Primary productivity and the coupling of photosynthetic electron transport and carbon fixation in the Arctic Ocean

• Published in: Limnology and Oceanography
• Main Authors: Schuback, Nina, Hoppe, Clara J. M., Tremblay, Jean‐Éric, Maldonado, Maria T., Tortell, Philippe D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2017
• Subjects: Arctic Ocean; Phytoplankton; Subarctic
• Online Access: http://dx.doi.org/10.1002/lno.10475; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Flno.10475; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.10475

Abstract We examined the light absorption properties and light‐dependent rates of photosynthetic electron transport (ETR RCII ) and 14 C‐uptake in phytoplankton of the Canadian Subarctic and Arctic Ocean. Our results reveal high variability in the light‐saturated, chlorophyll a ‐specific rate of 14 C‐uptake ( P Chl a max 0.7 to 8.0 mg C mg chl a −1 h −1 ) , and the light‐dependant efficiency of 14 C‐uptake ( α Chl a 0.01 to 0.09 mg C mg Chl a −1 h −1 [μmol quanta m −2 s −1 ] −1 ). Variability in P Chl a max correlated with light availability in the stratified water‐column, while both P Chl a max and α Chl a were correlated to the degree of nitrate depletion in the mixed layer. For all samples, we observed that 14 C‐uptake rates reached light saturation at lower irradiances than ETR RCII , leading to significant, light‐dependent de‐coupling of carbon fixation and photosynthetic electron transport. For samples taken from within the mixed layer, we found that the conversion factor from ETR RCII to carbon fixation was strongly correlated to the magnitude of non‐photochemical quenching, as derived from fast repetition rate fluorometry (FRRF) measurements. This correlation supports recent findings from the Subarctic Pacific Ocean, and has the potential to improve FRRF‐based estimates of phytoplankton carbon fixation. Our observations reveal distinct environmental regulation of phytoplankton light absorption, electron transport and carbon fixation in phytoplankton assemblages within and below the shallow summer mixed layer, and will help to inform more robust predictions of future primary production in a rapidly changing Arctic Ocean.