GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 21, PAGES 2675-2678, NOVEMBER 1, 1997
Seasonal emissionsof isoprene and other reactive hydrocarbon gasesfrom the ocean WendyJ. Broadgate,PeterS. LissandStuartA. Penkett Schoolof Environmental Sciences, Universityof EastAnglia,Norwich,UnitedKingdom
Sea Abstract. In thispaperwe showevidence thatisoprene emission and December1993 and April 1994, and in the Bellingshausen from the oceansis stronglyseasonallydependentand is correlated (51 - 70ø S, 60 - 85ø W) in November/December1992. Further with the chlorophyllcontentof the waterfrom measurements in the sampleswere collectednearshore(3 miles offshore)in the southern North SeaandSouthernOcean. We estimatethe seasonally averaged North Sea(52.5ø N, 1.8ø E), monthlyfrom July 1993 to July 1994 fluxofisoprene totheatmosphere tobe1.7x 107molecules cm'2s'•, using a stainlesssteel bucket. All sampleswere immediately to groundglassstoppered bottles. Cruisesampleswere which may be significantfor atmosphericchemistryin locations transferred analysedin situ andnearshore sampleswerestoredin an insulated remote from land as it is the only known sourceof atmospheric containerin the darkandanalysedwithin 3 to 30 hours. Storagedid isoprenein theseregions. We observea strongseasonalcycle of not significantly affectmostcompounds (e.g.maximumvariationin severalotherNMHCs in seawaterat high latitudes,with a maximum isopreneconcentration in storagetestsof up to 20 hoursin both in summer. This will distort current estimates of the annual marine
productive and non-productive waterswas 0.8prooil'l). To
flux of NMHCs to the atmosphere which may needto be reducedby up to an orderof magnitude to accountfor loweremissions in winter.
determine the stateof saturationof the gasesin seawater,air samples werecollectedby filling 3 1electropolished stainless steelcanisters to 35 psi nearthe bow of the vessel,whenthe wind wasincidentover
Introduction
the bow.
The NMHC concentrations were determinedin a similar way to Non-methanehydrocarbons(NMHCs) are importantreactive Plasset al., [ 1991]andSwinnerton andLinnenbom [ 1967]. A 1.4 1 gasesin the atmosphere, whichprovidea sinkfor hydroxylradicals sampleof seawaterwaspurgedwith C. P. nitrogengas(BOC) at 60 (OH) andplaykeyrolesin theproduction anddestruction of ozonein mlmin'l for30 min(recovery > 90%). Theeffluent wasdriedin a thetroposphere [DonahueandPrinn, 1990]. Little is knownabout water condenserimmersedin an ice bath and a nation dryer and the production mechanisms of NMHCs in seawater,althoughit has subsequently thetracegaseswerecryogenically preconcentrated in a been suggested that alkenesare producedby a photochemical
mechanism actingon dissolved organicmatter[Ratteet al., 1993, 1995; Wilsonet al., 1970]. The seasonalvariationhas been little studiedand in a recentreview paperPlass-Diilmeret al., [1995] pointedout that the lack of seasonalinformationwas severely restricting ourunderstanding of annualfluxes.Globally,the marine flux is• probablya minor componentof atmosphericNMHCs, however,the dominantmarine NMHCs, etheneand propene,may havea localimpactonphotochemistry [Plass-Diilmeret al., 1995]. A highlyreactiveNMHC, isoprene(2-methyl-l,3-butadiene), is emittedby particularspeciesof terrestrialplant with an estimated
global fluxofbetween 250Tgyr'• [Mi•ller,1992]and450Tgyr'• [Rasmussen and Khalil, 1988]. Reactions of isoprenecontribute to regional photochemicaloxidant formation,the productionof formaldehyde, per0xy radicals,organicaerosolsand ultimately carbonmonoxide,the dominantsink for OH in the-atmosphere [Fehsenfeld et al., 1992,Miyoshieta!., 1994].Emissions of isoprene estimatedfrom measurements in the Meditei'r. anCanand Pacific
1/8"(o.d.)stainless steeltrapfilledwith80 meshglassbeadsand
heldat-185øC usingliquidnitrogen. The gaseswerereleasedfrom thetrapby heatingto 95øCandsweptintoa gaschromatograph with an A1203PLOT column(Chrompack)andFID [Broadgate,!995]. Air (I L) was analysedin an identicalfashionto the purgevessel effluent. Peakidentificationwasby retentiontime (injectionof pure compounds) andconfirmed by massspectrometry. Calibrationwas carriedout daily using standards(a clean air sample,and ppm commercial gasstandards).The daily standards werecalibratedby staticdilution[Broadgate,1995]. The precisionof the analysiswas betterthan 11%. Chlorophyllsampleswere filteredat the time of analysisof NMHC samplesandthe filtersfrozen(for severalweeks) beforefluorometric analysis[Parsonset al., 1989]. Taxonomic identification of phytoplankton wasby the Uterm/Jhlinvertedmicroscopemethodand convertedto C biomassusingappropriate cell volumeandcell carbonconversionfactors[Holligan et al., 1984].
