REPRINTS OF PERTINENT LITERATURE
APPENDIX B CONTENTS AND COPYRIGHT PERMISS1ONS
Goyet, C., and Peltzer, E., 1994. Comparison of the August-September 1991 and 1979 surface partial pressure of C02 distribution in the Equatorial
Pacific Ocean near 150° W. Reprinted from Marine Chemist~ 45:257–266 (1994) with kind permission of Elsevier Science – NL, Sara Burgerhartstraat 25,
1055 KV Amsterdam, The Netherlands . ... B-5 Inoue, H., 1998. C02 exchange between the atmosphere and the ocean.
Reprinted fkom Dynamics and Characterization of Marine Organic Matter (eds. N. Handa, E. Tanoue, and T. Hama) 1998, with kind permission of Terra
Scientific Publishing Company, To@o, Japan ... B-15 Kortzinger, A., H. Thomas, B. Schneider, N. Gronau, L. Mintrop, and
J. C. Duinker. 1996. At-sea intercomparison of two newly designed underwaypC02 systems —Encouraging results. Reprinted horn Marine
Chemistry 52: 133–145 (1996) with kind permission of Elsevier Science
-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands . ... B-39 Ohtaki, E., E. Yamashita, and F. Fujiwara. 1993. Carbon dioxide in stiace
seawaters of the Seto Inland Sea. Reprinted from Journal of Oceanography 49:295–303 (1993) with kind permission of the The Oceanographic Society
of Japan, Tokyo, Japan . ... B-53 Poisson, A., N. Metzl, C. Brunet, B. Schauer, B. Bres, D. Ruiz-Pine,
and F. Louanchi. 1995. Variability of sources and sinks of COZ in the Western Indian and Southern Oceans during the year 1991.
Reprinted horn Journal of Geophysical Research 98(C12):22759–22778 (1993) with kind permission of the American Geophysical Union,
Washington, D. C. ... B-63 Neill, C., K. M. Johnson, E. Lewis, and D. W. R. Wallace. 1997.
Accurate headspace analysis offlOz in discrete water samples using batch equilibration. Reprinted from Limnology and Oceanography 42(8):
1774-1783 (1997) with kind permission of the American Society of
Limnology and Oceanography, Canmore, Alberta, Canada . ... B-73
,
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Marine Chemistry, 45 (1994) 257-266
0304-4~03/94/$07.00 @ 1994- ElsevierScienceB.V. All rightsreserved
257
Comparison of the August-September 1991 and 1979
surface partial pressure of
C02
distribution in the Equatorial Pacific Ocean near 150”WCatherine Goyet, Edward T. Peltzer
Woo& Hole OceanographicInstitution,Departmentof MarineChemistryandGeochcmisfry.WoodsHole. MA 02543. USA (ReceivedApril 16. 1993;revision accepted October 4, 1993)
Abstract
The partial pressure of C02 (PC02)in the surface seawater and marine air from17”Sto 22”Nnear151°W (WOCE legP-16cj during the period from August 31 to September 29, 1991, were measured continually. The surtlace semwter PCOZ showed large latitudinal variation with a maximum of425 patm near the equator. These results arc compared with pC02 measurements in 1979, in the same area and same months. The short-scale (temporal and spatial) variations in surfa:e seawater pC02 (+6.1 @m) do not allow us to unequivocally quantify the variation in ApC02 (pCO~ - pCO~) between the years 1979 and 1991 due to oceanic uptake of fossit’fuel C02. However, the data suggest that this ocean area might be a stronger source of C02 for the atmosphere than may be expected from results of ocean models.
1. Introduction.
The global ocean regulates the Earth’s climate by continuously exchanging heat and greenhouse gases with the atmosphere. These exchange processes are poorly known. In the surface ocean, pC02 is controlled by the complex inter-actions of biological activities, the ocean chem-ical C02 buffer capacity, and the ocean circulation dynamics. The relative importance of these processes is only broadly known over the world ocean and varies with time and space. Currently, two of the principal ocean observing programs (the Joint Global Ocean Flux Study [JGOFS], and the World Ocean Circulation Experiment ~OCE]), are cooperat-ing to address these’ questions and to study the oceanic carbon cycle and its interactions with the atmosphere at the world ocean scale. It is in this context that we participated in WOCE cruise P-16c in the Equatorial Pacific Ocean aboard
SSD( 0304-4203(93)EO064-6
B-5
R/V Thomas Washington,to cmy out a JGOFS C02 program to create a global oceanic C02 data set.
