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

Abstract

Photosynthesis-irradiance ( P B – E ̄ ) 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 – E ̄ approach is different from the conventional P B– 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 ) against the daytime averaged irradiance ( E ̄ ) , the optimal rate of photosynthesis ( P B opt) 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 – E ̄ curve, however, remained around 0.01 mgC [mgChl a] -1 h -1 [μEinstein m -2 s -1] -1 throughout the year. Below the mixed layer, the P B opt 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 – E ̄ parameters was close to that measured in situ, with relative error less than 6%. Based on the measured P B – E ̄ 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 – E ̄ relationships may serve as a better regional algorithm in the assessment of primary production for Kuroshio waters.