Have you ever gone down to the beach and playing some games got really thirsty and, after exhausting the little water you had and still wanting more, you look towards the sea wondered why should such a vast pool of water be so undrinkable? Why is the ocean salty? Where did the salt come from?
Before we delve too deep into explanations it is very important to know that all water forms – water bodies – that exist on the planet contains chemicals in a dissolved state though in varying amounts and these chemicals are referred to by scientists as ‘salts. So next time you see sea water don’t think of table salt, it is more than that kind of salt.
Where did the ‘salt’ in the ocean come from?
Most of the salt in the oceans and seas actually come from land, rocks to be specific. Just a minute portion coming from undersea volcanoes and sea rock floors. Surprised? Everyone is familiar with the processes of erosion and evaporation; these are the simple processes that combine leading to the saltiness of oceans.
Rain, Erosion and Evaporation
The seas and oceans however, were not as salty in primeval times as they are today. Thanks to rainfall they are getting saltier by the day. Rain falling on rocks washes the surface off a tiny bit at a time (over millions of years) through the process of erosion dissolving mineral salts of the rock surfaces. This salt solution flowing through streams and rivers, ultimately end up in seas and oceans which are essentially reservoirs.
An estimated 225 millions tons of dissolved solids a large part of which is mineral salt is discharged into seas by streams and rivers from the United States alone. However, this alone does not explain why the seas are salty. Why the oceans and not rivers and streams especially since they carry the dissolved salts. That can only be answered by a process known as evaporation.
Since oceans are closed systems (water flows in but not much flows out) when water evaporates it leaves the salts behind and more stream and rivers flows bring in more water and part of these also evaporate and so on creating a cycle (part of the hydrologic cycle) of salt accumulation which is what is seen today.
It is important also to note that salinity is not the same in all seas and oceans. This disparity is due to a variation of reasons which include amount of rainfall in the region, terrain, and slope, amount of runoff, intensity evaporation and also ice formation.
So, when next someone around you or at the beach wonders ‘Why Oceans are salty?’, you can smile and give them a very concise and informed answer!
Ocean Water: Salinity – Science and Technology Focus – http://www.onr.navy.mil/focus/ocean/water/salinity1.htm
Why is the Ocean Salty? – By Herbert Swenson, US Geological Survey Publication – http://www.palomar.edu/oceanography/salty_ocean.htm
Why is the Ocean Salty? – The USGS Water Science School – http://water.usgs.gov/edu/whyoceansalty.html