Impact of a Coccolithus braarudii bloom on the carbonate system of Portuguese coastal waters.

In the adjacent Tagus and Sado coastal waters (off SW Portugal), a phytoplankton bloom dominated by diatoms (up to 1000 cells ml -1 ) was observed, in spring 2002, under upwelling conditions. Overlapping with the phytoplankton bloom, but spatially differentiated from the diatoms and other phytoplankton groups, a pronounced development of the coccolithophore Coccolithus braarudii (up to 60 cells ml-1) occurred, associated with a thermal- ly stratified water-mass localised in the Tagus Bay. Some cells of the C. braarudii hyalinus-phase were also observed. A production of about five tons of calcite was calculated for the upper 30m of the water-column, based on the integration over depth of a total of 6.7g CaCO 3 m-2, covering 0.7km2 of the Tagus Bay. An average CaCO 3 pre- cipitation rate of 11.2mmol CaCO3 m-2 d-1 was estimated, resulting in the release of 7.4mmol CO2 m-2 d-1 during the C. braarudii bloom. These results indicate that the studied coastal system contributed an additional source of CO2 to the water, and eventually to the atmosphere.