The coastal upwelling has profound influence on the surrounding ecosystem by supplying the nutrient-replete water to the euphotic zone.Nutrient biogeochemistry was investigated in coastal waters of the eastern Hainan Island in summer 2015 and autumn 2016.From perspectives of nutrient dynamics and physical transport,the nutrient fluxes entered the upper 50 m water depth(between the mixed layer and the euphotic zone)arisen from the upwelling were estimated to be 2.5-5.4 mmol/(m2·d),0.15-0.28 mmol/(m2·d),and 2.2-7.2 mmol/(m2·d)for dissolved inorganic nitrogen(DIN),phosphate(DIP),and dissolved silicate(DSi),respectively,which were around 6-to 12-fold those in the background area.The upwelled nutrients supported an additional plankton growth of(14.70±8.95)mg/m2 for chlorophyll a(Chl a).The distributions of nitrate δ15N and δ18O above the 300 m water depth(top of the North Pacific Intermediate Water)were different among the upwelling area,background area in summer,and the stations in autumn,and the difference of environmental and biogeochemical conditions between seasons should be the reason.The higher DIN/DIP concentration ratio,nitrate concentration anomaly,and lower nitrate isotope anomaly(A(15,18))in the upper ocean in summer than in autumn indicated the stronger nitrogen fixation and atmospheric deposition,and the following fixed nitrogen regeneration in summer.The higher values of Chl a and nitrate δ15N and δ18O within the euphotic zone in autumn than the background area in summer suggested the stronger nitrate assimilation in autumn.The differences in relatively strength of the assimilation,nitrogen fixation and atmospheric deposition,and the following remineralization and nitrification between the two seasons made the higher 818O:815N and larger difference of enzymatic isotope fractionation factors 15ε and 18ε for nitrate assimilation in summer than in autumn above the North Pacific Tropical Water.

Nan Zhou;Sumei Liu;Guodong Song;Yunyan Zhang;Lingyan Wang;Xiaoyan Ning

Frontiers Science Center for Deep Ocean Multispheres and Earth System,and Key Laboratory of Marine Chemistry Theory and Technology of Ministry of Education,Ocean University of China,Qingdao 266100,China;Laboratory for Marine Ecology and Environmental Science,Pilot National Laboratory for Marine Science and Technology(Qingdao),Qingdao 266237,China

海洋学报（英文版）

[1]Nan Zhou;Sumei Liu;Guodong Song;Yunyan Zhang;Lingyan Wang;Xiaoyan Ning-.Responses of nutrient biogeochemistry and nitrogen cycle to sea-sonal upwelling in coastal waters of the eastern Hainan Island)[J].海洋学报（英文版）,2022(06):99-113

euphotic,upwelled,remineralization

Responses,biogeochemistry,nitrogen,cycle,sonal,upwelling,coastal,waters,eastern,Hainan,Island,has,profound,influence,surrounding,ecosystem,by,supplying,replete,zone,Nutrient,was,investigated,summer,autumn,From,perspectives,dynamics,physical,transport,fluxes,entered,upper,depth,between,mixed,layer,arisen,from,were,estimated,dissolved,inorganic,DIN,phosphate,DIP,silicate,DSi,respectively,which,around,fold,those,background,area,nutrients,supported,additional,plankton,growth,chlorophyll,Chl,distributions,nitrate,above,North,Pacific,Intermediate,Water,different,among,stations,environmental,biogeochemical,conditions,seasons,should,reason,higher,concentration,anomaly,lower,isotope,ocean,than,indicated,stronger,fixation,atmospheric,deposition,following,fixed,regeneration,values,within,suggested,assimilation,differences,relatively,strength,nitrification,two,made,818O,815N,larger,enzymatic,fractionation,factors,Tropical

0.457798