Benthic environmental changes in the Eastern Mediterranean Sea during sapropel S5 deposition
Abstract High resolution benthic foraminiferal analyses of sediment cores collected at different sites in the Eastern Mediterranean Sea revealed that profound changes occurred in deep-sea ventilation over the past 124–119 ka BP. The three cores (SIN97-GC01, BAN89-GC09, BD02-GC01) were selected in order to investigate middle and deep bathyal ecosystems in the Eastern Mediterranean basin. At site SIN97-GC01 (933 m water depth, Urania Basin), the presence of benthic fauna in the sapropel layer, and the gradual increase in benthic foraminiferal abundance from the middle part of the sapropel, suggest that the sea-floor was partially ventilated and that re-oxygenation had increased considerably during the late phase of S5 deposition. Cores BAN89-GC09 (2011 m water depth, Napoli Dome) and BD02-GC01 (2470 m water depth, Ionian Sea) show a different pattern. During sapropel S5, benthic abundance and diversity strongly decrease and microfauna even disappears in some levels, suggesting the establishment and maintenance of stagnant and anoxic conditions at the seafloor until the end of S5 deposition. In the deepest part of the basin, the re-establishment of the benthic foraminiferal community at the top of the S5 layer indicates a relatively slow bottom re-oxygenation. At the southernmost site, the foraminiferal assemblage records a short oxygenation pulse during the deposition of sapropel S5 linked to a short cold spell. The results of this study suggest that the evolution of the dysoxic–anoxic conditions, as well as the re-oxygenation pattern at the end of the stagnant period, were characterised by spatial and temporal variability, possibly controlled by basin physiography.