Coccolithophores and calcite saturation state in the Baltic and Black Seas

Abstract

Abstract. The Baltic and Black Seas are both brackish, that is to say both have salinities intermediate between freshwater and seawater. The coccolithophore Emiliania huxleyi is abundant in one, the Black Sea, but absent from the other, the Baltic Sea. Here we present summertime coccolithophore measurements confirming this difference, as well as data on the calcium carbonate saturation state of the Baltic Sea. We find that the Baltic Sea becomes undersaturated (or nearly so) in winter, with respect to both the aragonite and calcite mineral forms of CaCO 3 . Data for the Black Sea are more limited, but it appears to remain strongly supersaturated yearround. The absence of E. huxleyi from the Baltic Sea could therefore potentially be explained by dissolution of their coccoliths in winter, suggesting that minimum annual (wintertime) saturation states could be most important in determining future ocean acidification impacts. In addition to this potential importance of winter saturation state, alternative explanations are also possible, either related to differences in salinity or else to differences in silicate concentrations.

How will Ocean Acidification Affect Baltic Sea Ecosystems? An Assessment of Plausible Impacts on Key Functional Groups

“…Seasonally high pCO 2 levels such as those noted by Tyrrell et al (2008) are typically the result of remineralisation of organic material rather than a direct result of ocean acidification. But ocean acidification is likely to augment these effects (see above), and therefore the capacity for seasonal limitation of species distributions due to high pCO 2 (and accordant reduced pH) is likely to increase.…”

“…For planktonic microalgae, early work on ecosystemscale pCO 2 effects in the Baltic Sea suggested that seasonal under-saturation of calcite 1 may explain the absence of calcifying coccolithophores from Baltic Sea waters (Tyrrell et al 2008). Seasonally high pCO 2 levels such as those noted by Tyrrell et al (2008) are typically the result of remineralisation of organic material rather than a direct result of ocean acidification.…”

Morphology of <i>Emiliania huxleyi</i> coccoliths on the northwestern European shelf – is there an influence of carbonate chemistry?

“…Holligan et al, 1993;van Wal et al, 1995;Buitenhuis et al, 1996;Harlay et al, 2010). The widespread abundance of Emiliania huxleyi in the area and the limited occurrence of other species meant it was the inevitable focus of our study.…”

Mesocosm CO<sub>2</sub> perturbation studies: from organism to community level

“…With regards to ocean acidification, survival rates during the winter months, when CO 2 concentrations are generally higher and pH, carbonate ion concentrations and saturation states lower than during the productive spring and summer seasons, may turn out to be critical for the overall success of OA-sensitive groups, such as calcifying organisms (e.g. Tyrrell et al, 2008).…”