The Messinian Salinity Crisis

When I think of the word ‘crisis’, I imagine many things. Natural disasters, political upheaval, and impeding doom spring immediately to mind. But all of these pale in comparison (and geological significance) in the face of the Messinian Salinity Crisis (MSC) and the Zanclean Flood. Before you panic, let me assure you that you have nothing to fear. The crisis is thankfully over … and has been for the past 5.3 million years.

I sense eyerolls and shaking heads, so let me tell you just how terrifying this event was. Roughly 6 million years ago (hardly a glimmer in the mind of a geologist), the Strait of Gibraltar closed, likely due to movement along the tectonic fault that divides Europe and Africa, This effectively isolated the Mediterranean Sea from the Atlantic Ocean. In just a thousand years, evaporation far exceeding recharge, the Mediterranean was transformed into little more than a puddle. Imagine taking a walk from Spain to northern Africa. Looking to your right, you see the towering cliff that once was the Strait of Gibraltar, rising more than 3 kilometers (2 miles) above the sea floor. To your left, you see pockets of water with as much salt as the Dead Sea occupying what were once the deepest trenches of the Mediterranean.

800px-Inserciomamifers

Artist’s rendition of the extent of the Mediterranean Sea during the peak of the crisis

How can we possibly know this? The two strongest lines of evidence are evaporite deposits and paleocanyons (sorry, I had to throw long words in somewhere). As seawater evaporates, it leaves behind behind salt and other minerals such as gypsum and anhydrite. Rock outcrops at sites across the Mediterranean region show massive deposits of these evaporite minerals with ages between 5.3 and 6 million years (rock deposits from the seafloor have since been pushed upwards by tectonic activity). Seismic surveys have found similar salt deposits below the sea floor. The second clue is the canyons eroded by major rivers as the sea level fell. Sediments near Cairo show that the Nile River cut almost 2.5 kilometers (1.5 miles) down into the rock to come to equilibrium with the new water level. Remember that these processes took place over thousands of years, which gave rivers such as the Nile enough time to transform the landscape from giant waterfalls where they poured off the margins of Europe and Africa to deep canyons, some larger even than the Grand Canyon.

800px-Yesares_gypsum

Gypsum deposit

And so we come to the last chapter of our story – the Zanclean Flood. When the Strait of Gibraltar finally reopened 5.3 million years ago, water from the Atlantic Ocean came surging in. So much water, in fact, that the entire basin was refilled in 1 to 2 years. To give you a sense of scale, this would have involved a discharge 1000 times larger than the Amazon River, with sea level in the Mediterranean rising more than 10 meters (30 feet) per day.

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Artist’s rendition of the refilling of Zanclean Flood

So, can this event happen again? Not only is it possible but very probable that it will. As Europe and Africa continue to be pushed towards each other by plate tectonics processes, the Strait of Gibraltar will eventually close again. And this time, it may not reopen. In fact, several million years from now, the Mediterranean will likely have disappeared completely as a new supercontinent is formed. But don’t worry, chances are we won’t be around to see it.

And because geologists are awesome, you can watch a 50-second simulation of the Messinian Event and a short animation of plate tectonics in the past and future.

This has been your daily dose of mostly harmless science.

If you enjoyed this article, please comment below and check out more of my posts! I’d love for you to follow me on WordPress or on Twitter @harmlessscience (just click Follow on the right sidebar). Thanks for reading!

Images from Wikimedia Commons. Cover photo courtesy of Mark, Flickr Creative Commons.

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8 responses to “The Messinian Salinity Crisis

  1. Engaging lesson ! Thanks! Great website!
    Do you know if there is a tally detailing how much earth science and/or engineering education (high school, college, military, post-grad) each member of U.S. Congress has experienced? I’m trying to find a knowledge analysis of the U.S. legislature. Many German, Italian, Scandinavian legislators are engineers or scientists.

    • Thanks! I found a couple of resources. Wikipedia has an analysis of the 111th Congress(2009-2010). Under ‘occupational background’, it lists 121 military personnel, 24 health care professionals, 6 scientists, and 5 engineers (out of a total 541 members). This link has info on the 112th Congress, but in less detail. Hope that helps!

      • Gracias! I’ll save my reaction & thoughts for a blog post at PeatOneil.com on this. Meanwhile, shaking my head in grave dismay. Stay tuned.

    • Reese – Thanks for sharing my piece! I think our favorite perspective is to focus on the world that our societies know and have grown accustomed to. I think that once we start to look at the planet as a whole, we realize that earth systems are dynamic in nature and that change itself is not an oddity but the norm.

  2. Thank you for enthusiastic response to my blog and I like your lecture – I find it mentally stimulating. I read some geology before I start my ‘landscapes’ – geo-scapes or geoaesthetics so I will find this website very helpful. At present I’m depicting a series on 3.5 billion (approx.) year old rocks found in the Pilbara in Western Australia.

    • Thank you Elaine for the comment and email! If there’s something in particular you’re working on that you’d like to know more about, I’d love to write an article for you 🙂 I’ve never heard the term geoaesthetics, but if fits perfectly! Look forward to seeing more of your work.

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