Research vessel returns from voyage across the Pacific

After four and a half months, and 23,186 nautical miles, a New Zealand research vessel is finally coming home.

Since mid-October, NIWA’s 28-metre research vessel Kaharoa has deployed more than 100 high tech ocean-profiling floats at prescribed locations in the South and Eastern Tropical Pacific.

The ‘Argo’ floats are used by operational climate and weather centres, and by scientists studying changes in the world’s oceans.

RV Kaharoa and crew of five are currently due to arrive in Auckland on the morning of Sunday 12 March.

This is Kaharoa’s fourth Argo deployment voyage, and the longest to date. Over the course of those four voyages, the sturdy ship has travelled a total of 63,375 nautical miles and deployed 333 Argo floats. Three of the current crew are the most seasoned ‘Argonauts’: Master Ron Palmer, Assistant Mate John Hunt, and Cook/Deckhand Mark Styles have all travelled over 58,000 nautical miles on Argo missions.

The Argo programme aims to have a network of about 3000 floats operating around the globe. In many places, the floats have been deployed from regular container ships, or even from the air. Neither option was feasible for much of the Pacific, so, in 2004, Scripps Institution of Oceanography (San Diego) and the University of Washington (Seattle) formed a collaboration with NIWA to use RV Kaharoa. NIWA has now deployed more Argo floats than any other organisation in the world.

RV Kaharoa’s next Argo mission will be to Mauritius later this year. Before then, it’ll be staying closer to home, helping NIWA scientists conduct fisheries surveys and other research around the New Zealand coast.

Background

What Argo floats do: a typical ten day cycle

How deep a float goes and how long it spends there is pre-programmed.

In general, Argo floats first sink to about 1000 metres. At a rate of about 10 centimetres per second, this takes about 6 hours. Floats usually drift at this depth for about 9 days. They then descend further, down as far as 2000 metres, before rising back to the surface profiling the temperature, pressure, and salinity of the water on the way.

Some of the floats deployed on this voyage also measure dissolved oxygen

A float will spend 6–12 hours on the surface transmitting data to passing satellites.

How long does an Argo float last?

Floats have a lifespan of approximately 4–5 years.

How much does an Argo float cost?

Each float is worth about NZ$20,000.

How are Argo data being used?

There are many different uses for Argo data. All data are available free: anyone can download data from two global data servers (in France and the USA).

Thirteen operational weather and climate centres are currently using the data. For example, Argo data can be combined with satellite altimetry (measure of sea surface height) to improve predictions of hurricane intensity. The data can help improve understanding of variations such as El Niño. It’s been suggested that about ten years of Argo data would be required to get a good indication of longer term changes in the world’s oceans associated with global warming.

For more detail, see www.argo.ucsd.edu