Implications of bio‐optical modeling of phytoplankton photosynthesis in Antarctic waters: Further evidence of no light limitation in the Bransfield Strait

Abstract

During the cruise ECOANTAR 94 photosynthesis versus irradiance relationships, phytoplankton spectral absorption, quantum yield of carbon fixation, and water column light regime were determined in the eastern Bransfield Strait and surrounding areas of the Weddell Sea and Weddell‐Scotia Confluence, to determine if photosynthesis is light limited in these areas. There were no significant differences in the light‐saturated chlorophyll‐specific rate of photosynthesis (P Bm), light‐limited slope (±B), light saturation parameter (EkPAR), and the maximum quantum yield (Φm) between surface and subsurface water for several water masses in the area, which indicates that the photosynthetic response in the upper mixed layer was uniform. There were also no significant differences between the spectral light saturation parameter (EkPUR) and the mean absorbed irradiance by phytoplankton in the upper mixed layer (EumlPUR). These similarities suggest that phytoplankton photosynthesis was not light limited in this Antarctic region during the cruise period. This was also affirmed by the fact that the average operational quantum yield of the water column (0.03 mol C [mol photons]−1) was half of the mean maximum quantum yield (0.06 mol C [mol photons]−1). Primary production is underestimated by 24% when broadband models are compared with spectral ones. These results have important implications for the modeling of carbon flows in the Southern Ocean.