Regional Patterns of Sea Level Change Related to Interannual Variability and Multidecadal Trends in the Atlantic Meridional Overturning Circulation*

Abstract Some studies of ocean climate model experiments suggest that regional changes in dynamic sea level could provide a valuable indicator of trends in the strength of the Atlantic meridional overturning circulation (MOC). This paper describes the use of a sequence of global ocean–ice model experiments to show that the diagnosed patterns of sea surface height (SSH) anomalies associated with changes in the MOC in the North Atlantic (NA) depend critically on the time scales of interest. Model hindcast simulations for 1958–2004 reproduce the observed pattern of SSH variability with extrema occurring along the Gulf Stream (GS) and in the subpolar gyre (SPG), but they also show that the pattern is primarily related to the wind-driven variability of MOC and gyre circulation on interannual time scales; it is reflected also in the leading EOF of SSH variability over the NA Ocean, as described in previous studies. The pattern, however, is not useful as a “fingerprint” of longer-term changes in the MOC: as shown with a companion experiment, a multidecadal, gradual decline in the MOC [of 5 Sv (1 Sv ≡ 106 m3 s−1) over 5 decades] induces a much broader, basin-scale SSH rise over the mid-to-high-latitude NA, with amplitudes of 20 cm. The detectability of such a trend is low along the GS since low-frequency SSH changes are effectively masked here by strong variability on shorter time scales. More favorable signal-to-noise ratios are found in the SPG and the eastern NA, where a MOC trend of 0.1 Sv yr−1 would leave a significant imprint in SSH already after about 20 years.

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Intrinsic Variability of the Atlantic Meridional Overturning Circulation at Interannual-to-Multidecadal Time Scales

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0163.1 ◽

2015 ◽

Vol 45 (7) ◽

pp. 1929-1946 ◽

Cited By ~ 37

Author(s):

Sandy Grégorio ◽

Thierry Penduff ◽

Guillaume Sérazin ◽

Jean-Marc Molines ◽

Bernard Barnier ◽

...

Keyword(s):

Time Scales ◽

Gulf Stream ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Intrinsic Variability ◽

Meridional Heat Transport ◽

Overturning Circulation ◽

Spectral Peaks ◽

Meridional Overturning

AbstractThe low-frequency variability of the Atlantic meridional overturning circulation (AMOC) is investigated from 2, ¼°, and ° global ocean–sea ice simulations, with a specific focus on its internally generated (i.e., “intrinsic”) component. A 327-yr climatological ¼° simulation, driven by a repeated seasonal cycle (i.e., a forcing devoid of interannual time scales), is shown to spontaneously generate a significant fraction R of the interannual-to-decadal AMOC variance obtained in a 50-yr “fully forced” hindcast (with reanalyzed atmospheric forcing including interannual time scales). This intrinsic variance fraction R slightly depends on whether AMOCs are computed in geopotential or density coordinates, and on the period considered in the climatological simulation, but the following features are quite robust when mesoscale eddies are simulated (at both ¼° and ° resolutions); R barely exceeds 5%–10% in the subpolar gyre but reaches 30%–50% at 34°S, up to 20%–40% near 25°N, and 40%–60% near the Gulf Stream. About 25% of the meridional heat transport interannual variability is attributed to intrinsic processes at 34°S and near the Gulf Stream. Fourier and wavelet spectra, built from the 327-yr ¼° climatological simulation, further indicate that spectral peaks of intrinsic AMOC variability (i) are found at specific frequencies ranging from interannual to multidecadal, (ii) often extend over the whole meridional scale of gyres, (iii) stochastically change throughout these 327 yr, and (iv) sometimes match the spectral peaks found in the fully forced hindcast in the North Atlantic. Intrinsic AMOC variability is also detected at multidecadal time scales, with a marked meridional coherence between 35°S and 25°N (15–30 yr periods) and throughout the whole basin (50–90-yr periods).

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Local and Downstream Relationships between Labrador Sea Water Volume and North Atlantic Meridional Overturning Circulation Variability

Journal of Climate ◽

10.1175/jcli-d-18-0735.1 ◽

2019 ◽

Vol 32 (13) ◽

pp. 3883-3898 ◽

Cited By ~ 11

Author(s):

Feili Li ◽

M. Susan Lozier ◽

Gokhan Danabasoglu ◽

Naomi P. Holliday ◽

Young-Oh Kwon ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Sea Water ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Labrador Sea ◽

Overturning Circulation ◽

Meridional Overturning ◽

Labrador Sea Water

Abstract While it has generally been understood that the production of Labrador Sea Water (LSW) impacts the Atlantic meridional overturning circulation (MOC), this relationship has not been explored extensively or validated against observations. To explore this relationship, a suite of global ocean–sea ice models forced by the same interannually varying atmospheric dataset, varying in resolution from non-eddy-permitting to eddy-permitting (1°–1/4°), is analyzed to investigate the local and downstream relationships between LSW formation and the MOC on interannual to decadal time scales. While all models display a strong relationship between changes in the LSW volume and the MOC in the Labrador Sea, this relationship degrades considerably downstream of the Labrador Sea. In particular, there is no consistent pattern among the models in the North Atlantic subtropical basin over interannual to decadal time scales. Furthermore, the strong response of the MOC in the Labrador Sea to LSW volume changes in that basin may be biased by the overproduction of LSW in many models compared to observations. This analysis shows that changes in LSW volume in the Labrador Sea cannot be clearly and consistently linked to a coherent MOC response across latitudes over interannual to decadal time scales in ocean hindcast simulations of the last half century. Similarly, no coherent relationships are identified between the MOC and the Labrador Sea mixed layer depth or the density of newly formed LSW across latitudes or across models over interannual to decadal time scales.

