Discussion: Reporting and Calibration of Post-Bomb 14C Data

Abstract

The definitive paper by Stuiver and Polach (1977) established the conventions for reporting of radiocarbon data for chronological and geophysical studies based on the radioactive decay of 14C in the sample since the year of sample death or formation. Several ways of reporting 14C activity levels relative to a standard were also established, but no specific instructions were given for reporting nuclear weapons-testing (post-bomb) 14C levels in samples. Because the use of postbomb 14C is becoming more prevalent in forensics, biology, and geosciences, a convention needs to be adopted. We advocate the use of fraction modern with a new symbol F14C to prevent confusion with the previously used Fm, which may or may not have been fractionation-corrected. We also discuss the calibration of post-bomb 14C samples and the available data sets and compilations, but do not give a recommendation for a particular data set. © 2004 by the Arizona Board of Regents on behalf of the University of Arizona.

Full text

RADIOCARBON, Vol 46, Nr 3, 2004, p 1299–1304 © 2004 by the Arizona Board of Regents on behalf of the University of Arizona
1299
DISCUSSION: REPORTING AND CALIBRATION OF POST-BOMB 14C DATA
Paula J Reimer1,2,3 • Thomas A Brown1 • Ron W Reimer2,4
ABSTRACT. The definitive paper by Stuiver and Polach (1977) established the conventions for reporting of radiocarbon
data for chronological and geophysical studies based on the radioactive decay of 14C in the sample since the year of sample
death or formation. Several ways of reporting 14C activity levels relative to a standard were also established, but no specific
instructions were given for reporting nuclear weapons-testing (post-bomb) 14C levels in samples. Because the use of post-
bomb 14C is becoming more prevalent in forensics, biology, and geosciences, a convention needs to be adopted. We advocate
the use of fraction modern with a new symbol F14C to prevent confusion with the previously used Fm, which may or may not
have been fractionation-corrected. We also discuss the calibration of post-bomb 14C samples and the available data sets and
compilations, but do not give a recommendation for a particular data set.
REPORTING OF POST-BOMB 14C DATA
Atmospheric nuclear weapons testing doubled the amount of radiocarbon in the atmosphere in the
late 1950s and early 1960s. The use of this nuclear weapons-testing (post-bomb) 14C spike to pro-
vide age information in forensics, environmental forensics, biology, and the geosciences has accel-
erated over the last few years (e.g. Campana and Jones 1998; Kaplan 2003; Kirner et al. 1997;
Reddy et al. 2003; Wild et al. 1998), but there is no consensus as to what data should be reported in
such studies. 14C measurements of these samples cannot be considered indicative of an age. The 14C
content of post-bomb samples must be interpreted in relation to the 14C content of the atmosphere or
ocean reservoir, which has very little to do with the radioactive decay of 14C. Negative 14C ages have
been utilized for the convenience of calibration with existing computer programs (Goslar et al.,
forthcoming). While this works mathematically, it is philosophically objectionable, because the
decay of 14C used to calculate the 14C age is unrelated to time of formation of a post-bomb sample.
Negative 14C ages could also provoke a misunderstanding or mistrust of 14C analyses in general.
The basic information needed for comparing the 14C content in a post-bomb sample at the time of
growth or formation to that of the atmosphere or ocean is the ratio of the sample activity to the stan-
dard activity measured in the same year, both activities background-corrected and δ13C-normalized,
which is equivalent to ASN/AON in the notation of Stuiver and Polach (1977). The decay counting
activity ratio is equivalent to the ratio of the sample 14C/13C (or 14C/12C) isotope ratio to the standard
14C/13C (or 14C/12C) isotope ratio measured by accelerator mass spectrometry (AMS) in the same
year, both ratios background-corrected and δ13C-normalized, which is also known as fraction mod-
ern or Fm (Donahue et al. 1990). Unfortunately, the term fraction modern has been used with and
without δ13C-normalization of the sample activity. The term percent Modern (pM) can cause confu-
sion since “absolute” percent Modern is also in use for geochemical and equilibria studies and the
symbol is widely used to stand for picomoles. The terms ∆14C and D14C are a step away from the
basic data of interest in that they represent fractional deviation from the standard activity. Also, there
is potential for confusion of ∆14C with ∆, which is age-corrected for year of sample growth.
