| The idea that one of the sources of Antarctic Bottom Water (AABW) comes from the Prydz Bay region in the Indian sector of the Southern Ocean has been proposed for a long time, which is based on rather limited hydrographic observations. Following recent chlorofluorocarbon (CFC) observations and ocean circulation model simulations supporting the hypothesis, we seek further evidence of the AABW source in the Prydz Bay region based on Japanese Whale Research Program in the Antarctic (JARPA) data. JARPA carried out by the Institute of Cetacean Research provides long-term and extensive hydrographic data in the Antarctic Ocean from the Antarctic coastal area to 60 degree south in the Indian and the Pacific sectors every summer (Dec.-Mar.) since December 1987: Expendable Bathythermograph (XBT) data from December 1987 to March 1997, Expendable Conductivity-Temperature-Depth profiler (XCTD) data from December 1997 to the present, and Conductivity-Temperature-Depth profiler (CTD) data from December 1998 to the present. The Prydz Bay region was investigated intensively in the cruises from December 1999 to March 2000 and from December 2001 to March 2002. The topography in Prydz Bay is characterized by typical depths of 500-600m and a deep basin in the inner part of the Bay. Isopynal maps based on our dataset confirm Circumpolar Deep Water (CDW) as a salty and relatively warm water mass approaching the shelf break of the Bay. Hydrographic sections from the two cruises clearly show intrusions of modified CDW over the shelf. AABW production is supposed to be associated with the mixing CDW with cold shelf water. This shelf water must be saltier than 34.6psu to produce AABW; this type of water is called High Salinity Shelf Water (HSSW). HSSW is observed in the abysal layer of the basin deeper than 600m. The present sections show that the bottom layer below the intrusion of modified CDW is filled with relatively high salinity shelf water and that active mixing of the two water masses occurs. We further present a single XCTD section demonstrating the existence of HSSW in vicinity of the shelf break. This HSSW appears close enough to unmodified CDW to be mixed with it in continental slope, giving weighty evidence of the AABW source in Prydz Bay. |
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