Why is the sea salty?

Question

I found out that when i got out from the sea water there are salt on my arms and legs. Why is that so? Are they really salt?

Answer 1

Because the sea has many dissolved minerals in it.

Answer 2

Everyone who has been to the beach knows that seawater is salty. Everyone also knows that fresh water in rain, rivers, and even ice is not salty. Why are some of Earth’s waters salty and others not? There are two clues that give us the answer. First, “fresh” water is not entirely free of dissolved salt. Even rainwater has traces of substances dissolved in it that were picked up during passage through the atmosphere. Much of this material that “washes out” of the atmosphere today is pollution, but there are also natural substances present.

As rainwater passes through soil and percolates through rocks, it dissolves some of the minerals, a process called weathering. This is the water we drink, and of course, we cannot taste the salt because its concentration is too low. Eventually, this water with its small load of dissolved minerals or salts reaches a stream and flows into lakes and the ocean. The annual addition of dissolved salts by rivers is only a tiny fraction of the total salt in the ocean. The dissolved salts carried by all the world’s rivers would equal the salt in the ocean in about 200 to 300 million years.

A second clue to how the sea became salty is the presence of salt lakes such as the Great Salt Lake and the Dead Sea. Both are about 10 times saltier than seawater. Why are these lakes salty while most of the world’s lakes are not? Lakes are temporary storage areas for water. Rivers and streams bring water to the lakes, and other rivers carry water out of lakes. Thus, lakes are really only wide depressions in a river channel that have filled with water. Water flows in one end and out the other.

The Great Salt Lake, Dead Sea, and other salt lakes have no outlets. All the water that flows into these lakes escapes only by evaporation. When water evaporates, the dissolved salts are left behind. So a few lakes are salty because rivers carried salts to the lakes, the water in the lakes evaporated and the salts were left behind. After years and years of river inflow and evaporation, the salt content of the lake water built up to the present levels. The same process made the seas salty. Rivers carry dissolved salts to the ocean. Water evaporates from the oceans to fall again as rain and to feed the rivers, but the salts remain in the ocean. Because of the huge volume of the oceans, hundreds of millions of years of river input were required for the salt content to build to its present level.

Rivers are not the only source of dissolved salts. About twenty years ago, features on the crest of oceanic ridges were discovered that modified our view on how the sea became salty. These features, known as hydrothermal vents, represent places on the ocean floor where sea water that has seeped into the rocks of the oceanic crust, has become hotter, and has dissolved some of the minerals from the crust, now flows back into the ocean. With the hot water comes a large complement of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of the oceans could seep through the oceanic crust in about 10 million years. Thus, this process has a very important effect on salinity. The reactions between seawater and oceanic basalt, the rock of ocean crust, are not one-way, however; some of the dissolved salts react with the rock and are removed from the water.

A final process that provides salts to the oceans is submarine volcanism, the eruption of volcanoes under water. This is similar to the previous process in that seawater is reacting with hot rock and dissolving some of the mineral constituents.

Will the oceans continue to become saltier? Not likely. In fact the sea has had about the same salt content for many hundred of millions if not billions of years. The salt content has reached a steady state. Dissolved salts are being removed from seawater to form new minerals at the bottom of the ocean as fast as rivers and hydrothermal processes are providing new salts.

We can summarize this discussion. Wherever water comes into contact with the rocks of Earth’s crust, either on land or in the ocean or within the oceanic crust, some of the minerals in the rock dissolve and are carried by the water to the ocean. The salt content of seawater does not change because new minerals are forming on the sea floor at the same rate as salt is added. Thus, the salt content of the sea is at steady state.

Answer 3

It's the Blue whale's fault.

Answer 4

All human waste products eventually end up in the seas.  Animals obtain salt from saltlicks.  Natural salt mines have been mined at an exponential rate in the past 2 centuries, and salt has been used as a food preservative since time immemorial, adding to the reserves in the oceans.  Salt helps to keep the water in the seas, otherwise more of it would evaporate as the Sun heats up over the milleniums.  Also, it's the Earth's "dynamo" which protects our water from being photo-dissociated by solar uv, stripping hydrogen from water molecules, while the solar wind blows it away.   Earth's dynamo also protects us from cosmic rays--galactic, solar, extragalactic, ultra high energy, and anamolous rays--which would otherwise bombard us.

Much of the water in the oceans and seas was made by mammals, including humans.  That's because water vapor and CO2 are the 2 primary byproducts of aerobic respiration, or oxygen intake:

Aerobic Respiration:

C6H12O6 + oxygen --> 6 CO2 + 6 H2O + energy

Combustion adds even more water to the atmosphere whenever fuels are burned, and whenever fires start--natural or man-made fires:

Combustion:

Butane C4H10 + 6.5 O2 --> 4 CO2 + 5 H2O

Now you know why we have such a problem with flooding.  The flooding will continue unabated and worsen over time since the Earth can be likened to a fishbowl, it just fills up with water unless some of it is removed.  Write to your space agency to ship potable bottled water to the moon and Mars.  160+ moons have been discovered so far in our very own solar system.