Chronology of taylor glacier advances in Arena Valley, Antarctica, using in situ cosmogenic ³He and ¹⁰Be

In situ produced cosmogenic nuclides provide a new technique for constraining exposure ages of glacial deposits. In situ³He and ¹⁰Be in quartz sandstone boulders from Arena Valley, southern Victoria Land, Antarctica, provide chronological constraints for a sequence of moraines (“Taylor II-IVb” moraines) related to expansions of Taylor Glacier and the East Antarctic Ice Sheet. Mean ³He ages are 113,000 ± 45,000 yr, 208,000 ± 67,000 yr, 335,000 ± 187,000 yr, and 1.2 ± 0.2 myr, for Taylor II, III, IVa, and IVb moraines, respectively (mean ± 1σ). Corresponding mean ¹⁰Be ages for Taylor II and IVb moraines are 117,000 ± 51,000 yr and 2.1 ± 0.1 myr. For the older deposits the ³He ages are probably lower limits due to diffusive loss. Although the exposure ages appear consistent with the few previous age estimates, particularly with an isotope stage 5 age for Taylor II, each moraine exhibits a broad age distribution. The distribution probably results from a variety of factors, which may include prior exposure to cosmic rays, ³He loss, erosion, postdepositional boulder movement, and radiogenic production of ³He. Nonetheless, the exposure ages provide direct chronological constraints for the moraine sequence, and suggest a maximum thickening of Taylor Glacier relative to the present ice surface of ∼500 m since the late Pliocene-early Pleistocene.