HR: 0830h
AN: OS11A-02    [Abstracts]
TI: Hypoxia in The East China Sea: One of The Largest Hypoxic Areas in The World
AU: * Chen, C
EM: ccchen@cc.ntnu.edu.tw
AF: Department of Life Science, National Taiwan Normal University, 88, Sec. 4, Ting-Chou Road, Taipei, 116 Taiwan
AU: Gong, G
EM: gcgong@mail.ntou.edu.tw
AF: Department of Oceanography, National Taiwan Ocean University, Keelung, 202-24 Taiwan
AU: Shiah, F
EM: fkshiah@gate.sinica.edu.tw
AF: Environment Change Center, Academia Sinica, NanKang, Taipei, Taiwan
AB: Anoxia and/or hypoxia have been widely observed in estuarine, coastal regions in the past few decades, however, there are limited reports focused on the East China Sea (ECS). The ECS is one of the largest continental shelves in the world. It receives significant amounts of allochthonous organic carbon and inorganic nutrients from riverine run-off, especially from the Yangtze River. In June and August 2003, two cruises sampled at stations that covered almost the entire ECS to exam temporal and spatial variations in hypoxic events, and their potential causes. Results showed that, in August, an area estimated at greater than 2 x 10⁴ km², with DO concentrations < 2-3 mg l^-1, extended from the Yangtze River plume ca. 400 km offshore and ca. 300 km southward along the coast. Vertically in the water column, DO became deficient below the mixed layer, ca. 10-20 m, to the bottom in this hypoxic area. In June however, DO concentration in the water column was higher than 4 mg l^-1 in most of the shelf region. When the hypoxic zone was compared between these two months, Chl a concentration in the euphotic zone was much higher in June (6.1 mg Chl m^-3) than that in August (0.8 mg Chl m^-3). Similar to the Chl a comparison, dissolved inorganic nitrogen was also higher in June than in August with values of 9.13 μ M and 7.48 μ M, respectively. Physically, a very sharp density gradient was observed under the mixed layer in August. Results suggest that hypoxia in the ECS might due to water column stratification, restricting vertical re-aeration, and increasing rates of respiration and bio-degradation of residual organic material, which result in a warmer sea floor water temperature.
DE: 4219 Continental shelf processes
DE: 4243 Marginal and semienclosed seas
DE: 4834 Hypoxic environments
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly