Destination of New Guinea Coastal Undercurrent in the western tropical Pacific: variability and linkages

Abstract

The New Guinea Coastal Undercurrent (NGCUC) is considered a bottleneck in the Equatorial Pacific, carrying upper-to-intermediate waters from the south to the northwestern Pacific. However, how the NGCUC links to the circulation in the northwestern Pacific and what mechanisms control their variability were insufficiently studied. This work explores the spatiotemporal changes in the destinations of the NGCUC and the physical processes linked with the downstream NGCUC using ocean reanalysis for 22 years (1994 – 2015). Lagrangian particle tracking analysis suggests eight major destinations of NGCUC: the Equatorial Undercurrent (35.26%), the North Equatorial Countercurrent (12.3%), the North (13.33%) and South (8.85%) Subsurface Countercurrents, the Equatorial Deep Jet (11.49%), the Mindanao Undercurrent (13.24%), and the Indonesia (3.47%) and Halmahera (0.86%) Throughflows. In addition, the present study suggests some minor and transient destinations of NGCUC. The NGCUC waters are distributed mainly to the east (81.65%) and their dissemination varies markedly with depth. Seasonal change in the NGCUC’s strength is accompanied by the seasonal change in the distribution of its water mass. Furthermore, spatial change of the NGCUC waters’ dissemination is investigated interannually, which is generally phased locking to the El Niño Southern Oscillation. These changes in the NGCUC waters’ distribution potentially transform the local and regional water mass characteristics around the northwest Pacific. The mechanisms of their spatiotemporal variation are discussed, as well as the important roles of eddies in trapping and redistributing the NGCUC waters.