ocean heat content

File:ThermoclineSeasonDepth.png) based on seasons and latitude]]

Ocean heat content is a term used in physical oceanography to describe a type of thermodynamic potential energy that is stored in the ocean. It is defined in coordination with the equation of state of seawater. TEOS-10 is an international standard approved in 2010 by the Intergovernmental Oceanographic Commission.{{cite web |url=https://www.teos-10.org/ |title=TEOS-10: Thermodynamic Equation of Seawater - 2010 |publisher=Joint Committee on the Properties of Seawater |access-date=12 February 2024}}

Calculation of ocean heat content follows that of enthalpy referenced to the ocean surface, also called potential enthalpy. OHC changes are thus made more readily comparable to seawater heat exchanges with ice, freshwater, and humid air.{{cite journal |last1=McDougall |first1= Trevor J. |date= 2003|title=Potential Enthalpy: A Conservative Oceanic Variable for Evaluating Heat Content and Heat Fluxes |journal= Journal of Physical Oceanography|volume=33 |issue= 5 |pages=945–963 |doi= 10.1175/1520-0485(2003)033<0945:PEACOV>2.0.CO;2|bibcode= 2003JPO....33..945M |doi-access= free}}{{Cite journal|last1=Graham|first1=Felicity S.|last2=McDougall|first2=Trevor J.|date=2013-05-01|title=Quantifying the Nonconservative Production of Conservative Temperature, Potential Temperature, and Entropy|journal=Journal of Physical Oceanography|language=en|volume=43|issue=5|pages=838–862|doi=10.1175/jpo-d-11-0188.1|bibcode=2013JPO....43..838G |issn=0022-3670|doi-access=free}} OHC is always reported as a change or as an "anomaly" relative to a baseline. Positive values then also quantify ocean heat uptake (OHU) and are useful to diagnose where most of planetary energy gains from global heating are going.

To calculate the ocean heat content, measurements of ocean temperature from sample parcels of seawater gathered at many different locations and depths are required.{{Cite web |last=US EPA |first=OAR |date=2016-06-27 |title=Climate Change Indicators: Ocean Heat |url=https://www.epa.gov/climate-indicators/climate-change-indicators-ocean-heat |access-date=2023-02-28 |website=www.epa.gov |language=en}} Integrating the areal density of ocean heat over an ocean basin, or entire ocean, gives the total ocean heat content. Thus, total ocean heat content is a volume integral of the product of temperature, density, and heat capacity over the three-dimensional region of the ocean for which data is available. The bulk of measurements have been performed at depths shallower than about 2000 m (1.25 miles).

The areal density of ocean heat content between two depths is computed as a definite integral:{{cite book|last=Dijkstra|first=Henk A.|title=Dynamical oceanography|year=2008|publisher=Springer Verlag|location=Berlin|isbn=9783540763758|page=276|edition=[Corr. 2nd print.]}}{{Cite journal|last1=McDougall|first1=Trevor J.|last2=Barker|first2=Paul M.|last3=Holmes|first3=Ryan M.|last4=Pawlowicz|first4=Rich|last5=Griffies|first5=Stephen M.|last6=Durack|first6=Paul J.|date=2021-01-19|title=The interpretation of temperature and salinity variables in numerical ocean model output, and the calculation of heat fluxes and heat content|url=https://gmd.copernicus.org/articles/14/6445/2021/gmd-14-6445-2021.html|journal=Geoscientific Model Development Discussions|volume=14 |issue=10 |language=English|pages=6445–6466|doi=10.5194/gmd-2020-426|s2cid=234212726 |issn=1991-959X|doi-access=free}}

$H=\; c\_p\; \backslash int\_\{h2\}^\{h1\}\; \backslash rho(z)\; \backslash Theta(z)\; dz$

where $c\_p$ is the specific heat capacity of sea water, h2 is the lower depth, h1 is the upper depth, $\backslash rho(z)$ is the in-situ seawater density profile, and $\backslash Theta(z)$ is the conservative temperature profile. $c\_p$ is defined at a single depth h0 usually chosen as the ocean surface. In SI units, $H$ has units of Joules per square metre (J·m⁻²).

