Ocean Acidification

Little is known about the distribution of coccolithophores in Arctic regions, or the reasons why they are absent from certain locations but thrive in others. Factors thought to affect cocco­lithophore distribution include nutrients, salinity, temperature and light, as well as carbonate chemistry parameters. Here we present data collected in summer 2008 along a transect between the North Sea and Svalbard (Arctic). Coccolithophore abundance and diversity were measured and compared with a set of environmental variables that included macronutrients, salinity, temperature, irradiance, pH and Ω_calcite. Eighteen coccolithophore species were found in the southern North Sea where cocco­lithophores were previously thought to be absent. In the ice-covered region north of Svalbard, cocco­lithophores were scarce and dominated by the family Papposphaeraceae. A multivariate approach showed that changes in pH and mixed layer irradiance explained most of the variation in cocco­lithophore distribution and community composition (Spearman’s r_S = 0.62). Differences between the Svalbard population and those from other regions were mostly explained by pH (r_S = 0.45), whereas mixed layer irradiance explained most of the variation between the North Sea, Norwegian Sea and Arctic water assemblages (r_S = 0.40). Estimates of cell specific calcification rates showed that species composition can considerably affect community calcification. Consequently, future ocean acidification (changes in pH) and stratification due to global warming (changes in mixed layer irradiance) may influence pelagic calcification by inducing changes in the species composition of cocco­lithophore communities.

Charalampopoulou A., Poulton A. J., Tyrrell T., & Lucas M. I., 2011. Irradiance and pH affect coccolithophore community composition on a transect between the North Sea and the Arctic Ocean. Marine Ecology Progress Series 431:25-43. Article (subscription required).