Do Surface Temperature Indices Reflect Centennial‐Timescale Trends in Atlantic Meridional Overturning Circulation Strength?

Little, Christopher M.; Zhao, Mengnan; Buckley, Martha W.

doi:10.1029/2020gl090888

Cited by 23 publications

(27 citation statements)

References 47 publications

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“…Indeed, a proxy for AMOC strength using the difference between 'warming hole' SSTs and global mean SSTs 25,123 suggests an AMOC weakening of 3 ± 1 Sv since the middle of the twentieth century. However, the interpretation of this proxy for changes in the AMOC 10,119,164,165 and its Stippling indicates statistically significant trends (P < 0.05). Analysis and regions adapted from ref.…”

Section: Linking To the Pastmentioning

confidence: 92%

“…applicability to the historical period 10,165 have substantial uncertainties. Although it has been suggested that this weakening is the result of fresh water from melting glaciers 123 (which climate models represent poorly or not at all), such impacts are not yet considered to be large enough to influence the AMOC 166,167 .…”

Section: ();mentioning

confidence: 99%

“…One approach might be to use large ensembles of simulations to quantify how individual drivers and variability affect the AMOC and wider ocean patterns, and to examine where they differ. Understanding how robust these patterns are in different models and scenarios might also help to reconcile the historical changes implied by proxies and climate models 10,26,164,165 . Partial coupling or coupled data assimilation might close the gap between forced ocean models and climate models, offering the opportunity to understand historical AMOC drivers while still correctly representing coupled processes.…”

Section: Future Projections and Predictionsmentioning

confidence: 99%

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The evolution of the North Atlantic Meridional Overturning Circulation since 1980

Jackson

Biastoch

Buckley

et al. 2022

Nat Rev Earth Environ

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The Atlantic Meridional Overturning Circulation (AMOC) (Box 1) is a system of ocean currents in the Atlantic that move warmer, upper waters northwards and cooler, deeper waters southwards. Accordingly, the AMOC is a major source of northward heat transport, accounting for 20-30% of total atmospheric and oceanic heat transport into the mid-latitudes 1 . The AMOC, therefore, has a key role in governing the climate of the North Atlantic region and beyond, influencing European air temperatures and precipitation, the frequency of Atlantic hurricanes and winter storms, spatial patterns of sea level and tropical monsoons 2,3 , and the global carbon budget 4 .The strength of the AMOC is typically 17 Sverdrups (Sv; 1 Sv = 10 6 m 3 s −1 ) 5 . However, both observations and models indicate that the AMOC exhibits substantial variability on daily to multi-decadal timescales. Coupled climate models suggest decadal variability can arise naturally due to internal interactions within the climate system [6][7][8] . The AMOC is also expected to respond to external forcing, including anthropogenic aerosols, volcanic eruptions and solar changes 9,10 , as well as anthropogenic greenhouse gas emissions 11 . Indeed, observations, reanalyses, models and proxies [12][13][14][15][16] indicate substantial contemporary decadal-scale changes in AMOC strength. The RAPID array at 26.5° N (refs 5,17 ), for example, revealed a statistically significant weakening from 2004 (refs 18,19 ), probably representing decadal variability rather than ongoing long-term weakening [20][21][22] . There are indications that the AMOC might be recovering in strength 12 .Despite evidence of decadal variability, many questions remain. For example, high-quality continuous observations, like the RAPID array, are short and sparse, making it difficult to assess longer-term AMOC variability and determine whether decadal changes are representative of those across the wider Atlantic. Moreover, there is uncertainty about the relative roles of internal variability and forced variability, owing to diverse AMOC variability 8,23 and externally forced AMOC trends 10,24 in models. Indeed, the AMOC might have already weakened over the twentieth century 25,26 , potentially implying that it is more sensitive to external forcing than previously thought. Understanding how and why the AMOC has changed on decadal timescales is thus crucial not only to understand the AMOC's role

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Section: Linking To the Pastmentioning

confidence: 92%

Section: ();mentioning

confidence: 99%

Section: Future Projections and Predictionsmentioning

confidence: 99%

See 1 more Smart Citation

The evolution of the North Atlantic Meridional Overturning Circulation since 1980

