The historical representation and near-future (2050) projections of the Coral Sea current system in CMIP6 HighResMIP

Abstract

Abstract. The Coral Sea houses expansive coral reefs. Reef health is inextricably linked to water temperatures, which are regulated by the hydrodynamic environment. The ocean current system in the Coral Sea is dominated by jets of the South Equatorial Current (SEC): the North Vanuatu Jet (NVJ), the North Caledonian Jet (NCJ) and the South Caledonian Jet (SCJ). We investigated the projected near-future (2050) changes in the temperature and transport structure of the Coral Sea using the three highest-resolution climate models from the high-resolution coupled modelling experiment (HighResMIP) conducted within the latest iteration of the Coupled Model Intercomparison Project Phase 6 (CMIP6). We found that the HighResMIP models successfully represented the historical temperature and transport structure of the SEC jets and their El Niño–Southern Oscillation-related variability. Surface ocean warming of 0.78 and 1.12 °C was projected in the Coral Sea under 1.5 and 2 °C global air temperature warming, respectively. The maximum depth of the warming signal deepened by 30 m per decade, penetrating to 400 m by 2050. This indicated the additional thermal stress that could be experienced by Coral Sea ecosystems. Interestingly, the surface warming was associated with a sub-surface cooling between 400 and 600 m. Decreases in the transports of the NVJ and NCJ and an intensification of the SCJ were also projected in the HighResMIP models. The magnitudes of the changes were relatively small (2 % to 7 % of historical means) and of a similar order to the variability in transport associated with the El Niño–Southern Oscillation. Our analysis further showed that the transport projections of the NVJ and NCJ varied with depth, where surface intensifications coincided with the areas of greatest warming. These changes could modify western boundary currents and upwelling dynamics on the Great Barrier Reef shelf.