CSIRO hydrological data from the south-west Pacific (0-45�S., 140°E.-160� W.)
during 1960-67 have been used to calculate annual means of salinity and oxygen,
within 5� squares, on the 26.00 sigma-t surface. In addition, for some squares it was
possible to calculate mean summer (December-February) and mean winter (July-
September) values of salinity and oxygen.
From the annual means the salinity-oxygen relations were used to characterize
four water types. Water type 1 of tropical origin had a salinity of 35.03‰ and an
oxygen content of 3.20 ml/l. Water type 2, also of tropical origin, had a salinity of
35.23‰ and an oxygen content of 2.30 ml/l. Water type 3 of subtropical origin had a
salinity of 35 +66‰ and an oxygen content of 5.45 ml/l. Water type 4 of Subantarctic
origin had a salinity of 34.80‰ and an oxygen content of 6.00 ml/l.
The ultimate origins of water types 1 and 2 are thought to be at considerable
distances from the south-west Pacific region. Water type 1 is suggested as a mixture of
waters of the North Equatorial Pacific, to the west of about 160°W., and waters of type 3
originating in the south Tasman Sea and other regions of the south Pacific. Water
type 2 forms at around 16O°W., by mixing of eastern tropical Pacific waters and water
type 3. It is thought that water types 1 and 2 form at different times of the year depending
upon the extent of meridional or zonal flow in the central Equatorial region. Water
types 3 and 4, however, are formed by southward spreading and winter cooling at the
surface of subtropical waters, and by northward spreading and summer warming at the
surface of Subantarctic waters, respectively. These two water types are therefore of
south-west Pacific origin. Generally in the Tasman Sea (south of 25�S.), the concentration
of water type 1 is very low (less than 10%); of water type 2 only a little
higher (20-30%), but that of water type 3 is high (around 60-75%). The concentration
of water type 4 was much greater (40%) off the west coast of South Island, New Zealand,
than off the east coast of Tasmania (15 %). Seasonal pulses in the concentrations of
water types 1 and 2 along 170�E., between 0 and 15�S., are in phase with seasonal
changes in the concentration of these two water types in the Tasman and Coral Seas,
if these water types spread southward at about 10 cm/sec. Summer increases in the
concentration of water type 3 in the Tasman Sea off New Caledonia have been explained
by the northward spreading of the previous winter's accumulation of this water type
in the central Tasman Sea.
Water types and volumetric considerations of the South-East Atlantic upwelling regime