(1.2TgCyr'• globally, [Bonsang et al., 1992])andthestraitsof ,2 1
Results
extrapolate to0.38TgC yr'• globally) areconsiderably smaller than the terrestrialflux. However,the spatialand temporalvariationin emissionand the factorscontrollingoceanproductionare poorly
Figure 1 shows the relationshipbetween concentrationsof isoprene and chlorophyll in water, which suggestsa direct correlation. The most surprisingaspectof this is that data from
Uncertainties. Our aims in this work were to determineif there was any rela-
slightly. Exceptingthe Decembercruise, each datasethas a correlationwhich is >99% significant(F statistic). Correlation
Florida (48.3nmole m"dy' [Milne et al., 1995], which would
waterbodies showsimilar regressions , although slopes vary understood, andestimates of a globalmarineflux containgreat diverse coefficients andslopes (pmolgg'•,in parenthesis) are:Southern Ocean r•= 0.54(3.45);NorthSeainJune r2= 0.62(5.55),Aprilr• =
tionshipbetweenphytoplankton andisoprenein surfacewatersand to investigate the seasonal variabilityof isopreneandotherNMHCs overa full seasonalcyclein theNorth Sea.
0.62(3.75); nearshore (all)rl= 0.56(2.5),without May/June rl=
Methods
for May/June showedvery high chlorophyll (> 101•g1'•), but
0.87(5.74). Theregression for all'thedatais shown(line(a)). Data isoprene levels were lower than expected. A bloom of the
Samples werecollected fromtheship'sunderway seawater supply prymnesiophyte, Phaeocystis, occurredduringthistime anda second
on cruisesin the southernNorth Sea(51 - 54ø N, 0 - 4ø E), in June
regression, excuding these data,is shown (line(b)). Phaeoqystis, a
Copyright1997by theAmericanGeophysical Union.
unicellularalgae,is rather excep-tionalas it can form coloniesof cells boundtogetherwith mucous.This environmentmay be less favourableto isopreneproduction,relativeto bloomsof otheralgae. Thereis somescatterin the dataat low levelsof chlorophyll;winter
Papernumber97GL02736. 0094-8534/97/97GL-02736505.00
2675
2676
BROADGATE ET AL.: SEASONAL EMISSIONS OF MARINE ISOPRENE AND HYDROCARBONS
1000 T
the water column is well-mixed throughoutthe year [Howarth,
1993]. LosSes of isoprene arelikelyto be physical (downward
I
mixing,lossto atmosphere), chemical/photochemical andbiological
(b) R 2=0.62
A * • . a • ..... •-A....••'•'ß•. 'a-Utb o
• 0.1
o.ol
• '
(consumption by algae,bacteriaand zooplankton). Sincewe have observeda correlationwith chlorophyllin surfacewaters,isoprene
& - •'•-a--•
• x
production is likelyto be related to phytoplankton activity, and
x
x x
i
I
i
I
0.1
1
10
100
Chlorophyll, I•gIn
further,lossesto the atmosphere occuron longertimescales in order to maintainthisrelationship. It is knownthatterrestrialemissions of isopreneare dependent on plant speciesand environmentalparameterssuch as light levels, temperature and CO2 contentof the atmosphere[Hewitt and Street, 1992;FehsenfeMet al., 1992]. However,thereis no strongevidence that observedmarineconcentrations are species-dependent, and the temperatureof seawater(-1.5 - 8øC) did not appearto havean 'effect on the isopreneconcentration in the SouthernOcean.