The surface seawaters of the Central Equa-torial Pacific Ocean are composed of the return flow of the North-Equatorial counter current and pf the South-Equatorial current. They are th~ “siteof high seawater pC02 and high “new”
production driven by upwelled nutrients (Chavez and Barber, 1987). Thus, this ocean area is potentially a major region of carbon cycling between the subsurface and deep” waters and with the atmosphere.
The numerous different estimates of the amount of C02 gas transferred between the ocean and atmosphere (Keeling, 1968; Miyake et al., 1974, Keeling and Revelle, 1985; Broecker et al., 1986; Feely et al., 1987; Fushimi, 1987;
Inoue and Sugimura, 1988, 1992; Bacastow and Maier-Reimer, 1990; Murphy et al., 1991;
Lefevre and Dandonneau, 1992; Wong et al.,
.,-- .—.-.--.x.,--- .F----K-7?-- . . . .a. . . .. ...-. . . .:T.-.7.-7 :7.?--- , . —. –-— .. ——-. —
258
1993), emphasize both the high variability of the flux of COZ gas across the air–sea interface and the need to acquire a better understanding of
~C02 dynamics in this area of research. Thus, one of the great scientific challenges today is to better quantify the seasonal and interannual variations of the COZ gas exchange across the air–sea interface.
Quantification of the net COZ flux across the ocean-atmosphere interface can, in principle, be accessed by direct measurements in the atmo-sphere (Jones and Smith, 1977; Jones, 1980). In ,practice however, this is extremely difficult (Broecker et al., 1986) because of the slow exchange rate. Calculation of the net flux from air–sea C02 partial pressure differences is the universally preferred scheme (Keeling, 1968;
Broecker et al., 1978; Liss, 1983a,b). Yet, the uncertainty associated with such calculations often exceeds 50°A (Goyet and Brewer, 1993) due to uncertainties in the transfer coefficient (Watson et al., 1991), and in the temperature of the skin layer (Robertson and Watson, 1992).
The validity of the results of such a calculation is further limited to a short time period’ since both the ApC02 [difference between surface sea-water .pC02 (pCO~) and atmospheric pC02
@CO~r)] and the wind speed used to estimate the transfer velocity are those measured instantaneously at a definite time of year and are usually not representative of an annual mean. Another uncertain y in the estimation of seasonal and interannual C02 flux is due to the uncertainty in the poorly documented spatial and temporal variations of pCO~. This is especially true in the Equatorial Pacific Ocean where El Nxno-Southem Oscillation (ENSO) events (an anomalous quasi-oscillatory warm-ing of the tropical Pacific Ocean) occur relatively frequently.
These ENSO events, which appear to be chaotic-like in nature (Gleick, 1987), change the “normal” state of the Equatorial Pacific Ocean over very large areas (Meyers, 1982;
Enfield, 1989). Consequently, in addition to the earlier investigations that describe pCO~=
C. Goyet, E.T. Pei!zcrlMarine Chemtktry 45 (1994) 257-266
variations in this area (Keeling, 1968; Miyake et al., 1974; Keeling and Revelle, 1985; Broecker et al., 1986; Feely et al., 1987; Fushimi, 198~
Inoue and Sugimura, 1988, 1992 Bacastow and Maier-Reimer, 1990; Murphy et al., 1991;
Lefevre and Dandonneau, 1992; Wong et al., 1993), repeated seasonal and interannual measure-ments ofpC02 in the Pacific Equatorial region are needed to better quantify the net long-term C02 flux across the ocean–atmosphere interface.
In this paper, we present the results of under-way pC02 measurements made in 1991 in the Central Equatorial Pacific Ocean and quantify the temporal and spatial variations of pC02 in this area. Our data are then compared with the
1979 data of Weiss et al. (1992).