In practice, the integral can be approximated by summation using a smooth and otherwise well-behaved sequence of in-situ data; including temperature (t), pressure (p), salinity (s) and their corresponding density (ρ). Conservative temperature $\backslash Theta(z)$ are translated values relative to the reference pressure (p0) at h0. A substitute known as potential temperature has been used in earlier calculations.{{citation |url=https://www.teos-10.org/pubs/gsw/pdf/Getting_Started.pdf |title=Getting started with TEOS-10 and the Gibbs Seawater (GSW) Oceanographic Toolbox |version=VERSION 3.06.12 |date=10 July 2020 |website=teos-10.org}}

Measurements of temperature versus ocean depth generally show an upper mixed layer (0–200 m), a thermocline (200–1500 m), and a deep ocean layer (>1500 m). These boundary depths are only rough approximations. Sunlight penetrates to a maximum depth of about 200 m; the top 80 m of which is the habitable zone for photosynthetic marine life covering over 70% of Earth's surface.{{cite web |url=https://www.britannica.com/EBchecked/topic/457662/photic-zone |title=photic zone (oceanography) |publisher=Encyclopædia Britannica Online |access-date=2021-12-15}} Wave action and other surface turbulence help to equalize temperatures throughout the upper layer.

Unlike surface temperatures which decrease with latitude, deep-ocean temperatures are relatively cold and uniform in most regions of the world.{{Cite web|last=MarineBio|date=2018-06-17|title=The Deep Sea|url=https://marinebio.org/oceans/deep-sea/|access-date=2020-08-07|website=MarineBio Conservation Society|language=en-US}} About 50% of all ocean volume is at depths below 3000 m (1.85 miles), with the Pacific Ocean being the largest and deepest of five oceanic divisions. The thermocline is the transition between upper and deep layers in terms of temperature, nutrient flows, abundance of life, and other properties. It is semi-permanent in the tropics, variable in temperate regions (often deepest during the summer), and shallow to nonexistent in polar regions.{{Cite web |title=What is a thermocline? |url=https://oceanservice.noaa.gov/facts/thermocline.html |publisher=National Oceanic and Atmospheric Administration |access-date=2021-12-23 |language=en}}

File: Argo_floats_in_Feb._2018_colour_coded_by_country.png

{{See also|Argo (oceanography)|Ocean temperature}}

Ocean heat content measurements come with difficulties, especially before the deployment of the Argo profiling floats. Due to poor spatial coverage and poor quality of data, it has not always been easy to distinguish between long term global warming trends and climate variability. Examples of these complicating factors are the variations caused by El Niño–Southern Oscillation or changes in ocean heat content caused by major volcanic eruptions.

Argo is an international program of robotic profiling floats deployed globally since the start of the 21st century.{{cite journal |author=Toni Feder |year=2000 |title=Argo Begins Systematic Global Probing of the Upper Oceans |journal=Physics Today |volume=53 |issue=7 |page=50 |bibcode=2000PhT....53g..50F |doi=10.1063/1.1292477}} The program's initial 3000 units had expanded to nearly 4000 units by year 2020. At the start of each 10-day measurement cycle, a float descends to a depth of 1000 meters and drifts with the current there for nine days. It then descends to 2000 meters and measures temperature, salinity (conductivity), and depth (pressure) over a final day of ascent to the surface. At the surface the float transmits the depth profile and horizontal position data through satellite relays before repeating the cycle.{{cite web |author=Dale C.S. Destin |date=5 December 2014 |title=The Argo revolution |url=https://www.climate.gov/news-features/features/argo-revolution |website=climate.gov}}

Starting 1992, the TOPEX/Poseidon and subsequent Jason satellite series altimeters have observed vertically integrated OHC, which is a major component of sea level rise.{{cite web |date=29 January 2020 |title=Ocean Surface Topography from Space: Ocean warming estimates from Jason |url=https://sealevel.jpl.nasa.gov/resources/85/ocean-warming-estimates-from-jason/ |publisher=NASA Jet Propulsion Laboratory}} Since 2002, GRACE and GRACE-FO have remotely monitored ocean changes using gravimetry.{{cite journal |last1=Marti |first1=Florence |last2=Blazquez |first2=Alejandro |last3=Meyssignac |first3=Benoit |last4=Ablain |first4=Michaël |last5=Barnoud |first5=Anne |last6=Fraudeau |first6=Robin |last7=Jugier |first7=Rémi |last8=Chenal |first8=Jonathan |last9=Larnicol |first9=Gilles |last10=Pfeffer |first10=Julia |last11=Restano |first11=Marco |last12=Benveniste |first12=Jérôme |display-authors=5 |title=Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry |journal=Earth System Science Data |year=2021 |doi=10.5194/essd-2021-220 |doi-access=free}} The partnership between Argo and satellite measurements has yielded ongoing improvements to estimates of OHC and other global ocean properties.

