Vegetation and climate history during the Last Interglacial on the Istrian coast (Northern Adriatic Sea)

The dynamics of Mediterranean-type ecosystems through the Last Interglacial (LIG) period are still poorly understood due to sparse records from fossil sites located in the coastal regions of Southern Europe. Here we present the first high-resolution multiproxy record from the infill of a karst estuary in the Istria Peninsula, northern Mediterranean borderlands. Our research explores the potential of the MIR1 core sediments as an archive of the sedimentary history, terrestrial vegetation, climate oscillations and sea-level changes from Termination II (TII) to the decline of the LIG optimum. Due to the absence of absolute ages, the timing was obtained by the correlation of biostratigraphical and climate events. We reconstructed major ecosystem changes from open vegetation of semideserts, steppe/forest steppe, and xerophytic scrub thriving during Termination II (i.e., penultimate deglaciation) to the interglacial spread of woodlands at the Last Interglacial onset. Here, the MIR1 record shows the abrupt expansion of deciduous and semi-evergreen oaks, mirroring a climatic event well depicted in oxygen isotopic records from Alpine speleothems around 129.7 ka. Fire played a relevant role in ecosystem dynamics during both TII and early LIG, owing to plant biomass abundance that triggered fires and favoured their spread. However, fires were never stand-replacing, but determined short-lived fluctuations in ecosystem structure. During the subsequent LIG optimum, Mediterranean sclerophyll forests largely developed in the coastal areas, whereas the Istrian inland hosted moist-demanding species preferring cooler winters. In the Alps, the decline of the LIG optimum occurred at an estimated age of ca 127.5 ka, but was only partially recorded in the MIR1 due to sequence truncation; nonetheless, it features the demise of sclerophyll communities and the increase of Carpinus betulus and Fagus. Micropaleontological indicators of sea-level change help to reconstruct sedimentary environments linked with the LIG sea-level rise, providing a full comprehension of the sedimentation process.