Studies on oceanic CO2 uptake in and around Kuroshio

In order to examine the oceanic CO_2uptake and factors controlling it in and around Kuroshio，measurements of partial pressure of CO_2(PCO_2)，dissolved inorganic carbon(DIC)，stable carbon isotopic ratio(^&lt；13&gt；C/^&lt；12&gt；C)of DIC were made at least four times a year in the western North Pacific Subtropical Gyre(NPSG)over the period from 2004 to 2006。In the NPSG，seasonal variation in pCO_2was mainly controlled by the temperature and biological activity.The former was caused by the thermodynamic temperature effect on carbonate system。From winter to summer，the net community production was estimated to be in the range from 10 to 26 mmol m^&lt；-2&gt；day^&lt；-1&gt；based on measurements of concentration and^&lt；13&gt；C/^&lt；12&gt；C of DIC.Dueto the oceanic uptake of anthropogenic CO_2，the pCO_2in surface seawater has increased at a rate(1.6µm atm yr^&lt；-1&gt；)which is nearly equal to that of the air.In the western North Pacific(5-35°N，132-142-E)the air-sea CO_2flux over the 1990 s was estimated to be in the range from16to52Mt-C yr^&lt；-1&gt；with a mean value of 32Mt-C yr^&lt；-1&gt；.During winter season，the CO_2flux south of the Kuroshio was about3mole m^&lt；-2&gt；yr^&lt；-1&gt；，which was relatively large as compared with those of the average of the world ocean。We have also examined the relationship between chemical constituents of sinking particles and biological activity in the surface mixed layer.Further，we have developed a eco-system model including nitrogen isotope，and used it to discuss the nitrogen cycle in the equatorial Pacific and the Sea of Okhotsuk.Details of our results are given in scientific journals.

In order to examine the oceanic CO_2 uptake and factors controlling it in and around Kuroshio, measurements of partial pressure of CO_2 (pCO_2), dissolved inorganic carbon (DIC), stable carbon isotopic ratio (^<13>C/^<12>C) of DIC were made at least four times a year in the western North Pacific Subtropical Gyre (NPSG) over the period from 2004 to 2006. In the NPSG, seasonal variation in pCO_2 was mainly controlled by the temperature and biological activity. The former was caused by the thermodynamic temperature effect on carbonate system. From winter to summer, the net community production was estimated to be in the range from 10 to 26 mmol m^<-2> day^<-1> based on measurements of concentration and ^<13>C/^<12>C of DIC. Dueto the oceanic uptake of anthropogenic CO_2, the pCO_2 in surface seawater has increased at a rate (1.6 μatm yr^<-1>) which is nearly equal to that of the air. In the western North Pacific (5-35°N, 132-142ー°E) the air-sea CO_2 flux over the 1990s was estimated to be in the range from 16 to 52 Mt-C yr^<-1> with a mean value of 32Mt-C yr^<-1>. During winter season, the CO_2 flux south of the Kuroshio was about 3 mole m^<-2> yr^<-1>, which was relatively large as compared with those of the average of the world ocean. We have also examined the relationship between chemical constituents of sinking particles and biological activity in the surface mixed layer. Further, we have developed a eco-system model including nitrogen isotope, and used it to discuss the nitrogen cycle in the equatorial Pacific and the Sea of Okhotsuk. Details of our results are given in scientific journals.