Convection above the Labrador Continental Slope

Cuny, Jérôme; Rhines, Peter B.; Schott, Friedrich; Lazier, J. R.

doi:10.1175/jpo2700.1

Cited by 31 publications

(28 citation statements)

References 26 publications

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“…12). The simulated early start of LSW transformation within the nearboundary current region agrees well with recent findings of an observational study by Cuny et al (2005), who have done a detailed analysis of heat fluxes and mixed layer depths in the Labrador Sea based on observed CTD profiles and moored stations. Using early winter density profiles and applying air-sea heat fluxes, they derived mixed layer depths in late winter/early spring and compared them with the observed profiles.…”

Section: Summary and Discussionsupporting

confidence: 87%

Ventilation and Transformation of Labrador Sea Water and Its Rapid Export in the Deep Labrador Current

Brandt

Funk

Czeschel

et al. 2007

Journal of Physical Oceanography

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A model of the subpolar North Atlantic Ocean is used to study different aspects of ventilation and water mass transformation during a year with moderate convection intensity in the Labrador Sea. The model realistically describes the salient features of the observed hydrographic structure and current system, including boundary currents and recirculations. Ventilation and transformation rates are defined and compared. The transformation rate of Labrador Sea Water (LSW), defined in analogy to several observational studies, is 6.3 Sv (Sv ϵ 10 6 m 3 s Ϫ1) in the model. Using an idealized ventilation tracer, mimicking analyses based on chlorofluorocarbon inventories, an LSW ventilation rate of 10 Sv is found. Differences between both rates are particularly significant for those water masses that are partially transformed into denser water masses during winter. The main export route of the ventilated LSW is the deep Labrador Current (LC). Backward calculation of particle trajectories demonstrates that about one-half of the LSW leaving the Labrador Sea within the deep LC originates in the mixed layer during that same year. Near the offshore flank of the deep LC at about 55°W, the transformation of LSW begins in January and is at a maximum in February/March. While the export of transformed LSW out of the central Labrador Sea continues for several months, LSW generated near the boundary current is exported more rapidly, with maximum transport rates during March/April within the deep LC.

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Section: Summary and Discussionsupporting

confidence: 87%

Ventilation and Transformation of Labrador Sea Water and Its Rapid Export in the Deep Labrador Current

Brandt

Funk

Czeschel

et al. 2007

Journal of Physical Oceanography

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“…This memory of the basin interior results from the relatively slow eddy transfer of the newly formed dense water from the interior of the basin to the surrounding boundary current, which finally damps the influence of changes in dense water formation on dense water transport by the DWBC. Observations show that convection takes place not only in the center of the Labrador Sea, but also in the boundary current (Pickart et al, 1997;Cuny et al, 2005), which is not taken into account in this study. In the latter case, newly formed dense water would directly contribute to dense water export, as suggested by hindcast simulations (Deshayes et al, 2007).…”

Section: B Dense Water Formation In the Boundary Currentmentioning

confidence: 88%

Mechanisms of variability in a convective basin

Deshayes¹,

Straneo²,

Spall³

2009

J Mar Res

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An idealized model for a convective basin is used to investigate the mechanisms of variability of the formation and export of dense water. In this model, which consists of two isopycnic layers, dense water formation is induced by surface buoyancy loss in the interior, which is at rest. Newly formed dense water is transmitted to the surrounding boundary current through parameterized eddy fluxes. Variability in the formation and export of dense water is due to changes in the two main drivers: variations in the surface buoyancy fluxes and variations in the large-scale wind via a barotropic boundary current. Numerical integrations of the nonlinear model, with parameters and forcings corresponding to the Labrador Sea, show that the rate of dense water formation in the interior of the basin is strongly affected by changes in the buoyancy forcing, but not significantly affected by seasonal to interannual changes in the wind-driven barotropic boundary current. The basin tends to integrate the buoyancy forcing variability with a memory time scale set by eddies, which is decadal for the Labrador Sea. Variability in dense water export, on the contrary, is strongly affected by changes in the wind-driven barotropic boundary current but hardly affected by changes in buoyancy forcing. Indeed changes in the transport of dense water at the basin outflow are dominated by those at the basin inflow, which, in this model, are directly related to fluctuations in the wind-driven barotropic boundary current. These results, which are consistent with analytical solutions of the linear model, suggest that fluctuations in the surface buoyancy fluxes in the interior Labrador Sea have little impact on the interannual variability of the dense water transport by the Deep Western Boundary Current at the outflow of the Labrador Sea, which is dominated by fluctuations in the wind-driven North Atlantic subpolar gyre, but influence the formation and export of recently ventilated waters.

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“…The freshwater transport across a section is given at time t by (1) where F is the freshwater (S 0 -S)/S 0 , with S 0 = 34.8 (the reference salinity for the Arctic used by Cuny et al 2005), v is the velocity normal to the section, x is the location along the section and z the depth. Time series of the yearly northward freshwater transport across section A25 and the southward one across section OFLW were calculated using monthly data.…”

Section: The Freshwater Budget Of the Eastern Subpolar Gyrementioning

confidence: 99%

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

2009

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An OGCM hindcast is used to investigate the linkages between North Atlantic Ocean salinity and circulation changes during . The focus is on the eastern subpolar region consisting of the Irminger Sea and the eastern North Atlantic where a careful assessment shows that the simulated interannual to decadal salinity changes in the upper 1500 m reproduce well those derived from the available record of hydrographic measurements. In the model, the variability of the Atlantic meridional overturning circulation (MOC) is primarily driven by changes in deep water formation taking place in the Irminger Sea and, to a lesser extent, the Labrador Sea. Both are strongly influenced by the North Atlantic Oscillation (NAO). The modeled interannual to decadal salinity changes in the subpolar basins are mostly controlled by circulation-driven anomalies of freshwater flux convergence, although surface salinity restoring to climatology and other boundary fluxes each account for approximately 25% of the variance. The NAO plays an important role: a positive NAO phase is associated with increased precipitation, reduced northward salt transport by the wind-driven intergyre gyre, and increased southward flows of freshwater across the Greenland-Scotland ridge. Since the NAO largely controlled deep convection in the subpolar gyre, fresher waters are found near the sinking region during convective events. This markedly differs from the active influence on the MOC that salinity exerts at decadal and longer timescales in most coupled models. The intensification of the MOC that follows a positive NAO phase by about 2 years does not lead to an increase in the northward salt transport into the subpolar domain at low frequencies because it is cancelled by the concomitant intensification of the subpolar gyre which shifts the subpolar front eastward and reduces the northward salt transport by the North Atlantic Current waters. This differs again from most coupled models, where the gyre intensification precedes that of the MOC by several years.3

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Convection above the Labrador Continental Slope

Cited by 31 publications

References 26 publications

Ventilation and Transformation of Labrador Sea Water and Its Rapid Export in the Deep Labrador Current

Ventilation and Transformation of Labrador Sea Water and Its Rapid Export in the Deep Labrador Current

Mechanisms of variability in a convective basin

The role of salinity in the decadal variability of the North Atlantic meridional overturning circulation

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