Sill-controlled salinity contrasts followed post-Messinian flooding of the Mediterranean

Abstract

million years ago, a mile-high marine cascade terminated the Messinian SalinityCrisis due to partial collapse of the Gibraltar sill that had isolated a largely desiccated Mediterranean from the Atlantic Ocean. Atlantic waters may have refilled the basin within 2 years. Prevailing hypotheses suggest that normal marine conditions were established across the Mediterranean immediately after the catastrophic flooding. Here we use proxy data and fluid physics-based modelling to show that normal conditions were likely for the western Mediterranean (wMed), but that flooding caused a massive transfer of salt from the wMed to the eastern Mediterranean (eMed) across the Sicily sill, which became a hypersalinity-stratified basin. Hyper-stratification inhibited deep-water ventilation, causing anomalously long-lasting organic-rich (sapropel) sediment deposition. Model-data agreement indicates that hyper-stratification breakdown by diapycnal diffusion required 26,000 years. An alternative hypothesis that Atlantic reconnection occurred after the Mediterranean had largely been refilled is inconsistent with our observations, as this would have led to hyper-stratification and sapropel formation in both basins. Our findings offer insight into the role of stratification in delaying the re-establishment of normal marine conditions following abrupt refilling of a previously desiccated ocean basin. The 630,000-year Messinian Salinity Crisis (MSC) resulted from progressive closure of the connection(s) between the Mediterranean Sea and Atlantic Ocean ~5.96 Million years ago (Ma) 1-3 . During the MSC, massive evaporite sequences were deposited. A phase of km-scale Nature Geoscience, 2022

Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years

“…The Mediterranean method is evidently affected by secular change, which most likely reflects a “ baseline shift in Mediterranean climate conditions from a warm/moist state to a warm/arid state at ∼1.5 Ma ” (Rohling et al., 2014). Hence, while the Mediterranean record extends back to ∼5.3 Ma, when the current Strait of Gibraltar opened (e.g., Amarathunga et al., 2022; and references therein), there are continuity (thus, interpolation) and secular offset issues. We avoid these issues here by only using the Mediterranean RSL reconstruction for age information about major sea‐level transitions within the last 150,000 years, based on data from core LC21, which has a particularly detailed chronology (K. M. Grant et al., 2012; Rohling et al., 2014).…”

Birth, evolution and demise of the Mediterranean Lago-Mare

“…6.2), which lies today (and possibly also during the Messinian; Heida et al, 2022) at >2000 mbsl. This model is in agreement with the idea that just before the M/P boundary the level was probably low enough to isolate many Mediterranean subbasins (Amarathunga et al, 2022) and is therefore consistent with the Zanclean flood model (Garcia-Castellanos et al, 2020).…”

A terminal Messinian flooding of the Mediterranean evidenced by contouritic deposits on Sicily

“…The theory of a Zanclean Flood generally implies a significant drawdown of the Mediterranean (1750 to 1900 m lower compared to modern‐day levels), with a relatively abrupt end of the crisis generating a Mediterranean‐wide flood of unprecedented discharge (Garcia‐Castellanos et al ., 2009; Micallef et al ., 2018; Spatola et al ., 2020; Amarathunga et al ., 2022). In this scenario, the Sicily Sill is the easternmost barrier of the terminal flood coming in from the Atlantic.…”

“…The preferred scenario presented here implies that just prior to Atlantic–Mediterranean reflooding, the western and eastern Mediterranean were disconnected (Garcia‐Castellanos et al ., 2020; Amarathunga et al ., 2022; Andreetto et al ., 2022a). One remaining question concerns the timing and duration of the actual flooding event.…”

“…3 The Mediterranean was oscillating with high-amplitude precession-controlled base-level fluctuations (Rouchy & Caruso, 2006;Andreetto et al, 2022a). Scenarios 1 and 3 imply a significant bathymetric contrast between the Messinian and Zanclean and suggest a catastrophic end to the MSC with the collapse of the Gibraltar Sill, and the abrupt re-establishment of open marine conditions all over the Mediterranean at the beginning of the Zanclean (Hs€ u et al, 1973;Garcia-Castellanos et al, 2009;Amarathunga et al, 2022).…”