Mean, Annual, and Interannual Circulation and Volume Transport in the Western Tropical North Pacific From the Western Pacific Ocean State Estimates (WPOSE)

Interannual volume transport anomalies in the far western tropical North Pacific were calculated using the Western Pacific Ocean State Estimates (WPOSE; 2009-2017; 115 degrees E-170 degrees E, 15 degrees S-27 degrees N) to assess the magnitude, phase, and vertical structure of volume transport, and the relationship of interannual transport to the El Nino-Southern Oscillation phenomena. The mean velocity and thermohaline structure for the WPOSE were verified using Argo climatology and autonomous glider observations. Transport was calculated for both an upper layer (surface-26 kg m(-3)) and a lower layer (26-27.3 kg m(-3)). Annual volume transport anomalies were small north of 8 degrees N but varied by 50% of the mean volume transport between the equator and 8 degrees N. Interannual anomalies exceeded annual anomalies throughout the region. Volume transports of the North Equatorial Current, the Mindanao Current, and the South Equatorial Current/New Guinea Coastal Undercurrent increased beginning in September 2014, leading to a large increase in transport in the North Equatorial Counter Current before the mature phase of El Nino in 2015/2016. The increase in transport was related to the meridional gradient in thermocline depth centered at 5 degrees N at the southern part of the Mindanao Dome, where extreme shoaling of the thermocline took place. Lower-layer volume transports were not always in phase with those of the upper-layer and made considerable contributions to total transport variability.