Moraines and dead ice in Taylor Valley, Antarctica, record retreat of alpine and outlet glaciers from Marine Isotope Stage 5 to 4

Debris-covered glaciers and dead ice are common in the Transantarctic Mountains. We investigated the origin and structure of a 0.1 km2 buried dead ice mass in Taylor Valley near the terminus of Taylor Glacier, an outlet from the East Antarctic Ice Sheet. The dead ice occupies a lobate landform on the northern valley wall with a 10-m-high, 25° terminus, indicative of previous or modern creep. We investigated the ice via ground-penetrating radar, stable isotopic analyses, and sedimentology of overlying debris. We also investigated stratigraphic relationships between the dead ice, moraines deposited by local alpine Rhone Glacier, and deposits associated with Taylor Glacier. The dead ice is 3 to 9+ m thick, with north-dipping sediment layers, opposite of slope direction. Stable isotopes from the ice are similar to those from modern Rhone Glacier. Based on cosmogenic 3He from dolerite boulders on two lateral moraines, Rhone Glacier was larger than present ~81 to 94 ka. The dead ice separated from Rhone Glacier during or after deposition of these moraines. We conclude that Taylor Glacier retreated from its Marine Isotope Stage (MIS) 5e (~125 ka) maximum (~250 m above present) to its present level or lower by ~62 ka but possibly as early as ~81 to 94 ka.