Ocean robots set course to the middle of nowhere
NIWA’s 28–metre long research vessel Kaharoa, will spend the next month deploying high tech ocean-profiling floats in the mid-Pacific.
19 June 2007
For the south-west Pacific, Argo data are showing that the ocean east of New Zealand (red line) has warmed up faster than the global average (grey line) for the past 40 years.
The 28–30 day journey will take the crew of five in a loop from Wellington up towards Tahiti then back to Auckland without making landfall.
The ‘Argo’ floats measure properties and currents of the upper ocean then surface to beam this data to satellites.
This is RV Kaharoa’s seventh Argo assignment: the ship has deployed more Argo floats than any other vessel in the world. In many places, the floats have been deployed from regular container ships, or even from the air. Neither option is 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 (National Institute of Water & Atmospheric Research) to use RV Kaharoa.
Argo programme leader Professor Dean Roemmich of Scripps Institution of Oceanogaphy says "without Kaharoa, there would not be a global Argo array today."
Argo data are used by operational weather and climate centres as well as researchers around the world. For the south-west Pacific, Argo data are showing that the ocean east of New Zealand has warmed up faster than the global average for the past 40 years.
RV Kaharoa is currently scheduled to leave Wellington on Wednesday 20 June or Thursday 21 June.
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.
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
