Evidence of double diffusion in the Brazil-Malvinas Confluence

• Main Authors: Bianchi, A.A., Piola, A.R., Collino, G.J.
• Format: Journal/Newspaper
• Language: unknown
• Subjects: Brazil/Malvinas Confluence; Double diffusion; Mixing; Salt finger; Southwestern Atlantic; Salinity measurement; Seawater; Thermal diffusion; Baroclinicity; Oceanography; fingering; salinity; vertical mixing; water mass; Atlantic Ocean; Antarc*; Antarctic; North Atlantic
• Online Access: https://hdl.handle.net/20.500.12110/paper_09670637_v49_n1_p41_Bianchi

Observation of thermohaline staircases and low-density ratios in the Brazil-Malvinas Confluence (BMC) suggests salt-fingering activity between the high salinity South Atlantic Central Water and low salinity Antarctic Intermediate Water. Vertical salt-finger induced salt fluxes are estimated in the BMC using a model for fastest growing fingers. Maximum salt-finger fluxes of 39.9 × 10-10 W kg-1 (5.3 × 10-7 m s-1) were estimated, similar to existing estimates in a Mediterranean salt lens embedded within the North Atlantic water. The fluxes normalized by the large-scale property gradients lead to fairly large estimates of diapycnal haline and thermal diffusivities, of up to 0.74 × 10-4 and 0.34 × 10-4 m2s-1, respectively, showing the enhancement of the haline diffusivity due to salt fingers. Estimated diffusive-convection fluxes based on flux laws derived from laboratory experiments are two orders of magnitude larger than salt-finger fluxes. These results suggest that, where cross-front interleaving leads to layering of relatively cold-fresh water over warm-salty water, diffusive upward convection dominates the vertical property fluxes in the frontal region. It appears that on the warm-salty side of the BMC, away from the narrow band dominated by interleaving, salt-finger integrated vertical fluxes nearly balance the cross-front lateral integrated fluxes. The effect of baroclinicity on the vertical property fluxes was evaluated and it was found that, in the BMC, the baroclinicity enhances the interleaving. © 2001 Elsevier Science Ltd. All rights reserved.