BOREAS TGB-12 Carbon Dioxide Isotopic Content Data over the NSA Summary: The BOREAS TGB-12 team made measurements of soil carbon inventories, carbon concentration in soil gases, and rates of soil respiration at several sites to estimate the rates of carbon accumulation and turnover in each of the major vegetation types. This data set contains information on the carbon isotopic content of carbon dioxide sampled from soils. The data are stored in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS TGB-12 Carbon Dioxide Isotopic Content Data over the NSA 1.2 Data Set Introduction The data collected by the BOREAS TGB-12 group include CO2 flux rates and concentrations in the soil atmosphere at selected sites, as well as 14C measurements of CO2. Our measurements were designed to cover the winter period. 1.3 Objective/Purpose The objectives were : 1. To estimate rates of carbon input, turnover, and accumulation in the soils of each of the major vegetation types at the BOREAS study sites. The primary tool was the measure of 14C content in soils, litter, and soil atmospheres, and the measurement of CO2 emissions from the soil. 2. To relate our estimates of dynamics of soil carbon to ecosystem models of the carbon cycle, to other measures of C cycling dynamics, to regional models of soil carbon accumulation, and to spatial and temporal models of soil moisture and drainage. 1.4 Summary of Parameters 14C data are presented in Delta notation (the per mil difference in the ratio of 14C/12C in the sample from that of an absolute standard - 1895 wood). We also express what fraction of the bulk soil was used for radiocarbon measurement - plant macrofossils, chemically extracted clay, etc.). 1.5 Discussion Winter fluxes of CO2 are often assumed to be zero in northern environments. Our goal in this series of measurements was to quantify the importance of winter CO2 emissions to the annual carbon balance at the NSA YJP, OJP and OBS tower sites. In addition, radiocarbon measurements of 14C in CO2 were used to determine whether winter and summer respiration had different sources. Sites were the same ones used by TGB-01 and TGB-03 for studies of soil respiration during May to October. The steady state 14C content of the atmosphere is determined by the exchange of carbon in CO2 with that in ocean and biospheric reservoirs. Because of the relatively rapid cycling of carbon between the atmosphere and living biomass, most short-lived plant tissues maintain a 14C specific activity that equals that of atmospheric CO2. CO2 derived from old organic matter that has resided in soils for several hundred years will have lower radiocarbon content than that derived from more recently fixed carbon. 1.6 Related Data Sets BOREAS TGB-12 Radon222 Soil Data over the NSA BOREAS TGB-12 Soil Carbon Isotope Data over the NSA BOREAS Soils Data over the NSA and Tower Sites in Raster Format BOREAS TGB-01 Soil CH4 and CO2 Profile Data over the NSA BOREAS TGB-01 NSA SF6 Chamber Flux Data over the NSA BOREAS TGB-03 Soil CO2 and CH4 Profile Data over the NSA 2. Investigator(s) 2.1 Investigator(s) Name and Title Susan Trumbore Earth System Science University of California Irvine 2.2 Title of Investigation Input, Accumulation and Turnover of Carbon in Boreal Forest Soils 2.3 Contact Information Contact 1 Sue Trumbore Earth System Science University of California Irvine, CA (714) 824-6142 (714) 824-3256 (FAX) setrumbo@uci.edu Contact 2 Eric Sundquist U.S. Geological Survey Woods Hole, MA 508-457-2397 sundquist@nobska.wr.usgs.gov Contact 3 Greg Winston U.S. Geological Survey Woods Hole, MA Contact 4 Sara K. Conrad Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-2624 (301) 286-1757 (FAX) Sara.Golightly@gsfc.nasa.gov 3. Theory of Measurements Soil fluxes were measured using chamber methods, that involve enclosing the airspace over soil and monitoring the mixing ratio of gases within the chamber over time. For radiocarbon, we needed to trap the CO2 out of the chamber headspace to collect enough carbon for the 14C measurement. Specifics are given in Winston et al. (1997) and section 4, below. Measurements of soil gas concentrations may be combined with estimates of the rate of diffusion in soils to determine the contribution to surface CO2 emissions derived from various soil depths (see Davidson and Trumbore, 1995 for an example). To do this in BOREAS, we measured CO2, temperature and moisture profiles, as well as 222Rn for estimating soil diffusivity. Special pits were instrumented with thermistors (for monitoring