Ocean Circulation at the Pacific Gateway into the Indonesian Throughflow

The tropical western Pacific Ocean features a large warm pool, which plays an important role in the evolution of ENSO and global climate variability. The ocean circulation in this area is characterized by multiple bands of narrow alternating zonal currents, strong western boundary currents, and a significant leakage into the Indonesian seas, a.k.a. the Indonesian Throughflow. The effects of these currents on the variations of the warm pool are not clear to date. In this study, we use Argo data, in situ research cruise observations, mooring measurements, and nonlinear dynamics analyses to disclose important features and dynamics of the ocean circulation in this area. The following are the conclusions:

1. The meridional geostrophic transport of the low-latitude western Pacific Ocean is in opposite direction to the Sverdrup theory, suggesting importance of eddy-driven circulation.

2. The Kuroshio decreases whereas the Mindanao Current increases significantly during the peak of the 2010 La Niña, the transport anomalies of which are much larger than the interior geostrophic meridional transport anomalies.

3. During the 2012 winter cruise, observations show that the Mindanao current shed an eddy in the eastern Sulawesi Sea, suggesting strong nonlinearity of the circulation at the entrance of the Indonesian Throughflow.

The above results suggest that oceanic nonlinearity at the western Pacific Gateway into the Indonesian Throughflow play an important role in ENSO dynamics. Finally, Mooring observations in the Maluku Channel during 2012 through 2015 will be presented to discuss the potential role of Indonesian Throughflow in the development of the 2014 premature and 2015 strong El Niños.