Labrador Sea winter heat and freshwater content observations from glider
and Argo data
Abstract
The Labrador Sea undergoes deep mixing in the wintertime, with mixed
layer depths frequently reaching down to 2000 m. The resulting water
mass that is formed - Labrador Sea Water (LSW) - has long been thought
to be important for the deep Western Boundary Current (dWBC) and the
upper limb of the AMOC. Direct observations of the overturning have,
however, been rather limited. Limited Argo profiles and moorings in key
locations offered winter measurements in a region challenged by severe
weather conditions. Here we discuss observations of a winter-spring
glider deployment in the Labrador Sea, but more specifically where deep
convection occurs, from December 2019- to June 2020. Using the glider
data, we describe the evolution of the mixed layer, changes in heat and
freshwater content for surface (0-500 m) and intermediate depth
(500-1000 m) layers for the central Labrador Sea convection region
inside a box 200 by 100 km wide and spatial scales of T and S. We
compare the observations with reanalysis data (air-sea heat fluxes and
winds) and Argo profiles to better understand the variability missed by
existing datasets. These observations highlight the role played by
eddies in the overall variability of heat and salt in this region,
something that is missed by Argo observations. They also show changes in
spatial scales of T-S over the months from January to May, pointing
towards the modulating effect of eddies on LSW winter formation.