Observation of Inter-Annual Variability of Spiciness in the Pacific Thermocline

Using gridded temperature and salinity field predominantly based on global Argo in situ data (ARIVO), we investigate the inter-annual variability of generation, propagation and fate of the density-compensated anomaly of salinity (spiciness) observed in the thermocline of the subtropical and tropical Pacific Ocean over the period 2004-2010. Successive anomalies of spiciness are evidenced on σθ = 25.0 and 25.5 in both hemispheres of the Pacific Ocean during 2004-2010. They propagate within the thermocline from the north- and south-eastern subtropical regions of subduction towards the western tropics, following the mean stream functions in about 5 years. In the southern hemisphere the dominant spiciness signal is generated in the eastern basin near 15-35°S. It is mainly associated with a 2 to 3-year variability, which is reminiscent to ENSO variability. This suggests a feed back of tropical variability on subtropical subduction. In the northern hemisphere, the dominant spiciness signal is subducted north of 35°N, and its generation develops within about 4-5 years which is comparable to PDO trend. The observations suggest that the spiciness anomalies reach the equator in the western tropics and could influence the long term trend of the freshwater and heat budget in the equatorial band (5°S-N).