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New estimation of N 2 fixation in the western and central Pacific Ocean and its marginal seas
Author(s) -
Shiozaki Takuhei,
Furuya Ken,
Kodama Taketoshi,
Kitajima Satoshi,
Takeda Shigenobu,
Takemura Toshihiko,
Kanda Jota
Publication year - 2010
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2009gb003620
Subject(s) - trichodesmium , upwelling , oceanography , biology , zoology , geology , nitrogen fixation , chemistry , nitrogen , diazotroph , organic chemistry
The distribution of N 2 fixation was examined using a 15 N 2 tracer with accompanying measurements of abundance of Trichodesmium spp. and Richelia intracellularis , nitrate plus nitrite (N+N) and soluble reactive phosphorus at the nanomolar level, and primary production in the western and central Pacific Ocean. N 2 fixation occurred only in >∼20°C oligotrophic (i.e., N+N < 100 n M ) waters except at a station in the equatorial upwelling zone where N+N was 1880 n M . High N 2 fixation rates were observed in the Kuroshio and East China Sea (KECS) and near Fiji and other isolated islands with concomitant high abundance of Trichodesmium spp. In contrast, N 2 fixation in the western and central oligotrophic North Pacific (WCONP) was significantly lower, and Trichodesmium spp. were rarely observed. These observations hint that KECS and waters around isolated islands are N 2 fixation “hot spots” because of the occurrence of Trichodesmium spp. The average N 2 fixation rate in the KECS of 232 ± 54.8 (±SE, n = 13) μ mol N m −2 d −1 was almost 1 order of magnitude higher than that in the WCONP of 39.2 ± 7.51 ( n = 26) μ mol N m −2 d −1 . On the basis of these estimates and reported values obtained using 15 N 2 , depth‐integrated N 2 fixation in the North Pacific was estimated to be 2.6 ± 0.3 × 109 ( n = 63) mol N d −1 , which is less than half of previous estimates. This difference was ascribed primarily to the unavailability of N 2 fixation rates in the WCONP, which occupies a vast area of the subtropical North Pacific, and the use of data obtained in the hot spots which represent small areas that likely led to the previous overestimation.