Quck answer
Ocean water is salty due to the presence of dissolved salts, primarily sodium chloride. These salts come from various sources, such as rivers, volcanic eruptions, and underwater volcanic vents. When rainwater falls on land, it dissolves minerals from rocks and soil, carrying them into rivers and eventually into the ocean. Over millions of years, these dissolved salts have accumulated, making the ocean water salty. Additionally, the process of evaporation increases the concentration of salts in the ocean, as water evaporates and leaves the salts behind. This is why ocean water has a salty taste.
Water, water, every where, / Nor any drop to drink
In these lines from a well-known poem— “The Rime of the Ancient Mariner” by Samuel Taylor Coleridge—an “ancient mariner,” or sailor, complains of being surrounded by water he cannot drink. He is on a ship in the ocean, suffering from thirst. Why would someone be thirsty when there is water all around? You guessed it! Because ocean water is too salty to drink. We know that sea water is salty—but do you know why? Let’s WONDER together!
Our planet is composed of approximately 70% water, and 97% of that water is salty. All the oceans—from the Atlantic to the Pacific, from the Arctic to the Indian—are all salty! What is in ocean water, anyway? It is primarily composed of water, of course. But there are numerous other elements present in the water. Ocean water contains dissolved salts and minerals. It even contains trace amounts of various chemicals, including metals like gold!
Some of these elements enter the ocean through runoff. But what is runoff? Runoff is the water that flows over the land and into streams and rivers. When it rains, some water seeps into the soil. Once the soil becomes saturated, the excess rainwater becomes runoff. Rainwater has a mild acidity. Similar to how acidic foods like orange juice or soft drinks can gradually erode tooth enamel, acidic rainwater erodes rocks and soil. Tiny particles of rock and soil mix with the rainwater as runoff. This runoff then flows into streams and rivers, which eventually flow into oceans. In this way, minerals and salts from runoff find their way into the ocean.
Two of the most common elements that end up in the ocean due to runoff are sodium and chloride. When sodium and chloride combine, they form sodium chloride. In other words, salt! However, runoff is not the only reason for the salinity of ocean water. Salt also originates from the deep parts of the ocean.
Deep beneath the ocean floor, there are hydrothermal vents. Hydro means water, and thermal means heat. Not surprisingly, these vents release hot water into the ocean. Where does this hot water come from? Great question! Initially, ocean water seeps into the oceanic crust, or the “floor” of the ocean. It is then heated by magma from the earth’s core. Subsequently, this heated water is expelled through the hydrothermal vents.
The warm water from the vents contains a high concentration of dissolved minerals, including salt. A similar reaction occurs when underwater volcanoes erupt. The seawater surrounding the volcano reacts with the hot rocks of the volcano, causing minerals and salts to dissolve into the ocean water.
So now we understand why ocean water is salty. But if part of the salt in the ocean comes from runoff from the land, why aren’t lakes and rivers salty? The answer is that they actually are! Most lakes and rivers are freshwater, meaning they are not salty. However, this does not mean they are completely devoid of salt. They contain some salt, but in lesser amounts compared to the ocean. Lakes and rivers are constantly replenished by rain, preventing them from becoming excessively salty. Oceans, on the other hand, have a constant influx of salt through rivers that empty into them.
There exist some lakes that have a high salt content. The Great Salt Lake and the Dead Sea are well-known examples of such salty lakes. These lakes are typically large and located inland, not connected to the ocean. The largest salt lake is the Caspian Sea. Australia has thousands of salt lakes, which not only have a high salt content but are even saltier than the ocean.
The reason for their high salt content is that these lakes receive runoff and groundwater, both of which contain salts and minerals. During periods of heavy rainfall, these lakes may have a lower salt concentration, but as the water evaporates and the lake dries up, the salt content increases. Some of these lakes completely dry up at certain times of the year and can be ten times saltier than the ocean.
