Udara Amarathunga is a 3rd year PhD student in the Climate and Ocean Geoscience group at the Research School of Earth Sciences. His research interests include climate & ocean sciences, palaeoceanography, palaeoclimatology and physical oceanography.
The Mediterranean Sea has been an iconic landmark since the old days. Referred to as Mare Nostrum (‘Our Sea’) by the Romans, some of the world’s greatest ancient civilizations flourished around the shores of the Mediterranean. The Mediterranean is a landlocked basin, connected to the Atlantic Ocean via the narrow Strait of Gibraltar. These reasons made the basin an important route of trade, food, colonization, and sometimes war, highly influencing the cultural development of the region. But wait! What do any of these have to do with science? Let me explain…
The Mediterranean basin is a natural laboratory for research in past climates and the ocean, because of its critical position on the boundary between climate zones, and because of its semi-enclosed nature that causes variability to be recorded in an amplified manner. Our planet has evolved substantially through time, passing by several critical stages of transformation. The Mediterranean basin provides important archives of such changes which guide scientists towards decoding the past and predicting the future of regional and global climate variability.
Udara Amarathunga at RSES Palaeoenvironments lab, searching for Mediterranean forams
One such significant transformation took place about 6 million years (Ma) ago (5.97 Ma, to be precise), when the gateway between the Atlantic and the Mediterranean was closed due to tectonics and sea-level lowering. This led to a kilometer-scale drawdown of the Mediterranean basin, due to excessive rates of evaporation of the region. Termed as the ‘Messinian Salinity Crisis’ (MSC), this is considered to be the most abrupt global scale environmental transformation since the Cretaceous-Paleogene extinction event! (In simple words, the demise of non-avian dinosaurs about 66 Ma ago). Deprived of the Atlantic inflow, the Mediterranean desiccation prevailed a 640,000-year period, probably making the basin one of the most inhabitable places on the planet at the time. At the peak of the salinity crisis, drawdown reached 2 km below present sea-level, and the remaining bodies of water surpassed halite saturation limit. It is estimated that a total salt volume of 800 thousand cubic kilometers may have deposited in the deep Mediterranean during this period!
Realmonte Salt Mine in Sicily, where Messinian salt is commercialized.
(Image source: http://www.geologypage.com/2016/05/the-realmonte-salt-mine-in-sicily.html)
These salt deposits were the clues which drove the attention of the 18th century geologists, who named the period the ‘Messinian’, after the city of Messina in Sicily (Tectonics caused some of these deposits to emerge on land, including Sicily). Later in the 19th century, seismic surveying in the basin began, and at the same time the Deep Sea Drilling Program, conducted with the Glomar Challenger, cored Messinian salts for the first time in 1970, confirming the drying of the Mediterranean. Fifty years have passed since its discovery, producing more than a thousand research papers. However, the sequence of events and the modes of progression of MSC are still under debate.
The Glomar Challenger
(Image source: https://pubs.usgs.gov/gip/dynamic/glomar.html)
The MSC ended 5.33 Ma ago as the Gibraltar sill collapsed, restoring the Mediterranean Sea as we see it today. Ending of the salinity crisis is also widely disputed among scientists. The most favorable scenario supported by existing evidence has revealed the largest ever flooding event in the Earth’s history, which abruptly refilled the Mediterranean ending its more than half a million years long agony. This catastrophic flooding event was coined the ‘Zanclean megaflood’, which is estimated to have replenished the basin within 2 years. At peak rates of flooding, more than 500 times the annual energy dissipated at the Niagara Falls may have been released to the Mediterranean basin within just a day! Not so conceivable!
Niagara Falls – At its peak, the Zanclean megaflood may have discharged volumes exceeding 150 million cubic meters every second (for comparison, present Niagara discharge is less than 2000 m3s-1), releasing 500 times the annual energy dissipation at Niagara Falls within a single day.
(Image source: https://www.dailyrecord.co.uk)
The MSC shaped the life and environment around the region for thousands of years, but most of the story is buried beneath the Mediterranean Sea. Earth’s tectonic plates are constantly in motion. Thus, we cannot exclude the possibility of the initiation of such an event again (Not in the near future, but someday for sure). It is time for us to dig deeper and unearth the hidden mysteries!
Header image: An illustration of the present Mediterranean Sea (source: https://www.scientia.global)