File:Oceans of Climate Change.ogv discusses the heat capacity of water, performs an experiment to demonstrate heat capacity using a water balloon and describes how water's ability to store heat affects Earth's climate.]]

{{See also|Causes of climate change}}

Ocean heat uptake accounts for over 90% of total planetary heat uptake, mainly as a consequence of human-caused changes to the composition of Earth's atmosphere.{{Cite journal |last1=Trenberth |first1=Kevin E |last2=Cheng |first2=Lijing |date=2022-09-01 |title=A perspective on climate change from Earth's energy imbalance |journal=Environmental Research: Climate |volume=1 |issue=1 |pages=013001 |doi=10.1088/2752-5295/ac6f74 |issn=2752-5295 |doi-access=free}} This high percentage is because waters at and below the ocean surface - especially the turbulent upper mixed layer - exhibit a thermal inertia much larger than the planet's exposed continental crust, ice-covered polar regions, or atmospheric components themselves. A body with large thermal inertia stores a big amount of energy because of its heat capacity, and effectively transmits energy according to its heat transfer coefficient. Most extra energy that enters the planet via the atmosphere is thereby taken up and retained by the ocean.{{cite web |author=Michon Scott |date=24 April 2006 |title=Earth's Big Heat Bucket |url=https://earthobservatory.nasa.gov/features/HeatBucket/heatbucket.php |publisher=NASA Earth Observatory}}{{cite web |url=https://scied.ucar.edu/learning-zone/earth-system/climate-system/transfer-and-storage-heat-oceans |title=Transfer and Storage of Heat in the Oceans |publisher=UCAR Center for Science Education |access-date=17 November 2023}}{{cite journal |last1=Hansen |first1=J. |last2=Russell |first2=G. |last3=Lacis |first3=A. |last4=Fung |first4=I. |last5=Rind |first5=D. |last6=Stone |first6=P. |url=https://pubs.giss.nasa.gov/docs/1985/1985_Hansen_ha09600g.pdf |title=Climate response times: Dependence on climate sensitivity and ocean mixing |journal=Science |volume=229 |pages=857–850 |year=1985 |issue=4716 |doi=10.1126/science.229.4716.857 |pmid=17777925 |bibcode=1985Sci...229..857H}}

File:Earth's Heat Accumulation.png

Planetary heat uptake or heat content accounts for the entire energy added to or removed from the climate system.{{cite web |url=https://ceres.larc.nasa.gov/science/ |title=CERES Science |publisher=NASA |access-date=17 November 2023}} It can be computed as an accumulation over time of the observed differences (or imbalances) between total incoming and outgoing radiation.

Changes to the imbalance have been estimated from Earth orbit by CERES and other remote instruments, and compared against in-situ surveys of heat inventory changes in oceans, land, ice and the atmosphere.{{cite journal |last1=Loeb |first1=Norman G. |last2=Johnson |first2=Gregory C. |last3=Thorsen |first3=Tyler J. |last4=Lyman |first4=John M. |last5=Rose |first5=Fred G. |last6=Kato |first6=Seiji |display-authors=4 |title=Satellite and Ocean Data Reveal Marked Increase in Earth's Heating Rate |journal=Geophysical Research Letters |date=15 June 2021 |volume=48 |issue=13 |doi=10.1029/2021GL093047 |bibcode=2021GeoRL..4893047L |doi-access=}}{{cite journal |last1=Hakuba |first1=M.Z. |last2=Frederikse |first2=T. |last3=Landerer |first3=F.W. |title=Earth's Energy Imbalance From the Ocean Perspective (2005–2019) |journal=Geophysical Research Letters |volume=48 |issue=16 |date=28 August 2021 |doi=10.1029/2021GL093624 |doi-access=|bibcode=2021GeoRL..4893624H }} Achieving complete and accurate results from either accounting method is challenging, but in different ways that are viewed by researchers as being mostly independent of each other. Increases in planetary heat content for the well-observed 2005–2019 period are thought to exceed measurement uncertainties.

