GSA Connects 2021 in Portland, Oregon

Paper No. 130-10
Presentation Time: 10:20 AM


BEHRENS, Bethany1, YOKOYAMA, Yusuke2, MIYAIRI, Yosuke1, SPROSON, Adam David3, YAMANE, Masako4 and JIMENEZ-ESPEJO, Francisco J.5, (1)Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-0882, Japan, (2)Ocean Research Institute/Department of Earth and Planetary Sciences, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639, Japan; Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-0882, Japan, (3)Japan Agency for Marine-Earth Science and Technology, JAMSTEC, 2-15 Natsushimacho, Yokosuka, 237-0061, Japan, (4)3Institute for Space-Earth Environmental Research, Nagoya University, Furocho, Chikusa Ward, Nagoya, 464-8601, Japan, (5)Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Av. de las Palmeras, Granada, 4-18100, Spain

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.