sign in sign up
<<
Home , Agulhas Passage, Brazil Current, Falkland Current

FEATURE

THE SOUTH ATLANTIC: AN OVERVIEW OF RESULTS FROM 1983-88 RESEARCH

By Arnold L. Gordon ~

EACH of the major ocean basins is unique, but the Initiative (SAARI) meeting repoll are available from South Atlantic is unrivaled in its number of singular Dr. Garzoli at Lamont-Doherty Geological Observa- features. In its polar region are formed intermediate tory, Palisades, NY, 10964. What follows is an and bottom water masses that cool and lower the abbreviated account of the primary results in the salinity of much of the global ocean. The subtropical SAAR1 report. Names mentioned here without at- region has an eastern boundary that doesn't quite tributive dates refer to the report, in which additional extend to the latitude of maximum westerlies, allow- information and extensive references may be ob- A curious ing thernmcline communication with its counterpart tained: an abbreviated list of references is included at feature of the in the South . Within the Argentine the end of the article. Basin of the South Atlantic one can sample deep Large Scale Circulation South Atlantic is water from the North Atlantic, deep and intermediate A curious feature of the South Atlantic is the the northward heat water from the Pacific, and bottom water formed in northward heat flux across 30°S, a consequence of the Weddell Sea. These water masses spread and the global cell driven by flux across 30°S vigorously mix within tiffs cosmopolitan basin and formation of North Atlantic Deep Water (NADW). throughout much of the South Atlantic. In the classical description, southward-moving Perhaps the most startling attribute of the South NADW is replaced by an upper layer return rio,:,' Atlantic is the significant equalorward heat flux derived from Pacific water, with the introduction of within the subtropical region. Estimates range from Antarctic Intermediate and Subantarctic Mode Wa- 18 to 86 x I()~W for the northward heat flux across ter (AAIW/SAMW: the latter terrn coined by Mc- the 8°S to 32°S belt. Associated with this flux is a Cartney ). Gordon (1986) suggested that at least some strong thennohaline circulation, as upper layer water of the return flow is derived from the thermocline spreads northward to compensate the southward water of the Indian Ocean, which has access to the export of colder North Atlantic Deep Water (NADW), South Atlantic around the southern tip of Africa. The The METEOR expedition of the 1920s and the relative influence of the wann and salty Indian water work during the International Geophysical Year (IG Y) and the colder and fresher Pacific water is crucial to of the late 1950s provide a glimpse of the large scale the larger scale climate system, because the Atlantic features of the South . In the last five meridional heat and fresh water fluxes are very years there has been a surge in our appreciation of the sensitive to the ratio of the volume fluxes of the two South Atlantic phenomena, mainly because of an water types. Gordon suggested that up to 50~ of the Office of Naval Research Accelerated Research Ini- required flow could be derived from the Indian tiative entitled "'The Southern Ocean," which was Ocean pathway. primarily directed toward improvement of the de- The SAAR1 research does indeed present evi- scription of the subtropical South Atlantic. The pro- dence of Indian Ocean water intrusion into the South gram focused on the poleward "corners" of the sub- Atlantic (Olson and Evans, 1986; Gordon et al., tropical gyre: the separation of the and 1987). It is still unknown what part of that inflow its confluence with the Malvinas or eventually contributes to cross equatorial transport in in the southwest, and the Agulhas Retroflection and the upper ocean and what part returns to the Indian in the southeast. Ocean along a surface route south of the Agulhas In May 1988, a meeting was organized by Silvia Retroflection. The Agulhas "'leakage" into the Atlan- Garzoli to discuss the program accomplishments. tic Ocean need not involve thermohaline forcing at Copies of the South Atlantic Accelerated Research all, because purely wind-driven models of the Agulhas Retroflection reveal transfer of Indian Ocean water A. L. Gordon, Latnont-Dohertv Geoloc, ical Ohservato#p;. Pah- into the Atlantic (cf. Fig. 3, p. 16). xade,~, N.Y 10964. :With conttibutio~t,~ fiom particq~ant,~ in the The application of inverse methods to data from ONR-sponsored Soztt/t ,.trio/trio rdsedrch l~VOk,#'dnt: S. Bennett, D. the International Geophysical Year (IGY) reveals no Boudra, O. Brown, R.Evans, R. Fine. S. Garzoh, J. Luyten, M. McCartne>. D. Olson, G. Roden. T. Whitw'orth, P. Zemba. significant Indian Ocean flow into the Atlantic

