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Assessment (C): banner shell, Geography (Low), Oceans (Low), Environment (Low), Climate change (Mid), Futures studies (Low), Limnology and Oceanography (Low), Weather (Mid) (Rater)
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:: They could be put in a footnote as university students might need them. [[User:Chidgk1|Chidgk1]] ([[User talk:Chidgk1|talk]]) 09:32, 13 April 2022 (UTC) |
:: They could be put in a footnote as university students might need them. [[User:Chidgk1|Chidgk1]] ([[User talk:Chidgk1|talk]]) 09:32, 13 April 2022 (UTC) |
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::: Who would want to check that they are all correct? I wonder if they are all taken from the same publication. It might be better to park them in a sub-article on "Stommel Box Model"? They don't really fit with the prose & encyclopedic style that we use for other articles. Or are such formulas common in other articles that I haven't looked at yet, perhaps the mathematical or electrical engineering ones.[[User:EMsmile|EMsmile]] ([[User talk:EMsmile|talk]]) 10:34, 13 April 2022 (UTC) |
::: Who would want to check that they are all correct? I wonder if they are all taken from the same publication. It might be better to park them in a sub-article on "Stommel Box Model"? They don't really fit with the prose & encyclopedic style that we use for other articles. Or are such formulas common in other articles that I haven't looked at yet, perhaps the mathematical or electrical engineering ones.[[User:EMsmile|EMsmile]] ([[User talk:EMsmile|talk]]) 10:34, 13 April 2022 (UTC) |
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== Global Warming == |
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The AMOC behaves like a large conveyor belt that redistributes heat across the planet. Because of this, it has a significant impact on our climate. In the past, the initial weakening of the AMOC occurred in the 19th century, and then a second more rapid decline in the mid 20th century<ref>Wang, H., Legg, S., & Hallberg, R. The Effect of Arctic Freshwater Pathways on North Atlantic Convection and the Atlantic Meridional Overturning Circulation. Journal of Climate. 31-13, 5165-5188 (2018). https://doi.org/10.1175/JCLI-D-17-0629.1 |
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</ref>. Now, there is evidence suggesting that it is slowing down again and is currently in its weakest state yet<ref>Caesar, L., McCarthy, G.D., THornalley, D.J.R., Cahill, N., & Rahmsorf, S. (2021). Current Atlantic Meridional Overturning circulation weakest in last millennium. Nature Geoscience, 14, 118-120. https://doi.org/10.1038/s41561-021-00699-z</ref>. Climate model studies have demonstrated a weakening of the AMOC due to anthropogenic sources. However, some project underestimations or overestimations of its weakening, and some do not account for physical processes, such as meltwater from Greenland. Since 2004, direct measurements of the AMOC have been calculated also identifying a weakening of the AMOC; however this is too short of a time-frame to identify a trend. |
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Published records of various proxies were used to develop a view of the AMOC’s flow history. Indirect proxies help us understand the characteristics of the AMOC during times when instruments were not yet developed to measure it. Looking at proxy records we can view a picture of the past 100 to 2000 years of the AMOC’s behavior<ref>L. Caesar, G. D. McCarthy, D. J. R. Thornalley, N. Cahill, S. Rahmstorf. Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nature Geoscience, 2021; DOI: 10.1038/s41561-021-00699-z</ref>. Reconstructions of surface or subsurface temperature patterns, subsurface water mass properties, and evidence of physical changes in deep sea currents have been used to demonstrate strong evidence in the weakening of the AMOC<ref>Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G. & Saba, V. Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature 556, 191–196 (2018).</ref>. Ocean sediments can tell scientists what kind of organisms once existed and how productive the oceans were in the past. Utilizing proxies from ocean sediment cores, reconstructions of subpolar gyres |
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temperatures were used to identify changes in the AMOC. In the late twentieth century, |
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the subpolar temperatures were at their lowest in over the past 1000 years. During this |
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same period, the AMOC index revealed a sharp decrease in temperature occurring ~1970 |
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with a subsequent event known as the Great Salinity Anomaly.<ref>Rahmstorf, Stefan & Box, Jason & Feulner, Georg & Mann, Michael & Robinson, Alexander & |
