Transient oxygenation of the Mediterranean after the Zanclean megaflood
Abstract
The Mediterranean basin reconnected to the Atlantic Ocean ~5.33 Myr ago, following its partial desiccation during the preceding Messinian salinity crisis (5.97 to 5.33 Myr). While the extent of terminal Messinian drawdown and abruptness of reconnection are debated, recent work inferred that an anomalously long-lasting eastern Mediterranean organic-rich “mystery sapropel” layer was deposited due to salinity-stratification and anoxia following catastrophic flooding that refilled the basin. However, independent evidence is required to test this hypothesis. Here, we present extensive proxy data and numerical model results to show that irrespective of the largely hypersaline or oligohaline conditions proposed for the terminal Messinian, the eastern Mediterranean became oxygenated due to the ~1.5-km-high, turbulent and aerated cascade that refilled the basin, which created a salinity-stratified but oxygenated water column that allowed preservation of only the most recalcitrant organic components. Next, oxygen was gradually depleted over a period of up to 12,000 y due to remineralization of sinking organic matter, culminating in a stratified, anoxic basin. It took 33,000 y after flooding (7,000 y longer than suggested previously) for turbulent diffusion to weaken the stratification and allow resumption of convective deep-water renewal, which marked the final return of normal oxygenated marine conditions throughout the Mediterranean.
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (19)
Udara Amarathunga
Department of Geosciences, Princeton University
Jochen J. Brocks
Research School of Earth Sciences, Australian National University
Paul Th. Meijer
Department of Earth Sciences, University of Utrecht
Janet M. Hope
Research School of Earth Sciences, Australian National University
Willem-Jan Zachariasse
Department of Earth Sciences, University of Utrecht
Rick Hennekam
Isabel van der Hoeven
Department of Ocean Systems, Royal Netherlands Institute for Sea Research (Nederlands Instituut voor Onderzoek der Zee)
Ursula Roehl
Center for Marine Environmental Sciences, University of Bremen
Susan Rule
School of Culture, History and Language, College of Asia and the Pacific, Australian National University
Ulrike Troitzsch
Research School of Physics, Australian National University
Simon Haberle
School of Culture, History and Language, College of Asia and the Pacific, Australian National University
Appy Sluijs
Department of Earth Sciences, University of Utrecht
Katharine M. Grant
Research School of Earth Sciences, Australian National University
Wout Krijgsman
Department of Earth Sciences, University of Utrecht
Daniel Garcia-Castellanos
Geosciences Barcelona, Consejo Superior de Investigaciones Científicas
Andrew McC. Hogg
Research School of Earth Sciences, Australian National University
Gert-Jan Reichart
Andrew P. Roberts
Research School of Earth Sciences, Australian National University
Eelco J. Rohling
School of Ocean & Earth Science, University of Southampton, Southampton, UK.