Mesoscale eddies in the Labrador Sea and their contribution to convection and restratification

• Published in: Journal of Physical Oceanography
• Other Authors: Chanut, Jérôme (author), Barnier, Bernard (author), Large, William (author), Debreu, Laurent (author), Penduff, Thierry (author), Molines, Jean (author), Mathiot, Pierre (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2008
• Subjects: Eddies; Ocean circulation; Ocean dynamics; North Atlantic Ocean; Boundary currents; Central Basin; Greenland; Labrador Sea; North Atlantic
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-002-429; https://doi.org/10.1175/2008JPO3485.1

The cycle of open ocean deep convection in the Labrador Sea is studied in a realistic, high-resolution (4 km) regional model, embedded in a coarser (⅓°) North Atlantic setup. This configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region, generation mechanism, and dynamics. Very energetic Irminger Rings (IRs) are generated by barotropic instability of the West Greenland and Irminger Currents (WGC/IC) off Cape Desolation and are characterized by a warm, salty subsurface core. They densely populate the basin north of 58°N, where their eddy kinetic energy (EKE) matches the signal observed by satellite altimetry. Significant levels of EKE are also found offshore of the West Greenland and Labrador coasts, where boundary current eddies (BCEs) are spawned by weakly energetic instabilities all along the boundary current system (BCS). Baroclinic instability of the steep isopycnal slopes that result from a deep convective overturning event produces convective eddies (CEs) of 20-30 km in diameter, as observed and produced in more idealized models, with a distinct seasonal cycle of EKE peaking in April. Sensitivity experiments show that each of these eddy types plays a distinct role in the heat budget of the central Labrador Sea, hence in the convection cycle. As observed in nature, deep convective mixing is limited to areas where adequate preconditioning can occur, that is, to a small region in the southwestern quadrant of the central basin. To the east, west, and south, BCEs flux heat from the BCS at a rate sufficient to counteract air-sea buoyancy loss. To the north, this eddy flux alone is not enough, but when combined with the effects of Irminger Rings, preconditioning is effectively inhibited here too. Following a deep convective mixing event, the homogeneous convection patch reaches as deep as 2000 m and a horizontal scale on the order of 200 km, as has been observed. Both CEs and BCEs are found to play critical roles in the lateral ...