Quantitative evaluations of ocean circulation and meridional themohaline transport in the Indian sector of Antarctic

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The purpose of this study is to make an analysis of our observational data in which the seasonal variability of volume transport for the northward flowing Antarctic Bottom Water in the Indian sector of the Antarctic could be successfully obtained for the first time. We have done the deployment of the current-mooring systems at 8 stations off the southeastern coast of the Kerguelen Plateau for two years from February 2003 to January 2005, as an international joint project together with CSIRO in Australia. Our primary data analyses have shown that this region has completely reverse current direction over the continental shelf slope and the far offshore; the former is northwestward flow while the latter is southeastward flow. Therefore, the water circulation system in this region is approximately composed of the northward flow as a western boundary current and southward flow due to the cyclonic recirculation.In this study, we have also derived the sea-ice thickness distribution in the coastal polynyas where are the formation areas of the Antarctic Bottom Water, using the SSMI microwave data. From the data analyses and heat-budget calculation, we also have successfully made the mapping of the amount of sea-ice production in the coastal polynyas. According to our study, the area of the largest amount of sea-ice production in the Antarctic is Ross Sea. However, the amount of the sea-ice production in the coastal polynyas of the Ross Sea decreases about 30% during the period from 1990's to 2000's; this may lead to the recent trend of the freshening of the Antarctic Bottom Water.Although we did not yet make all the data analyses, we will propose water circulation system in the Indian Ocean sector of the Antarctic quantitatively, in the nearfuture.