1 2 OCEANOGRAPHY,NOVEMBER.1~)88 Figure 2: The Brazil Current, the western Atlantic in a regton known as the Brazil-Malvinas Cop~/luence. associated with the subtropical gyre in the South Atlantic Ocean. Warmest smface waters (approx. 25°C) are coded in red. The flows southward along the continental margin r(South America sulfate temperature decreases are color-coded through yellow to a point off and Uruguay where, in the mean, it and green: the dark blue shows the coldest water (approv. 9 ° C). separates fi'om the coast at about 36°S. The cold.fi'esh subantarc- The image was taken at a time when the Brazil Current was in its tic water in the Malvinas or Falkland Current meets the warm. southward extension and a large anticyclonic (warm) eddy or saline Brazil Current. and both turn eastward into the open rin~ was being./brined.

(Rintoul, 1988). Gordon et al. (1987), using 1983 fresher when the Drake Passage route is favored? data, found 10 Sv of Agulhas water entering the Might this have important feedback to the production Atlantic (1 Sv = 106m3 s-~). Whitworth and Nowlin rate of NADW? (1987) calculated nearly 20 Sv of inflow using the The South Atlantic subtropical gyre has an elon- 1983/84 Ajax data set, which is subject to eddy gated crest stretching across the ocean near 30 °- aliasing because of a several month hiatus between 35°S. The gyre is marked at its poleward edge by the cruise legs. In her Ph.D. thesis, Bennett evaluated the Antarctic Circumpolar Current. The northern limb of 1985 CTD data from the Agulhas Retroflection and the subtropical gyre consists of a broad sweep to- found that only 2.8 Sv of water warmer than 9°C wards the northwest. In the northeastern comer of the flowed from the Indian into the Atlantic Ocean; her South Atlantic there is a weak cyclonic (clockwise) re-evaluation of the 1983 data set lowered the esti- gyre, described by Bosley and Gordon. The gyre is mate for that year to 6.3 Sv. formed by the South Equatorial Counter Current and If the Gordon suggestion is correct, it points to a the , which flows southward along potentially significant climate issue: Might the At- the African coast. J. Reid clarified this complex lantic become warmer and saltier during periods pattern by defining the absolute geostrophic circula- when the Agulhas route is favored, versus colder and tion of the South Atlantic.

