Inferring Advective Timescales and Overturning Pathways of the Deep
Western Boundary Current in the North Atlantic through Labrador Sea
Water Advection
Abstract
The Subpolar North Atlantic plays a critical role in the formation of
the deep water masses which drive Atlantic Meridional Overturning
Circulation (AMOC). Labrador Sea Water (LSW) is formed in the Labrador
Sea and exported predominantly via the Deep Western Boundary Current
(DWBC). The DWBC is an essential component of the AMOC advecting deep
waters southward, flowing at depth along the continental slope of the
western Atlantic. By combining sustained hydrographic observations from
the Labrador Sea, Line W, Bermuda basin, and offshore of Abaco Island
along 26.5°N, we investigate the signal propagation and advective
timescales of LSW via the DWBC from its source region to the Tropical
Atlantic through various approaches using robust neutral density
classifications. Two individually-defined LSW classes are observed to
advect on timescales that support a new plausible
hydrographically-observed advective pathway. We find each LSW class to
advect on independent timescales, and validate a hypothesized
alternative-interior advection pathway branching from the DWBC by
observing LSW outside of the DWBC in the Bermuda basin just prior to or
on the same timescale as at 26.5°N- 10-15 years after leaving the source
region. Advective timescales estimated herein indicate that this
interior pathway is likely the main advective pathway; it remains
uncertain whether a direct pathway plays a significant advective role.
Using LSW convective signals as advective tracers along the DWBC permits
the estimation of advective timescales from the subpolar to tropical
latitudes, illuminating deep water advection pathways across the North
Atlantic and the lower-limb of AMOC as a whole.