From the ocean perspective, the more abundant equatorial solar irradiance is directly absorbed by Earth's tropical surface waters and drives the overall poleward propagation of heat. The surface also exchanges energy that has been absorbed by the lower troposphere through wind and wave action. Over time, a sustained imbalance in Earth's energy budget enables a net flow of heat either into or out of greater ocean depth via thermal conduction, downwelling, and upwelling.{{cite web |year=2012 |title=Air-Sea interaction: Teacher's guide |url=https://www.ametsoc.org/ams/index.cfm/education-careers/education-program/k-12-teachers/project-atmosphere/training-opportunities/project-atmosphere-peer-led-training/project-atmosphere-peer-training-resources/air-sea/ |access-date=2022-02-22 |publisher=American Meteorological Society}}{{cite web |title=Ocean Motion : Definition : Wind Driven Surface Currents - Upwelling and Downwelling |url=http://oceanmotion.org/html/background/upwelling-and-downwelling.htm |access-date=2022-02-22}} Releases of OHC to the atmosphere occur primarily via evaporation and enable the planetary water cycle.{{cite web |title=NASA Earth Science: Water Cycle |url=https://gpm.nasa.gov/education/articles/nasa-earth-science-water-cycle |access-date=2021-10-27 |publisher=NASA}} Concentrated releases in association with high sea surface temperatures help drive tropical cyclones, atmospheric rivers, atmospheric heat waves and other extreme weather events that can penetrate far inland.{{cite web |author=Laura Snider |date=2021-01-13 |title=2020 was a record-breaking year for ocean heat - Warmer ocean waters contribute to sea level rise and strengthen storms |url=https://news.ucar.edu/132773/2020-was-record-breaking-year-ocean-heat |publisher=National Center for Atmospheric Research}} Altogether these processes enable the ocean to be Earth's largest thermal reservoir which functions to regulate the planet's climate; acting as both a sink and a source of energy.

{{ multiple image | total_width=450

| image1= 20230706 Excess heat absorbed through ocean's surface - global warming.svg |caption1= Surface air temperatures over land masses have been increasing faster than the sea surface temperature.

| image2= 1960- Warming stripes global temperature graphic - atmospheric heights and ocean depths.png |caption2= The greenhouse effect traps heat in the lower atmosphere and oceans, so that the upper atmosphere, receiving less reflected energy, cools.{{cite journal |last1=Hawkins |first1=Ed |last2=Williams |first2=Richard G. |last3=Young |first3=Paul J. |last4=Berardelli |first4=Jeff |last5=Burgess |first5=Samantha N. |last6=Highwood |first6=Ellie |last7=Randel |first7=William |last8=Roussenov |first8=Vassil |last9=Smith |first9=Doug |last10=Placky |first10=Bernadette Woods |title=Warming Stripes Spark Climate Conversations: From the Ocean to the Stratosphere |journal=Bulletin of the American Meteorological Society |volume=6 |issue=5 |date=1 May 2025 |pages=E964-E970 |doi=10.1175/BAMS-D-24-0212.1}}

}}

From the perspective of land and ice covered regions, their portion of heat uptake is reduced and delayed by the dominant thermal inertia of the ocean. Although the average rise in land surface temperature has exceeded the ocean surface due to the lower inertia (smaller heat-transfer coefficient) of solid land and ice, temperatures would rise more rapidly and by a greater amount without the full ocean. Measurements of how rapidly the heat mixes into the deep ocean have also been underway to better close the ocean and planetary energy budgets.{{cite web |url=https://argo.ucsd.edu/expansion/deep-argo-mission/ |title=Deep Argo Mission |publisher=Scripps Institution of Oceanography, UC San Diego |access-date=17 November 2023}}

Numerous independent studies in recent years have found a multi-decadal rise in OHC of upper ocean regions that has begun to penetrate to deeper regions. The upper ocean (0–700 m) has warmed since 1971, while it is very likely that warming has occurred at intermediate depths (700–2000 m) and likely that deep ocean (below 2000 m) temperatures have increased.{{rp|1228}} The heat uptake results from a persistent warming imbalance in Earth's energy budget that is most fundamentally caused by the anthropogenic increase in atmospheric greenhouse gases.{{rp|41}} There is very high confidence that increased ocean heat content in response to anthropogenic carbon dioxide emissions is essentially irreversible on human time scales.{{rp|1233}}

