Ocean temperature#Deep ocean temperature

{{excerpt|Sea surface temperature|paragraphs=1}}

Experts refer to the temperature further below the surface as ocean temperature or deep ocean temperature. Ocean temperatures more than 20 metres below the surface vary by region and time. They contribute to variations in ocean heat content and ocean stratification.Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G.  Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf Chapter 9: Ocean, Cryosphere and Sea Level Change] {{Webarchive|url=https://web.archive.org/web/20221024162651/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |date=2022-10-24 }}. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] {{Webarchive|url=https://web.archive.org/web/20210809131444/https://www.ipcc.ch/report/ar6/wg1/ |date=2021-08-09 }} [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L.  Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362, {{doi|10.1017/9781009157896.011}} The increase of both ocean surface temperature and deeper ocean temperature is an important effect of climate change on oceans.

Deep ocean water is the name for cold, salty water found deep below the surface of Earth's oceans. Deep ocean water makes up about 90% of the volume of the oceans. Deep ocean water has a very uniform temperature of around 0-3{{nbsp}}°C. Its salinity is about 3.5% or 35 ppt (parts per thousand).

Ocean temperature and dissolved oxygen concentrations have a big influence on many aspects of the ocean. These two key parameters affect the ocean's primary productivity, the oceanic carbon cycle, nutrient cycles, and marine ecosystems.{{Cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul B. |last3=Song |first3=Huyue |last4=Dai |first4=Xu |last5=Chu |first5=Daoliang |date=2019 |title=Seawater Temperature and Dissolved Oxygen over the Past 500 Million Years |url=http://link.springer.com/10.1007/s12583-018-1002-2 |journal=Journal of Earth Science |language=en |volume=30 |issue=2 |pages=236–243 |doi=10.1007/s12583-018-1002-2 |s2cid=146378272 |issn=1674-487X}} They work in conjunction with salinity and density to control a range of processes. These include mixing versus stratification, ocean currents and the thermohaline circulation.

Experts calculate ocean heat content by using ocean temperatures at different depths.

{{excerpt|Ocean heat content|paragraphs=1-2}}

{{See also|Ocean heat content#Measurements}}

There are various ways to measure ocean temperature.{{Cite web |date=2008 |title=Introduction to Physical Oceanography |url=https://open.umn.edu/opentextbooks/textbooks/20 |access-date=2022-11-14 |website=Open Textbook Library |language=en}} Below the sea surface, it is important to refer to the specific depth of measurement as well as measuring the general temperature. The reason is there is a lot of variation with depths. This is especially the case during the day. At this time low wind speed and a lot of sunshine may lead to the formation of a warm layer at the ocean surface and big changes in temperature as you get deeper. Experts call these strong daytime vertical temperature gradients a diurnal thermocline.{{cite book |author=Vittorio Barale |url=https://books.google.com/books?id=hH2NkL_318wC&pg=PA263 |title=Oceanography from Space: Revisited |publisher=Springer |year=2010 |isbn=978-90-481-8680-8 |page=263}}

The basic technique involves lowering a device to measure temperature and other parameters electronically. This device is called CTD which stands for conductivity, temperature, and depth.{{Cite web |title=Conductivity, Temperature, Depth (CTD) Sensors - Woods Hole Oceanographic Institution |url=https://www.whoi.edu/what-we-do/explore/instruments/instruments-sensors-samplers/conductivity-temperature-depth-ctd-sensors/ |access-date=2023-03-06 |website=www.whoi.edu/ |language=en-US}} It continuously sends the data up to the ship via a conducting cable. This device is usually mounted on a frame that includes water sampling bottles. Since the 2010s autonomous vehicles such as gliders or mini-submersibles have been increasingly available. They carry the same CTD sensors, but operate independently of a research ship.

Scientists can deploy CTD systems from research ships on moorings gliders and even on seals.{{Cite journal |last1=Boyd |first1=I.L |last2=Hawker |first2=E.J |last3=Brandon |first3=M.A |last4=Staniland |first4=I.J |date=2001 |title=Measurement of ocean temperatures using instruments carried by Antarctic fur seals |url=https://linkinghub.elsevier.com/retrieve/pii/S0924796300000737 |journal=Journal of Marine Systems |language=en |volume=27 |issue=4 |pages=277–288 |doi=10.1016/S0924-7963(00)00073-7|url-access=subscription }} With research ships they receive data through the conducting cable. For the other methods they use telemetry.

