Comparison of the Carbon System Parameters at the Global CO2 Survey Crossover Locations in the North and South Pacific Ocean, 1990-1996

ORNL/CDIAC-115

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By
Richard A. Feely, Marilyn F. Lamb, Dana J. Greeley, and Rik Wanninkhof

Additional Contributors (arranged alphabetically):
Robert H. Byrne, David W. Chipman, Andrew G. Dickson, Catherine Goyet,
Peter R. Guenther, Kenneth M. Johnson, Charles D. Keeling, Robert M. Key,
Frank J. Millero, Christopher L. Sabine, Taro Takahashi,
Douglas W. R. Wallace, Christopher D. Winn, and C. S. Wong

Prepared by
Linda J. Allison and Dana C. Griffith
Carbon Dioxide Information Analysis Center
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee, U.S.A.

Date Published: November 1999

Contents

Investigators

The authors and additional contributors along with their affiliations and addresses are listed below.

Richard A. Feely
NOAA, Pacific Marine Environmental Laboratory (PMEL)
7600 Sand Point Way N.E.
Seattle, WA 98115-0070

Marilyn F. Lamb
NOAA, Pacific Marine Environmental Laboratory (PMEL)
7600 Sand Point Way N.E.
Seattle, WA 98115-0070

Dana J. Greeley
NOAA, Pacific Marine Environmental Laboratory (PMEL)
7600 Sand Point Way N.E.
Seattle, WA 98115-0070

Rik Wanninkhof
NOAA, Atlantic Oceanographic and Meteorological Laboratory (AOML)
4301 Rickenbacker Causeway
Miami, FL 33149

Additional Contributors:

Robert H. Byrne
Department of Marine Science, University of South Florida (USF)
140 7th Avenue South
St. Petersburg, FL 33701

David W. Chipman
Lamont-Doherty Earth Observatory (LDEO) of Columbia University
Rt. 9W
Palisades, NY 10964

Andrew G. Dickson
Scripps Institution of Oceanography (SIO)
Marine Physical Laboratory
9500 Gilman Drive
University of California, San Diego
La Jolla, CA 92093

Catherine Goyet
Woods Hole Oceanographic Institution (WHOI)
Marine Chemistry and Geochemistry Department
360 Woods Hole Drive, MS 25
Woods Hole, MA 02543

Peter R. Guenther
Scripps Institution of Oceanography (SIO)
Geosciences Research Division 0220
9500 Gilman Drive
University of California, San Diego
La Jolla, CA 92093

Kenneth M. Johnson
DOE, Brookhaven National Laboratory (BNL)
Bldg. 318
Upton, NY 1197

Charles D. Keeling
Scripps Institution of Oceanography (SIO)
Geosciences Research Division
9500 Gilman Drive
University of California, San Diego
La Jolla, CA 92093

Robert M. Key
Department of Geosciences
Princeton University
Guyot Hall
Princeton, NJ 08544

Frank J. Millero
Rosenstiel School of Marine and Atmospheric Sciences (RSMAS)
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149

Christopher L. Sabine
NOAA, Pacific Marine Environmental Laboratory (PMEL)
7600 Sand Point Way N.E.
Seattle, WA 98115-0070

Taro Takahashi
Lamont-Doherty Earth Observatory (LDEO) of Columbia University
Climate/Environment/Ocean Division
Rt. 9W
Palisades, NY 10964

Douglas W. R. Wallace
DOE, Brookhaven National Laboratory (BNL)
Bldg. 318
Upton, NY 1197
(Now at: Abteilung Meereschemie
Institut für Meereskunde an der Universität Kiel
Düsternbrooker Weg 20
24105 Kiel, Germany)

Christopher D. Winn
University of Hawaii (UH)
Dept. of Oceanography
1000 Pope Rd.
Honolulu, HI 96822
(Now at: Marine Science Program
Hawaii Pacific University
45-045 Kamehameha Hwy
Kaneohe, HI 96744-5297)

C. S. Wong
Institute of Ocean Science (IOS)
9860 W. Saanich Rd.
Sidney, BC, V8L 4B2, Canada

Abstract

  • Feely, R. A., M. F. Lamb, D. J. Greeley, and R. Wanninkhof. 1999. Comparison of the Carbon System Parameters at the Global CO2 Survey Crossover Locations in the North and South Pacific Ocean, 1990-1996. ORNL/CDIAC-115. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. 74 pp.