Seasonalemissionof isopreneand other NMHCs
Figure 1. Concentration of isopreneas a functionof chlorophyllin Thereis a strongseasonalvariationof isoprenein seawaterof the the North Sea in June (triangles),December(crosses)and April southern North Sea, over a concentration range of two ordersof (opendiamonds); in the Bellingshausen Seain November/December (Figure2). The concentration of isoprenein seawaterwas (filled diamonds);andnearshorein the North Seamonthlyfor a year magnitude relative to atmosphericlevels throughoutthe year (squareswhere open symbols indicate incidenceof intense supersaturated 600% inFebruary to 106%inMay). OtherNMHCs(Table1, Phaeocystis bloom,May/June). Two regression linesare shown:(a) (from Figure 2) showed a similar variationto isopreneand all were all data,dashedline (b) all dataexceptopensquares,solidline. The supersaturated throughout the year, exceptethane,propane,/-butane, equationof regression line (b) isy = 6.43x + 1.2. n-butane,2/3-methylpentane, trans-andcis-2-pentene, 1-hexeneand 1,3-butadiene which were undersaturated on occasions between
OctoberandMarch. Seasonal variationsin NMHCs havenotbeen
datapredominantly fall belowthe line, whereassummerdataare previou,sly, as the maximumperiod of published generallyabove. Negativedeviations mightoccurin winteras recognised measurements is only 6 months[$winnertoneta!., 1977]. Although average windspeeds arehigherthanin summer, result'rag in greater lossto the atmosphere.In summertheremay havebeenhigh biological production priorto sampl'mg. 60? PhytOPlankton in Bellingshausen Seasamples weredominaned by $o Isoprene diatoms (on average 75% of the carbonbiomass) andweremainly
!
Thalassiosiraantarctica, Porosira glacialis and Coscinodiscus bouvet[$avidgeeta!., 1995]. Data for the April North Seacruise showedthat in areas dominatedby flagellates,chlorophylland
40 +
i.soprene werelowerthaninregions wherediatoms werepredominant
/
'• 30•-
(>60% of the population). The diatomsweremainlyThalassiosira
sp.(20- 30 tam,24%of diatoms), Guinardia flaccida, Fragi!!aria
lO
sp., and Coscinodiscus concinnus. For nearshore samplesin May/June, Phaeocystis wasthedominant species andisoprene levels werelowerthanexpected (seeabove).Theresultstentatively suggest that, with the exceptionof colonialPhaeocystis, the relationship
o
30 T
25i
betweenisopreneand chlorophyllmay be independentof species composition, unlikeDMS (Lisseta!., [ 1994]). The correlationbetween isoprene and chlorophyll strongly
20I
suggests thatisoprene production is closely related to phytoplankton acti.vity.The production process maybe directlyby phytoplankton, assuggested by observations frommicroalgaecultures[Mooreet al., 1994; Milne eta!., 1995], or indirectlyvia zooplanktongrazing.
as no obvious correlation
Propane
•15
5
Alternatively,a precursormay be releasedby phytoplanktonand photochemicallyconvertedto isoprene (as suggestedfor other NMHCs by Ratte eta!., [1993]). Direct productionof isoprenehas been observedfrom various bacteria [Kuzma eta!., 1995]. It is possiblethat productionof isopreneis a simpleror fasterprocess than that of other NMHCs
/
0
18 16
1 -Butene
14
has been
12
reportedbetweenany other NMHC and chlorophyll. All data
•'... lO
considered,the only NMHC other than isoprenewhich showsa
relationship withchlorophyll isethene, withapoorr2of0.39.Forthe June1993cruise relationships werefoundfor:ethene, r2 = 0.63, propane r2 = 0.67,/-butane r2 = 0.78,i-pentane r2 = 0.61,2,2dimethylbutane r2= 0.71.
o. 6 2 0
Isopreneconcentrations in surfaceseawaterare likely to vary on shorttimescalesdue to changesin the ratesof productionand loss
which canberapidinthenatural environment. Pulses ofisoprene may occurthroughcell lysis(viral) and zooplanktongrazing.Peaks
in
Figure 2. Monthlyvariationin the meanconcentration (n = 3; July,
sub-Surfacebiological production may affect surface n = 6) of isoprene,propaneand 1-butenein North Sea nearshore
concentrations due to mixing. However,in the southernNorth Sea
samples.Squarebracketsindicateno data.
