Seawater is salty primarily due to the dissolved salts it contains, which have accumulated over millions of years.
The Source of Saltiness
The saltiness of seawater comes from various dissolved minerals and chemical elements that are carried into the oceans over time. These substances originate from sources like:
- Runoff from land: Rivers and streams flow over rocks and soil, dissolving minerals that are then carried to the sea.
- Underwater volcanic activity: Volcanic eruptions on the seafloor release minerals and gasses directly into the water.
While many different ions are present in seawater, two specific ions are the most significant contributors to its saltiness.
The Main Components
According to the reference provided, the primary culprits behind seawater's saltiness are two specific ions:
- Chloride (Cl⁻)
- Sodium (Na⁺)
These two ions are present most often in seawater. In fact, chloride and sodium together make up over 90% of all dissolved ions found in seawater. When these two ions combine, they form sodium chloride (NaCl), which is the same chemical compound as table salt. However, seawater also contains other dissolved ions, albeit in smaller amounts.
Here are the main ions found in seawater:
- Sodium (Na⁺)
- Chloride (Cl⁻)
- Sulfate (SO₄²⁻)
- Magnesium (Mg²⁺)
- Calcium (Ca²⁺)
- Potassium (K⁺)
While this list includes several ions, sodium and chloride are by far the most abundant and are the dominant reason for the characteristic salty taste of the ocean.
Understanding Salinity
The term used to describe the concentration of salt in seawater is salinity. This is typically measured in parts per thousand (ppt) or as a percentage.
The reference states that the concentration of salt in seawater (its salinity) is about 35 parts per thousand. This means that for every thousand grams of seawater, about 35 grams are dissolved salts.
To put this into a percentage, about 3.5% of the weight of seawater comes from the dissolved salts. While 3.5% might sound like a small number, it's enough to give the ocean its distinct salty taste and significantly impacts its physical properties like density and freezing point.
Over geological timescales, water evaporates from the ocean surface, leaving the salts behind. This process concentrates the salts in the remaining water, maintaining the ocean's salinity level.
