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 than can be withdrawn by plants or can escape to the atmosphere.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 values southward 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 -- clearly in three traverses along the equator (;0 2 CONC, 550 -- (Figure 9). (p,p.m.)

In the final section in the Indian Ocean from 3,20 -- AIR Mombasa to Cape Town, sectionD, the CO• concentration in the water declined steadily .310 -- southward.The trend is strikingly similar to 0 4 8 12 16 that observedeast of MalagasyRepublic (Mad- øN LATITUDE agascar)seven months earlier (Figure 8). 17ig.5. CO•. concentration and water temper- ature near the ocean surface as a function of In the Atlantic Ocean (sectionsE, F, and latitude, sectionB, South China Sea, June 14-24, G; Figures 12 to 14) the CO•. concentrationin 1962. CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4533

30 WATER28 TEMP, ( øC) 26 24

56O

35O

340 CO2 CONC. (p.p.m.)330

320 AIR

310

40 45 50 55 60 65 70 75 80 85 90 95 I00 øE LONGITUDE Fig. 6. CO• concentration and water temperature near the ocean surface as a function of longitude along the equator, Indian Ocean, July 2-27, 1962'.

closeto atmosphericequilibrium in most other concentrationin the water rises from east to regionstraversed, except south of 25øS,where west near 5øN with valuesnear atmospheric it diminishesrapidly southward, and in the equilibrium for more than half of section tt CaribbeanSea, where a sharppeak occursover (Figure 15). It declinessharply from 5ø to the Beata ridge (75øW). 10øN, then increasesapproaching the conti- On the final leg of the expedition,in the nentalshelf of North America(Figure 16). The PacificOcean from Panamato San Diego (sec- distributionclosely approximates the distribu- tions H and I, Figures 15 and 16), the CO• tion obtained in the East Pacific in October

I I I I I I ! t ! I

WATER 30 TEMP. 28 (øC) 26

560

55O 7/51

C02 340 WATER -- CONC. (p.p.m.) 330 8/11

520 9/15• 9/2l--_

;510 - - --

"S 4 2 0 2 4 ON oS 4 2 0 2 4 øN øS 4 2 0 2 4 øN oS 4. 2 0 2 4 øN 55øE 62ø20' E 79øE 89øE Fig. 7. COx concentration and water temperature near the ocean surface as a function of latitude along four equatorial crosssections shown in Figure 2, Indian Ocean, July to Sep- tember 1962. The date (month/day) is shown for the beginning and end of each run. 4534 KEELING AND WATERMAN

3,0 ø I I I I I

20 ø WATER TEMP. (øC) I0 o

320

310

•oo CO•, CONC. (p.p.m.) 290

280

270

260

50 40 30 20 I0 0 o S LATITUDE ON

Fig. 8. CO• concentrationand water temperaturenear the ocean surfaceas a function of latitude,section C, Indian Ocean,October 5 to December21, 1962.

32 W AT E R 50 TEMP, (*c) 28 '26

360

5/25 350 •5/5 ///• m

34O CO2 CONC, v --...... _ (p.p.m.)3::50 2/28,,. ' ,•..•.._..,', __

AIR 320

510

40 45 50 55 60 65 70 75 80 85 90 95 ioo øE LONGITUDE Fig. 9. CO• concentrationand water temperaturenear the oceansurface as a functionof longitudealong the equator,Indian Ocean, February to May 1963.The date (month/day) is shownfor the beginning and end of each of three runs. CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4535

WATERTEMP.50-28 • ---- • -- (øC) 26

360 5/4

C0• 340 5/1•,* 2/26 CONC, 3/6 4/19 2/17 (p,p.m,) 550 3/13 520 ...•AIR .._.__• 4/25•/•

5,oøS 4 255øE 0 2 4 4 26tøE 0 2_4 4 285':' 0 E 2_4 øN]øS4 292':' 0 E 2_4 Fig. 10. COs concentration and water temperature near the ocean surface as a function of latitude along four equatorial cross sections shown in Figure 3, Indian Ocean, February to May 1963. The date (month/day) is shown for the beginning and end of each run.

