A Laboratory Model of Thermocline Depth and Exchange Fluxes across Circumpolar Fronts

Abstract

A laboratory experiment has been constructed to investigate the possibility that the equilibrium depth of a circumpolar front is set by a balance between the rate at which potential energy is created by mechanical and buoyancy forcing and the rate at which it is released by eddies. In a rotating cylindrical tank, the combined action of mechanical and buoyancy forcing builds a stratification, creating a large-scale front. At equilibrium, the depth of penetration and strength of the current are then determined by the balance between eddy transport and sources and sinks associated with imposed patterns of Ekman pumping and buoyancy fluxes. It is found that the depth of penetration and transport of the front scale like [(fwe)/g?]L and weL2, respectively, where we is the Ekman pumping, g? is the reduced gravity across the front, f is the Coriolis parameter, and L is the width scale of the front. Last, the implications of this study for understanding those processes that set the stratification and transport of the Antarctic Circumpolar Current (ACC) are discussed. If the laboratory results scale up to the ACC, they suggest a maximum thermocline depth of approximately h = 2 km, a zonal current velocity of 4.6 cm s?1, and a transport T = 150 Sv (1 Sv ≡ 106 m3 s?1), not dissimilar to what is observed.