Seasonal tracer subduction in the Subpolar North Atlantic driven by
submesoscale fronts
Abstract
Submesoscale flows (0.1 - 10 km) are often associated with large
vertical velocities, which can have a significant impact on the
transport of surface tracers, such as carbon. However, global models do
not adequately account for these small-scale effects, which still
require a proper parameterization. In this study, we introduced a
passive tracer into the mixed layer of the northern Atlantic Ocean using
a CROCO simulation with a high horizontal resolution of Δx = 800 m,
aiming to investigate the seasonal submesoscale effects on vertical
transport. Using surface vorticity and strain criteria, we identified
regions with submesoscale fronts and quantified the associated
subduction, that is the export of tracer below the mixed layer depth.
The results suggest that the tracer vertical distribution and the
contribution of frontal subduction can be estimated from surface strain
and vorticity. Notably, we observed significant seasonal variations. In
winter, the submesoscale fronts contribute up to 40% of the vertical
advective transport of tracer below the mixed layer, while representing
only 5% of the domain. Conversely, in summer, fronts account for less
than 1% of the domain and do not contribute significantly to the
transport below the mixed layer. The findings of this study contribute
to a better understanding of the seasonal water subduction due to fronts
in the region.