East Caledonian Current

Waters from the South Equatorial Current (SEC), the northern branch of the South Pacific subtropical gyre, are a major supply of heat to the equatorial warm pool,  and have an important contribution to climate variability and ENSO which motivated the Southwest PacIfic Ocean and Climate Experiment (SPICE, CLIVAR/WCRP). Initially a broad westward current extending from the equator to 30°S, the SEC splits upon arriving at the major islands and archipelagoes of Fiji (18°S, 180°E), Vanuatu (16°S, 168°E), and New Caledonia (22°S, 165°E), resulting in a complex system of western boundary currents and zonal jets that feed the Coral and Solomon Seas. We focus here on the formation of one specific jet feeding the Coral Sea, the North Caledonian Jet (NCJ). Using a combination of recent oceanographic cruises, we describe the ocean circulation to the northeast of New Caledonia, where the SEC forms a western boundary current that ultimately becomes the NCJ. This current, which we document for the first time and propose to refer to as the East Caledonian Current (ECC), has its core located 10 to 100 km off the east coast of New Caledonia, and extends vertically to at least 1000 m depth. Water mass properties show continuous westward transports through the ECC, from the SEC to the NCJ in both the South Pacific Tropical Waters in the thermocline and Antarctic Intermediate Waters near 700 m depth. The ECC extends about 100 km horizontally; its average 0-1000 m ECC transport was estimated at 14.5+/-3 Sv off the north tip of the New Caledonian reef, with a maximum of 20 Sv in May 2010. South of that, the upstream branch of the ECC east of the Loyalty is close to 8 Sv suggesting an important additional contribution from central Pacific waters carried by the SEC at 16°S and diverted to our region through the western boundary current system east of Vanuatu.

Hydrographic data, currents and transports east of New Caledonia. (Left) Hydrological station positions and Argo floats trajectories at 1000~m in the region of interest. Markers joined by lines indicate hydrological stations for each cruise (legend). Argo trajectories are indicated by the blue-purple curves. For best visibility, only Argo floats having a continuous trajectory along the SEC-ECC-NCJ pathways are shown. Fine continuous lines indicate the 500 m and 2000 m depth of the topography. The cruise trajectories are neither strictly straight nor perpendicular to the coast, and to facilitate comparisons we defined, in the following, a common axis which represents the distance perpendicular to the tilted east coast of NC. (Right) Topography, main water pathways and estimated transports from the present study. SEC = South Equatorial Current; ECC = East Caledonian Current; NCJ = North Caledonian Jet

Reference: Gasparin et al. 2011 (References)

2013 - Solwara: a SPICE/CLIVAR programme