This is the big one: 112 days on the high seas

Media Release 20 October 2005

This is the big one: 112 days on the high seas

A 28-metre research vessel from the National Institute of Water & Atmospheric Research (NIWA) will spend the next four and half months deploying ocean-profiling Argo floats across the Pacific.

RV Kaharoa is scheduled to leave Wellington on Friday (21 October) and will not return home until March 2006. During that time, the crew of five will deploy 133 Argo floats for Scripps Institution of Oceanography (San Diego), the University of Washington (Seattle), and NIWA.

The floats will measure ocean currents, temperature, salinity, pressure, and (in some cases) dissolved oxygen. The data are transmitted by satellite every ten days. There are over 2000 Argo floats operating world-wide. Each float is worth about $20,000 and has a lifespan of about 4–5 years.

Argo data are now being widely used by scientists, with abstracts for at least 100 papers submitted for the second international Argo science workshop to be held in March 2006. Thirteen operational weather and climate centres around the world also use Argo data because ocean conditions can have a significant effect on the weather and climate. For example, Argo data can be combined with satellite altimetry to improve predictions of hurricane intensity.

Dr Dean Roemmich of Scripps Institution of Oceanography is one of the founders of the Argo programme. Above all, he says, ‘Argo is the first programme to measure global change in the oceans. We need about ten years’ worth of float data to get a good indication of how the seas are changing, but we can already start to study variations such as El Niño.’

Dr Roemmich and NIWA scientist Dr Philip Sutton have also compared data from Argo floats with that collected from research vessels during the ‘World Ocean Circulation Experiment’ 10-15 years ago. This shows that a large area of water east of New Zealand has warmed up and freshened over that time.

Kaharoa is also deploying ‘surface drifters’ for the New Zealand Met Service and the US National Oceanic and Atmospheric Administration (NOAA). Surface drifters measure sea surface temperature, surface currents, and atmospheric pressure. Their main function is to calibrate satellite measurements of sea surface temperature, which have wide uses including weather forecasting and fishing operations.

ENDS

RV Kaharoa Schedule

- 21 Oct – 13 Nov: South Pacific (24 days from NZ to Chile)

- 14 – 19 Nov: Valparaiso, Chile (6 days for refuelling, restocking, maintenance, crew change)

- 20 Nov – 19 Dec: South/Central Pacific (30 days from Chile to USA)

- 20 Dec – 6 Jan: San Diego, USA (18 days for refuelling, restocking, maintenance, loading more floats, crew R&R)

- 7 Jan – 2 Feb: Central Pacific (27 days out & back to San Diego)

- 3–7 Feb: San Diego, USA (5 days for refuelling, restocking, maintenance, loading more floats)

- 8 Feb - 9 March: Central/South Pacific (30 days from USA to NZ)

Dates & travel times are approximate, depending on weather & other factors.

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.

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

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