Float observations of the Southern Ocean. Part II: Eddy fluxes

Abstract

Autonomous Lagrangian Circulation Explorer (ALACE) floats are used to examine eddy fluxes in the Southern Ocean. Eddy fluxes are calculated from differences between ALACE float data and mean fields derived from hydrographic atlas data or objectively mapped float observations. Heat fluxes indicate an average poleward eddy heat transport across the Antarctic Circumpolar Current (ACC) of about 3-7 kW m-2 at 900-m depth. Because analysis of current meter data suggests that ALACE's 9-25-day averaging underestimates the total heat flux, the initial ALACE estimates are resealed to account for this undersampling. This results in a total corrected heat flux of 5-10 kW m-2 at 900 m, depending on the mean field used for the calculations. If the cross-ACC heat flux is assumed to vary exponentially through the water column with an e-folding depth of 1000 m, then the implied net poleward heat flux across the ACC is between 0.3 ± 0.1 and 0.6 ± 0.3 (× 1015 W). These estimates are in agreement with previous Southern Ocean eddy flux estimates, which have suggested a cross-ACC heat fluxes ranging between 0.05 and 0.9 (× 1015 W). Cross-stream fluxes vary geographically, with the largest fluxes occuring in the Indian Ocean sector, near the Agulhas Retroflection. Statistically significant poleward fluxes also occur along the core of the ACC. Along-stream fluxes are comparable in size to cross-stream fluxes. Momentum fluxes observed by ALACE are isotropic and do not indicate statistically significant eddy-mean flow interactions.