University of Groningen
Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
Bakker, D.C.E.; de Baar, Henricus; Jong, E. de
Published in:
Physics and Chemistry of the Earth. Part B: Hydrology, Oceans and Atmosphere
DOI:
10.1016/S1464-1909(99)00019-2
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Bakker, D. C. E., Baar, H. J. W. D., & Jong, E. D. (1999). Dissolved Carbon Dioxide in Tropical East
Atlantic Surface Waters. Physics and Chemistry of the Earth. Part B: Hydrology, Oceans and Atmosphere,
24(5), 399 - 404. DOI: 10.1016/S1464-1909(99)00019-2
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Phys. Chem. Earth (B), Vol. 24, No. 5,
Pergamon
pp. 399-404, 1999
Q 1999 Elsevier Science Ltd
All rights reserved
1464-1909/99/S - see front matter
PII: S1464-1909(99)00019-2
Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
D. C. E. Bakker1g2,H. J. W. de Baar’ and E. de Jong’
‘Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), The Netherlands
2Presently at: School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, U.K.
Received IO May 1996; revised 9 January 1997; accepted 5 October 1998
inorganic carbon(DIG) 2 Mtthods
andthebgacityofcadxmdioxi&(fC02)isdiscwxdfor
tmpicalEastAtWicsurfacewa@rsinOctober-November Water from 12 m depth was intmduced
Ahstmet - Variabiity ofdissoM
into an
equiliir.Sampleafromtheh&zpaceoftheequilibratorantlmarbaircollectedat30mabobzsealevel
were dried with silicagel. Every 18 mimttes a gas chromatographanaly&theCO+mtcntofthnxcalibration
gases,mtuincairandthehesdspeceofthecquiliirator.
celibrationgaaCS@OC,UK)hadbeenC&bmtUlagaiMt
NOAAceMalsta&rdgasmixtmea.Acomxtiortwas
made for the temperaaue di&ence bdwccn in situ
seaw&r and water in the eqnilibrator(Copin-Montbgu~,
KM, 1989).
TheDICumtentofwaterfiom12m&pthwaameruRlred
every 10 tubtea by a coulometex @toll, 1994) adapted for
scmiu&mKms operation. The coulomctcr was calibrate4l
every~Qys~~prwidedby
Dr. A.G. Didcxm (DDE, 1994). lbovery was 98.7 % to
1993 and May-June 1994. High prscipiclltion asso&ed
z4me,riverinputand
withtheMelttqi~corrvergence
eqmtorialupwellingalbtedthecontentofDICandfCQ
OftlXSClIOpiCdSlUfiWEwaters.Individual~~C
had a characteristic CO~&emktry.
Elsevier Science Ltd. All rights reserved.
regions
Q 1999
1 IntnMuction
Air-sea exchange of carbon dioxide (CQ), F, is driven by a
axu&ation
dil&rence of COZ across the air-water
inter&e (L&s and Slater, 1974):
F = kwWOzrl~
- K’of;cQxiJ
(1)
98.8 96.
AsthefilgacityticozinInarineair(~)isleIativeIy
COMbS&t,CXCbUgCiSmainly-byChealgEsin
thetmwferveIoeityQ,thesolubilityofcoz~o)and
T~andsalinityufwaterat12mdepthwere
teco&dbytkahip’sonlinedataacquMonayatcm.Air
tempcmtme, humidity and atmosphexic ~rcsame wue
dakrmbdat25maboveaealevel.
theawcnt&onofdissohwICGinbulksnrfbcewater,
w&lk*
VsMbilityof~inorganiccubon(DIC)and~
areix~Wgated&rtmpicaiEastAtlanticsurb-waters.
ThedatawereoMai&dwingthesouthwardcnlise
3 blts
1993andthcno&vard
ANTXJ/linOt$Ok&VembCr
cmise ANT XI/5 in May-June 1994 at RV. Polarstem
(Fig. 1). During ANT XI/l an c&ward excarsion was
madetowardathbmouthofthcc!4mgoRiver.
Comspondence
Anglia
AlBeximmndsurfacewatertempmsn
waaabser=d
northofthequatorandinthetegionofthcCongooutflow
(xyl) (Fig. 2a). Temperatuns between 10” and 2o”
latih&zwcrelowerinapringthaninauttmm.
