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