Based upon cruise observations broadly covering the tropical North Pacific during July-November 2017,together with data obtained from the World Ocean Circulation Experiment Hydrographic Program,this study examined the distribution of dissolved inorganic nitrogen(DIN,nitrate(NO3-)+nitrite(NO2-)),dissolved inorganic phosphorus(DIP)and related N*(nitrogen-anomaly,N*=N-16P+2.9,where N and P are the concentrations of DIN(＞1.0 μmol/L)and DIP(＞0.1 μmol/L)),used as an index of N2 fixation,in the upper 1 000 m of the water column.Nutrient concentrations displayed distinct spatial variability in the upper ocean but became relatively constant at a depth of 1 000 m:they were high at low latitudes and in the eastern region,with an obvious nutricline at～150 m(DIN,～32.0 μmol/L;DIP,～2.4 μmol/L)and then generally increased with depth;they decreased markedly(DIN,～1.2 μmol/L;DIP,～0.1 μmol/L;at～150 m)at high latitudes and in the western region,where a nutricline was not apparent.The N*index showed significant meridional and zonal variation,with the most negative values located at low latitudes and in the eastern region(～10°N,～150°-170°E),while becoming positive towards the northwest(the north of～18°N,～160°E westward).A N*concentration larger than 2.0 μmol/L which often used as an indicator of N2 fixation,was observed between 155°E and 165°E;N*values were 2.0 μmol/L to 6.0 μmol/L at～15°-28°N,i.e.,much higher than those in the southern sector(0-2.0 μmol/L at～5°-10°N).Zonally,N*decreased gradually from west(-2.0 μmol/L to 4.0 μmol/L,～145°-165°E)to east(-2.0 μmol/L to-8.0 μmol/L,～155°W)along～10°N,which was consistent with the distribution of Trichodesmium abundance and N2 fixation rates.Furthermore,since such region was also supplied with aeolian deposition,high N*was probably not only induced by N2 fixation but also influenced by iron and/or nitrogen deposition.

Aiqin Han;Yu Wang;Yunlong Huo;Cai Lin;Kaiwen Zhou;Fangfang Kuang;Hui Lin

Third Institute of Oceanography,Ministry of Natural Resources,Xiamen 361005,China

海洋学报（英文版）

[1]Aiqin Han;Yu Wang;Yunlong Huo;Cai Lin;Kaiwen Zhou;Fangfang Kuang;Hui Lin-.Nutrient distributions and nitrogen-anomaly(N*)in the tropical North Pacific Ocean)[J].海洋学报（英文版）,2022(11):23-33

Hydrographic,+nitrite,16P+2,nutricline,Zonally

Nutrient,distributions,nitrogen,anomaly,tropical,North,Pacific,Ocean,Based,upon,cruise,observations,broadly,covering,during,July,November,together,data,obtained,from,World,Circulation,Experiment,Program,this,study,examined,dissolved,inorganic,DIN,nitrate,NO3,NO2,phosphorus,DIP,related,where,concentrations,used,N2,fixation,upper,water,column,displayed,distinct,spatial,variability,ocean,became,relatively,constant,depth,they,were,low,latitudes,eastern,region,obvious,then,generally,increased,decreased,markedly,western,was,not,apparent,showed,significant,meridional,zonal,variation,most,negative,values,located,while,becoming,positive,towards,northwest,westward,larger,than,which,often,indicator,observed,between,much,higher,those,southern,sector,gradually,along,consistent,Trichodesmium,abundance,rates,Furthermore,since,such,also,supplied,aeolian,deposition,probably,only,induced,by,influenced,iron

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