As a collaborative program to measure global ocean carbon inventories and provide estimates of the anthropogenic carbon dioxide (CO2) uptake by the oceans, the National Oceanic and Atmospheric Administration and the U.S. Department of Energy have sponsored the collection of ocean carbon measurements as part of the World Ocean Circulation Experiment and Ocean-Atmosphere Carbon Exchange Study cruises. The cruises discussed here occurred in the North and South Pacific from 1990 through 1996. The carbon parameters from these 30 crossover locations have been compared to ensure that a consistent global data set emerges from the survey cruises. The results indicate that for dissolved inorganic carbon, fugacity of CO2, and pH, the agreements at most crossover locations are well within the design specifications for the global CO2 survey; whereas, in the case of total alkalinity, the agreement between crossover locations is not as close.

1. Introduction

Human activity is rapidly changing the trace gas composition of the earth's atmosphere, apparently causing greenhouse warming from excess carbon dioxide (CO2) along with other trace gas species, such as water vapor, chlorofluorocarbons (CFCs), methane, and nitrous oxide. These gases play a critical role in controlling the earth's climate because they increase the infrared opacity of the atmosphere, causing the planetary surface to warm. Of all the anthropogenic CO2 that has ever been produced, only about half remains in the atmosphere; it is the "missing" CO2 for which the global ocean is considered to be the dominant sink for the man-made increase. Future decisions on regulating emissions of "greenhouse gases" should be based on more accurate models that have been adequately tested against a well-designed system of measurements. Predicting global climate change, as a consequence of CO2 emissions, requires coupled atmosphere/ocean/terrestrial biosphere models that realistically simulate the rate of growth of CO2 in the atmosphere, as well as its removal, redistribution, and storage in the oceans and terrestrial biosphere. The construction of a believable present-day carbon budget is essential for the skillful prediction of atmospheric CO2 and temperature from given emission scenarios.

The world's oceans, widely recognized to be the major long-term control on the rate of CO2 increases in the atmosphere, are believed to be absorbing about 2.0 GtC yr-1 (nearly 30 to 40% of the annual release from fossil fuels). Our present understanding of oceanic sources and sinks for CO2 is derived from a combination of field data, that are limited by sparse temporal and spatial coverage, and model results that are validated by comparisons with oceanic bomb 14C profiles. CO2 measurements taken on the World Ocean Circulation Experiment (WOCE) cruises, which began in 1990, have provided an accurate benchmark of the ocean inventory of CO2 and other properties. These measurements were cosponsored by the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Department of Energy (DOE) via the U.S. Joint Global Ocean Flux Study (JGOFS) Program. Investigators supported by these funding agencies have collaborated to examine data collected during the WOCE and Ocean-Atmosphere Carbon Exchange Study (OACES) cruises. This report addresses the consistency of oceanic carbon dioxide system parameters during 1990-1996 in the North and South Pacific.

The four parameters of the oceanic carbon dioxide system are dissolved inorganic carbon (DIC), fugacity of CO2 (fCO2), total alkalinity (TAlk), and pH. This report compares the carbon system parameters, along with salinity and dissolved oxygen (O2), against sigma theta (σθ) where cruises overlapped throughout the Pacific Ocean basin. Similar comparisons have been made for oceanic carbon in the Indian Ocean (Johnson et al. 1998; Millero et al. 1998). Additional comparisons have also been made by Robert Key of Princeton University and may be viewed at http://geoweb.princeton.edu/people/key/key.cross/crossover.html. In addition, comparisons of nutrient data have been compiled (Gordon et al. 1998). The cruise data for this report will be made available through the OACES and the Carbon Dioxide Information Analysis Center (CDIAC) data management centers.