BROADGATE ET AL.: SEASONAL EMISSIONS OF MARINE ISOPREN• AND HYDROCARBONS Fluxes
Table 1. Maximumandminimummeanmonthlyconcentrations and fluxesof NMHCs fromnearshorein theNorth Sea(mean,n = 3) for
UsingtheLissandMerlivat [ 1986]relationship, theconcentration differencebetweenthe ocean and the atmosphereand average windspeeds for eachmonth,it is possibleto estimateNMHC fluxes (Table1). Thefluxesvarywith season, asis to be expected fromthe variationsin concentration in seawater.Despitethe factthatthedata presentedin Table 1 are from nearshore,the fluxes are almost
gases which havea seasonal cycle similar toisoprene #. sConc, pmol1'1
õFluxtoatmosphere, 10?moleculescm'2 S'1
mon
max
mon
min
max
min
Compound
2677
annual
mean +
identicalto thosefor offshorein the North Sea. In addition,the total Ethane
Jn
57.9
Mr
5.6
6.5
Mr
14.4
28.1
-1.6D
1.4
1.9
10.1
Ethene
Jl
228
Propane
Jl
28.2 Mr
2.7
2.9
Propme
Jl
77.0
Mr
8.2
8.5
1.1
4.0
/-Butane
Jl
9.7
Fe
0.7
1.0
-0.1ø
0.3
1-Butene /-Butene
Jl
19.3 54.0
Fe
1.4 4.6
2.0
Fe
4.9
0.2 0.7
1.0 2.3
0.3
Jl
-0.1D
1.2
/-Pentane
Jn
6.1
Fe
0.4
0.5
0.1Mr
n-Pentane
Jl
10.2
Fe
0.6
1.0
0.1
0.5
1-/i-Pentene*
Jl
19.6
Mr
2.5
1.9
0.1ø
0.9
trans-2-Pentene Ap
2.1 Mr
0.06
0.2
-0.01ø
0.1
cis-2-Pentene
Jn
1.8
0.04
0.2
-0.01o
0.1
Isoprene
Ma
54.3
Fe
0.7
4.7
0.1
1.7
/-Octane
Ma
3.3
Mr
< 0.1
0.2
0.0ø
0.1
Jl
4.2
Fe
0.2
0.4
0.0
0.1
n-Octane
Mr
NMHC flux from the North Sea in April is very similar to that calculatedfromour own datacollectedin the SouthernOceanduring
E allcanes E alkenes
14.5Jn 41.8JI
0.3• 4.8Mr
6 20
E C2' C4
45.4a
5.0•u
21
TotalNMHC
54.3a
7.4•
26
austral spring (25x 107molecules cm'2s'l, Broadgate [1995]),which indicatesthattheNorth Seameasurements canbe extrapolated to the openoceanat highlatitudeswith someconfidence.The majorityof the NMHC flux from the ocean(81% on average)is due to the C2- C4 NMHCs, with the longer chain hydrocarbonscontributing substan-tiallyless. The emissionsare dominatedby the alkenes (which contri-bute77 % to the total MHC flux on average), particularlyethene(39 %), propene(15 %), the butenes(13 %) and isoprene(7 %). The emissionscalculatedin this studyare generallytowardsthe lowerendof the rangeof previousestimates (Table2) althoughthey are similarto the fluxesfrom three cruisesin mid latitudes[PlassDiJlmeret al., 1993 and Donahueand Prinn, 1993]. Previousmeasurementsdo not considerseasonalvariations,and much of the data
werecollectedat low latitudes.The uncertaintyin the flux is dueto a factor of 2 in the transfer velocity and the variation in concentrations of NMHCs in seawater(4 ordersof magnitude).
Themaximum fluxofisoprene fromtheNorthSeawas4.7x 107
#Other hydrocarbons didnotshowdistinct seasonal variations: n-butane,
molecule cm': s'zwhichis similarto thatcalculated byMilneet al., dimethyl propane, 2,2-dimethyl butane andthearomatic compounds; Smonths[1995]of3.4x 107molecule cm': s'zfromtheStraits ofFlorida buta
2- and3-methylpentane,n-hexane,1-hexene,1,3-butadiene, acetylene,2,2of maximum
and minimum
concentration
are denoted as follows:
F -
factor of two lower than that of Bonsanget al., [1992] from the Pacific and Mediterranean. When averagedover the year, the
February,Mr- March,Ap - April, Ma - May, Jn- June,Jl - July,O - October,
D - December; õmaximum and minimumflux coincides with thoseof
flux fromthe NorthSea(320tC yr'•) is an orderof concentration unless denoted bya superscript asfors;*mean of 12months; isoprene
magnitude lowerthanthe totalflux fromvegetationin GreatBritain
*sum; E sum.
