Effect of increased CO2 and dissolved iron on primary productivity and inorganic carbon uptake during a bloom of the coccolithophore Emiliania huxleyi

Abstract

Net primary production (NPP) and inorganic carbon uptake were analysed during a bloom of Emiliania huxleyi in mesocosms. The experiment lasted 25 days and was carried out in the Raunefjord off Bergen (Norway, June 2012) in order to investigate the interactive effects of increased CO2 and iron availability on the phytoplanktonic community. For this purpose two different partial pressures of CO2 corresponding to present (390 ppmV) and predicted levels for year 2100 (900ppmV) (LC and HC respectively) were used. The siderophore desferoxamine B (DFB) was added to half of the mesocosms to create two different iron conditions (+DFB and –DFB). Three mesocosm bags were used for each treatment. NPP was estimated using short-term 14C uptake assays. The isotope disequilibrium assay (ID) was used to determine the relative fraction of HCO3- and CO2 uptake in concentrated cell suspensions. Short-term cellular 14C fixation was monitored during a transient disequilibrium between 14CO2 and H14 CO3- in solution, and so, the fraction of HCO3- uptake (f) and the rate of extracellular CO2: HCO3- interconversion (α), as a measure of extracellular carbonic anhydrase activity (eCA), were calculated. Further details will be discussed.