🌊 Why the sea is salty

What you’ll learn

1. Salt arrives from the landExplain how rain, weathering and rivers move dissolved minerals from rocks into the ocean.Fresh rain and flowing rivers can carry dissolved ions without tasting salty; the ocean collects those inputs while evaporation removes water and leaves most salts behind.
2. The seafloor adds chemistryDescribe how hydrothermal vents and underwater volcanism connect seawater chemistry to plate tectonics.Seawater circulates through hot oceanic crust, reacts with rock and returns through vents carrying altered chemical material, making the seafloor an active part of the salt system.
3. Why the ocean does not become infinitely saltyUse salinity, evaporation and removal pathways to explain why average ocean salinity stays within a broad range.Seawater averages about 35 parts per thousand, but local salinity changes as evaporation, rain, rivers and ice alter freshwater balance while sediments, organisms and crustal reactions remove ions.
4. Salinity moves the oceanConnect salt-driven density differences with sea ice, sinking water and global ocean circulation.Cold salty water is dense and can sink; freezing rejects salt into the remaining water, so salinity helps link surface processes to deep circulation and climate.

Questions this course answers

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