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Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
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DON cycling in the South China Sea: insights from stable isotope
Monday 7th @ 1350-1410, Multifunction Hall
Run Zhang* , Xiamen University
Xingchen Wang, California Institute of Technology
Presenter Email: zhangrun@xmu.edu.cn |
| Dissolved organic nitrogen (DON) is the most dominant species of total dissolved nitrogen (TDN) in the upper water column oligotrophic tropical and subtropical surface ocean, and is of great implications for understanding marine C and N biogeochemical cycles. Given the large pool size of DON in the surface ocean, its putative role in regulating production and biological pump should be non-negligible, as there is some evidence suggesting that a portion of DON may be bioavailable. The isotope composition of DON can provide unique insights into the pathways of DON cycling, and determining the stable isotope composition of DON is important for understanding biogeochemistry in the ocean. Here we first present a dataset of isotopic composition of DON in the upper water column of the tropical western South China Sea (wSCS). Concentration and d15N of DON fell in a relatively narrow range (eg., 4.6 uM and 4.3 per mil at 5 m) in the wSCS. Concentration of DON was positively correlated to cholorophyll a concentration in surface waters, suggesting a main photosynthetic origin of DON. An isotope effect during DON consumption in the upper 50 m is revealed. We find a high similarity in the d15N of upper water column DON and subsurface nitrate (4.5 vs 4.6 per mil, suggesting that the upwelled nitrate is the primary source of N for DON. DON may represent a missing N source and fuel production in the N-depleted surface layers of the South China Sea. |
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