The benthic foraminiferal community in a naturally CO2-rich coastal habitat of the southwestern Baltic Sea

Abstract. It is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwest-ern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chem-istry and the ensuing response of the foraminiferal commu-nity with bi-monthly resolution in Flensburg Fjord. In com-parison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sedi-ment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 µatm. Nevertheless, in con-trast to the bottom water, sediment pore water was slightl