Elevated East Antarctic outlet glaciers during warmer-than-present climates in southern Victoria Land

摘要

We document Plio-Pleistocene changes in the level of Taylor Glacier, an outlet glacier in southern Victoria Land that drains Taylor Dome on the periphery of the East Antarctic Ice Sheet (EAIS). Chronologic control comes from 3He cosmogenic-nuclide analyses of 27 boulders sampled from drifts and moraines in Kennar Valley, a small hanging valley that opens onto a peripheral lobe of Taylor Glacier in the Quartermain Mountains. Assuming a constant boulder-erosion rate of 10 cm Myr~(-1) our preferred age model spans the last 3.1 Myr and calls for stepped ice recession from a local highstand -200 m above the present base of Taylor Glacier at the mouth of Kennar Valley. The texture and sedimentology of all mapped moraines and drifts indicate deposition from cold-based ice, analogous with the modern Taylor Glacier at the mouth of Kennar Valley. The Kennar Valley glacial record shows an uncharacteristic relationship with average global temperatures, exhibiting higher-than-present ice levels during globally warm periods, including the Pliocene climatic optimum (-3.1 Ma) and Marine Oxygen Isotope Stage (MIS) 31 (-1.07 Ma). The Kennar Valley record also suggests that the rate of ice-surface lowering accelerated after the mid-Pleistocene transition at -0.9 Ma. Correlation of our moraine record with published reports for fluctuations of Taylor Glacier elsewhere in the Quartermain Mountains, and with a dated moraine record from Ferrar Glacier (a second outlet for Taylor Dome), reveals similar ice-surface changes, highlighting minor, but widespread ice recession in southern Victoria Land since the mid- to late-Pliocene. Our record for minimal variability in the East Antarctic Ice Sheet contrasts with recent data from nearby marine cores that call for dynamic fluctuations in the volume of grounded ice in the Ross Embayment, and significant reduction of the West Antarctic Ice Sheet (WAIS) during warmer-than-present intervals. Taken together, these records from the Ross Embayment call for considerable variation in the response of marine-based West Antarctic ice and terrestrial East Antarctic outlet glaciers during Plio-Pleistocene time.