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NOAA buoy deployed in the Agulhas Return Current

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The Agulhas Return Current (ARC) Ocean Climate Station mooring preparing to be deployed on the South African Fisheries Research Ship Algoa at 38.5oS, 30oE, on the edge of the warm ARC southeast of South Africa (Picture: NOAA)
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Sea surface temperature simulation from NOAA’s Geophysical Fluid Dynamics Laboratory high resolution coupled atmosphere-ocean model. The Agulhas Return Current (ARC) mooring was deployed at 38.5oS, 30oE. The two drifters were deployed northwest of the ARC mooring in the core of the Agulhas current (Picture: NOAA/GFDL)
Click to enlarge
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The Agulhas Return Current (ARC) Ocean Climate Station mooring deployed at 38.5oS, 30oE, on the edge of the warm ARC southeast of South Africa (Picture: NOAA)
- Meghan F. Cronin, NOAA Pacific Marine Environmental Laboratory, Seattle, WA USA

 

To better understand the effects of the ocean on global climate and weather, scientists from NOAA’s Pacific Marine Environmental Laboratory (PMEL) on 30 November 2010 deployed an Ocean Climate Station mooring — an anchored buoy — at 38.5oS, 30oE, on the edge of the warm Agulhas Return Current (ARC) southeast of South Africa. While there is an array of climate buoys in the tropics, this is one of only two deep ocean climate buoys south of 20oS on the globe. The other buoy is located south of Australia.

The ARC is a western boundary current, similar to the Gulf Stream in the North Atlantic and the Kuroshiro Extension in the North Pacific. While the PMEL Ocean Climate Station group has maintained a surface mooring off of the Kuroshio Extension for near seven years, the ARC mooring broke away from its anchor after only a month and a half. A full study of the break still needs to be done. However it is likely that the deep currents were extremely energetic at the ARC site and tore the buoy from its anchor. The break occurred in the nylon well below the deepest sensor. The buoy drifted in the eddies of the ARC for several weeks before getting swept eastward by the strong ARC jet.

Rescue

On 9 March 2011 the ARC buoy was fortuitously recovered over 1800 km east of its original location by a passing ship -- the French R/V Marion Dufresne on its way to Le Crozet. The work done by the Captain and crew and the patience of the science party are gratefully acknowledged. The rescue took nearly a half a day, since the operation needed to be done during daylight. The buoy was off-loaded in Mauritius on 29 March 2011. At the end of April Dr Cronin will disassemble it and ship it back to Seattle, WA USA. Dr Cronin will be in Mauritius for the joint meeting of the SCOR working group 136 on the Climatic Importance of the Greater Agulhas System, and the Second Data Buoy Cooperation Panel (DBCP) In-Region Western Indian Ocean Capacity Building Workshop, to be held from 2 to 6 May 2011.

Data

PMEL designed, built, and deployed the heavily instrumented ARC surface mooring, with support from the National Science Foundation and NOAA, to monitor weather and the heat and carbon dioxide absorbed and released by this region of the ocean. Sensors include those that measure air and sea surface pCO2, wind, air temperature, relative humidity, rain, solar and infrared radiation, barometric pressure, sea surface temperature and salinity, near-surface currents, and subsurface temperature at 15 m, 25 m, and 300 m.

Data were relayed to shore in near-real time and made available through PMEL and other climate and weather data centres. ARC is part of a family of NOAA PMEL Ocean Climate Stations, which include the Kuroshio Extension Observatory located east of Japan and Station Papa located in the Gulf of Alaska. As with these other reference stations, data from the ARC buoy will be used to assess the air-sea fluxes in satellite and numerical weather prediction products. In addition, data from the drifting ARC buoy will be used to compute the heat lost by the current as it transports warm water eastward away from the African landmass.

The ARC mooring was deployed from the South African Fisheries Research (FRS) Algoa using shiptime provided by the Agulhas and Somali Current Large Marine Ecosystems Project (ASCLME). ASCLME also played a critical role in identifying possible rescue opportunities, including the successful rescue by the R/V Marion Dufresne.

Adopt-a-Drifter

During the deployment cruise, the FRS Algoa deployed two free-floating buoys, or drifters, provided by the NOAA Adopt-a-Drifter programme that are now part of the Global Drifter Array. These drifters measure surface temperature, current velocity, and atmospheric barometric pressure. Students from Washington state and South Africa are tracking the drifters online and predicting where they might go and why.

Classroom participation within Africa is being coordinated through a partnership between NOAA, ASCLME, Global Learning and Observations to Benefit the Environment – Africa, the South African Weather Service and SAEON.

NOAA’s mission is to understand and predict changes in the Earth’s environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Find us online or on Facebook.

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