Circulation in the Lau Basin and Havre Trough

The ridge systems that frame the Lau Basin and Havre Trough, located east of Fiji and north of New Zealand, separating a large counterclockwise gyre at the surface into two smaller gyres at depth. A strong deep western boundary current (DWBC) has been observed flowing northward, following the Tonga and Kermadec Trench systems, transporting bottom water to the North Pacific. Though circulation has been described to some degree around the Lau Basin and the Havre Trough, these sub-basins have largely been ignored, presumed to act as a barrier to flow and separating the western South Pacific from the eastern South Pacific. An analysis of float data from several sources as well as traditional ship-board hydrographic data reveal a DWBC within the Lau Basin and Havre Trough that is fed by westward flowing jets from breaks within the ridge system. A simple analytical model predicts the large-scale dynamics observed in the basin, and indicates that the topographic structure of the ridge modulates the flow patterns. Sources of water into the Lau Basin and Havre Trough indicate intermediate water sources from the eastern South Pacific, while deep water sources originate to the west. This leads to a revised view of the role of the Lau Basin and Havre Trough with respect to circulation in the South Pacific.