The Pacific Ocean cruises occurred from 1990-1996, and data have been compared at 30 locations where cruises overlapped in the North and South Pacific Ocean (Fig. 1). We do not address survey stations in the Pacific where no crossovers occurred. In addition, carbon and hydrographic data collected during some of the Pacific expedition cruises (i.e., P2, P12, and S4I) were not available in time for this report.

2. Analytical Methods

Analyses of all carbon parameters were performed following the techniques outlined in the "Handbook of Methods for the Analysis of the Various Parameters of the Carbon Dioxide System in Sea Water" (DOE 1994). Certified Reference Materials (CRMs) were used on all cruises as secondary standards for DIC, unless otherwise noted. Discussion of the preparation and use of CRMs is available in detail (UNESCO 1991; Dickson 1992; Dickson, Anderson, and Afghan, unpublished manuscript; Dickson, Afghan, and Anderson, unpublished manuscript). These materials consisted of a matrix of natural, sterile seawater. They were bottled in large batches into 500-mL borosilicate glass containers, sealed to prevent contamination, and shipped to the institutes participating in this study. These secondary standards were then analyzed at sea over the course of each of the cruises as a means to verify accuracy. Certification of the reference material for DIC is based on manometric analyses in the shore-based laboratory of Charles D. Keeling of Scripps Institution of Oceanography (SIO) over a period of several months (UNESCO 1991; Guenther 1994; Keeling, C. D., personal communication, 1999). Since CRMs were analyzed routinely for DIC during most cruises used in this report, all groups analyzing for TAlk on those cruises subsequently analyzed CRMs as well; this enabled post-cruise corrections to be made to the TAlk data based on archived samples that were analyzed at Dr. Keeling's laboratory at SIO. CRMs were not available for any other carbon parameter discussed in this report. Analyses of salinity and O2 followed WOCE Hydrographic Program (WHP) protocol (WOCE 1994).

3. Results and Discussion

3.1 Statistical Methods

Tables 1 and 2 summarize the crossover sites and parameters measured, and Tables 3, 4, 5, and 6 are summaries of the statistical data for each parameter at the crossover locations. Eleven laboratories from two countries participated in this comparison study that examines crossovers in both the North and South Pacific. At some of the crossover locations, the site was occupied on more than one occasion [i.e., the crossover at 170° W and 10° S was frequented by NOAA on three different cruises (CGC90, EqS92, and P15S), as well as by the Institute of Ocean Science (IOS) (P15N) and the University of Hawaii (UH) (P31)]. A total of 30 crossover locations were studied in this analysis and 41 individual crossover comparisons were made. Individual plots of each carbon parameter, along with salinity and O2, were first created for every crossover against σθ using data from the entire water column (Appendix A). Only data sets that showed good agreement in both salinity and O2 data were used for the comparisons. An expanded area within the plot was examined further based on the region of reasonable agreement of the σθ vs salinity plot. In most cases, σθ > 27.0 was used in the expanded regions.

A curve-fitting routine was applied to the expanded plots (Appendix A) using a second-order polynomial fit (unless otherwise noted in Tables 3, 4, 5, and 6). The difference between each region of crossover was calculated based on evenly distributed intervals on the σθ axis; the intervals chosen were, on average, 0.04 σθ units apart. In the case where more than one station on a given cruise was computed at a particular crossover location, averages of the resulting fits of the two or more stations for that cruise were determined, and the total mean of the differences over the entire σθ range was compared. This procedure was performed for every carbon parameter measured (Tables 3, 4, 5, and 6). The mean and standard deviation of the differences were computed, along with the mean and standard deviation of the absolute value of the differences. For the DIC data, the results were calculated both uncorrected and corrected using the CRMs as a basis for the corrections.

