Geological scatter of cosmogenic-nuclide exposure ages in the Shackleton Range, Antarctica: Implications for glacial history

We use cosmogenic ²⁶Al/¹⁰Be ratios in rocks from the Shackleton Range, Antarctica to investigate geological scatter, a challenge that faces exposure-age studies in Antarctica. Examining the scatter helps reveal the long-term lowering of Slessor Glacier, an outlet glacier of the East Antarctic Ice Sheet (EAIS) which flows into the Weddell Sea embayment. 144 ²⁶Al and ¹⁰Be exposure ages from 72 samples are related to bedrock or clast sample characteristics and geomorphological measures of weathering, slope and stability. We explore this noisy dataset by using Principal Components Analysis (PCA) to identify patterns in the data. Despite noise, there exist correlations between age and degree of weathering and age and elevation above the adjacent ice surface. Clasts with young exposure ages have more complex exposure histories than those with old exposure ages. In terms of glacial history we show that (a) warm-based ice covered the upper slopes of the Shackleton Range millions of years ago and that the uplands have been mainly free of ice for more than 800ka, (b) that Slessor Glacier's surface elevation was c. 150m above present at c. 270ka and c. 700ka.