Taylor Glacier drains into Taylor Valley from Taylor Dome, a peripheral ice rise of the East Antarctic Ice Sheet (EAIS) located near the inland edge of the Transantarctic Mountains. Taylor Glacier and local alpine glaciers have expanded in the present-day interglaciation, so that they now occupy their maximum positions since the last global glacial maximum. Exposed on the floor and walls of Taylor Valley between Lake Bonney and Canada Glacier, Bonney drift represents the penultimate eastward (downvalley) advance of Taylor Glacier. Lacustrine algal carbonates, which form in shallow proglacial lakes, were found in most excavations into Bonney drift. Bath in situ and reworked carbonate samples produced 49 new uranium/thorium (U/Th) dates. U/Th dates of 70 to 130 ka for samples collected from excavations and natural sections, along with geomorphologic evidence reported elsewhere in this issue, confirm that the Bonney advance of Taylor Glacier, along with the concurrent expansion of local alpine glaciers, occurred during the interglaciation corresponding with marine isotope stage (MIS) 5. In addition, delta O-18 values (-35 to -43 parts per thousand) of the algal carbonates confirm deposition in a proglacial lake fed by Taylor Glacier meltwater. The detailed distribution of U/Th dates shows that Bonney ice advances occurred in substages 5a, 5c, and 5e. The delta O-18 record of the Taylor Dome ice core also indicates ice thickening during these same intervals. The inclusion of older carbonates in Bonney drift affords evidence for proglacial lakes during MIS 7 (160 to 240 ka), MIS 9 (270 to 330 ka), and MIS 11 or older (>370 ka). It is probable that these proglacial lakes were also associated with interglacial expansions of Taylor Glacier. This terrestrial U/Th geochronology affords a regional constraint on the late Quaternary behavior of the peripheral sector of the EAIS drained by Taylor Glacier, consistent with expansion during global interglaciations and recession during global glaciations.
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