How does salt get in the ocean

It is formed from super-saline water flowing from under 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. This 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. As you can calculate the residence time, for example, for the sodium and chloride in the ocean. But the oceans themselves are something like 4 billion years old.

Now it turns out the process for removing salt from the oceans is very like what the Romans were doing to produce salt we put in our food.

It is essentially evaporation of seawater in hot arid parts of the ocean to form what we call evaporite deposits which essentially suck the salt out of the ocean and keep it from building up to high levels.

So for example, organisms will precipitate calcium carbonate skeletons, and these calcium carbonate skeletons will then sink through the water column and form sediments on the sea floor.

And these sediments ultimately will become the limestone deposits we see on land. So this effectively keeps the calcium and carbonate content of the ocean well below that of the sodium chloride content. So one of the major processes that removes salt from seawater is hydrothermal circulation through young ocean crust.

So cold seawater will penetrate into the sea floor through the cracks and fissures at the sea floor, driven by that magma supply at depth where the temperatures are incredibly high. So as the sea water penetrates down into the rock, it gets hotter and hotter and chemical reactions will be driven by the temperature gradient and by the high pressure underneath the crust.

So the first reaction that happens is the magnesium, that major element in seawater, is stripped out to form clay minerals in the crust.

So magnesium is stripped from seawater. Following this, we get removal of the sulphate from seawater which precipitates as a white mineral will which we call anhydrite in the ocean crust. So the chemical composition of our fluid is changing. The fluid gets more acidic as it strips protons from the rocks, which in turn it becomes more corrosive towards the rock, and metals are stripped out and sulphides are dissolved from the rock so the fluid stinks of hydrogen sulphide.

So as that flow gets close to the magma supply, it gets hotter and hotter and hotter, maybe up to degrees Celsius. Share this post. Why is the ocean salty, but rivers flowing into it are not? The saltiness of the ocean is the result of several natural influences and processes ; water from rivers entering the ocean is just one of these factors. What happens next? Where does the salt go in the oceans and where does it end up over time. Share this post. Loved It 23 Jun, Visit the course. Exploring our Ocean 09 Apr, Review of Oceans Course 03 Apr, Perhaps too much on Salt, but the trip through the contents of Time well spent 31 Mar, In this step, Dr Will Homoky University of Leeds talks about the process of chemical weathering and the transport of water by rivers into the ocean.

But rivers contain just a tiny amount of salt compared to ocean waters so there must be something else that accounts for the difference. Want to keep learning? This content is taken from University of Southampton online course. See other articles from this course. This article is from the online course:.

News categories. Other top stories on FutureLearn.