Planktonic foraminifera response to the azores high and industrial-era global warming in the central-western Mediterranean Sea

The Mediterranean Sea is warming about 20 % more rapidly than global ocean and this phenomenon is impacting ecosystems and biodiversity. Planktonic foraminifera are an important component of surface and subsurface water ecosystems and food chains. Their species communities have been altering across the oceans since the Industrial Era, in response to the ongoing climate change, especially in the western Mediterranean Sea, where a significant productivity decrease has been recently reported.

Here we show planktonic foraminifera and multispecies stable isotopes from three short sediment cores, recovered on the eastern flank of the Sicily Channel, central Mediterranean Sea. Results fully confirm the planktonic foraminifera productivity decrease in the Industrial Era, which is especially relevant for the second half of the 20th century. The planktonic foraminifera productivity decrease matches with a higher number of Large Azores High events, i.e., the establishment of an exceptional and persistent winter atmospheric high-pressure ridge over the western-central Mediterranean Sea. This is an unprecedented atmospheric phenomenon for the last millennia Mediterranean Sea history, as a direct response of the global warming. Surface productivity and DCM species are especially declining since ∼1960 CE, at expenses of winter mixed layer taxa, suggesting that the Azores High activity prevents a sustained water column vertical mixing and surface water nutrient fuelling. Our results document and confirm that the climate change has already been affecting Mediterranean marine ecosystems and the basic level of the trophic chain, by extending the surface water stratification period.