Estimation of annual primary production in the Kuroshio waters northeast of Taiwan using a photosynthesis-irradiance model

Photosynthesis-irradiance (<(P-B)over bar>-(E) over bar) relationships for Kuroshio waters at different depths in different seasons were established using repeated measurements of primary productivity at a station northeast of Taiwan. The <(P-B)over bar>-(E) over bar approach is different from the conventional PB-E approach in that a much longer incubation time is required to measure primary productivity. By plotting the daytime averaged, chlorophyll specific primary productivity (<(P-B)over bar>) against the daytime averaged irradiance ((E) over bar), the optimal rate of photosynthesis (P-opt(B)) in the mixed layer was found to be 5.87 mgC [mgChl a](-1) h(-1) in summer and 2.88 mgC [mgChl a](-1) h(-1) in winter. The initial slope of the <(P-B)over bar>-(E) over bar curve, however, remained around 0.01 mgC [mgChl a](-1)h(-1) [mu Einstein m(-2) s(-1)](-1) throughout the year. Below the mixed layer, the P-opt(B) decreased substantially to less than half of that within the mixed layer. A similar. decrease was also observed in the initial slope. The euphotic zone integrated primary production as calculated from these <(P-B)over bar>-(E) over bar parameters was close to that measured ill situ. with relative error less than 6%. Based on the measured <(P-B)over bar>-(E) over bar parameters: it was estimated here that the annual primary production was 104 gC m(-2) yr(-1) (285 mgC m(-2) d(-1)). The established <(P-B)over bar>-(E) over bar relationships may serve as a better regional algorithm in the assessment of primary production for Kuroshio waters. (C) 1999 Elsevier Science Ltd. All rights reserved.