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Schaffernicht, Erik. (2015). Exceptional twentieth-Century slowdown in Atlantic Ocean |
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overturning circulation. Nature Climate Change. 5. https://doi.org/10.1038/nclimate2554. |
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</ref> Weakening in the AMOC |
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has been associated to this cold patch in the subpolar Atlantic due to its reduced |
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northward heat transport, causing cooler waters in this region. The export of sea-ice from |
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the Arctic Ocean was the major source of the freshwater input; however, the accumulated |
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input of meltwater from Greenland that began in the early nineteenth century may be an |
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additional contributing factor to this freshwater input. <ref>Rahmstorf, Stefan & Box, Jason & Feulner, Georg & Mann, Michael & Robinson, Alexander & |
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Schaffernicht, Erik. (2015). Exceptional twentieth-Century slowdown in Atlantic Ocean |
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overturning circulation. Nature Climate Change. 5. https://doi.org/10.1038/nclimate2554.</ref> |
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The minerals in the sediments can also help determine how far terrestrial minerals have traveled from their origin which can also suggest pathways of currents<ref>Sherwood, O. A., Lehmann, M. F., Schubert, C. J., Scott, D. B. & McCarthy, M. D. Nutrient regime shift in the western North Atlantic indicated by compound-specifc delta15N of deep-sea gorgonian corals. Proc. Natl Acad. Sci. USA 108, 1011–1015 (2011). |
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</ref>. Magnetic particles can be found in sediments which can show how Earth’s magnetic field has changed over thousands of millions of years. Records of concentration levels of methanesulfonic acid extracted from Greenland’s ice |
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core are associated with subarctic Atlantic productivity declines in response to the the |
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AMOC’s weakening due to increased Arctic sea-surface temperatures. A previous study |
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by Osman et al., utilized unpublished ice-core data to reconstruct previous variations in |
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marine productivity over multiple decades.<ref>Sherwood, O. A., Lehmann, M. F., Schubert, C. J., Scott, D. B. & McCarthy, M. D. Nutrient regime shift in the western North Atlantic indicated by compound-specifc delta15N of deep-sea gorgonian corals. Proc. Natl Acad. Sci. USA 108, 1011–1015 (2011).</ref> Their results showed an initial decline in |
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productivity in the subarctic Atlantic that coincided with the Arctic’s increased seasurface temperature during the first marked event of the AMOC’s slowdown in the |
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nineteenth century (industrial-era). In this study, high levels of |
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Greenland Ice Sheet runoff were found to potentially be a contributing factor in the |
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productivity decline events (in both the late nineteenth and twentieth century), suggesting |
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that there was a continual influx of freshwater driving the AMOC’s decline, that began in |
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the early nineteenth century.<ref>Osman, M.B., Das, S.B., Trusel, L.D. et al. (2019). Industrial-era decline in subarctic Atlantic |
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productivity. Nature 569, 551–555. https://doi.org/10.1038/s41586-019-1181-8</ref>. |
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Additionally, paleoclimate data provides valuable insight into our climate’s history and |
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variability. It is a fundamental source that can be implemented with modern climate |
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observations into computer models to deduce past and predict current and future climatic |
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conditions. Paleoclimate data suggests that in the past, large quantities of freshwater input |
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occurred in high latitudes (e.g., Labrador Sea) with multiple proxies associating its |
