New Databases Available Online from CDIAC

Typically, CDIAC checks all files that it receives and fully documents these files in the form of numeric data packages or computer model packages (NDPs and CMPs) before making them available to the general public. CDIAC is also offering files that have not been subjected to the normal CDIAC quality-control procedures to make them available more quickly. The abstracts that follow describe databases now available from CDIAC. These databases are available from CDIAC's World Wide Web site and its anonymous FTP area over the Internet and on magnetic media upon request. Files describing the contents of each database are furnished. No additional documentation is available from CDIAC. Questions about accessing the databases should be directed to CDIAC. Technical questions (e.g., methodology or accuracy) should be directed to the researchers listed for each database.

Global and Latitudinal Estimates of ¹³C from Fossil-Fuel Consumption and Cement Manufacture

Bob Andres, University of Alaska, Fairbanks, Alaska
Gregg Marland, CDIAC, Oak Ridge National Laboratory, Oak Ridge, Tennessee
Steve Bischof, Connecticut College, New London, Connecticut

DB1013 (1996)

This database contains estimates of the annual mean value of ¹³C of CO₂ emissions from fossil-fuel consumption and cement manufacture for 1860 to 1992 and estimates of the value of ¹³C for one-degree-latitude bands for the years 1950, 1960, 1970, 1980, 1990, 1991, and 1992. These estimates of the carbon isotopic signature account for the changing mix of fossil fuels used at different times and for the different geographic origins of those fuels.

This time series of fossil-fuel ¹³C signature provides an additional constraint for balancing the sources and sinks of the global carbon cycle and complements the atmospheric ¹³C measurements that are used to partition the uptake of fossil-carbon emissions among the ocean, atmospheric, and terrestrial reservoirs. All ¹³C values are expressed as a per mil
(^o/_oo) deviation from the PDB (PeeDee belemnite limestone) reference scale.

The global ¹³C value of CO₂ from fossil-fuel consumption and cement manufacture was calculated by using global CO₂-emission estimates for 1860 to 1949 and national CO₂-emission estimates for 1950 to 1992 for each major fuel type and multiplying the fuel-type emissions by the ¹³C value corresponding to the fuel. The 1°-latitudinal ¹³C signatures for select years (i.e., 1950, 1960, 1970, 1980, 1990, 1991, and 1992) were calculated with 1° latitude by 1° longitude CO₂-emissions estimates. These estimates were derived from national CO₂-emissions estimates, 1° latitude by 1° longitude maps of political units and human population density, and the ¹³C values for major fuel types. Latitudinal distributions were created by summing the CO₂ emissions for each 1° latitude band.

The database contains three files: a descriptive file; a file containing the global annual estimates of ¹³C for anthropogenic CO₂ fossil-fuel emissions for 1860 to 1992; and a file containing 1° latitudinal gradients of ¹³C from fossil-fuel CO₂ emissions for 1950, 1960, 1970, 1980, 1990, 1991, and 1992.

Global annual ¹³C values for 1860 to 1992.

In situ Carbon 13 and Oxygen 18 Ratios of Atmospheric CO₂ from Cape Grim, Tasmania, Australia: 19821993

R. J. Francey, C. E. Allison, E. D. Welch, I. G. Enting, and H. S. Goodman, CSIRO Division of Atmospheric Research, Mordialloc, Victoria, Australia

DB1014 (1996)

Since 1982, atmospheric CO₂ has been continually sampled at the Australian Baseline Air Pollution Station, Cape Grim, Tasmania, to determine stable-isotope ratios. This database has several unique factors as a globally representative signal from a surface site: the process of in situ extraction of CO₂ from air, the preponderance of samples collected in conditions of strong wind from the marine boundary layer of the Southern Ocean, and the determination of all isotope ratios relative to a common high-purity CO₂ reference gas with isotopic ¹³C close to atmospheric values.

Air samples are collected during baseline-condition episodes at a frequency of about one sample per week. Baseline conditions are characterized by specific wind direction, condensation nucleus concentration, and CO₂ concentration stability. Air samples are taken and dried and then analyzed by mass spectrometry in the laboratory one to three weeks later.

This record is possibly the most accurate representation of global atmospheric ¹³C behavior over the past decade and may be used to partition the uptake of fossil-fuel carbon emissions between ocean and terrestrial plant reservoirs. These data indicate a gradual decrease in ¹³C from 1982 to 1993 and a pronounced flattening from 1988 to 1990, a trend that appears to involve the terrestrial carbon cycle.

The database consists of two files, a descriptive file and a data file that contains the in situ carbon-13 and oxygen-18 ratios of atmospheric CO₂ from Cape Grim for 1982 through 1993. Each data record contains a decimal year value (e.g., 93.960; the decimal equivalent of the date only with no diurnal information), ¹³C and ¹⁸O values, and an indication of the height at which the measurement was taken (10 or 70 m).

Two mass spectrometers have been used to measure the ¹⁸O. During the 18 months that both spectrometers were used, varying differences were observed in the values they produced in the oxygen analyses. As a result, only the values for samples measured on the older of the two mass spectrometers are reported for ¹⁸O. (No similar differences influenced the ¹³C measurements.) The ¹³C and ¹⁸O values are expressed in per mil (^o/_oo).

¹³C in the atmosphere over Cape Grim for 1982 through 1993.

Global Patterns of Carbon Dioxide Emissions from Soils on a 0.5-Degree-Grid-Cell Basis

James W. Raich, Department of Botany, Iowa State University, Ames, Iowa
Christopher S. Potter, NASA Ames Research Center, Moffett Field, California

DB1015 (1996)

Semimechanistic, empirically based statistical models were used to predict the spatial (0.5-degree grid cells) and temporal (monthly and annual) patterns of global carbon emissions from terrestrial soils. Emissions include the respiration of both soil organisms and plant roots. Geographically referenced data of mean monthly air temperature and precipitation, soil organic carbon and nitrogen content, soil type and natural vegetation type were used in the model development. It was found that, at the global scale, the rates of soil CO₂ efflux correlate significantly with temperature and precipitation, have a pronounced seasonal pattern in most locations, and contribute to observed wintertime increases in atmospheric CO₂.

The DB1015 data are the predicted CO₂ emissions of the model based on untransformed precipitation data and the exponential (Q10) relationship between soil biological activity and temperature. The data at the half-degree-spatial and monthly temporal resolution represent the best resolved estimate to date of global CO₂ fluxes from soils and should facilitate investigations of net exchanges between the atmosphere and terrestrial biosphere.

The data files (about 10 MB, total) consist of 12 monthly model-output files, one annual model-output file, one geographic-information file, and a readme file with simple FORTRAN data-access information.