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Fantastic first for African science - South African Argo programme

Caren George, Intern, SAEON Egagasini Node

 

The launch of the first ever African Argo Program took place in December 2009 when the first South African Argo floats were procured and launched by SAEON and SANAP (South African National Antarctic Programme).

The launch marks a very exciting time for the African science community as the floats are integral in the understanding of ocean dynamics. The floats form part of a network of more than 3 000 floats (Figure 1) that have been launched by other international bodies, mostly from developed countries in the north. It is a momentous occasion when a developing nation is able to deploy these highly specialised instruments which aid in the global effort to unlock the secrets of the ocean.

Figure 1. Map of the world showing the distribution of floats and the countries that have

 

Argo floats are highly engineered instruments that assist in monitoring climate change signals in the oceans and also in long-range climate prediction (30 days to 2 years). Argo is capable of monitoring signals on intra-seasonal and longer scales. The floats collect pertinent information while they drift, glide and sink to depths of  2 000m. Once the float has reached 2 000m, it drifts for 10 days before starting to ascend. The float measures temperature, salinity, velocity and pressure as it moves up the water column.

Other instruments such as oxygen sensors or fluorometers (instrument that measures the amount of chl-a) may be attached to the floats. The floats store the information gathered and return to the surface where they transmit the data via satellite to a data centre. The data centre (ARGOS) distributes the data via their website to all interested parties as well as the public.

There are currently three different float models in use - the PROVOR, APEX and SOLO floats. The South African programme has acquired the PROVOR CTS3 model which is manufactured in France by NKE instrumentation. Click here to view the intricacies of the design of the float (Figure 2).

Figure 2. Diagram of an Argo float  (http://www.argo.ucsd.edu/FrHow_Argo_floats.html)

 

The logistics of setting up the South African Argo program were varied and proved challenging at times, but with the help of the French and South African teams these challenges were overcome. The South African science and support vessel, the SA Agulhas, served as the platform from which the floats were deployed.

Scientists from SAEON and the University of Cape Town (UCT) decided that the floats would be deployed at specific locations along the ship’s course, coinciding with interesting ocean features. The deployment of the two floats occurred at 41°S, 10°E, within an ocean eddy and ~60°S, at the Antarctic Polar Front, as planned. Young researchers and students were trained by Dr Isabelle Ansorge of UCT in the techniques of deployment of the floats and they successfully completed the launching of the two floats from the SA Agulhas.

The data collected by the South African floats (identity numbers 1901470 and 1901469) can be viewed and downloaded here.

An example of a profile from each float is included here to show the difference in temperature between the two regions and down the water column (see Figure 3).

Figure 3. Temperature profile of the float 1901470 at ~41° S (left) and 1901469 at ~60 ° S (right) on their first ascent   (http://www.coriolis.eu.org/cdc/floats/cdcFloats.asp)

 

Dr Sebastian Swart is one of the South African scientists who used Argo data in his PhD research. Dr Swart’s focus was on the Southern Ocean heat and salt fluxes, an area which still has many unanswered questions. With the help of Argo data he was able to add new understanding to this topic.

South African and international research being conducted south of South Africa and in the Southern Ocean region will benefit from the deployment of these floats as they provide more observations in a data poor area. Scientists, Oke & Schiller (2007), from the Commonwealth Scientific and Industrial Research Organization of Australia (CSIRO) have shown that Argo drifter paths play a vital role in the re-analysis and forecasting of meso-scale ocean systems (see Figure 4). The addition of the Argo drifter paths to the model creates a significantly more accurate representation of the ocean system.

Figure 4. Observed Sea Surface Temperature (SST) from (left) 6-day composite Advance Very High Resolution Radiometer (AVHRR); and (columns 2, 3, 4, 5, 6) 6-day averaged SST with virtual drifter paths overlayed for each Observing System Experiments (OSE) in the Tasman Sea for (top) mid-January, (middle) mid-February, and (bottom) mid-March of 2006 (Oke & Schiller, 2007)

 

SAEON’s Egagasini Node and UCT are teaming up to produce an educational poster which will introduce learners to the Argo floats. The scientific and engineering aspects related to the Argo floats will be explained. A workshop for educators was held by SAEON and UCT in December, with the aim to introduce the Argo floats and to explore the possibilities of how they can be used in the classroom environment. For further information on the South African Argo program, contact the SAEON Egagasini Node

 

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