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Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (predominantly sodium ( Na +
However, the salt content of oceans lowers the freezing point by about 1.9 °C [41] (due to freezing-point depression of a solvent containing a solute) and lowers the temperature of the density maximum of water to the former freezing point at 0 °C. This is why, in ocean water, the downward convection of colder water is not blocked by an ...
Only the top layer of water needs to cool to the freezing point. [11] Convection of the surface layer involves the top 100–150 m (330–490 ft), down to the pycnocline of increased density. In calm water, the first sea ice to form on the surface is a skim of separate crystals which initially are in the form of tiny discs, floating flat on the ...
As seawater freezes in the polar ocean, salt brine concentrates are expelled from the sea ice, creating a downward flow of dense, extremely cold, saline water, with a lower freezing point than the surrounding water. When this plume comes into contact with the neighboring ocean water, its extremely low temperature causes ice to instantly form ...
Deep ocean water (DOW) is the name for cold, salty water found in the deep sea, starting at 200 m (660 ft) below the surface of Earth's oceans. Ocean water differs in temperature and salinity. Warm surface water is generally saltier than the cooler deep or polar waters; [1] in polar regions, the upper layers of ocean water are cold and fresh. [2]
The temperature of the surface water of the Arctic Ocean is fairly constant at approximately −1.8 °C (28.8 °F), near the freezing point of seawater. The density of sea water, in contrast to fresh water, increases as it nears the freezing point and thus it tends to sink.
Salinity affects both the freezing and boiling points of water, with the boiling point increasing with salinity. At atmospheric pressure, [117] normal seawater freezes at a temperature of about −2 °C. Salinity is higher in Earth's oceans where there is more evaporation and lower where there is more precipitation.
The volume of the Pacific Ocean, representing about 50.1 percent of the world's oceanic water, has been estimated at some 714 million cubic kilometers (171 million cubic miles). [69] Surface water temperatures in the Pacific can vary from −1.4 °C (29.5 °F), the freezing point of seawater, in the poleward areas to about 30 °C (86 °F) near ...