Ocean Color and Atmospheric Dimethyl Sulfide on Their Mesoscale Variability

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 98, NO. D12, PAGES 23,469-23,476, DECEMBER 20, 1993

OceanColor and AtmosphericDimethyl Sulfide' On Their MesoscaleVariability

PATRICIAA. MATRAI. WILLIAM M. BALCH,DAVID J. COOPER, 1 AND ERIC S. SALTZMAN

Rosens#elSchool of Marine andAtmospheric Science, UniversiO• of Miami, Miami, Florida

Themesoscale variability of dimethylsulfide (DMS) andocean color is exploredto determinethe feasibilityof a predictiverelationship. During NASA's Global Tropospheric Experiment/Chemical hlstmmentationTest and Evaluation(GTE/CITE 3), simultaneousshipboard and aircraft studies were carriedout in the North Atlantic,Ibllowed by aircraftstudies in the SouthAtlantic. Surface concentrationsof chlorophyll a weremeasured with an airbornespectroradiometer, the OceanData AcquisitionSystem (ODAS), with simultaneousdetemfinations of troposphericDMS. Shipboard measurementsof DMS in air ;tndwater as well as in situ chlorophylla were takenin the North Atlantic. No relationwas observed between shipboard aquatic DMS and chlorophylla or primary productivity.Higher levels of aqueousDMS were not alxvaysreflected by atmosphericDMS, althoughshipboard and aircraft measurements of atmospheric DMS agreedvery. well. A significant relationshipbetween atmospheric DMS and oceancolor was seenonce at low altitudesin both the North and SouthAtlantic onl': underclean air conditions.Atmospheric DMS levelsduring the NorthAtlantic experiment were probablylowered by the presenceof mostlypolluted air massesin the studyarea and were, overall,probably not representativeof the in situ sea-to-airflux of DMS. Changesin concentrationof aircraft-sensedchlorophyllous pigments were not reflectedby atmosphericDMS. If a predictivealgoritlun is to be found,phytoplamkton blooms should probably be the first placeto studyan oceancolor-DMS relationship.

1. INTRODUCTION a (as an indicator of phytoplanktonbiomass), however, has been reportedas highly variable both spatiallyand The first nteasurementsof dimethylsulfide (DMS) in the temporally. A lack of correlationbetween seawater DMS surfaceoceans and quantitativeestimates of its sea to air and chlorophylla is most likely becauseonly certain flux were made more than a decade ago. Numerous phytoplanktonspecies are known to producesignificant subsequentshipboard measurements have cmffirmed the amountsof DMS. The biologicalproduction of DMS and ubiqui.ty of DMS in the surfaceoceans [Andreae, 1990 for its precursordimethylsulfoniopropionate (DMSP) seems review]. and suggestthat the flux of organosulfurinto the to be confined to dinoflagellatesand pu'mncsiophytes troposphereprovides a major sourcefor sulfur aerosolsin (including coccolithophorcs)both in the field and in remotemarine air masses[Nguyen et al., 1983: Putaud et cultures lAckman et al., 1966: Barnard et al., 1984; al., 1992]. It has been proposed[Charlxon et al., 1987] Turner et al., 1988: Keller et al., 1989]. There are that the distribution of sulfate aerosols in the marine numerousrecords of massiveblooms of DMS-producing atmosphereexerts significantcontrol (either directly or coccolithophores[Keller eta/., 1989: :llatrai and Keller, indirectly) over the Earth's albedo. If true, then the 1993]• other pr3'mnesiophytcs.and dinoflagellates responseof the sulfur cycle to climate change could [Holligan et al., 1987: Turner et al., 1988: Gibson et al., constitutean important feedback in the Earth climate 1990]. Basedon the distributionof suchbloom-forming system. species. it is evident that DMS and DMSP vary. The major sourceof DMS in seaxvateris phytoplankton. temporarily and spatially. dependent on the species The rclatio,',shipbetween seawater DMS and chlorophyll compositio• of the flora and the environmental factors controlling their abundance. Phytoplankton.by meansof their pigment content,are 1NowatPlymouth Marine Laboratow, Prospect Place, easily visible from space. Remote sensingtechniques Plymouth,United Kingdom. might bc used to perform a first-orderestimate of DMS concentrations,given a good algorithm to convert water- Copyright1993 by the AmericanGeophysical Union. leavingradiance to pigmentconcentration [Gordon et al., 1993] or primaD• production [Balch et al., 1992], and Paper number 92JD02968. relations to predict DMS from these quantities. In 0148-0227/93/92 JD-02968505.00 general.the atmosphericconcentrations of DMS appearto

