The sea is salty because rain erodes salts out of rocks, and rivers transport this salt to the oceans, where it accumulates. The sea is made up of:
- Potassium ions, among others…
Edmund Halley thought the oceans were getting saltier because rivers added salt to them. But we now know that the oceans were formed 3.8 billion years ago, and the early oceans were actually saltier than today.
Around five and a half million years ago, the Mediterranean Sea was cut off from the rest of the world and almost completely dried up. The Dead Sea fills a similar role today, and hydrothermal vents also impact the ocean’s saltiness.
The surface ocean is saltier as you get closer to the equator because it’s warmer, and evaporation rates are higher there. The Mediterranean and Red Seas are also saltier than average because of evaporation.
Salinity and temperature determine the density of seawater, and this movement drives global ocean circulation, which significantly affects how heat flows around our planet. The Aquarius satellite can measure the salinity of the oceans from space.
Does the Ocean Continually Get Saltier?
Salt enters the oceans from rivers, so they keep getting saltier. Nonetheless, several mechanisms help remove salt from the oceans at almost the same rate as it enters.
Evaporation forms evaporite deposits, which eventually cement into sedimentary rocks. Other sinks get rid of salt through chemical processes and mineral absorption. Salt is removed from the ocean by marine life. Freshwater from rivers and melted ice balances evaporation. All these inputs and outputs maintain the relative equilibrium of the world’s ocean salinity.
Ocean salinity plays an important role in the global climate because it helps maintain thermohaline circulation. It helps control the climate by helping the cold water sink closer to the poles.