Temperature and salinity variability at intermediate depths in the western equatorial Pacific revealed by TRITON buoy data

We investigated ocean variability at intermediate depths (300-750 m) in the western equatorial Pacific (WEP) using data from underwater sensors of the Triangle Trans-Ocean Buoy Network (TRITON) buoys. The data were specially processed because high accuracy is necessary for such an application, and we confirmed that sufficient accuracy was achieved. Variability of the temperature and salinity was large in the western boundary regions of the WEP. Seasonal variability is generally dominant at intermediate depths in the WEP; however, intraseasonal variability with period of 30-80 days is not negligible, particularly at 2 degrees N, 138 degrees E, where the New Guinea Coastal Undercurrent retroflects to the east as the Equatorial Undercurrent and/or Northern Subsurface Countercurrent. High correlation is seen between 12-month running means of the Nino 3.4 index anomaly and temperature at 300 and 750 dbar. In other words, the influence of El Nino/Southern Oscillation phenomena reaches to at least a depth of 750 dbar. We found a decreasing trend in salinity at intermediate depths in the WEP: - 0.0032 Practical Salinity Unit (PSU) year(-1) at 300 dbar and - 0.00053 PSU year(-1) at 750 dbar. This trend is likely associated with the freshening of the North Pacific Intermediate Water and Antarctic Intermediate Water.