[M-IS34_2PM2] Southern Ocean and Antarctic Ice sheet: Key to resolve global environmental change

[MIS34-09] Millennial-scale sea ice expansion in the glacial Southern Ocean

*Minoru IKEHARA¹, Kota KATSUKI², Masako YAMANE³, Yusuke YOKOYAMA⁴ (1.Center for Advanced Marine Core Research, Kochi University, 2.Korea Institute of Geoscience and Mineral Resources (KIGAM), 3.JAMSTEC, 4.Atmosphere and Ocean Research Institute, University of Tokyo)

Keywords:Southern Ocean, sea ice, millennial-scale, dust

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.