Back دوران انقلاب خط الزوال الأطلسي Arabic Circulació de retorn meridional de l'Atlàntic Catalan Atlantická meridionální cirkulace Czech Atlantic Meridional Overturning Circulation Danish Atlantische Umwälzzirkulation German Circulación de vuelco meridional del Atlántico Spanish Circulation méridienne de retournement atlantique French Imshruthú iompaithe an uisce feadh an Atlantaigh Irish Sjevernoatlantska meridijanska obrtajuća struja Croatian Capovolgimento meridionale della circolazione atlantica Italian

Atlantic meridional overturning circulation

"AMOC" redirects here. For other uses, see AMOC (disambiguation).

Topographic map of the Nordic Seas and subpolar basins with surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures.

The Atlantic meridional overturning circulation (AMOC) is the main ocean current system in the Atlantic Ocean.[1]: 2238  It is a component of Earth's ocean circulation system and plays an important role in the climate system. The AMOC includes Atlantic currents at the surface and at great depths that are driven by changes in weather, temperature and salinity. Those currents comprise half of the global thermohaline circulation that includes the flow of major ocean currents, the other half being the Southern Ocean overturning circulation.[2]

The AMOC is composed of a northward flow of warm, more saline water in the Atlantic's upper layers and a southward, return flow of cold, salty, deep water. Warm water from the south is more saline ('halocline') because of the higher evaporation rate in the tropical zone. The warm saline water forms the upper layer of the ocean ('thermocline'), but when this layer cools down, the density of the salty water increases, making it sink into the deep. This is an important part of the motor of the AMOC system. The limbs are linked by regions of overturning in the Nordic Seas and the Southern Ocean. Overturning sites are associated with intense exchanges of heat, dissolved oxygen, carbon and other nutrients, and very important for the ocean's ecosystems and its function as a carbon sink.[3][4] Changes in the strength of the AMOC can affect multiple elements of the climate system.[1]: 2238 

Climate change may weaken the AMOC through increases in ocean heat content and elevated flows of freshwater from melting ice sheets.[5] Studies using oceanographic reconstructions suggest that as of 2015, the AMOC was weaker than before the Industrial Revolution.[6][7] There is debate over the relative contributions of different factors and it is unclear how much of this weakening is due to climate change or the circulation's natural variability over millennia.[8][9] Climate models predict the AMOC will further weaken during the 21st century.[10]: 19  This weakening would reduce average air temperatures over Scandinavia, Great Britain, and Ireland, because these regions are warmed by the North Atlantic Current.[11] Weakening of the AMOC would also accelerate sea level rise around North America and reduce primary production in the North Atlantic.[12]

Severe weakening of the AMOC may lead to a collapse of the circulation, which would not be easily reversible and thus constitutes one of the tipping points in the climate system.[13] A collapse would substantially lower the average temperature and amount of rain and snowfall in Europe.[14][15] It may also raise the frequency of extreme weather events and have other severe effects.[16][17]

  1. ^ a b IPCC, 2021: Annex VII: Glossary Archived 5 June 2022 at the Wayback Machine [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Archived 26 May 2023 at the Wayback Machine [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. 2215–2256, doi:10.1017/9781009157896.022.
  2. ^ "NOAA Scientists Detect a Reshaping of the Meridional Overturning Circulation in the Southern Ocean". NOAA. 29 March 2023. Archived from the original on 28 January 2024. Retrieved 28 January 2024.
  3. ^ Buckley, Martha W.; Marshall, John (2016). "Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review". Reviews of Geophysics. 54 (1): 5–63. Bibcode:2016RvGeo..54....5B. doi:10.1002/2015RG000493. hdl:1721.1/108249. ISSN 8755-1209. S2CID 54013534.
  4. ^ Lozier, M. S.; Li, F.; Bacon, S.; Bahr, F.; Bower, A. S.; Cunningham, S. A.; de Jong, M. F.; de Steur, L.; deYoung, B.; Fischer, J.; Gary, S. F. (2019). "A sea change in our view of overturning in the subpolar North Atlantic". Science. 363 (6426): 516–521. Bibcode:2019Sci...363..516L. doi:10.1126/science.aau6592. ISSN 0036-8075. PMID 30705189. S2CID 59567598.
  5. ^ "Historic iceberg surges offer insights on modern climate change". The Current. 30 May 2024. Archived from the original on 30 May 2024. Retrieved 30 May 2024.
  6. ^ Cite error: The named reference Rahmstorf2015 was invoked but never defined (see the help page).
  7. ^ Caesar, L.; McCarthy, G.D.; Thornalley, D. J. R.; Cahill, N.; Rahmstorf, S. (25 February 2021). "Current Atlantic Meridional Overturning Circulation weakest in last millennium" (PDF). Nature Geoscience. 14 (3): 118–120. Bibcode:2021NatGe..14..118C. doi:10.1038/s41561-021-00699-z. S2CID 232052381.
  8. ^ Latif, Mojib; Sun, Jing; Visbeck, Martin; Bordbar (25 April 2022). "Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900". Nature Climate Change. 12 (5): 455–460. Bibcode:2022NatCC..12..455L. doi:10.1038/s41558-022-01342-4. S2CID 248385988.
  9. ^ Kilbourne, Kelly Halimeda; et, al. (17 February 2022). "Atlantic circulation change still uncertain". Nature Geoscience. 15 (3): 165–167. Bibcode:2022NatGe..15..165K. doi:10.1038/s41561-022-00896-4. hdl:2117/363518. S2CID 246901665.
  10. ^ IPCC, 2019: Summary for Policymakers Archived 18 October 2022 at the Wayback Machine. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate Archived 12 July 2021 at the Wayback Machine [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.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi:10.1017/9781009157964.001.
  11. ^ Lenton, T. M.; Held, H.; Kriegler, E.; Hall, J. W.; Lucht, W.; Rahmstorf, S.; Schellnhuber, H. J. (2008). "Inaugural Article: Tipping elements in the Earth's climate system". Proceedings of the National Academy of Sciences. 105 (6): 1786–1793. Bibcode:2008PNAS..105.1786L. doi:10.1073/pnas.0705414105. PMC 2538841. PMID 18258748.
  12. ^ Cite error: The named reference Schmittner2005 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference CarbonBrief was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference ArmstrongMcKay2022 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Phys2020 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference GTPR2023 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Hansen2015 was invoked but never defined (see the help page).

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