scholarly journals Simulated Variability of the Circulation in the North Atlantic from 1953 to 2003

2008 ◽  
Vol 21 (19) ◽  
pp. 4919-4933 ◽  
Author(s):  
Julie Deshayes ◽  
Claude Frankignoul
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
Labrador Sea ◽  
Ekman Pumping ◽  
Subpolar Gyre ◽  
Dense Water ◽  
The North ◽  
Irminger Sea ◽  
Dense Water Formation ◽  
The North Atlantic

Abstract The variability of the circulation in the North Atlantic and its link with atmospheric variability are investigated in a realistic hindcast simulation from 1953 to 2003. The interannual-to-decadal variability of the subpolar gyre circulation and the Meridional Overturning Circulation (MOC) is mostly influenced by the North Atlantic Oscillation (NAO). Both circulations intensified from the early 1970s to the mid-1990s and then decreased. The monthly variability of both circulations reflects the fast barotropic adjustment to NAO-related Ekman pumping anomalies, while the interannual-to-decadal variability is due to the baroclinic adjustment to Ekman pumping, buoyancy forcing, and dense water formation, consistent with previous studies. An original characteristic of the oceanic response to NAO is presented that relates to the spatial patterns of buoyancy and wind forcing over the North Atlantic. Anomalous Ekman pumping associated with a positive NAO phase first induces a decrease of the southern subpolar gyre strength and an intensification of the northern subpolar gyre. The latter is reinforced by buoyancy loss and dense water formation in the Irminger Sea, where the cyclonic circulation increases 1–2 yr after the positive NAO phase. Increased buoyancy loss also occurs in the Labrador Sea, but because of the early decrease of the southern subpolar gyre strength, the intensification of the cyclonic circulation is delayed. Hence the subpolar gyre and the MOC start increasing in the Irminger Sea, while in the Labrador Sea the circulation at depth leads its surface counterpart. In this simulation where the transport of dense water through the North Atlantic sills is underestimated, the MOC variability is well represented by a simple integrator of convection in the Irminger Sea, which fits better than a direct integration of NAO forcing.

scholarly journals The recent AMOC variability in the Subpolar Gyre: results across the OVIDE section

2020 ◽  
Author(s):  
Pascale Lherminier ◽  
Herlé Mercier ◽  
Fiz F. Perez ◽  
Marcos Fontela
Keyword(s):  
North Atlantic ◽  
Lower Limb ◽  
Deep Convection ◽  
Labrador Sea ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
Subarctic Front ◽  
The North Atlantic ◽  
Atlantic Current

<p><span>According to the subpolar AMOC index built from ARGO and altimetry, the AMOC amplitude across the OVIDE section (from Greenland to Portugal) was similar to that of the mid-1990s between 2014 and 2017, i.e. 4-5 Sv above the level of the 2000s. It then returned to average values in 2018. The same index computed independently from the biennial summer cruises over 2002-2018 confirms this statement. Interestingly, despite the concomitant cold and fresh anomaly in the subpolar Atlantic, the heat flux across OVIDE remains correlated with the AMOC amplitude. This can be explained by the paths taken by the North Atlantic Current and the transport anomalies in the subarctic front. In 2014, the OVIDE section was complemented by a section from Greenland to Newfoundland (GA01), showing how the water of the lower limb of the AMOC was densified by deep convection in the Labrador Sea. The spatial patterns of volume, heat, salt and oxygen transport anomalies after 2014 will be discussed at the light of the 2000s average.</span></p>

scholarly journals Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

2018 ◽  
Author(s):  
Manon Tonnard ◽  
Hélène Planquette ◽  
Andrew R. Bowie ◽  
Pier van der Merwe ◽  
Morgane Gallinari ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Sea Water ◽  
North Atlantic Ocean ◽  
Deep Convection ◽  
Labrador Sea ◽  
Intermediate Water ◽  
The North ◽  
Irminger Sea ◽  
The North Atlantic