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A New Index for the Atlantic Meridional Overturning Circulation at 26°N

Journal of Climate ◽

10.1175/jcli-d-13-00052.1 ◽

2014 ◽

Vol 27 (17) ◽

pp. 6439-6455 ◽

Cited By ~ 20

Author(s):

A. Duchez ◽

J. J.-M. Hirschi ◽

S. A. Cunningham ◽

A. T. Blaker ◽

H. L. Bryden ◽

...

Keyword(s):

Time Scales ◽

Decadal Variability ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Ekman Transport ◽

Current Estimate ◽

Overturning Circulation ◽

Main Hypothesis ◽

Meridional Overturning ◽

Sverdrup Transport

Abstract The Atlantic meridional overturning circulation (AMOC) has received considerable attention, motivated by its major role in the global climate system. Observations of AMOC strength at 26°N made by the Rapid Climate Change (RAPID) array provide the best current estimate of the state of the AMOC. The period 2004–11 when RAPID AMOC is available is too short to assess decadal variability of the AMOC. This modeling study introduces a new AMOC index (called AMOCSV) at 26°N that combines the Florida Straits transport, the Ekman transport, and the southward geostrophic Sverdrup transport. The main hypothesis in this study is that the upper midocean geostrophic transport calculated using the RAPID array is also wind-driven and can be approximated by the geostrophic Sverdrup transport at interannual and longer time scales. This index is expected to reflect variations in the AMOC at interannual to decadal time scales. This estimate of the surface branch of the AMOC can be constructed as long as reliable measurements are available for the Gulf Stream and for wind stress. To test the reliability of the AMOCSV on interannual and longer time scales, two different numerical simulations are used: a forced and a coupled simulation. Using these simulations the AMOCSV captures a substantial fraction of the AMOC variability and is in good agreement with the AMOC transport at 26°N on both interannual and decadal time scales. These results indicate that it might be possible to extend the observation-based AMOC at 26°N back to the 1980s.

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Signature of the Atlantic meridional overturning circulation in sea level along the east coast of North America

Geophysical Research Letters ◽

10.1029/2008gl036215 ◽

2009 ◽

Vol 36 (2) ◽

pp. n/a-n/a ◽

Cited By ~ 65

Author(s):

Rory J. Bingham ◽

Chris W. Hughes

Keyword(s):

North America ◽

Sea Level ◽

East Coast ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Meridional Overturning

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An abrupt slowdown of Atlantic Meridional Overturning Circulation during 1915–1935 induced by solar forcing in a coupled GCM

Climate of the Past Discussions ◽

10.5194/cpd-10-2519-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 2519-2546 ◽

Cited By ~ 1

Author(s):

P. Lin ◽

Y. Song ◽

Y. Yu ◽

H. Liu

Keyword(s):

Abrupt Change ◽

Polar Vortex ◽

Atlantic Meridional Overturning Circulation ◽

Total Solar Irradiance ◽

Heat Fluxes ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

High Latitudes ◽

Overturning Circulation ◽

Meridional Overturning

Abstract. In this study, we explore an abrupt change of Atlantic Meridional Overturning Circulation (AMOC) apparent in the historical run simulated by the second version of the Flexible Global Ocean–Atmosphere–Land System model – Spectral Version 2 (FGOALS-s2). The abrupt change is noted during the period from 1915 to 1935, in which the maximal AMOC value is weakened beyond 6 Sv (1 Sv = 106 m3 s−1). The abrupt signal first occurs at high latitudes (north of 46° N), then shifts gradually to middle latitudes (∼35° N) three to seven years later. The weakened AMOC can be explained in the following. The weak total solar irradiance (TIS) during early twentieth century decreases pole-to-equator temperature gradient in the upper stratosphere. The North polar vortex is weakened, which forces a negative North Atlantic Oscillation (NAO) phase during 1905–1914. The negative phase of NAO induces anomalous easterly winds in 50–70° N belts, which decrease the release of heat fluxes from ocean to atmosphere and induce surface warming over these regions. Through the surface ice–albedo feedback, the warming may lead to continuously melting sea ice in Baffin Bay and Davis Strait, which results in freshwater accumulation. This can lead to salinity and density reductions and then an abrupt slowdown of AMOC. Moreover, due to increased TIS after 1914, the enhanced Atlantic northward ocean heat transport from low to high latitudes induces an abrupt warming of sea surface temperature or upper ocean temperature in mid–high latitudes, which can also weaken the AMOC. The abrupt change of AMOC also appears in the PiControl run, which is associated with the lasting negative NAO phases due to natural variability.

