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Atmospheric chlorofluorocarbons (CFCs) dissolved in seawater observed during 1990 to 1994 in the South Pacific ocean are being assimilated to delineate large scale ocean circulation and ventilation processes. At present our working data set comprises one pre-WOCE expedition (NOAA CGC-90) and six WOCE WHP expeditions (WHP lines P6C, P16S, P17S&E, P18, P19S and S4P). Station profile data are at present interpolated linearly to obtain values on potential density surfaces which are then mapped using GMT (Generic Mapping Tools) software, but we are in the process of applying objective mapping techniques to improve the gridding of these results.
The regions of the cyclonic Ross Sea gyre and the western Ross Sea are apparently important sites for ventilation of subsurface waters. The ventilation time scale of Antarctic Intermediate Water is estimated by CFC "apparent age" to 15-20 years at ~40°S, and 20-25 years in the tropics. An extensive map of CFC age on this density surface is being constructed. Tongues of high-CFC waters show the northward transport of the deep western boundary flow between ~170°W and ~180° in the Upper Circumpolar Deep Water (UCDW) and in the Lower Circumpolar Deep Water (LCDW). UCDW in the Antarctic Circumpolar Current (ACC) is relatively well ventilated with CFCs, although its oxygen content is very low, implying that the UCDW is mixture of a small fraction of recently ventilated water with old water. The LCDW is apparently ventilated by mixing with newly-formed bottom water. CFC minimum water layer exists in and south of the ACC between LCDW and the Antarctic Bottom Water (AABW). The diapycnal mixing of AABW is probably responsible for discontinuities in the overlying CFC minimum, resulting in separate CFC minimum patches south of the ACC. Recently-formed Ross Sea AABW propagates westward with very high CFC content along the Antarctic continental shelf, and also flows eastward under the southward extension of the ACC, as well as spreading to the northeast along the western boundary of the mid-ocean ridge. The northward spreading of Ross Sea AABW is limited to the mid-ocean ridge in the west and to ~55°S in the east, while in the Bellingshausen Sea the westward tongue of low-CFC deep waters along ~65°S seems to be of northern origin.
By including other CFC data sets from this region, and by normalizing for changes in CFC distributions over the 5 year time span of the observations, we hope to obtain a more precise and detailed understanding of South Pacific circulation and ventilation processes.
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