The primary sources of salinity in the ocean are runoff from land and hydrothermal vents on the seafloor.
Runoff from Land: Weathering and Erosion
How It Works:
- Rainwater's Role: Rainwater is naturally slightly acidic due to dissolved carbon dioxide from the atmosphere. This acidity allows it to act as a weak solvent, gradually dissolving minerals from rocks during a process called weathering.
- Erosion and Transportation: As rainwater flows over land (runoff), it carries these dissolved minerals, including salts, into rivers and eventually to the ocean.
- Type of Minerals: Common dissolved minerals include sodium chloride (table salt), magnesium, calcium, and potassium.
Land as a Major Contributor:
Rocks on land represent the single largest source of dissolved salts found in seawater. Over geological timescales, the consistent erosion and transportation of these minerals have significantly increased ocean salinity.
Hydrothermal Vents: Seafloor Openings
How It Works:
- Seawater Penetration: Seawater seeps into cracks in the ocean floor near volcanically active areas.
- Heating and Dissolution: The water is superheated by magma and dissolves minerals from the surrounding rocks.
- Venting: This mineral-rich, hot water is then released back into the ocean through hydrothermal vents (also known as "black smokers").
Composition of Vent Fluids:
Hydrothermal vent fluids contain a variety of dissolved minerals, including metals and sulfur compounds, contributing to the overall salinity and chemical composition of the ocean.
In summary, ocean salinity arises from the gradual accumulation of dissolved minerals transported from land via runoff and from the addition of dissolved minerals released from the Earth’s interior via hydrothermal vents on the seafloor.
