A visit to the beach isn’t complete without a dip into the ocean and any swimmer is bound to notice that the ocean is salty. However, the world’s waters are not uniformly salty. Some parts of the ocean have more salt than others, most lakes and rivers taste fresh, and the Dead Sea is so salty it can barely support life. So where does all this salt come from and why are oceans salty but most lakes are not?
Where Does Salt Come From?
About 90% of the ocean’s saltiness can be attributed to the elements sodium and chloride, the same elements found in table salt (NaCl). However, almost all elements can be found dissolved in the world’s oceans, albeit in very small amounts, according to Herbert Swenson of the US Geological Survey in “Why is the Ocean Salty?” Most of these elements, including those which make sea salt, come from the erosion of land. As raindrops and rivers rush over rocks and mountains, parts of the earth are dissolved into ions and are taken out to the ocean.
The other sources of sea salt are hydrothermal vents and underwater volcanoes according to the University of Texas at Dallas in “Why is the Sea Salty?”. Hydrothermal vents are caused by cracks in the sea floor which bring seawater in contact with magma under the earth’s crust. The water becomes hot and gushes upwards, filled with minerals from below.
Why Lakes and Rivers Are Not Salty
Lakes often have fresh water but not always. The Dead Sea, one of the saltiest places in the world, is actually a very large lake. In fact, this landlocked body of water is far too salty for anything but the hardiest of bacteria to live in. What determines a body of water’s salinity is not whether it’s called an ocean, sea, or lake but rather how fast salts are added and water is evaporated. Rivers carry their salts and water out into the ocean. Water evaporates from the ocean and moves land-ward to rain down onto rivers. Thus the supply of water in rivers is replenished but not the supply of salts. The salts remained in the ocean – making it very salty.
Are the Oceans Becoming Saltier?
Since the first rains fell down onto Earth millions of years ago the oceans have become saltier. Since then however, the world’s oceans have reached a ‘steady state’ so that dissolved salts are being removed as fast as they are being added. According to Herbert Swanson the rivers of the world carry roughly 4 billion tons of dissolved salts into the oceans each year – however the same amount of salt is being deposited onto the sea floor at the same time. So, no, the oceans are no longer becoming saltier.
The Difference Between Sea Salt and Table Salt
People extract salt from the ocean to be used in foods, baths, and cosmetics. Salt is also extracted from salt mines found under the ground. Although similar, there is a difference between sea salt from the ocean and table salt generally found in mines. According to the Food Network in the article “Kosher vs. table vs. sea salts” the differences come down to texture and taste. Table salts are generally finer, with smaller granules, and dissolve more quickly into foods. Table salts usually have a little bit of calcium silicate added during processing to prevent clumping. Sea salts have larger granules and receive little to no processing, but lose much of their taste upon cooking.
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