The oceans cover about 71% of Earth’s surface, but what makes them distinct is not just their vastness, but also their salt content.

Ocean salinity plays a crucial role in regulating the climate, ocean currents, and sustaining marine life.

Why is the Ocean Salty?

The primary reason oceans are salty is due to runoff from rivers and streams, which transport minerals and salts from the land. When water from rainfall or rivers reaches the ocean, it brings with it dissolved salts and minerals. As the ocean's water evaporates due to heat, the salts remain behind.

This process results in an increase in the salt content of ocean water. Unlike freshwater bodies like lakes and rivers, oceans are constantly receiving minerals from the land but aren’t flushed of these minerals. Instead, they accumulate, making the water salty.

What is Ocean Salinity?

Ocean salinity refers to the amount of dissolved salt in the ocean’s water. It is measured in parts per thousand (ppt), which indicates how much salt is present in a given amount of seawater. On average, seawater has about 35 grams of salt for every liter of water, or 35 ppt.

This level can vary slightly depending on the region of the ocean, with higher salinity typically found in hot, dry areas where evaporation exceeds precipitation. In colder areas or where freshwater is abundant, salinity levels are lower.

How Much of Earth’s Water is Saltwater?

Of all the water on Earth, about 97.2% is saltwater. This includes the water in the five major oceans: the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Freshwater, which makes up only about 2.8% of Earth’s total water, is primarily found in glaciers, ice caps, rivers, lakes, and underground aquifers.

Even though the majority of Earth’s water is in the oceans, less than 1% of that water is accessible for human consumption, with most of it locked away in ice or deep groundwater reservoirs.

Distribution of Fresh and Saltwater

In total, Earth holds around 326 million trillion gallons (or 326,000,000,000,000,000,000 gallons) of water. The vast majority of this is saltwater, held in oceans and seas.

Freshwater is much rarer and is primarily stored in glaciers and ice sheets, with only about 0.3% of it found in rivers and lakes. Despite its scarcity, freshwater is crucial for life on Earth and supports all forms of terrestrial life.

The Role of Ocean Salinity in Climate and Ecosystems

Ocean salinity impacts several key elements of the Earth system. It influences the temperature of the oceans, the movement of ocean currents, and plays a part in regulating the global climate. The salinity levels in the ocean are connected to the water cycle, which includes evaporation, condensation, and runoff.

The ocean's salinity is not just a fascinating scientific phenomenon; it is a vital component of Earth’s water cycle and climate system. With the majority of Earth's water being saltwater, understanding ocean salinity helps us comprehend ocean currents, climate regulation, and the delicate balance that sustains marine life.

As we continue to study the oceans, understanding salinity will be key to addressing challenges like climate change and preserving the health of marine ecosystems.