Planktic Foraminifera changes in the western Mediterranean Anthropocene

<p>The increase in anthropogenic induced warming over the last two centuries is impacting marine environments. Marine planktic calcifying organisms interact sensitively to changes in sea surface temperatures (SST), and 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 (MCA) to present. Reconstructed SSTs are in good agreement with other results, tracing temperature changes through the Common Era, and show a clear 20^th century warming signal. 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 abundance ratios between these species show the switch between winter / spring surface productivity and 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 North Atlantic Oscillation (NAO), and, to lesser extent, by the Atlantic Multidecadal Oscillation (AMO). In the industrial era, starting from about 1800 Common Era (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 and influences are being overprinted by human influences.</p>