of 5- 7 ktyrq [Simpson, 1994]. However, theemission maybe
on localscalesconsidering the shortlifetimeof isoprene many of the other NMHCs we observedexhibit spring/summer significant assuming [OH]= 6.5x 10smolecules cm'3,[03]= 30ppb maxima similar to the variation in chlorophyll, correlation (3.9hour, from Atkinson[1990]) and the high coefficients were ratherpoor. Thus it is likely that thesegasesare and reactionrate co-efficients in the spring.In springandsummerisoprene mayhavean producedvia a natural processes somewhatdifferentto that of emissions in regionsremotefrom land. Our data isoprene. Many naturalprocesses covaryseasonally(eg. light, impacton the atmosphere Ocean showthattheisoprene fluxwas2.2x 107 temperature, chlorophyll),thereforeit is not currentlypossibleto fromtheSouthern cm'• s'• (average in spring)in an areaunlikelyto be identifywhich process(or combinationof processes)drivesthe molecules affectedby terrestrialisoprene. production of theseMHCs. Table 2. Literaturedatafor calculated emissionratesof NMHCs fromtheoceansbasedon oceanmeasurements. Fluxesaregivenin
10smolecules cm': s'•,withglobal extrapolations* inparenthesis (TgCyr'•). Author#
R&E 81
B 88
P 92
B 92
Latitude
70ø - 77øN
13øN- 25øS
35øN-30øS
43øN, 23øN - 16øS
Months
Aug
Apr
Sep-Oct
Oct,Apr-Jun
Aug-Sep
Feb-Mar
all year
Sep
Ethene Propene
4.1 (1.9) 2.3 (1.6)
33 (15) 16 (11)
3.4 (1.5) 1.7 (1.2)
-
2.4 (1.1) 1.0 (0.7)
-
1.9 (0.89) 1.1 (0.52)
-
l-Butene
-
4.4 (4)
1.0(0.9)
-
0.6 (0.5)
-
0.88(0.40)s
-
Ethane Propane /-Butane n-Butane
2.1 (0.9) 1.9 (1.3) -
6.6 (3) 4.4 (3) 1.1 (1) 2.2 (2)
2.1 (1.0) 0.7 (0.4) 0.07 (0.1) 0.3 (0.3)
-
1.1 (0.5) 0.3 (0.2) 0.03 (0.03) 0.15 (0.14)
-
0.35 (0.16) 0.22 (0.10)
-
0.13 (0.06)*
-
Acetylene Isoprene
-
-
0.02 (0.01) -
1.1 (1.2)
0.1 (0.04) -
-
-
0.34 (0.38)
68(39) ns(52)õ
9.3(5.3) -
-
5.7(3.2) -
5.6(ns)•
Z C2-Cn I TotalNMHC s
10.4(5.7) -
P 93 50øN-35øS
D&P 93 20øN- 20os
P 95 78øN. 77os
M 95 24øN
4.7(2.13) -
* using3.617x 1014 m2astotalocean area;#R&E81- Rudolph andEhhalt[1981],usingdatafromtheAtlantic of $wmnerton andLamontagne [1974]; B 88 - Bonsanget al., [1988], IndianOcean;P 92 - Plasset al., [1992], Atlantic; B 92 - Bonsanget al., [1992], PacificandMediterranean; P 93 - Plass-Diilmeret al., [1993] - Atlantic; D&P 93 - Donahueand Prinn [1993], Pacific; P 95 - Plass-Diilmeret a/.,[1995] openocean;M95 -
Milneetal.,[1995],Straits ofFlorida; ' sumbutenes; * sumbutanes; • notincluding acetylene; ns- notspecified; $quoted directly fromcited paper; õ C2- C6;• C2- Cs.
2678
BROADGATE ET AL.: SEASONAL EMISSIONS OF MARINE ISOPRENE AND HYDROCARBONS
of the emissionof nonThe work presented herewas carriedout at mid to highlatitudes HewittC.N. andR.A. Street,A qualitativeassessment
(>51øN andS) andspringblooms wereencountered in bo{hregions.
