Nutrients Transported From The Kuroshio To The East China Sea:Fluxes And Controlling Factors

Based on the investigations in the Kuroshio mainstream and the upwelling zone northeast of Taiwan island during spring 2014,autumn 2014,and summer of 2015,the vertical distribution patterns of dissolved inorganic froms,dissolved organic froms and particulate forms of Nitrogen?N?,Phosphorus?P?and Silicon?Si?,and their relevant parameters were systematically studied.The nutrients fluxes from the Kuroshio to the East China Sea?ECS?shelf area were estimated,and the impact of the Kuroshio intrusion water to the distribution pattern of biogenic elements in the ECS was preliminary evaluated.A series of results and recognition obtained in this study are as follows:1.The contents of different forms of biogenic elements in the Kuroshio mainstream and the upwelling water northeast of Taiwan island were distinctly varied with water depth in spring 2014,autumn 2014,and summer of 2015.Their distribution patterns,which were subjected to the combined influences of exchange of water masses,primary production,settling of paticulate matters,remineralization of organic matters and so on,vaired with different seasons,indicating that the influence factors vaired with different seasons.In the Kuroshio main stream,the contents of dissolved inorganic biogenic elements?NO₃-N,NO₂-N,PO₄-P and SiO₃-Si?,dissolved organic biogenic elements?DON and DOP?and particulate inorganic and organic biogenic elements?PIN,PIP,PON and POP?distinctly varied with water depth:NO₂-N has a high value zone in50¹50 m layer;the contens of NO₃-N,PO₄-P and SiO₃-Si are lowest in the Kuroshio Surface Water?KSW?,then increase with the increase of water depth in the Kuroshio Subsurface Water?KSSW?and Kuroshio Intermidiate Water?KIW?,and have uniform and the highest values in the Kuroshio Deep Water?KDW?;the contents of DON,DOP,PON and POP have the highest values in the KSW,then decrease with the increase of water depth in the KSSW,have uniform and lower values in the KIW and KDW;the contents PIN and PIP are relatively low throughout the water column.Their contents and vertical distribution patterns,which were subjected to the combined influences of exchange of water masses,primary production,settling of paticulate matters,remineralization of organic matters and so on,vaired with different seasons,indicating that the influence factors varied with different seasons.Staion TW0-1 locatted in the Kuroshio upwelling zone northeast of Taiwan island,its contents of biogenic elements are strongly influenced by the upwelling of KSSW and KIW.The contents of NO₃-N,PO₄-P,SiO₃-Si,PON and POP are basically higher than the contents in the corresponding layer of the Kuroshio water,while DON and DOP contents are basically lower than the contents in the corresponding layer of the Kuroshio water,which consist with the distribution patterns of biogenic elements in upwelling water.2.The composing characteristics of different forms of N and P in the Kuroshio mainstream and the upwelling zone northeast of Taiwan island were broadly similar in spring,summer and autumn:DON and DOP were main existing forms in upper water,while DIN and DIP were main existing forms in deep water.In the KSW,DON and DOP were the main existing forms of N and P,which accounted for about 80%and 66%of the TN and TP respectively;secondly was particulate forms,PN?PIN+PON?and PP?PIP+POP?accounted for around 10%of the TN and TP,respectively;the contents of DIN?NO₃-N+NO₂-N?and DIP?PO₄-P?were the lowest.Then increased with water depth,the contents of dissolved organic and particulate forms of N and P decreased,while the contents of dissolved inorganic forms of N and P increased.In KDW,DIN and DIP were the main existing forms of N and P,respectively;dissolved organic forms took the second place;and particulate forms accounted less than 1%.In the Kuroshio upwelling water,DON and DOP were main existing forms in the upper water,DIN and DIP were main existing forms in the deeper water,and their composing characteristics were influenced by the intrusion KSSW and KIW.3.The Kuroshio water intrudes and imports large amounts of nutrients into the ECS shelf area.The influxes of N,P and SiO₃-Si from the Kuroshio to the ECS are respectively 17.17,0.93 and 14.71 kmol/s during rainy season?May to October?;and respectively 15.70,0.75 and 9.73 kmol/s during dry season?November to April?.What's noticeable is that dissolved organic and particulate forms of N and P influxes,which accounted for nearly half of the TN and TP influxes,can not be ignored.The nutrients influxes from the Kuroshio to the ECS are influenced by the contents of biogenic elements in the Kuroshio and the water flux of the intrusion Kuroshio water.The Kuroshio import large amounts of nutrients into the ECS,and the influxes varies with seasons beacused of the seasonal variations of both the contents of nutrients and the intrusion water fluxes.Based on the box modle about water-salt balance,the influxes of different forms of nutrients from the Kuroshio to the ECS are estimated.The Kuroshio imports respectively 13.70,0.98,23.03,10.65,0.38,0.66 and 0.04 kmol/s of DIN,DIP,SiO₃-Si,DON,DOP,PN and PP in spring,imports respectively 4.24,0.27,6.38,4.84,018,0.25 and 0.02 kmol/s in summer,and imports respectively 5.25,0.37,9.73,9.80,0.34,0.65 and 0.04 kmol/s in autumn.Influxes of DIN and DIP accounted for 52%and 67%,respectively,of the total influxes of N and P in rainy season?May to October?;and influxes of DIN and DIP accounted for 33%and 50%,respectively,of the total influxes of N and P in dry season?November to April?.As well as dissolved inorganic forms of N and P,dissolved organic and particulate forms of N and P also plays importan role in the N and P distribution patterns in the ECS shelf area.4.During the rainy and the dry season,the DIN/DIP ratio of the nutrients influxes from Kuroshio intrusion water are 14.36 and 14.08,respectively;while the TN/TP ratio of the nutrients influxes are 18.41 and 20.91,respectively.The intrusion Kuroshio water,which is featured by high concentrations of nutrients,especially DIP,could intrude into the ECS coastal area nearby the Fujian and Zhejiang Province and mitigate the extreamly high DIN/DIP ratio caused by the river input,and therefore impact the distribution pattern of nutrients in the ECS.During the rainy season?May to October?,the DIN,DIP SiO₃-Si,DON,DOP,PN and PP accounted for 23%,34%,42%,20%,15%,1%,2%,respectively,of the total influxes of N,P and SiO₃-Si?the sum of the Kuroshio influxes,Taiwan Strait influxes and river influxes?.During the dry season?November to April?,the DIN,DIP,SiO₃-Si,DON,DOP,PN and PP accounted for 18%,25%,37%,33%,22%,2%,3%,respectively,of the total influxes of N,P and SiO₃-Si.The influxes of DIN,DIP,and SiO₃-Si in dry season are lower than those in rainy season,while influxes of DON,DOP,PN and PP in dry season are higher than those in rainy season.The influxes of DIN,DIP,SiO₃-Si,DON,DOP,PN and PP from Kuroshio intrusion water are 2.55,37.77,2.93,10.68,9.33,0.63 and 0.63 times of the riverine influxes during the rainy season,and 5.04,45.67,5.22,40.70,33.74,5.57 and 1.08 times of the riverine influxes during the dry season.The DIN/DIP ratio of riverine influxes during the rainy and dry season are 212.31 and 127.50,respectively,while the DIN/DIP ratio of Kuroshio influxes during the rainy and dry season are 14.36 and 14.08,respectively.The intrusion Kuroshio water,which is featured by high contents of nutrients,especially DIP,could intrude into the ECS coastal area nearby the Fujian and Zhejiang Province and mitigate the extreamly high DIN/DIP ratio caused by the riverine input,and therefore impact the distribution pattern of nutrients in the ECS.