OCEANOGRAPHY-NOVEMBER, 1988 13 The large scale circulation and the distribution of was in the process of separation, whereas the south- eddy' variability in the near surface layers of the ern one had been separated for at least a month and South Atlantic are another focus of research, pursued had been modified by the late winter atmosphere. by Olson. The dynamic height field relative to the These modified warm core eddies may not re-coa- 2000db level and surface velocities flom the SAARI lesce with the main thennocline, and hence they and FGGE drifter data sets show thai the 2000db represent a potentially significant salt flux into the reference level is best lk)r the eastern portion of the subantarctic zone of the South Atlantic. basin: however, that reference level clearly is inade- At depth, the most saline NADW is associated quate along the Brazilian coast, where the actual with the western meander of the Brazil Current. The level of no motion probably is higher in the water NADW continues tlowing south, beneath the Malv- column (cf. Fig. 1, p. 15). The drifter tracks also inas Current. which indicates that the separation of reveal the closed anticyclonic flows near the mid- the deep western boundary current need not be coher- Atlantic ridge that appear in most descriptions of the ent with the shallower thermocline separation lati- South Atlantic circulation. tude: this further complicates the definition of the BraziI-Malvinas Connuenee Brazil Current. Contrasting water masses are brought together in Piola and Gordon presented a detailed picture of the Argentine Basin by' a layer cake of boundary the AAIW/SAMW in the Argentine Basin. The ~, currents: The eddy-rich BraziI-Malvinas (Falkland) density interval 27.05 to 27.20 kg in 3 in the suban- Confluence dominates the upper layer, with deeper tarctic zone of the northern Drake Passage is charac- meridional flow involving NADW, Circumpolar terized by two water types with potential tempera- Deep Water and . At the tures of 3.7 ° and 4.8~C, respectively: both have meeting, there was not complete agreement as to the salinity of approximately 34.2 ppt. Thermohaline Contrasting exact definition of the Brazil Current, but in general, characteristics are modified by, winter sea-air inter- water masses are reference to the Brazil Current is confined to its action near Burdwood Bank and by' mixing with the thermocline expression. surrounding waters farther north. Low salinity water brought together in Dropsonde (Pegasus) measurements near 20°S derived from the Polar Front is introduced into a confirm the shallowness of the Brazil Current there, denser horizon (27.25 (~,,) along the axis of the cy- the Argentine Basin with a near- zero flow at 400m. Evans and Mascaren- clonic circulation feature described by the Malvinas by a layer cake of has reported Pegasus-referenced geostrophic trans- Current and its return to the south. The salinity, at the port of 17 Sv for the upper 800m at 31°S. Gordon salinity minimum increases rapidly across the Brazil/ boundary currents. calculated the geostrophic transport within the upper Malvinas Confluence, which suggests that the bulk 800m relative to 1500db to be 20 Sv at 38°S. The of the subantarctic water advected into the region main growth of the Brazil Current seems to occur from the south turns towards the interior, where it between Cab() Frio (24°S) and 31°S. spreads under the subtropical thermocline along a McCartney and Zemba pointed out that the trans- broader expanse of the South Atlantic. port of the Brazil Current is sensitive to the choice of Roden (1986) shows that the Brazil Current and relerence level. Without the benefit of an array of Antarctic Circumpolar Current (ACC) do not meet in direct current measurements, they chose a reference the central basin to form a common eastward flow, as level on the basis of water mass properties. With expressed in classical descriptions. Instead, the two reference levels from 600m in the north (27°S) to currents diverge near 42°W, where the former re- 3000m in the south (37°S), they estimated the Brazil turns to subtropical latitudes and the latter continues Current transport at four sections to be 9 to 76 Sv, eastward. The Brazil current extension typically increasing from north to south. The southward in- displays three meanders between the coast and 40°W, crease was associated with an increase in dynamic with a wavelength of about 400km and an amplitude height difference across the current and a tendency of about 200km. for the current to move offshore and develop a deep Olson presented a hypothesis for the wavelike shear. In the two most northern sections, a northward structure of the confluence region: the stationary core of intermediate water was found pressed against wave train acts as an energy reservoir into which the the coast. Brazil/Malvinas currents slowly impart energy. This The Brazil-Malvinas Confluence region was stud- energy is then periodically released back into the ied in October 1984 (cf. Fig. 2, p. 13). Gordon de- boundary as the wave train becomes transient. Theo- scribed the basic thermohaline structure, which fea- retically, this can occur if the large scale eastward tured two large poleward meanders of South Atlantic flow is reduced in amplitude. The drifter momentum thermocline water separated by a cold-core cyclonic fields and the satellite imagery suggests that such an eddy near 40°S and 50°W. The western meander event occurred in January-February 1985. During extended farther south, to 43°S, with a geostrophic this time, drifters reentered the boundary from the volume transport of 22.5 Sv relative to 1500db. The offshore recirculalion and the amplitude of the off- eastern meander had a weaker baroclinic structure, shore waves in the satellite imagery was reduced. As though it was associated with warmer surface tem- the event continued, drifters along the coast acceler- peratures. South of the western meander of the Brazil ated from speeds of order 0.30 m s" to speeds greater Current were two warm core eddies: the northern one than 1 m s ~. This mechanism for storing and periodi-

