The Eulerian‐Mean Downwelling in the Western Subpolar North Atlantic

Recent studies indicate that vertical downwelling associated with the Atlantic Meridional Overturning Circulation is concentrated along the boundaries of the subpolar gyre (SPG) and Nordic Seas. While the baroclinic component of this downwelling has been estimated from observations, a full assessment incorporating both barotropic and baroclinic transport remains lacking. This study provides refined estimates of Eulerian-mean downwelling along the western SPG boundary, extending from the Denmark Strait to the Flemish Cap. To enhance the robustness of the estimates, three long-term mean (2002–2019) horizontal velocity fields are reconstructed: (a) an observation-based field derived from hydrographic data and referenced to Argo float velocities at 1,000 m; (b) a second observation-based field using the same hydrographic data but referenced to surface geostrophic velocities from satellite altimetry; and (c) full-depth velocities directly obtained from the eddy-resolving VIKING20X ocean model. Observation-based downwelling is estimated at −4.0 ± 1.0 Sv at 1,300 m (float-referenced) and −4.8 ± 1.6 Sv at 1,000 m (altimetry-referenced), with contributions from barotropic (−2.2 ± 0.6 Sv and −3.0 ± 1.4 Sv) and baroclinic (−1.8 ± 0.7 Sv and −1.8 ± 0.8 Sv) components, respectively. The eddy-resolving model further yields a comparable estimate of −4.8 Sv at 1,100 m, with −2.5 Sv from barotropic and −2.3 Sv from baroclinic transport. All estimates consistently identify the western Greenland boundary as a key region of downwelling. This study underscores the essential role of barotropic and baroclinic transports in boundary currents in driving vertical transport within the subpolar North Atlantic's marginal seas. © 2025. American Geophysical Union.