Salinity, DIC and eC4 had relatively low values in a
‘Low Salinity Region (TSR) for 2.0°-10.0% (XI/l) and
0.6°-8.00N @I/5) (Fii. 2). The region with low salinity
shifkdtowatdstbealuatorbetwezncruiacs.Withinthe
LSR at 5.22% 16.45’W salinity imxasal tiom the sea
a&ceto4Omdep&whiletemperatureremabed
consmnt (XIb) (Fig. 3).
lo: D.C.E. Bakker, University of East
399
400
D. C. E. Bakker et al.: Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
60
40
20
7
tn
0
i
k
0
4
.Z
1
-20
-40
-so__
-m
-40
-20
0
20
40
Longitude eE +,“w -)
Flg.1.cmisetndrroftba
southwdauiscANTWlinodobs-NoMnba1993dofthsnalhward
mhe ANT w5
in May-Jum 1994 at
RV. Polcmmw.
Aminimmnofsm%cewatertempemtme,amaximumof
salinity and DIC, slightly elevated nitrate contents and
fluofescuxe were encountered at 0.3’-2.05 in &toberNovember 1993 and at 0.6%2.0°S in May-June 1994
(Fig. 2) and indicated nxent or active equatorial
-.
Surface water salinity, DIC and K& were highly
variable for O’W’S in the Gulf of Guinea during
ANTxI/l,probablyastheresultoffxastalandeqlatorial
upwell@and-tionofriverwateralongthe
South Eqllatorlal Current (Dessier and Donguy, 1994).
Low salinity and DIC dekeakd the Congo outflow for
4.70-8.YS (XI/l).
4 Discussion
lI&lllWIlOrthOftheequatoragrees
Thete1986,
with SeasOnaltemperam charts (philander,
Peterson and stramma# 1991; Reid, 1994) and with the
meanpositionofthethermalequatorwithintheInWtropical Convergence zooe (ITCZ) (Tchenl@ 1980,
Tomczak and Godfrey, 1994). High salinity of
(sub-)tropical surface water xfkcts high evaporation along
theNorthandSouthEquatorialbrents(NEC,SEC)
(Tomczak and Godfky, 1994).
Highmi&dlrelatedtotheITCzivsllltsinlowsluface
watersalinitynorthdtheequator@e&?.ierandDonguy,
1994).Thedi@WlWuoftheLSRbeWee-ncruisesis
lelatedtothescm&ardshiftoftheITczinnoxtbern
winter,whichprec&sthesouthwardmovementofthe
regionwithlowsu&cesalinitybytwomonths(Dessier
and Donglly, 1994). The gradual imxeaseofsallnity from
401
D. C. E. Bakker cr al.: Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
24-
ED
VI
Con00
ED
1.SR
ED
LSR v
Canary
Current
40
0
v
-40
I
I
I
I
-10
0
10
20
Latitude (“N +, OS-)
402
D. C. E. Bakker et al.: Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
Salinity
Temperature (“C)
15
04
20
25
30
0
34
*
35
38
37
a
120-
3. vatid
Fig.
h
‘;
B
3
5
pdila
of(a) mtatampa;lturs
aad (b) diaity d 5.22W 16.45%’ on 1 June 1994 (ANT xV5).
2100-
2000-
3
E
Congo
1900-
4 A.
4,
.,
....*
*.-*
...*
P .
LSRsouth,
33
34
,
35
.,
38
.,
37
Salinity
0 to 40 m depth at 5.22”N 16.45’W @I/5) supports the
tlwyofpro~dilutioaofsurfecewaterbyintheabsencedwindmixbg.Itisunlike@thattheNortb
lquaMal-(NEcc)has~low
salinitywaterfhmthcAmazonoutfbwasfbreastas
24%’ (Des&r and Donguy, 1994). In June-August 1986
33
34
35
38
37
Salinity
similarstNmgsaliaitygradientsoccuned-nuface
water with high saliaity p36.2) in the Guinea Dome
( loo-14w 25ow, 12% 22w) aud water with low salinity
(< 35.4) towanis the south in the NECC (ou&t$ 1989).
Rcgionalsalinitychartsindicatealatitudidbaddlow
salinitywatcrnorthdtllccqatorintheEastAualuic
D. C. E. Bakkeret al.: Dissolved CarbonDioxide in Tropical East Atlantic Surface Waters
.
b
r
a+1
7.5% - 15.m
99.3
-1575
0.97
8.6
254
1.008.4m
9s.s
-1415
0.99
5.s
208
5.00s - 10.008
54.0
109
O.%
14.1
149
Lailudc
#
oCean,htdonot8ugge8ttheob8ewed8tronghmizcmM
6dinitygradiarurmitSedge8.
