Spatial-temporal variability of thermohaline intrusions in the northwestern tropical Pacific Ocean

Using repeated hydrographic measurements at 137A degrees E, spatial-temporal variability of thermohaline intrusions in the northwestern tropical Pacific are investigated. Intrusions can be found in the main thermocline throughout the section, with their strength decreasing rapidly poleward. The strongest intrusions exist at the North Equatorial Countercurrent (NECC) where North/South Pacific thermocline water converges. These intrusions also exhibit temporal variations in strength which are closely associated with the meridional displacement of the NECC. Intrusion strength peaks in boreal winter when the NECC reaches its northernmost position of the year. At interannual time scale, intrusions tend to be weak (strong) during El Nio (La Nia) episodes. Variations in intrusion strength also lead to prominent fluctuation of lateral diffusivity K (L) and cross-front temperature flux F (theta) . F (theta) exhibits significant year-to-year changes which are well correlated with ENSO index, suggesting a possible role of intrusions in the low-latitude Pacific climate variability.