The effect of CO2 concentration on DMSP production in Gephyrocapsa oceanica (Isochrysidales, Coccolithophyceae)

Abstract

ABSTRACT Atmospheric CO2 is increasing at unprecedented rates, with modelling studies indicating this as a significant cause of continued warming of the planet. It has been suggested that if these conditions in some way lead to enhanced DMSP production by marine algae, then this compound, via the sulphate aerosols that result from its breakdown, might act to mitigate global warming by altering cloud albedo and so act as a natural thermostat. Among the major producers of DMSP in the oceans are the coccolithophores, with Gephyrocapsa oceanica being a common species that prefers warmer conditions than Emiliania huxleyi, and that arose in the Miocene when CO2 levels were higher than present. In this study we grew G. oceanica under CO2 concentrations equivalent to atmospheric values of 200, 390 and 1000 ppm, representative of glacial, near present and potential 2100 CE scenarios. As CO2 concentration increased, so did cell size, while both growth rates and intracellular DMSP concentrations decreased, consistent with the hypothesis that DMSP may act as part of an antioxidant mechanism within the cell. This led to a 50% decrease in net DMSP production under 1000 ppm CO2 relative to the 390 ppm treatment. While there are many variables in the open ocean environment that ultimately determine net DMSP production rates and flux of sulphur to the atmosphere, for the cellular response to increased atmospheric CO2 alone we conclude that elevated CO2 would reduce net DMSP production and, inasmuch as this reduces the production of sulphate aerosol in the atmosphere, reducing cloud albedo, then rather than acting to limit global warming, it will instead amplify it.