Studies show that 97% of all water on Earth is salty because the ocean covers around 70% of the Earth. It is estimated that the amount of salt in the sea can create a layer on the Earth’s crust measuring 500 feet thick. This is approximately the height of a 40-storey building.
While it’s common knowledge that the majority of the seas and oceans are salty, why they are isn’t. The fact that the oceans get most of their water supply from rivers and streams that carry freshwater further deepens the confusion. If you have often wondered why the sea is salty, worry not; we got you!
Factors That Make the Sea Salty
The reason why the sea is salty starts with rainwater. Rainfall is slightly acidic because it reacts with carbon dioxide in the air, which probably answers the other question of why it is unsafe to drink rainwater.
As it falls on the ground, it dissolves salts and minerals on rocks, which are washed into streams and rivers. These water bodies remain fresh because the amounts of salts flowing inside them are little. Also, regular rainfall ensures that streams and rivers have more freshwater than salt water.
As the freshwater flows into the ocean, bringing the salts and minerals with it, these salts are deposited at the bottom of the water body. Since this is the final salt destination, it ensures the ocean remains salty 24/7.
More salts and minerals also come from vents located on the sea floor. In the deeper parts of the ocean, there are cracks that lead to the Earth’s crust. In these cracks, water seeps into the Earth’s core, which is heated by magma. The water evaporates, leaving behind salts. It’s the same process that occurs when salt water is boiled. The dissolved minerals and salts are then carried up into the ocean.
Interestingly, a wide range of minerals is produced from the above-described process, with the major examples being copper, zinc, iron, chloride, and sodium. The first three are significantly depended upon by organisms in the ocean, leaving behind sodium and chloride, the key ingredients used to make salt.
The other factor that causes salinity in the ocean is evaporation. As the sun heats the sea surface, the water becomes warm, and some evaporates, leaving salt behind.
Why Are Some Lakes Salty
Usually, the seas and oceans are associated with having salty waters. However, there are cases where lakes have salty water, too, with the Great Salt Lake in Utah being a perfect example. Scientists attribute this to the fact that the lakes have no outlets.
As water escapes the lakes through evaporation, the salts brought by the rivers and streams are left behind. With time, these salts accumulate, thus increasing the salinity of the lakes. Also, most lakes in dry areas turn salty because of limited rainfall.
The Effects of Salt in Seawater
While it’s true that freshwater rivers have been flowing into oceans for a very long time, the same is true for the evaporation of seawater by magma. Therefore, the amount of salt in oceans has and will always be high.
With scientists estimating that seawater contains 3.5% salt, the presence of salt in the large water bodies makes them very different from freshwater. It makes it denser and more buoyant, with various oceans having different salinities. Seas located near the poles tend to have a lower salinity because of lower temperatures, heavy rain, and melting ice.
In contrast, those near the equator, where temperatures are higher, contain high traces of salt. A typical example is the Mediterranean, which is saltier compared to the Arctic Ocean.
How Do Salinity Levels Remain Balanced in Seas and Oceans
Scientists claim that about 4 billion tons of salt enter the ocean every year. This usually happens while some of the salt in the ocean drops to the floor, ensuring that salinity remains balanced.
Still on water salinity, let’s also touch on why the sea is blue. The reason behind this phenomenon is attributed to how light interacts with water. While white light comprises a wide range of colors with different wavelengths, water molecules are designed to absorb light with longer wavelengths like green, yellow, orange, and red.
Blue has a shorter wavelength, so water molecules do not readily absorb it. This results in ocean water having a blue hue. The colors become darker as you go much deeper into the ocean. Near the shores, seawater can appear browner because of the sand found beneath. Sea life, such as phytoplankton, can also change the color of the sea, making it look greener.