[M-IS15] グローバル南極学

[MIS15-P01] On the meridional distribution of oxygen isotope ratio across the Central Indian and Southern Oceans

*青木 茂¹、勝又 勝郎²、芳村 圭² (1.北海道大学、2.東京大学)

キーワード：酸素安定同位体比、インド洋、南大洋、緯度セクション

In austral summer in 2019/2020, top-to-bottom observations of stable oxygen isotope ratio (δ¹⁸O) were conducted along the GO-SHIP/WOCE Hydrographic Program sections across the central Indian Ocean and adjacent Southern Ocean. Spatial structure of δ¹⁸O is described with the associated watermass evolution. At the surface, δ¹⁸O is highest in the southern subtropics, low in the low-latitudes, and lowest in the southern high latitudes. At the bottom, δ¹⁸O varies among the basins, increasing from the south to north. δ¹⁸O of Cape Darnley Bottom Water is lower than ambient Antarctic Bottom Water varieties, revealing a higher fraction of glacial meltwater of shelf water origin. δ¹⁸O -salinity relationship of the surface layer reveals an overall dominance of precipitation and evaporation away from the coast. In the southern high latitudes, the δ¹⁸O -salinity relationship below the temperature minimum indicates the balance of precipitation and evaporation, while that above the temperature minimum reveals a prominent effect of sea ice melt. The information provides a useful measure of the freshwater cycle. The present dataset hence can be the baseline information of the present and future freshwater exchange in the Indian and Southern Oceans and contribute to construct the global compilation of δ¹⁸O observations.