3.2 Cruise Results

The most detailed carbon parameter results are for DIC, as this parameter was measured on all of the cruises (Table 3). The next most frequently measured parameter was fCO2, followed by TAlk and pH (Tables 4, 5, and 6), respectively. DIC CRMs were available to the investigators for almost every cruise during the survey. In general, there is excellent agreement between DIC data sets at the crossover locations. At the beginning of the program, the goal was to obtain agreements between cruises that were less than 4.0 µmol/kg. On 31 of 41 crossover comparisons the uncorrected DIC differences were less than this value, and on 24 of the comparisons the differences were less than 2.0 µmol/kg.

Most of the cruises that did not meet this criteria occurred at the beginning of the program when methods were still being developed, and one comparison was during a strong El Niño event where the upper water column hydrography was significantly different from normal (Feely et al. 1995). When the DIC data were corrected for CRMs, 36 of the 41 comparisons were less than 4.0 µmol/kg, and 31 comparisons were less than 2.0 µmol/kg. The mean of the absolute value of the differences was 2.4 ± 2.8 µmol/kg for the uncorrected data and 1.9 ± 2.3 µmol/kg for the corrected data (Fig. 2). For a mean DIC concentration of approximately 2260 µmol/kg in the deep Pacific, this difference is equivalent to an uncertainty of approximately 0.08%. The excellent agreement of the DIC data was likely due primarily to the use of the coulometer (UIC, Inc.) coupled with a SOMMA (Single Operator Multiparameter Metabolic Analyzer) inlet system developed by Ken Johnson (Johnson et al. 1985, 1987, 1993; Johnson 1992) of Brookhaven National Laboratory (BNL), as well as the use of CRMs as secondary standards during the cruises. The spirit of cooperation and close interactions among the scientists and technicians who were responsible for the measurements also contributed to the outstanding quality of the data set.

The crossover comparison of fCO2 in seawater is not as straightforward as the comparison of the other carbon parameters because the measurement temperature for fCO2 differs for different cruises. The comparison thus requires a temperature normalization, which is performed by using the carbonate dissociation constants, and measured DIC. For comparison purposes, all values were normalized to 20°C in this report. The normalization is dependent on the dissociation constant used. In this comparison, we used the constants of Mehrbach et al. (1973) as refitted by Dickson and Millero (1987). An example of the effect of constants on the final comparison is given in Table 7 in which we use typical deep-sea DIC and fCO2 values as found in the southeastern Pacific. Also included in the table are the ΔfCO2@20°C/ΔDIC values in µatm/(µmol/kg to illustrate the sensitivity of discrete fCO2 measurements relative to DIC in deep waters.

We analyzed 16 crossover comparisons for fCO2, and observed differences ranging between -28.7 and 34 µatm, excluding the large difference during the 1992 El Niño at 5° N, 110° W. The mean of the absolute value of the difference was 17.6 ± 16.3 µatm. In deep water 10 atm of fCO2 measured at 20°C is approximately equivalent to an uncertainty of 1.5 µmol/kg DIC. Thus, with the possible exception of two or three crossover locations, the systematic differences in the fCO2 data corresponded to a similar uncertainty to that of the majority of the DIC results. Since there were no CRMs available for fCO2 during the Pacific expeditions, the analysts used their own compressed gas standards for the measurements. Some of the differences between the data sets may have resulted from systematic differences between standards and/or differences between methods employed.

The agreement of the TAlk data between the 15 crossover locations is not quite as good as the DIC results. The differences between cruises ranged from -11.5 to 7.8 µmol/kg; generally, the smallest differences correspond to the excellent agreement by the same laboratory on different cruises. As with DIC and fCO2, the largest offsets generally occur during the strong El Nino event in 1992. The mean of the absolute value of the difference was 5.7 ± 3.3 µmol/kg; this corresponds to a mean uncertainty of approximately 0.2%. CRMs were available for TAlk where crossover comparisons were made for this report, and all data have been normalized to the certified values.

Three laboratories performed pH analyses, and as a result, only five crossover locations were available to compare the pH results. All comparisons were made on the total seawater scale. The differences ranged from -0.0005 to 0.0062 and the mean of the absolute value of the difference was 0.0023 ± 0.0025. In the deep Pacific, an uncertainty of 1 µmol/kg DIC is equivalent to approximately 0.003 pH units. These results suggest that the limited amount of pH data in the Pacific were in excellent agreement with each other.

