Why is the Ocean Salty?

by Derek Kaden

Why is the Ocean Salty?

The Ocean is salty because of dissolved land materials that are deposited into the Ocean through streams and rivers. Stream and river water does not taste salty because it is moving, compared to the Ocean, which is essentially a giant bath tub. The concept is the same for most lake water. The Great Lakes are not salty because the water contained within them is on the move. According to an article by Science Daily, a drop of water in the Great Lakes will stay there for approximately 200 years before it makes its way out to sea, whereas a droplet of water in the Ocean can take up to 200 million years before it goes anywhere!

Farming for sea salt in Thailand.

Farming for sea salt in Thailand.

Why are Some Lakes Salty?

The most well-known salty inland lakes are the Great Salt Lake in Utah and the Dead Sea in Western Asia. These bodies of water are so salty because they receive a lot of dissolved river deposits and offer no further outlet for those deposits to go. In addition, evaporation is greater than rainfall in these areas. The more evaporation in an area, the higher the salinity (saltiness of water) will be. Rainfall causes salinity levels to sink. The Great Salt Lake has an approximate salinity of 280 parts per thousand, which is 8 times saltier than the average salinity of the Ocean. The Dead Sea’s salinity is 330 parts per thousand, or almost 10 times saltier than the Ocean. The saltiest known inland body of water is the Don Juan Pond in Antarctica, a very small and shallow patch of water that has a salinity of 440 parts per thousand, which is 12 and a half times saltier than the Ocean!

The dense salty water of the Dead Sea makes it very easy to float - without a floaty!

The dense salty water of the Dead Sea makes it very easy to float – without a floaty!

What are the Key Differences Between Fresh Water and Salt Water?

Some of the most marked differences between fresh water and salt water are in their freezing points and boiling points. Pure water freezes at a very familiar temperature: 32 degrees Fahrenheit (o Celsius). Average Ocean water that has salinity of 35 parts per thousand freezes at a lower temperature: 28.6 degrees Fahrenheit (-1.9 Celsius). In fact, the more saline a body of water is, the lower the temperature must be for that water to freeze. Since the Don Juan Pond is so salty, it still doesn’t freeze even when temperatures reach -22 degrees Fahrenheit (-30 Celsius)!

The boiling point of average Ocean water is only slightly higher than the boiling point of fresh water. Fresh water boils at 212 degrees Fahrenheit (100 Celsius), whereas Ocean water boils at 213.1 Fahrenheit (100.6 Celsius). This means that adding salt to your soup or pasta water will actually make the food cook slightly quicker, and it will of course make it taste better! It’s important to add the salt after the water starts boiling, otherwise it will take longer to reach a boil.

Surface Temperature Differences in the Great Lakes

By Derek Kaden

Have you ever heard someone say that the water along Illinois’ or Wisconsin’s beaches is colder compared to Michigan’s? How could that even be possible? I mean, the air temperature in Chicago and Benton Harbor in Michigan could be the exact same, but the lake temperatures in these two places could be completely different. Why?

The answer has everything to do with geography.

All water is propelled by the wind. In the Great Lakes region, the dominant winds – called the Prevailing Westerlies – generally move from the west to the east. They travel in this direction because the Earth rotates counterclockwise. Therefore, the Westerlies push lake water away from the western shore and toward the east.

One important characteristic of water is that the colder it gets in temperature, the heavier it gets as well. Warm water is lighter, less dense, which means its molecules are more spread out. Therefore warm water rises to the surface, while cold water sinks to the bottom. Fresh water is at its densest when it is at a cold 39.2°F. This means that the water at the bottom of the Great Lakes – or any lake that extends deeper than the pycnocline (1,000m) – is always going to be 39.2°F! Learn more about lakes, differences between fresh and salt water, and the ocean in this blog post.

When the wind pushes water away from Chicago’s shore, the water it pushed needs to be replaced. At the same time, the water being pushed toward Michigan’s shore needs somewhere to go. This movement of water is called upwelling and downwelling.

Chicago’s shore experiences upwelling, meaning the water being pushed away by the wind gets replaced by the dense cold water from the bottom of the lake. Downwelling is the reverse of this. In Michigan, the warm surface water gets shoved to the bottom, leaving no chance for the cold water at the bottom to rise.

Take a look at these pictures I drew which help to illustrate the point:



The fluctuation in temperature is greatest between late spring and early fall. In these months, the surface temperatures on Lake Michigan can vary by as much as 15 or 20 degrees between the western and eastern shores. The same goes for any of the other four lakes. During the winter, the lakes’ surface temperatures are pretty much as cold as at the bottom. It’s either frozen (32°F) or just covered in cold dense water. Take a look at these temperature maps produced by the National Oceanic and Atmospheric Association (NOAA).

The first one is from spring of 2014. Notice the warmer surface temperatures beginning in the middle of Indiana on Lake Michigan. They go on past Muskegon.


The same fluctuation can be seen in the summer. The biggest difference is on Wisconsin’s shoreline, between Milwaukee and Green Bay (light green), compared to shoreline north of Muskegon (brown and red). Both of these regions are at basically the same latitude, but the difference in water temperature is up to 15 degrees! This is upwelling and downwelling in full effect.



The trend continues into the fall.



And by winter, the fluctuation subsides and we’re left with a combination of cold dense water and…ice.