Diverse ecological responses of foraminifera to the Middle Eocene Climatic Optimum (MECO) in shallow-water settings (Provençal Domain, NW Italy)

The Bartonian sedimentary succession of the drowning ramp of the Provençal-Dauphinois Domain records the Middle Eocene Climatic Optimum (MECO), the prominent global warming event, centered at ~40 Ma and lasting ~400–600 kyr. In this work, we study the response of foraminifera (planktic, smaller benthic and larger benthic foraminifera) as one of the main groups of marine calcifiers, highlighting their ecological behavior across the MECO climatic perturbation. Herein we present new data on the Olivetta San Michele section (NW Italy) across the MECO perturbance. We compare our findings with previous data from a wider geographic realm encompassing a large portion of the Provençal-Dauphinois ramp. The palaeoenvironmental reconstruction consists of slightly different depositional conditions in terms of riverine input, water depth, and distance from the mainland, which are reflected in faunal distribution. Nonetheless, the main part of the successions is interpreted as deposited within the photic zone and with a relatively high hydrodynamic regime. Planktic foraminiferal assemblages differ in the investigated successions both in abundance and diversity, suggesting major differences in the studied shallow-water setting. The variations in abundance of Subbotina and Acarinina appear to be controlled by both the MECO warming and a moderate increase of eutrophic conditions, related to an enhanced hydrological cycle. Shallow benthic communities, being already adapted to seasonal variations in salinity and temperature, proved to be resilient to long-term climatic perturbation. Their population shifts appear indeed directly impacted by changes in sedimentary rates and nutrient input modulated by the new hydrological cycle, in turn largely triggered by the warming.