Bicarbonate transport and extracellular carbonic anhydrase activity in Bering Sea phytoplankton assemblages: Results from isotope disequilibrium experiments
Martin, Cheryl L., and Philippe D. Tortell
Limnol. Oceanogr., 51(5), 2006, 2111–2121

We used a ¹⁴C isotope disequilibrium technique to provide quantitative estimates of both direct HCO₃^- transport and extracellular CA activity in Bering Sea phytoplankton assemblages. The method revealed that direct HCO₃^- transport was the dominant mechanism of inorganic C uptake in both coastal and open ocean waters, accounting for more than half of the total C flux to the phytoplankton. The relative importance of HCO₃^- transport was not related to phytoplankton biomass, productivity, or ambient CO₂ concentrations at individual sampling stations. However, HCO₃^- transport and total inorganic C uptake rates decreased in response to elevated CO₂ in direct manipulation experiments. Kinetic analysis of the ¹⁴C time-course data revealed low levels of extracellular carbonic anhydrase activity at most stations. This activity was related to phytoplankton taxonomic compositions and/or CO₂ concentrations, but was relatively unaffected by direct CO₂ manipulations.