elevations of the East Antarctic Ice Sheet inland of the Transantarctic Mountains were slightly lower than now, except near outlet glaciers that were dammed by grounded ice in the Ross Embayment. The probable reason for this contrasting behavior is that lowered global sea level at the LGM, from growth of Northern Hemisphere ice sheets, caused widespread grounding of the marine portion of the Antarctic Ice Sheet, whereas decreased LGM accumulation led to slight surface lowering of the interior terrestrial ice sheet in East Antarctica. Rising sea level after the LGM tripped grounding-line recession in the Ross Embayment, which has probably continued to the present day (Conway et al. 1999). Hence, gravitational collapse of the grounded ice sheet from the Ross Embayment, accompanied by lowering of the interior West Antarctic ice surface and of outlet glaciers in the Transantarctic Mountains, occurred largely during the Holocene. At the same time, increased Holocene accumulation caused a slight rise of the inland East Antarctic ice surface.