Abstract
Abstract. The Labrador Sea is one of a small number of deep convection sites in the North Atlantic that contribute to the meridional overturning circulation. Buoyancy is lost from surface waters during winter, allowing the formation of dense deep water. During the last few decades, mass loss from the Greenland ice sheet has accelerated, releasing freshwater into the high-latitude North Atlantic. This and the enhanced Arctic freshwater export in recent years have the potential to add buoyancy to surface waters, slowing or suppressing convection in the Labrador Sea. However, the impact of freshwater on convection is dependent on whether or not it can escape the shallow, topographically trapped boundary currents encircling the Labrador Sea. Previous studies have estimated the transport of freshwater into the central Labrador Sea by focusing on the role of eddies. Here, we use a Lagrangian approach by tracking particles in a global, eddy-permitting (1/12∘) ocean model to examine where and when freshwater in the surface 30 m enters the Labrador Sea basin. We find that 60 % of the total freshwater in the top 100 m enters the basin in the top 30 m along the eastern side. The year-to-year variability in freshwater transport from the shelves to the central Labrador Sea, as found by the model trajectories in the top 30 m, is dominated by wind-driven Ekman transport rather than eddies transporting freshwater into the basin along the northeast.
Highlights
In the Labrador Sea deep mixing and the formation of deep dense water are possible due to intense winter heat loss that removes surface buoyancy (Lazier, 1973; Clarke and Gascard, 1984; Pickart et al, 2002)
An example of a complete shutdown of deep water formation due to anomalous surface buoyancy and weak air–sea fluxes was observed during the Great Salinity Anomaly (GSA) in the 1970s (Dickson et al, 1988; Gelderloos et al, 2012)
To analyze the origin of the water that entered the basin in the northeast and southeast, we consider water originating in the East Greenland Current (EGC) as well as water from other regions in the North Atlantic separately
Summary
In the Labrador Sea deep mixing and the formation of deep dense water are possible due to intense winter heat loss that removes surface buoyancy (Lazier, 1973; Clarke and Gascard, 1984; Pickart et al, 2002). An eddy-resolving ice–ocean model that, according to the authors, performed better in the Labrador Sea than previous models, found that near-surface freshwater advection into the Labrador Sea basin increased (Kawasakim and Hasumi, 2014) This and previous studies failed to explain all of the seasonal freshwater fluxes by eddies alone. In this study we use Lagrangian trajectories in a high-resolution (1/12◦) numerical model to investigate how, when, and where surface freshwater from boundary currents enters the central Labrador Sea, in particular the relative importance of eddies vs wind in allowing freshwater to escape the shelves and enter the basin.
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