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Imaggeo on Mondays: The ephemeral salt crystals

Imaggeo on Mondays: The ephemeral salt crystals

Rock salt stalactites (Speleothems) are the indicators of entrance in a salt cave. These crystal stalactites precipitate from brine only at the entrance in the salt caves, as that is the only place where the physical and chemical properties of the air and the brine dripping from the ceiling allow these crystals to grow and be preserved. And they are extremely fragile – if there is just a small change in the brine’s chemistry or the air’s moisture, the crystals will vanish away, dissolved in a pool of brine or a stream of salt water flowing out of the cave. These stalactites of salt crystals are what we call secondary salt; that means the original salt (formed million years ago) dissolved in water and re-precipitated recently.

Yes, you heard right, the sediments that contain these caves are made of rock-salt in the ground. Actually, caves can be formed in various types of soluble materials, from limestone and gypsum to halite (rock salt) or even ice. The salt caves denote the presence of salt near the surface of the earth.

How does the salt get there? Well we do know that there have been moments in the history of the Earth when certain seas (salt giants) have accumulated enormous deposits of salt instead of the more familiar mud sediments. However, we still don’t completely understand the process. That is also due to the fact that, unlike other rocks, salt has a plastic behavior, it tends to ‘flow’ upwards through other rocks, towards the surface (pretty much like wet sand between your feet when at seaside). As salt squeezes its way up, it deforms the rocks around it and creates salt domes that are later dissolved by water. This dynamic behavior of salt means that there are very few places where we can find salt in its original location and the understanding of the natural mechanisms that form salt remains incomplete.

Earth scientists like me, try to understand the mechanism of salt formation. Because the big picture of the past environments where salt is formed is currently blurred, we try to recreate a ‘movie’ of the past, that starts long before the formation of salts and ends long after. In this ‘movie’ we look at the past geography (paleogeography) and past environment (paleoenvironmental) changes from before to after the formation of the salts in order to single out key patterns that can bring us closer to removing the blur from this interesting episode in the story of oceans and seas.

I took this photo while doing field work in eastern Romania. The photo was taken on a tributary of the ‘Slănicul de Buzău’ river in the Buzău Land Geopark, an area of outstanding geological beauty, in the outer hills of South-East Carpathians. When I was stumbling on the salt caves in the field, I had to put mapping and sample collecting on pause. The layers of rock I was following had disappeared, replaced by a chaotic pile of mud, salt and small rock fragments. All I could do was check these rock fragments scattered in the landscape, try to figure out from where they come from, what layers of rock  the salt destroyed and of course, enjoy the geometric beauty of the ephemeral crystals.

By Dan V. Palcu, postdoctoral researcher at the University of São Paulo, Brazil

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Salt shoreline of the Dead Sea

Imaggeo on Mondays: Salt shoreline of the Dead Sea

This beautiful aerial image (you’d be forgiven for thinking that it was a watercolour) of the Dead Sea was captured by a drone flying in 100m altitude over its eastern coastline.

Climate change is seeing temperatures rise in the Middle East, and the increased demand for water in the region (for irrigation) mean the areas on the banks of the lake are suffering a major water shortage. As a result, the lake is shrinking at an alarming rate. Currently, it is shrinking by over 1m/year. The image was captured as part of a survey in the wider project DESERVE (Kottmeier et al. 2016) addressing the environmental changes accompanying the lake level drop.

In this case, the special focus is to look for e.g. submarine springs or other geomorphological evidence in the shallow lake water that can later turn into hazardous sinkholes (cf. recent publication on that topic Al-Halbouni et. al. 2017). Learn more about the environmental challenges and geohazard risks the region faces in this December 2016 Imaggeo on Mondays post.

The round features see in this image, nevertheless have been identified as salt accumulations following basically the sinusoidal shoreline.

The different colours of the lake indicate water of varying densities, e.g. fresh water floating on top of saltier water and possible sediments inside.

The shoreline appears with different colours each year depending on the sediment mud & evaporite material. Each line represents the retreat of a given year!

[Editor’s note: this image was a finalsit in the 2017 Imaggeo Photo Contest]

By Laura Robert and Djamil Al-Halbouni of the German Research Center for Geosciences, Physics of the Earth, Potsdam, German

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Geosciences Column: Did Mediterranean salt change the global climate?