∆14C is a very useful way of reporting 14C measurements for geochemical studies, including com-
parisons to model results. Unfortunately, under Stuiver and Polach’s definition, ∆14C is based on
ASN/Aabs, and the value obtained for a sample grown/formed in a particular year depends on the year
in which it is measured; e.g., a sample grown/formed in 1962 will give a different ∆14C if measured
1Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
2Queen’s University Belfast, Belfast BT7 1NN, United Kingdom.
3Corresponding author. Email: P.J.Reimer@qub.ac.uk.
4Ocean Sciences Department, University of California-Santa Cruz, Santa Cruz, California 92697, USA.
RADIOCARBON, Vol 46, Nr 3, 2004, p 1299–1304 © 2004 by the Arizona Board of Regents on behalf of the University of Arizona
1299
DISCUSSION: REPORTING AND CALIBRATION OF POST-BOMB 14C DATA
Paula J Reimer1,2,3 • Thomas A Brown1 • Ron W Reimer2,4
ABSTRACT. The definitive paper by Stuiver and Polach (1977) established the conventions for reporting of radiocarbon
data for chronological and geophysical studies based on the radioactive decay of 14C in the sample since the year of sample
death or formation. Several ways of reporting 14C activity levels relative to a standard were also established, but no specific
instructions were given for reporting nuclear weapons-testing (post-bomb) 14C levels in samples. Because the use of post-
bomb 14C is becoming more prevalent in forensics, biology, and geosciences, a convention needs to be adopted. We advocate
the use of fraction modern with a new symbol F14C to prevent confusion with the previously used Fm, which may or may not
have been fractionation-corrected. We also discuss the calibration of post-bomb 14C samples and the available data sets and
compilations, but do not give a recommendation for a particular data set.
REPORTING OF POST-BOMB 14C DATA
Atmospheric nuclear weapons testing doubled the amount of radiocarbon in the atmosphere in the
late 1950s and early 1960s. The use of this nuclear weapons-testing (post-bomb) 14C spike to pro-
vide age information in forensics, environmental forensics, biology, and the geosciences has accel-
erated over the last few years (e.g. Campana and Jones 1998; Kaplan 2003; Kirner et al. 1997;
Reddy et al. 2003; Wild et al. 1998), but there is no consensus as to what data should be reported in
such studies. 14C measurements of these samples cannot be considered indicative of an age. The 14C
content of post-bomb samples must be interpreted in relation to the 14C content of the atmosphere or
ocean reservoir, which has very little to do with the radioactive decay of 14C. Negative 14C ages have
been utilized for the convenience of calibration with existing computer programs (Goslar et al.,
forthcoming). While this works mathematically, it is philosophically objectionable, because the
decay of 14C used to calculate the 14C age is unrelated to time of formation of a post-bomb sample.
Negative 14C ages could also provoke a misunderstanding or mistrust of 14C analyses in general.
The basic information needed for comparing the 14C content in a post-bomb sample at the time of
growth or formation to that of the atmosphere or ocean is the ratio of the sample activity to the stan-
dard activity measured in the same year, both activities background-corrected and δ13C-normalized,
which is equivalent to ASN/AON in the notation of Stuiver and Polach (1977). The decay counting
activity ratio is equivalent to the ratio of the sample 14C/13C (or 14C/12C) isotope ratio to the standard
14C/13C (or 14C/12C) isotope ratio measured by accelerator mass spectrometry (AMS) in the same
year, both ratios background-corrected and δ13C-normalized, which is also known as fraction mod-
ern or Fm (Donahue et al. 1990). Unfortunately, the term fraction modern has been used with and
without δ13C-normalization of the sample activity. The term percent Modern (pM) can cause confu-
sion since “absolute” percent Modern is also in use for geochemical and equilibria studies and the
symbol is widely used to stand for picomoles. The terms ∆14C and D14C are a step away from the
basic data of interest in that they represent fractional deviation from the standard activity. Also, there
is potential for confusion of ∆14C with ∆, which is age-corrected for year of sample growth.
