Why Are Oceans Salty?
Oceans are salty because they contain dissolved minerals and salts that have accumulated over millions of years. Rainwater absorbs small amounts of carbon dioxide and becomes slightly acidic, allowing it to slowly weather rocks on land. As rivers flow toward the oceans, they carry dissolved minerals and ions such as sodium and chloride with them.
Additional minerals enter the oceans through underwater volcanic activity, hydrothermal vents, and the weathering of rocks on the seafloor. Over time, water evaporates from the ocean surface, but the dissolved salts remain behind. This continuous process gradually increases the concentration of salts in seawater.
The most abundant dissolved ions in seawater are sodium and chloride, which together form ordinary salt. However, seawater contains many other dissolved substances, including magnesium, calcium, potassium, and sulfate. The average salinity of the world's oceans is about 35 parts per thousand, meaning roughly 35 grams of dissolved salts are present in every kilogram of seawater.
