Study of a mesoscale anticyclonic eddy in the western part of the Gulf of Lion

Description

Niveau: Supérieur, Doctorat, Bac+8
Study of a mesoscale anticyclonic eddy in the western part of the Gulf of Lion. Z. Y. Hu a,?, A. A. Petrenko a, A. M. Doglioli a, I. Dekeyser a aUniversite de la Mediterranee - Aix Marseille II, CNRS, Laboratoire d'Oceanographie Physique et Biogeochimique, UMR 6535, OSU/Centre d'Oceanologie de Marseille, Campus de Luminy case 901, 13288 Marseille Cedex 9, France. Abstract Acoustic Doppler Current Profiler (ADCP) and Expendable Bathy Thermograph (XBT) data were collected during the Latex08 cruise (September 1 - 5, 2008) throughout the western part of the gulf of Lion. These data, combined with Sea Surface Temperature (SST) satellite images and Lagrangian drifter trajectories, show the presence of an intense anticyclonic eddy in the western part of the gulf of Lion. The eddy is elliptic in shape and the estimated radii are 21.5 (15.5) km for its major (minor) axis. The vertical extent of the eddy reached about 35 m depth and was limited by the bottom of the seasonal mixed layer. The eddy interacts with the Northern Current at the end of the cruise, maybe leading to its deformation. More- over complementary drifter data suggest that this anticyclonic eddy was already present at the beginning of August 2008. Hence the eddy lasted around 50 days in the same region.

• latex08 cruise


• adcp


• surface waters


• khz adcp


• drifter


• waters inputs


• can generate


• sea state


• structures could play

Sujets

• Drifter
• Sea state

Informations

• Publié par: profil-zyak-2012
• Nombre de lectures: 27
• Langue: English

Extrait

Studyofamesoscaleanticycloniceddyinthe westernpartoftheGulfofLion. Z.Y.Hu a , ∗ ,A.A.Petrenko a ,A.M.Doglioli a ,I.Dekeyser a a Universite´delaMe´diterrane´e-AixMarseilleII,CNRS,Laboratoire d’Oce´anographiePhysiqueetBioge´ochimique,UMR6535,OSU/Centre d’Oce´anologiedeMarseille,CampusdeLuminycase901,13288MarseilleCedex 9,France. Abstract AcousticDopplerCurrentProfiler(ADCP)andExpendableBathyThermograph (XBT)datawerecollectedduringtheLatex08cruise(September1-5,2008) throughoutthewesternpartofthegulfofLion.Thesedata,combinedwithSea SurfaceTemperature(SST)satelliteimagesandLagrangiandriftertrajectories, showthepresenceofanintenseanticycloniceddyinthewesternpartofthegulfof Lion.Theeddyisellipticinshapeandtheestimatedradiiare21.5(15.5)kmforits major(minor)axis.Theverticalextentoftheeddyreachedabout35mdepthand waslimitedbythebottomoftheseasonalmixedlayer.Theeddyinteractswiththe NorthernCurrentattheendofthecruise,maybeleadingtoitsdeformation.More- overcomplementarydrifterdatasuggestthatthisanticycloniceddywasalready presentatthebeginningofAugust2008.Hencetheeddylastedaround50daysin thesameregion.Inlightofpreviousnumericalstudy,somehypothesesaboutthe formationandbehaviouroftheeddyarealsodiscussed. Keywords:mesoscaleeddies;GulfofLion;northwesternMediterraneanSea; LATEXproject 1 1Introduction 2 Oceaniceddiesmayhaveanimportantimpactontransferandredistributionof 3 heat,energyandmatter.Severalstudieshavepreviouslyfocusedonmesoscale 4 eddiesandtheirinfluencesonbiogeochemicaldistributions(e.g.Garonetal., ∗ Correspondingauthor. Emailaddress: [e-mail] (Z.Y.Hu). PreprintsubmittedtoElsevier27April2010

5 2001;Taupier-Letageetal.,2003;McGillicuddyetal.,2007;Benitez-Nelson 6 etal.,2007).Nevertheless,questionsremain,particularlyincoastalwaters 7 wheredynamicalprocessesareverycomplexandfluxesofnutrientsandsedi- 8 mentsarehigh. 9 TheGulfofLion(hereafterGoL)isalargecontinentalmarginwithasemi- 10 circleshapelocatedinthenorthwesternMediterraneanSea(Fig.1).The 11 hydrodynamicsoftheGoLarecomplexandhighlyvariable,asdescribedby 12 Millot(1990).Threemainforcingscoexist: 13 i)strongcontinentalwinds:theMistral(northerly)andtheTramontane(north- 14 westerly,sometimeswesterly).Theyarecoldanddryandcangeneratestrong 15 upwellingsanddownwellingsalongtheentirecoastoftheGoL(Millot,1979); 16 ii)aquasi-geostrophicalongslopecurrent:theNorthernCurrent(hereafter 17 NC).Itisthenorthernpartofthecyclonicgyreoccurringinthewestern 18 Mediterraneanbasin.TheNCflowsalongthecontinentalslopefromtheLig- 19 urianSeatotheCatalanSea(Millot,1990,1999).Asafirstapproximation, 20 theNCcanbeconsideredingeostrophicbalance,actingasadynamicalbar- 21 rierforcoastalwaters.Nevertheless,severalstudieshavedemonstratedthe 22 presenceoftransientageostrophicprocesses(Albe´rolaetal.,1995;Sammari 23 etal.,1995;Petrenko,2003); 24 iii)importantfreshwatersinputs,bringingnutrientsthatenhanceprimary 25 productivityontheshelf(e.g.MinasandMinas,1989;Ludwigetal.,2009). 26 TheRhoneriveronthenorth-easternpartofthegulfdeliversabout80%of 27 thetotalriverinewaterinputsandconstitutesthemainfreshwatersourceof 28 theGoL.TheplumeextensionoftheRhonecanextendoffshoretowardsthe 29 southwestpartoftheGoLundercertainmeteorologicalconditions(Estournel 30 etal.,1997). 31 Previous insitu studiessuggestedthepresenceofananticycloniccirculationin 32 thewesternpartoftheGoL,inSeptemberduringstratifiedconditions(Millot, 33 1979,1982).Estourneletal.(2003)havealsoshownwithnumericalmodelling 34 thatananticycloniccirculationcanbepresentinthisregioninwinter.These 35 coastaleddiescouldpotentiallybeinfluencedbytheRhonedistalplumewhich 36 couldbringnutrientsandphytoplanktoninsidetheeddy.Numericalmodelling 37 suggeststhattheeddycaninteractwiththeNC(Huetal.,2009).Suchin- 38 teractions,whetherwiththeriverplumeortheneighboringcurrent,indicate 39 thattheseeddystructurescouldplayanimportantroleinthecoastal-offshore 40 transportofnutrientsandphytoplankton,aswellasheatandenergy.Toour 41 knowledge,noexperimentalstudieshavebeendedicatedonthestudyofthe 42 eddydynamicsinthisareasincetheearlyhypothesisofMillot(1979,1982) 43 citedearlier. 44 Themainobjectiveofthispaperistoinvestigatethedynamicalcharacteris- 45 ticsofananticycloniceddyobservedduringtheLatex08cruise,addingcruise 46 datatothepreviousnumericalstudybyHuetal.(2009),tobetterunder- 2