File:Ocean heat anomaly map 2020.jpg

Studies based on Argo measurements indicate that ocean surface winds, especially the subtropical trade winds in the Pacific Ocean, change ocean heat vertical distribution.{{cite journal |title = Distinctive climate signals in reanalysis of global ocean heat content |year = 2013 |author = Balmaseda, Trenberth & Källén |doi= 10.1002/grl.50382 |volume=40 |issue = 9 |journal=Geophysical Research Letters |pages=1754–1759|bibcode = 2013GeoRL..40.1754B |doi-access = free }} [http://www.rmets.org/weather-and-climate/climate/has-global-warming-stalled Essay] {{Webarchive|url=https://web.archive.org/web/20150213035703/http://www.rmets.org/weather-and-climate/climate/has-global-warming-stalled |date=2015-02-13 }} This results in changes among ocean currents, and an increase of the subtropical overturning, which is also related to the El Niño and La Niña phenomenon. Depending on stochastic natural variability fluctuations, during La Niña years around 30% more heat from the upper ocean layer is transported into the deeper ocean. Furthermore, studies have shown that approximately one-third of the observed warming in the ocean is taking place in the 700–2000 meter ocean layer.{{cite journal |last1=Levitus |first1=Sydney |title=World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 |journal=Geophysical Research Letters |date=17 May 2012 |volume=39 |issue=10 |pages=1–3 |doi=10.1029/2012GL051106 |bibcode=2012GeoRL..3910603L |s2cid=55809622 |issn=0094-8276|doi-access=free }}

Model studies indicate that ocean currents transport more heat into deeper layers during La Niña years, following changes in wind circulation.{{cite journal |title = Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods |year = 2011 | author = Meehl|doi= 10.1038/nclimate1229 |display-authors=etal |volume=1 |issue = 7 |journal=Nature Climate Change |pages=360–364|bibcode = 2011NatCC...1..360M }}{{cite web|url=http://www.skepticalscience.com/The-Deep-Ocean-Warms-When-Global-Surface-Temperatures-Stall--.html |title= The Deep Ocean Warms When Global Surface Temperatures Stall |website=SkepticalScience.com |author=Rob Painting |date=2 October 2011 |access-date=15 July 2016}} Years with increased ocean heat uptake have been associated with negative phases of the interdecadal Pacific oscillation (IPO).{{cite journal |title = A Looming Climate Shift: Will Ocean Heat Come Back to Haunt us? |date =24 June 2013 |url= http://www.skepticalscience.com/A-Looming-Climate-Shift-Will-Ocean-Heat-Come-Back-to-Haunt-us.html| website=SkepticalScience.com | author = Rob Painting |access-date=15 July 2016 }} This is of particular interest to climate scientists who use the data to estimate the ocean heat uptake.

The upper ocean heat content in most North Atlantic regions is dominated by heat transport convergence (a location where ocean currents meet), without large changes to temperature and salinity relation.{{cite journal|title=Heat content variability in the North Atlantic Ocean in ocean reanalyses|doi=10.1002/2015GL063299|author1=Sirpa Häkkinen |author2=Peter B Rhines |author3=Denise L Worthen |year=2015|pmc=4681455|pmid=26709321|volume=42|issue=8|journal=Geophys Res Lett|pages=2901–2909|bibcode=2015GeoRL..42.2901H}} Additionally, a study from 2022 on anthropogenic warming in the ocean indicates that 62% of the warming from the years between 1850 and 2018 in the North Atlantic along 25°N is kept in the water below 700 m, where a major percentage of the ocean's surplus heat is stored.{{cite journal |last1=Messias |first1=Marie-José |last2=Mercier |first2=Herlé |title=The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic |journal=Communications Earth & Environment |date=17 May 2022 |volume=3 |issue=1 |page=118 |doi=10.1038/s43247-022-00443-4 |bibcode=2022ComEE...3..118M |s2cid=248816280 |language=en |issn=2662-4435|doi-access=free }}

A study in 2015 concluded that ocean heat content increases by the Pacific Ocean were compensated by an abrupt distribution of OHC into the Indian Ocean.{{cite journal |last1=Lee |first1=Sang-Ki |last2=Park |first2=Wonsun |last3=Baringer |first3=Molly O. |last4=Gordon |first4=Arnold L. |last5=Huber |first5=Bruce |last6=Liu |first6=Yanyun |date=June 2015 |title=Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus |journal=Nature Geoscience |volume=8 |issue=6 |pages=445–449 |bibcode=2015NatGe...8..445L |doi=10.1038/ngeo2438 |hdl-access=free |hdl=1834/9681|url=http://oceanrep.geomar.de/28807/3/pm_2015_23_indo-pacific_en.pdf }}

