Cold deep water in the South China Sea |
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Authors: | Ya-Ting Chang Wei-Lun Hsu Jen-Hua Tai Tswen Yung Tang Ming-Huei Chang Shenn-Yu Chao |
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Institution: | (1) Key Laboratory of Climate, Resources, and Environment in Continental Shelf Sea and Deep Sea, College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China;(2) Physical Oceanography Laboratory, Ocean University of China, Qingdao, 266003, China;(3) State Key Lab of Marine Geology, Tongji University, Shanghai, 200092, China |
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Abstract: | Two deep channels that cut through the Luzon Strait facilitate deep (>2000 m) water exchange between the western Pacific Ocean
and the South China Sea. Our observations rule out the northern channel as a major exchange conduit. Rather, the southern
channel funnels deep water from the western Pacific to the South China Sea at the rate of 1.06 ± 0.44 Sv (1 Sv = 106 m3s−1). The residence time estimated from the observed inflow from the southern channel, about 30 to 71 years, is comparable to
previous estimates. The observation-based estimate of upwelling velocity at 2000 m depth is (1.10 ± 0.33) × 10−6 ms−1, which is of the same order as Ekman pumping plus upwelling induced by the geostrophic current. Historical hydrographic observations
suggest that the deep inflow is primarily a mixture of the Circumpolar Deep Water and Pacific Subarctic Intermediate Water.
The cold inflow through the southern channel offsets about 40% of the net surface heat gain over the South China Sea. Balancing
vertical advection with vertical diffusion, the estimated mean vertical eddy diffusivity of heat is about 1.21 × 10−3 m2s−1. The cold water inflow from the southern channel maintains the shallow thermocline, which in turn could breed internal wave
activities in the South China Sea. |
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