DOM的紫外可见光谱吸收

Limnol.Oceanogr,26(1),1981,43-53(1981,bytheAmericanSocietyofLimnologyandOceanography,Inc.Absorptionbydissolvedorganicmatterofthesea(yellowsubstance)intheUVandvisibledomains'AnnickBricaud,Andre'Morel,andLouisPrieurLaboratoiredePhysiqueetChimieMarines,BP8,StationMarinedeVillefranche-sur-Mer,UniversitePierreetMarieCurie,F06230Villefranche-sur-Mer,FranceAbstractSpectralvaluesofabsorptionoflightbydissolvedorganicmatterweremeasuredinsamplesoriginatingfromdiversepartsoftheocean,quitedifferentwithrespecttopigmentandpar-ticlecontent.Theuseof110-cmcellsandthenof10-cmcells,withahighlysensitivespec-trophotometer,allowedmeasurementthroughouttheUV-visiblerange(200-700nm)evenforthelowconcentrationsofyellowsubstanceencounteredintheopensea.Theconcentra-tionappearsinfluencedpredominantlybynaturalandindustriallanddischarges.Inoceanicwaters,itremainslowandseemstoberelatedtothebiologicalactivityaveragedoveralongperiodratherthantothelocalandtemporaryphytoplanktoncontent.However,evenatsuchlowconcentrations,yellowsubstanceintheopenseamayhaveaneffectonabsorptionandhenceonoceancolorsimilartothatoflowormoderatealgalbiomass.Thespectraldepen-dencelawofabsorptionappearstovarywithinarestrictedrange,andanaveragelawcanbeconsideredrepresentativeofrapidmeasurementsatoneselectedwavelength.Theincreasingabsorptionoflightbyfilterednaturalwaterswithdecreasingwavelengthiswellknown.ThedissolvedandcolloidalorganiccompoundspresentinnaturalwatersandresponsibleforthisabsorptionwerecollectivelycalledGelbstoff'byKalle(1938),i.e.yellowsubstance,andmorerecentlyGilvin(Kirk1976).Thissubstancehasbeensubjectedtomanyinvestigationstodetermineitsori-ginandchemicalcomposition.Mostab-sorptionmeasurementshavebeenre-strictedtotheUVpartofthespectrum,whereabsorptionismuchhigherthaninthevisiblepart.However,yellowsub-stance(y.s.),inadditiontopigmentsandnonlivingmaterial,isoneofthefactorsdeterminingtheshapeofthetotalab-sorptionspectruminthevisiblerange,andthuscausesvariationsinoceancolor(MorelandPrieur1977).Tostudytheeffectofthissubstanceontheopticalpropertiesofseawater,forinstanceforremotesensingapplications,wemustknowitsspectralabsorptioncoefficientsthroughoutthevisiblerange.Thesecan-1ThisworkwassupportedbyCNRS(RCP247andERA278),CNd'EtudesSpatiales(contract79/250),andCNd'ExploitationdesOceans(77/1695and79/2010).notbeinferredfromcoefficientsintheUVdomain,aslongasithasnotbeenclearlydemonstratedthatanunequivocalrelationexistsbetweenUVandvisibleabsorption.Inthevisibledomain,whereabsorp-tionbyy.s.isoftenhardlymeasurable,moststudieshavebeenrestrictedtowatershavinghighy.s.concentrations,liketheBalticsea,lakes,andsomecoast-alwaters(JamesandBirge1938;Jerlov1955;Kalle1961,1966;H0jerslev1974;Lundgren1976;Kirk1976).Inoceanicareas,someattemptshavebeenmadetoseparatetheinfluenceofparticlesanddissolvedmaterial(ClarkeandJames1939;Hulburt1945;Burt1953,1958),butthesestudiesproposednolawforthewavelengthdependenceofabsorptionbyy.s.Atypicalabsorptioncurve,repre-sentedbyastraightlineonasemilogplot(logarithmoftheabsorptioncoefficient,a,vs.wavelength)wasgivenbyJerlov(1968).Thisrepresentationisattheori-ginoftheexponentialform:a(X)=Cexp(-0.015X),usedbyseveralworkersinmodelingoceancolor(Mueller1973;MaulandGordon1975).MorelandPrieur(1976)mademorecompletemea-surementsforweaklyabsorbingwatersintheupwellingregionsoffMauritaniaand4344Bricaudetal.Table1.Locationofsamplingareas:A-oceanicwaters,remotefromlandinfluences,withlow(An-tiprodI),high(CinecaV),ormoderatelyhigh(Ciprea)concentrationsofpigmentsandnonlivingmaterial;B-coastalzones,weakly(VillefrancheBay)orstrongly(Var,Baltic)affectedbyfreshwatersupply;C-highlycontaminatedareas,wheredissolvedsubstancesarelikelyquitedifferentinnature(GulfofFos-sur-MerandEtangdeBerre,influencedbyoutletofRhonewaters,industrialdischarges,andeutrophi-cation;areaaffectedbyurbaneffluentsfromdrainsofMarseilles).CruiseLocationDatesampledStorageA.CinecaV-J.CharcotMauritanianupwellingMar,Apr74afewhoursregionAntiprodI-M.DufresneIndian-AntarcticOceanMar773months66030'ECiprea-SuroitGulfofGuinea,Aug784monthsequatorialdivergenceB.VillefrancheBayJul,Sep,Oct77,afewhoursFeb,Dec78MouthofRiverVarFeb78afewhoursBalticSea*Jan7948hC.Fos-BerreGulfofFos-sur-Mer,May774-6weeksEtangdeBerreEmicortNeardischargeofDec77afewhoursMarseillesdrains*SamplescollectedbyN.K.H0jerslev.foundanearlyconstantrelationsimilartotheaboveexpression:a(X)=Cexp(-0.014X).Nevertheless,fewdatathroughoutthevisibledomainhavebeenreported.Theaimsofthisworkaretodetermineifanydissolvedorganicmattercanreasonablybeassumedtoshowafeaturelessandex-ponentialincreaseinabsorptiontowardshorterwavelengths,ifthesamerelationisvalidthroughouttheUV-visibledo-main,andtodeterminethey.s.concen-trationrangeinnaturalseawatersanditsrelativeimportanceinvariationsinoceancolor.Wewilluseyellowsubstancetorefertotheopticalpropertyofthisdissolvedorganicmatter,regardlessofitsoriginandchemicalcomposition.Thatconven-tion,althoughquestionablefromachem-icalpointofview,enablesustoincludeinasingleparameteranydissolvedmat-tercausingvariationsinoceancolor.Consequently