Lu Y. Y., Wen Z. Z., Shi D. L., Lin W. F., Bonnet Sophie, Dai M. H., Kao S. J. (2019). Biogeography of N-2 fixation influenced by the western boundary current intrusion in the South China Sea. Journal of Geophysical Research : Oceans, 124 (10), p. 6983-6996. ISSN 2169-9275.
Titre du document
Biogeography of N-2 fixation influenced by the western boundary current intrusion in the South China Sea
Lu Y. Y., Wen Z. Z., Shi D. L., Lin W. F., Bonnet Sophie, Dai M. H., Kao S. J.
Source
Journal of Geophysical Research : Oceans, 2019,
124 (10), p. 6983-6996 ISSN 2169-9275
The N-2 fixation and primary production rates were measured simultaneously using N-15(2) and C-13 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 mu mol N center dot m(-2)center dot day(-1) and 62 +/- 19 mmol C center dot m(-2)center dot day(-1), respectively, significantly higher than those for stations with KI index lower than 0.5 (50 +/- 10 mu mol N center dot m(-2)center dot day(-1) and 28 +/- 10 mmol C center dot m(-2)center dot 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.