14 OCEAN~,)GRAPIIY.NOVEMBf:R,b)88 10°S

20°S

30°S

40°S

50os 60°W 50°W 40°W 30°W 20°W lO°W 0 lO°E 20°E

Figure 1: Surface drtJter-derivcd velocme,~ arc stzcm'n ,~upcritn- shown, The d,,yrecnlcnt hetwccn chilter t#qjec'toric's and the haso- Current posed (m the dynamic topo~rap/ly f(tx'#l ul) o/ the aea ,~ur/M'e. clink pressure 17ehl re/crave to 2000 dhar Is l~urticular/y .stlwkulk' relative to 2000 direr./ron~ the Lcvitus data. DrUthers iucluded are ill the equatorward port/on o/ the mthtropical ,~3're o/7".,lfi'lccl. strength in both those ol"flle FiJwt Global G,YRP E t7wrinlent ( FGGE J and the ONR None of the drl/tcrs esccqw the suhtropical gyre. C/t~,~er analysis Southern Ocean Studie.~. "/Tie dri/k'r vdocities in lhe,/ic, ure arc of lilt driller &/ta ~sel ,Glows the dri/7 to he acluss the dvnatnic regimes frequently ttl('(lllS OV('I" ~1 t~l'~; H'~'t']~ period, WhiCh cxuccd,~ ttl£" [Oll q~e.~[ LLI- Ilei.~ht contours ill quantitative tl.gl'eenlcnl witll e.Vwcled (fl~'('t,s c!/" ,grant.tall tmlc scales cotlqmted /)ore file drl/}cr recurd,s To the ~ktllatl /0"¢0" Otl the Slllt~l{'{' velocity. reached 50 cm s -~ at preserve le.glhtlio', only every lhlrd I"('¢'t¢~1 /)'O/it each drifter is depths of 5000 to cally releasing energy is probably responsible for the occurred when the Malvinas Current had penetrated 6000m. highly energetic rings, despite the fact that the Brazil farther north: the increase could have resulted from Current is a weak boundary current, compared to the a composite of the Brazil Current and Malvinas . Current transport. The analysis of the IES records Roden finds that the Brazil current and its associ- (supported by the infrared images studied by Olson ated eddies have deep, vertically coherent signatures and others) indicates that the confluence exhibits a that are recognizable to 3000m, in common with low frequency east-to-west displacement, with an other western boundary currents. Strong thennohal- amplitude of about 100km. It appears to be related to ine fronts accompany the boundaries of the Brazil the maximum northward penetration of the Malvinas current and the ACC. Hydrostatic stabilities in these Current, which raises several questions: Does the frontal zones are low, favoring seasonal convection Malvinas Current extend farther north because a and formation of mode waters. Density-compen- weaker Brazil Current separates at a lower latitude'? sated temperature and salinity Donts occur not only Or does a stronger Mal,Ynas Current forced by in the upper layers of the subantarctic frontal zone, stronger winds farther south induce a more northerly but also at abyssal depths below 3500m. separation of the Brazil Current'? Three reverted echo sounders (IES) were de- [n April 1987, the first Abyssal Boundary Current ployed for 18 months in the confluence region by' Studies field program concluded with the recovery of Garzoli, in order to develop a time series of the a 14-mooring current meter array from the southern complex and highly variable baroclinic field (Garzoli Argentine Basin. The program was designed to sample and Bianchi, 1987). Since dynamic height is linearly current, temperature and conductivity between 1000m proportional to the travel time measured by' the IES and the bottom, to study the spreading paths and array', time series of geostrophic baroclinic flow can volume transport of cold Weddell Sea Deep Water be successfully, traced relative to the initial condition entering the South Atlantic. Whitworth presented set by CTD data. Garzoli lbund the mean surface preNminary results from this experiment, which was geostrophic velocity associated with the Brazil Cur- sponsored by the National Science Foundation, with rent to be 35 cm s ~ corresponding to a geostrophic supplementary analysis support from ONR. The transport of 11 Sv for the upper g00m, relative to westward boundary current on the northern flank of 800db. During the monitored period, the 0/800db the Falkland Plateau varied between 50 and 100kin in geostrophic velocity reached a maximum value of 55 width and was bounded on the north by an eastward cm s-~ in September-October 1985, corresponding to abyssal recirculation. Current strength in both re- a transport of 18 Sv relative to 800 db. The latter gimes frequently reached 50 cm s t at depths of 5000

OCEANOGRAPII~ °NOVEMBER°Iogg ] 5 to 6000m. The coldest water sampled in the Argen- tine Basin had a potential temperature of -0.4°C, almost 0.2°C colder than recorded in the historical hydrographic data base for the South Atlantic. Pre- liminary analysis of the data suggest that the influx of Weddell sea water is influenced by the location and strength of the ACC and the clockwise abyssal circu- lation of the Argentine Basin. Agulhas Retroflection and Benguela Current The carries warm, salty thermocline water poleward in the Indian Ocean. However, the current effectively leaves behind its western boundary where the African continent termi- nates near 35°S. The Agulhas rounds the tip of Africa and turns toward the South Atlantic, but before entering the open Atlantic it curls back toward the Indian Ocean, forming the Agulhas Retroflection. However, not all of the Agulhas water participates in the retroflection. Hydrographic, infrared and satel- lite-tracked drifter observations indicate that as much Figure 3: A "'snapshot" visualization ¢i'om a three-layer numeri- cal model simulation q[the Agulhas Current Retrq[lection region as 15% of the Agulhas water continues into the South off South ,~[rica (Boudra and Chassignet. 1988). Rings of warm Atlantic. The presence of separated rings, however, Agulhas waterj)'om the southwest Indian Ocean waterform near The energy flux into makes it difficult to partition the transport between the tip c~ ,~[rica and drift m)rthwestward into tile subtropical South Atlantic: however, the largest part o[ the Current the South Atlantic for time dependent and mean circulation. Gordon et al. (1987) described the Agulhas "retrc~Tects.' turning back into the subtropical South Indian Ocean. A fidl-length arrow represetlts an upper level current each eddy amounts to Retroflection as observed in late 1983. The main velociO' of 0.25 m s ~. and each barb on an arrow adds a 0.25 m

