We all know that the ocean water is salty, but have you ever wondered why? Isn’t it weird that ocean water is always salty but other waters like lakes and rivers aren’t salty at all, of course except some lakes like the great salt lake. Well, if it boggles your mind, don’t worry, we did a bit of research and today we will answer why the ocean water is salty.
On average our oceans consist of about 3.5 percent salt, that equates to a million billion tons of salt in our seas. If we pile all of that ocean salt onto the Earth’s land, it would create a layer of 152 metres high. So, the question is how did it get there?
Well, salt in the ocean comes from two sources: runoff from the land and openings in the seafloor.
Rocks on land are the major source of salts dissolved in seawater. Rainwater that falls on land is slightly acidic, so it erodes rocks which in turn releases ions that are carried away to streams and rivers that eventually feed into the ocean. Many of the dissolved ions are used by organisms in the ocean and are removed from the water. Others are not removed, so their concentrations increase over time.
Water in rivers and lakes also contains salt, but the amount of salt in these waters is very little, about 220 times less than sea water but it is there and this salt is then deposited into the sea when the river has run its course. Importantly, the salt becomes more concentrated in the sea because the sun’s heat distills the water from the ocean surface leaving the salt behind.
Another source of salts in the ocean is hydrothermal fluids, which come from vents in the seafloor. Ocean water seeps into cracks in the seafloor and is heated by magma from the Earth’s core. The heat causes a series of chemical reactions. The water tends to lose oxygen, magnesium, and sulfates, and pick up metals such as iron, zinc, and copper from surrounding rocks. The heated water is released through vents in the seafloor, carrying the metals with it. Some ocean salts come from underwater volcanic eruptions, which directly release minerals into the ocean.
Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up around 85 percent of all dissolved ions in the ocean. Magnesium and sulfate make up another 10 percent of the total. Other ions like calcium are found in very small concentrations because living organisms like Mollusca, Crustacean, and corals use huge amounts of calcium to build their body structure. Without this influx of salt and minerals from rivers and streams, life in oceans will be very different.
There are differences in salinity across the globe. Towards the poles, seawater is diluted by melting ice caps and heavy precipitation meanwhile in areas bordering the equator, where it’s hot, evaporation rates exceeds the amount of rainfall so water here is much saltier. There is evidence to suggest that these differences are increasing as sea temperatures rise. Parts of the Atlantic have already shown greater evaporation rates and with it a rise in salinity levels.
Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up around 85 percent of all dissolved ions in the ocean. Magnesium and sulfate make up another 10 percent of the total. Other ions are found in very small concentrations.
Here is an interesting video explaining why the oceans are salty: