Chlorofluorocarbons in the western North Pacific in 1993 and formation of North Pacific intermediate water |
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| Authors: | Takayuki Tokieda Shuichi Watanabe Shizuo Tsunogai |
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| Institution: | (1) Department of Chemistry, Graduate School of Fisheries Science, Hokkaido University, 041 Hakodate, Japan;(2) Laboratory of Marine and Atmospheric Geochemistry, Graduate School of Environmental Earth Science, Hokkaido University, 060 Sapporo, Japan |
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| Abstract: | Chlorofluorocarbons (CFC-11 and CFC-12) in the intermediate water having   between 26.4 and 27.2 were determined at 75 stations in the western North Pacific north of 20°N and west of 175.5°E in 1993. The intermediate water of 26.4–26.6 was almost saturated with respect to the present atmospheric CFC-11 in the zone between 35 and 45°N around the subarctic front. Furthermore, the ratios of CFC-11/CFC-12 of the water were also of those formed after 1975. These suggest that the upper intermediate water (26.4–26.6) was recently formed by cooling and sinking of the surface water not by mixing with old waters. The water below the isopycnal surface of 26.8 contained less CFCs and the area containing higher CFCs around the subarctic front was greatly reduced. However, the CFC age of the lower intermediate water (26.8–27.2) in the zone around the subarctic front was not old, suggesting that the water was formed by diapycnal mixing of the water ventilated with the atmosphere with old waters not containing appreciable CFCs, probably the Pacific Deep Water. The southward spreading rate decreased with depth and it was one sixth of its eastward spreading rate of the North Pacific Intermediate Water (NPIW). |
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