Abstract:
The Labrador Sea, as one of a few places of deep water formation, plays an important
role in the Meridional Overturning Circulation. While the interior of the Labrador
Sea, where the deepest convection takes place, is known to experience variability on
time scales ranging from days to decades, little is known about the variability of the
other components of the Labrador Sea circulation - the boundary current system and
the eddies that connect it with the interior.
Using various types of in situ data combined with the surface flux and satellite altimetry
data products, I studied the variability of both the boundary current system and
the eddies on different time scales as well as their influence on the post-convective
restratification of the Labrador Sea interior. The analysis presented in the thesis
supports the result of the previous theoretical studies that argue that lateral fluxes,
driven by the boundary current/interior gradients, play an important role in the
post-convective restratification of the Labrador Sea. I found that both components
of the boundary current, the surface West Greenland Current and the subsurface
Irminger Current, have a strong seasonal cycle. In the spring both the West Greenland
and Irminger Currents are colder and fresher than in the fall. However, the West
Greenland Current is faster and thicker in the spring while the Irminger Current is
the fastest and thickest in the fall. My analysis suggests that the observed seasonal
changes in the velocity are primarily due to the baroclinic component of the current
while the barotropic component remains nearly unchanged.
The Subpolar Gyre, and the Labrador Sea in particular, have experienced a decline
in the circulation accompanied by the warming of the water column over the last
decades. I found that a similar trend is seen in the West Greenland Current system
which slowed down from 1992 to 2004, primarily due to a decrease in the barotropic
flow. At the same time, the subsurface Irminger Current has become warmer, saltier,
and lighter, something that is also reflected in the properties of the eddies. Two
years exhibited pronounced anomalies: in 1997 and 2003 the velocity, temperature
and salinity of the Irminger Current abruptly increase with respect to the overall
trend. Finally, I discuss the impacts of the boundary current changes on the lateral
fluxes that are responsible for the restratification of the Labrador Sea and the properties
of the interior.