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connection to a weakened AMOC. As the Earth’s major ocean circulation system, |
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combining climate models, paleoclimate data, and observational methods to further |
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research its characteristics will expand a greater understanding of the effects and |
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consequences associated with the weakening of the AMOC.<ref>Thornalley, David & Oppo, Delia & Ortega, Pablo & Robson, Jon & Brierley, Chris & Davis, |
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Renee & Hall, Ian & Moffa-Sanchez, Paola & Rose, Neil & Spooner, Peter & |
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Yashayaev, Igor & Keigwin, Lloyd. (2018). Anomalously weak Labrador Sea convection |
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and Atlantic overturning during the past 150 years. Nature. 556. |
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https://doi.org/10.1038/s41586-018-0007-4</ref> |
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Due to its significant impact on climate, a shift (weakening) in the circulation would lead to a cause and effect like scenario. The AMOC is driven by differences in density.<ref>Fedorov, A., Barreiro, M., Boccaletti, G., Pacanowski, R., & Philander, S. G. (2007). The |
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freshening of surface waters in high latitudes: Effects on the Thermohaline and winddriven circulations. AMETSOC. https://journals.ametsoc.org/view/journals/ phoc/ |
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37/4/jpo3033.1.xml</ref> Deep convection plays a major component to the overturning circulation. As temperatures continue to increase, more rainfall occurs and melting of icebergs and glaciers in the North Atlantic and Greenland add freshwater to the surface layer of the ocean. This reduces the density, thus inhibiting deep convection, which further weakens the AMOC. |
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With continued weakening, the warm, tropical waters that move from the equator and redistribute heat to the northern latitudes will become sluggish, affecting northern North America and Europe’s climate dramatically. And as subtropical waters become warmer, hurricanes would intensify and increase in frequency. Some scientists are suggesting that the northern portion of the Gulf Stream, and its associated deep ocean currents are slowing down due to the meltwater in Greenland<ref>Grootes, P., Stuiver, M., White, J. et al. (1993). Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores. Nature, 366, 552–554. https://doi.org/10.1038/366552a0</ref>. Additionally, a sharp rise in sea levels on the US east coast and parts of Europe would result from further weakening of the AMOC, as well as shifts in rainfall patterns causing droughts in Africa.<ref>Haile, G. G., Tang, Q., Hosseini-Moghari, S.-M., Liu, X., Gebremicael, T. G., Leng, G., et al. (2020). Projected impacts of climate change on drought patterns over East Africa. Earth's Future, 8, e2020EF001502. https://doi.org/10.1029/2020EF001502</ref> Advance climate models suggest many different outcomes. Some predict less weakening while others show severity to possible shutdown. Scientists do not agree that it has slowed to date, arguing that changes are being seen while others say its soon to tell. However, there is consensus that if we continue to warm the atmosphere, it will slow down. |
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The article would benefit from discussion of AMOC in biogeochemical cycling, specifically carbon sequestration. The following sources may be useful: Glacial CO2 cycle as a succession of key physical and biogeochemical processes Glacial greenhouse-gas fluctuations controlled by ocean circulation changes Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability Kdarr (talk) 03:10, 21 October 2017 (UTC)[reply]
The figure below describes this variation []. The repetitive cycle obvious in this figure I don't see any such figure.--94.222.124.187 (talk) 18:50, 14 April 2018 (UTC)[reply]
Some sections of this article should be merged with Shutdown_of_thermohaline_circulation or at least link to it.
The article uses a rather good deal of abbreviations, some of which probably make the article harder to read compared to just spelling out what they stand for. Some, such as LSW, aren’t even defined. Furthermore, it suddenly uses the unit “Sv” without ever describing what it is and what it measures. I assume it isn’t referring to Sievert (unit)?Dan Villiom Podlaski Christiansen (talk) 18:23, 27 December 2019 (UTC)[reply]
Hi, Not an expert at all, but it would be great if anyone could explain in the article the link (or indeed lack thereof) to the North Atlantic Current.