Although the upper 2000 m of the oceans have experienced warming on average since the 1970s, the rate of ocean warming varies regionally with the subpolar North Atlantic warming more slowly and the Southern Ocean taking up a disproportionate large amount of heat due to anthropogenic greenhouse gas emissions.{{rp|1230}}

Deep-ocean warming below 2000 m has been largest in the Southern Ocean compared to other ocean basins.{{rp|1230}}

A large-ensemble reanalysis of ocean warming published in 2024 estimated a 1961–2022 warming trend of 0.43{{nbsp}}±{{nbsp}}0.08{{nbsp}}W/m², along with a statistically significant acceleration rate of 0.15{{nbsp}}±{{nbsp}}0.04{{nbsp}}W/m² per{{nbsp}}decade.{{cite journal |last1=Storto |first1=Andrea |last2=Yang |first2=Chunxue |title=Acceleration of the ocean warming from 1961 to 2022 unveiled by large-ensemble reanalyses |journal=Nature Communications |date=16 January 2024 |volume=15 |page=545 |doi=10.1038/s41467-024-44749-7}}

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

Warming oceans are one reason for coral bleaching{{Cite news |date=6 June 2016 |title=The Great Barrier Reef: a catastrophe laid bare |newspaper=The Guardian |url=https://www.theguardian.com/environment/2016/jun/07/the-great-barrier-reef-a-catastrophe-laid-bare}} and contribute to the migration of marine species. Marine heat waves are regions of life-threatening and persistently elevated water temperatures.{{cite web |date=2019-10-08 |title=So what are marine heat waves? - A NOAA scientist explains |url=https://research.noaa.gov/article/ArtMID/587/ArticleID/2559/So-what-are-marine-heat-waves |publisher=National Oceanic and Atmospheric Administration |access-date=2021-10-12 |archive-date=2022-01-24 |archive-url=https://web.archive.org/web/20220124041431/https://research.noaa.gov/article/ArtMID/587/ArticleID/2559/So-what-are-marine-heat-waves |url-status=dead }} Redistribution of the planet's internal energy by atmospheric circulation and ocean currents produces internal climate variability, often in the form of irregular oscillations,{{Cite web |title=El Niño & Other Oscillations |url=https://www.whoi.edu/main/topic/el-nino-other-oscillations |access-date=2021-10-08 |website=Woods Hole Oceanographic Institution}} and helps to sustain the global thermohaline circulation.

The increase in OHC accounts for 30–40% of global sea-level rise from 1900 to 2020 because of thermal expansion.{{cite web |date=2020-08-21 |title=NASA-led study reveals the causes of sea level rise since 1900 |url=https://sealevel.nasa.gov/news/191/nasa-led-study-reveals-the-causes-of-sea-level-rise-since-1900 |publisher=NASA}}

It is also an accelerator of sea ice, iceberg, and tidewater glacier melting. The ice loss reduces polar albedo, amplifying both the regional and global energy imbalances.{{cite journal |author=Garcia-Soto, Carlos |date=2022-10-20 |title=An Overview of Ocean Climate Change Indicators: Sea Surface Temperature, Ocean Heat Content, Ocean pH, Dissolved Oxygen Concentration, Arctic Sea Ice Extent, Thickness and Volume, Sea Level and Strength of the AMOC (Atlantic Meridional Overturning Circulation) |journal=Frontiers in Marine Science |volume=8 |doi=10.3389/fmars.2021.642372 |doi-access=free|hdl=10508/11963 |hdl-access=free }}

The resulting ice retreat has been rapid and widespread for Arctic sea ice,{{cite web |author=Rebecca Lindsey and Michon Scott |date=2021-09-21 |title=Climate Change: Arctic sea ice |url=https://www.climate.gov/news-features/understanding-climate/climate-change-minimum-arctic-sea-ice-extent |publisher=National Oceanic and Atmospheric Administration}} and within northern fjords such as those of Greenland and Canada.{{cite web |author=Maria-Jose Viñas and Carol Rasmussen |date=2015-08-05 |title=Warming seas and melting ice sheets |url=https://climate.nasa.gov/news/2328/warming-seas-and-melting-ice-sheets/ |publisher=NASA}}

