Blooms of Emiliania huxleyi are sinks of atmospheric carbon dioxide: A field and mesocosm study derived simulation

During field measurements in a bloom of Emiliania huxleyi in the North Sea in 1993, an apparently inconsistent combination of observations was measure d: (1) fCO(2), was lower in the center of the bloom than in the surrounding nonbloom areas and undersaturated with respect to the atmosphere in both c ases, (2) within the bloom, enhanced sedimentation of coccoliths-containing fecal pellets was observed, (3) a large atmospheric sink of 1.3 mol C m(-2 ) was derived, and (4) in the same bloom a positive correlation between CaC O3 and fCO(2) was observed, which was interpreted as an increase of fCO(2) during production of CaCO3. In order to resolve the inconsistency between o bservations (1, 2, 3) and 4 a one-dimensional three-layer model was constru cted. A positive correlation between CaCO3 and fCO(2) as obtained when the model was parameterized with data obtained from field and mesocosm studies. The correlation is a feature of the decay phase of a bloom and represents a decrease of fCO(2) with a decrease of CaCO3. Thus it represents the disso lution and sedimentation of CaCO3 rather than its production. Having resolv ed the ambiguity within the field data by adding the dimension of time in t he model, blooms of E. huxleyi can be identified as sinks for atmospheric c arbon dioxide. This sink is a function of the calcification to photosynthes is (C:P) ratio of the nitrate-using phytoplankton and is maximal when the C :P ratio is 0.42 (that is, E. huxleyi constitutes 97% of the nitrate-using phytoplankton). Rather than using the model for making accurate predictions about the magnitude of this sink, a sensitivity analysis was performed to give a range of magnitudes for the range of parameter values that were obta ined during previous studies. Furthermore, gaps were identified in the curr ent knowledge of carbon fluxes within blooms of E. huxleyi.