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Article #160 South African Journal of Science 6 7 3 in April in and the 4 9

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t /s on average, with average, on /s 3 was held, attracting while the University the while 1 3 m 6 It has previously been 3 S Afr J Sci urren Figure 1). from many previous investigations, C 10 vide A remarkable new discovery has been at the eastern extremity of the Agulhas 13 is the major contribution by South to and to the south of .

12 to fill the most glaring knowledge gaps. This has, This gaps. knowledge glaring most the fill to 11 gulhas A Dr. Fridtjof Nansen. recognised

er Therefore, it is clear that this process of ring shedding south of 8 t are programmes instituted by the Global Environmental Facility

to study mainly the palaeoceanographic implications of the Agulhas the of implications palaeoceanographic the mainly study to 2 /s. The maintenance of this array is crucial for a proper understanding 3 being

m grea 6 adjacent to the east coast of (Figure 1). All of these currents

5 and this has now been carefully quantified to be 14 × 10 × 14 be to quantified carefully been now has this and

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Vol. 106 No. 3/4 Page 1 of 4 Vol. of

ance increasingly Agulhas Current system, Current Agulhas a seasonal signal of 5 × 10 the ASCLME. Its activities are concentrated along the east coast of South Africa and, full its along Current Agulhas the of edge landward the of study in first a include Cruises Bight. the particular, in length and coverage of the , the south of Africa (Figures 1 and 2). latter The will include the unusual cell these of at knowledge existing the Port to substantially Alfred add to bound are investigations these again, Once Bank. regions. With the advent of current with global out carried warming, being is it Dutch, the has by monitoring, been Such locations. become crucial imperative at out that carried be long-term ocean monitoring of the meter moorings in the narrows of the Channel shown that the ( volume transport through the Channel may be an important contributor to the greater to help countries manage marine ecosystems across political boundaries. In the Current Agulhas Large and Somali Marine Ecosystem (ASCLME) project, two ecosystems have been combined the potential to affect the meridional overturning of the whole Atlantic, and this in turn can have a major a have can turn in this and Atlantic, whole the of overturning meridional the affect to potential the impact on global climate. Models have, in fact, shown that recent probably anthropogenically induced shifts – have led in to a greater input the of Agulhas water wind into the Atlantic. patterns of This the may Southern inhibit the Hemisphere effect – of the climatically indicated important have studies palaeoceanographic Furthermore, Greenland. of icecap the of melting freshening increased of the North Atlantic due as such to climate, global in changes the substantial with correlated closely are leakage this in fluctuations that glaciations and even decadal changes. interest. international growing the hence – interest local just than more considerably of worthy is Africa It is immediately evident the of that sources upstream the where is This understand. to important also are rings) Agulhas of shedding the dynamic processes that mediate role. decisive a play sources, these in perturbations particularly and 1), (Figure proper Current Agulhas this Agulhas leakage, (i.e. the These include eddies formed in the features and their respective frequencies of formation. is a growing interest in the formation of these 2010. Why this sudden explosion of international interest in the greater Agulhas Current? explosion of international interest in the greater 2010. Why this sudden Each large ocean basin on the globe has a basin-wide, wind-driven circulation. These circulations are not longitudinally symmetric, but each has an intensified, strong current on its western side: a western . In the North this is the and in the South it is the Agulhas Current of exception the with gyres, subtropical respective their into directly back water their all feed eventually amount significant a south, far very extend not does Africa of mass land the Since Current. Agulhas the of Agulhas water can leak into the South Atlantic Ocean. This leakage comes about predominantly by the shedding of large current rings at the Agulhas Retroflection (Figure 1) south of Africa. has rings Agulhas these of shedding the by Atlantic the into injected is that salt and heat of flux the that The results are still being analysed. Furthermore, the ASCLME has helped in deploying current meter moorings (Figure 1) and deep-sea weather buoys for other projects (see below). piracy of scourge the In Regrettably, effort. research extensive an such short, seen before never has Ocean the Indian western has, up until now, prevented work off and, currently, a north of the 10 °S latitude (Figure 2). zone of exclusion has been defined The African Coelacanth Ecosystem Programme (ACEP II) Current system in the global climate. Having recognised this role, one may want to identify the most important dynamical processes that now need greater Agulhas Current system. programmes are currently investigating the to be understood. To this end, a number of Large major Marine Ecosystems (LMEs) ocean region in question, therefore, covers the whole western Indian Ocean (Figure 2). Whereas other LME projects have been based on a solid knowledge foundation this has not been possible for the ASCLME because this ocean region is one of the least explored. This designed be to had has ASCLME the that meant has to a large extent, been accomplished during the last deep- the and Current Madagascar three East the as such adequately, observed been never have that systems years (Figure 2) and is continuing. Ocean sea environment of the island of , have been studied in a multidisciplinary way for the first time, using the Norwegian research vessel that the deep-sea circulation at Mauritius is strongly influenced by passing mesoscale eddies. Regions in the Mozambique Channel, the Comores Gyre and the Mascarene Plateau have also been explored. The reason for the growing international interest is, therefore, clearly the key role of the greater Agulhas greater the of role key the clearly therefore, is, interest international growing the for reason The system. In conjunction with the conference, the Research (SCOR) Working firstGroup on the global influence meeting of the Agulhas Current of a Scientific Committeerepresentatives of on Oceanic 13 countries. In addition, towards the end of GATEWAYS 2009 called approved was a new EU research programme Current. In the meantime, the Dutch are maintaining an expensive array of current meter moorings in (LOCO), Observations Climate Ocean Long-term called Channel Mozambique the London East near Current Agulhas the across moorings of set similar a placing be will Miami of In February 2010, the annual Ocean Science meeting was held in Portland, Oregon, USA. For Current the Agulhas the of aspects at first aimed were sessions two least at conference this of history the in time t

