The global-scale circulation has long been one of oceanography's most
challenging and exciting research topics. A few features of the abyssa
l (near bottom) and deep circulation of the Atlantic Ocean have been k
nown for over 50 years, and in the past decade or so there has been a
developing focus on the world oceans' thermohaline circulation. The te
rm thermohaline circulation as used here applies not only to a direct
response to atmospheric buoyancy fluxes but also in the general sense
of water mass modification or conversion, where mechanisms may be asso
ciated with internal mixing processes and even wind forcing (i.e., win
d-induced upwelling or wind-driven mixing). The thermohaline circulati
on components reviewed and summarized in the following are associated
with water mass conversion processes that are involved with interbasin
exchange, Updated summary maps of the volume transports (in sverdrups
; 1Sv = 10(6) m(3) s(-1)) for the interbasin-scale pathways of the aby
ssal and deep thermohaline circulation and associated upper level comp
ensating flows are developed for two to four vertical layers or potent
ial density intervals, based primarily on a synthesis of published obs
ervational results. The cell(s) involving the largest worldwide exchan
ge transport-wise (53 Sv) are associated with an interaction between v
arious deep and bottom water components via Circumpolar Deep Water (CD
W). The first major conversion step in the replacement path for the re
newal (14 Sv) of North Atlantic Deep Water (NADW) is taken to be prima
rily to CDW. Bottom water in the Indian Ocean originates as lower CDW
which recirculates while also moving equatorward in deep western bound
ary currents with eventual conversion to both deep and intermediate la
yer flows. Some of the intermediate water so formed in the Indian Ocea
n moves through the Agulhas Current system (ACS) and may ''leak'' into
the Benguela Current regime (BCR), although probably primarily flowin
g through the ACS into the Subantarctic Frontal Zone (SFZ). It is modi
fied throughout its transit in the SFZ south of the Indian Ocean, sout
h of Australia, and across the South Pacific. Up to 10 Sv of the least
dense brand of intermediate water flows through the northern sector o
f Drake Passage, becomes involved in a Malvinas Current-Brazil Current
-Subtropical Gyre interaction, and then joins the BCR after perhaps al
so interacting with the ACS again. This compensating flow is warmed an
d becomes more saline in the South Atlantic and is later further modif
ied and upwelled in the equatorial Atlantic, crossing the equator and
moving through the Gulf Stream system to replace NADW. There is also a
n NADW replacement path of secondary importance westward around the ti
p of Africa (similar to 4 out of 14 Sv) associated with an interbasin
circulation pattern throughout the southern hemisphere oceans involvin
g an O(10 Sv) Indonesian Throughflow.