Estimation of primary production in the northwestern part of the Sea of Japan by ship- and satellite-based observations

The study analyzes data of ship-based observations on 45 stations performed aboard the R/V Akademik M.A. Lavrentyev on cruise 33 May 7–18, 2004, in the northwestern part of the Sea of Japan (35–44° N, 130–137° E). The following in situ data were used: CTD-data, assimilation number, concentrations of nutrients (nitrogen, phosphorus, and silicon compounds) and chlorophyll a (Сhl a). Satellite data on Сhl a concentration, diffuse attenuation coefficient at a wavelength of 490 nm, primary production (PP), and Photosynthetically Active Radiation (PAR) available from the Climate Change Initiative Ocean Colour (CCI-OC) and Ocean Productivity databases were also used for the same stations. The Chl a concentration in the first optical layer estimated from the results of ship-based measurements, was on average 0.55 ± 0.58 mg/m3, but the satellite-derived estimates were almost twice as high (0.95 ± 0.36 mg/m3). Ship assessments of PP were 1870 ± 900 mgC m–2 day–1; the value obtained using satellite data was 1.5 times smaller: 1226 ± 432 mgC m–2 day–1. Vertical Chl a profiles showed that the largest amount of Chl a was concentrated in the 20–45 m layer. Measurements of the assimilation number showed that most production occurs within the 0–55 m layer in the south of the study area and within the 0–30 m layer in the north. The weak correlation between ship- and satellite-derived Chl a and PP values can be explained by low accuracy of satellite-derived estimates.