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 900C.  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  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  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