Closing the Gap Between the Coral Sea and the Equator: Direct Observations of the North Australian Western Boundary Currents

This is the authors' abstract. We don't add key points for this paper.

Boundary currents along northeastern Australia provide source waters for the East Australian Current and redistribute water to the equator within the Gulf of Papua Current (GPC). These currents are formed following the bifurcation of two Coral Sea westward jets, the North Vanuatu Jet (NVJ) and the North Caledonian Jet. While the existence of the boundary currents has been inferred from limited geostrophic sections, gridded climatological analyses, and modeling studies, no direct measurements have been collected. This study synthesizes current and water property measurements from a 7‐year record at Lizard Island and multiple Seaglider deployments between 2010 and 2014. Both repeat glider transects at 14.5 and 18°S and deployments spanning latitudes between 18 and 11°S are included. Cross‐track velocities of these currents show their vertical structure, seasonal changes, and the spatial translation of the bifurcation latitude. The NVJ bifurcation varies seasonally about a mean latitude between 14.4 and 14.7°S. It has a peak northward extent in summer, when the East Australian Current and GPC exhibit maximum and minimum transports, respectively. The deeper GPC originates from the North Caledonian Jet south of 18°S and varies seasonally by 4 Sv. When the westward flow of the NVJ reaches the boundary, the GPC's northward transport grows by ~13 Sv. The salinity signature of the glider data confirms that up to 6 Sv of this influx is sourced from the base of the NVJ. The observed seasonal cycle of current strength and changes in along boundary transport are consistent with the results from an ocean general circulation model.