The near‐surface waters off eastern Tasmania represent both a global warming and a biodiversity hotspot. Marine ecosystems there are under significant stress. The sensitivity of these local ecosystems to both warming and transient marine heatwave events has been observed but historical temperature patterns and salinity variability over space and time are less well‐known.
To understand how these had changed, researchers used a numerical ocean model to provide high‐resolution estimates of the seawater temperatures, salinity and circulation over the eastern Tasmanian continental shelf. They performed a systematic analysis of multidecadal‐scale trends and yearly variability off eastern Tasmania over a 24‐year period from 1993 to 2016.
The researchers found a significant increase in East Australian Current (EAC) Extension penetration into the region with an associated increase in temperature and salinity throughout the water column, particularly in summer and autumn.
The variability of the circulation on the shelf was dominated by the interplay of the EAC Extension and an extension of the Leeuwin current south of Tasmania, known as the Zeehan Current. This interplay could be captured in an annual index developed by the researchers indicating the relative strength of these two currents over time.
In summer and winter, they found an unusually strong EAC Extension leads to an increase in the probability of marine heatwave days. Conversely, a strong Zeehan Current during these seasons decreased the probability of marine heatwave days.
- Paper: Oliver, E.C.J, and N.J. Holbrook. (2018), Variability and long‐term trends in the shelf circulation off eastern Tasmania, J. Geophys. Res. Oceans. https://doi.org/10.1029/2018JC013994