[M-IS34_2PM2] 全球環境変動解明の鍵： 南大洋・南極氷床

[MIS34-09] 最終氷期の南大洋における千年スケールの海氷拡大イベント

*池原 実¹、香月 興太²、山根 雅子³、横山 祐典⁴ (1.高知大学海洋コア総合研究センター、2.韓国地質資源研究院、3.海洋研究開発機構、4.東京大学大気海洋研究所)

キーワード：南大洋, 海氷, 千年スケール変動, ダスト

The Southern Ocean has played an important role in the evolution of the global climate system. Area of sea ice shows a large seasonal variation in the Southern Ocean. Sea ice coverage on sea surface strongly affects the climate of the Southern Hemisphere through its impacts on the energy and gas budget, on the atmospheric circulation, on the hydrological cycle, and on the biological productivity. In this study, we have conducted fundamental analyses of ice-rafted debris (IRD) and diatom assemblage to reveal a rapid change of sea ice distribution in the glacial Southern Ocean. A piston core COR-1bPC was collected from the Conrad Rise, Indian sector of the Southern Ocean. Core site is located in the Polar Frontal Zone. Sediments are composed of diatom ooze. Age model of COR-1bPC was established by 14C dating and oxygen isotope stratigraphy of planktic foraminifera. Records of IRD concentration suggest millennial-scale pulses of IRD delivery during the last glacial period. The depositions of rock-fragment IRD excluding volcanic glass and pumice were associated with increasing of sea-ice diatoms, suggesting that the millennial-scale events of cooling and sea-ice expansion were occurred in the glacial South Indian Ocean. Similar episodic IRD depositions were identified in the South Atlantic during the last glacial period (Kanfoush et al., 2000). However, Nielsen et al. (2007) proposed that the tephra-rich grains in the South Atlantic IRD events (SA-IRD events) were mainly derived from South Sandwich Island volcanic arc, and concluded that sea-ice was the dominant ice rafting transport of such IRD grains. Preliminary provenance study of IRD grains suggest that the source of IRD in the South Indian Ocean was also volcanic arc in the South Atlantic, based on chemical compositions of rock-fragment IRD grains. Thus prominent IRD layers in the glacial South Indian Ocean correlate the SA-IRD event, suggesting episodes of sea ice expansion and cooling in the Atlantic and Indian sectors of the Southern Ocean.