This question must have risen in everyone’s mind during childhood after accidentally gulping a mouthful of ocean water. You probably know the taste. But if you don’t – it’s not recommended for anyone to directly taste ocean water in the first place, but you can try it right now by mixing a tablespoon of salt into one glass of water. Sounds gross, right?
Where Does the Salt Come From?
Over 70 percent of the earth’s surface is covered with ocean, 97 percent of which is found saline in nature. From folk stories to mythology, every culture has its own story explaining how the oceans became salty. It is indeed very thought-provoking that water found in the lakes and rivers is considered to be freshwater but when they channelize into oceans, the salinity increases on a major scale. So why is that?
The Salt is Everywhere
Well, first you need to understand that virtually any type of water on Earth contains minuscule amounts of salt. Scientists employ sophisticated methods such as ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS) to measure trace amounts of substances. These techniques have revealed that even bodies of water typically considered fresh, such as lakes, rivers, and ponds, contain minute concentrations of salt. This is true even for the smallest streams and puddles. Salinity, which refers to the concentration of salts in water, is typically very low in these freshwater sources compared to ocean water.
There’s only one exception to this, and that is rainwater. The water falling from the sky has no salt in it at all and is considered to be 100 percent completely freshwater.
Rainfall Turns Salty When it Touches the Ground
When raindrops fall into the ground or trickle down into rivers and streams, that’s when they starts to become a little bit more salty. Geologists (who study rocks and soil) figured out that most of the rocks and soil contain tiny amounts of salt, and when the rainwater touches the ground, it absorbs some of that salt.
Raindrops absorb carbon dioxide from the surrounding air. This causes the rainwater to be somewhat acidic due to the formation of carbonic acid. The acidic content in the rain gradually erodes the rock and takes away the minerals and salts in a dissolved state as ions after the chemical breakdown.
Subsequently, when lakes and rivers pour their water into the ocean, they carry their salt with them. With time, the salt accumulates in the ocean, and it never leaves. Some of the dissolved salt ions are used up by marine organisms, and some remain for long periods, which leads to an increase in their concentration over time.
It is estimated that the rivers and streams flowing from the United States alone discharge 225 million tons of dissolved solids and 513 million tons of suspended sediment annually to the ocean.
Hydrothermal Vents
Hydrothermal vents are fissures located on the ocean floor, primarily along mid-ocean ridges, where geothermally heated water is discharged. These vents are significant sources of ocean salinity. As cold seawater seeps into the Earth’s crust, it is heated by underlying magma and re-emerges loaded with dissolved minerals, significantly enhancing local salinity levels. This superheated, mineral-rich water is more acidic and warmer compared to the surrounding deep ocean waters, and it carries high concentrations of various salts, which contribute to the overall salinity of the ocean.
Fun fact: It is also believed that the complete bulk of the oceans could trickle through the oceanic crust in around 10 million years.
The entire process is part of a larger phenomenon known as submarine volcanism, which involves underwater volcanic activities that further influence ocean chemistry. Like hydrothermal vents, submarine volcanoes release hot, mineral-rich fluids into the ocean. This interaction between magmatic materials and seawater not only contributes to the salinity but also affects the water’s clarity and temperature around these geological features.
How Salty is the Ocean?
By some estimates, if the salt in the ocean could be removed and spread evenly over the Earth’s land surface it would form a layer more than 500 feet (166 meters) thick, about the height of a 40-story office building.
NOAA
On average, seawater contains about 3.5 percent salt. This means that it contains about 35 parts salt per thousand, or that approximately 3.5% of its entire weight comes from dissolved salts. In a cubic mile of seawater, the weight of salt (as sodium chloride) totals about 120 million tons.
Additionally, a cubic mile of seawater may contain up to 25 pounds of gold and 45 pounds of silver. However, before attempting alchemy on seawater, one must consider the immense volume of a cubic mile, containing over a trillion gallons of water. However, isolated ocean bodies can be ten times saltier – one such example is the Dead Sea.
The most saline water body is the Red Sea, where evaporation rates are higher, has lower rainfall rates, and has low river run-off due to confined circulation.
The current standard for salinity is the “Reference Salinity” scale with the salinity expressed in units of “g/kg.”
The Chemical Composition of Salt Water
Just like normal salt, the two ions most prevalent in seawater are chloride and sodium (salt ions), comprising over 90% of all dissolved ions. The concentration of NaCl (salt) in seawater is around 28 grams per liter.
Magnesium and sulfate make up another 10 percent of the total. Other ions are found in very small concentrations. The concentration of salt in seawater (salinity)varies with temperature, evaporation, and precipitation. Some seas, like the Mediterranean, are saltier than the rest of the ocean.