1957 on Downwind Expedition [Keeling el al., to the gradient (perhaps true for sectionsA, 1965, p. 6091]. C, D, and F; Figures 4, 8, 11, and 13) or parallel to lines of equal concentration (likely DISCUSSION for sectionsE, G, and the western half of sec- The data of Lusiad Expedition are very ex- tion H; Figures 12, 14 and 15). In most waters tensive,but the area investigatedwas also very visited the CO, concentration was measured for extensive. We cannot accurately determine the the first time, and the data must be assessed surface distribution of oceanic CO• except in solely on their own merit. In this article we a few limited regions where relationships are selected for discussion a few well-defined fea- clearly revealed. More often we must guess tures to illustrate the typical character of the whether the ship's track tended to run parallel distribution so far observed. We shall give major attention to the Indian Ocean, where the coverageis most detailed. Across the North Pacific Ocean (section A,

TEMP, 25 (øC)WATER WATER20 TEMP, 20 -- (%) 18

310 310

COz C02 CONC 300 CONC, 300 (p,p,m.)

(p,p,m.) 290

290 280

aS0 270

25 15 5 20 15 I0 5 0 5 I0 15 øW LONGITUDE LATITUDE Fig. 11. COs concentration and water tem- Fig. 12. COs concentration and water temper- perature near the ocean surface as a function of ature near the ocean surface as a function of latitude, section D, Mozambique Channel, May longitude, section E, Cape Town, South Africa, 18-26, 1963. to 15øW, June 4-14, 1963. 4536 KEELING AND WATERMAN

I I 3O

WATER TEMP, 20 (øC)

340

530

32O

310

C02 CONC, 300 (p,p,m.)

290

28O

270

26O

4O 30 2O I0 0 I0 øS LATITUDE øN

Fig. 13. CO• concentration and water temperature near the ocean surface as a function of latitude, section F, Cape Town, South Africa, to Freetown, Sierra Leone, June 4 to July 8, 1963.

Figure 4) the oceanicCO• data reveal a single northward and eastward the water cools 10 ø sink for atmosphericCO• 10,000 km wide. The to 15øC in about 150 days. center shows the lowest concentration so far For all of Lusiad section A west of the ob- observed anywhere in the Pacific Ocean. We served CO• minimum at 35øN, 175øE the attribute this sink principally to the cooling concentrationfollows closelya prediction based of surface water carried northward and east- on cooling.From west to east the temperature ward by the Kuroshio Current and its exten- decreasedby 12øC; the CO• concentration,by sion [Sverdrup et al., 1942, p. 721]. The Kur- 70 ppm. The CO• decreasepredicted by cooling oshio transports warm surface water, with an is 90 ppm [Harvey, 1955; Tables 25, 26]. (We initial temperature of about 28øC, from the assumea ehlorinity of 19% and an alkalinity tropical west Pacific to the vicinity of Japan. of 2.32 millequivalents.) A major branch extendseastward into the open East of 175øE, where Kuroshio water grad- ocean as a relatively strong current along 34ø- ually loses its identity, the CO•. concentration 36øN as far as 175øE [Defant, 1961, p. 570]. increased rapidly toward equilibrium with the Farther east the rate of flow diminishes and atmosphere while the temperature remained water derived from the Kuroshio gradually close to the observed minimum. mixes with subarctic water. While flowing Absorption of CO• from the atmosphere CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4537

WATER .30 TEMP, 28 ("C) 26

350

340 R

3.30

C02 CONC, 32O AIR (p,p,m)

310

300

290 I I 85 80 75 70 65 60 55 50 45 40 35 30 25 20 •5 •0 øW CARIBBEAN SEA EQUATORIAL ATLANTIC OCEAN øW Fig. 14. CO• concentration and water temperature near the ocean surface as a function of longitude, section G, Freetown, Sierra Leone, to Panama Canal, July 11-30, 1963.