1,2 impor 2,3

he T Agulhas and Somali South African Institute Department of Authors: Johann R.E. Lutjeharms Thomas Bornman G. Publishing. This work is licensed under the Creative Commons Attribution License. © 2010. The Authors. © 2010. Licensee: OpenJournals http://www.sajs.co.za v106i3/4.160 This review is available at: is increasingly being recognised. S Afr J Sci. Art. 4 #160, 2010;106(3/4), pages. DOI: 10.4102/sajs. How to cite this Article: Lutjeharms JRE, Bornman TG. The importance of the greater Agulhas Current , University of , Rondebosch 7700, South Africa ac.za Postal address: Department of Correspondence to: Johann Lutjeharms email: Johann.Lutjeharms@uct. of Aquatic Biodiversity, Aquaticof Biodiversity, Grahamstown, South Africa (ASCLME), Grahamstown,(ASCLME), South Africa 3 2 Current Project Affiliations: 1 Oceanography, University Cape of Town, South Africa http://www.sajs.co.za The importance of the greater Agulhas Current News & Views Lutjeharms & Bornman Article #160 South African Journal of Science

ACT, Agulhas Current Time-series. UTR, underwater temperature recorder. ARC, reference station. ADCP, acoustic Doppler current profiler.

Figure 1: Some of the major currents in the western Indian Ocean, indicated schematically, with the existing mooring locations, as well as some of those planned for future deployment, shown in orange

S Afr J Sci Vol. 106 No. 3/4 Page 2 of 4 http://www.sajs.co.za Article #160 South African Journal of Science News& Views S Afr J Sci S latitude and how the 2009 cruises skirted the border ° Vol. 106 No. 3/4 Page 3 ofVol. 4 FigureThewestern2: Indian Ocean withthe hydrographic station positions indicated yearstheASCLMEfor3 of (Agulhas andSomaliprogramme Current Large Marine and Ecosystem)other cruises. Note the exclusion zone thatof this is zonenow in at .place owing Note alsoto piracy the manner to the in which north the East of Madagascar10 covered Current for the (see first Figure time. and 1) the deep-sea environment of Mauritius have been extensively http://www.sajs.co.za The importance of the greater Agulhas Current News & Views Lutjeharms & Bornman

