Editing Salinity (section)

===Seawater===
{{See also|Ocean#Salinity}}
[[File:Aquarius flat 2048x1024.ogv|thumb|300px|
[https://www.youtube.com/watch?v=5xQP_B18vMw <sup>Full 3 minute NASA video Feb 27,2013</sup>]
The NASA Aquarius instrument aboard Argentina's SAC-D satellite is designed to measure global sea surface salinity. This movie shows salinity patterns as measured by Aquarius from December 2011 through December 2012. Red colors represent areas of high salinity, while blue shades represent areas of low salinity.]]

The term ''salinity'' is, for oceanographers, usually associated with one of a set of specific measurement techniques. As the dominant techniques evolve, so do different descriptions of salinity. Salinities were largely measured using [[titration]]-based techniques before the 1980s. Titration with [[silver nitrate]] could be used to determine the concentration of [[halide]] ions (mainly [[chlorine]] and [[bromine]]) to give a [[chlorinity]]. The chlorinity was then multiplied by a factor to account for all other constituents. The resulting 'Knudsen salinities' are expressed in units of [[parts per thousand]] (ppt or [[Per mille|‰]]).

The use of [[electrical conductivity]] measurements to estimate the ionic content of seawater led to the development of the scale called the ''practical salinity scale 1978'' (PSS-78).<ref name="pss78a">Unesco (1981). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. ''Tech. Pap. Mar. Sci.'', 36</ref><ref name="pss78b">Unesco (1981). [http://unesdoc.unesco.org/images/0004/000479/047932eb.pdf Background papers and supporting data on the Practical Salinity Scale 1978]. ''Tech. Pap. Mar. Sci.'', 37</ref> Salinities measured using PSS-78 do not have units. {{anchor|PSU}}The suffix '''psu''' or '''PSU''' (denoting ''practical salinity unit'') is sometimes added to PSS-78 measurement values.<ref name=rant>{{cite journal|last=Millero|first=F. J.|journal=Oceanography| year=1993|volume=6| issue=3| pages=67|title=What is PSU?}}</ref> The addition of PSU as a unit after the value is "formally incorrect and strongly discouraged".<ref name=key />

In 2010 a new standard for the properties of seawater called the ''thermodynamic equation of seawater 2010'' ([[TEOS-10]]) was introduced, advocating absolute salinity as a replacement for practical salinity, and [[conservative temperature]] as a replacement for [[potential temperature]].<ref name="teos10"/> This standard includes a new scale called the ''reference composition salinity scale''. Absolute salinities on this scale are expressed as a mass fraction, in grams per kilogram of solution. Salinities on this scale are determined by combining electrical conductivity measurements with other information that can account for regional changes in the composition of seawater. They can also be determined by making direct density measurements.

A sample of seawater from most locations with a chlorinity of 19.37&nbsp;ppt will have a Knudsen salinity of 35.00&nbsp;ppt, a PSS-78 practical salinity of about 35.0, and a TEOS-10 absolute salinity of about 35.2&nbsp;g/kg. The electrical conductivity of this water at a temperature of 15&nbsp;°C is 42.9 mS/cm.<ref name="teos10"/><ref name=culk>{{cite journal|last1=Culkin|first1=F.|last2=Smith|first2=N. D.|title=Determination of the Concentration of Potassium Chloride Solution Having the Same Electrical Conductivity, at 15C and Infinite Frequency, as Standard Seawater of Salinity 35.0000‰ (Chlorinity 19.37394‰)|journal=IEEE J. Oceanic Eng.|year=1980|volume=OE-5|issue=1|pages=22–23|doi=10.1109/JOE.1980.1145443|bibcode=1980IJOE....5...22C}}</ref>

On the global scale, it is extremely likely that human-caused climate change has contributed to observed surface and subsurface salinity changes since the 1950s, and projections of surface salinity changes throughout the 21st century indicate that fresh ocean regions will continue to get fresher and salty regions will continue to get saltier.<ref name=":0">{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=H.T. |author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S.S. |last6=Edwards |first6=T.L. |last7=Golledge |first7=N.R. |last8=Hemer |first8=M. |last9=Kopp |first9=R.E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S.L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Ocean, Cryosphere and Sea Level Change |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press |publication-place=Cambridge, UK and New York, New York, US |volume=2021 |pages=1211–1362 |bibcode=<!-- not 2021AGUFM.U13B..09F --> |doi=10.1017/9781009157896.011 |isbn=9781009157896 |url=https://www.vliz.be/imisdocs/publications/84/371584.pdf }}</ref>

Salinity is serving as a tracer of different masses. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. Salinity distribution contributes to shape the oceanic circulation.