∆14C is a very useful way of reporting 14C measurements for geochemical studies, including com-
parisons to model results. Unfortunately, under Stuiver and Polach’s definition, ∆14C is based on
ASN/Aabs, and the value obtained for a sample grown/formed in a particular year depends on the year
in which it is measured; e.g., a sample grown/formed in 1962 will give a different ∆14C if measured
1Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
2Queen’s University Belfast, Belfast BT7 1NN, United Kingdom.
3Corresponding author. Email: P.J.Reimer@qub.ac.uk.
4Ocean Sciences Department, University of California-Santa Cruz, Santa Cruz, California 92697, USA.

1300 P J Reimer et al.
today versus if it had been measured in 1962. Hence, relating the ∆14C value measured today of a
forensics sample which grew/formed in an unknown year, to bomb-14C records, based on samples
measured at various times and expressed in ∆14C units, is problematic. For forensics and similar
studies, such difficulties would be avoided if the 14C values obtained for the unknown samples and
for the bomb-14C records were expressed as ratios that do not change with time (i.e. ASN/AON rather
than ASN/Aabs). While the difference between ASN/Aabs and ASN/AON is small at present, it will
become more important as time progresses. The ratio ASN/AON has also been given the symbol 14aN
(Mook and van der Plicht 1999), but this nomenclature has not been widely adopted. We suspect this
is due to a reluctance to depart from the Stuiver and Polach (1977) definitions, and because the sym-
bols do not convey the information that carbon is involved. We propose to establish F14C as an
unequivocal term that is in keeping with the Stuiver and Polach (1977) ASN/AON definition, yet con-
veys the information needed for atom-counting and decay-counting measurements in bomb-14C-
based studies.
It is worth noting at this point that δ13C-normalization differs between 14C methods that measure the
14C/12C activity or isotope ratio (all radiometric methods and many AMS systems) and those that
measure the 14C/13C isotope ratio (some AMS systems). While the laboratories generally supply
data normalized to –25‰ with respect to VPDB, in some cases the δ13C is measured or estimated at
a later time and retroactive corrections must be made. Because of this difference, a correction for a
1‰ shift in δ13C results in a correction factor to F14C of approximately 0.002 for a 14C/12C activity
or isotope ratio measurement or 0.001 for a 14C/13C isotope ratio measurement. This is equivalent to
approximately a 16-yr and 8-yr correction to the 14C age, respectively. For clarity, we reiterate the
basic equations for δ13C-normalization of the sample for (1) 14C/12C measurements (Stuiver and
Robinson 1974) and (2) 14C/13C measurements (Brown 1994; Donahue et al. 1990), substituting
F14C for ASN/AON:
F14C = (AS/0.95 AOX) × (0.975/0.981)2 × [(1+δ13COX/1000) / (1+δ13CS/1000)]2(1),
where A is the activity or 14C/12C isotope ratio, and subscripts S and OX refer to sample and oxalic
acid standard, respectively;
F14C = (RS/0.95 ROX) × (0.975/0.981)2 × (1+δ13COX/1000) / (1+δ13CS/1000) (2),
where R is the 14C/13C isotope ratio and subscripts S and OX as above.
Therefore, if a sample has been normalized with an estimated value of δ13C and the oxalic acid nor-
malized to δ13COX = –19‰, then the following formulae apply to the retroactive correction for a
measured δ13CS:
1′) F14C = F14Cest × [(1+δ13Cest/1000)/(1+δ13CS/1000)]2; for 14C/12C measurements,
and
2′) F14C = F14Cest × (1+δ13Cest/1000)/(1+δ13CS/1000); for 14C/13C measurements.
Note that these corrections can be applied to 14C ages, since t = –8033 × ln(F14C).