Dil~of(sub-)tropicalaeamterwithasalinityof36.1
with rainwamta asalinlty of35.1DIC by
55to64pmolb$‘andf;cozby14to18patm@akkeret
al., 1999). Tk cawatal demase OffCoz by dilution with
minwatwiscmutemMbyasimul~imeeseof
tuqwahmby 1.9”CfbrtheLSR.ObsuvalDICand~
arcwdltJcknv~valucsforoo-~of
a@-~(~~l)tlgal
swface water and ratttwatcr
Two &lines
with the equations:
DIC = 99.3 S - 1575
(2)
DIC = 95.5 S - 1415
(3)
canbedi&g&h&lMweensu&ewaterintbeLow
S8lhtiQRCglOItiUKlwl@XUt(SUb-)&Ol&lwaterWithhigh
saliMy(T~le1).Fwhthemgativco&stonthey-axisof
tbaellMtlgl&SindthC1oW-VlthtCSOffC&
and DIC in the LSR relative to v&es calatlati for
comuwlw
tnixing India& that c&r
a&cent
(SUh-)@OpMStU&CCWa&lSltOttbe-lnvohwllnthemlXlngwithfaimvaworthatauadditional
pmccsshaschaq@DICand~.Upw&tgatthe
cqwOrorlnthi~hdwcentbeNEccandthe
NECmayhavclncmwdDICand~ofthehigh
salinlty water a&r the mixing took place. Biologiatl
~dCQmayhaw&matsalDICand~inthe
LSRMKlUghthCdl6UVCdflwaslow,ocealt
a&tu ohmvatitms it&ate seasonal algal bloom at
5°-1m (Lon%nwt, 1993).
Stnfmwamwlthlowsallnityand~waspmiausly
cummtc& at 4%W 17oW-2O’Win Jum-July 1986 in
thccmvagmmhctwccntheNEccarbdSEc(oudotand
AndM 1989).0tlmobKmatlonsoflow&ialinilywatu
withlowfC@wmum&inoctoher1995by~etal.
(1998). who amibai the low m
to high prwlpitation
andwbgicalt#takeofCQ.
403
shnilartoalr-mcan~~~at
227 wm lomf far V3W than for OVPS ln JmnatyFcbmary 1983-84 and July-Aqust 1982-S4 (Antt& aad
m
1989). All&%ml oldot (1989) au&& that high
KQsatthdtheqmtortua&BbathBa~
~StMhdthCccpldor(IGd&196QtilRlb
scqumtwan&gofthcwlerilItbemtnrdhmofthc
SEC.ThedeumcofDICand~hyl~@~
andhwgitmluptwdCQzmthd*oqmator
C0tMbUk%tOmridioaoldi&mnasOfDICrd~.
Amixinglincwlthtbccqtwlon:
DIC = 54.0 S + 109
(4)
canbcdisbuioguishdbaweenwaterillt.hc~apttlow
andadjrcaatarfacew&er(Fig.4,Table1).Tl~apittim
qgcststhatCoqowatcrhasartavcmgcDIC~of
109 pmolkg-‘, n@azGng DIC&angcs after the water
cntclcdtlRoccatL
ThelatltudinaldistrllofDICwasclowlyrdatcdto
thatofsalinity.Anewntual&%ctof~onDIC
was-hystrtmg~~inthc
(sub-w--waters.-ww
quawial~andandgicalupllreafcQL~andDICoftmpicalstt&ewatc.rs.Thweprocuw,
whicharegowncdhyoceancimMonandthctqical
climatcsyramSlcavcauchastrongimprintonaurfac+
watercX&cbamistrythat-~regiaas
havespccl6cCQ+-.
An&i& c.. clud& c.. oadbx& c. md Maiint.
I., CG nuxa io the
tlOpidAihlSiCdUiQgFOCALUilk.JOlldOf~COf
Ruearch
91.11.741-11,755,1986.
LUcka, D.C.B. do Bmr, H.J.W. ml Q Jang E, ‘Ito dqmdaim
011
turQMumadnliaayddldvod~alboainEu~
alhwwan
Marin# Chomi~,
w
1999.
CopiwMcd@~&C..Amwfimmhfalhe&ofttqadmonthe
paid pmum ofco,
in mav8ta. Ma?ho chaata&y, 25, l9-37,19S8.
CO+hkld&l&C.,C4X+lhLAlWWfiDrrrmhtalbE~d
hlpdUU0lltkplti8lpMBlEBOfdCO,in#OWVddfmlnrC~~
27.143-144.1989.
Da8k,AaalDmgly,J.R,Tlneam~nUaityinlhotqidAtb&
a vhtiam
bdwmlmd3Ow-dmi”
1989% LkqdmFbwmh
I, II. Sl-100.1994.
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D. C. E. Bakker et al.: Dissolved Carbon Dioxide in Tropical East Atlantic Surface Waters
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hcastanbupialA~~~satin~~~
t~~ryrtaoin~111114;yg~~2.~AO.~OOY4C.
6x&n
(A),
~RO.Mld~L.UppX-lW8lcirculrtiaaiDtboSOUIhAtlmtic
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dioxdc in adcc
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af Pcq
in the impial
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