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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Apr 2019

Research article | 04 Apr 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

Seasonal and regional variations of sinking in the subpolar North Atlantic from a high-resolution ocean model

Juan-Manuel Sayol1, Henk Dijkstra2, and Caroline Katsman1 Juan-Manuel Sayol et al.
  • 1Department of Hydraulic Engineering, Delft University of Technology, Delft, The Netherlands
  • 2Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, The Netherlands

Abstract. Previous studies have indicated that most of the net sinking associated with the downward branch of the Atlantic Meridional Overturning Circulation (AMOC) must occur near the subpolar North Atlantic boundaries. In this work we have used monthly mean fields of a high-resolution ocean model (0.1 deg at the equator) to quantify this sinking. To this end we have calculated the Eulerian net vertical transport (WΣ) from the modelled vertical velocities, its seasonal variability and its spatial distribution under repeated climatological atmospheric forcing conditions. Based on this simulation, we find that for the whole subpolar North Atlantic WΣ peaks at about −14 Sv at a depth of 1139 m, matching both the mean depth and the magnitude of the meridional transport of the AMOC at 45° N. It displays a seasonal variability of around 10 Sv. Three sinking regimes are identified according to the characteristics of the accumulated W with respect to the distance to the coast: one within the first 110 km and onto the bathymetric slope at around the peak of the boundary current speed (regime I), the second between 110 km and 290 km covering the remainder of the shelf where mesoscale eddies exchange properties (momentum, heat, mass) between the interior and the boundary (regime II), and the third sinking regime at larger distances from the coast where WΣ is mostly driven by the ocean's interior eddies (regime III). Regimes I and II accumulate ∼ 90 % of the total sinking and display smaller seasonal changes and spatial variability than regime III. We find that such a distinction in regimes is also useful to describe the characteristics of WΣ in marginal seas located far from the overflow areas, although the regime boundaries can shift a few tens of km inshore or offshore depending on the bathymetric slope and shelf width of each marginal sea. The largest contributions to the sinking come from the Labrador Sea, the Newfoundland region and the overflow regions. The magnitude, the seasonal variability and the depth at which WΣ peaks vary for each region, thus revealing a complex picture of sinking in the subpolar North Atlantic.

Juan-Manuel Sayol et al.
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Juan-Manuel Sayol et al.
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Publications Copernicus
Short summary
This work uses high-resolution global ocean model data to quantify the sinking of waters in the subpolar North Atlantic. The largest amount of sinking is found at the depth of maximum AMOC below the mixed layer depth, occurring mostly near the boundaries (90 %), in the first 300 km off the coast. However, the characteristics of the sinking (total amount, seasonal variability and vertical structure) varies largely according to the region considered, revealing a complex picture for sinking.
This work uses high-resolution global ocean model data to quantify the sinking of waters in the...