Introduction to special section: World Ocean Circulation Experiment: South Atlantic Results

scale thermohaline circulation. What is the role of the South Atlantic in the global reference frame? WOCE observational (Figures 1 and 2)and model studies have done much to address this topic. The subtropical South Atlantic forms varied types of Subtropical Mode Water; shallow upwelling occurs in the eastern boundary regions and within the equator belt, as with other oceans. However, what it does uniquely is that it exposes the North Atlantic water mass products to the Antarctic Circumpolar Current, giving it global access. Equally important is the associated climate issue of the nature of the upper ocean flow that balances the export of deep water. The South Atlantic thermocline exchange with the Indian Ocean thermocline and the injection of Pacific Ocean derived Antarctic intermediate and mode water masses in Drake Passage are all part of the hotly debated "warm route, cold route" subject, echoed in this collection of WOCE based articles. At the crux of the debate is that the South Atlantic displays the most curious feature of the global ocean: oceanic heat flux toward the equator! Warm upper waters move northward, compensating southward moving, cooler deep water. Ultimately, this heat warms the northern climes of the North Atlantic. Estimates range from 0.2 to 0.9 PW for the northward heat flux across the subtropical belt, with the error estimated in excess of 0.2 PW. There appears to be significant northsouth divergence of the meridional heat flux with seasonal (large) and interannual (weaker) variability, hence a large range in heat flux estimates is to be expected. Recent attention to this issue by models and observations has not yet