retroflection was near 21°E, with two large warm- s / velocity increment: the ma):inutm speeds shown are about i m about 7% of the annual core Agulhas rings to its west. The transport into the s J in the ring.fbrming near the tip ofAJHca. Colors represent the wind energy input over main retroflection through the Agulhas Passage was depth of the first model inte@we. Tile shallowest depths (darkest blue) are less than ]OOm, and tile deepest depths (darkest red) are 70 Sv relative to 1500db (95 Sv relative to the sea greater than 550m: the eololw change at depth intervals of 5Om. the entire South floor). Most of the transport entered the retroflection Atlantic. and returned to the Indian Ocean, but 10 Sv (relative Malvinas extension, all trace out a uniform arc, to 1500db) continued into the South Atlantic within which corresponds to a frontal system that separates the region between the two eddies and the African South Atlantic subtropical gyre waters from waters mainland. The ring immediately to the west carried emanating from the Benguela upwelling region. 40 Sv relative to the 1500db level; its core properties Gordon and Haxby discussed a sequence of Geosat were identical to the water enclosed by the retroflec- data from November 1986 to September 1987, which tion. These characteristics suggest that the retroflec- disclosed numerous transient sea level highs within tion eddy was formed just prior to the field work. The the South Atlantic subtropical gyre in the latitude second eddy, which was centered about 250kin south- range of 25-30°S. The highs migrated from the west of Cape Town, carried 35 Sv relative to 1500db. Agulhas Retroflection and drifted northwestward at It encircled a core of Agulhas water that had been 5 to 7 cm s-L The 1987 population of eddies in the highly altered by the action of the winter atmosphere. South Atlantic and their mean drift velocity suggest Olson and Evans (1986) reported that the two a production rate of 3 to 4 per year. One of the larger Agulhas rings moved westward into the South Atlan- eddy features revealed by Geosat was crossed by tic after formation. Their trajectories suggest that the R/V Discovery during a CTD survey of the Benguela rings, some of the most energetic in the world ocean, Current in May 1987. The dynamic height of the sea interact with the bottom topography. The energy flux surface relative to 3000db revealed a 30 dyn cm crest into the South Atlantic for each eddy amounts to near 8°E, in excellent agreement with the Geosat about 7% of the annual wind energy input over the data. The CTD data revealed a distinct sign of Indian entire South Atlantic. Their large horizontal scales, Ocean stratification in the upper segment of the however, make the rings more linear than rings thermocline within the eddy: an isohaline layer in the associated with the Gulf Stream. The rates of ring 15-18°C interval. There is some evidence for surface translation are significantly higher than expected modification caused by enhanced evaporation from from theoretical computations of self-induced mo- the warm eddy into the colder atmosphere above it. tion, so the rings also must be steered by the mean Such a process could eventually remove the Indian currents. Ocean signature of the eddy. Olson reported on the results of drifter launches Luyten deployed a two-year array of 10 moorings during the 1983 and 1985 Agulhas cruises. These designed to explore the eddy field and mean flow of drifters, along with eight FGGE drifters that entered the Agulhas Retroflection region. Each mooring had this area and one SAARI drifter from the Brazil/ current meters at nominal depths of 200, 750, 1500

