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,
Prepared by Linda J. Allison and Dana C. Griffith Date Published: November 1999 |
INVESTIGATORS
ABSTRACT
1. INTRODUCTION
2. ANALYTICAL METHODS
3. RESULTS AND DISCUSSION
4. CONCLUSIONS
5. REMOTE ACCESS TO DATA LISTED IN THIS REPORT
6. ACKNOWLEDGMENTS
7. REFERENCES
APPENDIX A: PLOTS OF THE CROSSOVER COMPARISONS IN THE NORTH AND SOUTH PACIFIC
The authors and additional contributors along with their affiliations and addresses are listed below.
Authors:
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 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.
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 () 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/staff/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.
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).
3.1 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
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 vs salinity
plot. In most cases, > 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 axis; the intervals
chosen were, on average, 0.04 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 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 fCO2@20�C/DIC 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 the
fCO2 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.
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.
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: For DOE Global CO2 ocean survey data: Graphics of the data contained in this report are also available at
http://www.pmel.noaa.gov/co2/oaces_doe/home.htm.
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.
A.2. Comparison of salinity and dissolved inorganic carbon (DIC) at 178� W and 32� S.
A.3. Comparison of salinity and dissolved inorganic carbon (DIC) at 175� W and 32� S.
A.5. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 170� W and 32� S.
A.7a. Comparison of salinity, oxygen (O2), and total alkalinity (TAlk)
at 170� W and 10� S.
A.8a. Comparison of salinity, oxygen (O2), and total alkalinity (TAlk) at 170� W and 5� S.
A.9a. Comparison of salinity, oxygen (O2), and
total alkalinity (TAlk) at 170� W and 0�.
A.10. Comparison of salinity and dissolved inorganic carbon (DIC) at 152� W and 53� N.
A.12. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 150� W and 32� S.
A.15. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 135� W and 33� S.
A.16. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 135� W and 17� S.
A.17. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 135� W and 5� S.
A.18. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 135� W and 35� N.
A.19. Comparison of salinity, oxygen (O2), and dissolved
inorganic carbon (DIC) at 135� W and 40� N.
A.21a. Comparison of salinity, oxygen (O2), and total
alkalinity (TAlk) at 110� W and 0�.
A.21b. Comparison of fugacity of CO2
(fCO2) and dissolved inorganic carbon
(DIC) at 110� W and 0�.
A.22a. Comparison of salinity, oxygen (O2), and total
alkalinity (TAlk) at 110� W and 5� N.
A.22b. Comparison of fugacity of CO2 (fCO2) and dissolved inorganic carbon (DIC) at 110� W and 5� N.
A.24. Comparison of salinity, oxygen (O2), and
dissolved inorganic carbon (DIC) at 103� W and 32� S.
A.27. Comparison of salinity, oxygen (O2), and
dissolved inorganic carbon (DIC) at 88� W and 32� S.
A.29. Comparison of salinity, oxygen
(O2), and
dissolved inorganic carbon (DIC) at 86� W and 17� S.
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.
1. INTRODUCTION
2. ANALYTICAL METHODS
3. RESULTS AND DISCUSSION
4. CONCLUSIONS
5. REMOTE ACCESS TO DATA LISTED IN THIS REPORT
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
Carbon Dioxide Information Analysis Center
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, Tennessee 37831-6335
U.S.A.
Telephone:
(865)574-3645 (voice)
(865)574-2232 (fax)
Internet:http://cdiac.esd.ornl.gov/oceans/home.html
6. ACKNOWLEDGMENTS
7. REFERENCES
APPENDIX A: PLOTS OF THE CROSSOVER COMPARISONS IN THE NORTH AND SOUTH PACIFIC
l.j.allison 1/4/2000