of long-term changes to the Agulhas Current system, but the but the question may legitimately be asked if elements of this logistics to accomplish this have not been easy. The moorings large collection of individual projects do not overlap and if all will soon be extended to include an array in the southern branch this, therefore, optimal use of funds and equipment. Building of the East (Figure 1). appropriate links between all oceanographers working in the south-west Indian Ocean is one of the main aims of the new One of the most prominent mooring arrays in the global ocean SCOR Working Group 136: Climatic importance of the greater has been the Tropical Atmosphere Ocean programme along the Agulhas Current system.1 This working group includes formal equator over the full width of the Pacific Ocean. This array has participants from seven countries that are carrying out research been maintained since 1985 and has been essential in monitoring in the region as well as a host of volunteers from many others and predicting the El Niño phenomenon. These successes have countries. led to attempts to build a similar array in the tropics of the 14 Indian Ocean. This will clearly have a great impact on a better It would seem abundantly clear that the greater Agulhas Current understanding of the monsoon system over the Indian Ocean system is the subject of an unprecedented international research and its predictability, weather prediction for east Africa and 11 effort. It also seems clear that by the time most of these projects in long-term climate studies. The first ATLAS moorings have are completed, the level of knowledge and understanding of the been placed along the 55 °E longitude in 2008 (vide Figure 1). system may well have increased significantly. All this research is One of the key elements for a proper understanding of the bound to leave a legacy of better educated scientists in the region Agulhas system is detailed knowledge of the volume, heat and and also a broader base of understanding of the ecosystems to salt fluxes of the Agulhas Current and their possible variations. inform decision makers. Since the fluxes in the Mozambique Channel exhibit seasonality, as do the atmospheric driving forces of the South Indian Ocean, REFERENCES the question that arises is: are these and other variations reflected 1. Beal L, Biastoch A. SCOR Working Group #136: The climactic in the fluxes of the Agulhas Current? If so, this might havea direct effect on the Agulhas leakage since it has been suggested importance of the greater Agulhas System. Eos, Trans Amer that a weaker Agulhas Current might lead to more leakage while Geophys Un. In press 2010. others maintain that, on the contrary, it will lead to less leakage. 2. Zahn R, Lutjeharms J, Biastoch A, et al. GATEWAYS: To address this important question, an array of current meter Investigating the Agulhas Current off southern Africa moorings is to be placed across the current in 2010. This project, and its global impacts. Eos, Trans Amer Geophys Un. called Agulhas Current Time-series,4 is building on a very 2010;91:109−110. successful past deployment, during which the volume flux of 3. Long-term ocean climate observations (LOCO): A proposal the current was established accurately for the first time and the for investments in ocean observation capacity [document on

Agulhas undercurrent was discovered. The line of current meter the Internet]. Available from: http://www.nioz.nl/public/ moorings off East London, on the east coast of South Africa, fys/projects/loco/loco.pdf will be along a ground track of satellite altimetry observations 4. Rosenstiel School of Marine and Atmospheric Science. NSF (Figures 1 and 2). It is hoped that if it can be shown that there is provides $3.4 million to study climatically important Agulhas a firm relationship between the volume transport of the current and the sea surface gradient as measured by altimetry, records of Current [homepage on the Internet]. Available from: http:// the temporal variations of the fluxes may be extended backward www.rsmas.miami.edu/pressreleases/20090629-beal.html as far as the altimetric record allows. 5. Lutjeharms JRE. The Agulhas Current. Heidelberg: Springer– Verlag; 2006. Once the water in the Agulhas Current has passed through 6. Biastoch A, Böning C, Schwarzkopf F, Lutjeharms JRE. the retroflection loop, that part of it that has not been taken up Increase in Agulhas leakage due to poleward shift of Southern

