Rapid Export of Waters Formed by Convection Near the Irminger Sea's Western Boundary

Bras, Isabela Le; Straneo, F.; Holte, James; Jong, M. Femke de; Holliday, N. Penny

doi:10.1029/2019gl085989

Cited by 40 publications

(59 citation statements)

References 58 publications

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“…With regard to the latter, the sea surface height anomaly generated by such winds trigger coastally trapped waves which propagate southward and lead to the enhancement of the EGCC downstream of the region of strong winds (Harden et al 2014a(Harden et al ,b, 2016Le Bras et al 2018). Seasonally, the wind stress field peaks in fall in the Irminger Sea, which is consistent with the increased EGCC transport measured at the MA4 array during that season (Le Bras et al 2018). We now investigate the role of wind forcing for the WGCC using the ERA5 wind stress fields.…”

Section: ) Upper Polar Watersupporting

confidence: 52%

“…With regard to the former, downwellingfavorable winds along the east coast of Greenland intensify the EGCC via Ekman setup (Sutherland and Pickart 2008;Daniault et al 2011). With regard to the latter, the sea surface height anomaly generated by such winds trigger coastally trapped waves which propagate southward and lead to the enhancement of the EGCC downstream of the region of strong winds (Harden et al 2014a(Harden et al ,b, 2016Le Bras et al 2018). Seasonally, the wind stress field peaks in fall in the Irminger Sea, which is consistent with the increased EGCC transport measured at the MA4 array during that season (Le Bras et al 2018).…”

Section: ) Upper Polar Watermentioning

confidence: 99%

“…In addition to advecting water masses equatorward via the mean flow, strong mesoscale variability (e.g., Lilly et al 1999) and Ekman transport play important roles in the exchange of waters between the boundary current and the interior Labrador Sea (Luo et al 2016;Schulze Chretien and Frajka-Williams 2018). This is vital for modulating the convective overturning during winter, restratifying the interior during spring (e.g., Straneo 2006), and fluxing the newly ventilated LSW to lower latitudes (e.g., Le Bras et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

Pacini

Pickart

Bahr

et al. 2020

Journal of Physical Oceanography

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The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014-2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper-slope and UPW at the surface; and the Deep Western Boundary Current which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The four-year mean transport of the full boundary current system is 31.1 ± 7.4 Sv, with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air-sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anti-correlation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.

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Section: ) Upper Polar Watersupporting

confidence: 52%

Section: ) Upper Polar Watermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

Pacini

Pickart

Bahr

et al. 2020

Journal of Physical Oceanography

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“…The length of this delay—between the formation of dense water and its export to the boundary current in a marginal sea, such as the Irminger Sea—is consistent with modeling studies that attribute the exchange between the convective region and the boundary current to an eddy transport mechanism (Brüggemann & Katsman, 2019; Sayol et al, 2019). The delay depends upon the location of the convection and ranges from 3 months if convection takes place along the Irminger Current to more than 12 months if it is in the interior of the Irminger Sea (Le Bras et al, 2020).…”

Section: Resultsmentioning

confidence: 99%

Atlantic Deep Water Formation Occurs Primarily in the Iceland Basin and Irminger Sea by Local Buoyancy Forcing

Petit

Lozier

Josey

et al. 2020

Geophysical Research Letters

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The Atlantic Meridional Overturning Circulation (AMOC), a key mechanism in the climate system, delivers warm and salty waters from the subtropical gyre to the subpolar gyre and Nordic Seas, where they are transformed into denser waters flowing southward in the lower AMOC limb. The prevailing hypothesis is that dense waters formed in the Labrador and Nordic Seas are the sources for the AMOC lower limb. However, recent observations reveal that convection in the Labrador Sea contributes minimally to the total overturning of the subpolar gyre. In this study, we show that the AMOC is instead primarily composed of waters formed in the Nordic Seas and Irminger and Iceland basins. A first direct estimate of heat and freshwater fluxes over these basins demonstrates that buoyancy forcing during the winter months can almost wholly account for the dense waters of the subpolar North Atlantic that are exported as part of the AMOC.

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“…Traditionally, the LSW was considered the product of deep convection that takes place in the central Labrador Sea (Marshall & Schott, 1999;Talley & McCartney, 1982). However, more recent studies revealed that deep convection also occurs in the southern Irminger Sea and that this results in a water mass with similar properties similar to LSW (de Jong et al, 2012;Le Bras et al, 2020;Pickart et al, 2003;Piron et al, 2016;Våge et al, 2008).…”

mentioning

confidence: 99%

Direct and Indirect Pathways of Convected Water Masses and Their impacts on the Overturning Dynamics of the Labrador Sea

et al. 2021

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The dense waters formed by wintertime convection in the Labrador Sea play a key role in setting the properties of the deep Atlantic Ocean. To understand how variability in their production might affect the Atlantic Meridional Overturning Circulation (AMOC) variability, it is essential to determine pathways and associated timescales of their export. In this study, we analyze the trajectories of Argo floats and of Lagrangian particles launched at 53°N in the boundary current and traced backward in time in a high-resolution model, to identify and quantify the importance of upstream pathways. We find that 85% of the transport carried by the particles at 53°N originates from Cape Farewell, and it is split between a direct route that follows the boundary current and an indirect route involving boundary-interior exchanges. Although both routes contribute roughly equally to the maximum overturning, the indirect route governs its signal in denser layers. This indirect route has two branches: part of the convected water is exported rapidly on the Labrador side of the basin and part follows a longer route toward Greenland and is then carried with the boundary current. Export timescales of these two branches typically differ by 2.5 years. This study thus shows that boundary-interior exchanges are important for the pathways and the properties of water masses arriving at 53°N. It reveals a complex three-dimensional view of the convected water export, with implications for the arrival time of signals of variability therein at 53°N and thus for our understanding of the AMOC.

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Rapid Export of Waters Formed by Convection Near the Irminger Sea's Western Boundary

Cited by 40 publications

References 58 publications

Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

Atlantic Deep Water Formation Occurs Primarily in the Iceland Basin and Irminger Sea by Local Buoyancy Forcing

Direct and Indirect Pathways of Convected Water Masses and Their impacts on the Overturning Dynamics of the Labrador Sea

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