Equatorward pathways of Solomon Sea water masses and their modifications

The Solomon Sea is a key region of the southwest Pacific Ocean, connecting the thermocline subtropics to the equator via western boundary currents (WBC). Modifications to water masses are thought to occur in this region because of the significant mixing induced by internal tides, eddies, and the WBCs. A high-resolution model incorporating a tidal mixing parameterization was implemented to depict and analyze water mass modifications and the Solomon Sea pathways to the equator in a Lagrangian quantitative framework. The main routes from the Solomon Sea to the Equatorial Pacific occur through the Vitiaz and Solomon straits, in the thermocline and intermediate layers, and mainly originate from the Solomon Sea south inflow and from the Solomon Strait itself. Water mass modifications in the model are characterized by a reduction of the vertical temperature and salinity gradients over the water column: the high-salinity of upper thermocline water (Subtropical Mode Water; STMW) is eroded and exported towards surface and deeper layers, while a downward heat transfer occurs over the water column. Consequently, the thermocline water temperature is cooled by 0.15 to 0.3°C from the Solomon Sea inflows to the equatorward outflows. This temperature modification could weaken the STMW anomalies advected by the subtropical cell and thereby diminish the potential influence of these anomalies on the tropical climate. The Solomon Sea water mass modifications can be partially explained (~ 60%) by strong diapycnal mixing in the Solomon Sea. As for STMW, about a third of this mixing is due to tidal mixing.

Streamfunction averaged for the surface (SW, top left), upper thermocline (TW, top right), lower thermocline (LTW, middle left), intermediate (IW, middle right) and deep (DW, bottom) layers in Sv. Contour spacing is 0.5 Sv except for DW (0.1 Sv). For each panel, the total transports through the Vitiaz Strait (blue), St George's Channel (green) and the Solomon Strait (red) are mentioned in the upper-right corner box. The following percentages represent the part of the transport that is achieved by the south inflow / Solomon Strait pathways.

T-S diagrams from the Coriolis database (dots) and from the model (line) upstream (red, 147°E-153°E 11.5°S-13°S) and downstream (blue, 143°E-147°E 3°S-5°S) of the Solomon Sea. Only profiles flagged as “good data” were extracted from the Coriolis database, from 01/01/1950 to 06/01/2010.

Reference : A. Melet, J. Verron, L. Gourdeau & A. Koch-Larrouy, 2011

2013 - Solwara: a SPICE/CLIVAR programme