HOLOCENE GLACIAL DYNAMICS OF EAST ANTARCTICA DETECTED BY BERYLLIUM ISOTOPE RATIOS FROM THE ADÉLIE BASIN

The Adélie Basin is a small, semi-enclosed basin located on the continental shelf of Terre Adélie, East Antarctica, near the largest subglacial basin in East Antarctica, the Wilkes Basin. Last Glacial Maximum ice retreat opened the basin to sediment deposition, resulting in a laminated sediment record ideal for examining post-Last Glacial Maximum ice sheet dynamics. One way to identify periods of ice sheet retreat is by using the cosmogenic isotope beryllium-10 (¹⁰Be), produced by interactions between cosmic rays and molecules in the atmosphere (meteoric ¹⁰Be). Meteoric ¹⁰Be is deposited with snowfall and wind-blown dust onto the ice sheet where it is stored until the ice melts. A sediment core from the Adélie Basin was previously analyzed for meteoric ¹⁰Be to evaluate periods of meltwater discharge during the Holocene. However, since meteoric ¹⁰Be is affected by grain size, normalizing to the stable isotope ⁹Be can provide improved estimations of the timing of glacial retreat and advance.

The stable isotope ⁹Be is released through chemical weathering of bedrock and leaves the weathering zone with meltwater discharge. Therefore, in Antarctica high values of ⁹Be reflect periods of increased basal erosion. Here, we re-examine the Adélie Basin marine sediment core using ¹⁰Be/⁹Be ratios to assess periods of East Antarctic meltwater fluctuations during the Holocene. The ¹⁰Be/⁹Be isotope data indicate increased meltwater discharge after grounded ice retreated from the Adélie Basin from 9.9 to 9.2 ka BP. Sediment from basal erosion and freshwater from the local retreating ice sheet in Wilkes Basin supplied the Adélie Basin with ⁹Be and meteoric ¹⁰Be. This is reflected in the lithology of the core and the Al₂O₃/TiO₃ ratio, which has the highest values at the bottom of the core indicating enhanced weathering. The increase in ¹⁰Be/⁹Be from 4 to 3.3 ka BP and again from 2 ka BP occurs concurrently with continent-wide ice retreat due to late Holocene strengthening of the Southern Westerly Winds and associated Circumpolar Deep Water upwelling onto the continental shelf resulting in increased Southern Ocean stratification and enhanced sea ice cover. Warm subsurface waters due to the insulating effect of sea ice cover may have enhanced the melting effect during this period.