The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion - Valorisation des savoir-faire des membres de LOCEAN Accéder directement au contenu
Article Dans Une Revue Journal of Physical Oceanography Année : 2022

The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion

Résumé

Abstract The stratification is primarily controlled by temperature in subtropical regions (alpha ocean) and by salinity in subpolar regions (beta ocean). Between these two regions lies a transition zone, often characterized by deep mixed layers in winter and responsible for the ventilation of intermediate or deep layers. While of primary interest, no consensus on what controls its position exists yet. Among the potential candidates, we find the wind distribution, air–sea fluxes, or the nonlinear cabbeling effect. Using an ocean general circulation model in an idealized basin configuration, a sensitivity analysis is performed testing different equations of state. More precisely, the thermal expansion coefficient (TEC) temperature dependence is explored, changing the impact of heat fluxes on buoyancy fluxes in a series of experiments. The polar transition zone is found to be located at the position where the sign of the surface buoyancy flux reverses to become positive, in the subpolar region, while wind or cabbeling are likely of secondary importance. This inversion becomes possible because the TEC is reducing at low temperature, enhancing in return the relative impact of freshwater fluxes on the buoyancy forcing at high latitudes. When the TEC is made artificially larger at low temperature, the freshwater flux required to produce a positive buoyancy flux increases and the polar transition moves poleward. These experimets demonstrate the important role of competing heat and freshwater fluxes in setting the position of the transition zone. This competition is primarily influenced by the spatial variations of the TEC linked to meridional variations of the surface temperature.
Fichier principal
Vignette du fichier
1520-0485-JPO-D-21-0295.1.pdf (2.03 Mo) Télécharger le fichier
Origine : Fichiers éditeurs autorisés sur une archive ouverte

Dates et versions

hal-03811174 , version 1 (03-03-2023)

Identifiants

Citer

Romain Caneill, Fabien Roquet, Gurvan Madec, Jonas Nycander. The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion. Journal of Physical Oceanography, 2022, 52 (8), pp.1887-1902. ⟨10.1175/jpo-d-21-0295.1⟩. ⟨hal-03811174⟩
45 Consultations
32 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More