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Carbon Dioxide in Surface Ocean Waters 3. Measurements on Lusiad JOURNALOF GEOPHYSICALRESEARCH VOL. 73, NO. 14, JULY 15, 1968 Carbon Dioxide in Surface Ocean Waters • 3. •easurements on Lusiad Expedition 1962-1963 CHARLES D. KEELING AND LEE S. WATERMAN ScrippsInstitution o/ Oceanography,University o/ Cali/ornia at San Diego La Jolla, California 92037 Direct measurementsof carbon dioxide in equatorial surface waters during Lusiad Expedi- tion, 1962-1963, indicate that high concentration relative to atmospheric CO'• is associated with eastward-flowing equatorial undercurrents in the Indian and Atlantic oceans. In the tropical Indian Ocean the measurements are sufficient to construct the areal distribution during two seasons.A broad band of high COO.occurs during the northeast monsoon but not during the southwest monsoon.An undercurrent is observed only during the former period. Adjacent to the equatorial zone the COO.concentration is generally lower than equilibrium with the atmospherein all oceans.In the South Indian Ocean the concentrationrises sharply southward on approaching the northern limit of the antarctic circumpolar current. In the western North Pacific Ocean the concentration attains very low values in the east-flowing extension of the I(uroshio Current. In general, low concentration in surface waters exists when rapid cooling occurs and when withdrawal of COo.by marine organismsexceeds re- plenishment by physical transport; high concentrationexists when rapid warming occurs and when upwelling or vertical mixing suppliesmore CO•. than can be withdrawn by plants or can escape to the atmosphere. INTRODUCTION 1961; Takahashi, 1961; Hood et al., 1963; At present,about half of the carbondioxide Ibert, 1963; Keeling et al., 1965] indicatethat releasedby the burning of coal and petroleum the concentration of CO• in surface water of is accum•fiatingin the atmosphere[Pales and the Atlantic and Pacific oceans varies in a Keeling,1965]. The remainderis beingabsorbed complicatedway with geographiclocation. Al- by the oceansand possiblyto someextent by though these published data are too few to land plants [Hutchinson,1954, p. 389]. If reveal time variations, we expect the concen- chemical equilibrium were achieved between tration to vary with seasonas well. Clearly atmosphericCOO., inorganic carbon dissolved we need to improve our understandingof con- in oceanwater, and carbonatesediments on the temporary conditions. To this end we now re- ocean bottom, the oceanscould absorb most port a survey of the North Pacific,the Indian, of the COO. from combustion [Bolin and and the Atlantic oceans that extends consider- Eriksson,1959, p. 133].. Under present condi- ably the areal coverageof oceanicCO• and for tions,however, the rate of injectionof COO.into the tropical Indian Ocean furnishes data to the air by c.ombustionis too rapid for the assessseasonal variability. atmosphereand the oceansto approachequi- librium. We are therefore obliged to document EXPERIMENTAL I:)ROCEDURE the transient responseof the atmosphereand Measurements of COO.were made on the re- oceansto the burning of fossil fuels, if we are to explainthe presentrise in atmosphericCO•. search vessel Argo during Lusiad Expedition, and make a reliable prediction of future trends. the second of three expeditions made by the A major step in documentingthis responseis Scripps Institution of Oceanographybetween to determine the present distribution of CO• 1961 and 1965 as part of the International In- dian Ocean Expedition. Equipment and meth- gas in surfaceocean water. Direct measure- mentson oceanicexpeditions since 1957 [Leahy, ods closely duplicated those of Downwind and Monsoon expeditions,as describedby Keeling x Contribution from the Scripps Institution of et al. [1965]. The output from a nondispersive Oceanography.New Series. infrared gas analyzer was continuouslymoni- 4529 4530 KEELING AND WATERMAN ocean water was determined by recording the concentration of CO, in a closed volume of air that was circulated continuouslyso as to ap- proach equilibrium with a constantlyrenewed supply of water obtained from an intake in the ship'shold 2 to 3 meters below the surface.An improved version of the equilibrator used on MonsoonExpedition was employed. The concentration of CO, in the air and ocean water, as reported below, is expressed as a volume fraction (mixing ratio) in ppm. This quantity is the partial pressure of CO• divided by the total pressure exerted in the atmosphereor ocean water by the gasesthat pass through the infrared analyzer. Methods for computingthe partial pressurefor the air and water are described by Keeling et al. [ 1965,pp. 6088-6091]. DESCRIPTION OF CONTINUOUS I)ATA A total of 14,231 atmosphericair and 12,040 ocean surface water measurements,each repre- sentinga 5- to 20-minute