23,469 23,470 MATRAIET AL.' OCEANCOLOR AND ATMOSPHERIC DIMETHYL SULFIDE var3.• in concertwith DMS in oceanicwaters [,4ndreaeet iodine solution and settled once ashore for cell counts a!., 1985: •altzman and Cooper', 1988' •(atrai eta!., [Sournia, 1978]• which were done with an OlympusBH2 1992]. To the extent that the DMS ill air and water are lnicroscope. covariant.one can relate either concentrationto pigment 2.1. Ocean Color •leasurements concentrationin sea surface. Nonetheless,because of the temporal a•d spatial scalesinvolved in oceanicsystems, Aircrat'tocean color measurements were performed from the prediction of the global sea-to-air DMS flux will ultimatelyinvolve remotesensing techniques. the NASA Wallops Flight Facility LockheedElectra leaving froin Wallops Island, Virginia, for the North In this paperwe ilwestigatethe feasibilityof obtaininga Atlantic Ocean flights and from Natal, Brazil, for the predictiverelationship between DMS emissionsand ocean South Atlantic flights. In the North Atlantic missions, color as observedfroin an aircraft, on a regional basis. CITE 3 flight pathswere plannedto accommodatethree The Global TroposphericExperiment (GTE) calibration sea-truthpasses over the vessel. At thosetimes, shipboard comparisonfor airbornechelnical sensorsof sulfur gases water and air samples were collected for DMS, and (Chemical InstrumentationTest and Evaluation (CITE 3)) chlorophyllwas measuredin surfacewaters. providedthe opportunityto conductcoordinated shipboard and airborne measurements. Field seasons occurred over The ODAS measurementsconsisted of two primary instruments: an infrared radiometer (PRT-5) to measure the pollutedNorth Atlantic and the relativelyunpolluted sea surface temperature and a three-channel visible tropical SouthAtlantic, in an effort to contrastthese two environments. spectroradiometerfor 460, 490, and 520 nm wavelengths. ODAS operatesas a line-of-flight instrument. The instrument was calibrated before and after CITE 3 at the 2. METHOD GoddardSpace Flight Center in Greenbelt,Maryland, as The projectwas carried out in two phases,consisting of well as after each flight. A compilationof calibrations sinmltaneousshipboard (R/V .,ttlantis II) and aircr,-fft run during 1988 and 1989 was finally used for each studies in the North Atlantic ocean during July and channel and at each gain setting (E. Itsweire, personal Augustof 1989 followedby aircraftstudies in the South communication, 1992) [Harding eta!., 1992]. No Atlantic in Septemberof 1989. The aircraft work was atmospheric.correction is necessaryin the algorithm for done in conjunctionwith the NASA CITE 3 program aircraft altitudesof less than 150 m (500 ft) [Campbell which involved airborne measurelnents of DMS and other and Esaias, 1983]. The upwelled radiances were sulfurgases [Cooper' and Saltzman,this issue;Gregory et simultaneouslysampled every 0.1 s, then reducedto 2-s a/., this issue:Hoel/et a/., this issue]. The Ocean Data averages corrected for sunglint, reflection from other AcquisitionSystem (ODAS) [Campbelland Esaias, 1985] sources,and aircraft changesin elevation,pitch and yaw. radiometerwas mountedand operatedaboard the NASA Pigment concentrations were determilled using a Electra aircraft to measure ocean color and sea surface curvature algorithln [Ilarcling eta!., 1992] that first telnperatureduring a seriesof flights over the northern calculatesa ratio among the three radiancesmeasured, and southernAtlantic Ocean. includingoverflight of the then incorporatesit into a linear regressionwith factors ship'scruise track. Stationlocation as well asflight paths determinedempirically from our data (in situ chlorophyll are shown in Plate 1. and ODAS measurements)collected during the ship Every day at approxilnatelylocal apparent noon we overflightsin the North Atlantic. Finally, the data for measuredprofiles of scalarirradiance using a PNF-300 each flight were reducedto blocksof time matchingthose optical profiling system(Biospherical Instrulnents) and during which aircraft atmosphericsamples of DMS were collected salnples for DMS. chlorophyll. prilnary collected, usually 600 s long. Navigation data were productivity,nutrients. and cell countswith 10-L Niskin obtained from ODAS or the aircraft system. bottlesattached to the wire. Pigmentconcentrations were determined in acetone extracts using a Turner-Designs 2.2. Dimethyl&t/fide.ztna/.vxis fluorolnetcr[}'entsch and •,llenzel, 1963]. 14C-based productMtymeasurements were performed at eachdepth The shipboarddetermination of DMS in seawaterand air [Stricklandand Parsonx, 1972]. Spikedsalnples in 250- is similar to that reportedin Sa/tzmanand Cooper'[1988] mL acid-cleanedpolycarbonate bottles were incubated for and Cooperand Sa/tzman[ 1991], with a detectionlimit of 24 hours on deck under natural sunlight in seawater- 0.2 nM in a 5 mL sample. The precisionof the method cooledtubular incubators wrapped in blue acetate(Madico was better than 5% (plus or minus I standarddeviation) Film TS-51) to reduce the light intensi•' to the for most of the working range and roughly 10% at the appropriatcrelative irradiance. Following the incubation, lowest concentrations. Standard additions were done the sampleswere filtered onto Whatman GF/F filters, routinely during the courseof this study to confirm the rinsed, and countedin Ecolulne. Nutrient sampleswere accuracyof the measurementsof atmosphericDMS. filteredand frozenfor analysisashore of NO-3, NO-2, Airborne analysisof DMS in the atmosphericboundary NH+4. andpO3-4 [Strickland and Parsons, 1972; layer was done using an automatedgas chromatography k2•ro!•//: lV83]. Water salnpleswere preserved in lugols /flame photometricdetection (GC/FPD) systemwith a MATRAI ET AL.' OCEAN COLOR .aND ATMOSPHERIC DIMETHYL SULFIDE 23,471

