Boat floating on the sea
Boat floating on the sea along the coast

For the next three months New Zealand is helping seed the Pacific Ocean with high[1]tech floats that are taking the ‘pulse’ of the world’s oceans; local marine researchers are also using the floats to understand waters closer to home.

In mid-July, the National Institute of Water and Atmospheric Research (NIWA) vessel, Kaharoa, set sail on a 90-day voyage to deploy high-tech floats between New Zealand and Peru. Kaharoa will carry 84 floats, which is the largest number ever deployed in a single voyage.

The floats, part of an international project called Argo, can help scientists measure global warming, predict the strength of tropical cyclones, and even get a better fix on the path of toxic algal blooms.

“Many people don’t realize that both the ocean and the atmosphere are important for controlling the climate over the long[1]term,” says NIWA oceanographer, Dr Philip Sutton. “We need to know what’s happening in the oceans just as much as we need weather-balloons and other atmospheric-observing tools.”

Each float sinks to a depth of 1000 meters and parks there, carried along by ocean currents. After nine or ten days, it sinks further to between 1250 and 2000 meters, then rises to the surface, measuring the temperature and salinity of the water on the way up. Once on the surface, the float transmits data and its location via satellite.

The voyage is a joint collaboration between NIWA, the Scripps Institution of Oceanography, and the University of Washington in Seattle. Two of the leaders of the project, Dr Dean Roemmich of Scripps and Dr Steve Riser of the University of Washington, were in Wellington to prepare the floats before the voyage.

If you want to observe global warming, the ocean is the place to look because it’s absorbing more than 90 per cent of the additional heat,” said Dr Roemmich in a statement.

“At first look, the floats deployed by Kaharoa between here and Chile are confirming that the sea along the route is becoming less salty. That’s consistent with global warming, where temperate regions get more rain and so the upper layers of the ocean have more fresh water in them.”

“Another example of Argo’s use is in tropical cyclones,” said Dr Riser. “In the Atlantic, we’ve now had 140 cases where a hurricane has travelled over an Argo float. Such storms suck heats out of the ocean – the floats have measured up to a one-degree Celsius drop in temperature even at depths of 100 to 150 meters.”

For now, the communication from the floats is just one way, but the hope is that over the life of the Argo project, which aims to deploy and maintain 3,000 floats by early 2007, the communication will become two way.

“If you were in a really interesting spot you could tell it to go up and down continuously until you stop it,” explains Dr Sutton. “So, if you were under a tropical cyclone and really interested in what was going on, you could tell it to change its behavior because you’d have two-way communication.”

NIWA has bought three of the floats and has them deployed in waters near New Zealand; this month NIWA will put two more floats into New Zealand waters in a separate voyage. Having data from these Kiwi floats, along with the international ones, should give NIWA’s researchers more information about what is happening in the oceans around New Zealand.

“Ten years from now we will be able to compare what floats are doing in the Tasman with what they are doing now and you will actually have an idea of change,” says Dr Sutton.

The Argo floats have been progressively deployed into the world’s oceans over the past five to six years; the Pacific and the Southern Oceans have been some of the last areas to be covered. Taking the ocean’s ‘pulse’ is a time-consuming business: “It’s early days,” says Dr Sutton. “The idea would be that when Argo is ten years old you can see how things have changed.”

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