Article #160 by the formation of Agulhas rings flows eastward along the Hemisphere westerlies. Nature. 2009;462:495–498. Subtropical Convergence (see Figures 1 and 2) as the Agulhas 7. Peeters FJC, Acheson R, Brummer G-JA, et al. Vigorous

Return Current. This juxtaposition of front and warm current exchange between Indian and Atlantic Ocean at the end of the creates one of the most intense horizontal thermal gradients in 5 last five glacial periods. Nature. 2004;430:661–665. the world’s . It is also known for its very high ocean-to- 8. Biastoch A, Böning CW, Lutjeharms JRE. Agulhas leakage

South African Journal of Science atmosphere heat fluxes. The Agulhas Return Current reference dynamics affects decadal variability in Atlantic overturning station project, therefore, will aim at monitoring of the ocean- atmosphere interactions here,15 by placing a specialised mooring circulation. Nature. 2008;456:489–492. (vide Figures 1 and 2). 9. ASCLME. Welcome to the ASCLME Project. [homepage on the Internet] c 2007. Available from: http://www.asclme.org Notwithstanding all these sophisticated observations, 10. Cochrane KL, Augustyn CJ, Bianchi G, et al. Results and predicting future climate change, including the potential role conclusion of the project: Ecosystem approaches to fisheries of the Agulhas Current in this, remains fraught with obvious management in the Benguela Current Large Marine Ecosystem difficulties. However, palaeoceanographic records spanning [homepage on the Internet] FAO Fisheries Circular No. 1026. the last several 100 000 years demonstrate the sensitivity of the Rome: FAO; 2007. Available from: http://www.fao.org/ Agulhas Current system to varying climatic factors. Integrating docrep/010/ a1343e/a1343e00.htm the complex circulation processes with palaeoceanographic 11. Vousden D, Scott LEP, Sauer W, et al. Establishing a basis for reconstructions and numerical ocean modelling may be the only ecosystem management in the western Indian Ocean. S Afr J way to fully understand the system and its climatic variations Sci. 2008;104:417–420. and, to this end, the GATEWAYS project2 has been designed. New sediment cores have been collected from sites with high 12. ACEP [homepage on the internet]. c 2007 [updated 22 sediment accumulation rates, located in a number of sectors of September 2009]. Available from: http://www.saiab.ac.za/ the Agulhas regime. The analysis of these has recently started. index.php?pid=138 13. Lutjeharms JRE, Cooper J, Roberts M. Upwelling at the inshore Of all the ocean basins, the North Atlantic has a particularly edge of the Agulhas Current. Cont Shelf Res. 2000;20:737–761. special role in the global overturning circulation. It is here that 14. McPhaden MJ, Meyers G, Ando K, et al. RAMA: The research salty surface water is cooled in the Labrador Sea and sinks down moored array for African–Asian–Australian monsoon analysis to form the deep water mass of most of the world’s oceans. and prediction. Bull Am Meteorol Soc. 2009;90:459–480. It has been noted in some palaeoceanographic studies that 15. Agulhas Return Current reference station, vetting page this overturning circulation has, at times, been stopped, with [homepage on the Internet]. Available from: http:// considerable climatic impacts. At a time when the global climate www.pmel.noaa.gov/people/cronin/ARC/ ARC.html is changing due to anthropogenic forcing, knowledge of any 16. Speich S, Garzoli SL, Piola A, et al. A monitoring system for changes in the oceanic overturning circulation is crucial. To this end, an optimal monitoring array needs to be designed to study the South Atlantic as a component of the MOC. In: Hall J, the influence of the South Atlantic on meridional overturning, Harrison DE, Stammer D. Proceedings of the OceanObs’09: a task taken up by an international group under the auspices of Sustained Ocean Observations and Information for Society the South Atlantic Meridional Overturning Circulation.16 Conference, 2009 Sep 21–25; Venice, Italy. ESA Publication To the uninitiated, this veritable letter soup of project acronyms WPP-306 Vol. 2; 2009. may be thoroughly confusing and disheartening. Not only that,

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