Global maps of the large-scale potential vorticity field, 
, on deep isopycnals have been calculated (O'Dwyer and Williams, 1996). For adiabatic flow, contours of Q on isopycnals are coincident with streamlines. As in the thermocline (McDowell et al., 1983; Keffer, 1985) there are a variety of patterns observed, varying with depth, basin, and hemisphere which suggest a complex baroclinic flow field.
At mid-depth coutours of Q are zonal, in accord with the standard Stommel and Arons (1960) idealized model of deep circulation. Any meridional flow has to be forced in order to cross Q contours.
On deeper isopycnals, below about 4000 m, there is a greater variety in the distribution of Q possibly reflecting a variety of dynamical regimes. In the South Pacific and western South Atlantic Q contours run south-east to north-west allowing a free meridional component to the flow, and forcing may be confined to the boundaries. The meridional component of the contours increases with depth, suggesting that the flow become increasingly free. In the North Pacific and the eastern Atlantic at this depth there are regions of nearly uniform, low magnitude Q, allowing free recirculation of fluid around the basin.
Large contrasts in Q across a basin may result from several sources with different characteristic values of Q, or from a single source with a high magnitude Q which contrasts with the value of zero set at the equator. This is probably the case in the western Atlantic and the South Pacific. The eastern Atlantic and the North Pacific are both supplied by inflows at low latitudes, so they have sources with low Q, reflected in the low magnitude of Q throughout the basins. The water in these basins in relatively old and lateral mixing may be responsible for the uniformity of Q across the basin, possibly caused by the mechanism of eddy stirring discussed by Rhines and Young (1982) for the thermocline.
Keffer, T. 1985. The ventilation of the World's Oceans: Maps of the potential vorticity field. J. Phys. Oceanogr., 15: 509-523.
McDowell, S., P. B. Rhines, and T. Keffer. 1982. North Atlantic potential vorticity and its relation to the general circulation. J. Phys. Oceanogr., 12: 1417-1436.
O'Dwyer, J. and R. G. Williams. 1996. On the potential vorticity distribution in the abyssal waters over the global ocean. Submitted to J. Phys. Oceanogr.
Rhines, P. B. and W. R. Young. 1982. J. Mar. Res., 40: 559-596.
Stommel, H. and A. B. Arons. 1960. On the abyssal circulation of the world ocean. I. Stationary planetary flow patterns on a sphere. Deep-Sea Res., 6: 140-154.
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