17 
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Fig. 2. Schematic diagram of the upper-layer ocean circulation based on the mass and fresh- 
water balance of each ocean north of the Antarctic Circumpolar Current. Upper layer transports 
and salinities are given through the southern boundary of each ocean and through the 27.60 sur- 
face which divides the upper layer from the deep waters. R represents the recirculation in the 
upper layers within the Antarctic Circumpolar Current. 
In today's ocean simple balances suggest that the primary transfer of heat and salt into the 
abyssal ocean is not necessarily NADW but rather cross thermocline mixing (Gordon, 1975). 
The other aspect of NADW process which hasn't received much attention is the return 
route of abyssal water to the upper layer and back to the North Atlantic. The standard picture 
presented is one in which abyssal water upwells, migrates to the Antarctic Circumpolar Current 
(presumably the sub-Antarctic zone) for advection to the Atlantic equator (which from energy 
considerations would mainly be in the lower thermocline or Antarctic Intermediate Water). This 
is essentially a cold water route. An alternative warm water route may be effective, as brought 
to light by recent global fresh water budgets for the ocean (Piola and Gordon, 1984) and field 
work in the region of the Agulhas retroflection south of Africa. By this route abyssal water 
upwells into the thermocline at a rate to balance NADW formation rate. It is warmed and 
generally made saltier. Pacific to Indian transfer of thermocline water occurs in the Indonesian 
Passages (Fig. 2) and transfer into the Atlantic is achieved by an arm of the Agulhas current 
which does not participate in the general retroflection circulation pattern (Fig. 3). 
The warm water route has significant impact in inter-ocean heat and fresh water transfer. 
An effective role which the ocean may play in global climate is the ability to transfer these pro- 
perties across longitudes on a hemispheric scale. The warm water route essentially moves heat 
and low salinity water from the Pacific to the Atlantic by way of the Indian Ocean. 
The large oceanic to atmosphere heat transfer in the North Atlantic is derived from the 
Pacific Ocean, and the net evaporation of the Atlantic is balanced by the net precipitation of the 
Pacific. 
