Photosynthetic characteristics of phytoplankton off Adelie Land, Antarctica, during the austral summer

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The photosynthesis-irradiance characteristics (P-E curves) and quantum yields of natural phytoplankton were investigated in the Southern Ocean off Adelie Land, Antarctica, during the austral summer. Data were acquired at eight stations during a cruise of T/V Umitaka-Maru III. The photosynthetic P-E curves showed low light adaptation of phytoplankton. Mean value (±standard deviation) of the P-E curve parameters, α^*, and I_k, were 0.014 (±0.013) mgC (mg chl. α)^<-1> h^1 (μmol photons m^<-2> s^<-1>)^<-1> and 76 (±55) μmol photons m^<-2> s^<-1>, respectively. Although phytoplankton were adapted to low irradiance, the phytoplankton in the SCM were not fully adapted to the low irradiance prevailing at those depths. P^*_<max> in the studied region was low (mean of 0.66 (±0.37) mgC (mg chl. α)^<-1> h^<-1>) and generally lower than the previously reported values in waters near the Antarctic Peninsula. The maximum quantum yield varied widely, ranging from 0.001 to 0.038mol C (mol photons absorbed)^<-1> at the surface and from 0.007 to 0.092mol C (mol photons absorbed)^<-1> near the bottom of the euphotic zone. These values were within the range of published data. Comparison of photosynthetic parameters with historical data indicated that primary productivity from remotely sensed data for the whole of the Southern Ocean, based on these field estimates of photosynthetic parameters, has been overestimated.
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