8• 74hi . ,.- IL4 ;;':hi

REMP•.S

78bl ?4hi • -' , REHAS D o

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-4

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-8

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: G C F Comp 36 34 32 30 ,26 Longitude(ow)

Plate 1 (a-c) Flight pathsfor NASA'saircraft and stationposition (crosses) for the R/V Atla, tis H duringtile North Atlantic missions(flights 4-10) (August22 to September1, 1989) displayedoil an AVI• theruralcomposite for August23-26, 1989 (courtesyof D. Olson,RSMAS, Universityof Miami) and(d) flight pathsfor the threeODAS samplingmissions (flights 13-18) in the SouthAtlantic (September 1989). sampling frequencyof one sample every 600 s. The generallyshallower than the chlorophyllor the primary detectionlimit of this FPD was approximately3 ppt of productionmaximum, with the latter usually located at DMS in a 10-L air sample. Complete details are the depth of the 1% light level. Surfacechlorophyll was describedin Cooperand Saltzman[this issue]. generally less than I pg/L while the subsurfacemaxima reachedconcentrations as high as 4 pg/L. Except for an 3. RESULTS abundantbut veo, patchybloom of Osci!!atoria sp. strictly in surface waters. diatoms were most abundant with Depth distributions of DMS in the North Atlantic dinoflagcllatcs. small flagellates. and prymnesiophytes showed a subsurfacemaximum (except after one wind also present. Very. low DMS concentrationswere event, when uniform distributions reflected a well-mixed measuredin surfacewaters dominatedby Osci!!atoria sp. upperwater column). This maximum, when present,was Nutrient lex-elsdid not show any correlationxxith DMS 23,472 MATRAIET AL.' OCEANCOLOR AND ATMOSPItERIC DIMETItYL SULFIDE levels. Figure 1 presents the relationship between 250 chlorophylla, primary.production and DMS. The North Atlantic scattergrams do not show any relation between 200 thesetwo measuresof ph.vtoplanktonactivity and DMS. Shipboard DMS measurements in air were done •. •5o throughoutthe North Atlantic cruise, both on a transect o from St. George,Bermuda, to 38ø 48'N 72ø 47.2'W as 100 o well has while on station. These valuesare comparedto o

