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  • Argo is an international project with nearly 4,000 scientific floats drifting around the ocean. They measure currents, temperature and salinity of water to a depth of 2,000 m. The Argo project involves more than 30 countries, and New Zealand plays an important role. NIWA (National Institute of Water and Atmospheric Research) has deployed hundreds of Argo floats for other countries, and NIWA oceanographer Dr Phil Sutton uses the real-time data in his research.

    Rights: Argo

    Positions of Argo floats 4 May 2010

    The 3,255 Argo floats are well spread around the globe, collecting temperature and salinity data from the upper 2,000 m of the ocean.

    These data were collected and made freely available by the International Argo Project and the national programmes that contribute to it.

    Argo is a pilot programme of the Global Ocean Observing System.

    How Argo floats work

    Each Argo float spends most of its time drifting about 1,500 m down in the ocean, but every 10 days, it sinks to 2,000 m, then rises to the surface. On the way up, instruments measure depth, temperature and salinity at regular intervals to provide what is called a profile. At the surface, data is sent to a satellite, which also records the float’s position. The new position is compared with the previous one, so the path of the float, and therefore currents, can be calculated. After the data has been sent, the float sinks back down to 1,500 m and drifts for another 10 days. This cycle carries on until the battery runs out. Technological innovations allow Argo to continually improve data quality and coverage. Battery performance has increased beyond 6 years and some Argo floats are designed to go as deep as 6,000 m.

    How Argo floats work

    Dr Phil Sutton of NIWA explains how Argo scientific floats are deployed and how they work in the water.

    The buoyancy mechanism works by changing the density of a liquid reservoir. When the liquid is allowed to expand, it becomes less dense and the float rises. When the liquid is compressed, it becomes denser and the float sinks. Explore this concept in the activity Buoyancy in water.

    The need for Argo

    Argo floats let scientists like Dr Phil Sutton keep an eye on the state of the ocean. To understand what role the ocean plays in climate and climate change, we need to know what is happening beneath the surface of the ocean. Scientists use the data from Argo to construct models of the ocean and to look for clues that show how it is changing.

    There was no large-scale collection of temperature and salinity data before Argo started in 2000. Similar sensors to the ones on Argo floats were used from ships, but these could only cover small areas for short times. Argo floats now give wide coverage over long time periods. Despite this huge improvement, there is still only one float for every 90,000 km2 of ocean, so care needs to taken about relating data to the whole ocean.

    Rights: Argo

    RV Kaharoa deployment of Argo floats

    By 2010, RV Kaharoa had deployed 750 Argo floats across the southern Pacific and Indian Oceans. On the map, each dot represents a float deployed, with voyages shown in different colours. A decade later, RV Kaharoa has deployed an additional 350 floats! Image what the map would look like today!

    These data were collected and made freely available by the International Argo Project and the national programmes that contribute to it.

    Argo is a pilot programme of the Global Ocean Observing System.

    Argo continues to develop. Future plans include floats that go deeper and floats with more sensors that measure pH and dissolved oxygen.

    Working alongside the Argo project are Jason satellites that measure the height of the ocean surface very accurately to within a few centimetres. Water expands as it warms and stands slightly taller than surrounding water – a slight dome in the surface indicates a large mass of warm water below.

    The Argo and Jason projects

    Dr Phil Sutton of NIWA outlines the aims of the international Argo and Jason projects. Argo uses over 3,000 scientific floats to continuously measure the salinity and temperature of the ocean. Jason uses satellites to monitor sea surface height.

    Check on the Argo website to see where all the floats are – the data is updated daily.

    NIWA role in Argo

    NIWA buys two Argo floats each year and plays another vital role by placing floats for other countries – with more than 1,100 deployments as of 2020. NIWA research vessels, mainly the RV Kaharoa, reach areas of ocean less accessible to other countries. The ship has had over 22 deplyment voyages in the Pacific, Indian and Southern Ocean, more than any other individual vessel. There is even a shield proudly displayed on the Kaharoa with a model of a float and the words ‘World Champion Argo float deployers’.

    New Zealand and the Argo project

    Dr Phil Sutton explains how New Zealand has been able to make a large contribution to the international Argo project. New Zealand is close to vast areas of ocean inaccessible to other countries. The NIWA research vessel Kaharoa is well suited to deploying Argo floats in several oceans.

    Useful links

    Main site of the Argo project, including the latest float information.

    Use this interactive map to see where the thousands of Argo floats are located. Click on one of the green dots to to find out who is operating the float, details of its deployment and lifecycle, and a map that tracks its movements.

    New Zealand educator Carol Brieseman has created resources about the Argo floats.

    LEARNZ has a 2014 field trip that features the RV Tangaroa and Argo floats.

    Find out more about NIWA's work with the Argo programme here.

    Studies using the Argo measurements show that about 93% of the global warming caused by burning carbon for fuel is felt as changes in ocean temperature, while only a very small amount of this warming occurs in the air.

      Published 18 June 2010, Updated 27 May 2021 Referencing Hub articles
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