Evidence from Taylor Valley for a Grounded Ice Sheet in the Ross Sea, Antarctica

ABSTRACT

Four glacial drifts are exposed in eastern Taylor Valley and on Cape Bernacchi on the western side of McMurdo Sound, Ross Sea, Antarctica: Alpine I, Ross Sea, Wilson, and Bonney drifts. Bonney drift is the oldest, underlying Ross Sea drift near Canada Glacier. Ross Sea and Wilson drifts are contemporaneous. Alpine I drift is the youngest, overlying and commonly composed of reworked older deposits. Ross Sea drift extends to 350 m elevation at the Hjorth Hill moraine at the mouth of Taylor Valley. The slope of the moraine, as well as the areal extent of the drift, indicates that Ross Sea drift was deposited by a thick lobe of westward-flowing ice grounded in Explorers Cove. This ice lobe blocked the mouth of Taylor Valley and dammed Glacial Lake Washburn. Relict deltas and shore-lines extend up to 336 m elevation and mark the former level of the lake. A lake-ice conveyor, similar to that now operating on Trough Lake 100 km south of Taylor Valley, transported Ross Sea drift from the ice lobe westward across Glacial Lake Washburn. Kenyte erratics in Ross Sea drift indicate that the ice lobe grounded in Explorers Cove was fed by ice from a flow line that extended around Cape Bird, across western Ross Island, and across McMurdo Sound before terminating in the mouth of Taylor Valley. Overall, the extent of Ross Sea drift, as well as the elevation and slope of its moraines, and the presence of kenyte erratics, all suggest that a large grounded ice sheet existed in the Ross Sea Embayment during the deposition of Ross Sea drift in Taylor Valley. This ice sheet formed during advance of the West Antarctic Ice Sheet across the Ross Sea continental shelf at the last glacial maximum and has implications for the contribution of Antarctica to global sea-level change at that time. The areal extent of Wilson drift, as well as former ice-flow directions inferred from striated and glacially molded bedrock, both indicate that the Wilson Piedmont Glacier deposited Wilson drift during a seaward advance over Marble and Gneiss Points. The piedmont glacier merged with the Ross Sea ice lobe on Cape Bernacchi and Hjorth Hill. Alpine I drift relates to the modern advance of alpine and outlet glaciers. Bonney drift represents an advance of Taylor Glacier during the penultimate interglaciation 70,000–120,000 yr bp.