16 OCEANOGRAPHY,NOVEMBERo1988 and 4000m. Several moorings were deployed in the sively in the Ajax data along the prime meridian. Agulhas Current and showed velocities of 80-100 cm Thus, wintertime modification of upper thermocline s ~. The moorings deployed in the retroflection re- waters in Agulhas eddies could be considered a gion showed very strong and variable flow extending possible source for Subtropical Mode Water of the to 4000m. The eddy kinetic energy at 4000m was 165 South Atlantic Ocean, cm-" s--', comparable in amplitude to the Gulf Stream Single- and multiple-layerexperiments performed recirculation. Most of this variability occurred with with a primitive-equation numerical model in quasi- periods between 80 and 120 days, and there was isopycnic coordinates (Boudra and deRuijter. 1986; significant variability at the longest periods of 2 Boudra and Chassignet, 1988) have shown that the years. The mean flow, defined as a record-length Agulhas Current separates from the tip of Africa, average, revealed a large scale flow pattern consis- provided the no-slip condition is specified on that tent with the presence of a smeamd-out, meandering boundary (Fig. 3). The strength of the model retroflec- Agulhas Current. The moorings west of the retroflec- tion may then be viewed in the context of the result- tion showed northwestward flow at all depths, which ing changes in the Agulhas' vorticity balance. Along suggests a net flow from the South Indian into the the coast, the gain in positive vorticity induced by South Atlantic basin. The transport between the decreasing planetary vorticity is balanced largely by westernmost moorings along 37°S and between 200 diffusion into the no-slip boundary. After separation, and 4000m depths was approximately 20 Sv. potential vorticity is essentially conserved, and in a The Agulhas Current introduces several Indian one-layer case, the further decrease of planetary Ocean water types into the Agulhas Retroflection vorticity induces turning back toward the Indian region, all at densities less than (y(, = 27.7 kg m -3 Ocean. With more than one layer, the "'stretching" (shallower than 1500 meters). Within the Agulhas vorticity term complements the planetary vorticity Retroflection, Indian Ocean water masses are modi- advection term. The stretching becomes increasingly fied in two ways: 1. the upper thennocline water, important as the contrast between mean upper ocean upon exposure to the colder atmosphere, forms water potential vorticity in the southwestern Indian and the that is anomalously salty relative to the Agulhas southeastern Atlantic Oceans increases. Fluid par- inflow: 2. the deeper thermocline water mixes with cels attempting to leave the retroflection toward the South Atlantic water. The "contamination" of the west are imparted a torque through the stretching Agulhas Retroflection thermocline with South At- term, which turns them back toward the Indian Ocean. lantic water increases with depth, until density 27.7 Large upstream transport favors large values of plane- kg m ~ is reached, below which the water is almost tary vorticity advection and stretching and thus a totally from the South Atlantic. strong retroflection. Chlorofluoromethane (CFM) data collected as Conclusion part of the 1983 Agulhas Retroflection cruise were The ONR-sponsored research on the circulation used by Fine et al. (1988) to investigate the modifi- of the South Atlantic has revealed a more quantita- cation of water masses in the Agulhas Retroflection tive picture of and additional insight into many of the region. South Atlantic waters are generally higher in special features of that ocean. The research has CFM concentration and consequently more recently exposed new features as well, and has stimulated ventilated (by at least two years) than the waters of interest for continued study. Some ongoing work is the South Indian Ocean. A probable explanation is the tracer chemistry South Atlantic Ventilation that the Indian Ocean water is farther downstream Experiment, which will provide more specific infor- from the more convectively active South Atlantic mation on origin and time scales of the various water subantarctic sector. In the temperature range of 14 ° mass that influence the property fields and fluxes of to 4°C, there are substantially greater amounts of the South Atlantic. As part of the World Ocean more highly ventilated South Atlantic water in the Circulation Experiment, the South Atlantic Ocean Agulhas return flow to the Indian Ocean, which will be the subject of numerous observational and points to the importance of the retroflection region in modeling programs during the 1990"s. ventilating the thermocline and intermediate waters of the South Indian Ocean. References Olson, Fine and Gordon examined the winter Boudra, D.B. and W,P.M. de Ruijter, 1086: The wind-driven circulation of the South Atlantic-lndian Ocean. II: Experi- modification of upper thennocline waters in the ments using a multi-layer numerical model. Deep-Sea Rcs.. Agulhas Retroflection region. Consideration of the 33, 447-482. CFM concentration of the convected layers found in Boudra. D. B, and E. P. Chassignet, 1988: The dynamics of Agulhas rings observed in the 1983 data suggest that Agulhas Retroflection and Ring Formation in a Numerical the convective changes in the surface layers are Model. I: The Vorticity Balance. ,l Phys.Oceanogr.. 18, 280-303. highly episodic, which can be demonstrated using Fine, R.. M.J. Warner and R.F. Weiss, 1988: Water mass modi- the relative CFM concentrations in a simple mixed fication at the Agulhas Retroflection: Chlorofluoromethane layer model. Model calculations of the CFM fluxes Studies, Deep-Sea Res. 35(3): 311-332. constrain the actual time for convection in Agulhas Garzoli, S. and A. Bianchi, 1987: Time-Space Variability of the ring cores to a total period of one to two months. Local Dynamics of the Malvinas/Brazil confluence as Mode waters warmer than 15.5°C are found exten- [ PLEASE TURN TO PAGE 58 ]