The summary data in Tables 3, 4, 5, and 6 should be viewed as one of several indicators of the overall quality of the carbon data from the Pacific. In addition to these results, there also are the shore-based analyses of replicate DIC samples taken during each of the cruises (Guenther et al. 1994) and the interlaboratory analyses of the CRMs (Dickson 1992). These three pieces of information should be used together with thermodynamic models in the process of evaluating the overall quality of the database. In several cases, particularly with respect to the NOAA data sets, three or four carbon parameters were measured during the cruises. In these situations, the internal consistency of the individual parameters in the data sets can be checked using an appropriate thermodynamic model (Millero et al. 1993; Byrne et al., in press; Wanninkhof et al., 1999). In this way, two parameters may be used to check the validity of the third and, in some cases, fourth parameter. For example, very precise and accurate DIC and pH data may be used to validate thefCO2 and TAlk data. We recommend that individual data sets be evaluated in this manner before they are used in physical and biogeochemical models. In addition, it is our recommendation that DIC data are reported to the database manager as both uncorrected and corrected with respect to CRMs, and that the CRM results are appended in a "meta" file. This file should contain at minimum CRM batch number, number of CRMs run, the given value and observed values, along with the standard deviation and number of CRM results rejected. The method of correction of the data should be clearly described, including if the correction was applied per cell, per cruise, using a longer-term mean, or if the correction was an additive or a ratio. In order to obtain a coherent data set of DIC from this program, it is imperative that the data be corrected in the same way. As shown in this report, the crossover data for DIC are statistically improved when the correction is applied. We also recommend the TAlk data be reported to the database manager in a similar way, appending a "meta" file containing a description of the CRM results. In addition, it is useful for both CRM corrected and uncorrected TAlk data to be submitted.

4. Conclusions

The comparison of the carbon system parameters during the WOCE and OACES cruises in the North and South Pacific has provided unique information on data quality at the crossover locations. For DIC, fCO2, and pH, the agreement at most crossover locations is well within the design specifications for the global CO2 survey, despite the lack of CRMs for both fCO2 and pH. In a statistical analysis performed on DIC data that were corrected to CRM values vs noncorrected values, results indicate there is a significant difference between the two. On the other hand, although normalized to CRM values for TAlk, the comparisons made in this report for that parameter were not as good. The outcome of this comparison stresses the importance of CRMs, as well as the value of building some redundant measurements into the program to provide an independent check on data quality.

Since the inception of this document, we have made every attempt to include the most up-to-date information available; however, large data sets are constantly evolving. Some of the data presented in this report are expected to change as the data are further evaluated. To access the latest data sets, please check the web sites listed in Section 5.

5. Remote Access to Data Listed in This Report

Much of the data presented in this report are available on the World Wide Web (WWW). For information regarding electronic access to the data sets contact:

For NOAA/OACES data:

NOAA/AOML/OCD
4301 Rickenbacker Causeway
Miami, Florida 33149-1026
U.S.A.
Telephone:
(305)361-4399 (voice)
(305)361-4392 (fax)

Internet: http://www.aoml.noaa.gov/ocd/oaces

For DOE Global CO2 ocean survey data:

Carbon Dioxide Information Analysis Center
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, Tennessee 37831-6290
U.S.A.
Telephone:
(865)574-3645 (voice)
(865)574-2232 (fax)

Internet: http://cdiac.ornl.gov/oceans/

Graphics of the data contained in this report are also available at http://www.pmel.noaa.gov/co2/oaces_doe/home.htm.

6. Acknowledgments

This research was supported by the NOAA Climate and Global Change Program as part of the joint NOAA/DOE/NSF cosponsored carbon component of the Ocean-Atmosphere Carbon Exchange Study and the World Ocean Circulation Experiment. It is also a componet of the U.S. JGOFS Synthesis and Modeling Project and NOAA Global Carbon Cycle Program. We thank Drs. Lisa Dilling and James F. Todd of the NOAA Office of Global Programs; Drs. John Downing, Curtis Olson, and Mike Riches of the Department of Energy; and Dr. Donald Rice of the National Science Foundation for program coordination and support. We also thank all the scientists and technicians involved with the Pacific expeditions. Their excellent spirit of cooperation played a significant role in obtaining the high-quality data used in this report.