averageof the orig- inal continuousrecord, have been processed. Where the ship traverseda predominatelyeast- west course,the data were averagedover longi- tudinal intervals, otherwisethey were averaged over latitudinal intervals. For the South China Sea and equatorial crossingsin the Indian and Atlantic oceans, 1ø intervals were used. Else- where 2• ø intervals were employed. These averagesare assembledin tables similar to Tables 1 and 2 of Kee[{ng ei al. [1965] and are contained in a report by Kee[{ng and ier•a• [1967].' This report also presents all relevant calculations and supporting data for the Lusiad Expedition and for two earlier ex- peditionsreported by Kee[{ngei a[. [1965]. The ship'strack is shownin Figure 1 divided Fig. 1. Ship track for Lusiad Expedition. into nine sections,A through I. The compli- cated track patterns in the equatorial Indian tored on a stripehart recorder, calibrated in Oceanare shownin Figures 2 and 3. Observa- parts per million of dry air by volume (ppm). tions of the concentration of CO• and of sur- The averageamplitude of the instrument noise was I ppm. ' This information has been deposited as Docu- ment 9946 wi•h the American Documentation Atmospheric CO, was measureddirectly by Institute Auxiliary Publications Project, Photo- drawing in air at mast height (10 to 20 meters duplication Service, Library of Congress,Wash- above sea level) through intake cups protected ing•on, D.C. 20002.A copy may be obtained by against oceanspray. Water vapor was removed citing the documentnumber and remitting $23.75 before the air was analyzed by passingthe gas for photoprin•s or $6.75 for 35-mm microfihn. Advance payment is required. Make check or stream through a cold trap maintained below money order payable to: Chief, Photoduplication --40øC by a refrigerator.The CO_•in surface Service, Library of Congress. CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4531 ..........;.;;.•.•CC•1om bo' / •" ß ß '•' A • •. "•,"4•Singapore ...' • • ,• , ,om.,oß" ,,½,:....... k....> .....=,,,,• t •SeychellesIs. I0 • • - • I I I I I •J•. 2. Ship •r•ck fo• •rst equ•to•J•]cu•e• s•udy,3u•e 2,6•o Sep•embe•2•, zg62. facewater temperatureare plottedversus lati- monsoon,the CO• concentrationin the water rudeor longitudein Figures4 to 16. was everywhereabove equilibrium. Along the SectionA, acrossthe North PacificOcean equator (Figure 6) maximawere observed fromSan Diego to Manila (Figure4), is both near 70øEover the mid-Indianand Carlsberg the northernmostand the longesteast-west ridgesand near 50øE over the westernslope profileso far obtained.The atmosphericCO• of the Somalibasin. North-south cross sections concentrationappears, as it doesin all sections, showa trend towardlower valuessouthward as an almostregular horizontal line; the CO• (Figure7). concentrationin the water variesalmost sym- SectionC revealsthat this latter trend is a metricallyabout a sharpminimum at 175øE majorfeature of the SouthIndian Ocean (Fig- longitude. ure 8). Strikinglylow valueswere observed SectionB (Figure 5) occursin relatively overa broadzone from 25 ø to 45øS.South of shallow water of the South China Sea from 45 ø the CO• concentration in the water rises Manila to Singapore.The CO• concentration abruptly. On the run northwardfrom Ker- in the water relativeto equ!libriumwith the guelenIsland (49øS)the meanvalues do not atmosphereis high throughoutthe section. departmarkedly from the valuesobtained on In the first of two detailed studies in the the run southward,nor is the retracing as close equatorialIndian Ocean,during the southwest as was observedat the samelatitudes in the '0ø •• ••CEYLON . • 5• •/• •,ombo••/,• •/'•- •.•" .•en•n ' • 3/•5 • •=• 3/4 / + _ ,, •o•]Momboso" / .. .......• _• _••.... ;...... •- •3/13v.=•=.=.=,.=.: .....=.=.'=.==•.•••.==•.•. MATRA II0 • •.... •-5•1 '•Seychelles Is, /26"4/25 SU•• ,,, , • , , , , , Fig. 3. Ship track for secondequatorial current study, February 16 to May 15, 1963. 4532 KEELING AND WATERMAN 30' 20' WATER TEMP (*C) I0 ß 330 :520 __• AIR -=; $1o 300 COz CONC. 290 (p.p.m.) 280 , 270 260 250 ,1 I 120 140 160 180 160 I 4.0 120 OE LONGITUDE Fig. 4. COs concentration and water temperature near the ocean surface as • function of longitude,section A, North PacificOcean, M•y 18 to June 9, 1962. Pacific Ocean during Downwind Expedition the water showsa narrowband of high values [Keeling e• al., 1965]. between 6øS and IøN. The concentration is In the second equatorial study, which in- eluded the seasonof the northeast monsoon, .3O four cross-sectional traverses and three runs WATER TEMP, alongthe equatorwere made (Figure 3). North- (øC) 28 south crosssections show a variety of features individually (Figure 10) but, viewed together, showa steadytrend toward higherCOs concen- WATER tration westward. This trend shows even more 540 --
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