Glacial-interglacial faunal shifts in rift ecosystems during the Quaternary: dynamics and drivers of change from the Corinth Gulf record (Greece).

The Corinth Gulf is a young, active rift with high rates of tectonic activity, high sediment fluxes, and a closed drainage system. The Gulf is currently connected to the Ionian Sea and the Mediterranean Sea by the Rion Sill and Acheloos-Cape Pappas Sill in the west (currently at 60 m and 55 m below sea level, respectively), and the Corinth Canal (completed in 1893) in the east. During glacial lowstands, the sea level dropped below the sill height and separated the Gulf from the Mediterranean The International Ocean Discovery Program (IODP) Expedition 381 focused on sampling sediments in the Corinth Basin to better understand past environmental changes, especially during glacial to interglacial transitions. Ostracode assemblages have been studied from the sediment core M0078, drilled in the center of the basin to a depth of 610 mbsf. This study relies on benthic ostracodes, which are persistent in the core and inform large changes in chemical-physical parameters and water depth within the basin We find ostracode fauna are particularly sensitive to environmental conditions driven by global sea level oscillations, which cause the Gulf of Corinth to be connected or isolated from the Mediterranean and therefore global oceans. In core M0078, ecosystem shifts are documented by coeval changes in the ostracode assemblages, reflecting variations in water depth (deep-shallow marine environments) degree of confinement-salinity (marine-lacustrine environments).
Two different types of assemblages have been identified from the ostracode assemblages: Mediterranean marine (Cytheropteron spp.; Henryhowella spp.; Aurila spp.; Cytherois spp.) and brackish with Black Sea influences (Amnicythere spp.; Tuberoloxoconcha spp.; Candonidae). Thirteen environmental-ecological stages followed one another crossing six tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. Such faunal turnovers identify glacials (brackish assemblage, low sea level) and interglacials (marine assemblage, high sea level) and indicate a complex history of sea level changes that changed the drainage and depth of the Corinth Gulf during the Quaternary.