Mediterranean paleoceanography
The Mediterranean is a semi-enclosed marginal basin that connects to the Atlantic Ocean at the shallow & narrow Strait of Gibraltar. The limited communication of the basin with the global ocean causes past climate-related ocean properties to be recorded in the sediment records in an amplified manner. The sediment records provide information on both high-latitude (eg: ice volume changes) and low-latitude (African monsoon strength) climate change, making the Mediterranean a paleoclimate mini-laboratory.
The Messinian Salinity Crisis (MSC)
The Mediterranean was disconnected from the Atlantic around 6 million years ago, due to the tectonic closure of the Atlantic-Mediterranean marine gateway. At the peak of the MSC, the Mediterranean was drawndown to >1.5 km, causing the formation of massive salt deposits. Despite 5 decades of research (over one thousand publications), the mechanisms driving the onset, peak and the demise of the MSC are still debated.
In this article, we review the existing hypotheses and recent developments on the evolution of the MSC.
Video source- PBS Eons | www.youtube.com/@eons
The Zanclean Megaflood
One hypothesis proposed for the termination of the MSC is an abrupt flooding event refilling the Mediterranean at ~5.3 million years ago, following collapse of the Camarinal Sill at the Strait of Gibraltar. The megaflood hypothesis was proposed by Dr. Daniel Garcia-Castellanos, adopting a strait incision model in an article published in 2009.
In Mediterranean sediment records with continuous sections across the Miocene-Pliocene boundary (5.3 Myr), a striking difference exists between western and eastern basins. In the eastern basin, an anomalously lengthy phase of organic matter deposition (and preservation) can be observed immediately after the boundary, whereas in the western basin this feature is absent. My recent work develops upon the 2009 incision model to include physical oceanographic theory on flood energy and basin mixing dynamics to quantify the salinity evolution in both western and eastern Mediterranean basins. This work shows that the eastern Mediterranean was salinity-stratified due to brine transfer from the western Mediterranean during a catastrophic flooding event, subsequently causing a 20-30 thousand year-long phase of organic matter preservation (the 'mystery sapropel'). Model results validate this interpretation, suggesting that upward salt diffusion may have taken >15 thousand years to remove all the salt back to the Atlantic.
Video source- Daniel Garcia-Castellanos