scholarly journals Impact of the Atlantic meridional overturning circulation on the decadal variability of the Gulf Stream path and regional chlorophyll and nutrient concentrations

2015 ◽  
Vol 42 (22) ◽  
pp. 9889-9887 ◽  
Author(s):  
A. Sanchez-Franks ◽  
R. Zhang
Keyword(s):  
Gulf Stream ◽  
Decadal Variability ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Nutrient Concentrations ◽  
Overturning Circulation ◽  
Meridional Overturning

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

2015 ◽  
Vol 45 (7) ◽  
pp. 1929-1946 ◽  
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).

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

2014 ◽  
Vol 27 (17) ◽  
pp. 6439-6455 ◽  
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.

A New Pacific Influence on the Atlantic Meridional Overturning Circulation

2021 ◽  
Author(s):  
Leon Hermanson ◽  
Doug Smith ◽  
Nick Dunstone ◽  
Rosie Eade
Keyword(s):  
Decadal Variability ◽  
Atlantic Meridional Overturning Circulation ◽  
Tropical Pacific ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Strong Impact ◽  
Overturning Circulation ◽  
Southern Us ◽  
Volcanic Forcing ◽  
Meridional Overturning

<p>The Atlantic Meridional Overturning Circulation (AMOC) at 26N has been measured since 2004 by the RAPID-MOCHA array. On a multi-year timescale it shows a decline with signs of a recovery since around 2012. This variability is likely to be part of longer decadal variability. We examine here the decadal variability of the AMOC and its drivers in a coupled model run nudged to observations from 1960-2017. Temperature and winds are nudged throughout the atmosphere and potential temperature and salinity are nudged in the ocean, but the ocean velocities are allowed to vary freely. We nudge an ensemble of 10 ocean analyses into the ocean model to get an ensemble of responses, the mean of which reproduces the observed AMOC. We use these ocean-atmosphere re-analyses to study the drivers of the AMOC. The North Atlantic Oscillation (NAO) is well known to have an impact on the AMOC and is an important driver here. We find that the tropical Pacific also has a strong impact on the subtropical AMOC on multi-annual to decadal timescales. Together these two factors can explain more than half of all variability of the AMOC at 26N through wind forcing associated with Rossby waves and western boundary waves. This Pacific impact, not reported on before, is from windstress curl anomalies close to the East Coast of the southern US due to changes in the Pacific storm track and the Walker Circulation. As both the NAO and tropical Pacific variability is associated with solar and volcanic forcing, it is possible that solar and volcanic forcing are important for multi-annual to multi-decadal AMOC variability. We use observations of the NAO and tropical Pacific to reconstruct the AMOC from 1870 to present day and predict a continued recovery in the future.</p>

scholarly journals Observed decline of the Atlantic meridional overturning circulation 2004–2012

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 29-38 ◽  
Author(s):  
D. A. Smeed ◽  
G. D. McCarthy ◽  
S. A. Cunningham ◽  
E. Frajka-Williams ◽  
D. Rayner ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Gulf Stream ◽  
Atlantic Meridional Overturning Circulation ◽  
North Atlantic Deep Water ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
Southward Flow

Abstract. The Atlantic meridional overturning circulation (AMOC) has been observed continuously at 26° N since April 2004. The AMOC and its component parts are monitored by combining a transatlantic array of moored instruments with submarine-cable-based measurements of the Gulf Stream and satellite derived Ekman transport. The time series has recently been extended to October 2012 and the results show a downward trend since 2004. From April 2008 to March 2012, the AMOC was an average of 2.7 Sv (1 Sv = 106 m3 s−1) weaker than in the first four years of observation (95% confidence that the reduction is 0.3 Sv or more). Ekman transport reduced by about 0.2 Sv and the Gulf Stream by 0.5 Sv but most of the change (2.0 Sv) is due to the mid-ocean geostrophic flow. The change of the mid-ocean geostrophic flow represents a strengthening of the southward flow above the thermocline. The increased southward flow of warm waters is balanced by a decrease in the southward flow of lower North Atlantic deep water below 3000 m. The transport of lower North Atlantic deep water slowed by 7% per year (95% confidence that the rate of slowing is greater than 2.5% per year).

scholarly journals Observed decline of the Atlantic Meridional Overturning Circulation 2004 to 2012

2013 ◽  
Vol 10 (5) ◽  
pp. 1619-1645 ◽  
Author(s):  
D. A. Smeed ◽  
G. McCarthy ◽  
S. A. Cunningham ◽  
E. Frajka-Williams ◽  
D. Rayner ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Gulf Stream ◽  
Atlantic Meridional Overturning Circulation ◽  
North Atlantic Deep Water ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
Southward Flow

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) has been observed continuously at 26° N since April 2004. The AMOC and its component parts are monitored by combining a transatlantic array of moored instruments with submarine-cable based measurements of the Gulf Stream and satellite derived Ekman transport. The time series has recently been extended to October 2012 and the results show a downward trend since 2004. From April~2008 to March 2012 the AMOC was an average of 2.7 Sv weaker than in the first four years of observation (95% confidence that the reduction is 0.3 Sv or more). Ekman transport reduced by about 0.2 Sv and the Gulf Stream by 0.5 Sv but most of the change (2.0 Sv) is due to the mid-ocean geostrophic flow. The change of the mid-ocean geostrophic flow represents a strengthening of the subtropical gyre above the thermocline. The increased southward flow of warm waters is balanced by a decrease in the southward flow of Lower North Atlantic Deep Water below 3000 m. The transport of Lower North Atlantic Deep Water slowed by 7% per year (95% confidence that the rate of slowing is greater than 2.5% per year).

scholarly journals On the Path of the Gulf Stream and the Atlantic Meridional Overturning Circulation

2010 ◽  
Vol 23 (11) ◽  
pp. 3146-3154 ◽  
Author(s):  
Terrence M. Joyce ◽  
Rong Zhang
Keyword(s):  
Gulf Stream ◽  
Climate Model ◽  
Numerical Models ◽  
Internal Variability ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
The Relationship ◽  
Ocean Observations

Abstract The Atlantic meridional overturning circulation (AMOC) simulated in various ocean-only and coupled atmosphere–ocean numerical models often varies in time because of either forced or internal variability. The path of the Gulf Stream (GS) is one diagnostic variable that seems to be sensitive to the amplitude of the AMOC, yet previous modeling studies show a diametrically opposed relationship between the two variables. In this note this issue is revisited, bringing together ocean observations and comparisons with the GFDL Climate Model version 2.1 (CM2.1), both of which suggest a more southerly (northerly) GS path when the AMOC is relatively strong (weak). Also shown are some examples of possible diagnostics to compare various models and observations on the relationship between shifts in GS path and changes in AMOC strength in future studies.

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