Keeping current: Investigator’s latest voyage to boost deep water moorings

But much of our surrounding ocean and our four major currents, including the East Australian Current (EAC) remains a mystery.

Deepening our understanding of these colossal currents is core business for the Integrated Marine Observing System (IMOS) and its Deep Water Moorings Facility, led by CSIRO’s and DCFP Team Leader, Dr Bernadette Sloyan.

Wait – what exactly is the EAC?

Bernadette and her science and engineering team have been continuously observing a key slice of the EAC since 2015. To break down what the EAC is all about, we chatted to the Bernadette, who has just returned from a three-week voyage aboard our research vessel Investigator in the Coral Sea.

“The EAC is the largest ocean feature off Australia’s east coast,” says Bernadette.

“Changes in the EAC just beyond our beaches impact our coastal industries and communities. Over in Australia’s regional and rural centres, life beats to a drum of climate conditions that is partly influenced by our dynamic ocean and its relationship with the atmosphere.”

From Queensland to Tasmania, the powerful EAC is up to 100 kilometres wide, 1.5 kilometres deep, and can carry up to 40 million cubic metres of water each second. In other words – that’s 70 billion pint glasses, refilled sixty times a minute.

Bernadette explains that the EAC serves an important role beyond its powerful flow.

“It acts as a kind of salty delivery van for the warmth that drives our climate and nutrients that fertilise ocean ecosystems,” says Bernadette.

“The EAC is also very fickle, hugging the coast one day and then flowing hundreds of kilometres out to sea the next. This unstable behaviour renews fish stocks, impacts water quality, weather, and sets the water temperature for swimmers and surfers.”

Keeping tabs on the EAC

One way we can monitor how the EAC is changing over time is to use an array of deep-water moorings. This is what has been established through IMOS –  creating a network of advanced marine equipment that tracks changes in the EAC. The array is currently lined up, across and down the slope of the seabed off Brisbane. This underwater observatory continuously monitors the EAC’s complex and highly energetic nature, discovering links to changes in our climate and coastal ecosystems.

However, nothing lasts forever. Just like a new smartphone, its advanced sensors and tiny computers working away under the waves still need to be recharged every now and then, and about every year and a half the mooring’s “batteries” go flat.

The good news is that Bernadette and her team of scientists and engineers have just recovered the six deep-water moorings, boosted their batteries, downloaded their data, and have put the gear back to work for Australian science.

Biologists and oceanographers, unite!

Our oceanographers were accompanied on board by biological specialists – collaborators from both University of New South Wales and Griffith University. Professors Iain Suthers, Kylie Pitt, and their crew were exploring how the energetic EAC and its eddies (swirling ocean circulations) that weave their way through its great flow can support abundant and diverse communities of larval fish and sea jellies found there.

To sample the ecology of this ever-changing region off Queensland, voyagers deployed specialised towed instruments and net systems off Investigator.

It’s this expert partnership and cooperation between ocean physics and marine biology boffins that will help connect the dots between the apparent chaos of a mammoth ocean current and its often unappreciated impact on our lives.