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Abstract:
The ocean region around Tasmania forms an interface between major ocean basins and represents a significant global ocean hotspot due to a rate of warming higher than the global average. We use a high-resolution (0.02x 0.02, 1992-2020) satellite SST received at local stations (validated against in situ temperature) to explore the seasonal, interannual, decadal variability and long-term trends of SST. The SST is used a proxy for seasonal circulation by removing the broad-scale radiative forcing (estimated by a region-wide latitudinal gradient of SST). The main circulation drivers of nearshore SST are the East Australian Current (EAC, east coast) and Zeehan Current (ZC, west) with peaks in summer and winter. New results include the seasonality of three summer upwelling systems, the first evidence of EAC inflow into eastern Bass Strait, a time series of the endpoint of the ZC/EAC intersection, and a full year description of the ZC, from warm winter inflow transitioning into a cooler than ambient summer intrusion. We have identified two modes of low frequency SST variability associated with the EAC (63% of the variance) and the ZC (12%). The EAC mode induces a rapid adjustment of the entire ocean region around Tasmania. Multi-decadal warming trends occur in all regions, with nearshore values of order 0.40°C decade-1 up to a peak of 0.55°C decade-1 on the west coast. SST trends in the eastern shelf arise from intrusions of EAC waters, with local processes (suppression of upwelling and outflow from enclosed bays) driving trends on the western shelf
