View source for Deep ocean water

{{short description|Cold, salty water deep below the surface of Earth's oceans}}
'''Deep ocean water''' ('''DOW''') is the name for cold, [[salt]]y [[water]] found in the [[deep sea]], starting at {{cvt|200|m|ft}} below the surface of Earth's [[ocean]]s.  Ocean water differs in [[temperature]] and [[salinity]]. Warm surface water is generally saltier than the cooler deep or [[polar climate|polar]] waters;<ref>{{cite web |title=Ocean Stratification |url=http://eesc.columbia.edu/courses/ees/climate/lectures/o_strat.html |website=The Climate System |publisher=[[Columbia University Press]] |access-date=2015-09-22 |archive-date=29 March 2020 |archive-url=https://web.archive.org/web/20200329070232/https://eesc.columbia.edu/courses/ees/climate/lectures/o_strat.html |url-status=dead}}</ref> in [[polar regions of Earth|polar regions]], the [[photic zone|upper layers]] of ocean water are cold and fresh.<ref name=Meltdown>{{cite web |title=The Hidden Meltdown of Greenland |url=https://science.nasa.gov/science-research/earth-science/28aug_greenland/ |website=NASA Science News |publisher=[[NASA]] |access-date=2023-11-27}}</ref>  Deep ocean water makes up about 90% of the volume of the oceans. Deep ocean water has a very uniform temperature, around {{cvt|0|–|3|C|F}}, and a salinity of about 3.5% or, as [[oceanography|oceanographers]] state, 35‰ ([[per mille|parts per thousand]]).<ref>{{cite web |url=https://windows.ucar.edu/tour/link=/earth/Water/temp.html |publisher=[[University Corporation for Atmospheric Research|UCAR]] |access-date=2012-09-05 |title=Temperature of Ocean Water |archive-url=https://web.archive.org/web/20100327205743/http://www.windows.ucar.edu/tour/link=/earth/Water/temp.html |archive-date=2010-03-27 |url-status=dead}}</ref>

In specialized locations, such as the [[Natural Energy Laboratory of Hawaii]], ocean water is pumped to the surface from approximately {{cvt|900|m|ft}} deep for applications in research, commercial and pre-commercial activities. DOW is typically used to describe ocean water at {{clarification needed span|text=sub-thermal depths|reason=What does this term mean, and what is its application here?|date=February 2024}} sufficient to provide a measurable difference in water temperature.

When deep ocean water is brought to the surface, it can be used for a variety of things. Its most useful property is its temperature. At the surface of the Earth, most water and air is well above 3&nbsp;°C. The difference in temperature is indicative of a difference in [[energy]]. Where there is an energy [[gradient]], skillful application of engineering can harness that energy for productive use by humans.

The simplest use of cold water is for [[air conditioning]]: using the cold water itself to cool air saves the energy that would be used by the compressors for traditional [[refrigeration]]. Another use could be to replace expensive [[desalination]] plants. When cold water passes through a pipe surrounded by humid air, condensation results. The condensate is pure [[water]], suitable for humans to drink or for crop [[irrigation]]. Via a technology called [[ocean thermal energy conversion]], the temperature difference can be used to run a [[heat engine]] to generate electricity.

==Cold-bed agriculture==
A potential indirect use of cold ocean water is "cold-bed agriculture".  During condensation or ocean thermal energy conversion operations, the water does not reach [[ambient temperature]], because a certain temperature gradient is required to make these processes viable. The water leaving those operations is therefore still colder than the surroundings, and a further benefit can be extracted by passing this water through underground pipes, thereby cooling agricultural soil. This reduces evaporation, and even causes water to condense from the atmosphere.<ref>{{cite web|title=Energinat - DOW Technologies - Cold Agriculture|url=http://www.energinat.com/dow_cold.shtml|website=www.energinat.com|access-date=14 July 2016|archive-date=29 January 2016|archive-url=https://web.archive.org/web/20160129013413/http://www.energinat.com/dow_cold.shtml|url-status=dead}}</ref> This allows agricultural production where crops would normally not be able to grow. This technique is sometimes referred to as "cold agriculture"<ref>[http://nelha.hawaii.gov/event/west-hawaii-tech-pau-hana-4/ West Hawaii Tech Pau Hana]</ref> or "cold-bed agriculture".<ref>{{cite web|title=What is OTEC|url=http://www.otecnews.org/what-is-otec/|website=OTEC News|date=30 September 2011|publisher=the OTEC foundation|access-date=14 July 2016}}</ref>

==See also==
{{portal|Oceans}}
* [[Deep sea fish]]
*[[Deep ocean minerals]]

==References==
{{reflist}}

{{physical oceanography|expanded=other}}

[[Category:Oceanographical terminology|Deep water]]
[[Category:Marine energy]]