7. References

  • Byrne, R. H., S. McElligott, R. A. Feely, and F. J. Millero. The role of pHT measurements in CO2 system characterizations. Deep-Sea Res. (in press).
  • Dickson, A. G. 1992. The determination of total dissolved inorganic carbon in sea water using extraction/coulometry: The first stage of a collaborative study. DOE/RL/01830T-H14. U.S. Department of Energy.
  • Dickson, A. G., J. D. Afghan, and G. C. Anderson. Sea water based reference materials for CO2 analysis: 2. A method for the certification of total alkalinity. Mar. Chem. (unpublished manuscript).
  • Dickson, A. G., G. C. Anderson, and J. D. Afghan. Sea water based reference materials for CO2 analysis: 1. Preparation, distribution and use. Mar. Chem. (unpublished manuscript).
  • Dickson, A. G., and F. J. Millero. 1987. A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media. Deep-Sea Res. 34:1733-43.
  • Dickson, A. G., and F. J. Millero. 1989. Corrigenda. Deep-Sea Res. 36:983.
  • DOE (U.S. Department of Energy). 1994. Handbook of methods for the analysis of the various parameters of the carbon dioxide system in sea water. Version 2. ORNL/CDIAC-74. A. G. Dickson and C. Goyet (eds.), Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn.
  • Feely, R. A., R. Wanninkhof, C. E. Cosca, P. P. Murphy, M. F. Lamb, and M. D. Steckley. 1995. CO2 distributions in the equatorial Pacific during the 1991-1992 ENSO event. Deep-Sea Res. Part II 42(2-3):365-86.
  • Gordon, L. I., C. Mordy, J. Wilson, and A. A. Ross. 1998. A study of discrepancies in observed nutrient concentrations at WHP Pacific line intersections: An accuracy estimate. pp. 24-29. In Ocean Circulation and Climate, Proceedings of the 1998 Conference of the World Ocean Circulation Experiment (WOCE), May 24-29, 1998, Halifax, Nova Scotia, Canada.
  • Goyet, C., and A. Poisson. 1989. New determination of carbonic acid dissociation constants in seawater as a function of temperature and salinity. Deep-Sea Res. 36:1635-1654.
  • Guenther, P. R., C. D. Keeling, and G. Emanuele III. 1994. Oceanic CO2 measurements for the WOCE Hydrographic Survey in the Pacific Ocean, 1990-1991: Shore based analyses. Scripps Institution of Oceanography Reference Series, Ref. No. 94-28. University of California, San Diego, Calif.
  • Hansson, I. 1973a. A new set of acidity constants for carbonic acid and boric acid in sea water. Deep-Sea Res. 20:461-78.
  • Hansson, I. 1973b. The determination of dissociation constants of carbonic acid in synthetic sea water in the salinity range of 20-40° and temperature range of 5-30°C. Acta Chemica Scandanavia 27:931-44.
  • Johnson, K. M. 1992. Operator's Manual: Single Operator Multiparameter Metabolic Analyzer (Somma) for Total Carbon Dioxide (Ct) with Coulometric Detection. Brookhaven National Laboratory, Upton, N.Y.
  • Johnson, K. M., A. G. Dickson, G. Eischeid, C. Goyet, P. Guenther, R. M. Key, F. J. Millero, D. Purkerson, C. L. Sabine, R. G. Schottle, D. R. W. Wallace, R. J. Wilke, and C. D. Winn. 1998. Coulometric total carbon dioxide analysis for marine studies: Assessment of the quality of total inorganic carbon measurements during the WOCE Indian Ocean CO2 Survey 1994-1996. Mar. Chem. 63:21-37.
  • Johnson, K. M., A. E. King, and J. McN. Sieburth. 1985. Coulometric T CO2 analyses for marine studies: An introduction. Mar. Chem. 16:61-82.
