Cladocora caespitosa and Pinna nobilis: useful climatic archives to reconstruct Last Interglacial paleotemperatures

The Mediterranean Sea is a semi-enclosed basin hosting more than 7% of global marine biodiversity. It is among the areas most exposed to human pressure and climate change. The study of the pristine status of ecosystems and marine shallow habitats can be used as a reference for evaluating current human-derived impacts. The Last Interglacial (LIG, ~129 to 116 ka ago) was a warm time interval that could be considered a modern analogue lacking an anthropogenic fingerprint and represents a useful scenario for future climate change. It can be used to reconstruct key environmental variables sustaining non-anthropically modified Mediterranean shallow-water ecosystems under warm climate. Traces of past climatic features are indeed recorded in some biotic archives, whose geochemical properties record seawater parameters. For instance, the bivalve Pinna nobilis (Linnaeus, 1758) and the coral Cladocora caespitosa (Linnaeus, 1767) are endemic to the Mediterranean Sea and their stable oxygen isotope and trace element compositions are useful proxies to reconstruct the paleoclimate, potentially tracing the history of the Mediterranean Sea from the Pliocene to the present. In this study, we investigated climatic proxies in fossil specimens of C. caespitosa and P. nobilis from Last Interglacial (LIG) marine-terrace deposits in the Taranto area (Puglia, Italy), in order to reconstruct paleo–seawater temperatures during the organisms’ lifetimes. We performed X-ray imaging on the coral to investigate the alternation of annual density bands. The annual growth pattern was used as a guide to cut corallites with a dental drill, allowing the preparation of samples at sub-annual resolution for geochemical analyses. A drill was used to collect calcite powder sub-samples from fossils of P. nobilis at ~1 mm resolution following the correct growth sequence. Subsequently, geochemical analyses were carried out on trace elements in the C. caespitosa aragonite and on the oxygen stable isotope ratio (δ¹⁸O) in the P. nobilis calcite. The aim of this work was to reconstruct paleotemperatures of the Last Interglacial period with an annual or sub-annual resolution, comparing our results with present-day temperature records to better define a LIG climate scenario.