Argo floats

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Since the early 2000s, NIWA has been part of the international Argo programme, which is deploying floats to measure temperature and salinity throughout the world's oceans.

The data being gathered will improve our understanding not only of our oceans, and in particular the oceans' role in climate, but also of our weather and climate prediction systems.

Overview

Argo floats are instruments able to measure temperature and salinity in the top 2000m of our oceans. This information helps us to better understand:

  • oceanographic research. Near-real time information about the oceans' changes is revolutionising knowledge of ocean dynamics. To date about 1100 peer-reviewed papers have used Argo data. Topics include water mass properties and formation, air-sea interaction*, ocean circulation (large scale currents), mesoscale eddies (ocean weather systems), ocean dynamics, and seasonal to decadal variability .
  • climate variability. It helps us to understand variability on a range of time scales, interpret previous changes and ultimately improve climate predictability.
  • knowledge of the state of our oceans is beginning to allow us to understand the conditions which affect fish stocks and biological productivity, as well as better understand how our oceans function as complex systems. Because the data are near-real-time and easily available, they are also being assimilated into operational modelling, including for short-term prediction of currents (e.g. offshore oil spills, search and rescue) and temperature (e.g. for fisheries), for seasonal-to-interannual forecasting (e.g. El Niño), and for initializing decadal predictions of the ocean/atmosphere climate system (such as those of the IPCC). Eventually, the data could even feed into short-range weather forecasting.

Read the Water & Atmosphere article 'Ocean circulation: the planet's great heat engine'

More information on forecasting ocean 'weather'

The Southern Hemisphere and South Pacific, however, have tended to be data-poor regions.

 

*See the links below for examples:

How they work

Argo floats have been deployed since 2000.

A typical Argo float cycle consists of an 'initial floating depth' in the ocean about 1km below sea level. After 9 days at this depth, the float then sinks down to 2km before coming back up to the ocean surface. As the float rises, it measures temperature and salinity through the water column. Once on the surface, these data, along with the position of the float, are then transmitted via satellite to data facilities, before the float repeats the process. The data are freely available from websites in the USA and Europe within hours of collection.

The buoyancy of an Argo float, which allows it to rise and sink in the water column, is controlled by pumping oil between internal and external bladders.

A benefit of the 1km primary floating depth is that animals like barnacles don't grow at this depth, due to the lack of light, and so won't attach themselves to the floats (this would affect the floats' buoyancy and could foul the sensors). Additionally, flows at 1km tend to be fairly slow, so the floats don't generally travel great distances (except in the southern ocean).

Argo floats are deployed all over the world - the aim is to have over 3000 of them, distributed roughly every 3 degrees (300km). Deployments began in 2000, and continue at a rate of about 800 a year.

The results

In the early 2000s, NIWA was already active in Argo at a regional level, having deployed several Argo floats around New Zealand. During one of Dean Roemmich's (Scripps Institution of Oceanography) visits to New Zealand, the challenge of deploying floats in the southern hemisphere was discussed. It was realised that NIWA's Kaharoa, predominantly used for coastal research, would make an ideal deployment platform.

The Kaharoa – a NIWA vessel – is used to deploy floats, and a collaboration between NIWA, the Scripps Institution of Oceanography,the University of Washington and more recently, CSIRO, will have been responsible for deploying over 1000 floats by the end of the October/November voyage in 2012.

More information about Karahoa

More information about NIWA Vessels

The Kaharoa has done some very large transects while deploying Argo floats. As of 2012, she has been to Chile at least 5 times, as well as Durban (South Africa), Mauritius, Tahiti, San Diego and Hawaii. While she hasn't yet been to the South Atlantic, there are hopes that she will be able to go there in the future.

ARGO - measuring salinity and temperature across the oceans [from NIWA].

Page last updated: 
3 October 2017
At some 3500 floats, the global Argo deployment is now complete, but a further 800 new ones must be placed each year as older floats fail. Their data will help develop more comprehensive ocean-coupled climate models. Credit: NIWA
Argo Float: the 10-day cycle of data collection
All of the Argo floats deployed by NIWA between 2004 and 2011. The 5 voyages that went south of 45°S were done by Tangaroa, the rest by Kaharoa .
RV Kaharoa, at Wellington Harbour. [Dave Allen]