Due to the high salinity, very few animals can survive in these environments, and saltwater is also unhealthy for humans. Drinking saltwater can make us sick because it contains too much salt. In fact, consuming saltwater can lead to increased thirst and dehydration as the body tries to eliminate the excess salt through urine.
You might wonder if there is a way to remove salt from water to make it drinkable. Many people share this curiosity, especially as droughts become more frequent and severe. Desalination is the process of removing salt from seawater, but it is a challenging and energy-intensive process. Salt dissolves easily in water, making it difficult to separate the two. Desalination requires a significant amount of energy, making it expensive and also has environmental consequences.
There is still much to learn about saltwater. What specific aspects are you interested in?
Let’s dive deeper into the topic of ocean water!
- Have you ever observed that it is simpler to float in the ocean compared to a pool? Why is that? With the assistance of an adult, attempt this experiment on the density of saltwater versus freshwater. Then, utilizing Canva or any materials you have, create a poster to educate others about your findings on water density. Share it with friends or family members!
- Saltwater differs from freshwater in other aspects as well. Discover more about how salt affects the freezing point of water! With the help of an adult, conduct this experiment or gather more information from your local library. Share your newfound knowledge with a friend!
- What does science have to do with art? More than you might think! Let’s experiment with watercolor salt painting. You can find ideas here, here, or at your local library. Share your creations with a friend or family member!
Wonder Sources
- https://www.britannica.com/dictionary (accessed 6 Apr., 2023)
- https://www.usgs.gov/special-topics/water-science-school/science/why-ocean-salty (accessed 13 Mar. 2023)
- https://oceanservice.noaa.gov/facts/riversnotsalty.html (accessed 13 Mar. 2023)
- https://www.scientificamerican.com/article/why-dont-we-get-our-drinking-water-from-the-ocean/ (accessed 13 Mar. 2023)
- https://earthobservatory.nasa.gov/blogs/earthmatters/2017/01/18/waiter-theres-salt-in-my-lake/ (accessed 13 Mar. 2023)
- https://www.poetryfoundation.org/poems/43997/the-rime-of-the-ancient-mariner-text-of-1834 (accessed 13 Mar. 2023)
- https://oceanservice.noaa.gov/facts/drinksw.html (accessed 16 Mar. 2023)
FAQ
1. Why is ocean water salty?
Ocean water is salty due to the presence of dissolved salts and minerals. When rain falls, it washes over land, picking up various minerals and salts along the way. This water eventually finds its way to the ocean through rivers and streams. Over time, the water in the ocean evaporates, leaving behind the dissolved salts and minerals. This process is repeated over millions of years, resulting in the high salt content of ocean water.
2. What are the main salts present in ocean water?
The main salts present in ocean water are sodium chloride (table salt), magnesium chloride, and calcium chloride. These salts make up the majority of the dissolved solids in the ocean. Other minerals and salts, such as potassium, sulfate, and bicarbonate, are also found in smaller concentrations.
3. Is the salt content of ocean water the same everywhere?
No, the salt content of ocean water can vary slightly depending on the location and other factors. Generally, the average salinity of ocean water is around 3.5%. However, areas with high evaporation rates, such as the Red Sea, can have saltier water, while regions with heavy rainfall or freshwater input from rivers may have lower salinity levels.
4. Can humans drink ocean water?
No, humans should not drink ocean water because it is too salty. Consuming large amounts of saltwater can actually lead to dehydration rather than quenching thirst. The high salt content in ocean water can dehydrate the body by drawing water out of the cells through osmosis. It is essential to only drink freshwater that is safe for consumption.
5. How is salt extracted from ocean water for commercial use?
Salt can be extracted from ocean water through a process called desalination. There are two main methods: distillation and reverse osmosis. Distillation involves heating the saltwater to create steam, which is then condensed to obtain freshwater and separate the salt. Reverse osmosis uses a membrane to filter out the salt and other impurities, leaving behind freshwater. These methods allow for the production of freshwater from ocean water, which is especially important in areas with limited freshwater resources.
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