Kinematic Subduction Rate Of Labrador Sea Water From an Eddy-Permitting Numerical Model

We use an eddy-permitting, 1/12 degrees regional configuration of the Nucleus for European Modelling of the Ocean (NEMO) model to examine water mass subduction rates in the Labrador Sea for the 2002-2013 period. An instantaneous kinematic subduction approach is implemented to calculate the subduction rate of Labrador Sea Water (LSW). By following the outcrop positions of a given isopycncal range, we calculate the vertical transport of a water mass from the mixed layer into the permanent thermocline over the course of a year. We examine the importance of the various terms in this approach, including the evolution of the Mixed Layer Depth (MLD), the advection across the base of the Mixed Layer (ML), and the vertical velocity at the base of the ML. We find that the subduction rate is not greatly affected by the definition of the MLD, as long as the integration time is long enough for the subduction-obduction processes to balance each other. The total LSW subduction rate is similar to 4-5 Sv, with similar rates for both Upper (ULSW) and Classical LSWs (CLSW), (similar to 2-2.5 Sv). After 2008, a shift in the LSW density is found in the simulation. CLSW reaches a maximum rate of 6 Sv in 2008, which is mainly inferred by the instantaneous ML change.