Recent Decadal Change in the North Atlantic Subtropical Underwater Associated With the Poleward Expansion of the Surface Salinity Maximum

AbstractSubtropical underwater (STUW) and its year-to-year variability in annual subduction rate are investigated using recently available Argo data in the North Atlantic. For the period of observation (2002–14), the mean annual subduction rate of the STUW is 7.3 ± 1.2 Sv (1 Sv = 106 m3 s−1) within the density range between 25.0 and 26.0 kg m−3. Once subducted, the STUW spreads in the subtropical gyre as a vertical salinity maximum. In the mean, the spatial changes in temperature and salinity of the STUW tend to compensate each other, and the density of the water mass remains rather stable near 25.5 kg m−3 in the southwestern part of the subtropical gyre. The annual subduction rate of the STUW varies from year to year, and most of this variability is due to lateral induction, which in turn is directly linked to the variability of the winter mixed layer depth. Through modulation of surface buoyancy, wind anomalies associated with the North Atlantic Oscillation are primarily responsible for this variability. Sea surface salinity anomalies in the formation region of the STUW are conveyed into the thermocline, but their westward propagation cannot be detected by the present data.

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Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

10.5194/egusphere-egu21-4608 ◽

2021 ◽

Author(s):

Jing Sun ◽

Mojib Latif ◽

Wonsun Park

Keyword(s):

North Atlantic ◽

Climate Model ◽

Deep Convection ◽

Meridional Overturning Circulation ◽

Subpolar Gyre ◽

Surface Salinity ◽

The North ◽

Ocean Coupling ◽

Meridional Overturning ◽

The North Atlantic

<p>There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA&#8217;s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.</p>

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Surface Salinity in the North Atlantic Subtropical Gyre During the STRASSE/SPURS Summer 2012 Cruise

Oceanography ◽

10.5670/oceanog.2015.09 ◽

2015 ◽

Vol 28 (1) ◽

pp. 114-123 ◽

Cited By ~ 12

Author(s):

Gilles Reverdin ◽

◽

Simon Morisset ◽

Louis Marieé ◽

Denis Bourras ◽

...

Keyword(s):

North Atlantic ◽

Subtropical Gyre ◽

Surface Salinity ◽

The North ◽

The North Atlantic

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Very low zonally asymmetric ozone values in March 1997 above the North Atlantic-European region, induced by dynamic processes

Annales Geophysicae ◽

10.1007/s00585-999-0933-4 ◽

1999 ◽

Vol 17 (7) ◽

pp. 933-940 ◽

Cited By ~ 5

Author(s):

G. Entzian ◽

D. Peters

Keyword(s):

North Atlantic ◽

Total Ozone ◽

Meteorological Parameters ◽

Middle Atmosphere ◽

European Region ◽

Dynamic Processes ◽

Decadal Change ◽

The North ◽

Pattern Correlation ◽

The North Atlantic

Abstract. The total ozone distribution in March 1997 showed very low values in the North Atlantic-European region, even lower than in the years before. A spatial pattern correlation between the zonally asymmetric part of total ozone and that of the 300 hPa surface geopotential of the Northern Hemisphere was applied to examine the spatial structure of the low ozone values and its dynamic dependence. A trend analysis in the North Atlantic-European region was carried out to determine to what extent the low March 1997 ozone values are related to the decadal change of meteorological parameters in the lower stratosphere, observed since the 1980s, in comparison to the interannual variability. The conclusion is that the very low ozone values above the North Atlantic-European region in March 1997 were mainly induced by dynamic processes, namely their decadal change as well as their interannual variability.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics)

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Comments on “Decadal Changes in the North Atlantic and Pacific Meridional Overturning Circulation and Heat Flux”

Journal of Physical Oceanography ◽

10.1175/2008jpo3827.1 ◽

2008 ◽

Vol 38 (9) ◽

pp. 2104-2107 ◽

Cited By ~ 15

Author(s):

Peter M. Saunders ◽

Stuart A. Cunningham ◽

Beverly A. de Cuevas ◽

Andrew C. Coward

Keyword(s):

Heat Flux ◽

North Atlantic ◽

Cold Water ◽

Current Level ◽

Meridional Overturning Circulation ◽

Decadal Change ◽

Overturning Circulation ◽

The North ◽

Meridional Overturning ◽

The North Atlantic

Abstract It is demonstrated that current level models, both with and without assimilation, generate too shallow an overturning in the North Atlantic (just like their predecessors) because they do not reproduce the descent of plumes of cold water from the Greenland and Norwegian Seas. Consequently, the prediction of decadal change from one such model reported by C. Wunsch and P. Heimbach is queried.

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Changes in surface salinity of the North Atlantic Ocean during the last deglaciation

Nature ◽

10.1038/358485a0 ◽

1992 ◽

Vol 358 (6386) ◽

pp. 485-488 ◽

Cited By ~ 191

Author(s):

J. C. Duplessy ◽

L. Labeyrie ◽

M. Arnold ◽

M. Paterne ◽

J. Duprat ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Last Deglaciation ◽

Surface Salinity ◽

The North ◽

The Last Deglaciation ◽

The North Atlantic

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Size Matters: Another Reason Why the Atlantic Is Saltier than the Pacific

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0075.1 ◽

2017 ◽

Vol 47 (11) ◽

pp. 2843-2859 ◽

Cited By ~ 6

Author(s):

C. S. Jones ◽

Paola Cessi

Keyword(s):