The Importance of Ocean Salinity
While it may seem peculiar, the salty properties of the ocean actually play a crucial role in the global ecosystem.
Climate Regulation
Ocean water’s density is directly linked to its salt content: saltier water is denser and sinks below less salty, warmer water. This density variation plays a crucial role in driving ocean currents, which in turn regulate global climate patterns.
Animal Adaptations
Salinity also significantly influences marine and estuarine ecosystems. Variations in salt levels can affect the distribution of species, limiting the habitats suitable for freshwater species. For marine life, changes in salinity require physiological adaptations. For instance, seabirds possess specialized salt glands to excrete excess salt from drinking seawater, while marine mammals like whales rely on their prey’s moisture content, avoiding the direct ingestion of salt water. Sea otters, however, can drink salty water due to their highly efficient kidneys.
Global Water Cycle Dynamics
Additionally, salinity levels are higher in deeper waters and regions with high evaporation rates, low rainfall, and minimal freshwater input from rivers and melting ice. The constancy of seawater’s chemical composition is maintained despite these variations, thanks to the stability of its principal salt-forming elements. Research shows that the overall salinity of the ocean is a delicate balance maintained by the water cycle, influenced by factors such as evaporation and the formation of sea ice, which is why the global warming of the planet and the glacial melting could have catastrophic impacts on the delicate saline ecosystem.
The 6 Saltiest Water Bodies On Earth
Now that we understand the reason behind this phenomenon, let’s explore some of the saltiest water formations that exist on Eart:
Don Juan Pond
Salinity: 40 %
Temperature: -50°C
Situated in Antarctica, the Don Juan pond is the saltiest water body among all of the world’s lakes. Containing more than 40 percent of salt content, its water never freezes even at the lowest temperature (-58 degrees Fahrenheit).
Dead Sea
Salinity: 33.7 %
Temperature: 20°C– 32°C
The Dead sea is the most famous saline body in the world, also known as the “Salt Sea”. It is situated between Jordan and Israel. It is named the Dead Sea because no life can survive here due to the high salinity rate.
Great Salt Lake
Salinity: 6 % to 27 %
Temperature: -18°C-38°C
Great Salt lake is the largest Salt Lake in northern Utah. The salinity of the lake’s main basin, Gilbert Bay, is highly variable and depends on the lake’s level. It is a great site for hiking and biking, with marvelous views of the lake. Dissolved salts accumulate in the lake by evaporation. The high salinity supports a mineral industry that extracts about 2 million tons of salt from the lake each year.
Caspian and Aral Seas
Salinity of Caspian Sea: 1.2% / Salinity of Aral Sea: 1%
Temperature of Caspian Sea: 0°C-26°C/ Temperature of Aral Sea: 4 °C and 26 °C
Situated in Central Asia, both the Caspian Sea and the Aral Sea have been a victim of environmental concerns in recent years like pollution and shrinkage of the water body. It has eventually led to the death of the fish which once lazed in its waters.
The Caspian sea is still a big lake bordering various countries, like Kazakhstan, Armenia, Turkmenistan, etc. The Aral sea is gone. It has dried up, because of Soviet diversion of the water from the river Amu Daria to irrigation fields in the former Soviet Republics in Central Asia.
Mono Lake
Salinity: 8.1%
Temperature: 1°C- 24°C
Mono Lake is situated in California, USA. It is a saline soda lake in Mono County. Periodic eruptions of volcanic ash have also added considerably to Mono Lake’s chemical mix. It has great outdoors and is surrounded by many volcanoes and mountains, and has a rich birdlife.
FAQs
How does ocean salinity affect climate prediction models?
Ocean salinity plays a critical role in enhancing the accuracy of climate prediction models by providing data on water density and ocean circulation patterns, which are crucial for forecasting climate changes and weather patterns.
What are the main challenges in measuring ocean salinity at great depths?
Measuring salinity at great depths poses challenges due to high pressure, low temperatures, and the remoteness of deep-sea environments. Advanced technologies like CTD sensors (which measure conductivity, temperature, and depth) are used, but maintaining their calibration and handling the data from such depths require sophisticated techniques.
How do scientists monitor global ocean salinity changes over time?
Scientists monitor global ocean salinity changes using a combination of satellite observations, such as those from NASA’s Aquarius and the SMAP (Soil Moisture Active Passive) satellites, along with in-situ measurements from drifting buoys and ships. These data help track salinity patterns and trends, which are vital for understanding the global water cycle and climate change impacts.
