The oceanic equivalent of finding a needle in a haystack

GPS positions from float on land
Fishing vessel that picked up the float
Close up of the sensor head fouled with barnacles

By Craig Macaulay

The search for an ocean robot used to monitor the ocean east of Australia has turned up 'gold', thanks to the fishing community on Queensland's Sunshine Coast.

The Argo profiling float is one of a fleet of around 3200 in the world's oceans used by scientists to observe sub-surface ocean conditions and report them to agencies such as CSIRO and the Bureau of Meteorology, which make the data available to the public within 24 hours. Profilers drift with the ocean currents and, with the aid of a built-in hydraulic power system, cycle between the surface and a depth of two kilometres to record and relay ocean temperatures and salinity levels.

The temporarily lost profiler was deployed by the San Diego-based Scripps Institution of Oceanography near New Caledonia 18 months ago. It grounded on the seafloor near the south east Queensland centre, Mooloolaba, late last year and failed to surface as part of its routine cycle. It has just been spared the ignominious fate of conversion to a letterbox through the timely intervention of CSIRO Wealth from Oceans scientist, Dr Ann Thresher.

Around midnight on 20 January, Mooloolaba prawn fishing veteran, Robert Wilson, was working in 40 metres of water east of south-east Queensland on his vessel Castlemain when the profiler turned up in his nets. Barnacled, scraped and filthy, the Argo float resumed its normal 10-day transmissions to the satellite - but this time from the back of Mr Wilson's blue van.

"We knew the general vicinity it was in thanks to GPS and Google," said Dr Thresher, who travelled to Mooloolaba from her base in Hobart on 19 February and could locate the float to within a block of the town but no closer.

"I returned to Brisbane ready to fly home to Tasmania but thought it has to be there somewhere and so changed flights and headed back north again. I walked the yacht club marina with a photograph of the float to show to anyone I met and then headed for the fishing boats. Believe it or not, on the last vessel I got to the crew recognised it and got in touch with Robert who brought it around," Dr Thresher said.

She praised the Mooloolaba community – from the local news media to the Mooloolaba Yacht Club and Marina – for their help. Until Dr Thresher walked along the marina, the aluminium profiler was just days away from being converted, with an angle grinder, into a letterbox. (Note that this is not recommended - apart from the expense of such an instrument, opening a float could cause the lithium batteries to explode).

Dr Thresher said that while the data gathered in the past 18 months had been transmitted, locating the float meant its condition could be evaluated by CSIRO engineers.

"Rarely do we have the opportunity to recover the profilers because they are mostly drifting with the remote currents in the ocean basins anywhere between the Arctic and Antarctic," she said.

"Through the information these floats deliver on ocean conditions and their influence on climate, Australians ashore and marine industries, such as fishing and shipping, benefit from knowing how the oceans are changing."

Dr Dean Roemmich, from Scripps Institution of Oceanography said: "It appears that the east coast of Australia is a place that floats will occasionally travel thousands of kilometers to visit. They need to be secured safely, hopefully without a need for such brilliant detective work on a routine basis. It really is an amazing story."