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Marine Ecology Progress Series

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MEPS 377:19-32 (2009)  -  DOI:

Contribution of N2 fixation to new production in the western North Pacific Ocean along 155°E

Takuhei Shiozaki, Ken Furuya*, Taketoshi Kodama, Shigenobu Takeda

Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku 113-8657, Japan
*Corresponding author. Email:

ABSTRACT: Nitrogen (N2) fixation and nitrate assimilation activities were examined simultaneously using a 15N tracer in February and March 2007 along the 155°E meridian from the equator to 44°N in the western North Pacific Ocean. N2 fixation was detected only to the south of 28°N, where the nitrate + nitrite (N+N) concentration was <30 nM in the upper mixed layer; the concentration ranged from 12.8 to 152 µmol N m–2 d–1. High N2 fixation rates were observed from 16°N to 24°N, where relatively high dust depositions and low concentrations (<100 nM) of soluble reactive phosphorus (SRP) were observed. The depth-integrated nitrate assimilation in the euphotic zone showed no significant latitudinal trend, varying between 184 and 349 µmol N m–2 d–1 in the area from the equator to 24°N, where the water column was stable. Toward the north of 28°N, nitrate assimilation was enhanced, while N2 fixation became insignificant. The contribution of N2 fixation to new production (= N2 fixation + nitrate assimilation) ranged from 2 to 37%, and the highest contribution was observed at 24°N at the center of the subtropical gyre, where the highest N2 fixation occurred. From the equator to 24°N, the coefficient of variation of nitrate assimilation was 20%, while that of N2 fixation was 80%, indicating that the latter is more responsible for the latitudinal variation in the contribution of N2 fixation to new production.

KEY WORDS: New production · N2 fixation · Nitrate assimilation · ƒ-ratio · Western North Pacific Ocean

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Cite this article as: Shiozaki T, Furuya K, Kodama T, Takeda S (2009) Contribution of N2 fixation to new production in the western North Pacific Ocean along 155°E. Mar Ecol Prog Ser 377:19-32.

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