Hobart

Seminar Abstract

Friday 19 March 2010, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Alberto Naveira Garabato
National Oceanography Centre, Southampton (NOCS), UK

Eddy-induced mixing in the Southern Ocean

There is an ongoing debate concerning the distribution of eddy-induced mixing across the Antarctic Circumpolar Current (ACC) and the nature of its controlling processes. The problem is addressed here by estimating the isentropic eddy diffusivity K from a collection of hydrographic and altimetric observations, analyzed in a mixing length theoretical framework. It is shown that, typically, K is suppressed by an order of magnitude in the upper kilometre of the ACC frontal jets relative to their surroundings, primarily as a result of the modulation of the mixing length by eddy - mean flow interaction. This observation is reproduced by a quasi-geostrophic theory of eddy-induced mixing across a broad barotropic jet. The theory indicates that the observed widespread reduction of K in the upper layers of frontal jets is the kinematic consequence of eddy propagation relative to the mean flow within jet cores. It is contended that the characteristic T-S structure of the Southern Ocean, consisting of multiple upper-ocean thermohaline fronts separating and underlaid by regions of homogenized properties, is largely a result of eddy - mean flow interaction mechanism. Nonetheless, pronounced deviations from this prevalent mixing regime are encountered in a few special sites, where mixing suppression breaks down at the core of upper-ocean jets. The conditions for the occurrence and the significance of such "leaky" jet segment will be discussed.

Seminar recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 11/05/10