[M-IS08] 南大洋・南極氷床が駆動する全球気候変動

[MIS08-P07] Reconstruction of paleoceanographic changes in the Antarctic zone during the Pleistocene based on the newly developed GDGT-based water mass proxy

石井 花菜²、*関 宰¹、山本 正伸³、ウェーバー マイク⁴ (1.北海道大学低温科学研究所、2.北海道大学大学院環境科学院、3.北海道大学地球環境科学研究院、4.ボン大学)

キーワード：GDGT、南極海、更新世、水温変動

There is growing concern that the melting of the Antarctic ice sheet due to global warming. Recent observations reveal that the basal melting of the ice shelf due to the intrusion of warm deep water under the ice shelf is the key processes leading to Antarctic ice mass loss. The warm deep water intrusion beneath ice shelves is thought to be related to changes in the large-scale atmosphere and ocean circulations in the Southern Hemisphere, such as the Antarctic Circumpolar Circulation (ACC) and Southern Westerly Wind (SWW), but this has not been fully tested. The reconstruction of ocean circulation and temperature in the Antarctic zone during the past warm periods provides an insight into the causal link between the Southern Ocean circulation and ice sheet changes. However, the palaeoceanographic changes in the Antarctic zone during the Pliocene remain uncertain due to the lack of robust water mass and temperature proxies applicable to the Antarctic zone. In this study, we developed the GDGT (isoprenoid Glycerol dialkyl glycerol tetraethers) based new index, which can reconstruct past changes in ocean circulation and temperature in the Antarctic zone, based on reanalysis of the reported core-top GDGT data in the Southern Ocean. Then, we applied the new method to sediment cores U1537 and U1538 to reconstruct changes in ocean circulation and temperature in the Antarctic zone (Scotia Sea) during the Late Pleistocene. The results show that seawater temperature fluctuated in sync with the late Pleistocene glacial-interglacial cycle with significant southward migration of ACC and an increase in temperature during the super interglacials when the Antarctic ice sheet retreated significantly. These results suggest that changes in large-scale ocean circulation in the Southern Ocean could play an important role in the Antarctic ice sheet changes during the past warm periods.