Abstract. Dissolved Fe (DFe) samples from the GEOVIDE voyage (GEOTRACES GA01, May–June 2014) in the North Atlantic Ocean were analysed using a SeaFAST-picoTM coupled to an Element XR HR-ICP-MS and provided interesting insights on the Fe sources in this area. Overall, DFe concentrations ranged from 0.09 ± 0.01 nmol L−1 to 7.8 ± 0.5 nmol L−1. Elevated DFe concentrations were observed above the Iberian, Greenland and Newfoundland Margins likely due to riverine inputs from the Tagus River, meteoric water inputs and sedimentary inputs. Air-sea interactions were suspected to be responsible for the increase in DFe concentrations within subsurface waters of the Irminger Sea due to deep convection occurring the previous winter, that provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth. Increasing DFe concentrations along the flow path of the Labrador Sea Water were attributed to sedimentary inputs from the Newfoundland Margin. Bottom waters from the Irminger Sea displayed high DFe concentrations likely due to the dissolution of Fe-rich particles from the Denmark Strait Overflow Water and the Polar Intermediate Water. Finally, the nepheloid layers were found to act as either a source or a sink of DFe depending on the nature of particles.

scholarly journals Arctic/Atlantic Exchanges via the Subpolar Gyre*

2012 ◽  
Vol 25 (7) ◽  
pp. 2421-2439 ◽  
Author(s):  
Helene R. Langehaug ◽  
Iselin Medhaug ◽  
Tor Eldevik ◽  
Odd Helge Otterå
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Decadal Variability ◽  
Sea Water ◽  
Similar Response ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
Atmospheric Variability ◽  
The North ◽  
The North Atlantic

Abstract In the present study the decadal variability in the strength and shape of the subpolar gyre (SPG) in a 600-yr preindustrial simulation using the Bergen Climate Model is investigated. The atmospheric influence on the SPG strength is reflected in the variability of Labrador Sea Water (LSW), which is largely controlled by the North Atlantic Oscillation, the first mode of the North Atlantic atmospheric variability. A combination of the amount of LSW, the overflows from the Nordic seas, and the second mode of atmospheric variability, the East Atlantic Pattern, explains 44% of the modeled decadal variability in the SPG strength. A prior increase in these components leads to an intensified SPG in the western subpolar region. Typically, an increase of one standard deviation (std dev) of the total overflow (1 std dev = 0.2 Sv; 1 Sv ≡ 106 m3 s−1) corresponds to an intensification of about one-half std dev of the SPG strength (1 std dev = 2 Sv). A similar response is found for an increase of one std dev in the amount of LSW, and simultaneously the strength of the North Atlantic Current increases by one-half std dev (1 std dev = 0.9 Sv).

Interannual and decadal variability of the oceanic carbon sink in the North Atlantic subpolar gyre

Tellus B ◽  
2007 ◽  
Vol 59 (2) ◽  
Author(s):  
Antoine Corbière ◽  
Nicolas Metzl ◽  
Gilles Reverdin ◽  
Christian Brunet ◽  
Taro Takahashi
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
Carbon Sink ◽  
Subpolar Gyre ◽  
The North ◽  
North Atlantic Subpolar Gyre ◽  
Interannual And Decadal Variability ◽  
The North Atlantic ◽  
Oceanic Carbon

First Records of the Gymnoblastic Hydroid, Ichthyocodium sarcotretis, on the Copepod, Sphyrion lumpi, from Redfish of the Northwest Atlantic

1973 ◽  
Vol 30 (11) ◽  
pp. 1655-1660 ◽  
Author(s):  
Wilfred Templeman
Keyword(s):  
Continental Shelf ◽  
North Atlantic ◽  
Labrador Sea ◽  
Northwest Atlantic ◽  
The North ◽  
Irminger Sea ◽  
The North Atlantic ◽  
Sebastes Mentella ◽  
Colonial Hydroid

