Observing the local emergence of the Southern Ocean residual-mean circulation

• Published in: Geophysical Research Letters
• Main Authors: Sévellec, F., Naveira Garabato, A.C., Vic, C., Ducousso, N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Antarctic; Drake Passage; Southern Ocean; Antarc*
• Online Access: https://eprints.soton.ac.uk/430530/; https://eprints.soton.ac.uk/430530/1/sevellec_et_al_grl19.pdf; https://eprints.soton.ac.uk/430530/2/S_vellec_et_al_2019_Geophysical_Research_Letters.pdf

The role of mesoscale turbulence in maintaining the mean buoyancy structure and overturning circulation of the Southern Ocean is investigated through a 2-year-long, single-mooring record of measurements in Drake Passage. The buoyancy budget of the area is successively assessed within the Eulerian and the Temporal-Residual-Mean frameworks. We find that a regime change occurs on time scales of 1 to 100 days, characteristic of mesoscale dynamics, whereby the eddy-induced turbulent horizontal advection balances the vertical buoyancy advection by the mean flow. We use these diagnostics to reconstruct the region's overturning circulation, which is found to entail an equatorward downwelling of Antarctic Intermediate and Bottom Waters and a poleward upwelling of Circumpolar Deep Water. The estimated eddy-induced flow can be accurately parameterized via the Gent-McWilliams closure by adopting a diffusivity of ∼2,000 m 2 s −1 with a middepth increase to 2,500 m 2 s −1 at 2,100 m, immediately underneath the maximum interior stratification.