methanehydrocarbon compounds fromthebiosphere to theatmosphere in
the U.K.: presentknowledgeand uncertainties,,4tmos.Environ., 26,4, With the exceptionof isoprene,NMHCs show no consistent 3069-3077, 1992. relationshipwith chlorophyll and it is suggestedthat their Holligan,P.M., R.P. Harris,R.C. Nedwell,D.S. Harbour,R.N. Head, E.A.S. concentrations are relatedto a combinationof light and biological Linley, M.I. Lucas,P.R.G. Tranterand C.M. Weekley,Vertical distribuproductivity.The flux of NMHCs, includingisoprene,aretherefore tion and partitioningof organiccarbonin mixed frontal and stratified likely to showa seasonal variationwith a muchgreateramplitudeat watersof the EnglishChannel,Marine EcologyProgressSeries,14, 111higherlatitudesthanlowerlatitudes.If the observed seasonal cycles 127, 1984. occurwith the sameamplitudein the openocean,then previously HowarthM.J., K.R. Dyer, I.R. Joint,D.J. Hydes,D.A. Purdie,H. Edmunds, calculatedfluxesat high latitudesmay havebeenoverestimated by J.E.Jones,R.K. Lowry, T.J. Moffat, A.J. PomroyandR. Procter,Seasonal cyclesandtheirspatialvariability,Phil. Trans.R. Soc.Lond.`4, 343, 383up to anorderof magnitude, whichmaypropagate intolargeerrorsin 403, 1993. atmospheric models.
Kuzma,J.,M. Nemeck-Marshall, W.H. PollockandR. Fall, Bacteriaproduce thevolatilehydrocarbon isoprene.CurrentMicrobiol.,30, 97-103, 1995. Liss P.S. and L. Merlivat, Air-sea exchangerates: introductionand synthesis.,in Therole of air-sea exchangein geochemicalcycling,edited A correlationbetweenisopreneconcentrations and the chloroby P. Buat-Mtnard,D. Reidel.,Dordrecht, p. 113-127,1986. phyllcontentof seawater hasbeenobserved in two contrasting water LissP.S.,G. Malin, S.M. Turner,andP.M. Holligan,Dimethylsulphideand bodies(North Seaand SouthernOcean),andoverthe seasons in the Phaeocystis: A review,J. MarineSystems, 5, 41-53, 1994. North Sea,suggesting that isopreneis produceddirectlyby algae,or Milne P.J., D.D. Riemer,R.G. Zika and L.E. Brand,Measurementof vertical asa resultof rapiddegradation of dissolved organicmatterproduced distributionof isoprenein seawater,its chemicalfate, and its emission by phytoplanktonin the ocean. However,much work needsto be from severalphytoplanktonmonocultures,Mar. Chem., 48, 237-244, Conclusions
doneto elucidatethe productionand lossprocesses of isoprenein surfaceseawater.This work suggests that chlorophylldata(from in situ measurements or satellite imagery) can be used to estimate isopreneconcentrations, whichwhencombinedwith wind speedscan be used to calculatefluxes of isoprenefrom the ocean to the atmosphere in remotemarine locations. Althoughthe observed fluxes are very small, it is possiblethat the rapid reactionsof isoprenewith hydroxylradicalsin the atmosphere could influence the production of formaldehydelocally over the ocean (as investigated by Ayerset al., [ 1997]), whichin turnmay increasethe concentration of peroxyradicals. Large seasonalvariationsin the concentrations of isopreneand manyotherNMHCs havebeenobservedin the North Seaovera full seasonalcycle. This suggeststhat many NMHCs are produced naturallyin the ocean,and also pointsto a large uncertaintyin previousflux estimates of NMHCs fromthe oceanto the atmosphere
1995.
Miyoshi,A., S. Hatakeyamaand N. Washida,OH radical-initiated photooxidationof isoprene: an estimateof globalCO production, J. Geophys. Res.,99, 18779- 18787, 1994.
MooreR.M., D.E.Oramand S.A.Penkett,Productionof isopreneby marine phytoplankton cultures,Geophys. Res.Lett.,21, 2507-2510,1994. M'uller J-F., Geographicaldistributionand seasonalvariation of surface emissionsand depositionvelocities of atmospherictrace gases,J. Geophys.Res.,97, 3787-3804, 1992. Parsons T. R., Y. MaitaandC. M. Lalli,,4 manualof chemicaland biological methods for seawateranalysis,Pergamon Press,Oxford,173pp., 1989. PlassC.,R. Koppmannand J. Rudolph,Measurementsof dissolvednonmethanehydrocarbons in seawater,FreseniusJ. ,4hal Chem.,339, 746 749, 1991.
PlassC.,R. Koppmannand J. Rudolph,Light hydrocarbons in the surface
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W.J. Broadgate, P.S. Liss and S.A. Penkett,Schoolof Environmental Sciences,Universityof East Anglia, Norwich NR4 7TJ, UK. (e-mail:
[email protected];
[email protected]; M.Penkett•uea.ac.uk)
(Received February 28, 1997;revisedSeptember 10, 1997, accepted September 22, 1997.)