North Atlantic ◽

Deep Water ◽

Western Boundary Current ◽

Meridional Overturning Circulation ◽

Western Boundary ◽

Subpolar Gyre ◽

Boundary Current ◽

Surface Salinity ◽

The North ◽

The North Atlantic

AbstractThe surface salinity in the North Atlantic controls the position of the sinking branch of the meridional overturning circulation (MOC); the North Atlantic has higher salinity, so deep-water formation occurs there rather than in the North Pacific. Here, it is shown that in a 3D primitive equation model of two basins of different widths connected by a reentrant channel, there is a preference for sinking in the narrow basin even under zonally uniform surface forcing. This preference is linked to the details of the velocity and salinity fields in the “sinking” basin. The southward western boundary current associated with the wind-driven subpolar gyre has higher velocity in the wide basin than in the narrow basin. It overwhelms the northward western boundary current associated with the MOC for wide-basin sinking, so freshwater is brought from the far north of the domain southward and forms a pool on the western boundary in the wide basin. The fresh pool suppresses local convection and spreads eastward, leading to low salinities in the north of the wide basin for wide-basin sinking. This pool of freshwater is much less prominent in the narrow basin for narrow-basin sinking, where the northward MOC western boundary current overcomes the southward western boundary current associated with the wind-driven subpolar gyre, bringing salty water from lower latitudes northward and enabling deep-water mass formation.

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Salinity Trends within the Upper Layers of the Subpolar North Atlantic

Journal of Climate ◽

10.1175/jcli-d-17-0532.1 ◽

2018 ◽

Vol 31 (7) ◽

pp. 2675-2698 ◽

Cited By ~ 16

Author(s):

Jan-Erik Tesdal ◽

Ryan P. Abernathey ◽

Joaquim I. Goes ◽

Arnold L. Gordon ◽

Thomas W. N. Haine

Keyword(s):

North Atlantic ◽

Surface Wind ◽

Temporal Trends ◽

Labrador Sea ◽

Subpolar Gyre ◽

Surface Salinity ◽

Wind Stress Curl ◽

Near Surface ◽

The North ◽

The North Atlantic

Examination of a range of salinity products collectively suggests widespread freshening of the North Atlantic from the mid-2000s to the present. Monthly salinity fields reveal negative trends that differ in magnitude and significance between western and eastern regions of the North Atlantic. These differences can be attributed to the large negative interannual excursions in salinity in the western subpolar gyre and the Labrador Sea, which are not apparent in the central or eastern subpolar gyre. This study demonstrates that temporal trends in salinity in the northwest (including the Labrador Sea) are subject to mechanisms that are distinct from those responsible for the salinity trends in the central and eastern North Atlantic. In the western subpolar gyre a negative correlation between near-surface salinity and the circulation strength of the subpolar gyre suggests that negative salinity anomalies are connected to an intensification of the subpolar gyre, which is causing increased flux of freshwater from the East Greenland Current and subsequent transport into the Labrador Sea during the melting season. Analyses of sea surface wind fields suggest that the strength of the subpolar gyre is linked to the North Atlantic Oscillation– and Arctic Oscillation–driven changes in wind stress curl in the eastern subpolar gyre. If this trend of decreasing salinity continues, it has the potential to enhance water column stratification, reduce vertical fluxes of nutrients, and cause a decline in biological production and carbon export in the North Atlantic Ocean.

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Sea Surface Salinity and Temperature Budgets in the North Atlantic Subtropical Gyre during SPURS Experiment: August 2012-August 2013

Frontiers in Marine Science ◽

10.3389/fmars.2015.00107 ◽

2015 ◽

Vol 2 ◽

Cited By ~ 4

Author(s):

Anna Sommer ◽

Gilles Reverdin ◽

Nicolas Kolodziejczyk ◽

Jacqueline Boutin

Keyword(s):

North Atlantic ◽

Subtropical Gyre ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

The North ◽

The North Atlantic

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Spatial Optimal Interpolation of Aquarius Sea Surface Salinity: Algorithms and Implementation in the North Atlantic*

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00241.1 ◽

2014 ◽

Vol 31 (7) ◽

pp. 1583-1600 ◽

Cited By ~ 20

Author(s):

Oleg Melnichenko ◽

Peter Hacker ◽

Nikolai Maximenko ◽

Gary Lagerloef ◽

James Potemra

Keyword(s):

North Atlantic ◽

Estimation Error ◽

Sea Surface ◽

Sea Surface Salinity ◽

Optimal Interpolation ◽

Uniform Grid ◽

Surface Salinity ◽

The North ◽

The North Atlantic ◽

Along Track

Abstract A method is presented for mapping sea surface salinity (SSS) from Aquarius level-2 along-track data in order to improve the utility of the SSS fields at short length [O(150 km)] and time [O(1 week)] scales. The method is based on optimal interpolation (OI) and derives an SSS estimate at a grid point as a weighted sum of nearby satellite observations. The weights are optimized to minimize the estimation error variance. As an initial demonstration, the method is applied to Aquarius data in the North Atlantic. The key element of the method is that it takes into account the so-called long-wavelength errors (by analogy with altimeter applications), referred to here as interbeam and ascending/descending biases, which appear to correlate over long distances along the satellite tracks. The developed technique also includes filtering of along-track SSS data prior to OI and the use of realistic correlation scales of mesoscale SSS anomalies. All these features are shown to result in more accurate SSS maps, free from spurious structures. A trial SSS analysis is produced in the North Atlantic on a uniform grid with 0.25° resolution and a temporal resolution of one week, encompassing the period from September 2011 through August 2013. A brief statistical description, based on the comparison between SSS maps and concurrent in situ data, is used to demonstrate the utility of the OI analysis and the potential of Aquarius SSS products to document salinity structure at ~150-km length and weekly time scales.

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