REGIONAL CLIMATE VARIABILITY AND OCEAN HEAT-TRANSPORT IN THE SOUTHWEST PACIFIC-OCEAN

The winter of 1992 was the coldest on record in New Zealand since the 1940s. Temperatures in New Zealand were as much as 3 degrees C below a verage, with heavy rain and unusual snow. The oceanic surface layer in the southwest Pacific was also anomalously cold over the same period. A World Ocean Circulation Experiment (WOCE) hydrographic section (P14 C) between Auckland and Fiji during September 1992 found cold sea surf ace temperatures and deep mixed layers near New Zealand when compared to 8 years of high-resolution expendable bathy thermograph (XBT) tempe rature measurements collected along the same transect. High nutrient a nd low dissolved oxygen concentrations in the surface layer indicated recent entrainment of thermocline waters. The Auckland to Fiji XBT sec tion is ope of three WOCE high-resolution XBT survey lines in the ''Ta sman Box'' region, whose boundaries are Auckland-Fiji, Fiji-Brisbane a nd Wellington-Sydney transects plus the Australian coast. Geostrophic shear and transport were estimated from 10 realizations of the Tasman Box during the period 1991-1993. The time series of geostrophic transp ort shows that following a convergence in late 1991, early in 1992 the re was a substantial divergence of mass in the upper waters, equivalen t to a thinning of the warm water layer. The phase of this anomalous d ivergence is matched to an observed amplification of the seasonal ocea nic heat storage cycle in 1991-1992. The top 200-m average temperature was warmer in the 1992 summer than in 1991 or 1993, but the winter of 1992 was the coldest of the 8-year record along the Auckland-Fiji lin e. The divergence (thinning) of the warm water layer appears to have p reconditioned the region for the exceptionally cold 1992 winter. The a lternative, cool conditions from anomalous air-sea heat exchange cause d by variability in the wind field, is considered unlikely as large fl uctuations in heat loss are not observed in the air-sea flux data duri ng this period. The severe weather conditions and anomalous ocean heat transport are most likely related to the prolonged El Nino-Southern O scillation episode that began in early 1991.