Have you ever wondered why ocean water is salty, but rivers flowing into it aren’t? Well, the water in our oceans is salty due to two separate sources: runoff from the land and openings in the seafloor.
The main cause for salt in the sea (or ocean salinity) is rain washing mineral ions from land into the water. This refers to the acidity of rainwater – when rain falls, it wears down and erodes rocks.
This releases ions (sodium/salt) that are carried away into the sea by rivers and streams that feed into the ocean.
Most dissolved ions that make their way into the ocean are used by organisms that live in the water – removing these ions. However, some ions aren’t removed so their concentration builds up over time which gives the ocean its salty taste.
Hydrothermal Fluids from the Seafloor
The second source is from hydrothermal fluids which come from vents in the seafloor. When cracks appear in the ocean floor, ocean water seeps through these cracks and is heated by the magma from the Earth’s core.
When heated, the water loses oxygen, magnesium, and sulfates. These are replaced by metal like copper, iron, and zinc from surrounded rocks.
The heated water is then released from vents in the seafloor – carrying the metals with it. Ocean salts can also come from underwater volcanic eruptions.
Rivers and streams are replenished every time rain falls, so they don’t taste salty. That is why they are referred to as ‘freshwater’ and not ‘saltwater’ bodies of water.
Hopefully this article has helped you understand why our oceans are salty, but other sources of water, like rivers and streams, are not. Now, if anyone ever asks you “why is the ocean salty” you can fill them in.
Do you have questions about why ocean water is salty? Let us know in the comments below!