Phytoplankton photosynthetic parameters and primary production in some Arctic regions during the summer of 2020

Abstract

In August 2020, during the 80th cruise of the R/V “Akademik Mstislav Keldysh”, phytoplankton photosynthetic parameters were measured in the Norwegian Sea, the Barents Sea and the adjacent area of the Arctic Ocean. Primary production in the Arctic area was estimated using full spectral approach that took into account quantum yield of photosynthesis (ϕ), phytoplankton spectral light absorption coefficient and spectral downwelling irradiance. Total light absorption by all optically active components except water influenced spectral features of downwelling irradiance: increase of the total non-water light absorption at the sea surface layer resulted in a shift of the wavelength of the downwelling irradiance spectrum maximum to the longer wavelength (from 500 ± 7 nm to 530 ± 5 nm). Phytoplankton photosynthetic parameters (maximum quantum yield (ϕ_max) and light intensity saturating photosynthesis) were depth-dependent variables due to phytoplankton photoacclimation. Relationships between photosynthetically available radiation (PAR) vs. ϕ_max and PAR vs. ϕ were described. Although chlorophyll-a specific photosynthetic rate (P^B) ranged from 0.5 to 1.5 mgC/mgChl-a/h in the surface layer, daily primary production (1.1 mgC/m³/d - 32 mgC/m³/d) was correlated to chlorophyll-a concentration (Chl-a) (r = 0.97, n = 22, p < 0.0001), which is likely to be caused by higher variability of Chl-a (0.07 mg/m³–1.5 mg/m³) compared to P^B. The full spectral approach developed for the Black Sea is relevant for correct assessment of primary production in the Arctic area.