Seawater is water containing dissolved salts and other constituents. Its salinity changes mass density, freezing behaviour and other material properties, so specifying temperature alone does not fix its buoyancy. At a given temperature and pressure, a change in composition can alter whether a parcel rises or sinks relative to neighbouring fluid.
This makes seawater central to ocean circulation and open-ocean convection. Freezing sea ice rejects much of the salt into the surrounding liquid through brine rejection, while melting supplies relatively fresh water. Measuring temperature, salinity and pressure together therefore supplies information that a surface-temperature map alone cannot recover.
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Seawater is water from the world's oceans and seas, characterized primarily by its high salt content. On average, seawater has a salinity of about 35 parts per thousand (ppt), meaning that in every liter of seawater, there are approximately 35 grams of dissolved salts, mainly sodium chloride (table salt). Other components of seawater include various minerals, dissolved gases (such as oxygen and carbon dioxide), organic matter, and microorganisms.