soil temperature), Time Domain Reflectometry (TDR) probes (for monitoring soil water content), and soil gas probes (1/8" stainless steel tubing, perforated at one end and inserted 50 to 100 cm laterally into the soil pit wall, capped with 1/8" swagelock union fittings sealed with a septum). Further details are given in Winston et al. (1998) and in Section 4, below. Calculation of a radiocarbon age requires the assumption that the 14C content of the carbon originally fixed in plant tissues equaled that of the atmospheric CO2 in 1950 (0.95 times the activity of oxalic acid, or Modern). In fact, the 14C content of the atmosphere has varied with time because of changes in the production rate of 14C (cosmic ray flux and magnetic field variations) and because of changes in the distribution of carbon among ocean, biosphere and atmospheric reservoirs. These variations, deduced from the 14C content of cellulose of known age taken from the annual growth rings of trees, are generally less than 10% over the past 7,000 years. More recent changes in the 14C content of atmospheric CO2 have resulted from dilution by 14C-free fossil-fuel-derived carbon and by the production of 14C during atmospheric testing of thermonuclear weapons (bomb 14C). The latter effect dominates other natural and fossil fuel effects, as the atmospheric burden of 14C was approximately doubled in the few years preceding the implementation of the Nuclear Test Ban Treaty in 1964. This isotopic spike in the global carbon system provides a means for radiocarbon to be a useful tracer of carbon cycle processes on the scale of decades. We express 14C data in the geochemical Delta notation, the deviation in parts per thousand (per mil) from an absolute standard (95 times the activity of NBS oxalic acid measured in 1950). In this notation, zero equals the 14C content of 1895 wood, positive values indicate the presence of 'bomb' radiocarbon, and negative values indicate the predominance of C fixed from the atmosphere more than several hundred years ago. For seeds, deciduous leaves, etc, that represent a single year's growth, the 14C content of recent samples may be used to determine the age of a sample to within a year or two (for samples in the 'bomb' period, <30 years old). The 14C content of the sample is compared to the 14C record of atmospheric C in the Northern Hemisphere (see Burcholadze reference, below, as an example). Evergreen needles, that may average several years' growth, will have higher 14C signatures than deciduous leaves that grew since 1964. For samples prior to 1960, radiocarbon ages in years may be calculated from the given Delta values as -8033*(ln(Delta*.995/1000 +1)). The conventional radiocarbon age must be converted to a calibrated age using the tree-ring based calibration curves which correct for known variations in atmospheric 14C over time Both ages are usually rounded to the nearest decade or pentade. One application of radiocarbon to soil science lies in the relatively straightforward 14C dating of charcoal and plant macrofossils to determine the accumulation rate of C in vertically aggrading soils (like peats, or moss layers). Unlike the closed systems represented by intact macrofossils, such as seeds or pollen, bulk SOM is a heterogeneous reservoir with a variety of turnover times, to which carbon is continuously added (as new plant matter) and lost (as leached organic carbon or CO2). The radiocarbon content of SOM can not be interpreted as a 'date', but represents the average age of a carbon atom in this reservoir. The breakdown of C into faster and slower-cycling pools may be determined by combining several approaches - see the articles in the reference list below for more information (this is an evolving research field and no one approach is accepted as valid for all soils). 4. Equipment: Because all of the equipment used in this project is common to many other projects and no special procedures were used, description detail has been minimized in this section, and the reader is referred to the appropriate publications. Davidson and Trumbore 1995 Stephens and Sundquist 1998 Trumbore and Harden 1997 Winston et al. 1997 Harden et al. 1997 4.1 Sensor/Instrument Description Flux chambers were used to measure CO2 fluxes and to collect CO2 for radiocarbon measurements. See Stephens and Sundquist (1998) and Winston et al (1997) for details. Stainless steel (1/8 inch) probes were used to collect soil atmosphere samples from different depths. Samples for CO2 concentration measurement were removed by syringe, larger volume samples for 14C determination were collected by attaching pre-evacuated, electropolished, stainless steel cans of 500cc volume. Lab Equipment - Carlo Erba NA1500 carbon and nitrogen combustion analyzer; vacuum lines for purification of CO2 from combusted samples and graphite target preparation. Accelerator mass spectrometer used for 14C measurement is described in Southon et al. and Trumbore (1998). 