February 24: "Mechanisms of the Meridional Heat Transport in the Ocean"

" Mechanisms of the Meridional Heat Transport in the Ocean "



A global ocean data synthesis product at eddy-permitting resolution from Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project is used to estimate the oceanic meridional heat transport (MHT) and investigate its mechanisms. Heat in the ocean is transported poleward by both the overturning circulation (zonally integrated flow) and the horizontal circulation (gyre transport). We demonstrate that the overturning dominates in the subtropical gyres while the horizontal circulation is responsible for most of the MHT in the subpolar oceans. We analyze contributions from the time-mean circulation and temperature fields and from the correlation of the time-varying velocity and temperature fields. We define the eddy heat transport as the deviation of the zonally integrated heat transport from the heat transport due to the 3-month average fields of velocity and temperature. The estimated heat transport thus contains signals only with periods shorter than 3 months, which are mainly associated with the eddy variability. We show that in a number of locations the time-mean eddy heat transport constitutes a considerable portion of the total time-mean MHT, in particular, in the tropics, in the Southern Ocean and in the Kuroshio Current. Eddies are also found to explain a significant portion of the interannual heat transport variance. Finally we investigate the mechanisms of the MHT in the Southern Ocean. We demonstrate that the southward total MHT is mainly maintained by the geostrophic horizontal shear flow associated with the Antarctic Circumpolar Current that balances the equatorward MHT due to the Ekman transport.