The Messinian paleoenvironment in the Mediterranean (Monte dei Corvi, Ancona): A comparison with the modern oceanographic conditions,

The Messinian was characterized by peculiar biogeochemical dynamics and climate in the Mediterranean region, testified by widespread deoxygenation events (sapropel) and evaporite deposition. To constrain the Mediterranean response to past perturbation it is crucial to understand the current environmental crisis related to climate change. In this regard, benthic and planktic calcareous fossils provide valuable insights into surface and bottom water conditions during deoxygenation events. Here we studied in high resolution 4 sapropel-bearing cycles of the Monte dei Corvi (Ancona, Italy), which recorded the behavior of the Adriatic Deep-Water formation, a major controlling factor for the oxygenation in the modern Eastern Mediterranean. Our analysis unveils fluctuations in planktic and benthic assemblages driven by variations in insolation parameters. Sapropel interbeds deposited during insolation maxima exhibit warm-oligotrophic and Deep Chlorophyll Maximum taxa, suggesting warming and freshening of surface water, leading to weakened Adriatic Deep-Water formation and reduced oxygen delivery to the bottom. Marly limestone/marlstone interbeds exhibit the dominance of cold-eutrophic taxa and an abundance of fecal pellets with monospecific/oligospecific calcareous nannofossils taxa (Umbilicosphaera jafari and Reticulofenestra perplexa), suggesting moderately high salinity and sustained productivity during phases of strong mixing. Comparisons between Messinian and the present-day setting reveal significant differences in the abundance and distribution of calcareous planktic assemblage, mostly due to heightened productivity during the Messinian, a response to restricted conditions that increased the basin's susceptibility to nutrient-delivering runoff. This circumstance played a significant role in the widespread deoxygenation and accumulation of organic carbon during the Messinian. The uncertain trajectory of primary production in the Mediterranean complicates precise predictions of the future oxygen balance. Insights from the Messinian underscore the crucial role of primary productivity in shaping bottom oxygen conditions, emphasizing the necessity for ongoing investigations