OCKANOGRAPHY-NOVEMBER.1988 ] 7 great success during the forty-five years rectly to the education and training of marine The importance of effective communica- since the school's founding. The resources science students. tion is fully recognized among students at available to students in the form of facili- The OTMSS sponsors a number of field the RSMAS, and the planned workshops ties, curriculum and fitculty are extensive. trips to various environments in South will combine expert instruction with prac- The RSMAS library is accessible to stu- Florida and the Caribbean, stressing the tical experience. Individual workshops will dents 24 hours a day, 365 days a year. Each importance of an interdisciplinary approach cover written and verbal skills, and will be student receives nearly unlimited time on in the marine sciences. Through these or- lead by selected faculty members noted for the school's computing system, which in- ganized trips, students gain direct exposure their presentation skills. cludes links to a variety of academic and to, and an increased appreciation of, the The above are just a few of the ways that research networks. And, of course, individ- sub-disciplines of their fellow students. graduate students at the University of ual divisions provide facilities equipped to Field trip leaders are faculty members or Miami's Rosenstiel School of Marine and satisfy research needs within their respec- students with specialties in the areas to be Atmospheric Science are enriching the tive sub-disciplines. The small student-to- visited. Beginning this fall, the OTMSS educational experience for themselves and faculty ratio (-2) enables students to work will sponsor a series of workshops directed their fellow students. We encourage other closely with their advisors and to play an at improving students' presentation skills. students to share their successes. active role in research. These factors and more come together at the RSMAS to cre- inertial boundary current from an irregular ate an exceptional educational environment. THE SOUTH ATLANTIC coastline. ,I. Phvv. Occam~gr., 16,281)-289. [CONTINUED FROM PAGE 17] Despite the excellent provisions of the Rintoul, S., 1988: Mass, heal and nument fluxes in the RSMAS, students have gone a step further Revealed by hwerled Echo sounders..l.Geophys. Atlantic Ocean determined by inverse methods. and established two organizations to ad- Res.. 92. rC'2j, 1914-1922. Ph,D. thesis, Massachusetts Institute of Tech- dress student needs and concerns. These Gordon, A. L.. 1986: hater-Ocean Exchange of Th- nologyfWoods Hole Oceanographic Institute Joint Program, 287 pp. are the Marine Science Graduate Student ermocline Water..I Geophys. Rcs.. 91(C4~: Roden. G., 1986: Thermohaline fronts and baroclinic Organization (MSGSO) and the Organiza- 5037- 5046. Gordon, A. L. J. R. E. Lutjeharms and M. L. flov, m the Argentine Basin during the austral tion of Tropical Marine Science Students Gri.indlingh 1987: Stratification and Circulation spring of 1984..I Gcophys. Res., Ol. 5075- (OTMSS). Soon after the founding of the at the Agulhas Retroflcction. D¢'¢7~-Sea Res 5093. RSMAS, the MSGSO was established to ,']4(4). 565-599. Whitworth, T. and W. Nowlin, 1987: Water masses and currents of the Southern Ocean at the insure student representation within the Olson. D. B. and R. H. Evans, 1986: Rings of the Greenwich meridian.,l. Ge,q#zys Res.. 92,6462- University. It has remained an active voice Agulhas Current. De(T Sea Rcs, 33, 27-42. Ou, H.W. and W. de Ruuter, 1986: Separation of an 6476. I throughout the school's history. A repre- sentative of the MSGSO occupies a voting position on the school's Academic Com- timetry. J. Ge(q~hys. Rex. 92, 74%754. mittee and participates in the formulation SATELLITE ALTIMETRY Fu, L.