Why is the sea salty?
Ever thought why is the ocean salty, but the lakes, rivers, and streams are not?
On this week's "how and why", we will be talking about how and why seas and oceans are salty.
Think of the ocean like a basin. When it rains, tiny amounts of mineral ions from land and dissolved rocks are carried by rivers and streams into the sea.
Part of these mineral ions is salt content. These salts aren't just sodium chloride but also contain elements such as calcium, magnesium, and potassium. Rivers from all around the world carry almost 4 billion tonnes of salts to the sea each year.
What makes the sea salty?
But why are rivers not as salt from the Dead Sea as the sea? It is because they only continuously carry small amounts of salt content into the ocean where salinity (amount of dissolved salts in water) has built up over millions of years. The ocean has been around for a long time but during the prehistoric period, its seawater was not as salty as it is now.
When water evaporates, the mineral ions and salt contents get left behind. The ocean also gets its salinity from hydrothermal vents, undersea volcanoes, and rocks in the oceanfloor.
Today, we have an average of 35 grams of salt in every kilogram of seawater. If all this salt is taken out the water and laid on the Earth's land surface, it would be 150 meters (~500 feet) thick!
Variation in salinity of seas and oceans
The ocean is salty in general, but some places tend to be saltier than others. The salinity of a sea depends on its location and environmental factors.
Seas in the subtropics have a higher salinity because evaporation is also higher due to warm and dry air temperatures. Seas that experience little rain are high in salinity as well. Enclosed seas such as the Mediterranean Sea and the Red Sea can be very salty because evaporation is high, but rainfall is low.
Seas near the north and south poles have lesser salinity because of the melting icebergs that dilute the saltwater with freshwater. Parts of the ocean that receive lots of rain and snow are also less salty because of the freshwater added at the surface. The seawater near rivers are also less salty; one example is the Baltic Sea.
Although the Baltic Sea is an enclosed sea between northern Europe and Scandinavia, it has a very low salinity of 10 ppt (parts per thousand- the unit used to measure salinity). The Baltic Sea has hundreds of rivers flowing into it and melting ice caps.
How does the sea balance its salinity?
The changes in salinity affect the density of the water. The saltier the water, the denser it is. In estuaries, where rivers meet the sea, freshwater stay above saltwater since saltwater is heavier because of its salinity.
Nature always has a sense of balance in all its form. The ocean balances its salinity with the help of marine life and other natural processes. Salt is removed from the ocean at the same rate they are added.
One is by the process of evaporation. When water is evaporated, it leaves the salt components behind. In regions where evaporation is high and the supply of freshwater is low, the salt deposits form into sedimentary rock salts.
Another is a chemical process from sea volcanoes. Lava on the ocean floor reacts with dissolved salts by heating up the salt molecules. Certain clays also absorb salts and minerals. All these continually contribute to keeping the salinity in the ocean balanced.
Marine animals help remove salts from the ocean. In fact, some aquatic animals can't live without the salinity. Corals, for example, use calcium carbonate found in salts to build coral reefs. Shellfishes also use calcium carbonate to make their shells hard and tough.
The ocean is not the only body of water that contains saltwater. Some lakes are as salty as the ocean and one, even saltier!
The Dead Sea is not an actual sea, but an endorheic lake, which means that water flows into it but can not flow out. The Dead Sea's primary source of freshwater is the Jordan River. The only way water can escape is by evaporating.
Because of its high density and saline levels (solution of salt in water), it surpasses the normal salinity of the ocean and people can effortlessly float in it. It is also very salty that no living creatures can survive in its waters, hence its name- the Dead Sea.
Why is the sea salty Researches and References
If you want to know more about why is the sea salty, take a look at our references below.
Below are few links we have used as references, images we use are from wikipedia, NASA, and Patrice Laborda (and no, the picture you think is from Google map is from Patrice 😊 ).
- I have always wondered: Why is the sea salty?
- Why is the sea salty?
- Why are lakes freshwater and oceans saltwater?
- Does the Ocean Continually Get Saltier?
- Why is the sea so salty?
- Why is the sea salty?
- Why is the Dead Sea called the Dead Sea?
Last, but not Least
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Thanks for reading, and if you wish, see you next week!
The Research and Media Team at Scotty's.