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The Relationship Between U.S. East Coast Sea Level and the Atlantic Meridional Overturning Circulation: A Review

Journal of Geophysical Research Oceans ◽

10.1029/2019jc015152 ◽

2019 ◽

Vol 124 (9) ◽

pp. 6435-6458 ◽

Cited By ~ 6

Author(s):

Christopher M. Little ◽

Aixue Hu ◽

Chris W. Hughes ◽

Gerard D. McCarthy ◽

Christopher G. Piecuch ◽

...

Keyword(s):

Sea Level ◽

East Coast ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Meridional Overturning ◽

The Relationship

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Does the Atlantic Multidecadal Oscillation Get Its Predictability from the Atlantic Meridional Overturning Circulation?

Journal of Climate ◽

10.1175/jcli-d-16-0030.1 ◽

2016 ◽

Vol 29 (14) ◽

pp. 5267-5280 ◽

Cited By ~ 18

Author(s):

Laurie Trenary ◽

Timothy DelSole

Keyword(s):

Time Scales ◽

Autoregressive Model ◽

Climate Models ◽

Optimization Technique ◽

Atlantic Multidecadal Oscillation ◽

Atlantic Meridional Overturning Circulation ◽

Statistical Optimization ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Meridional Overturning

Abstract This paper investigates the predictive relation between the Atlantic multidecadal oscillation (AMO) and Atlantic meridional overturning circulation across different climate models. Three overturning patterns that are significantly coupled to the AMO on interannual time scales across all climate models are identified using a statistical optimization technique. Including these structures in an autoregressive model extends AMO predictability by 2–9 years, relative to an autoregressive model without these structures.

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Links between the Southern Annular Mode and the Atlantic Meridional Overturning Circulation in a Climate Model

Journal of Climate ◽

10.1175/2010jcli3576.1 ◽

2011 ◽

Vol 24 (3) ◽

pp. 624-640 ◽

Cited By ~ 14

Author(s):

Camille Marini ◽

Claude Frankignoul ◽

Juliette Mignot

Keyword(s):

Time Scales ◽

North Atlantic ◽

Time Scale ◽

Climate Model ◽

Drake Passage ◽

Atlantic Meridional Overturning Circulation ◽

Southern Annular Mode ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Meridional Overturning

Abstract The links between the atmospheric southern annular mode (SAM), the Southern Ocean, and the Atlantic meridional overturning circulation (AMOC) at interannual to multidecadal time scales are investigated in a 500-yr control integration of the L’Institut Pierre-Simon Laplace Coupled Model, version 4 (IPSL CM4) climate model. The Antarctic Circumpolar Current, as described by its transport through the Drake Passage, is well correlated with the SAM at the yearly time scale, reflecting that an intensification of the westerlies south of 45°S leads to its acceleration. Also in phase with a positive SAM, the global meridional overturning circulation is modified in the Southern Hemisphere, primarily reflecting a forced barotropic response. In the model, the AMOC and the SAM are linked at several time scales. An intensification of the AMOC lags a positive SAM by about 8 yr. This is due to a correlation between the SAM and the atmospheric circulation in the northern North Atlantic that reflects a symmetric ENSO influence on the two hemispheres, as well as an independent, delayed interhemispheric link driven by the SAM. Both effects lead to an intensification of the subpolar gyre and, by salinity advection, increased deep convection and a stronger AMOC. A slower oceanic link between the SAM and the AMOC is found at a multidecadal time scale. Salinity anomalies generated by the SAM enter the South Atlantic from the Drake Passage and, more importantly, the Indian Ocean; they propagate northward, eventually reaching the northern North Atlantic where, for a positive SAM, they decrease the vertical stratification and thus increase the AMOC.

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Causes of Interannual–Decadal Variability in the Meridional Overturning Circulation of the Midlatitude North Atlantic Ocean

Journal of Climate ◽

10.1175/2008jcli2404.1 ◽

2008 ◽

Vol 21 (24) ◽

pp. 6599-6615 ◽

Cited By ~ 162

Author(s):

Arne Biastoch ◽

Claus W. Böning ◽

Julia Getzlaff ◽

Jean-Marc Molines ◽

Gurvan Madec

Keyword(s):

North Atlantic ◽

Decadal Variability ◽

North Atlantic Ocean ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Overturning Circulation ◽

Linear Character ◽

The North ◽

Basin Scale ◽

Meridional Overturning

Abstract The causes and characteristics of interannual–decadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models [the Family of Linked Atlantic Model Experiments (FLAME)] and global ocean–ice models (ORCA), varying in resolution from medium to eddy resolving (½°–1/12°), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the midlatitude MOC variability by demonstrating that the anomalies of a (non–eddy resolving) hindcast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep-water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and midlatitude North Atlantic, this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30°–35°N, by internally induced (eddy) fluctuations.

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