Oceans are salty because water flowing from rivers to oceans carries dissolved minerals, such as salt, which come from the erosion of continental rocks.
Sea salt mainly comes from the minerals found in the rocks of the Earth's crust. When rain falls, it contains dissolved carbon dioxide, which makes it slightly acidic. This acidic water then flows over land, erodes the terrestrial rocks, and becomes loaded with various mineral salts. Eventually, these salts are carried by rivers to the oceans. The water from the oceans eventually evaporates, but the salts remain, gradually leading to an increase in their concentration in the sea over time and giving it that little salty taste we know so well.
Rain trickles over solid ground, seeping into soils and rocks. As it flows towards rivers, it picks up many minerals like calcium, magnesium, and sodium. These elements come from rocks that gradually wear away over time—that's erosion. Little by little, all this mineral-rich water joins the rivers, which eventually flow into the oceans. There, the water evaporates into the sky, but the mineral salts remain in the ocean. After millions of years, this explains why today we find so much salt in the oceans!
Submarine volcanoes and hydrothermal vents continuously release dissolved minerals into the oceans. Underwater eruptions release chlorine, sulfur, and magnesium, directly from the hot magma, which easily dissolves in the sea. For their part, hydrothermal vents, which are like smoking chimneys on the ocean floor, spew out scalding water rich in mineral salts. Upon contact with cold seawater, these minerals disperse. This constant activity regularly supplies the ocean with salt, thus directly contributing to its high salinity.
Under the ocean, chemical reactions are constantly occurring between oceanic rocks and seawater. When hot water seeps into volcanic rocks on the ocean floor, it triggers a series of chemical phenomena that release dissolved minerals, including calcium, magnesium, and sodium. These elements mix with ocean water, further increasing its salinity. Some reactions, such as the one between water and oceanic basalts, instead remove components from the water, exchanging certain minerals and continuously altering the overall chemical composition of the oceans. In short, the continuous exchange of minerals between water and rocks contributes to the salty taste you experience every time you drink a cup of seawater (which, let's be honest, is rarely a good idea).
The warm climate and high temperatures increase the evaporation of seawater, leaving behind a higher amount of salt, as only pure water evaporates. As a result, in regions where it is hot and dry, such as the Mediterranean, saltier waters are obtained. Conversely, in areas where precipitation (rain, snow) is high, there is more influx of freshwater, which slightly dilutes the seawater.
For their part, the winds aided by ocean currents redistribute this salty water across the oceans, constantly mixing water masses and thus balancing the salt concentration. These ocean currents, like the famous Gulf Stream, mix the warmer, saltier waters with the fresher, less saline waters from the poles. It’s somewhat like a large natural blender, but on a very large scale.
If all the salt present in the oceans were evenly distributed across the surface of the Earth, it would form a layer of salt about 150 meters thick. Impressive, isn't it!
Human tears also contain a slight salt content. In fact, the salinity of our tears is similar to that of our bodily fluids and has a concentration close to that of ancient oceans when the first living beings appeared on Earth.
Oceans contain so many dissolved minerals that if we could extract all the dissolved ocean gold, each individual on our planet could have up to about 4 kilograms! However, the extraction process would currently be far too expensive.
Did you know that some coastal areas use shallow natural basins called salt pans to produce salt from seawater? The sun evaporates the water, leaving behind salt ready to be harvested.
Yes, ocean salinity can fluctuate due to climate changes, variations in precipitation, and glacial periods or ice melting. Major geological events or human activities can also temporarily influence marine salinity.
Indeed, not all bodies of water are equal in salinity. For example, the Baltic Sea is relatively low in salinity due to its numerous freshwater inflows, while lakes like Lake Baikal are completely made up of freshwater. Salinity directly depends on the incoming and outgoing freshwater flows and evaporation.
Certainly. Salinity is crucial for aquatic organisms as it affects their osmotic balance. Some species can tolerate a wide range of salinity, while others are extremely sensitive to these variations. This is why each species is adapted to a specific level of salinity that often defines its natural habitat.
The oceans collect dissolved salts from the erosion of soils and terrestrial rocks, transported via rivers and precipitation. While freshwater regularly evaporates from rivers, the minerals brought along remain permanently trapped in the oceans, making the water salty over time.
Yes, today, sea salt is harvested through controlled evaporation in salt marshes. However, extracting ocean salt on a very large scale is energy- and economically costly, which limits this practice to regions where the climate favors natural evaporation, such as along the Mediterranean coast.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