DMS concentrationsin surface seawaterin Figure 2a. 5O Higher levels of aqueousDMS were sometimesbut not alwaysreflected in the atmosphere.DMS in water and in o o air was, in general, lower in and over the oceanicareas o.o 0.5 1.o 1.5 2.0 2.5 3.0 3.5 4.0 4.5 than in the more coastal stations. The shipboard DMS [nM] atmosphericDMS measurementscorresponded well to the levels deter'.ninedon board the aircraft during the ship overpassesat lessthan 150 m of altitude(Figure 2b), with 6O the high-altitude(400 m) DMS levels being lower by a 0 factor of 4. 5O Seven missionswere flown over the temperateNorth Atlantic (Plates la-lc). The spatialcoverage provided by ODAS indicated surface chlorophyll numbersranging from 0.2 to 1.4 pg•, while atmosphericDMS levels 3O simultaneouslymeasured aboard the aircraft averaged 0 2O about 20 ppt, except during one mission (mission 4) in 0 which valuesexceeding 80 ppt were observedalong with 10

15 0 24 25 26 27 28 29 30 31 1 'nm• Fig. 2. (a) Shipboardatmospheric DMS concentrationsin the ,- 10 o o o North Atlanti'zduring a trailsectt¾om 13ennuda to station(solid circle)and or, station(open circle) versussurthce seawater DMS concentration.(b) Comparisonbetween atmospheric DMS o concentrationsoil boardship (circles) and aircraft at 100-150m (squares)and 1300 m (triangles)during three North Atlantic o o o overflights. , •-v I I I 0 1.0 2.0 3.0 4.0 5.0 the lowest ozone levels measured during the North Chlorophylla [ug/I] Atlantic flights [Cooper and Saltzman, this issue]. Pigmen!values during this missionwere in the rangeof 0.4-0.6 !,tgchl/L. This is the only North Atlantic ntission 15 when a significant relationshipwas observedbetween pigmentlm els and atmosphericDMS (r=0.535, p<0.001). Pigmentco:•centrations observed only from altitudesof 10 00 0 less than I50 m are plotted in Figure 3a. Overall, 0 0 pigmentobservations from altitudesof 1300 and 5000 m •0 0 were not significantlyhigher (range 0.4-1.4 lag chl/L) o •o o than thosesensed from 150 m abovesea surface (Figure 5 0o • o ao 3b). RepeatedODAS samplingof one locationfrom two altitudes(150 and 1300m) with a delayof 1 hourresulted oo o in a similar pigmentconcentration (within 3%). 0 f i i i ! i ot A paucityof data for the SouthAtlantic flights is due 0 5 10 15 20 25 30 35 mostly to the constantchanges in altitude specifically rngC/rn3/day programmedfor thosemissions; ODAS providedusable Fig. l. (a) SeawaterDMS versusextracted chlorophyll a and(b) data for only three of the seven missionsflown. Hence, primaryproductivity from on-deck incubations in the North data from various altitudes are included in Figure 4. Atlantic. Atmospl•er•c DMS concentrationswere lower in the MATRAI ET AL.' OCEANCOLOR .AND ATMOSPHERIC DIMETHYL SULFIDE 23,473

Northern Hemisphere Southern Hemisphere 140 45

120 oø0 ß 35 lOO

80 • 25 20 60 o o 15 4o o o 10 2o eøo o ø 5 I I I o I I ! I I I 0 0.2 0.4 0.6 0.8 1.0 o.o 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.0 ODASpigment [mg/m 3] ODASpigment [mg/m 3] Fig.4. AtmosphericDMS versusODAS chlorophyll a observationsduring three South Atlantic flightsat <15()m

5O (opencircles), 300 m (solidcircles) (Ilight 14), 1300m (open triangles),anJ >2000 m (solidtriangles).

