{{Short description|Physical oceanography of internal waves}} {{for|the novel by Ngaio Marsh|Dead Water (novel)}}{{for|lifeless water|Hypoxia (environmental)}}{{for|the cult and political party in Russia, also called "Dead Water"|Conceptual Party "Unity"}}
[[File:Castro Battle of Actium.jpg|alt=The Battle of Actium by Laureys a Castro, 1672|thumb|It has been speculated that the "dead water" phenomenon played a role in the Battle of Actium<ref>{{Cite journal |last1=Fourdrinoy |first1=Johan |last2=Dambrine |first2=Julien |last3=Petcu |first3=Madalina |last4=Pierre |first4=Morgan |last5=Rousseaux |first5=Germain |date=2020-07-08 |title=The dual nature of the dead-water phenomenology: Nansen versus Ekman wave-making drags |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=29 |pages=16770–16775 |doi=10.1073/pnas.1922584117 |issn=0027-8424 |pmc=7382212 |pmid=32641509|bibcode=2020PNAS..11716770F |doi-access=free }}</ref>]] '''Dead water ''' is the nautical term for a phenomenon which can occur when there is strong vertical density stratification due to salinity or temperature or both. It is common where a layer of fresh or brackish water rests on top of denser salt water, without the two layers mixing.<ref name=NPG>{{cite thesis |last=Danieletto |first=Marco |date=September 2018 |title=Immortal Science of Dead Water: Effects of Internal Wave Drag on Submersibles |publisher=Naval Postgraduate School, Monterey, CA |url=https://calhoun.nps.edu/bitstream/handle/10945/60388/18Sep_Danieletto_Marco.pdf?sequence=1&isAllowed=y |access-date=22 September 2020}}</ref> The phenomenon is frequently, but not exclusively, observed in fjords where glacier runoff flows into salt water without much mixing.<ref>{{cite journal |last=Hambling |first=David |date=31 Aug 2018 |title=Weatherwatch: 'dead water' makes ships seem dead in the water |journal=The Guardian |url=https://www.theguardian.com/science/2018/aug/31/weatherwatch-dead-water-ships-arctic-nansen-explorer |access-date=18 September 2020}}</ref> The phenomenon is a result of energy producing internal waves that have an effect on the vessel. The effect can also be found at density boundaries between sub surface layers.<ref name=NPG/>
In the better known surface phenomenon a ship traveling in a fresh water layer with a depth approximately equal to the vessel's draft will expend energy creating and maintaining internal waves between the layers. The vessel may be hard to maneuver or can even slow down almost to a standstill and "stick". An increase in speed by a few knots can overcome the effect.<ref>{{cite book |year=2019 |title=The American Practical Navigator |location=Washington, D.C. |publisher=National Geospatial Intelligence Agency |page=598 |url=https://msi.nga.mil/Publications/APN}}</ref> Experiments have shown the effect can be even more pronounced in the case of submersibles encountering such stratification at depth.<ref name=NPG/>
The phenomenon, long considered sailor's yarns, was first described for science by Fridtjof Nansen, the Norwegian Arctic explorer. Nansen wrote the following from his ship ''Fram'' in August 1893 in the Nordenskiöld Archipelago near the Taymyr Peninsula: {{Blockquote | text = When caught in dead water Fram appeared to be held back, as if by some mysterious force, and she did not always answer the helm. In calm weather, with a light cargo, Fram was capable of 6 to 7 knots.<ref>{{convert|6|to|7|kn|km/h mph|1}}</ref> When in dead water she was unable to make 1.5 knots.<ref>{{convert|1.5|kn|km/h mph|1}}</ref> We made loops in our course, turned sometimes right around, tried all sorts of antics to get clear of it, but to very little purpose.<ref name=Walker>{{cite journal |last=Walker |first=J.M. |title=Farthest North, Dead Water and the Ekman Spiral |journal=Weather |volume=46 |issue=6 |pages=158–164 |date= June 1991 |doi=10.1002/j.1477-8696.1991.tb05733.x |url=https://rmets.onlinelibrary.wiley.com/doi/10.1002/j.1477-8696.1991.tb05733.x |access-date=22 September 2020|url-access=subscription }}</ref> }}
Nansen's experience led him to request physicist and meteorologist Vilhelm Bjerknes to study it scientifically. Bjerknes had his student, Vagn Walfrid Ekman, investigate. Ekman, who later described the effect now bearing his name as the Ekman spiral, demonstrated the effect of internal waves as being the cause of dead water.<ref name=Walker/>
A modern study by the Université de Poitiers entities CNRS' Institut Pprime and the Laboratoire de Mathématiques et Applications revealed that the effect is due to internal waves moving the vessel back and forth. Two types occur. The first as observed by Nansen causes a constant abnormally slow progress. The second, Ekman type, causes speed oscillations. The Ekman type may be temporary and become Nansen type as the vessel escapes the particular regime causing the oscillating speed. An interesting historical possibility is that the effect caused Cleopatra's ships difficulties and loss at the Battle of Actium in 31 BC in which legend attributes the loss to remora (suckerfish) attaching to the hulls.<ref>{{cite journal |date=July 15, 2020 |title=Scientists find clue to mysterious 'dead water' effect that stops a ship |journal=The Week |url=https://www.theweek.in/news/sci-tech/2020/07/15/scientists-find-clue-to-mysterious-dead-water-effect-that-stops-a-ship.html |access-date=18 September 2020}}</ref>
== See also == {{colbegin}} *Ekman spiral *Ice drift *Iceberg *Internal wave *Nansen's Fram expedition *Nordenskiöld Archipelago *Polar ice cap *Polar ice packs *Polynya *Sea ice *Shelf ice *Vagn Walfrid Ekman – Swedish oceanographer{{colend}}
== References == <references/>
== External links == * [https://www.youtube.com/watch?v=bzcgAshAg2o Short movie demonstrating the phenomenon with a model] * [http://www.leelanau.com/waterfall/underwater.html Description of Dead Water] * [https://web.archive.org/web/20051226030604/http://www.es.flinders.edu.au/~mattom/IntroOc/lecture10.html Explanation of dead water] * [https://www.newscientist.com/channel/fundamentals/dn15003-mysterious-dead-water-effect-caught-on-film.html ''New Scientist'' article] *[http://www.britannica.com/EBchecked/topic/154296/dead-water 'dead water'] Encyclopædia Britannica Online. 3 December 2009
Category:Nautical terminology Category:Physical oceanography Category:Waves
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