Argo

Introduction

Argo is an array of profiling floats designed to provide observations from the global oceans with an average spacing of around three degrees in latitude and longitude (approximately 200 km). Since 2000 the Argo programme, which involves more than 30 countries, has deployed more than 5,000 floats into the seas around the world. The floats measure ocean temperature, salinity (dissolved salt content) and pressure (depth).

How the Argo floats work

Float is deployed from a ship and remains at the surface for six hours sending engineering 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 process (2 to 6) is repeated every ten days until the batteries run out; each float is expected to operate for about four years.

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) launched from vessels along the main commercial 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 of 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 prediction (from seasonal to decadal). 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.

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 for Environment, Food and Rural Affairs (Defra), the Ministry of Defence (MoD) and the Natural Environment Research Council (NERC), and is undertaken by a partnership involving the Met Office (which also manages the project), the National Oceanography Centre, Southampton (NOC), the British Oceanographic Data Centre (BODC) and the UK Hydrographic Office (UKHO).

For more information on UK Argo, read the UK Argo Project Report (PDF, 2.3 Mb).

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