The pH value at the surface of oceans in pre-industrial time (before 1850) was around 8.2. pH value įurther information: pH § Seawater, and Ocean acidification The density of typical seawater brine of 120 g/kg salinity at 25 ☌ and atmospheric pressure is 1088 kg/m 3. Brines generated by seawater desalination plants can have salinities up to 120 g/kg. The density of seawater also changes with salinity. Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg/m 3 or higher. At a temperature of 25 ☌, the salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6 kg/m 3. The density of surface seawater ranges from about 1020 to 1029 kg/m 3, depending on the temperature and salinity. The current standard for salinity is the "Reference Salinity" scale with the salinity expressed in units of "g/kg". A popular scale was the "Practical Salinity Scale" where salinity was measured in "practical salinity units (PSU)". Historically, several salinity scales were used to approximate the absolute salinity of seawater. The salinity in isolated bodies of water can be considerably greater still – about ten times higher in the case of the Dead Sea. The most saline open sea is the Red Sea, where high rates of evaporation, low precipitation and low river run-off, and confined circulation result in unusually salty water. Monsoon), seawater can be substantially less saline. Where mixing occurs with freshwater runoff from river mouths, near melting glaciers or vast amounts of precipitation (e.g. Data from the World Ocean Atlas Īlthough the vast majority of seawater has a salinity of between 31 and 38 g/kg, that is 3.1–3.8%, seawater is not uniformly saline throughout the world. Properties Salinity Īnnual mean sea surface salinity expressed in the Practical Salinity Scale for the World Ocean. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units. Seawater pH is typically limited to a range between 7.5 and 8.4. The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 ☌ (27.3 ☏). At typical salinity, it freezes at about −2 ☌ (28 ☏). The freezing point of seawater decreases as salt concentration increases. Seawater is denser than both fresh water and pure water (density 1.0 kg/L at 4 ☌ (39 ☏)) because the dissolved salts increase the mass by a larger proportion than the volume. The average density at the surface is 1.025 kg/L. 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 + On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). Seawater, or salt water, is water from a sea or ocean.
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