Ocean heat content

In oceanography and climatology, ocean heat content (OHC) is a term for the energy absorbed by the ocean, which is stored for indefinite time periods as internal energy or enthalpy. Ocean warming accounts for about 90% of Earth's energy accumulation from global warming since year 1970.[1][2] About one third of this added thermal energy has propagated to depths below 700 meters as of 2020.[3][4] Changes in ocean heat content have far-reaching consequences for the planet's marine and terrestrial ecosystems; including multiple impacts to coastal ecosystems and communities.[5]

Over 90% of the thermal energy that has accumulated on Earth from global heating since 1960 is stored in the ocean.

The more abundant equatorial solar irradiance which is absorbed by Earth's tropical surface waters drives the overall poleward propagation of ocean thermal energy.[3] Warming oceans are directly responsible for coral bleaching[6] and contribute to the migration of marine species.[7] Redistribution of the planet's internal energy by atmospheric circulation and ocean currents produces internal climate variability, often in the form of irregular oscillations,[8] and helps to sustain the global thermohaline circulation.[9][10] Marine heat waves are regions of life-threatening and persistently dense ocean heat.[11] Releases of OHC to the atmosphere occur primarily via evaporation and enable the planetary water cycle.[12] Concentrated releases in association with high sea-surface temperatures help drive tropical cyclones, atmospheric heat waves and other extreme weather events.[13][14]

The increase in OHC accounts for 30-40% of global sea-level rise from 1900 to 2020 because of thermal expansion.[15][16] It is also an accelerator of sea ice, iceberg, and tidewater glacier melting. The resulting ice retreat has been most consistent and pronounced for Arctic sea ice,[17] and within northern fjords such as those of Greenland and Canada.[18] Impacts to Antarctic sea ice and the vast Antarctic ice shelves which terminate into the Southern Ocean have been more varied.[19][20]

Definition and measurementEdit

 
Global Heat Content in the top 2000 meters of the ocean, NOAA 2020.

The areal density of ocean heat content between two depth levels is defined using a definite integral:[21]

 

where   is seawater density,   is the specific heat of sea water, h2 is the lower depth, h1 is the upper depth, and   is the temperature profile. In SI units,   has units of J·m−2. Integrating this density over an ocean basin, or entire ocean, gives the total heat content, as indicated in the figure to right. Thus, the total heat content is the product of the density, specific heat capacity, and the volume integral of temperature over the three-dimensional region of the ocean in question.

Ocean heat content can be estimated using temperature measurements obtained by a Nansen bottle, an ARGO float, or ocean acoustic tomography.[22] Sea surface temperatures are also measured by the Global Drifter Program. The World Ocean Database Project is the largest database for temperature profiles from all of the world’s ocean.

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.[23]

Recent changesEdit

 
Schematic drawing of Earth's excess heat inventory as it relates to the planet's energy imbalance for two recent time periods.[1]

Several studies in recent years have found a multi-decadal rise in OHC of the deep and upper ocean regions. The studies attribute the heat uptake to anthropogenic warming which is equivalently expressed as a change to Earth's energy balance.[1][24]

Studies based on ARGO indicate that ocean surface winds, especially the subtropical trade winds in the Pacific Ocean, change ocean heat vertical distribution.[25] 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.

Model studies indicate that ocean currents transport more heat into deeper layers during La Niña years, following changes in wind circulation.[26][27] Years with increased ocean heat uptake have been associated with negative phases of the interdecadal Pacific oscillation (IPO).[28] This is of particular interest to climate scientists who use the data to estimate the ocean heat uptake.

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.[29]

