Contribution of Phytoplankton Blooms to Export Production

The oceans absorb one quarter of the fossil fuel CO2 emitted to the atmosphere every year. The interannual and decadal variations of this sink are of strong interest, yet they are poorly constrained by observations and we have low understanding of the physical and biological processes that control the surface ocean partial pressure (pCO2). An important drawdown of pCO2 is driven by the sinking of organic matter following the intense phytoplankton spring blooms. The current assumption is that phytoplankton blooms will continue into the future with the same level of activity as today. We estimate the contribution of phytoplankton blooms to the biological export production (EP) using satellite chlorophyll data from CZCS and SeaWiFS sensors and carbon export fluxes from an inverse model based on climatological nutrient concentrations. Phytoplankton blooms are characterized by their initiation date, amplitude and duration. In the North Atlantic Ocean, long blooms of 10-15 weeks occur in the subtropics and are associated with low amplitudes and low EP. Short blooms of less than five weeks occur in the subpolar region and are associated with high amplitudes and high EP. The relation between bloom duration and EP can be characterized by an exponential inverse function. Using this function, we estimate changes in dissolved inorganic carbon and derive the associated changes in surface oceanic pCO2. Interannual and decadal patterns of EP and pCO2 distribution are evidenced for the entire basin.