14CO2 efflux from soil: Samples for 14C measurement of total soil respiration are collected from the headspace of a dynamic chamber using molecular sieve 13X traps. First, atmospheric CO2 trapped during chamber emplacement is removed by circulating headspace air at flow rates of ~500 cm3min-1 through a soda lime column. Scrubbing continues until the equivalent of two chamber volumes has been passed over the soda lime. The molecular sieve trap then replaces the soda lime scrubber and CO2 is trapped from circulating chamber air until enough has been collected for isotopic (13C and 14C) measurements. Trapping times vary from about 10 minutes to an hour, depending on the soil CO2 emission rate. CO2 is released from the trap at 500 8C, and purified cryogenically. One aliquot of the sample is measured for 13C content by stable isotope mass spectrometry. A second aliquot is reduced to graphite for 14C measurement by AMS. Comparison of 13C data for ambient air (sampled at the same site) with the 13C content of soil organic matter is used to correct the 14C data for small amounts of ambient air remaining in the sample. 4.1.1 Collection Environment Samples were collected mostly in over two winters, though summer measurements were also made for isotopes. 4.1.2 Source/Platform Ground. 4.1.3 Source/Platform Mission Objectives None given. 4.1.4 Key Variables The key variables are the CO2 concentration, CO2 flux and del14C of CO2. 4.1.5 Principles of Operation None given. 4.1.6 Sensor/Instrument Measurement Geometry None given. 4.1.7 Manufacturer of Sensor/Instrument A Licor CO2 analyzer was used to measure CO2 fluxes in the field. The gas chromatography system described by TGB-01 (Crill) was used to determine CO2 concentrations in soil air. 4.2 Calibration 4.2.1 Specifications See Winston et al., 1997 4.2.1.1 Tolerance See Winston et al., 1997 4.2.2 Frequency of Calibration See Winston et al., 1997 4.2.3 Other Calibration Information See Winston et al., 1997 5. Data Acquisition Methods 14C. Carbon-14 is measured by Accelerator mass spectrometry of graphite targets prepared from CO2 (see one of several references, including Trumbore, 1995). Samples (of 1-2 mg carbon equivalent) are combusted in vacuum in quartz tubes with cupric oxide wire at 900°C. The resulting CO2 is purified cryogenically, then reduced to graphite coating cobalt powder in a sealed Pyrex tube at 500- 550oC with zinc and titanium hydride powder. Accelerator mass spectrometry measurements were made at the Lawrence Livermore National Laboratory Center for Accelerator Mass Spectrometry. One sigma precision is usually +/- 8-10 per mil (.8-1.0 % Modern) and overall accuracy (based on repeated measurements of substandards prepared in the same way as samples) is 1.0 - 1.5% of Modern (10 - 15 per mil). 6. Observations 6.1 Data Notes None Given. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage The North American Datum 1983 (NAD83) coordinates for the sites are: Site Latitude Longitude ------- --------- --------- NSA-OBS 55.88007N 98.48139W NSA-YJP 55.89575N 98.28706W NSA-OJP 55.92842N 98.62396W 7.1.2 Spatial Coverage Map Not applicable 7.1.3 Spatial Resolution These data are point measurements at the given locations. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The data were collected over the period of 14-NOV-93 to 10-OCT-96. Data collection was not continuous ñ most CO2 fluxes were measured in winter. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution None given. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tgb12ci.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tgb12ci.def). 8. Data Organization 8.1 Data Granularity All of the BOREAS TGB-12 Carbon Dioxide Isotopic Content Data over the NSA data are contained in one dataset. 8.2 Data Format(s) The files contain numerical and character fields of varying length separated by commas. The character fields are enclosed with single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (tgb12ci.def). 9. Data Manipulations 9.1 Formulae None given. 9.1.1 Derivation Techniques and Algorithms None. 9.2 Data Processing Sequence None given. 