There is a scientific question that is right for everyone, but many people don’t know why, and that is “Why is seawater salty?”
The saltiness of seawater comes from the fact that it contains a considerable amount of salt (around 35‰). There are two reasons why there is so much salt in seawater.
The first reason lies in the formation process of the ocean. When the earth was just formed (in billions of years), due to a lot of rainfall and volcanic eruptions, the water on the earth gradually gathered into the low-lying places to form the ocean. The sea has a salty taste. However, the sea water was not as salty as it is now. As the soluble salts in the seabed rocks continue to dissolve, and there are continuous volcanic eruptions on the seabed, some soluble salts in the volcanic eruptions dissolve in the seawater, and the seawater gradually becomes salty.
The second reason is the rivers that flow to the ocean. The sea is inclusive of all rivers, and the ultimate destination of most rivers is the sea. In the process, currents constantly wash salt from the soil and rocks and carry them to the sea. It is estimated that the world’s rivers bring at least 3 billion tons of salt into the ocean each year.
Then the question comes again, is the seawater all over the world the same “taste”?
The seawater we mentioned earlier contains about 35‰ of salt, which actually refers to the average salinity of ocean water. That is, there is 35 grams of salt per kilogram of ocean water. Ocean water refers to the water of the four oceans, with an average salinity of about 35 – indicating that the salinity of seawater varies in different sea areas and sea areas, and there are certain changes.
First, the salinity of seawater in the four oceans is different, and secondly, in the interior of several oceans, the change of salinity is more obvious with the change of latitude. Studies have shown that the salinity of sea water is the highest at about 20° north and south latitude. In the North Atlantic, the salinity at the center of this hypersaline zone is above 37.25; in the South Pacific, the hypersaline zone has values of 36.50 and 35.50, respectively; and in the Indian Ocean, the hypersaline zone has a value of 36.00. In contrast, the salinity of seawater in other regions of the equator and higher latitudes is significantly lower than that of the 20° north latitude region. The reason is that this area is the trade wind belt of the earth. The weather in the whole area is dry and the rainfall is small. The precipitation is far less than the evaporation, and the salinity naturally increases.
However, they are not yet the region with the saltiest water on Earth, which occurs in “isolated basins” within the ocean. Because the precipitation and river inflow in these places are very small, the terrain is relatively closed, and the exchange with the adjacent ocean water is not smooth enough.
From another perspective, from a vertical perspective, the seawater on each layer is also different. In the equatorial region, the saltiest seawater layer is located at a depth of 100 to 200 meters, and the seawater higher or lower than it will be a little fresher. In subtropical regions, the reverse is true, where the middle water is the freshest, and the surface and deep waters are saltier. In high latitudes, the freshest seawater is on the surface, and it becomes more and more salty as the depth changes. When the depth is about 1,800 meters underwater, the salinity does not change.
In the vast ocean, there are several mischievous “children” whose seawater salinity is far from the average salinity of ocean water. The Baltic Sea is the lowest salinity sea area in the world. Due to more rainfall, freshwater input from land rivers and less exchange with Atlantic water, its seawater salinity is mostly less than 10 – compared to the average ocean salinity of 35, which is how low. In the Gulf of Bothnia in the north, the salinity of sea water is only 1-2, which is close to the fresh water that people use daily.
In contrast, the Karagazi-Golo Bay in the Black Sea has a salinity of 200, which is 5.7 times that of normal seawater. But the water with the highest salinity is still known as the Dead Sea. Its surface salinity is 227-275, and it is 281 at a depth of 40 meters, which is 8 times the average salinity of ocean water!
