Variability of South Pacific Tropical Water Subduction

Abstract:

Collection of Argo data provides an opportunity to carefully examine South Pacific Tropical Water (SPTW) subduction rate variability. SPTW is characterized by a vertical salinity maximum exceeding 36.2 psu centered at 20°S and 120°W and lying in the upper thermocline between 24.0 and 25.0 σ_θ. Subduction rates for SPTW for two different periods are calculated using two methods. Monthly one degree by one degree Argo data covering the South Pacific are used to calculate subduction rates from September 2005 to August 2013, also lateral induction and vertical pumping are calculated. There are two spatial subduction maxima, and the lateral induction process dominates in both maxima. Subduction rates from Argo data vary from 15 to 26 m/yr +/- 7.5% during the 8 year period. Subduction rates are shown to be positively and highly correlated with Southern Oscillation Index. Additionally, using CFC-12 data from the 1990s World Ocean Circulation Experiment, average subduction rate is calculated to be 35 +/- 16.5 m/yr. Some of the difference between Argo and tracer rates is due to a difference in the methods, and some difference may be due to decadal variability. Thus, SPTW subduction rates are shown to vary on interannual and possible decadal time scales.