9.2.1 Processing Steps None given. 9.2.2 Processing Changes None given. 9.3 Calculations None given. 9.3.1 Special Corrections/Adjustments None given. 9.3.2 Calculated Variables None. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error We have assumed -25 per mil 13C in correcting 14C data for fractionation (error of 2 per mil in this term leads to a 4 per mil error in DEL 14C - as long as vegetation is predominantly C3 photosynthetic pathway, this is not a large contributing error in 14C analyses. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgement None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center Data was examined for general consistency and clarity. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data None given. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None. 12. Application of the Data Set None given. 13. Future Modifications and Plans None given. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or FAX. 15.4 Data Center Status/Plans The TGB-12 carbon dioxide flux data are available from the EOSDIS ORNL DAAC (Earth Observing System Data and Information System) (Oak Ridge National Laboratory) (Distributed Active Archive Center). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products Comma delimited ASCII text file. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation None given. 17.2 Journal Articles and Study Reports Davidson, E.A. and S.E. Trumbore. 1995. Gas diffusivity and production of CO2 in deep soils of the eastern Amazon. Tellus. 47B: 550-565. Donahue, D. J., T. W. Linick and A. J. T. Jull, Isotope-ratio and background corrections for accelerator mass spectrometry radiocarbon measurements, Radiocarbon 32: 135-142 (1990). Goulden, M. L., S. C. Wofsy, J. W. Harden, S. E. Trumbore, P. M. Crill, S. T. Gower, T. Fries, B. C. Daube, S-M. Fan, D. J. Sutoon, A. Bazzaz, J. W. Munger. Sensitivity of boreal forest carbon balance to soil thaw, Science 279:214-217 (1998). Harden, J., K. P. O'Neill, S. E. Trumbore, H. Veldhuis, and B. J. Stocks, Moss and soil contributions to the annual net carbon flux in a maturing boreal forest. JGR Atmospheres 102:28,817-28,830 (1997). Sellers, P., F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J., Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P., F. Hall, K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P., F. Hall, K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P. J., F. G. Hall, R. D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan, K. J. Ranson, P. M. Crill, D. P. Lettenmaier, H. Margolis, J. Cihlar, J. Newcomer, D. Fitzjarrald, P. G. Jarvis, S. T. Gower, D. Halliwell, D. Williams, B. Goodison, D. E. Wickland, and F. E. Guertin. 1997. BOREAS in 1997: Experiment Overview, Scientific Results and Future Directions. Journal of Geophysical Research 102 (D24): 28,731-28,770. Southon, J., R., J. S. Vogel, S. E. Trumbore and others, Progress in AMS measurements at the LLNL spectrometer, Radiocarbon 34: 473 - 477 (1992). Stuiver, M. and H. Polach., Reporting of 14C data. Radiocarbon 19: 355-363 (1977). Trumbore, S.E., Radiocarbon geochronology, in, J. M. Sowers, J. S. Noller and W. R. Lettis, eds., Dating and Earthquakes: Review of Quaternary Geochronology and its Application to Paleoseismology: NUREG-5562, US Nuclear Regulatory Commission, Washington DC, pp.2-69 ñ 2-101 (1998). Trumbore,S. E., Comparison of carbon dynamics in two soils using measurements of radiocarbon in pre-and post-bomb soils. Global Biogeochemical Cycles 7:275-290 (1993). Trumbore, S. E. and J. W. Harden, Input, accumulation and turnover of carbon in soils of the BOREAS northern study area, JGR Atmospheres 102:28,805-28,816 (1997). Winston, G., E. T. Sundquist, B. B. Stephen and S. E. Trumbore, Winter CO2 fluxes in a boreal forest, JGR Atmospheres 102:28,795-28,804 (1997). 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None given. 19. List of Acronyms BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GSFC - Goddard Space Flight Center NASA - National Aeronautics and Space Administration ORNL - Oak Ridge National Laboratory URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date Written: 19-Jan-1998 Revision: 14-Sep-1998 20.2 Document Review Date(s) BORIS Review: 19-Jan-1998 Science Review: 20.3 Document ID 20.4 Citation The data will also be published as a USGS open file report. 20.5 Document Curator 20.6 Document URL Keywords CH4, CO2, methane, Carbon dioxide, permafrost, Canada, carbon, trace gas TGB12_Iso_CO2 08/20/98