The latest Geosciences Column is brought to you by Annabel Slater, who describes a time of dramatic change in the Mediterranean. Slater shares the results of a recently published Climate of the Past study and sheds light on how – in the context of global climate – a little salt can go a long way…

Many of us worry about the effects of too much salt on our health, not its effects on global climate. Often the amount we get goes up and down as we sprinkle miserly, health-conscious pinches into cooking, or give in and gladly seize the salt shaker when there’s a cone of chips in hand. Over 5 million years ago, the Mediterranean Sea also experienced salty extremes, swinging from periods of hypersalinity to salinities so low, it approached freshwater. Now, for the first time, scientists from the UK and Germany have shown that this variable Mediterranean salt diet could have had weighty consequences for global climate.

Around 5.96 – 5.33 million years ago during the latest Miocene period, the Messinian, tectonic changes closed off the Mediterranean Sea from the Atlantic Ocean. The salinity of the Mediterranean Sea fluctuated dramatically as water evaporated, increasing salt concentrations up to ten times what they are today.  At other times, regions of near-fresh water accumulated as water flowed in from surrounding rivers and lakes. This event is known as the Messinian Salinity Crisis, and its story is written out in sequences of evaporites and rich fossil records of brackish marine species in the region.

An artist’s impression of the Messinian Salinity Crisis. (Credit: Wikimedia Commons user Paubahi)

An artist’s impression of the Messinian Salinity Crisis. (Credit: Wikimedia Commons user Paubahi)

It had long been thought that, during the event, the Mediterranean Sea remained isolated from the Atlantic and even dried up completely. But recent research suggests that periodically, the connection was remade and outflows of either hypersaline or brackish Mediterranean water flowed into the Atlantic Ocean, like it does today through the Strait of Gibraltar.

The Atlantic Ocean hosts a major ocean current, the Atlantic Meridionial Overturning Circulation (AMOC), which circulates warm surface water from the mid-Atlantic to the higher Arctic latitudes. This looping current is powered by changes in water density, based on temperature and salt content. The more salt there is in water, the denser it is, and the deeper it sinks. The movement of the AMOC influences worldwide ocean circulation and climate. So what would have been the consequences of receiving this variable Mediterranean salt diet?

Led by Ruza Ivanovic, a team of scientists from the University of Leeds and the University of Bristol, UK, and GEOMAR Helmoltz Centre for Ocean Research, Germany, ran several simulations to investigate the effects of fluctuating salt input. They used a climate prediction model known as HadCM3 from the UK Met Office to generate several scenarios of Mediterranean water outflow.

Their simulations showed that any Mediterranean outflows during the Messinian Salinity Crisis would cause significant cooling. Outflows of the saltiest, densest water would cause a shift in the AMOC pattern, and cooling of a few degrees as far north as the Labrador and the Greenland-Iceland-Norwegian seas. But outflows of the freshest water would completely shut down the AMOC and generate a bipolar climate effect. Strong cooling reaching –8 degrees Celsius would occur in the northern seas, with weak warming occurring in the south. This simulation also showed a lasting southern shift in precipitation patterns.

The Mediterranean Sea today. (Credit: NASA/Eric Gaba)

The Mediterranean Sea today. (Credit: NASA/Eric Gaba)

These are the first major findings to unveil a connection between the Messinian Salinity Crisis and worldwide changes in climate. The simulations also show that flows or lack of flow from the Mediterranean Sea had more impact on the AMOC then, in comparison to conditions today. Palaeoclimate researchers investigating this relationship will now know where to look and also what to look for to find more evidence. As the North Atlantic sea surface temperature showed the most variability throughout all the simulations, the team think this region could be key to confirming their modelled results.

And as more evidence is uncovered about the connections between the Mediterranean and the Atlantic, the team will be able to refine their simulations to find out more about the duration and reach of the Messinian Salinity Crisis’ effects.

With much about the cause and nature of the Messinian Salinity Crisis still unknown, this research is a new step towards unpicking the mystery. One thing seems clear – either a little or a lot of salt can go a long way.

By Annabel Slater, Freelance Science Writer

Reference:

Ivanovic, R. F., Valdes, P. J., Flecker, R., and Gutjahr, M.: Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis, Clim. Past, 10, 607-622, 2014.