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Sea temperatures and climate change in Tasmania

Dr Alistair Hobday and Jason Hartog (CSIRO).

Many coastal waters around Australia are warming up, according to monitoring by the CSIRO Marine and Atmospheric Research. And Tasmania is no exception.

The CSIRO has analysed ocean temperatures around Tasmania since records began in the late 1800s.
Strong coastal warming has been recorded on Tasmania’s east coast, with ocean temperatures rising about 0.8°C since the 1960s compared to the long-term average.  This region is part of the “Tasman Sea hotspot” for ocean warming, along with eastern Victorian and southern NSW seas. There has been less warming on Tasmania’s west coast over the last few decades (~0.4 °C). It’s estimated that Tasmania’s east coast seas are warming at rates 3 to 4 times the global average.
How do currents influence sea temperatures around Tasmania? On the east coast, summer water temperatures are strongly influenced by the extent of the East Australia Current (EAC). In warm years (e.g. 2012), the EAC extends south warming the entire east coast and brings with it warm-water marine species. In weaker EAC years (e.g. 1994), sub-Antarctic waters from the south extend along the east coast resulting in cooler coastal temperatures (this is illustrated in the satellite image of 1994 versus 2012).

Left image: A relatively cool summer in Tasmania (1994). Right: A relatively warm summer (2012)(CSIRO).

Coastal heating and cooling, related to atmospheric conditions, is often visible at many coastal bays around Tasmania. On the west coast of Tasmania, the extension of the Leeuwin Current can also bring relatively warm water in winter.

A temperature rise of 0.8°C since the 1960s doesn’t sound like much. But for marine ecosystems this can have a significant impact on the distribution and physiology of species.

Marine species have their own set of conditions they prefer to live in, like temperature and pH.  Some biota will move (if they can) - also known as shifting their range - in search of these conditions if things get too hot at home.  Others may adapt well to warming seas; while some will not survive in the changing conditions. For example, warming has seen some species heading further south than usual down Tasmania’s east coast, such as eastern rock lobster (Jasus verreauxi), yellowtail kingfish (Seriola lalandi) and herring cale (Olisthops cyanomelas).

It’s no wonder some marine animals are being spotted further away from their usual range: possibly looking for cooler waters?

(Story edited by: Yvette Barry)

Above: changes in Sea Surface Temperature (SST) since 1880 for southern and eastern Australia (Image: CSIRO). Notice in the graphs, that water temperatures start rising above the long-term average after about the 1960s.

Acknowledgement: Data shown in these images represent the temperature of water at the surface and are collected by satellite, and processed at CSIRO by Chris Rathbone and colleagues. Further information is available at Images and movies prepared by Alistair Hobday and Jason Hartog (CSIRO).

For more information see:

Sketch of thermometer: Elsa Gartner, IMAS.

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