 | This article is of interest to the following WikiProjects: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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. — Preceding unsigned comment added by Laura Kostrzewski (talk • contribs) 19:21, 29 April 2022 (UTC)[reply]
References
This section is unusually speculative, especially when compared to the rest of the article. After I spent quite some time to ensure that all scientific citations have up-to-date links, I was able to look at the 7 citations cited there, and frankly, all of them are only vaguely related to the rest of the article.
Light penetrates only about 100 meters to 200 meters of the ocean top layer.[80] - Reference "How far does light travel in the ocean?" Reliable, self-explanatory reference, which mentions nothing about the subject of this article.
Since light is required for photosynthesis to take place, oxygen production by phytoplankton can occur only at this level. The thermohaline cycle causes mixing of the deep ocean water (that would be oxygen-free) with the oxygen-rich water from the surface. [81] - Reference The Ocean Takes a Deep Breath (Interestingly, that paper is 18 years old, yet appears not to have been cited in any other literature.) It does mention that "Deep convection is the major mechanism for replenishing oxygen in the deep interior of the world ocean, and its variability affects the use of atmospheric oxygen to monitor the global carbon cycle."
Thus, the thermohaline cycle brings oxygen into the deep layers of the ocean and allows marine life to breathe, and degradation to happen aerobically. If the thermohaline cycle shut down, it has been proposed that the marine life dies off and sinks to the ocean ground. It has been established that climate change is responsible for the loss of oxygen in the ocean, both because oxygen dissolves worse in warm water, and because of weakening thermohaline circulations.[82] - Reference Declining oxygen in the global ocean and coastal waters only appears to provide explicit support for the final sentence. "it has been proposed that the marine life dies off and sinks to the ocean ground" - proposed by whom? Certainly not by any of the citations used in the article. Never mind that it should say "ocean floor" instead of ocean ground, but that is the least of this paragraph's problems.
With too little oxygen, anaerobic digestion through bacteria would create methane and hydrogen sulfide from the biomass. [83][84] - Two papers, both over 15 years old. Notably, both are focused on the deep past, and appear to have nothing to say about either the AMOC or the recent climate change.
The toxic hydrogen sulfide gas could then, when the ocean contains too much, get released into the atmosphere in a so called chemocline upward excursion.[83] Hydrogen sulfide poisoning of the atmosphere is one of the potential causes that might have led to the Permian-Triassic extinction event.' [85][84] [86][citation needed] - The section ends here. The final two new references are another 16-year old study (which at least does mention "a stagnate global ocean circulation in concert with paleodata indicating low oxygen levels at ocean depth" in its abstract) and a book from 2008.
All in all, there is only one post-2010 reference in this section, and no references which appear to draw an explicit link between the shutdown of the AMOC in the present or future climate and a chemocline upward excursion. I tried to look up any more recent studies myself, but the three closest studies are still very far from what this section currently implies. Moreover, one 2015 study appears to suggest that the AMOC collapse would actually increase oxygen concentrations in the ocean interior.
The reduction in the export production decreases the biological O2 utilization below the subsurface waters (Figure 4c), leading to oxygen increase in the ocean interior. The enhanced remineralization rate due to seawater warming also decreases O2 utilization in the deep water because of decreased transfer efficiency of organic matter to the deep water. Consequently, the global mean O2 increases by ~35 µmol/L in the deep ocean (below 1000 m; see Figure 5b). The biological effect in the deep ocean is marked in the tropical oceans where the present export production is larger (Figure 6b), which is consistent with the findings of a previous study [Matear and Hirst, 2003]. The reduced biological O2 utilization accumulates in proportion to the ventilation time. Therefore, in the deep North Pacific and tropical deep oceans, the biological effects become the dominant mechanism of oxygen recovery: a more than 40 µmol/L increase of oxygen concentration is found. Biological effects play a greater oxygen-enhancing role in the 4 × CO2 experiment than in the 2 × CO2 experiment (Figure 5), because the AMOC collapse in the 4 × CO2 experiment would decrease the export production and hence increase the oxygen concentration. Schmittner et al. [2007], who derived the AMOC collapse from freshwater input, similarly ascribed the increase in thermocline oxygen concentrations to reduce export production.
So, what do we do with this section as it stands? Does it make sense to update it, or should we just remove it entirely, and only add the few relevant references above to the other sections of this article? InformationToKnowledge (talk) 15:31, 4 October 2022 (UTC)[reply]
