[M-IS15] Global Antarctic Science: connecting the chain of changing huge ice sheets and global environments

[MIS15-16] Evaluation and establishment of CDW proxy based on Be isotope distribution of surface marine sediments from East Antarctica

*Yuri Yamazaki¹, Yusuke Suganuma^2,1, Takuya Itaki³, Atsuko Amano³, Takeshige Ishiwa^2,1, Motohiro Hirabayashi^2,1, Hiroyuki Matsuzaki⁴, Takeyasu Yamagata⁴, Jun'ichi Okuno^5,2,1, Daisuke Hirano^2,1, Takeshi Tamura^2,1, Keiji Misawa^2,1, Kosei E Yamaguchi⁶ (1.The Graduate University for Advanced Study, SOKENDAI, 2.National International Polar Research, 3.Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology, 4.Tokyo University, 5. Joint Support-Center for Data Science Research, Research Organization of Information and Systems, 6.Toho University)

Keywords:Proxy, Circumpolar Deep Water (CDW), East Antarctica, oceanic paleoenvironment

The Antarctic Ice Sheet has experienced massive ice mass loss. It is, therefore, a primary focus of attention due to its significant societal impacts, including sea level rise. The primary cause of the ice mass loss has been thought to be the Circumpolar Deep Water (CDW) inflow onto the continental shelf, causing the basal melting of the ice sheet and ice shelves. However, the temporal variability of ice sheet/shelf and CDW inflow on longer time scales remain uncertain; hampered by the limited availability of observational data covering only the last few decades. Long-term geological records have the potential to reconstruct ice sheet variability and associated environmental changes in the past, helping us to understand the relationship between CDW and ice sheet/shelf variability. Therefore, our research aims to reveal the spatial distribution of Be isotopes in marine sediments from East Antarctica and develop them as a proxy for CDW to reconstruct their variability in the recent past. Although Be isotopes in marine sediments have been studied as indicators of ice sheet variability, what their behavior indicates remains controversial. In this study, we used the surface sediment from 11 sites from Totten Glacier (TG) and eight sites from Lützow-holm Bay (LHB) recovered during the 47th and 61st Japanese Antarctic Research Expedition. In addition, we estimated the main factor affecting the Be isotope distributions using oceanographic and satellite observational data.
¹⁰Be concentrations and ¹⁰Be/⁹Be ratios of the surface sediments are higher at the sites along the path of CDW inflow than at sites outside the inflow in both regions. Their values decrease from upstream to downstream along the inflow from offshore toward the ice sheet margin. In contrast, ⁹Be concentrations tend to be higher near the ice margin and downstream along the CDW inflow in both regions, suggesting that they are released from beneath the icesheet and transported by the return flow of CDW. The ice coverage at all collecting sites during the summer from 2012 to 2020 was estimated to have been more than 10% in TG and 80% in LHB, showing decoupling between Be isotope and ice coverage. These findings indicate that ¹⁰Be concentrations are strongly influenced by the CDW inflow, suggesting ¹⁰Be concentrations and ¹⁰Be/⁹Be ratios can be used as a proxy for reconstructing the past variability in CDW inflow. ⁹Be concentrations are thought to reflect sediment release from beneath the ice sheet, implying that they can serve as a proxy for ice sheet retreat. This study is fundamental for understanding the relationship in trend between the recent warming and the melting of the Antarctic ice sheet. To improve the accuracy of ¹⁰Be as a CDW proxy, we need to clarify the interaction between sediments and seawater by comparing their Be isotope compositions.