Mechanisms of the meridional heat transport in the Southern Ocean |
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Authors: | Denis L Volkov Lee-Lueng Fu Tong Lee |
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Institution: | (1) Joint Institute for Regional Earth System Science and Engineering, University of California Los Angeles, Los Angeles, CA, USA;(2) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA |
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Abstract: | The Southern Ocean (SO) transports heat towards Antarctica and plays an important role in determining the heat budget of the
Antarctic climate system. A global ocean data synthesis product at eddy-permitting resolution from the Estimating the Circulation
and Climate of the Ocean, Phase II (ECCO2) project is used to estimate the meridional heat transport (MHT) in the SO and to
analyze its mechanisms. Despite the intense eddy activity, we demonstrate that most of the poleward MHT in the SO is due to
the time-mean fields of the meridional velocity, V, and potential temperature, θ. This is because the mean circulation in the SO is not strictly zonal. The Antarctic Circumpolar Current carries warm waters
from the region south of the Agulhas Retroflection to the lower latitudes of the Drake Passage and the Malvinas Current carries
cold waters northward along the Argentinian shelf. Correlations between the time-varying fields of V and θ (defined as transient processes) significantly contribute to the horizontal-gyre heat transport, but not the overturning
heat transport. In the highly energetic regions of the Agulhas Retroflection and the Brazil-Malvinas Confluence the contribution
of the horizontal transient processes to the total MHT exceeds the contribution of the mean horizontal flow. We show that
the southward total MHT is mainly maintained by the meridional excursion of the mean geostrophic horizontal shear flow (i.e.,
deviation from the zonal average) associated with the Antarctic Circumpolar Current that balances the equatorward MHT due
to the Ekman transport and provides a net poleward MHT in the SO. The Indian sector of the SO serves as the main pathway for
the poleward MHT. |
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