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Biogeography of N 2 Fixation Influenced by the Western Boundary Current Intrusion in the South China Sea

By Yangyang Lu, Zuozhu Wen, Dalin Shi, Wenfang Lin, Sophie BONNET, Minhan Dai and Shuh‐Ji Kao

Abstract

International audienceThe N 2 fixation and primary production rates were measured simultaneously using 15 N 2 and 13 C incubation assays in the northern South China Sea influenced by the Kuroshio intrusion (KI) seasonally. The degree of KI (KI index, range from 0 to 1) was assessed by applying an isopycnal mixing model. The water column integrated N 2 fixation and primary production for stations with KI index larger than 0.5 were 463 ± 260 μmol N·m −2 ·day −1 and 62 ± 19 mmol C·m −2 ·day −1 , respectively, significantly higher than those for stations with KI index lower than 0.5 (50 ± 10 μmol N·m −2 ·day −1 and 28 ± 10 mmol C·m −2 ·day −1 , respectively). Trichodesmium was the dominant diazotroph at stations with KI index larger than 0.5, with 2 orders of magnitude higher nifH gene abundance than that at stations with KI index lower than 0.5. However, the highest N 2 fixation rates were found in waters with moderate KI index around 0.6, suggesting that frontal zone mixing might stimulate N 2 fixation. Our results demonstrated that diazotrophs (mainly Trichodesmium) were tightly associated with the KI, which modulated the biogeographic distribution of N 2 fixers. In summary, we found the transportation of Trichodesmium by KI, then, we quantified the fraction of KI and N 2 fixation rates in the northern South China Sea. The results suggested that KI generated a new biogeographic regime which could significantly influence the carbon and nitrogen cycles far away from the main stream

Topics: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere
Publisher: 'American Geophysical Union (AGU)'
Year: 2019
DOI identifier: 10.1029/2018JC014781
OAI identifier: oai:HAL:hal-02461797v1
Provided by: HAL AMU
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