-L.. and D.B. Chelton, 1985: Observing large- ]CONTINUED FROM PAGE I1] scale temporal variability of ocean currents by of policy regarding students. The MSGSO satellite altimetry: with application to the Antarc- also provides a number of services such as References tic Circumpolar Current..I. Ge(q~hy,s'. Res., 90, short-term, no-interest loans and new stu- Bernstem. R.L., G.H. Born and R.H. Whrimer, 1982: 4721-4739. dent orientation intended to help with the Seasat altimeter detemfinanon of ocean curi'ent Marsh. J.G., (and 19 other authors~, 1988: A new problems of "'student life.'" As a means of variability. ,I Geophys. Re,~.. ,~7, 3261-3268. gravitational model for the earth from satellite Born, G.H., M.A, Richards and G.W. Rosborough. tracking data: GEM-T1. ,I. Geoph)'s Rcs.. 93, promoting student-faculty exchange as well lqS2: An empirical determination of the eflects 6169-6215. as student-student interaction, the MSGSO of sea-state bias on the SEASAT altimeter. J. Mazzega, P.. 1985:M2 model of the global ocean tide operates a commons complete with music Ge,g#U.~. Re,Y, 87, 3221-3226. derived from SEASAT altimetry. Mar. Geod., 9, and a full bar. Finally, the MSGSO has Chehon, D.B., 1988: WOCE/NASA Altimeter Algo- 335-363. created a travel fund program to provide rithm Workshop. U.S, WOCE Tech. Rep. No. 2. Parke, M.E.. R.H. Stewart. DL. Farless and D.E. U.S. Plalming Office for WOCE, College Sta- Carlwright, 1987: On the choice of orbits for an financial assistance to students presenting tion, TX., 70 pp. altimetric satelhte to ~,tudy ocean circulation and the results of their research at scientific Chene>, R.E., J.G. Marsh and B.D. Beckley, 1983: tides. ,1. Gc(q)h3".~. Res.. 92, 11,693-11,707. meetings. Global mesoscale variability from col linear tracks Tat, C,-K., and C. Wunsch, 1984: An estimate of Monies allotted to this fund annually are of Seasat altimeter data. ,I. Gccq~h3'.s Res, ."¢& global absolute dynamic topography. ,I. Phvs 4343-4354. Oceam~er,. 14. 457-463. matched by the Office of the Dean. Exclud- Cheney. R.E., and L. Miller. 1988: Mapping the Tapley. B.D., G.H. Born, and M.E. Parke, 1982a: The ing the Dean's matching funds, the MSGSO 1986-I987 El Nifio with Geosat alnmeter data. SEASAT altimeter data and its accuracy receives no monetary support from the Eos Trans. Amer. Geop/Us. Ulfion. h9 754-755. assessment. ,I. Ge~q#Us. Res.. h'7, 317%3188. University, and all of its annual budget is Douglas. B.C., R.E. Cheney and R.W. Agreen. 1983: Tapley, B.D., J.B. Lundberg and G.H. Born, 1982b: met through fund-raising activities. Chief Eddy energy of the Nowthwest Atlantic and Gulf The SEASAT altimeter ,set tropospheric range of Mexico determined from Geos-3 altimetry..I con-cotton. ,I. Geophys. Res., 87. 3213-3220. among these is the Annual MSGSO Stu- Ge~q#n's Res , &~.'. t~595-9603. Topex Science Working Group, 1981: Satellite al- dent Auction, an event in which businesses Douglas, B.C., D.C. iMcAdoo and R.E. Cheney, tinletllC measurements of the ocean. Doc. 400- and individuals donate their services and 1087: Oceanographic and geophysical applica- 1 I I, Jet Propul. Lab., Pasadena, Calif. merchandise. The donations are auctioned tions of satellite alnmetry. Rcv. Gcophys.. 25. Woodworth, P.L., and D.E. Caltwrlght. 1986: Ex- with earnings going to the MSGSO. Last ~75-880. traction of the M2 ocean tide from SEASAT Fu, L.-L., 1983: Recent progress in the apphcation of ahimeter data. G(,ophys J Roy. ,,1silo. Sot., N4, year the event raised nearly $8,000. satellite altunelrv to observing the mesoscule 227-255. The Organization of Tropical Marine variability and general circulation of the oceans. Yunck, T.P,, S.C. Wu and S.M. Lichtcn, 1985: A Science Students was established in 1986 Roy. Geol~hys. Spa('e Phys., 2 l, 1657-1666. GPS measurement system for prect',e satellite to promote activities which contribute di- Fu, L-5., J. Vasquez and M.E. Parke, 1987: Seasonal tracking and geodesy. ,I. Astromlul. Sot.. 33, variability of the Gulf Stream from satellite al- 367-380. I

58 OCEANOGR \PItY.NOVEMBER. Igx8