accountssatisfactorily for a smaller decrease % year for the time requiredfor the water to in CODconcentration at 175øE than is predicted cool from 29øC off the coast of Formoss to by cooling.The depthof the mixedlayer in the 17ø near the temperatureminimum at 175øE. KuroshioCurrent is about50 meters[Sverdrup Although the distributionof CODwest of et al., 1942,pp. 131-132]. If we assumethat 175øEmay be due to physicalprocesses alone, the CODfrom the atmospherepenetrated to as the abovecalculation suggests, the calculated this depth, the amount of absorptiondeduced amount of absorptionis uncertainto at least from the observedchange in temperatureand a factor2. We cannotrule out the possibility CODconcentration, using the tablesof Harvey that the C02 concentrationis influencedby the [1955], is 0.12 mM. If we acceptas the ab- presenceof relatively high concentrationsof sorptionrate 7 molescm -• atto-• yr-• in ac- plankton,as mappedby Reid [1962,pp. 300- cordancewith an atmospheric residencetime of radiocarbonof five years [Broecker, 1963; Skitrow, 1965, p. 316], we obtain a value of 28 WATER26 TEMP, 24

22

20 T.EMP,28 • ß ; : •- -- : -- e

36O

340•- 35O

CO2 34O CO2 520 CONC, CONC (pp m ) (p,pm)310 • 32O[-

290• I I I I I I 1 310• I I I . t I I • 120 115 110 105 I00 95 90 85 80 0 5 I0 15 20 25 30 35 oW LONGITUDE øN LATITUDE Fig. 15. CO2concentration and water temper- Fig. 16. CO• concentrationand water temper- ature near the ocean surface as a function of ature near the ocean surface as a function of longitude,section I-I, PanamaCanal to 117øW, latitude, sectionI, 5øN to San Diego, August August2-10, 1963. 10-15, 1963. 4538 KEELING AND WATERMAN 301]. Furthermore,the observationswere made other times. North-south cross sections pre- in May, when the northern oceansoften show pared by Ta[t and Knauss [1967] indicate intensebursts of photosyntheticactivity, and that the northeast monsoonwas accompanied the observedposition and strength of the CO2 by a spreadingof the isoplethsfor temperature, sink may have been partly determinedby time oxygen,and inorganicphosphate in the ther- variations in productivity. toocline near the equator. During the south- Most of the Indian Ocean measurements west monsoon, when the undercurrent was south of 5 ø were made during a single season absent or weak and variable, no equatorial (November and December 1962; seeFigure 8), spreadingof the isoplethswas observed.Iso- but one track six months later furnished data pleth spreadingnear the equatoroccurs at all (Figure 11) that accordso well with the earlier seasonsin the Pacific Ocean, a circumstance resultsthat we are led to proposethat the CO• that Knauss [1963] attributes to upwellingor in surface waters of the subtropical South In- vertical mixing associatedwith the undercurrent. dian Ocean is without strong seasonalor east- In the easterntropical PacificOcean a band west variation. We thus infer a broad zone of of high CO• concentrationis found in the sur- low concentrationin temperate and subtropical face water near the regionof the undercurrent. latitudes, which gives place gradually to high Keeling et al. [1965] attributed this band to concentrationsnear the equator and terminates the upward transport of CO• from CO•-rich abruptly southward closeto the northern limit subthermoclinewaters, the transport at least of the antarctic circumpolarcurrent [Wyrtki, in part owing to the same mechanismthat 1960, p. 159]. Rising values on approachingthe causesthe isoplethsof oxygenand temperature Antarctic Current were also observed south- to spread. In the equatorialAtlantic (see be- east of New Zealand in March 1961 [Keeling low) the same features occur and the same et al., 1965] and are probably characteristicof mechanismevidently operates. In the Indian the antarctic polar front. Ocean vertical CO• transport appears to be In the equatorial Indian Ocean continuous synchronized with an intermittent undercur- CO• measurementswere obtained during two rent. A band of high C02 in surfaceequatorial 3-month studies of the equatorial current sys- waters is thus strong evidencefor the presence tem [Knauss and Ta•t, 1964; Ta•t and Knauss, of an undercurrent and vice versa. 1967]. The data are sufficient to sketch the That the CO• in surface waters of the Indian distribution of C02 in surface water from Ocean adjusts rapidly to changesin vertical June to September 1962, during the southwest transport is indicatedby the sharp decreasein monsoon,and from February •o May 1963, CO• from springto summer.The exchangeof toward the end of the northeast monsoon,and CO• acrossthe ocean atmosphereinterface is at the onset of the southwest monsoon. The too slow [Skitrow, 1965, p. 315] to account average distributionsfor the two periods (Fig- fully for this rapid adjustment,and it may be ures 17 and 18) indicate that major changes due partly, if not principally,to a northerly in CO• occur as the wind regime and oceanic flow of surface waters driven by the south- circulation change with the seasons.During west monsoonthat displacesthe band of high- the southwest monsoon the concentration al- CO• water with surface water of lower concen- most everywhere diminished southward from tration lying to the south. It may also be due the northern limits of measurement; during partly to photosyntheticactivity that reduces the northeast monsoona band of high CO• ex- the CO• after the vertical transport ceases. tended over two-thirds of the equatorial zone. A clearly definedregion of high CO.•concen- Direct velocity measurements,made at the tration was observed in the east equatorial time of the CO• measurements,indicate that Atlantic in July 1963 (Figure 9). North of 2øS a steady east-flowingequatorial undercurrent, it is associatedwith low surface water temper- about one-third as strong as the Pacific under- ature, an associationthat alsooccurs north of current [Knauss, 1966], was present at depths the equator in the eastern equatorial Pacific between 50 and 200 meters across most of the Ocean [Keeling et al., 1965] and suggestsup- Indian Ocean during the northeast monsoon welling. Vertical crosssections of temperature, but was either absent or weak and variable at salinity, and oxygen prepared from data ob- CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4539

