Melissa Bowen (Univ. Auckland NZ)- What causes interannual variability of sea surface temperatures in the South West Pacific?

Sea surface temperatures (SSTs) in the SW Pacific vary interannually by +/- 1oC and are correlated with air temperatures over New Zealand. SST is also significantly correlated with the El Nino Southern Oscillation, but previous studies have failed to establish what causes the ocean temperatures to vary. We estimate the upper ocean heat balance from observations and show that over much of the region interannual variations in SST cannot be explained by air-sea heat fluxes or by heat transport due to Ekman and geostrophic currents in the upper ocean. We investigate how heat flux from the deeper ocean may be contributing to interannual variations of SST. Finally, we show that temperatures in the region are correlated with barotropic Rossby waves arriving along the eastern New Zealand coast suggesting isotherms at depth may be adjusting to winds over the South Pacific. Thus, much of the variability of SST may be driven by the deeper ocean and linked to ENSO through the wind-driven adjustment of the South Pacific.