4. DISCUSSION • 30 o o The rate c f release of DMS from the sea surface is a ß 20 complexfunction of the concentrationof DMS at the sea q• •3o o surface,the physicalstate of' the air/sea interface,and lO molecularproperties of DMS whichcontrol its diffusMty oøo o in aqueoussolution. In the atmosphere,DMS has a o o.o 0.2 0.4 0.6 0.8 1.0 1.2 1.4 lifetime on the order of a day or less. To the extentthat atmosphericDMS samplesreflect emissions from the sea ODASpigment [mg/m 3] surfacein the immediatevicinity, the signatureof the sea- Fig. 3. Simultaneousatmospheric DMS versusODAS to-air DMS flux in pollutedenvironments can be greatly chlorophylla observations during all sevenNorth Atlantic disturbed bv enhanced oxidant levels [.4n&'eae et al., flights(a) in theboundar3.' layer (15() m or less)(flight 4 1985]. This meansthat changesin atmosphericDMS are observationsrepresented by solidcircles; see text tbr Ibrther unlikelyto reflectany enhancement in the sea-to-airDMS explanations)and (b) at higherelevations of 1300m (open flux dueto a changein biologicalactivity, assuming fairly circles)and 5000 m (solid circles). constant winds. Air masstrajectory analyses for CITE 3 confirm the SouthernAtlantic, while pigmentvalues ranged from 0.2 presenceof' mostlypolluted air in the North Atlantic to 0.8 lag chl/L, overlappingwell with those obsel'ved [Shiphame, at., thisissucl. Measurements of sulfurgases duringthe North Atlanticflights. Flight 13, southward other than DMS and comprehensivesupport measure- along the Brazilian coast,obselwcd the highestpigment mentscollected during CITE 3 suchas NOx, CO, and concentrations,at about 0.7 lag chl/L with little spatial ozone also indicate a substantialdegree of pollution variability. Field observationsindicate the presenceof [Hoe# et at., this issue]. Continentalair, either from the haze and l•igh sunglintduring this mission,especially northeasternUnited Statesor of Canadian polar origin, above6000 ft. (approximately2000 m). Atmospheric was sampledduring all the North Atlantic flights, except DMS duringthe sameflight, on the other hand, showed for flight 4 and the offshoreleg of flight 5. These two an increaseof about25 ppt for severalhours, most likely flights sampled North Atlantic tropical maritime air due to samplingof the lowerboundary layer. Flight 14, masses,resulting in the highestatmospheric DMS values northwardalong the Braziliancoast during a clearday, is (Figure 3a) and the only instancewhen a significant the only South Atlantic mission when a significant relationshipwas observedbetween ocean color and relationshipwas obsclwcdbetween pigment levels and atmosphericDMS. The mostlylow and fairly uniform atmosphericDMS (r=0.823, p<0.001). It encountered levelsof DMS seenduring the rclnainingNorth Atlantic little spatialvariability for bothatmospheric DMS andsea flightsprobably resulted from suchchemical interactions surfacepigment, with valuesaround 20-25 ppt and 0.2 lag [Cooper'and Saltzman,this issue]. chl/L, respectively.Flight 18,eastward, showed a distinct During the SouthAtlantic flights, maritimeair masses fourfold decreasein atmosphericDMS and threefold were transportedwestward across the equatorialAtlantic increasein chlorophylla. duringall flightsand at all flight altitudes,but the highest 23,474 MATRAIET AL.' OCEANCOLOR AND ATMOSPItERIC DIMETHYL SULFIDE ones [Shiphameta/., this issue].implying that, unlike the correlationof DMS in seawaterand measuredprimary North Atlantic. pollutionwould not be a goodexplanation production[Barnard et al., 1984: Bates et al., 1987], even for the apparentuniformity in DMS distribution. Cooper though large-scale. spatially averaged. aqueous DMS and Saltzman [this issue,and referencestherein] indicate concentrationsappear to be covariant with averaged that the DMS levels encounteredduring this period were productivit.•estimated from global maps [•,•lndreaeand considerablylower than thosereported by previousstudies Barnard, 1984]. Despite uncertaintiessuch as winds and over tropicalwaters. suggesting the low DMS may be due transferrates and variationsin regional DMS production to a seasonaleffect [Bates et al., 1987; Ngttyen et al., and release,when we averagedall of our seawaterDMS 1992]. as the samplingoccurred at the end of the southern and productivitydata. the mean would fit perfectly the winter, perhapsprior to any spring phytoplanktonbloom. spatially macroscale relationship between primary It is also possiblethat althoughthe air trajectoriesduring productionand seawaterDMS concentrationsdescribed by the experiment did not indicate advection over land Andreae and Barnard [1984] for area-weighted masses.the sourcesmay have originatedfrom different biogeographicalregions classified according to Koblentz- regions as