Tutorial galleryEdit

See alsoEdit

ReferencesEdit

  1. ^ a b c von Schuckman, K.; Cheng, L.; Palmer, M. D.; Hansen, J.; et al. (7 September 2020). "Heat stored in the Earth system: where does the energy go?". Earth System Science Data. 12 (3): 2013-2041   Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. doi:10.5194/essd-12-2013-2020.
  2. ^ "Summary for Policymakers, Assessment Report 5, Working Group I" (PDF). www.climatechange2013.org. Intergovernmental Panel on Climate Change. 2013. Retrieved 15 July 2016.
  3. ^ a b LuAnn Dahlman and Rebecca Lindsey (2020-08-17). "Climate Change: Ocean Heat Content". National Oceanic and Atmospheric Administration.
  4. ^ "Study: Deep Ocean Waters Trapping Vast Store of Heat". Climate Central. 2016.
  5. ^ "Ocean warming : causes, scale, effects and consequences. And why it should matter to everyone. Executive summary" (PDF). International Union for Conservation of Nature. 2016.
  6. ^ "The Great Barrier Reef: a catastrophe laid bare". The Guardian. 6 June 2016.
  7. ^ Poloczanska, Elivra S.; Brown, Christopher J.; Sydeman, William J.; Kiessling, Wolfgang; Schoeman, David S.; Moore, Pippa J.; et al. (2013). "Global imprint of climate change on marine life". Nature Climate Change. 3: 919–925. doi:10.1038/nclimate1958.
  8. ^ "El Niño & Other Oscillations". Woods Hole Oceanographic Institution. Retrieved 2021-10-08.
  9. ^ Rahmstorf, Stefan (2003). "The concept of the thermohaline circulation" (PDF). Nature. 421 (6924): 699. Bibcode:2003Natur.421..699R. doi:10.1038/421699a. PMID 12610602. S2CID 4414604.
  10. ^ Rahmstorf, Stefan; Box, Jason E.; Feulner, George; Mann, Michael E.; Robinson, Alexander; Rutherford, Scott; Schaffernicht, Erik J. (2015). "Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation" (PDF). Nature Climate Change. 5 (5): 475–480. Bibcode:2015NatCC...5..475R. doi:10.1038/nclimate2554. ISSN 1758-678X.
  11. ^ "So what are marine heat waves? - A NOAA scientist explains". National Oceanic and Atmospheric Administration. 2019-10-08.
  12. ^ "NASA Earth Science: Water Cycle". NASA. Retrieved 2021-10-27.
  13. ^ Cheng, Lijing; Abraham, John; Trenberth, Kevin; Fasullo, John; Boyer, Tim; Locarnini, Ricardo; et al. (2021). "Upper Ocean Temperatures Hit Record High in 2020". Advances in Atmospheric Sciences. 38: 523-530. doi:10.1007/s00376-021-0447-x.
  14. ^ Laura Snider (2021-01-13). "2020 was a record-breaking year for ocean heat - Warmer ocean waters contribute to sea level rise and strengthen storms". National Center for Atmospheric Research.
  15. ^ Frederikse, Thomas; Landerer, Felix; Caron, Lambert; Adhikari, Surendra; Parkes, David; Humphrey, Vincent W.; et al. (2020). "The causes of sea-level rise since 1900". Nature. 584: 393-397. doi:10.1038/s41586-020-2591-3.
  16. ^ "NASA-led study reveals the causes of sea level rise since 1900". NASA. 2020-08-21.
  17. ^ Rebecca Lindsey and Michon Scott (2021-09-21). "Climate Change: Arctic sea ice". National Oceanographic and Atmospheric Administration.
  18. ^ Maria-Jose Viñas and Carol Rasmussen (2015-08-05). "Warming seas and melting ice sheets". NASA.
  19. ^ Slater, Thomas; Lawrence, Isobel R.; Otosaka, Inès N.; Shepherd, Andrew; et al. (25 January 2021). "Review article: Earth's ice imbalance". The Cryosphere. 15 (1): 233–246. Bibcode:2021TCry...15..233S. doi:10.5194/tc-15-233-2021. ISSN 1994-0416.
  20. ^ Michon Scott (2021-03-26). "Understanding climate: Antarctic sea ice extent". National Oceanographic and Atmospheric Administration.
  21. ^ Dijkstra, Henk A. (2008). Dynamical oceanography ([Corr. 2nd print.] ed.). Berlin: Springer Verlag. p. 276. ISBN 9783540763758.
  22. ^ Cheng L. J., Zhu J. (2014). "Artifacts in variations of ocean heat content induced by the observation system changes". Geophysical Research Letters. 41 (20): 7276–7283. Bibcode:2014GeoRL..41.7276C. doi:10.1002/2014GL061881.
  23. ^ Sirpa Häkkinen, Peter B Rhines, and Denise L Worthen (2015). "Heat content variability in the North Atlantic Ocean in ocean reanalyses". Geophys Res Lett. 42 (8): 2901–2909. Bibcode:2015GeoRL..42.2901H. doi:10.1002/2015GL063299. PMC 4681455. PMID 26709321.CS1 maint: uses authors parameter (link)
  24. ^ Abraham; et al. (2013). "A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change". Reviews of Geophysics. 51 (3): 450–483. Bibcode:2013RvGeo..51..450A. CiteSeerX 10.1.1.594.3698. doi:10.1002/rog.20022.
  25. ^ Balmaseda, Trenberth & Källén (2013). "Distinctive climate signals in reanalysis of global ocean heat content". Geophysical Research Letters. 40 (9): 1754–1759. Bibcode:2013GeoRL..40.1754B. doi:10.1002/grl.50382. Essay Archived 2015-02-13 at the Wayback Machine
  26. ^ Meehl; et al. (2011). "Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods". Nature Climate Change. 1 (7): 360–364. Bibcode:2011NatCC...1..360M. doi:10.1038/nclimate1229.
  27. ^ Rob Painting (2 October 2011). "The Deep Ocean Warms When Global Surface Temperatures Stall". SkepticalScience.com. Retrieved 15 July 2016.
  28. ^ Rob Painting (24 June 2013). "A Looming Climate Shift: Will Ocean Heat Come Back to Haunt us?". SkepticalScience.com. Retrieved 15 July 2016.
  29. ^ Sang-Ki Lee, Wonsun Park, Molly O. Baringer, Arnold L. Gordon, Bruce Huber & Yanyun Liu (18 May 2015). "Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus" (PDF). Nature Geoscience. 8 (6): 445–449. Bibcode:2015NatGe...8..445L. doi:10.1038/ngeo2438. hdl:1834/9681.CS1 maint: uses authors parameter (link)

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