There are other ways of measuring sea surface temperature.{{cite book |author1=Alexander Soloviev |url=https://books.google.com/books?id=tZary8a4HMwC |title=The near-surface layer of the ocean: structure, dynamics and applications |author2=Roger Lukas |journal=The Near-Surface Layer of the Ocean: Structure |publisher=シュプリンガー・ジャパン株式会社 |year=2006 |isbn=978-1-4020-4052-8 |page=xi |bibcode=2006nslo.book.....S}} At this near-surface layer measurements are possible using thermometers or satellites with spectroscopy. Weather satellites have been available to determine this parameter since 1967. Scientists created the first global composites during 1970.{{cite journal |author=P. Krishna Rao |author2=W. L. Smith |author3=R. Koffler |date=January 1972 |title=Global Sea-Surface Temperature Distribution Determined From an Environmental Satellite |journal=Monthly Weather Review |volume=100 |issue=1 |pages=10–14 |bibcode=1972MWRv..100...10K |doi=10.1175/1520-0493(1972)100<0010:GSTDDF>2.3.CO;2 |doi-access=free}}

The Advanced Very High Resolution Radiometer (AVHRR) is widely used to measure sea surface temperature from space.{{rp|90}}

There are various devices to measure ocean temperatures at different depths. These include the Nansen bottle, bathythermograph, CTD, or ocean acoustic tomography. Moored and drifting buoys also measure sea surface temperatures. Examples are those deployed by the Global Drifter Program and the National Data Buoy Center. The World Ocean Database Project is the largest database for temperature profiles from all of the world’s oceans.{{cite web |date=14 June 2017 |title=World Ocean Database Profiles the Ocean |url=https://www.ncei.noaa.gov/news/world-ocean-database-profiles-ocean |publisher=National Centers for Environmental Information}}

A small test fleet of deep Argo floats aims to extend the measurement capability down to about 6000 meters. It will accurately sample temperature for a majority of the ocean volume once it is in full use.{{Cite web |last=Administration |first=US Department of Commerce, National Oceanic and Atmospheric |title=Deep Argo |url=https://oceantoday.noaa.gov/deepargo/welcome.html |access-date=24 December 2021 |website=oceantoday.noaa.gov |language=EN-US}}{{Cite web |date=24 December 2021 |title=Deep Argo: Diving for Answers in the Ocean's Abyss |url=https://www.climate.gov/news-features/climate-tech/deep-argo-diving-answers-ocean%E2%80%99s-abyss |website=www.climate.gov}}

The most frequent measurement technique on ships and buoys is thermistors and mercury thermometers.{{rp|88}} Scientists often use mercury thermometers to measure the temperature of surface waters. They can put them in buckets dropped over the side of a ship. To measure deeper temperatures they put them on Nansen bottles.{{rp|88}}

{{excerpt|Argo (oceanography)|paragraphs=1|file=no}}

File:Increased_Trend_in_Sea_Temperature.png

{{Further|Effects of climate change on oceans}}

{{excerpt|Effects of climate change on oceans#Rising ocean temperature|file=no}}

{{excerpt|Sea surface temperature#Recent increase due to climate change|file=no}}

{{See also|Causes of climate change}}

The cause of recent observed changes is the warming of the Earth due to human-caused emissions of greenhouse gases such as carbon dioxide and methane.{{Cite journal |last1=Doney |first1=Scott C. |last2=Busch |first2=D. Shallin |last3=Cooley |first3=Sarah R. |last4=Kroeker |first4=Kristy J. |date=2020-10-17 |title=The Impacts of Ocean Acidification on Marine Ecosystems and Reliant Human Communities |journal=Annual Review of Environment and Resources |language=en |volume=45 |issue=1 |pages=83–112 |doi=10.1146/annurev-environ-012320-083019 |issn=1543-5938 |doi-access=free}} (CC BY 4.0 International license) Growing concentrations of greenhouse gases increases Earth's energy imbalance, further warming surface temperatures. The ocean takes up most of the added heat in the climate system, raising ocean temperatures.

