JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. Cll, PAGES 25,985-26,009, NOVEMBER 15, 1999 Signatures of the Mediterranean outflow from a North Atlantic climatology 1. Salinity and density fields Michaela Ciobotaru Iorga Department of Mechanical Engineeringand Material Science,Duke University, Durham, North Carolina M. Susan Lozier Earth and Ocean Sciences,Duke University,Durham, North Carolina Abstract. Using historicaldata from the National Oceanic Data Center, the climatology of the easternNorth Atlantic basin has been investigatedfor the purposeof detailing the Mediterranean outflowwater in terms of its salinity,density, and flow patterns.Part 1 of this work is a descriptiveanalysis of the fate of the MediterraneanWater once it flows out of the Strait of Gibraltar. Tracing the salinity and densitysignatures, high-resolution maps of the climatologicaloutflow are presented,with an emphasison the continuityof the water from its source.From the climatologicalfields a continuoussignal of Mediterranean Water is tracked northwardto ---50ø20'N,yet its westwardadvection is limited to the Tagus Basin. Recirculationsof Mediterranean Water in the Gulf of Cadiz and in the Bay of Biscay,deduced from property signals,are also detailed.Iorga and Lozier [this issue] presentabsolute velocity fields from a diagnosticmodel constrainedby geostrophic dynamics,conservation of mass,and no-flux boundary conditions. 1. Introduction McCartneyand Mauritzen, submittedmanuscript, 1999). With this latter scenario,Mediterranean Water is relegated to an Warm and saltywaters flowing from the Mediterranean Sea indirectrole on the sourcewaters in the Norwegian/Greenland into the North Atlantic Ocean form one of the most pro- Sea since it is assumedthat the waters carried by the Gulf nouncedtongue-like property distributions in the globalocean. Stream/NorthAtlantic Current Systemgain saltby mixingwith At ---1000-1200 m the temperatureand salinitysignatures of the adjoining Mediterranean Water at subtropicallatitudes MediterraneanWater nearlyfill the entiretyof the subtropical [Lozier et al., 1995]. Ambiguity also surroundsthe issue of North Atlantic basin(Figure 1). The distincttemperature and whether the MediterraneanWater extendsinto the subtropical salinitycharacteristics of Mediterranean Water can be traced basin(where it is likely to mix with the Gulf Streamor North westward to the Bermuda Rise [Armi and Bray, 1982] and Atlantic Central Waters) by advectiveor diffusivemeans. Reid northwardto the Rockall Channel [Reid, 1979;Harvey, 1982]. [1994] has suggesteda westwardadvective pathway for Medi- During the past 2 decadesan interestin MediterraneanWater terranean Water in the range 35ø-45øN, and this has been has focusedon its possibleinfluence on deep water formation supportedby the model resultsof Hogg[1987] andBogden et al. processesin the northernNorth Atlantic. Althoughit hasbeen [1993].However, from a studyof zonaltransports in the eastern suggested[Reid, 1979, 1994; Harvey, 1982] that the source North Atlantic,Maze et al. [1997]argued that therewas no direct waters to the formation sitesare influencedby the warm and advection of Mediterranean Water into the ocean interior. Model saline Mediterranean Water at middepths, the particular resultsfrom Paillet and Mercier [1996] supportthis argument. venue of this influence remains unknown. The influence is Before the question of whether and how Mediterranean assumedto be either directly through advectionor indirectly Water influencesdeep water processesin the North Atlantic throughmixing. The directroute hypothesis,first promulgated can be answereda detailed analysisof the fate of the Medi- by Reid [1979], is that a branch of the Mediterranean outflow terraneanoutflow is needed.Since this influenceis presumably penetrates northward along the eastern boundaries to the on a climatologicalscale, we have chosento investigatehistor- Greenland-Scotland Sill where its salt content influences the ical hydrographicdata in order to detail the climatological productionof deep watersin the Nordic Seas.Alternatively, it signatureof the Mediterranean Water in the eastern North is proposedthat the warm and saltysource waters in the Nor- Atlantic. Specifically,we use a recent high-resolutionclimato- wegian/GreenlandSea derivemainly from the upper watersof logicaldatabase [Lozier et al., 1995] of the North Atlantic to the North Atlantic Current, which carry saltywaters into the examinethe salinityand densityfields of the easternbasin. Our Nordic Seas (M. S. McCartney and C. Mauritzen, On the primarygoal is to establishthe continuityof the Mediterranean origin of the warm water inflow to the Nordic Seas,submitted signalinto the open Atlantic on a climatologicalscale. High- to Deep-SeaResearch, Part I, 1999, hereinafter referred to as resolutionisopycnal maps and meridionaland zonal crosssec- tionsof salinity,density, potential temperature, and oxygenare Copyright1999 by the American GeophysicalUnion. presentedin this descriptiveanalysis of the climatologicalflow Paper number 1999JC900115. pattern of the MediterraneanWater. Of particularinterest are 0148-0227/99/1999JC900115509.00 the possible northward and westward penetrations of this 25,985 25,986 IORGA AND LOZIER: MEDITERRANEAN OUTFLOW--SALINITY AND DENSITY FIELDS ......