Argo

Introduction

Argo is an array of around 3,000 profiling floats that provide observations from the global oceans with an average spacing of around three degrees in latitude and longitude (approximately 300 km). Since 2000 the Argo programme, which involves more than 30 countries, has deployed more than 6,000 floats into the ice-free deep oceans around the world. The present status of the array is shown in the figure on the right (produced by the JCOMMOPS Argo Information Centre).

The floats measure ocean temperature, salinity (dissolved salt content) and pressure (depth) between the surface and 2,000 metres depth.

How the Argo floats work

Float is deployed from a ship and remains at the surface for six hours sending engineering (housekeeping) data
Float sinks to its 'drifting' depth of 1,000 metres
Float drifts for nine days
Float descends to its maximum depth of 2,000 metres
Float ascends to the surface, recording temperature, salinity and pressure (typically at 50-100 levels) as it rises
Float transmits its data to satellite and its position is determined by the satellite

This cycle (steps 2 to 6) is repeated every ten days until the batteries run out; each float is expected to operate for about four years (approximately 140 cycles).

Why use Argo floats?

Before Argo began in 2000, routine observations of the oceans were mainly limited to temperatures above 500 metres depth, gathered from Expendable Bathythermographs (XBTS) mostly launched from commercial vessels along the main shipping lanes. XBTs are expendable probes which are fired into the water from a gun and transmit the data back along a thin wire. With Argo, we now have around five times as many observations from the world’s oceans than previously — to a higher accuracy, greater depth and with salinity. Additionally, Argo also delivers data from many previously data-sparse regions, especially in the Southern Hemisphere.

The oceans have a major influence on the climate system but we still have relatively little information about them. Data gathered by the floats are vital for ocean climate monitoring and for long-range prediction. Now, for the first time, scientists are able to observe variability within the oceans over annual and longer timescales. The data are also essential (along with satellite data) for operational ocean forecasting. By examining the floats’ positions every 10 days, scientists are also able to deduce the deep ocean circulation patterns at 1,000 metres depth.

For more information about the use of Argo data, read the report Argo – a cornerstone of UK earth observation and climate science (PDF, 549 kB).

Person about to deploy a float from a ship

What role does the UK play?

The UK's contribution to Argo is being funded by the Department of Energy and Climate Change (DECC), the Ministry of Defence (MoD) and the Natural Environment Research Council (NERC), and is undertaken by a partnership involving the Met Office, the National Oceanography Centre, Southampton (NOCS), the British Oceanographic Data Centre (BODC) and the UK Hydrographic Office (UKHO). The UK Argo programme is managed and co-ordinated by the Met Office, with specialist scientific advice provided by NOCS, while BODC operate the UK Argo Data Centre and the Southern Ocean Argo Regional Centre.

For more information on UK Argo, read the UK Argo Project Report (PDF, 1.3 MB).

We also have a significant role in the Euro-Argo Project which aims to develop the European infrastructure to the level where the European partners have the capacity to procure and deploy ~250 floats per year, such a European contribution would support approximately 1/4 of the global array and provide an additional 50 floats per year for enhanced coverage in the European and marginal seas.

UK float deployments

Our first Argo floats were deployed in January 2001, with nearly 290 UK floats having been deployed to the end of 2009. They’ve been deployed in a variety of ways.

From both UK and foreign research ships
By the Royal Navy
From Voluntary Observing Ships (VOS)
From the air (by the US Navy)

This includes five floats that have been donated to Mauritius.

UK float deployments
Year	Floats funded through DECC and MoD	Floats funded through NERC
2001	24	5
2002	29	9
2003	23	15
2004	47
2005	26	2
2006	26
2007	28	5
2008	29
2009	20

In 2010 and 2011 we expect to deploy around 35-40 more floats each year.

More information on UK Argo floats that have been deployed is available from the UK Argo Data Centre at the British Oceanographic Data Centre.

Argo data

A key aspect of Argo is that all Argo data are freely available without any restrictions, both in real-time (within approximately 24 hours of their transmission) and in ‘delayed-mode’ after scientific quality control. Tbe real-time data are made available to the operational community via the World Meteorological Organization Global Telecommunications System (GTS) and from the two Argo Global Data Acquisition Centres (GDACs) in the US and France. In addition to the GDACs, Argo has also established a number of Regional Centres (ARCs) to compile consistent regional data sets and Argo-based products.