40 ø E 50 ø 60 ø 70 ø 80 • 90 ø I00 • I I0 ø •

I0 o

0 o

I0 o

S 20 •

Fig. 17.

40 ø E 50 ø 60 ø 70 ø 80 e 90 ø I00 ø I I0 ø 20 ø N ......

!0 • .'50 2.0• ! ioo - __ __----" •' -/ KeelingI ___.0 •

S I I I I 2o ø 40 ø E 50 ø 60 ø 70 • 80 • 90 • I00 ø I10 • Fig. 18. Figures 17 and 18 show the areal distribution of carbon dioxide in surface water of the equatorial Indian Ocean during two seasons,as indicated by measurements from June 28 to September 24, 1962 (Figure 17), and February 16 to May 15, 1963 (Figure 18). Concentra- tions are expressedas departures in ppm from 315 ppm. The latter value is approximately the concentration of atmospheric CO, as indicated by atmospheric measurements made at the time of the water measurements.Solid lines are drawn where the data control is good; dashedlines, where it is poor. 4540 KEELING AND WATERMAN

28

WATER TEMP, 26 (øC)

24

.'54O TER

.'53O

32O

C02 CONC, .'51 0 (p,p,m,)

.'500

29O

28O

16 12 8 4 0 4 8 os LATITUDE ON Fig. 19. The concentrationof CO• near the oceansurface in the atmosphereand in ocean water and surface ocean water temperature as a function of latitude in the eastern Atlantic Ocean, June 28 to July 7, 1963.

