Round the world - and again - for ocean science

20 April 2005

Round the world - and again - for ocean science

NIWA’s smaller research vessel, Kaharoa, leaves Wellington tomorrow (Thursday 21 April) on a 2-month voyage to deploy high-tech ‘Argo’ floats all the way to Hawaii and back.

Already, the crew of Kaharoa have deployed more Argo floats (141 so far) than any other vessel in the world. By the end of this trip, they will have deployed over 200 floats and clocked up over 40,000 nautical miles on Argo missions. That is almost the equivalent of sailing to the UK and back twice. (A round trip to the UK is approximately 24,000 nautical miles.)

The Argo programme is a worldwide effort to deploy a network of high tech floats which will help scientists measure global warming, predict the strength of tropical cyclones, and even get a better fix on the path of toxic algal blooms.

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

Information from the floats is available for anyone to analyse. Comparisons between data from Argo floats deployed last year (largely from Kaharoa) and data collected from research vessels 10-15 years ago indicate that a large area of water east of New Zealand
has warmed up.

This warming is also evident in the elevated sea surface height measured from satellites. “The South Pacific Ocean flows anticlockwise in a large circle called the subtropical gyre,” says NIWA scientist Dr Philip Sutton. “It seems that the gyre has sped up, probably because of stronger westerly winds to the south of New Zealand and weaker westerlies to the north”.

These changes, in what is called the Antarctic Oscillation, may be entirely a natural cycle in the atmosphere and ocean, or they may include a long-term trend indicative of climate change. Information like this is valuable for fisheries and climate scientists, not just oceanographers. “The beauty of Argo is that we get much more precise information beamed back to us on regular intervals, so we can start to understand much more about the complexities of the ocean.”

The floats cost about $20,000 (NZ) each. The voyage is a joint collaboration between NIWA, the University of Washington (Seattle), and Scripps Institution of Oceanography (San Diego).

Kaharoa is 28 metres long. When not on Argo voyages, the vessel is generally used for scientific research close to shore.

This will be the first time Kaharoa has crossed the Equator, but it has been right across the Pacific to Chile and almost to Peru, deploying Argo floats. Later this year, the vessel will deploy another 134 floats on a lengthy voyage which will take the crew back across to Chile and up to San Diego, California.

ENDS