INTERANNUAL AND DECADAL TEMPERATURE VARIABILITY IN THE SOUTHWEST PACIFIC-OCEAN BETWEEN 1955 AND 1988

The spatial and temporal variability of the southwest Pacific Ocean is examined with the aim of describing the physical processes operating on interannual and decadal timescales. The study takes advantage of a new temperature atlas of the upper 450 m of the southwest Pacific Ocea n, obtained from 40 000 bathythermograph profiles between 1955 and 198 8. Rotated principal components analysis was used to filter the import ant spatial and temporal scales of temperature variability in the data . Three different analyses are presented. They include two intraocean analyses and a joint analysis of subsurface ocean temperature, sea lev el pressure, and surface winds. The dominant El Nino mode describes th e large vertical excursions of the thermocline in the western tropical Pacific in response to atmospheric forcing at a 3-6-month lag. More i mportantly, most of the retained modes, outside of the equatorial regi on, have time variations that correlate with El Nino. One ocean mode, with a spatial pattern representing sea surface temperature anomalies in the western Coral Sea (linked to the interannual migration of the S outh Pacific convergence zone), correlates significantly with (at the 99% level) and leads (by 3-6 months) the Southern Oscillation index (S OI), suggesting that sea surface temperature anomalies in this region may be a useful indicator for the onset of El Nino. A separate mode wh ose spatial pattern corresponds to the main oceanographic gyre also sh ows statistically significant temperature variations in phase with, or slightly leading, the SOI. The main decadal variations occur in the m idlatitudes, in the subtropical gyre, and in another mode associated w ith sub-Antarctic mode water (SAMW). The subtropical gyre warmed to a maximum in the mid-1970s and has been cooling since. In the SAMW a lon g-term warming of the upper 100 m of the southwest Tasman Sea is ident ified between 1955 and 1988. The depth-integrated warming in this regi on is found to be about 0.015 degrees C yr(-1), representing a contrib ution to sea level rise, through thermal expansion, of about 0.3 mm yr (-1).