2023-07-22 04:00:09
The oceans are salty for a very simple reason: there is salt in them! In one liter of seawater there are approximately 35 grams of salt. A real cooking recipe… And yet, no matter how much I look at the sea or the ocean, I don’t see anything… maybe seaweed, sand, but I don’t see any salt. But why don’t we see it? What is this salt made of? And first, where does it come from?
Illustration of an ocean floor.
Natali Snailcat / Shutterstock
Sea salt comes from a mixture of two sources: mineral salts, extracted from rocks, and gases emitted by volcanoes and ridges (underwater mountain ranges). Mineral salts are chemical elements found in rocks and found in water.
For example, limestone rocks contain three different types of chemical elements: calcium, which chemists denote “Ca”, carbon (Carbon is a chemical element of the family of crystallogens, symbol C,…) “C” and oxygen (Oxygen is a chemical element of the family of chalcogens, of…) “O”. Some rocks formed by the cooling of magmas (such as granites) or lava flowing from volcanoes (such as basalts), contain, among other things, an element called sodium (Sodium is a chemical element, with symbol Na and atomic number 11. It’s a…), which chemists denote “Na”.
Gases emitted by volcanoes make rainwater acidic. This is particularly the case of carbon dioxide, CO2 which forms an acid in water called carbonic acid. So when these waters come into contact with the rocks, they attack them, they dissolve part of them.
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It is possible to experience, for example, in the bathroom. If white spots appear on the faucets or the shower screen, it is often limestone (limestones are sedimentary rocks, third most abundant following…), as in the rocks of the same name. Pour some vinegar (Vinegar is an acidic liquid (usually pH 2-3), got…) on it and it will go away. Carbonic acid acts in the same way as vinegar on rocks, limestones, granites or basalts. We then say that the rocks are weathered. They become more fragile and lose certain elements. These elements, including sodium, calcium or magnesium (Magnesium is a chemical element, symbol Mg and atomic number 12.), flow with rainwater to rivers and then to the ocean (Oceans stylized Ωceans is a French documentary directed by…).
In addition, volcanoes release other gases such as chlorine, noted “Cl”, which also accumulates in the ocean (An ocean is often defined, in geography, as a vast expanse of water…). There is therefore in the ocean sodium, Na, and chlorine, Cl, and the combination (A combination can be:) of the two forms salt chloride “NaCl”, the salt, the one we eat! You can also find other elements in sea salt: such as calcium or magnesium.
Salt marshes in Noirmoutier with piles of white salt.
Patrick Depoix/Wikimedia, CC BY
But then why can’t we see it, this salt? Because in water these elements are dissolved. It is possible to do two experiments. First, make seawater at home (A house is a medium-sized building intended for a family, etc.). Take 100 milliliters of tap water. Taste there: it is not salty. Take 3.5 g of salt and put them in water, mix well. After a while, the salt crystals will be dissolved, and the water has become salty.
Conversely, by evaporating sea water, putting it in the sun (The Sun (Sol in Latin, Helios or Ήλιος in Greek) is the star…) for example, crystals are formed. They are salty. It is the salt crystals, the famous NaCl, which have reformed. This process of evaporation (Evaporation is a gradual passage from the liquid state to the gaseous state. It is different…) to recover the salt, this is what is done in the salt marshes.
Sometimes large amounts of seawater evaporate naturally and form huge amounts of salt, so huge that the salt deposits form rocks, called evaporites. For example, in Lorraine, the large salt formations come from an ocean that existed more than 200 million years ago. The salt mines, which exploit these evaporites, provide salt that can be used for food or to put on the roads in winter.
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#sea #oceans #salty