{{Main|Ocean stratification|ocean deoxygenation}}

Higher air temperatures warm the ocean surface. And this leads to greater ocean stratification. Reduced mixing of the ocean layers stabilises warm water near the surface. At the same time it reduces cold, deep water circulation. The reduced up and down mixing reduces the ability of the ocean to absorb heat. This directs a larger fraction of future warming toward the atmosphere and land. Energy available for tropical cyclones and other storms is likely to increase. Nutrients for fish in the upper ocean layers are set to decrease. This is also like to reduce the capacity of the oceans to store carbon.

Warmer water cannot contain as much oxygen as cold water. Increased thermal stratification may reduce the supply of oxygen from the surface waters to deeper waters. This would further decrease the water's oxygen content.{{Cite book |last1=Chester |first1=R. |url=https://www.wiley.com/en-us/Marine+Geochemistry%2C+3rd+Edition-p-9781118349090 |title=Marine geochemistry |last2=Jickells |first2=Tim |date=2012 |publisher=Wiley/Blackwell |isbn=978-1-118-34909-0 |edition=3rd |location=Chichester, West Sussex, UK |chapter=Chapter 9: Nutrients oxygen organic carbon and the carbon cycle in seawater |oclc=781078031}} This process is called ocean deoxygenation. The ocean has already lost oxygen throughout the water column. Oxygen minimum zones are expanding worldwide.Bindoff, N.L., W.W.L. Cheung, J.G. Kairo, J. Arístegui, V.A. Guinder, R. Hallberg, N. Hilmi, N. Jiao, M.S. Karim, L. Levin, S. O'Donoghue, S.R. Purca Cuicapusa, B. Rinkevich, T. Suga, A. Tagliabue, and P. Williamson, 2019: [https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/09_SROCC_Ch05_FINAL-1.pdf Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities] {{Webarchive|url=https://web.archive.org/web/20191220141419/https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/09_SROCC_Ch05_FINAL-1.pdf |date=2019-12-20 }}. In: [https://www.ipcc.ch/srocc/ IPCC Special Report on the Ocean and Cryosphere in a Changing Climate] {{Webarchive|url=https://web.archive.org/web/20210712081923/https://www.ipcc.ch/srocc/ |date=2021-07-12 }} [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.{{rp|471}}

{{Main|Ocean#Ocean currents and global climate|Atlantic meridional overturning circulation}}

Varying temperatures associated with sunlight and air temperatures at different latitudes cause ocean currents. Prevailing winds and the different densities of saline and fresh water are another cause of currents. Air tends to be warmed and thus rise near the equator, then cool and thus sink slightly further poleward. Near the poles, cool air sinks, but is warmed and rises as it then travels along the surface equatorward. The sinking and upwelling that occur in lower latitudes, and the driving force of the winds on surface water, mean the ocean currents circulate water throughout the entire sea. Global warming on top of these processes causes changes to currents, especially in the regions where deep water is formed.{{cite journal |last1=Trenberth |first1=K |last2=Caron |first2=J |year=2001 |title=Estimates of Meridional Atmosphere and Ocean Heat Transports |url=https://zenodo.org/record/1234671 |journal=Journal of Climate |volume=14 |issue=16 |pages=3433–43 |bibcode=2001JCli...14.3433T |doi=10.1175/1520-0442(2001)014<3433:EOMAAO>2.0.CO;2|doi-access=free }}

{{Main|Geologic temperature record}}

Scientists believe the sea temperature was much hotter in the Precambrian period. Such temperature reconstructions derive from oxygen and silicon isotopes from rock samples.{{cite journal |last1=Knauth |first1=L. Paul |date=2005 |title=Temperature and salinity history of the Precambrian ocean: implications for the course of microbial evolution |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=219 |issue=1–2 |pages=53–69 |bibcode=2005PPP...219...53K |doi=10.1016/j.palaeo.2004.10.014}}{{cite journal |last1=Shields |first1=Graham A. |last2=Kasting |first2=James F. |date=2006 |title=A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts |journal=Nature |volume=443 |issue=7114 |pages=969–972 |bibcode=2006Natur.443..969R |doi=10.1038/nature05239 |pmid=17066030 |s2cid=4417157}} These reconstructions suggest the ocean had a temperature of 55–85 °C {{Ma|2000|3500}}. It then cooled to milder temperatures of between 10 and 40 °C by {{Ma|1000}}. Reconstructed proteins from Precambrian organisms also provide evidence that the ancient world was much warmer than today.{{cite journal |last1=Gaucher |first1=EA |last2=Govindarajan |first2=S |last3=Ganesh |first3=OK |date=2008 |title=Palaeotemperature trend for Precambrian life inferred from resurrected proteins |journal=Nature |volume=451 |issue=7179 |pages=704–707 |bibcode=2008Natur.451..704G |doi=10.1038/nature06510 |pmid=18256669 |s2cid=4311053}}{{cite journal |last1=Risso |first1=VA |last2=Gavira |first2=JA |last3=Mejia-Carmona |first3=DF |date=2013 |title=Hyperstability and substrate promiscuity in laboratory resurrections of Precambrian b-lactamases |journal=J Am Chem Soc |volume=135 |issue=8 |pages=2899–2902 |doi=10.1021/ja311630a |pmid=23394108|hdl=11336/22624 |hdl-access=free }}