CALIBRATION OF POST-BOMB 14C DATA
Comparison of atmospheric 14CO2 records indicates that the distribution of bomb 14C at the height
of nuclear testing was not nearly as uniform as pre-bomb 14C (Levin and Kromer 1997; Manning
and Melhuish 1994; Nydal and Lˆvseth 1983; Tans 1981). In addition, CO2 from fossil fuel, which
1300 P J Reimer et al.
today versus if it had been measured in 1962. Hence, relating the ∆14C value measured today of a
forensics sample which grew/formed in an unknown year, to bomb-14C records, based on samples
measured at various times and expressed in ∆14C units, is problematic. For forensics and similar
studies, such difficulties would be avoided if the 14C values obtained for the unknown samples and
for the bomb-14C records were expressed as ratios that do not change with time (i.e. ASN/AON rather
than ASN/Aabs). While the difference between ASN/Aabs and ASN/AON is small at present, it will
become more important as time progresses. The ratio ASN/AON has also been given the symbol 14aN
(Mook and van der Plicht 1999), but this nomenclature has not been widely adopted. We suspect this
is due to a reluctance to depart from the Stuiver and Polach (1977) definitions, and because the sym-
bols do not convey the information that carbon is involved. We propose to establish F14C as an
unequivocal term that is in keeping with the Stuiver and Polach (1977) ASN/AON definition, yet con-
veys the information needed for atom-counting and decay-counting measurements in bomb-14C-
based studies.
It is worth noting at this point that δ13C-normalization differs between 14C methods that measure the
14C/12C activity or isotope ratio (all radiometric methods and many AMS systems) and those that
measure the 14C/13C isotope ratio (some AMS systems). While the laboratories generally supply
data normalized to –25‰ with respect to VPDB, in some cases the δ13C is measured or estimated at
a later time and retroactive corrections must be made. Because of this difference, a correction for a
1‰ shift in δ13C results in a correction factor to F14C of approximately 0.002 for a 14C/12C activity
or isotope ratio measurement or 0.001 for a 14C/13C isotope ratio measurement. This is equivalent to
approximately a 16-yr and 8-yr correction to the 14C age, respectively. For clarity, we reiterate the
basic equations for δ13C-normalization of the sample for (1) 14C/12C measurements (Stuiver and
Robinson 1974) and (2) 14C/13C measurements (Brown 1994; Donahue et al. 1990), substituting
F14C for ASN/AON:
F14C = (AS/0.95 AOX) × (0.975/0.981)2 × [(1+δ13COX/1000) / (1+δ13CS/1000)]2(1),
where A is the activity or 14C/12C isotope ratio, and subscripts S and OX refer to sample and oxalic
acid standard, respectively;
F14C = (RS/0.95 ROX) × (0.975/0.981)2 × (1+δ13COX/1000) / (1+δ13CS/1000) (2),
where R is the 14C/13C isotope ratio and subscripts S and OX as above.
Therefore, if a sample has been normalized with an estimated value of δ13C and the oxalic acid nor-
malized to δ13COX = –19‰, then the following formulae apply to the retroactive correction for a
measured δ13CS:
1′) F14C = F14Cest × [(1+δ13Cest/1000)/(1+δ13CS/1000)]2; for 14C/12C measurements,
and
2′) F14C = F14Cest × (1+δ13Cest/1000)/(1+δ13CS/1000); for 14C/13C measurements.
Note that these corrections can be applied to 14C ages, since t = –8033 × ln(F14C).
