Accueil > Actualités > Séminaires > Séminaire de Johan NILSSON


Titre : Ocean-basin geometry and the salinization of the Atlantic
Nom du conférencier : Johan NILSSON
Son affiliation : Department of Meterology, Stockholm University.
Laboratoire organisateur : LOCEAN
Date et heure : 24-04-2012 12h15
Lieu : UPMC, 4 place Jussieu, Paris 5e, LOCEAN, Tour 45-55, 4ème étage, salle de séminaires
Résumé :

Using a coupled atmosphere--sea--ice--ocean model in an aqua-planet setting, we examine the role of the basin geometry for the climate and ocean circulation. We focus on a present-day like setting with two northern basin (defined by two narrow land barriers, extending southward from the north pole) and a circumpolar ocean in the south, and have conducted a suite of experiments in which the southward extents of the land barriers and basin widths have been varied. The main focus is the role of these two key asymmetries of the basin geometry for the salinization of the Atlantic Ocean. 


When the two basins are identical, we find asymmetric states with the deep water formation localized to one of the basin. Remarkably, these states have the key hydrographic features of real ocean: A saline ''Atlantic'' like basin, which forms the deep water, and a ''Pacific'' like basin, with a halocline in the high northern latitudes. Asymmetries in the basin geometry can enhance as well as reduce the basin difference in flow and hydrography. 


More importantly, the basin geometry asymmetries can serve to uniquely localize the deep water formation to one of the basins. Our simulations with two equally wide basins show that when the short ''African'' continent is located near or equatorward of the zero wind line in the southern hemisphere, the deep water formation becomes uniquely localized to the ''Atlantic'' like basin with the long western boundary. The mechanistic link is that the maximum Ekman pumping is encountered near the zero wind line; a quantity which in interplay with the basin geometry controls zonal flow of thermocline water. A difference in basin width alone is also sufficient for uniquely localizing the deep water formation to the narrow ''Atlantic'' like basin.


Our idealized experiments suggest that the deep sinking is uniquely located to the ''Atlantic'' like basin because it is narrow and the ''African'' like short terminates just equatorward of the zero wind line. Furthermore, the asymmetry in basin width is presumably more decisive for the localization of the sinking than the difference in continental extents. Thus, in the present model the detailed features of the land-ocean distribution are not necessary for creating a unique equilibrium state with Atlantic sinking; nor is the presence of mountain ranges. 

Contact :

Giovanni Aloisi,