Late Quaternary ice-surface fluctuations of Beardmore Glacier, Transantarctic Mountains

Former longitudinal profiles of Beardmore Glacier, an outlet through the Transantarctic Mountains, constrain polar plateau elevations near the center of Antarctica and ice-shelf grouding in the southern Ross Embayment. Three gravel drift sheets of late Quaternary age occur alongside Beardmore Glacier. Plunket drift, the youngest, is parallel to and 7–30 m above the present ice surface. The upper limit of Beardmore drift, intermediate in age, is within 35–40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth. The upper limit of Meyer drift, the oldest, is parallel to and 30–50 m above Beardmore drift. From correlation with numerically dated drifts farther north, we assign an early Holocene age to Plunket drift, a late Wisconsin age to Beardmore drift, and an age of marine isotope Stage 6 to Meyer drift. By our age model, Beardmore Glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by Beardmore and Meyer drifts. Most likely, grounded ice in the southern Ross Embayment caused such thickening of Beardmore Glacier almost to the polar plateau. A concomitant decline in precipitation is implied by ice-cap retreat on the nearby Dominion Range and is consistent with little change of upper Beardmore Glacier. Ice-shelf grounding most likely resulted from lowered sea level and/or basal melting. Lower than present precipitation was probably caused by colder air temperatures and more-distant open water. The Plunket profile records Holocene ice-surface lowering from increased surface ablation, decreased ice flow, or grounding-line recession.