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Marine Ecology Progress Series

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MEPS 447:77-86 (2012)  -  DOI:

Nitrogen fixation in the East China Sea and southern Yellow Sea during summer 2006

Run Zhang1, Min Chen1,2,*, Jianping Cao1, Qiang Ma1, Junhong Yang1, Yusheng Qiu1,2

1Department of Oceanography, and 2State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, 361005, PR China

ABSTRACT: Nitrogen fixation in the subtropical East China Sea (ECS) and the southern Yellow Sea (YS) were measured using 15N2 tracer assay during June and July 2006. Depth-integrated nitrogen fixation (2 to 221 µmol N m−2 d−1) was highest in the oceanic main path of the Kuroshio Current in the northeastern ECS, and in the mesohaline (surface salinity 30 to 34) stations. Very little N2 fixation was encountered in the low-salinity (surface salinity <30) area, and we suggest that N2 fixation was hindered by the nutrient conditions (lack of ‘excess’ phosphate relative to nitrate, xsPO4 = [PO4] − [NO3]/16) near the Changjiang (Yangtze River) mouth. In the mesohaline waters, N2 fixation was positively correlated with the vertical density (σt) gradient in the upper water column (30 m), indicating that N2 fixation can also be controlled by physical regime, and enhanced water column stratification may promote N2 fixation during summer. N2 fixation met 0.01 to 4.6% of nitrogen demand by primary production, suggesting that N2 fixation was not a major contributor to primary production in the study area. Estimated new N flux by N2 fixation to the ECS continental shelf (13 Gg N) during summer is at the same order of magnitude as atmospheric deposition, but much lower than either the Kuroshio subsurface water upwelling or the Changjiang riverine input.

KEY WORDS: Nitrogen fixation · East China Sea · Southern Yellow Sea · 15N2 assay

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Cite this article as: Zhang R, Chen M, Cao J, Ma Q, Yang J, Qiu Y (2012) Nitrogen fixation in the East China Sea and southern Yellow Sea during summer 2006. Mar Ecol Prog Ser 447:77-86.

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