Millions of years ago, an unprecedented geological event drastically transformed the Mediterranean landscape. During the Messinian Salinity Crisis, which occurred between 5.97 and 5.33 million years ago, the Mediterranean was cut off from the Atlantic Ocean. This isolation caused the near-total evaporation of the sea, leaving behind vast salt plains.

However, new research published in Communications Earth & Environment reveals that the Mediterranean did not refill slowly, as previously believed. Instead, a colossal megaflood, known as the Zanclean Deluge, filled it with water over a surprisingly short period.

An international team of scientists, including participants from the University of Southampton, identified a series of geological features in southeastern Sicily that point to this catastrophic event. According to Dr. Aaron Micallef, the study’s lead researcher, the Zanclean Megaflood was an awe-inspiring natural phenomenon, with discharge rates and flow speeds surpassing any other known flood in Earth’s history.

Zanclean Deluge Evidences
a) Poorly sorted and clast-supported breccia (Br) unit with polygenic sand matrix and boulder size sub-rounded clasts. b) Clast-supported breccia with angular monogenic clasts. c) Erosional surface defining the stratal break-up in the Tripoli Formation overlain by the breccia unit. d) 3D photomosaic of a ridge with outcrops of the breccia unit, the overlying Trubi and underlying Tripoli Formations. Credit: Aaron Micallef et al.

During the Messinian Salinity Crisis, the disconnection of the Mediterranean from the Atlantic led to the formation of extensive salt deposits. Scientists had believed this period ended gradually over approximately 10,000 years. However, the discovery in 2009 of an erosional channel connecting the Gulf of Cádiz with the Alboran Sea altered this narrative, suggesting that a single massive event lasting between two and 16 years was responsible for refilling the Mediterranean.

The study estimates that the flood had a discharge rate between 68 and 100 Sverdrups (one Sverdrup equals one million cubic meters per second), vastly exceeding any other known flood.

The researchers combined new geological findings with geophysical data and numerical models to reconstruct a more detailed picture of the Zanclean Megaflood. They analyzed over 300 elongated, asymmetric ridges in the Sicilian Strait, a submerged land bridge connecting the western and eastern basins of the Mediterranean. These ridges, eroded by large-scale, turbulent water flows, provide evidence of the magnitude of this phenomenon.

Zanclean Deluge Evidences
Artistic representation of the Gibraltar sill break at the end of the Messinian salinity crisis. At the end of this crisis, the level of the Mediterranean Sea was about one kilometer lower than that of the Atlantic Ocean. Credit: Pibernat & Garcia-Castellanos

Additionally, the ridges were covered by a layer of rocky debris formed from eroded materials rapidly deposited by the force of the water. This layer marks the boundary between the Messinian and Zanclean periods, pinpointing the moment when the flood occurred.

Using seismic reflection data—a technique similar to a geological ultrasound—the researchers identified a “W”-shaped channel on the seabed east of the Sicilian Strait. This channel, connecting the ridges to the Noto Canyon, acted as a funnel directing water into the eastern Mediterranean basin. Computational models indicated that flow velocities could have reached up to 32 meters per second, enough to carve deeper channels and transport sediments over long distances.

The study not only sheds light on a critical moment in Earth’s geological history but also highlights the persistence of landscape features over more than five million years. According to Dr. Micallef, these findings pave the way for future research on Mediterranean margins and how similar events may have influenced other regions of the planet.


SOURCES

University of Southampton

Micallef, A., Barreca, G., Hübscher, C. et al. Land-to-sea indicators of the Zanclean megaflood. Commun Earth Environ 5, 794 (2024). doi.org/10.1038/s43247-024-01972-w


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