Western Mediterranean marine cores show that foraminiferal mass and flux are being influenced by enhanced anthropogenic pressure

Increasing atmospheric CO₂ concentration during the last century is evidently altering marine environments. Specifically, marine planktic calcifying organisms interact sensitively to changes in surface water, being strongly linked to the marine carbon cycle and the food web. The study sites are in the Western Mediterranean Sea, a region highly affected by both climate change and direct anthropogenic pressure. By analyzing high resolution multicores spanning the last 200 to 1500 years BP, conclusions can be drawn on how increasing environmental changes have altered the biogeochemistry of the region, including species diversity, assemblages and shell morphologies of planktic foraminifera. Reconstructed sea surface temperature (SST) and productivity data obtained through XRF and biomarker analysis further complete the proxy faunal database for the region. At all sites, prominent planktic foraminiferal community changes and decreases of absolute abundance and mass during the post-industrial era are reported. In particular during the last century, G. ruber s.l. test size normalized weight drops significantly. These changes are generally accompanied by increasing SSTs. The reduction in planktic foraminiferal flux is related to increased surface ocean stratification and less intense winter/spring mixing. The decline of foraminiferal calcification mass might be due to changes in seawater carbonate chemistry and food availability. The complex response of foraminiferal calcification might relate to the species-specific physiological and ecological response to seasonal environmental change. This evidence suggests that sea warming and acidification due to increasing anthropogenic CO₂ emissions have already affected productivity, biodiversity and calcification of planktic foraminifera.