Inter-Annual Variation of the Annual New Production of Phytoplankton in the Southwestern East/Japan Sea Estimated from Satellite-Derived Surface Nitrate Concentration

Abstract

The new production of phytoplankton based on nitrate is very important to understand how much portion of primary production passes on to higher trophic levels and sinks into deeper ocean. In this study, the inter-annual variation of the annual new production estimated from MODIS-aqua satellite-derived sea surface nitrate (SSN) concentration was analyzed in the southwestern East/Japan Sea from 2003 to 2015. Climatological SSN concentrations averaged in this study period ranged from 0.47 mu M (+/- 0.16 mu M) to 6.95 mu M (+/- 0.20 mu M) during the study period. The annual new production based on the estimated SSN ranged from 41.7 g C m(-2) yr(-1) to 62.8 g C m(-2) yr(-1). Overall, the average annual new production was 55.8 g C m(-2) yr(-1) (S.D = +/- 11.8 g C m(-2) yr(-1)) in the southwestern East/Japan Sea for 13 years from 2003 to 2015. This value is comparable to those from previous studies but considerably lower than that based on nitrogen stable isotope measurements in the southwestern East/Japan Sea. We found a strong relationship between the annual new production and the sea surface temperature (SST) on February during the study period (y = -11.461 x + 180.52, r(2) = 0.8796, p < 0.01, n = 13). This result has a very significant ecological meaning in an ocean surface warming scenario since a warming SST could lead a lower annual new production and thus cause significant effects on upper trophic levels in the southwestern East/Japan Sea.