The Cambrian Explosion approximately 538.8 million years ago was a key event in the evolution of life on Earth. This event took place at a time when scientists believe sea surface temperatures reached about 60 °C.{{Cite journal |last1=Wotte |first1=Thomas |last2=Skovsted |first2=Christian B. |last3=Whitehouse |first3=Martin J. |last4=Kouchinsky |first4=Artem |date=2019 |title=Isotopic evidence for temperate oceans during the Cambrian Explosion |journal=Scientific Reports |language=en |volume=9 |issue=1 |pages=6330 |doi=10.1038/s41598-019-42719-4 |issn=2045-2322 |pmc=6474879 |pmid=31004083|bibcode=2019NatSR...9.6330W |doi-access=free}} 50px Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }} Such high temperatures are above the upper thermal limit of 38 °C for modern marine invertebrates. They preclude a major biological revolution.{{Cite journal |last1=Wotte |first1=Thomas |last2=Skovsted |first2=Christian B. |last3=Whitehouse |first3=Martin J. |last4=Kouchinsky |first4=Artem |date=2019 |title=Isotopic evidence for temperate oceans during the Cambrian Explosion |journal=Scientific Reports |language=en |volume=9 |issue=1 |pages=6330 |doi=10.1038/s41598-019-42719-4 |issn=2045-2322 |pmc=6474879 |pmid=31004083|bibcode=2019NatSR...9.6330W }}

During the later Cretaceous period, from {{Ma|100|66}}, average global temperatures reached their highest level in the last 200 million years or so.{{cite journal |last1=Renne |first1=Paul R. |last2=Deino |first2=Alan L. |last3=Hilgen |first3=Frederik J. |last4=Kuiper |first4=Klaudia F. |last5=Mark |first5=Darren F. |last6=Mitchell |first6=William S. |last7=Morgan |first7=Leah E. |last8=Mundil |first8=Roland |last9=Smit |first9=Jan |date=7 February 2013 |title=Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary |journal=Science |volume=339 |issue=6120 |pages=684–687 |bibcode=2013Sci...339..684R |doi=10.1126/science.1230492 |pmid=23393261 |s2cid=6112274}} This was probably the result of the configuration of the continents during this period. It allowed for improved circulation in the oceans. This discouraged the formation of large scale ice sheet.{{Cite journal |last=Beltran |first=Catherine |last2=Golledge |first2=Nicholas R. |last3=Ohneiser |first3=Christian |last4=Kowalewski |first4=Douglas E. |last5=Sicre |first5=Marie-Alexandrine |last6=Hageman |first6=Kimberly J. |last7=Smith |first7=Robert |last8=Wilson |first8=Gary S. |last9=Mainié |first9=François |date=2020-01-15 |title=Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31 |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379119306122 |journal=Quaternary Science Reviews |volume=228 |pages=106069 |doi=10.1016/j.quascirev.2019.106069 |issn=0277-3791}}

Data from an oxygen isotope database indicate that there have been seven global warming events during the geologic past. These include the Late Cambrian, Early Triassic, Late Cretaceous, and Paleocene-Eocene transition. The surface of the sea was about 5-30º warmer than today in these warming period.

{{portal|border=no|Oceans|Geography|Ecology|Environment|Weather|World}}

• {{annotated link|Global surface temperature}}
• {{annotated link|Marine heatwave}}
• {{annotated link|Ocean current}}
• {{annotated link|Sea surface skin temperature}}
• {{annotated link|Upwelling}}

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Category:Temperature

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