JOURNAL OF GEOPHYSICALRESEARCH,VOL. 101, NO. C1, PAGES885-895, JANUARY 15, 1996 CFC-113 shows Brazil Eddy crossing the South Atlantic to the Agulhas Retrofiection region D. Smythe-Wright, A. L. Gordon, 2 P. Chapman, 3 and M. S. Jones TM Abstract. Usingthe newocean tracer CFC-113andother hydrographic andchemical data, we have identified and"aged" a Brazileddy transported across theSouth Atlantic to theCape Basin. This is thefirst observation of such an eddysofar east. It wasobserved during two RRS Discovery cruises in January andMay 1993,andusing TOPEX-POSEIDON altimeter data,we have been able to track it between the two locations. TS and nutrient characteristics show that the eddycouldnot havean eastern Atlanticorigin. Comparison with eddies found in the Brazil /Falklands Confluence suggests thatthisis the mostlikely source. From the CFC- 113:CFC- 11 ratioit appears thattheeddy is in excess of 4 years old, and fromthetwo sightings andthe altimeter datawe haveestimated a transport ratefor the eddy andgivencredence to the CFC- 113:CFC-11 andCFC-113:CFC-12ageing technique in surface waters. Introduction The formation of eddiesat the polewardend of the Atlantic and Indian Ocean western boundary currents, the Brazil and Agulhas Currents respectively, is well documented [e.g., Legeckis and Gordon, 1982; Gordon et al., 1987; Gordonand Haxby, 1990; Duncombe Rae, 1991; Olson, 1991]. The eddies are spawned at the polewardextensions of each current. The Brazil Current separates from the coast of Argentina near 40øS after confluence with the northward flowing cold Falkland Current. Offshoreof the continental marginthe Brazil Current penetrates further to thesouth, on average to 45øS, before turning eastward in a meander pattern[Roden, 1986]. The Agulhas Current is somewhat different, in that it is able to flow westward into the eastern edgeof the South Atlanticbefore feeding backto theIndianOcean(theAgulhas Retroflection) because the African continent terminates north of the maximum westerlies, the natural separation latitudeof the Agulhas Current[Harris et al., 1978]. In both currentsystems, the eddies formedtrap a pool of warm salinethermocline water, that is then exposed to winter cooling by sensible and latent heat loss, inducing a positive salinity anomaly relative to theinitial stratification [ Gordon, 1981, 1989]. The overall circulation of the South Atlantic (seeFigure 1) is considered to be a gyral system incorporating both subtropical and subantarctic waters [Peterson and Stramma, 1991; Reid, 1989]. Eddies shedfrom the AgulhasRetroflection move west and cross the subtropical South Atlantic in the northern arm of the gyre [Gordon and Haxby, 1990;McCartney and Woodgate- Jones, 1991; Dunco•nbe Rae et al., 1992; Byrne et al., 1995). Similarly, eddiesshed from the Brazil Currentare known to drift 1Southampton Oceanography Centre, Southampton, Hampshire, England. •LamontDoherty EarthObservatory andDepartment of Geological Sciences, Columbia University, Palisades, New York. 3U.S. World Ocean Circulation Experiment Office, Texas A&M University, CollegeStation. 4Mullard Space Science Laboratory, University College London, Dorking, Surrey, England. Copyright 1996 by theAmerican Geophysical Union. Paper number 95JC02751. 0148-0227/96/95CJ-02751 $05. O0 885 southeastward into the subantarctic waters south of the Subtropical Convergence Zone [Legeckis and Gordon, 1982; Provost and Le Traon, 1993], but evidence of their movement across the South Atlantic in the southern limb of the gyre is limited. One possible exception is theidentification of an eddy, of possible Brazil Current origin, at 37.5øS and 10.1øWin South AtlanticVentilation Experiment (SAVE) 4 cruise data[ Gordon et al., 1992]. In this paper we presentevidencefor the first observation of a Brazileddy east of theGreenwich Meridian.We believethat it hasbeentransported to the eastern South Atlantic alongthe boundary of the subtropical/subantarctic circulation of the South Atlanticgyre. Data Hydrographic and chemical tracer data were collected in January 1993, duringRRS Discovery cruise199 (U.K. World Ocean Circulation Experiment (WOCE) cruise A11), from Punta Arenas to Cape Town (see Figure 2 for cruise track). Conductivity, temperature, depth andoxygen data wereobtained witha Neil Brown Mk 3 CTD fitted witha Sensormedics oxygen cell. Onboard measurements of nutrients and oxygen weremade according to modifications of Smythe-Wright et al. [1992a, b]. CFCswere measured using an earliersingle-detector version of that described by Boswell and Smythe-Wright [1995]. In this system, CFCs are trapped at -50øCusing a Poracil B purge and trap systemfor subsequent separation using a 75-m DB624 megabore column and electroncapture detection(ECD). The chromatographic flows are adjusted such that the retention time for CFC-113 is 25 min. With sucha slow flow, we have found it possible to eliminate the problems of coelution andinterferences commonly seen in CFC analysis. Precisions for the seawater measurements are < 0.5% for oxygen, < 2.5% for nitrate and phosphate, < 1.1% forsilicate, < 1% or0.005 pmol L -1for CFC- 11, < 1% or 0.008 pmol L -1for CFC12, and < 2% or 0.006 pmol L -1 forCFC-113. The precisions forCFC-12 atlow values are not as good as for CFC-11 and CFC-113 due to contamination problems asdescribed in Saunders [1993]. At the time of the cruisethe position of the main transition between subantarctic and subtropical water was marked by an intense front at 35.5øS 5.5øE (Plate 1). To the west, surface