2. Sampling and analysis
The R/V Thomas Washington on WOCE P16c departed from Papeete, Tahiti on August 31, 1991, and arrived in Honolulu, Hawaii on October 1, 1991, with cruise track in Fig. 1.
The mole fraction of C02 (xC02) in the sea-water equilibrated air and in the atmosphere were continuously measured along this cruise track using an automated underway C02 monitoring system with an infra-red detector.
The automated underway COZ monitoring system consists of a “shower-head” type equilibrator (Broecker and Takahashi, 1966 Keeling, 1968; Takahashi et al., 1970) and a non-dispersive infra-red (NDIR) C02 and HZO analyzer (L1-COR 6262) with solid state detector. A system of automated valves (Fig. 2) controls the frequent and regular switching of gas flows to the NDIR analyzer between sea-water equilibrated air (SEA), seasurface air sampled at the ship bow (AIR), and two gas standards (high and low C02 concentration,
513.5 and 320.0 pmol/mol, respectively). The small size (approximately 40 cm high) equili-brator (modified from a design used by Weiss) consists of two concentric cylindrical stages con-structed of plexiglass, with a drain in the center.
The seawater “showers” through the top of B-6
C. Goyel, E.T. Pc[t:er/Marine Chemistry 45 (1994) 257-266 259
Fig. 1. Cruise track for WOCE P-16c (R/V Thomas Washington), between Tahiti and Hawaii, 31 August 1991-1 October 1991.
the equilibrator at a rate of about 4 l/rein, and the first stage of the equilibrator is vented to the clean marine atmosphere to maintain ambient pressure. The gas phase is continuously re-circulated, at a rate of 200 ml/min, by an air pump, through a closed loop passing through the infra-red analyzer where the measurement is made. The seawater temperature in the equili-brator, as well as both atmospheric pressure and the gas pressure in the closed loop are monitored. The pressure traducers (SETRA
model 270, range 600-1100 mbar) used for the pressure measurements were calibrated and certified per the National Institute of Standards and Technology (NIST) traceable primary standard with an accuracy of A0.05°A of full scale. The temperature sensor used to measure the seawater temperature in the equilibrator was calibrated (against a platinum resistance thertno-meter) in our laboratory before the cruise.
The COz/HzO differential, NDIR analyzer is of small size, precise, and insensitive to vibrations and lateral accelerations. The sample cells are gold-plated to enhance infra-red (IR)
reflectivity and resist tarnishing over time. One set of cells is used for both H20 and C02 measurements by using a dichroic beam splitter to provide radiation to two separate detectors. A 150 nm bandpass optical filter is used to select the 4.26 pm absorption band for C02 detection, and the H20 detector is filtered for the 2.59 pm absorption band. Both filters provide excellent rejection of IR radiation outside the desired band, allowing the analyzer to reject the response of other IR absorbing gases. The filters are mounted directly on the detectors for thermal stability. The lead selenide solid state detectors are cooled and regulated at - 12°C by thermoe-lectric coolers, and electronic circuits con-tinuously monitor and maintain a constant detector sensitivity. The detector housing is maintained free of water vapor and C02 by internally mounted dessicant and absorbants.
In order to maximize the signal sensitivity, the infra-red radiation from the source is focused through the gas cell and onto the detector by lenses at each end of the optical bench. The typical C02 noise level is 0.2 pmol/mol peak-to-peak (at 350 pmol/mol) when using one second signal averaging. The LLCor C02/H20 analyzer uses an internal algorithm to correct the measurements to a dry gas scale and to a pres-sure of one atmosphere. Thus, this automated system allows us to dkectly monitor XCOZ (mole fraction of COQ gas corrected to dry air and to the pressure of 1 atm) in the gas phase without having to pretreat it (no drying nor gas separation are required). This not only simplifies the measurement procedure, but also minimizes the potential errors in the measurements.
