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An ARGO float being deployed in the Southern Ocean.
An Argo float designed to measure ocean temperature and salinity being deployed in the Southern Ocean.
What if I told you that on Nov. 4, 2012 an army of robots succeeded in completing its one millionth mission?  You might say "Whoah!". But, there is no need to panic.  The army of robots is actually a group of autonomous profiling floats that have been patrolling the oceans since 2000, and the mission in question is a vertical profile of temperature, salinity and pressure (a measure of depth) through the upper 2000 meters of the water column.  This is the international Argo program ( and its goal is to maintain a global array of 3000 profiling floats to monitor the ocean in real-time.  As of this writing there are 3675 active floats, funded by 31 partner nations, distributed globally in our vast oceans.  An advantage of this distributed and autonomous network is that, compared to collecting similar data from oceanographic research vessels, Argo is about 25 times more cost effective.

How the floats work

The floats themselves are the size of a small hot water tank and can be deployed from ships or airplanes.  The battery powered floats are autonomous and designed to take advantage of slow-moving ocean currents to travel great distances as they collect real-time data on changing ocean conditions.  Argo floats operate on a 10 day duty cycle where they spend a majority of their time at a “parking” depth of 1000 meters, neutrally buoyant, and carried along by deep-ocean currents. After 9.5 days the float dives to 2000 meters where it starts to collect data as it begins a 6 hour ascent to the surface.  Buoyancy control is achieved by a pump which moves fluid in and out of a flexible bladder connecting the interior and exterior of the float.  Upon arriving at the surface, newer float models fix their position using the Global Positioning System (GPS) and connect to the Iridium satellite network to transmit its data which is subsequently relayed to a land receiving station.  This data is then made publicly available in near real time through the Argo website. This process takes roughly 6-12 hours after which the float makes its 3 hour descent to 1000 meters to begin the 10 day cycle once more.  With current battery technology floats have roughly a 5 year lifespan after which they can no longer ascend to the surface and they will "die" when their pressure cases corrode and deliver them to the ocean floor.

Active Argo floats as of Dec. 12, 2012.  Colors indicate floats deployed by different countries. Image courtesy of the Argo program.

Ocean research using the Argo network

The importance of the Argo program relates to our ongoing efforts to understand how the ocean moderate the planets climate.  The dataset so far accumulated represents an unprecedented resource for researchers investigating how the temperature, salinity and the circulation of the ocean changes on timescales from days to decades. The role of the oceans in ongoing climate change relates to its ability to store and then redistribute heat from the tropics to high latitudes through the circulation of major ocean currents.  In fact more than 90% of the heat absorbed by the Earth over the last 50 years is stored in the ocean.  The Argo array also monitors changes in ocean salinity which relate directly to changes in the hydrologic cycle – e.g. freshwater input from melting glaciers and polar ice caps and spatial and temporal variability in the balance between evaporation and precipitation.  Researchers have also used Argo data to study ocean circulation and changes in water mass distributions that have global climate impacts like El Niño.

The future of Argo

Now that it has one million missions under its belt what is next for Argo?  Well, in addition to continuing its core mission to determine temperature and salinity fields in the ocean the community is working on expanding the reach of the floats (operating under ice and in shallow coastal waters) and enabling the measurement of biogeochemically relevant parameters (e.g. oxygen, pH).  

If this is a network that you would like to plug into you can find more information on the Argo program, its mission, and data products at and answers to FAQ's here at

Originally posted to MarineChemist on Mon Dec 17, 2012 at 02:56 PM PST.

Also republished by Community Spotlight.

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