rained at the time of the COs measurements where physicaltransport by the water is slight, [Reid, 1964] show features characteristicof we may expect COs concentrationsin the sur- the Atlantic equatorial undercurrent as de- face water to be lessthan equilibrium with the scribedby variousinvestigators [Metcal/et al., atmosphere.North-south surface currents which 1962; Newman and Williams, 1965; Rinkel promote warming or coolingof surface water eta/., 1966]. modify the distribution,because the CO• con- It is perhaps not too early to hypothesize centration in ocean water dependson tempera- a generalmechanism to explainthe distribu- ture and becausetemperature equilibration with tion of COs in surface water, even though we the atmosphereproceeds more rapidly than COs cannotjudge it adequatelywithout more knowl- equilibration. The data from Lusiad Expedi- edgeof water motion, chemicalconcentrations, tion are to a high degree consistentwith this and biologicalactivity of oceanwater. Plants proposed mechanism,which is discussedin withdraw COsfrom surfacewater during photo- greater detail in the article that follows [Keel- synthesis.Decaying organisms sink belowthe ing, 1968]. thermocline and release CO• to the subsurface Acknowledgments. We are indebted to Rob- water. Surface waters are thus persistentlyde- ert L. Fisher, director of the Scripps Indian Ocean pleted of the COs, whereasthe deep waters program, for providing excellent working condi- are enriched.Where upwellingor vertical mix- tions during Lusiad Expedition and to Arnold Bainbridge, John A. Knauss, Joseph L. Reid, ing promotesupward transportof COs from Roger Revelle, and Bruce A. Taft for beneficial the deep water, we encountersurface concen- discussions of the results. The measurements were trations higher than equilibrium.Conversely, taken by Lee S. Waterman assistedby Dr. Norris CARBON DIOXIDE IN SURFACE OCEAN WATERS, 3 4541 W. Rakestraw and Messrs. Vernon L. Chi, Hill, pp. 235-252, Interscience, New York, 1963. James L. Coatsworth, and Frank P. Manley. Knauss J. A., Further measurements and obser- We gratefully acknowledge the financial sup- vations on the Cromwell current, J. Marine port of the Atmospheric SciencesProgram of the R es.,24, 205-240, 1966. National Science Foundation through grants Knauss, J. A., and B. A. Taft, Equatorial under- G-19168 and GP-4193 and of the oceanographic current of the Indian Ocean, Science, 143, 354- section of that foundation through grant G-22255 1964. for support of the ship operations. Leahy, R. G., Carbon dioxide, Oceanus,8(1), 19, 1961. REFERENCES Metcalf, W. G., A.D. Voorhis, and M. C. Stal- Bolin, B., and E. Eriksson, Changesin the carbon cup, the Atlantic equatorial undercurrent, J. dioxide content of the atmosphere and sea due Geophys.Res., 67, 2499-2508,1962. to fossil fuel combustion, in The Asmosphere Newman, G., and R. E. Williams, Observations and the Sea in Motion, Rossby Memorial Vol- of the equatorial undercurrent in the Atlantic ume, edited by B. Bolin, pp. 130-142, Rocke- Ocean at 15øW during Equalant I, J. Geophys. feller Institute Press, New York, 1959. Res., 70, 297-304, 1965. Broecker, W., Radioisotopes and large scale Pales, J. C., and C. D. Keeling, The concentra- oceanic mixing, in The Sea, vol. 2, chapter 4, tion of atmospheric carbon dioxide in Hawaii, edited by M. N. Hill, pp. 88-108, Interscience, J. Geophys.Res., 70, 6053-6076,1965. New York, 1963. Reid, J. L., On the circulation, phosphate-phos- Derant, A., Physical Oceanography, vol. 1, 729 phorous content, and zooplankton volumes in pp., Pergamon, London, 1961. the upper part of the Pacific Ocean, Limnol. Harvey, H. W., The Chemistry and Fertility o/ Oceanog.,7, 287-306, 1962. Reid, J. 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Riley and G. Skirrow, pp. 227-322, Aca- demic Press, London, 1965. sity of Chicago Press, Chicago, Ill., 1954. Sverdrup, H. V., M. W. Johnson, and R. G. Ibert, E. R., An investigation of the distribu- tion of carbon dioxide between the atmosphere Fleming, The Oceans, 1087 pp., Prentice Hall, Englewood Cliffs, N.J., 1942. and the sea, Ph.D. dissertation, 131 pp., Texas A&M University, College Station, 1963. Taft, B. A., and J. A. Knauss, The equatorial undercurrent of the Indian Ocean as observed Keeling, C. D., Carbon dioxide in surface ocean by the Lusiad expedition, Bulletin o/ the waters, 4, Global distribution, J. Geophys. Res., 73, this issue, 1968. Scripps Institution o• Oceanography, 9, 163 pp., University of California Press, Berkeley, Keeling, C. I)., N. W. Rakestraw, and L. S. 1967. Waterman, Carbon dioxide in surface waters of the Pacific Ocean, 1, Measurements of the Takahashi, T., Carbon dioxide in the atmosphere and in Atlantic Ocean water, Y. Geophys. 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