The gymnoblastic colonial hydroid Ichthyocodium sarcotretis was found on the copepod Sphyrion lumpi on redfish from three areas of the northwest Atlantic: on copepods (three of ten) on deepwater redfish (Sebastes mentella) from about 200–500 m over great depths at the mouth of the Labrador Sea and, in bottom otter trawling, on copepods on S. mentella or possibly S. fasciatus from the Labrador Shelf (6 of 686) and the northeast Newfoundland Shelf (1 of 364). None were found on 492 S. lumpi from redfish taken on the continental shelf south and west of the northeast Newfoundland Shelf.The characteristics of the hydroid colonies and of their feeding polyps and reproductive hydranths and medusae are compared with published information on this hydroid found on the same hosts in the Irminger Sea and on the copepod, Sarcotretes scopeli, on the lantern fish, Benthosema glaciale, in the North Atlantic. The incidence of the hydroid on S. lumpi on redfish may possibly help in distinguishing Sebastes species in the northwest Atlantic.

The Origins of Late-Twentieth-Century Variations in the Large-Scale North Atlantic Circulation

2014 ◽  
Vol 27 (9) ◽  
pp. 3222-3247 ◽  
Author(s):  
Stephen Yeager ◽  
Gokhan Danabasoglu
Keyword(s):  
Twentieth Century ◽  
North Atlantic ◽  
Decadal Variability ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
The North ◽  
Late Twentieth ◽  
The North Atlantic ◽  
Late Twentieth Century

Abstract Surface forcing perturbation experiments are examined to identify the key forcing elements associated with late-twentieth-century interannual-to-decadal Atlantic circulation variability as simulated in an ocean–sea ice hindcast configuration of the Community Earth System Model, version 1 (CESM1). Buoyancy forcing accounts for most of the decadal variability in both the Atlantic meridional overturning circulation (AMOC) and the subpolar gyre circulation, and the key drivers of these basin-scale circulation changes are found to be the turbulent buoyancy fluxes: evaporation as well as the latent and sensible heat fluxes. These three fluxes account for almost all of the decadal AMOC variability in the North Atlantic, even when applied only over the Labrador Sea region. Year-to-year changes in surface momentum forcing explain most of the interannual AMOC variability at all latitudes as well as most of the decadal variability south of the equator. The observed strengthening of Southern Ocean westerly winds accounts for much of the simulated AMOC variability between 30°S and the equator but very little of the recent AMOC change in the North Atlantic. Ultimately, the strengthening of the North Atlantic overturning circulation between the 1970s and 1990s, which contributed to a pronounced SST increase at subpolar latitudes, is explained almost entirely by trends in the atmospheric surface state over the Labrador Sea.

On the Temporally Varying Northward Penetration of Mediterranean Overflow Water and Eastward Penetration of Labrador Sea Water

2008 ◽  
Vol 38 (9) ◽  
pp. 2097-2103 ◽  
Author(s):  
M. Susan Lozier ◽  
Nicole M. Stewart
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Sea Water ◽  
Labrador Sea ◽  
Subpolar Gyre ◽  
The North ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
The North Atlantic Oscillation ◽  
Water Mass Transformations

Abstract Historical hydrographic data in the eastern North Atlantic are used to suggest a connection between the northward penetration of Mediterranean Overflow Water (MOW) and the location of the subpolar front, the latter of which is shown to vary with the North Atlantic Oscillation (NAO). During persistent high-NAO periods, when the subpolar front moves eastward, waters in the subpolar gyre essentially block the northward-flowing MOW, preventing its entry into the subpolar gyre. Conversely, during low NAO periods, the subpolar front moves westward, allowing MOW to penetrate past Porcupine Bank into the subpolar gyre. The impacts of an intermittent penetration of MOW into the subpolar gyre, including the possible effect on water mass transformations, remain to be investigated.

scholarly journals Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning

2006 ◽  
Vol 33 (21) ◽  
Author(s):  
C. W. Böning ◽  
M. Scheinert ◽  
J. Dengg ◽  
A. Biastoch ◽  
A. Funk
Keyword(s):  
North Atlantic ◽  
Decadal Variability ◽  
Subpolar Gyre ◽  
The North ◽  
The North Atlantic

scholarly journals Salinity Trends within the Upper Layers of the Subpolar North Atlantic

2018 ◽  
Vol 31 (7) ◽  
pp. 2675-2698 ◽  
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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