Planktic foraminiferal changes in the western Mediterranean Anthropocene

The increase in anthropogenic induced warming over the last two centuries is impacting marine environment. Planktic foraminifera are a globally distributed calcifying marine zooplankton responding sensitively to changes in sea surface temperatures and interacting with the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly to present. Reconstructed sea surface temperatures are in good agreement with other results, tracing temperature changes through the Common Era (CE) and show a clear warming emergence at about 1850 CE. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides), a common group of marine calcifying zooplankton. The relative abundance changes of Globorotalia truncatulinoides plus Globorotalia inflata describe the intensity of deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of the North Atlantic Oscillation, and, to a lesser extent, by the Atlantic Multidecadal Oscillation. In the industrial era, starting from about 1800 CE, this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles are being overprinted by human influences.

We are grateful to George Kontakiotis and an anonymous reviewer for their helpful comments and suggestions. We thank the captain and crew of the Spanish R/V Ángeles Alvariño, and the researchers as part of the MedSeA cruise for supporting the sampling of this study. We thank Adam Subhas for conducting radiocarbon analysis at the NOSAMS facility at Woods Hole Oceanographic Institution (Massachusetts, USA). We also thank Marta Casado, Yolanda Gonzalez-Quinteiro, Bibiano Hortelano and Inma Fernandez for laboratory assistance, and Joan Manuel Bruach for his work on the analysis of 210Pb. This work contributes to the ICTA-UAB “Unit of Excellence” (FPI/MDM-2015-0552-16-2; CEX2019-000940-M) and received further funding by the EU-FP7 “Mediterranean Sea Acidification in a Changing Climate” project (MedSeA; grant agreement 265103), the CALMED project (CTM2016-79547-R), and the Generalitat de Catalunya (MERS, 2014 SGR – 1356). The Spanish Ministry of Science and Innovation, Severo Ochoa Project CEX2018-000794-S is likewise acknowledged. The data used in this paper can be found in the supporting information and is uploaded online at the PANGAEA repository.

Peer reviewed