Interannual Variability of Thermal Conditions in the Extratropical Zone of the South Pacific at the Turn of the XX–XXI Centuries

Abstract

The aim of the study consists in identifying the spatial-temporal features of interannual changes in the surface air temperature Ta, the sea surface temperature (SST) and the upper 1000-meter water layer temperature Tw in the extratropical zone of the South Pacific Ocean over the past four decades, which are manifested as a result of the planetary changes and a shift in the climatic regime at the turn of the XX-XXI centuries. Besides, the revealed features' trends and their possible cause-andeffect relationships with the processes in the atmosphere and on the ocean surface are planned to be assessed. Methods and Results. Based on the Global Meteorological Network and Reanalysis data (NOAA), regional features and trends of the water and air temperature interannual fluctuations, and their relation to variations in the pressure and wind fields, intensity of the atmosphere action centers (AAC) and climatic indices (CI) over the past 4 decades have been determined. Applied were the methods of the cluster, correlation and regression analysis, as well as the apparatus of empirical orthogonal functions (EOF). The positive trends in changes of the Ta and SST fields are manifested mainly in the northwestern part of the region, where they are statistically significant and reach their maximum 0.4-0.6°C over 10 years in the Tasman Sea region and to the northeast of New Zealand. The water areas with minimal, negative or insignificant values of the air and water temperature trends are located on the southern and eastern peripheries of the water area under study -in the areas of influence of cold currents. Over the entire investigated water area, the trends in the mean annual SST and Ta were ~ 0.04-0.06°C/10 years that are 2-3 times less than those in the subarctic region of the North Pacific Ocean. The features of spatial-temporal variability of the water temperature trends at different horizons differ significantly from the characteristics of the SST trends. The trends' spatial distribution is already transformed within the upper 200-m layer; and deeper, maximums of this value are observed in the southeastern part of the water area. Conclusions. The results obtained made it possible to characterize the degree of heterogeneity of response of the atmosphere surface layer, SST and vertical distribution of Tw in the extratropical zone of the South Pacific to the ongoing global changes, to identify the isolated areas, to estimate quantitatively the warming rate in these water areas, and to compare these estimates with those of the other regions in the Pacific Ocean. It is shown that the individual phases of alternation of the warm and cold periods in the interannual temperature variation are consistent with the changes of the regional CI and the AAC state; this fact emphasizes the inhomogeneous nature of these processes in space and time.