Impacts to Antarctic sea ice and the vast Antarctic ice shelves which terminate into the Southern Ocean have varied by region and are also increasing due to warming waters.{{cite web |author=Michon Scott |date=2021-03-26 |title=Understanding climate: Antarctic sea ice extent |url=https://www.climate.gov/news-features/understanding-climate/understanding-climate-antarctic-sea-ice-extent |publisher=National Oceanic and Atmospheric Administration}} Breakup of the Thwaites Ice Shelf and its West Antarctica neighbors contributed about 10% of sea-level rise in 2020.{{cite web |author=Carly Cassella |date=2021-04-11 |title=Warm Water Under The 'Doomsday Glacier' Threatens to Melt It Faster Than We Predicted |url=https://www.sciencealert.com/warm-water-underneath-the-doomsday-glacier-threatens-to-its-main-support-point |website=sciencealert.com}}{{cite web |author=British Antarctic Survey |date=2021-12-15 |title=The threat from Thwaites: The retreat of Antarctica's riskiest glacier |url=https://phys.org/news/2021-12-threat-thwaites-retreat-antarctica-riskiest.html |website=phys.org}}

The ocean also functions as a sink and source of carbon, with a role comparable to that of land regions in Earth's carbon cycle.{{cite web |last1=Riebeek |first1=Holli |date=16 June 2011 |title=The Carbon Cycle |url=http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features |url-status=live |archive-url=https://web.archive.org/web/20160305010126/http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features |archive-date=5 March 2016 |access-date=26 February 2022 |website=Earth Observatory |publisher=NASA |df=dmy-all}} In accordance with the temperature dependence of Henry's law, warming surface waters are less able to absorb atmospheric gases including oxygen and the growing emissions of carbon dioxide and other greenhouse gases from human activity.{{cite web |last1=Riebeek |first1=Holli |date=1 July 2008 |title=The Ocean's Carbon Cycle |url=https://earthobservatory.nasa.gov/features/OceanCarbon/page1.php |access-date=26 February 2022 |website=Earth Observatory |publisher=NASA}} Nevertheless the rate in which the ocean absorbs anthropogenic carbon dioxide has approximately tripled from the early 1960s to the late 2010s; a scaling proportional to the increase in atmospheric carbon dioxide.{{cite journal |last1=Gruber |first1=Nicolas |last2=Bakker |first2=Dorothee |last3=DeVries |first3=Tim |last4=Gregor |first4=Luke |last5=Hauck |first5=Judith |last6=Landschützer |first6=Peter |last7=McKinley |first7=Galen |last8=Müller |first8=Jens |title=Trends and variability in the ocean carbon sink |journal=Nature Reviews Earth & Environment |date=24 January 2023 |volume=4 |issue=2 |pages=119–134 |doi=10.1038/s43017-022-00381-x |bibcode=2023NRvEE...4..119G |s2cid=256264357 |url=https://www.nature.com/articles/s43017-022-00381-x|hdl=20.500.11850/595538 |hdl-access=free }} The increase in CO2 levels causes ocean acidification, which is where the pH of the ocean decreases due to the uptake of CO2. This impacts the various species including reducing growth and calcification rates for calcifiers, lowering the capacity of acid base regulation in bivalves, and being harmful to the metabolic pathways of organisms which can lower the amount of energy these organisms are able to produce. {{cite journal |last1=Bock, C., Götze, S., Pörtner, H. O., & Lannig, G. |title=Exploring the mechanisms behind swimming performance limits to ocean warming and acidification in the Atlantic king scallop, Pecten maximus |journal=Frontiers in Ecology and Evolution |date=8 April 2024 |volume=12 |doi=10.3389/fevo.2024.1347160 |doi-access=free |bibcode=2024FrEEv..1247160B }}

Warming of the deep ocean has the further potential to melt and release some of the vast store of frozen methane hydrate deposits that have naturally accumulated there.{{Cite web |author=Adam Voiland and Joshua Stevens |date=8 March 2016 |title=Methane Matters |url=https://earthobservatory.nasa.gov/features/MethaneMatters |access-date=26 February 2022 |publisher=NASA Earth Observatory}}

• {{annotated link|Ocean acidification}}
• {{annotated link|Ocean stratification}}
• {{annotated link|Special Report on the Ocean and Cryosphere in a Changing Climate}}
• {{annotated link|Tropical cyclones and climate change}}

{{Notelist-lr}}

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