@Deniseruijsch: I propose merging Multiple equilibria in the Atlantic meridional overturning circulation into Atlantic meridional overturning circulation as it is moderate size. Chidgk1 (talk) 12:07, 12 April 2022 (UTC)[reply]
The AMOC behaves like a large conveyor belt that redistributes heat across the planet. Because of this, it has a significant impact on our climate. In the past, the initial weakening of the AMOC occurred in the 19th century, and then a second more rapid decline in the mid 20th century[1]. Now, there is evidence suggesting that it is slowing down again and is currently in its weakest state yet[2]. Climate model studies have demonstrated a weakening of the AMOC due to anthropogenic sources. However, some project underestimations or overestimations of its weakening, and some do not account for physical processes, such as meltwater from Greenland. Since 2004, direct measurements of the AMOC have been calculated also identifying a weakening of the AMOC; however this is too short of a time-frame to identify a trend. Published records of various proxies were used to develop a view of the AMOC’s flow history. Indirect proxies help us understand the characteristics of the AMOC during times when instruments were not yet developed to measure it. Looking at proxy records we can view a picture of the past 100 to 2000 years of the AMOC’s behavior[3]. Reconstructions of surface or subsurface temperature patterns, subsurface water mass properties, and evidence of physical changes in deep sea currents have been used to demonstrate strong evidence in the weakening of the AMOC[4]. Ocean sediments can tell scientists what kind of organisms once existed and how productive the oceans were in the past. Utilizing proxies from ocean sediment cores, reconstructions of subpolar gyres temperatures were used to identify changes in the AMOC. In the late twentieth century, the subpolar temperatures were at their lowest in over the past 1000 years. During this same period, the AMOC index revealed a sharp decrease in temperature occurring ~1970 with a subsequent event known as the Great Salinity Anomaly.[5] Weakening in the AMOC has been associated to this cold patch in the subpolar Atlantic due to its reduced northward heat transport, causing cooler waters in this region. The export of sea-ice from the Arctic Ocean was the major source of the freshwater input; however, the accumulated input of meltwater from Greenland that began in the early nineteenth century may be an additional contributing factor to this freshwater input. [6]
The minerals in the sediments can also help determine how far terrestrial minerals have traveled from their origin which can also suggest pathways of currents[7]. Magnetic particles can be found in sediments which can show how Earth’s magnetic field has changed over thousands of millions of years. Records of concentration levels of methanesulfonic acid extracted from Greenland’s ice core are associated with subarctic Atlantic productivity declines in response to the the AMOC’s weakening due to increased Arctic sea-surface temperatures. A previous study by Osman et al., utilized unpublished ice-core data to reconstruct previous variations in marine productivity over multiple decades.[8] Their results showed an initial decline in productivity in the subarctic Atlantic that coincided with the Arctic’s increased seasurface temperature during the first marked event of the AMOC’s slowdown in the nineteenth century (industrial-era). In this study, high levels of Greenland Ice Sheet runoff were found to potentially be a contributing factor in the productivity decline events (in both the late nineteenth and twentieth century), suggesting that there was a continual influx of freshwater driving the AMOC’s decline, that began in the early nineteenth century.[9].
Additionally, paleoclimate data provides valuable insight into our climate’s history and variability. It is a fundamental source that can be implemented with modern climate observations into computer models to deduce past and predict current and future climatic conditions. Paleoclimate data suggests that in the past, large quantities of freshwater input occurred in high latitudes (e.g., Labrador Sea) with multiple proxies associating its connection to a weakened AMOC. As the Earth’s major ocean circulation system, combining climate models, paleoclimate data, and observational methods to further research its characteristics will expand a greater understanding of the effects and consequences associated with the weakening of the AMOC.[10]
Due to its significant impact on climate, a shift (weakening) in the circulation would lead to a cause and effect like scenario. The AMOC is driven by differences in density.[11] Deep convection plays a major component to the overturning circulation. As temperatures continue to increase, more rainfall occurs and melting of icebergs and glaciers in the North Atlantic and Greenland add freshwater to the surface layer of the ocean. This reduces the density, thus inhibiting deep convection, which further weakens the AMOC. With continued weakening, the warm, tropical waters that move from the equator and redistribute heat to the northern latitudes will become sluggish, affecting northern North America and Europe’s climate dramatically. And as subtropical waters become warmer, hurricanes would intensify and increase in frequency. Some scientists are suggesting that the northern portion of the Gulf Stream, and its associated deep ocean currents are slowing down due to the meltwater in Greenland[12]. Additionally, a sharp rise in sea levels on the US east coast and parts of Europe would result from further weakening of the AMOC, as well as shifts in rainfall patterns causing droughts in Africa.[13] Advance climate models suggest many different outcomes. Some predict less weakening while others show severity to possible shutdown. Scientists do not agree that it has slowed to date, arguing that changes are being seen while others say its soon to tell. However, there is consensus that if we continue to warm the atmosphere, it will slow down.
