Rapid regional-scale ice-surface lowering at 6.5 ka in southern Victoria Land, Antarctica.

The observational record of outlet glaciers in Antarctica covers the last 50 years. This decadal record is insufficient to address the long-term stability of outlet glaciers in Antarctica. Ice sheets adjust and respond to external forcings on the centennial to millennia time scale. Augmenting the observational record with geological dating, we can better understand the timing, rate, and magnitude of changes to these nontrivial and complex systems and can better model how they may respond to natural and anthropogenic climate change.

Cosmogenic surface-exposure dating of rocks deposited by outlet glaciers provides insight to the style and rate of change for outlet glacier surface-elevation through geological time. A sampling campaign to southern Victoria Land in 2016 has produced two robust, high-resolution age-elevation transects for a large outlet glacier draining the East Antarctic Ice Sheet along the Transantarctic Mountains.

We present 29 new ¹⁰Be ages with a clear and internally-consistent evidence for a rapid ice-surface lowering signal at 6,500 ± 700 years ago from Mawson Glacier in southern Victoria Land. This new ice surface elevation chronology is temporally indistinguishable from previous work conducted nearby at Mackay Glacier. Together, these data sets show synchronous, non-linear behavior of two spatially distinct outlet glaciers, which may provide critical insight to regional Holocene ice sheet history in southern Victoria Land.