Warm water formation in the midst of the Southern Ocean

The global heat budget at high latitudes is thought to be dominated by heat and buoyancy loss, yielding intermediate or deep water formation. The net heat loss, however, is ill-known, not only because of poor observational coverage, but also because several climatologies of air-sea heat flux over the Southern Ocean show, imbedded in a larger region of heat loss, bands of heat gain which could potentially reverse the global budget. One purpose of this work is to assess the significance of such heat gain. First we explore which of the parameters involved in the computation of the various components of air-sea heat flux can cause sign reversals of the net flux as one progresses poleward. We show that regions of net heat gain, typically near 50S, coincide with regions of strong meridional gradients of sea surface temperature (SST). To the north, net heat loss results from net radiative gain offset by latent heat loss. To the south, net heat loss results from net short wave gain offset by net long wave loss. In between, values for evaporation and thus latent heat abruptly drop as SST drops, leaving the net short wave gain to dominate. Second we discuss whether a region of heat gain and the shallow upwelling cell with warm water formation that it would imply is compatible with what we know of the hydrography and oceanic circulation of the Southern Ocean.