Extending our understanding of South Pacific gyre “spin-up”: Modeling the East Australian Current in a future climate

The western Tasman Sea represents a global warming marine hot spot, where the waters arewarming at almost 4 times the global average rate, argued in the literature to be due to a spin-up of theSouth Pacific subtropical gyre and extension of the East Australian Current (EAC). To further investigate andtest this paradigm, we analyze climate change simulations of Tasman Sea circulation and metrics on outputfrom the Ocean Forecasting Australia Model for the 20th and 21st centuries, forced by a global climatemodel simulation under the A1B carbon emissions scenario. First, we show that the 1990s simulation estimatesof mean dynamic topography, present-day location of the EAC separation point, and volume transportsof the EAC, EAC extension, and flow along the Tasman Front, are consistent with recent observations.We further demonstrate that between the 1990s and 2060s, the volume transport of the EAC extension isprojected to increase by 4.3 Sv at the expense of the flow along the Tasman Front (projected to decrease by2.7 Sv). The transport of the EAC core flow (equatorward of the separation point) is projected to changevery little (increase of 0.2 Sv). The model projects a Tasman Sea-wide warming, with mean increases of upto 3C. These results are interpreted using a simple linear, barotropic model which captures both the signand meridional distribution of the projected changes in mean transport, including negligible change in coreEAC transport but enhanced EAC extension. This meridional asymmetry in the transports is consistent withthe wind-forced ocean response to changes in the basin-wide wind stress curl.