evidenced by the presenceof haze layers Mislhkeet al.'s [1970] productivitymap. The error bars of (ODAS operator field observations) and lack of our average.however. are large and tell us nothing about homogencityin the relative levelsof variousatmospheric finer scale covariabilityin the entire range of values for gases [Coo?er and Saltzman, this issue], encountered DMS and primary productionin the oceans. Given that during some flights and at different altitudesduring a airborne DMS sampleswere collectedcontinuously with single flight. If so. DMS levels would be lower and an integrationtime of 10 rain per sample,this length of reflectanceshigher than expected. time representsan average distance of 60 km at the Although logistics clearly restricted the number of velocity of the aircraft. For phytoplamktonspatial overflights of the ship by the aircraft. pigment values distribution. hence the ocean color signal sensed by calculatedwith the algorithm developedwith our data ODAS. this is a large-scaleaverage, not necessarilythe (only case I waters.i.e.. watersfor which phytoplankton most meaningfulsampling distance [1-[att•tv et al., 1978]. and their associateddebris control the optical properties) Two other large-scale estimates of the ocean-to- were not significantlydifferent from thosecalculated with atmosphereflux of DMS have involved remote sensing. an algorithm of mostly case I waters developedfor the Thompsonctal. [1990] used chlorophyll concentrations Multichannel Ocean Color Sensor. a 20-channel obtainedfrom a CZCS monthly mean to derive a signal predecessorof ODAS [Campbell amt Esaias, 1983; for the concentrationof DMS in seawaterfor a specific Campbell et al., 1986]. ODAS has been extensively region and time. assuming an empirical relationship tested and used in one other study in the more turbid between seawaterchlorophyll and DMS [.4ndreae and ChesapeakeBay [Itarding et al., 1992]; althougha wide Barnard, 1984]. This relationshipwas highly significant range of conditionsand time scaleswere used in their over a long transectacross the Atlantic Ocean. Within stud), the accuracy of the ODAS chlorophyll a the region of 0-35øN and 20-35øW, Thompsonet al. measurementswas consideredcomparable to that of the [1990] calculate a regional mean DMS flux of similar coastal zone color scanner (CZCS). In the case of the magnitude or slightly higher than other published South Atlantic, previouspigment measurementsdone in estimates [Barnard et al., 1982; Erickson et al., 1990]. waters off Brazil indicate the ODAS-derived pigment Their large-scaleaveraging at 2.5ø latitude probably concentrationswere reasonable [e.g., Herbland et al., smoothesover any mesoscale(•-100 km) phytoplamkton 1985' DeAl•aster et al., 1986]. However, the extent to patchiness.similar to our averagingin the SouthAtlantic. which the extrapolationof our algorithm is possiblefor Erickson et al. [1990] calculatedDMS fluxes using an the South Atlantic waters, with no in situ data available, is atmospheric general circulation model with DMS unknown. Furthermore,our radiance-pigmentconversion concentrations derived from incident solar radiation at the is valid for altitudes lower than 150 m; the apparent Earth's surfhce. No explicit calculation,simulation, or increaseof chlorophylllevels as measuredby ODAS when field data of global phytoplanktonbiomass or primary flown at higher altitudessuggests reflectance interference productivit).• were includedin the model. The calculations by other sc,urces such as atmosphericaerosols, sunglint, were confi•ed to oceanicregions only. The calculated and airbornepollen [Harding et al., 1992]. DMS concentrations tend to underestimate the surface The DMS data collected in and over the Mid-Atlantic ocean DMS concentrations. especially in productive Bight duringthe summerof 1989 were similarto previous regions.while vers.'high concentrationsare calculatedfor shipboard[Andreae et al., 1985; Cooper and Saltzman, polar regions,where DMS data are scarce. Determining 1991] and aircraft studies [Van Valin and Luria, 1988]. the spatialand. mostlikely. temporalscale dependence of Phytoplanktonbiomass and productivi.ty, as an indicator the relationshipbetween biological actix,it).,'and DMS of the magnitude of the source of DMS, were fairly concentrations is one of the major challenges in uniform in surfacewaters of the Mid- Atlantic Bight. The understandingthe biogeochemicalcycling of organic measurementstaken by ODAS reflect best the in situ sulfur. pigmentn•easurements. not productivity. Other regional If our relationshipsbetween DMS in oceanwaters and samplings have also riffled to provide any simple chlorophyllas well as betweenaqueous and atmospheric MATRAI ET AL.' OCEAN COLOR AND ATMOSPItERIC DIMETHYL SULFIDE 23,475

