CO2 emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO2 enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater pCO2 in Kiel Fjord is elevated for large parts of the year due to upwelling of CO2 rich waters. Peak pCO2 values of >230 Pa (>2300 µatm) and pHNBS values of 400 Pa (>4000 µatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Lavigne and Gattuso, 2011) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI).

Supplement to: Thomsen, Jörn; Gutowska, Magdalena A; Saphörster, J; Heinemann, Agnes; Trübenbach, Katja; Fietzke, Jan; Hiebenthal, Claas; Eisenhauer, Anton; Körtzinger, Arne; Wahl, Martin; Melzner, Frank (2010): Calcifying invertebrates succeed in a naturally CO2-rich coastal habitat but are threatened by high levels of future acidification. Biogeosciences, 7(11), 3879-3891