Among the world's western boundary currents the Agulhas Current has a uniquely global significance. Its variability has been linked upstream to tropical Indian Ocean Dipole events which are largely coupled to Pacific winds and ENSO (El Nino- Southern Oscillation). Downstream, it feeds an inter-ocean transport of warm and saline waters into the South Atlantic which directly impacts the strength of the Atlantic meridional overturning circulation. This makes the Agulhas Current an effective link between the Indian and Atlantic tropical arrays of the Global Ocean Observing System. It is of significance not just to Indian Ocean variability, but to global climate.
Intellectual Merit: The goal of this project is to build a multi-decadal time series of Agulhas Current Transport (ACT). This will be done in a manner similar to what was started in the mid nineties for monitoring Kuroshio transport via satellite altimeter. The first phase of ACT requires deployment of an array of instruments across the Agulhas Current and along an altimeter (TOPEX/Jason) ground track, to obtain a three-year time series of transports via in situ measurements. The second phase involves calibrating the along- track altimeter data with these measured transports to produce a time series of Agulhas Current transport from 1992 and into the future, for as long as altimeter missions continue to along this track. Jason-2 has just been launched (June 2008) ensuring a continuing time series through 2012. This twenty-year time series will provide an important climate index for the Indian Ocean, which can be compared to other climate indices and to the Florida Current and Kuroshio time series. The importance of understanding climatic variability on decadal time scales has come to the forefront over the last decade with the need to distinguish natural modes of variability of the atmosphere/ocean system from anthropogenic changes. In response, the international oceanographic community, particularly through the CLIVAR (Climate Variability and Predictability) program, have developed a collaborative plan for a global ocean observing system, consisting largely of tropical moored arrays, sub-surface floats, repeat XBT (eXpendable BathyThermograph) sections, and satellite data. The CLIVAR Indian Ocean Panel recognizes that western boundary observations of the Agulhas Current are an important and missing element to this observing system. Both the Kuroshio and Gulf Stream transports are continuously monitored, providing a link from tropical to mid-latitude variability in their basins. However, there is no monitoring capability for the Agulhas Current, which has links not only to the tropical Indian Ocean, but also to Pacific variability through the Indonesian throughflow and Tasman leakage, and to the Atlantic via Agulhas Rings.
The broader impact of the project concerns the societal value of monitoring a current that has climate and marine impacts on Africa, a region lacking the capacity to monitor the current themselves. African scientists and students will benefit from active participation in the project, in particular through participation on cruises and via a student exchange between the University of Cape Town and the University of Miami. These collaborations will build local oceanographic experience and knowledge. Finally, the ACT array itself, and subsequent long-term time series of Agulhas transports, will allow a broad assessment of the relationship of the Agulhas to other observed climate indices, making an important contribution to the Global Ocean Observing System by building long-term regional capacity.
