Yz. You, INTERMEDIATE WATER CIRCULATION AND VENTILATION OF THE INDIAN-OCEAN DERIVED FROM WATER-MASS CONTRIBUTIONS, Journal of marine research, 56(5), 1998, pp. 1029-1067
The intermediate water circulation and ventilation of the Indian Ocean
is somewhat unique among the world oceans (in terms of the source wat
ers). This has been studied with historical and recently obtained hydr
ographic data including potential temperature, salinity, dissolved oxy
gen, phosphate and silicate in a mixing model of applying optimum mult
iparameter analysis (OMP). The mixing model comprises three source wat
er masses, Antarctic Intermediate Water (AAIW) (applied the transforme
d AAIW north of the Antarctic frontal zone and central South Indian Oc
ean), Indonesian Intermediate Water (IIW) and Red Sea Intermediate Wat
er (RSIW) (including the influence of Persian Gulf Intermediate Water)
. A possible source from south of Australia has also been considered a
nd accommodated into the water type definition of AAIW. This study was
performed on six closely spaced neutral density surfaces which encomp
ass the intermediate layer of the Indian Ocean from 500 m (in the nort
hern Indian Ocean) to 1500 m (in the subtropical latitudes) with a dis
tance of about 100-150 m between a pair of surfaces. Water-mass mixing
contributions were plotted on the neutral surfaces and in three cross
sections, the western Indian Ocean along 60E, the eastern Indian Ocea
n along 90E, and a zonal section along 10S. The intermediate water cir
culation and ventilation of the Indian Ocean can thus be inferred from
the spreading paths and mixing patterns of these source water masses.
A schematic intermediate water circulation of the Indian Ocean theref
ore emerges from the water-mass and dynamical information. The latter
is derived from the acceleration potential (10 m(2) s(-2)) mapped on t
he neutral surfaces. The equatorward AAIW enters the Indian Ocean from
the mid-ocean of the southern Indian Ocean, is advected with the subt
ropical gyre and transits to the north through the western boundary. I
n the western equatorial Indian Ocean, AAIW flows northeastward to eas
tward. At about 80E, AAIW bifurcates into northward and southward flow
s. The former continues into the Bay of Bengal through the western bou
ndary (east of Sri Lanka) with up to 10% of the contribution. It retur
ns southward in the eastern Bay of Bengal and along the Sumatra and Ja
va Islands, zonally westward with IIW. The latter recirculates southwa
rd and then westward, forming a cyclonic gyre. The AAIW then turns sou
thward into the Agulhas Current system through either side of Madagasc
ar. AAIW contributes about 10-20% of its water into the equatorial Ind
ian Ocean. Its northward flow in the western Indian Ocean is limited t
o 5N. IIW flows zonally westward and bifurcates into a northward and a
southward how in the western Indian Ocean. The direction of the latte
r is southward into the Agulhas Current system through either side of
Madagascar. The former flows northward by the way of AAIW. Although AA
IW does not flow into the Arabian Sea, IIW is found flowing into the A
rabian Sea via the west coast of India. The main how path of IIW into
the Bay of Bengal is through the south of Sri Lanka. IIW largely contr
ibutes about 50-60% of its water into the Bay of Bengal. The northward
flow of IIW is interrupted at the central equatorial region by the ea
stward AAIW. These circulations form two cyclonic gyres in the western
and eastern equatorial Indian Ocean. The latter gyre straddles the eq
uator in the eastern Indian Ocean. RSIW flows to the southern Indian O
cean through both the western and eastern boundaries with much stronge
r flow in the west. The western boundary flow directly feeds the Agulh
as Current and the Agulhas Return Current.