This system is regularly calibrated every 2 h, using C02 standard gases (320.0 and 513.5 pmol/
mol) that we calibrated using a primary standard gas (352.2 pmol/mol) purchased from the National Institute of Standards and Technology (NIST). The 2 h calibration measurement indi-cated that the infra-red analyzer was remarkably stable to *0.2 pmol/mol; a 6 h calibration interval would have been sufficient.
The computer recorded one XC02 datum per B-7
260 C. Goyct, E.T. Pcltzer/Marine Chemismy 45 (1994) 257-266
Fig. 2.
f~= filt~ gefman1.0fgreference f~. filt~ gefman1.0wsample
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PT1.PressureTransducer(finepressure)
PTZ=PressureTransducer(ambient)
RMR=rofomekqreference FW$=mbnetecsample
TR=~ ref.(scdafime&Mg(Cf04)2) T~=w sample(sodafime&Mg(CIO&) PA=pump,Air
PR. pum~reference P~=pum~sample
WA,3VB--Way valves Xl,Xz,X~,X4=regulatingvalves
D.P.G.= DewPointGenerator 7M=7pfilter
from bow
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vent + AfR—~V5
o
PT2vent---”-”-”; :
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..”-4air
A “M
Schematic diagmm of infra-red anaiWer basedsystem for the determination of pC02 in seawater.
minute consisting of an average of 10 readings taken every 6s. A typical duty cycle consisted of a 5-rein cell flush, followed by five 1-rein averages. Next, this cycle is repeated for the measurement -of air (the air intake was located at the bow of the ship). The air intake system consisted of an inverted polyethylene funnel mounted on the jack-staff at the bow of the ship
B-8
and 3/811id. Dekoron (R, type 1300, Furon Co Inc., Aurora, OH) line. Sea surface air was pumped from the bow of the ship with an Air-Cadet@ (Cole-Parmer, Chicago, IL) pump at several liters per minute. After the pump line was split, part of the air supply went to our instrument.
A portion of the air we received (> 500 ml/min) was used to flush a “ballast” chamber which was
!,
c. Goyet, E.T. Pe!I:er/Marine Chemistry 45 (1994) 257-266 261
vented to the ambient atmosphere. This ballast chamber was then used to maintain ambient pres-sure in the equilibrator head-space. When analyz-ing sea air, a flowrate of 200 ml/min was maintained through the NDIR. Every 2 h the alternation of the two sample gases is interrupted with the measurement of the two reference gases according to the same 10min cycle.The variations of pC02 on the time scale of 1 min or less are of little interest. We report here data averaged over the final 4 min of the duty-cycle.
We computed pC02 from the measured XC02 using the relationships (UNESCO,1987):
pcoz = xCOZ x pressure x [1 - (vapour/pressure)]
with
vapour = 0.981 x exp(27.029 - 0.098T – 6163/T)
(a] Equatorial Pacific Ocean
420 .
where “pressure” represents the ambient atmospheric pressure, “vapour” represents the
saturation water vapour pressure at the air-sea interface, and T isthe surface temperature in the equilibrator.
Since the obsertied temperature of the water in the equilibrator was generally 0.2 + 0.1‘C warmer than the in-situ temperature at the water intake, we made a small temperature correction using the relationships given by Copin-Montegut (1988). The accuracy associated with the present pC02 data set is estimated to be close to 2 patm.
3. Results
Fig. 3 shows the in-situ pC02 distributions
@CO~ and pCO~, corrected to 10O”/Ohum-idity, in-situ temperature and barometric pressure) along the N–S transects at 150°W in
(b) Equatorial Pacific Ocean 430~
“ Hg. 3. In-situpC02 distribution in surface seawater and in the skin layer along transects between Tahiti and Hawaii near 1So”w
in theEquatorialpa~ficOcean.(a) 199I dam.(b)1979data from Weisset al. (1992).The dashed linesare smooth fits to the , data.
B-9
...,-,
,,~..!-.-r-,--....,,,-,.... >.,,.+......... ....,‘.. . . .0,...,..7--, . - <>.~-’=” -.--1~ .... —.262
the Central Pacific Ocean. Along 151°W, between 2“N and 7°S, the surface seawater pCOz was above 390 patm with a maximum close to 425 p.atm near the Equator.