Pathways of Denmark Strait Overflow Water in the Subpolar North Atlantic
A Lagrangian Perspective
I.C.J. Backers (TU Delft - Civil Engineering & Geosciences)
R. Gelderloos – Mentor (TU Delft - Environmental Fluid Mechanics)
Dennis H.A. Vermeulen – Mentor (TU Delft - Environmental Fluid Mechanics)
M. Vizcaino – Graduation committee member (TU Delft - Physical and Space Geodesy)
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Abstract
Denmark Strait Overflow Water (DSOW) forms a major component of the deep limb of the Atlantic Meridional Overturning Circulation (AMOC). This study investigates the main pathways along which DSOW spreads through the subpolar North Atlantic (SPNA) and how its temperature, salinity and density evolve along these routes. We used a Lagrangian particle-tracking approach based on velocity and tracer fields from the Global Ocean Physics Analysis and Forecast system provided by Copernicus Marine Service. Particles were released at the Denmark Strait sill and tracked for three years. We found that DSOW spreads throughout the SPNA via pathways where particles stay in the boundary current and pathways where particles follow both the boundary current and enter an interior. The highest percentage of particles (72.4%) travels via only the boundary current; of the interiors, the Labrador Sea interior is most frequently entered (23.0%), while exchanges with the Irminger Sea (4.4%) interior is smaller. The fraction of particles entering an interior is highest in winter (36%), consistent with enhanced density gradients and eddy activity. Along its pathways, DSOW warms and becomes more saline through mixing with ambient waters. Particles that stay in the boundary currents experience the largest changes in temperature (+14°C), salinity (+2.5 g/kg) and density (-1.2 kg/m3, while particles that enter an interior experience smaller changes (temperature +9°C, salinity +0.5 g/kg and density -0.7 kg/m3). Particles that travel via both the boundary current and enter an interior also experience the largest changes in density in the boundary current. These findings suggest that most transport and transformation of DSOW occurs within the boundary current, while exchange with the interior plays a smaller role.