DMS had been significant. as suggestedin the literature, Andreae,M. O., Ocean-atmosphereinteractions in the global and given that ocean color is mostly a measure of biogeochcnficalsulfitr cycle, Mar. Chem.,30, 1-29, 1990. chlorophyllouspigment concentration, a certain degreeof Andreac,M. O. andW. R. Barnard,The marinechenfistry of covariabilit¾ between atmospheric DMS and surface dimethylsulfide, ,•.lar. Chem.,14, 267-279, 1984. chlorophyllmight have been expected. The presenceof Andreae,M. O., R. J. Ferek, F. Bennond,K. P. Byrd, R. T. mostly polluted air massesduring the North Atlantic Engstrom,S. Hardin, P. D. Houmere,F. LeMarrec, and H. sectionof the experimentas lnentioncdabove may have Raemdonck,Dimethyl sulfide in the marineatmosphere, J. maskedthe natural signal present. While up to 30% of Geophys.Res., 90, 12891-12900,1985. the variabili.ty of DMS in seawaterhas been explainedby Balch, W., R. Evans, J. Broxvn,G. Feldnmn, C. McClain, and its relationshipto chlorophyllin different oceans[Cline W. Esaias,The remotesensing of oceanprimary productivity: and Bates, 1983' Andreae, 1990]. the lack of relationship Use of a new datacompilation to test satellitealgorithlns, d. betweenDMS and chlorophyll as we saw has also been Geophys.Res., 97, 2279-2293, 1992. previously reported [.4ndreae and Barnard, 1984]. A Barnard,W. R., M. O. Andreae,W. E. Watkins. H. Bingeruer, correlation between piglncnt and DMS concentrations and H. W. Georgii,The tlux of dimethylsulfide l?om the could also be dralnaticallyaffected by the physiological oceansto the atmost•here,,]. Geophys.Res., 87, 8787-8793, history of the cells' a healthy. bloolning population of 1982. phytoplanktol•lnight producemuch different quantitiesof Barnard.W. R., M. O. Andreae,and R. L. Iverson,Dimethyl DMS than a decayingbloom. yet the piglnent values are sulfideand Phaeoo,stis pottchetii in the SoutheasternBering the same 1•[atrai and Keller, 19931. This is also a major Sea, CoutiueutalShel./'Res., 3, 103-113, 1984. factor preventinga good correlationbetween piglncnt and Bates,T. S., J. D. Cline, R. }I. Gammonand S. R. Kelly- prilnar).ß production [Balch et al., 1992]. In a similar Hansen,P, egional and seasonalw•riation in the flux of maimer. a "tilne-lag" approach might account for the oceanicdi,nethyl sulfide to the atmosphere,d. Geoph),s.Res., effectof "stageof the blooln"in theserelationships. 92, 2930-2938, 1987. Spring pl•ytoplankton blooms are occasionally. and Campbell,J. W. andW. E. Esaias,Basis tbr spectralcurvature often predictably,dominated by DMS-producingspecies algorithmsin remotesensing of chlorophyll,Appl. Opt., 22, 1084-1093, 1983. for prolonged periods of' time, covering mesoscale Campbell,J. W. andW. E. Esaias,Spatial patterns in [Barnard e! al., 1984; Holligan el al., 1987; •latrai and Keller,1993] to megascalcareas (500.000 kin 2, southof temperatureand chlorophyll on NantucketShoals from airbornerelnote sensing data, May 7-9, 1981,.l. ,5•lctr.Res., Iceland) (P. Holligan and W. Balch, personal 43, 139-161, 1985. communicaiion.1992). During such cases. significant relationshipshave been observed between aqueous DMS, Campbell,J. W., C. S. Yentsch,and W. E. Esaias,Dynamics of phytoplanktonpatches on NantucketShoals: An experiment chlorophylla, and/or cell nulnbers[Barnard el al., 1984' involvingaircraft, ships, and buoys, in Tidal • lixing and Tttrner et ai., 1988' AIatrai and Keller, 1993]. Whether PlanktonDynamics, Lecture Notes on Coastal amt Estuarine such "hot-spots"of biologicalproduction of DMS, now Studies,vol. 17, editedby M. J. Boxvman,C. M. Yentsch,and knownto be spatiallysignificant, can still be consideredto contributethe bulk of DMS to the atmosphereseems to be W. T. Peterson,Springer-Verlag, New York, 1986. Charlson,R. J., J. E. Lovelock, M. O. Andrcae, and S. E. debatable[Andreae, 1990]. Nonetheless,these blooms are Warren, Oceanicphytoplamkton, atmospheric sulphur, cloud still the first place to study an ocean color-DMS albedo, and climate, Nature, 326, 655-661, 1987. relationshipif a predictivealgorithm is to be found. Cline, J. D. andT. S. 13atcs,l)imethylsulfide in the equatorial PacificOcean' A naturalsource of sulfurto the atmosphere, AcbtowIedgments. The ODAS n•easurements were Geophys.Res. Lett., 10, 949-952, 1983. coordinatedby Wayne Esaias(Goddard SpaceFlight Center, Cooper,D. J. and E. S. Saltzman,Measurements of atmospheric Greenbelt,Maryland). He was responsiblefor the calibration, dimethyl sullide and carbon disulfide in the xvestem Atlantic installation,logistics, and operation of the ODAS. Jim Yungel boundnrvlayer, d. Am•os.Chem., 12, 153-168, 1991. did n,,ostof !!',eactt',a! flying of ODAS on the aircraft. We are Cooper,D. J., and E. S. Saltzman,Measurements of atmospheric gratetiffto Bill Ryan lbr shiptime on boardthe AtlantisH,' G. dimethylsulfide, hydrogen sulfide, and carbondisulfide Mountainfor coordination;R. Eppley,M. Keller, K. Kilpatrick, duringGTE/CITE 3, d. Geopto,s.ties., this issue. D. Olson,and R. Zika lbr assistanceand equipment;W. Esaias, DeMaster, D. J., S. A. Kuehl, and C. A. Nittrotter, Efiiectsof E. Itsweire,,red L. Hardingfor data disentanglement;and M. suspendedsediments on geochemicalprocesses near the Lewis Ibr cncouragemcnt.D. Olson also providedvaluable mouthof the/unazon River: Examinationof biologicalsilica connnents,statistical insight, as well as the AVHRR thermal uptakeand the thte of particle-reactiveelements, Continental imager5.'.This work was supportedby NASA grantsNAGW- 1845 and NAG-1918. ShelfRes.. 6, 1()7-125, 1986. Erickson, D. J. III, S. J. Ghan, and J. E. Penner, Global ocean-to-

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