•.... _....-;;•?•.;.-•.?•..-• .........;::;<.• . '.•?•;• ' '• • •":•............... "- 4>' :•..;-:•:&&•'-:'•:••'"•"•-•-.. Theta . •,. • • :•-• x • ' c-'?• = .-..•.:,.. c'x ',.• • •. ) •• / .• -.'" - .,...•;•........ - •.•..•.,•:::/ , _ •_.z-- /;z/.":: 7-'.----, •..: .........?'• • • • .•/. ':..•.. t • / - • • . .;::'• • '• • • • .----'z... i ' • • i..:-::•'.... • • ..• ' • '•-':-::" .-....:......:•.•:'.:•:-:•;,• _ _ - - ••O'N •,':. ."• : .•;/•••..• ....... '•- • • • •• _ _• .... 20 .:.'}i'".•"•:':;'"•t•..;. ". - '•::..•. lOW .. ,... -• . •"•:•.., .. .. ':%. • • • '• • .0' ß • • • ?'" • .... O' •o'• •ow •'w o' •'w row m'w •'w •'w •'w •o'w ww o' -. •,. '. .• -"••.'t:•' /•:•' I I'•;'•:•'-.'" '•':'•'";•'•-•:••"--:• . ; ..•::• t--z • ,? z .'I•/"•-•;;/•'i" '•:.;'•x•--'••'•••;• .....--•- •-s½-- -s•. ' -' •...... / I- [:'•;•'•':•........ •' '- ',.• ;•"•:"'' ' • • • " ' I :•'• -., . O.5 = 29.90...: ....-•.:.• •.. • / ///Z • I•• t •"•,'-•. '"•'.. • ...... .. '. •.•.ß'•'•.1•--•• -. ß• • •• ••/ •::.".•.".. ..' .. • ... '...... •."•:•'• ........ ';..:•.• •- _ • .;.'.• •, ' ..... .- I , • *• •.: •-' .. ,-,,.... ... :.• m m mmm m--•m m m m ß O* 80'W 70'W 60'W 50'W 40'W $O'W 20'W 10'W O' Figure 1. Propertydistributions at middepthin the North Atlanticbasin. These property fields were created usingthe hydrographicdatabase described by Lozieret al. [1995].The spatialresolution of thesefields is 0.5ø. water mass.An attempt has been made to compareand con- 2. Background trast the climatologicalsignals to thosederived from synoptic surveysor, as is the casewith Reid [1979, 1994], from quasi- Paststudies concerning the fate of the MediterraneanWater synopticstudies. Iorga and Lozier [this issue](hereinafter re- have generallyfocused on synopticdescriptions of the flow in ferred to aspart 2) presentresults from a diagnosticmodel that the local vicinity of the Strait of Gibraltar and/or the Gulf of usesgeostrophy and mass conservation, in conjunctionwith the Cadiz. A brief surveyof the collectiveknowledge from these Lozier et al. [1995] database,to estimatethe flow field in the studiesis given here as backgroundfor the larger context of easternNorth Atlantic. Backgroundfor our study is given in our study.The reader is referredto Daniaultet al. [1994]for a section2, followedby a discussionof our databaseand meth- more completesummary of thesestudies and to Figure 2a for ods in section3. Section4 containsthe resultsof our analysis, the location of topographicfeatures discussed in the text. A and a summaryis found in section5. detailedmap of the bathymetryin the Gulf of Cadiz is givenin IORGA AND LOZIER: MEDITERRANEAN OUTFLOW--SALINITY AND DENSITY FIELDS 25,987 I I I I I I I ..! I .. I !•. ß ' 55øN I • .. Promontorjr I:ß St.Vincent Canyon CapeSt. Vincent ' .•/! Sto...VincentSpur ...... Cape St. Maria Bank ....• .......• •. .•••.• Horseshoe A.P. -.. :. '/:•.•;•';?C"•nyon Bank:'•:•;•2).. A.P.Seine StraitofGibraltar I 35øN '•'..... ;.• •...•4•?:: :•:....... ...... ::?/•' ':'•:•' I 30'N I I I Figure 2a. Topographicfeatures in the eastern North Atlantic basin. Figure 2b. Mediterranean Water exitsthe Strait of Gibraltar as 1997], while a secondcore, generally transportinga larger a single, dense plume with typical properties of (0, S) = volume,is guidedby variouschannels down to ---1200m [Zenk (13øC,38.4 practicalsalinity units (psu) [Baringer,1993; Bar- and Armi, 1990; Baringer,1993; Boweret al., 1997]. The two ingerand Price, 1997]. The plume movesdown the northern branches,or cores,converge near Cape St. Vincent. A more continentalslope of the Gulf of Cadiz,flowing around complex detailed synopticdescription of the outflow in the Gulf of topographyas a bottom-drivenboundary current. As the out- Cadiz is presentedby Zenk [1975].Briefly, Zenk identifiesfour flow spreadsnorthwestward along the southernSpanish coast, branchesof MediterraneanWater that are determinedby the it slowly loses its high salinity as it mixes with fresh North local bathymetry:a shelfbranch in the depth rangeof 400-600 Atlantic Central Water [Madelain, 1967, 1970; Zenk, 1975; m; a main offshorebranch, at a depthvarying between 800 and Ambar, 1984, 1985; Zenk and Armi, 1990;Baringer and Price, 1000 m; an intermediate branch described as the southern core