  • Johnson, K. M., P. J. Williams, L. Brandstrom, and J. McN. Sieburth. 1987. Coulometric total carbon analysis for marine studies: Automation and calibration. Mar. Chem. 21:117-33.
  • Johnson, K. M., K. D. Wills, D. B. Butler, W. K. Johnson, and C. S. Wong. 1993. Coulometric total carbon dioxide analysis for marine studies: Maximizing the performance of an automated continuous gas extraction system and coulometric detector. Mar. Chem. 44:167-89.
  • Lewis, E., and D.W.R. Wallace. 1998. Program developed for CO2 system calculations. ORNL/CDIAC-105. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee.
  • Merhbach, C., C. H. Culberson, J. E. Hawley, and R. M. Pytkowicz. 1973. Measurement of the apparent dissociation constants of carbonic acid in seawater at atmospheric pressure. Limnol. Oceanogr. 18:897-907.
  • Millero, F. J., R. H. Byrne, R. Wanninkhof, R. A. Feely, T. Clayton, P. P. Murphy, and M. F. Lamb. 1993. The internal consistency of CO2 measurements in the equatorial Pacific. Mar. Chem. 44:269-80.
  • Millero, F. J., A. G. Dickson, G. Eischeid, C. Goyet, P. Guenther, K. M. Johnson, R. M. Key, K. Lee, D. Purkerson, C. L. Sabine, R. G. Schottle, D. R. W. Wallace, E. Lewis, and C. D. Winn. 1998. Assessment of the quality of the shipboard measurements of total alkalinity on the WOCE Hydrographic Indian Ocean CO2 survey cruises 1994-1996. Mar. Chem. 63:9-20.
  • Peng, T. H., T. Takahashi, W. S. Broecker, and J. Olafsson. 1987. Seasonal variability of carbon dioxide, nutrients and oxygen in the northern North Atlantic surface water: Observations and model. Tellus 39B:439-58.
  • Roy, R. N., L. N. Roy, K. M. Vogel, C. Porter-Moore, T. Pearson, C. E. Good, F. J. Millero, and D. M. Campbell. 1993. The dissociation constants of carbonic acid in seawater at salinities 5 to 45 and temperatures 0 to 45°C. Mar. Chem. 44:249-67.
  • Roy, R. N., L. N. Roy, K. M. Vogel, C. Porter-Moore, T. Pearson, C. E. Good, F. J. Millero, and D. M. Campbell. 1994. Erratum. Mar. Chem. 45:337.
  • Roy, R. N., L. N. Roy, K. M. Vogel, C. Porter-Moore, T. Pearson, C. E. Good, F. J. Millero, and D. M. Campbell. 1996. Erratum. Mar. Chem. 52:183.
  • Takahashi, T., R. T. Williams, and D. L. Bos. 1982. Carbonate chemistry. pp. 77-83. In W. S. Broecker, D. W. Spencer, and H. Craig. GEOSECS Pacific Expedition, Volume 3: Hydrographic Data 1973-1974. National Science Foundation, Washington, D.C.
  • UNESCO. 1991. Reference materials for oceanic carbon dioxide measurements. UNESCO Technical Papers in Marine Science No. 60.
  • Wanninkhof, R., E. R. Lewis, R. A. Feely, and F. J. Millero. 1999. The optimal carbonate dissociation constants for determining surface water p CO2 from alkalinity and total inorganic carbon. Mar. Chem. 60:15-31.
  • WOCE (World Ocean Circulation Experiment). 1994. WOCE Operations Manual, Volume 3: The Observational Program, Section 3.1: WOCE Hydrographic Program, Part 3.1.2: Requirements for WHP Data Reporting. (T. Joyce and C. Corry, eds.), WHP Office Report WHPO 90-1 (Revision 2), WOCE Report No. 67/91, Woods Hole, Mass.

Appendix A: Plots of the Crossover Comparisons in the North and South Pacific


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