Abstract
We mapped six distinct glacial moraines alongside Stocking Glacier in the McMurdo Dry Valleys, Antarctica. Stocking Glacier is one of several alpine glaciers in the Dry Valleys fringed by multiple cold-based drop moraines. To determine the age of the outermost moraine, we collected 10 boulders of Ferrar Dolerite along the crest of the moraine and analyzed mineral separates of pyroxene for cosmogenic 3He. On the basis of these measurements, the exposure age for the outermost moraine is 391 ± 35 ka. This represents the first documented advance of alpine glacier ice in the Dry Valleys during Marine Isotope Stage (MIS) 11. At this time, Stocking Glacier was ~20–30% larger than today. The cause of ice expansion is uncertain, but most likely it is related to increased atmospheric temperature and precipitation, associated with reduced ice extent in the nearby Ross Embayment. The data suggest complex local environmental response to warm climates in Antarctica and have implications for glacial response to Holocene warming. The study also demonstrates the potential for using alpine glacier chronologies in the Transantarctic Mountains as proxies for retreat of grounded glacier ice in the Ross Embayment.
Highlights
We present an alpine exposure-age chronology from the Dry Valleys
7 Stocking Glacier is located at the geographic transition between the relatively warm coastal-thaw zone and the inland-mixed zone, where modern summertime air temperatures occasionally rise above 0 °C for a few weeks per year
Annual and summertime ice loss at Stocking Glacier is dominated by sublimation, local meltwater forms alongside solar-heated rocks exposed on the glacier surface[8], and more significantly at lateral-ice margins where supraglacial debris is concentrated (Figs 1 and 2)
Summary
We present an alpine exposure-age chronology from the Dry Valleys. This chronology comes from Stocking Glacier, which is situated in the central Transantarctic Mountains at ~77°42′S and 161°51′E, near the center of the Dry Valleys region. The majority of ice accumulation for Stocking Glacier occurs in the westernmost of the three source cirque valleys in the Asgard Range (Fig. 1) From these local accumulation areas, Stocking Glacier flows for ~6 km, descending from ~1800 meters above sea level (masl) to ~800 masl. Like other glaciers in Taylor Valley[11,14], the terminus of Stocking Glacier is an ice cliff, 20–30 m high, that calves onto a low-angle ice apron below (Figs 2 and 3). This ice apron is a composite of ice chunks, occasional boulders, fine sediments, and refrozen meltwater. The lateral margins in the ablation zone of Stocking Glacier are characterized by stepped calving, seasonally-active meltwater streams, and ice-cored moraines overlain by fluvially-reworked, sand-rich sediments[15]
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