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

Abstract

The western Tasman Sea represents a global warming marine ‘‘hot spot,’’ where the waters are warming at almost 4 times the global average rate, argued in the literature to be due to a ‘‘spin-up’’ of the South Pacific subtropical gyre and extension of the East Australian Current (EAC). To further investigate and test this paradigm, we analyze climate change simulations of Tasman Sea circulation and metrics on output from the Ocean Forecasting Australia Model for the 20th and 21st centuries, forced by a global climate model simulation under the A1B carbon emissions scenario. First, we show that the 1990s simulation estimates of mean dynamic topography, present-day location of the EAC separation point, and volume transports of 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 is projected to increase by 4.3 Sv at the expense of the flow along the Tasman Front (projected to decrease by 2.7 Sv). The transport of the EAC core flow (equatorward of the separation point) is projected to change very little (increase of 0.2 Sv). The model projects a Tasman Sea-wide warming, with mean increases of up to 3C. These results are interpreted using a simple linear, barotropic model which captures both the sign and meridional distribution of the projected changes in mean transport, including negligible change in core EAC transport but enhanced EAC extension. This meridional asymmetry in the transports is consistent with the wind-forced ocean response to changes in the basin-wide wind stress curl.