The key role of submesoscale advection in the formation of Labrador Sea water.
Annalisa Bracco, Georgia Institute of Technology Main Campus, Earth and Atmospheric Sciences, Atlanta, GA, United States, Filippos Tagklis, Georgia Institute of Technology Main Campus, Earth and Atmospheric science, Atlanta, United States, Takamitsu Ito, Georgia Institute of Technology, Atlanta, United States and Renato M Castelao, University of Georgia, Marine Sciences, Athens, United States
Abstract:
The Labrador Sea (LS) is one of the North Atlantic sites where deep convection occurs, forming a fresh, cold and oxygenated water mass, the Labrador Sea Water (LSW). Several factors contribute to the LS hydrography and its variability, with the atmospheric heat fluxes and the hydrography of the Irminger Current that flows around Greenland being key players. Freshwater inputs from the Arctic and Greenland Ice Sheet (GrIs) melting and continental runoff are also important for setting the stratification in the basin, that in turns modulates the response of winter convection to atmospheric cooling. Over the recent decades, GrIS mass losses accelerated, resulting in increased freshwater inputs. Future projections suggest a further exponential acceleration over the next decade. Global climate models have been used to attribute to these freshwater anomalies the potential for reducing LS convection and weakening the Atlantic Meridional Overturning Circulation. Regionally focused experiments at 2.5 km horizontal resolution, however, have shown a more reduced impact with only 1-15% of the surface meltwater runoff from southwest Greenland being transported off-shore the continental shelf and up to 50-60% of the meltwater from southeast Greenland being carried into the LS interior whenever winds are favorable. Little is known of the contribution that submesoscale processes on spatial scales of O(1–5 km) in the horizontal and O(100 m) vertical, and temporal scales of O(1 day), bring to the advection and mixing of these freshwater anomalies.
To further explore the advection pathways of the GrIs meltwater and its role in modulating the LS convection in conjunction with the mesoscale and smaller circulations, we present results from two mesoscale permitting, two mesoscale resolving and four submesoscale permitting regional model simulations, focusing on the representation of LSW formation.
The volume of LSW formed in simulations that do not resolve well mesoscale eddies and do not include GrIs melting LSW is seven times greater than in the submesoscale permitting runs including GrIs melting. Convergence in the representation of LSW formation is found at/below 1.7 km horizontal resolution. A comparison with ARGO data completes the work. Implications for interpreting climate model outputs are discussed.
