Inorganic carbon uptake by Southern Ocean phytoplankton

• Published in: Limnology and Oceanography
• Main Authors: Tortell, Philippe D., Payne, Chris, Gueguen, Celine, Strzepek, Robert F., Boyd, Philip W., Rost, Björn
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2008
• Subjects: Antarc*; Antarctica; Ross Sea; Southern Ocean
• Online Access: http://dx.doi.org/10.4319/lo.2008.53.4.1266; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.4319%2Flo.2008.53.4.1266; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2008.53.4.1266

We report the results of laboratory and field studies examining inorganic carbon (C i ) utilization by Southern Ocean phytoplankton. Both in monospecific laboratory cultures of diatoms and Phaeocystis antarctica and in natural assemblages in the Ross Sea, C i uptake by phytoplankton was dominated by direct HCO 3 1 transport. The contribution of HCO 3 1 transport to total C i uptake ranged from 65% to 95%, with an overall average of ∼80%. There was no significant difference among diatoms and Phaeocystis in the extent of HCO 3 1 transport. Extracellular carbonic anhydrase activity (eCA) was detected in eight of nine laboratory phytoplankton cultures and in all natural assemblages in the Ross Sea. The effective catalytic enhancement of HCO 3 1 : CO 2 interconversion ranged from 1.5‐ to 13‐fold (overall mean ∼4‐fold). Diatom‐dominated Ross Sea assemblages had significantly greater eCA levels than did Phaeocystis‐dominated assemblages. We found no strong correlations between C i uptake parameters and in situ CO 2 concentrations or chlorophyll a levels in the Ross Sea assemblages. Incubation experiments with natural assemblages showed that HCO 3 1 uptake and eCA expression did not change significantly over an 8‐fold range in pCO 2 (10.1‐81.1 Pa), although total short‐term C fixation rates increased under low CO 2 conditions. Carbon‐concentrating mechanisms are widespread among Southern Ocean phytoplankton and constitutively expressed by natural assemblages in the Ross Sea.