Jackson

Biastoch

Buckley

et al. 2022

Nat Rev Earth Environ

Self Cite

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“…The decline occurred in a sharp reduction in early 2009 and not in a gradual, steady decline suggested by proxy time series. The proxies are often based on sea surface temperature records in the Atlantic and observed temperature changes may be related to global warming rather than changes in the AMOC [62]. In the subpolar gyre where temperature (and salinity) has steadily declined as a result of the reduced AMOC since 2009 [56], proxies based on surface temperature may capture accumulating effects of a change in the AMOC, but they do not reflect the sharp reduction in the strength of the AMOC.…”

Section: Is the Atlantic Meridional Overturning Circulation Declining?mentioning

confidence: 99%

Wind-driven and buoyancy-driven circulation in the subtropical North Atlantic Ocean

Bryden

2021

Proc. R. Soc. A.

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Continuous observations of ocean circulation at 26°N in the subtropical Atlantic Ocean have been made since April 2004 to quantify the strength and variability in the Atlantic Meridional overturning circulation (AMOC), in which warm, upper waters flow northward and colder deep waters below 1100 m depth return southward. The principal components of the AMOC are northward western boundary current transport in the Gulf Stream and Antilles Current, northward surface Ekman transport and southward thermocline recirculation, all of which are generally considered to be part of the wind-driven circulation. Southward flowing deep waters below 1100 m depth are usually considered to represent the buoyancy-driven circulation. We argue that the Gulf Stream is partially wind-driven but also partially buoyancy-driven as it returns upper waters upwelled in the global ocean back to water mass formation regions in the northern Atlantic. Seasonal to interannual variations in the circulation at 26°N are principally wind-driven. Variability in the buoyancy-driven circulation occurred in a sharp reduction in 2009 in the southward flow of Lower North Atlantic Deep Water when its transport decreased by 30% from pre-2009 values. Over the 14-year observational period from 2004 to 2018, the AMOC declined by 2.4 Sv from 18.3 to 15.9 Sv.

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“…Several studies have suggested that some of the dramatic hydrographic changes seen in the western North Atlantic near the Gulf of Maine, particularly the warming in the Gulf of St. Lawrence 12 and the decrease in nitrogen isotopes outside of the Gulf of Maine 25 , have been caused by a significant weakening of the AMOC over the last 50-150 years 25,61,62 . However, a weakened AMOC in the 21st century is still debated 63,64 , particularly as there are many other proxy records that do not suggest a recent weakening of the AMOC 16 .…”

Section: Discussionmentioning

confidence: 99%

Rapid 20th century warming reverses 900-year cooling in the Gulf of Maine

Whitney

Wanamaker

Ummenhofer

et al. 2022

Commun Earth Environ

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The Gulf of Maine, located in the western North Atlantic, has undergone recent, rapid ocean warming but the lack of long-term, instrumental records hampers the ability to put these significant hydrographic changes into context. Here we present multiple 300-year long geochemical records (oxygen, nitrogen, and previously published radiocarbon isotopes) measured in absolutely-dated Arctica islandica shells from the western Gulf of Maine. These records, in combination with climate model simulations, suggest that the Gulf of Maine underwent a long-term cooling over most of the last 1000 years, driven primarily by volcanic forcing and North Atlantic ocean dynamics. This cooling trend was reversed by warming beginning in the late 1800s, likely due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic circulation. The climate model simulations suggest that the warming over the last century was more rapid than almost any other 100-year period in the last 1000 years in the region.

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Do Surface Temperature Indices Reflect Centennial‐Timescale Trends in Atlantic Meridional Overturning Circulation Strength?

Cited by 23 publications

References 47 publications

The evolution of the North Atlantic Meridional Overturning Circulation since 1980

The evolution of the North Atlantic Meridional Overturning Circulation since 1980

Wind-driven and buoyancy-driven circulation in the subtropical North Atlantic Ocean

Rapid 20th century warming reverses 900-year cooling in the Gulf of Maine

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