CALIBRATION OF POST-BOMB 14C DATA
Comparison of atmospheric 14CO2 records indicates that the distribution of bomb 14C at the height
of nuclear testing was not nearly as uniform as pre-bomb 14C (Levin and Kromer 1997; Manning
and Melhuish 1994; Nydal and Lˆvseth 1983; Tans 1981). In addition, CO2 from fossil fuel, which

Reporting and Calibration of Post-Bomb 14C Data 1301
is depleted in 14C, is non-uniformly distributed and can be a substantial contribution of carbon to a
sample (Levin et al. 2003). In the tropics, 14C-enriched CO2 released from the terrestrial biosphere
may result in slightly elevated 14C levels compared to mid-Northern Hemispheric ones in recent
decades (Levin and Hesshaimer 2000; Randerson et al. 2002). Therefore, a regional, or even a local,
atmospheric 14C data set is the ideal for calibration of a post-bomb 14C measurement. However, it is
not feasible to develop a local calibration data set in most cases. A number of post-bomb atmo-
spheric 14C records are available (Levin and Kromer 1997; Levin and Kromer, this issue; Manning
and Melhuish 1994; Nydal and Lövseth 1983). These long-term observations provide the best
record of atmospheric 14C values at their respective locations.
Tree rings and other organic material also provide a record of growing season-averaged 14C, pro-
vided mobile carbon compounds are removed during pretreatment (Stuiver and Quay 1981). Hua
and Barbetti (this issue) have compiled zonal averages of 14C data derived from atmospheric, tree-
ring, and organic materials for the Southern Hemisphere and 3 zones in the Northern Hemisphere,
including a zone following the Northern Hemisphere summer Intertropical Convergence Zone
(ITCZ). These compilations, together with the summer means from the atmospheric observations
(Levin and Kromer, this issue), should provide adequate calibration for most purposes. However,
while the Southern Hemisphere is represented by 1 zonal compilation, mixing is likely to have an
influence along the ITCZ. Growing season differences should also be considered especially for the
tropics and for high-latitude sites, and during periods of rapid change in the atmospheric 14C levels.
Subannual measurements may be necessary to capture the rapid response of tree cellulose to atmo-
spheric 14C levels (Grootes et al. 1989).
Marine data sets derived from coral, coraline sponges, fish ootoliths, and shell chronologies are also
available for post-bomb calibration of marine samples, but show higher regional variation (Druffel
1996; Druffel and Griffin 1995; Fallon et al. 2003; Guilderson et al. 2000; Nydal et al. 1984;
Weidman and Jones 1993).
In addition to needing a calibration data set that reflects the 14C content of the atmosphere or ocean
in the locality of the sample growth, it is necessary to consider that some types of samples may have
incorporated carbon from numerous sources. Modern diets and petroleum-based carbon compounds
can introduce additional uncertainty in the calibration. Turnover time of human or animal tissues is
dependent on the type of tissue involved and may be affected by age or health of the organism (Geyh
2001; Harkness and Walton 1972; Lovell et al. 2002; Stenhouse and Baxter 1977). Proximity to dis-
charge from nuclear reactors or medical waste incinerators can introduce additional pulses of 14C,
which may not be observed in the regional or zonal calibration data sets (Cook et al. 1995; Trumbore
et al. 2002), although atmospheric mixing may be rapid enough in some cases to dilute a pulse
beyond detection (McGee et al. 2004).
POST-BOMB CALIBRATION PROGRAMS
Because the 14C content of the atmosphere changed rapidly, especially during the years immediately
preceding the nuclear test ban treaty, computer programs that are used to calibrate post-bomb 14C
data must step through the calibration data set in smaller increments than is normally done in cali-
bration programs, as noted by Puchegger et al. (2000). The resulting calibrated age ranges are thus
given in smaller increments. It must be realized that these narrow ranges may not be completely
realistic given the uncertainties discussed above. The calibration program assumes that the sample
is from a system closed to carbon exchange after its formation. Therefore, it is not appropriate for
use on open systems such as soil carbon, where more complex modeling is required to understand
the carbon dynamics (Trumbore 2000).
Reporting and Calibration of Post-Bomb 14C Data 1301
is depleted in 14C, is non-uniformly distributed and can be a substantial contribution of carbon to a
sample (Levin et al. 2003). In the tropics, 14C-enriched CO2 released from the terrestrial biosphere
may result in slightly elevated 14C levels compared to mid-Northern Hemispheric ones in recent
decades (Levin and Hesshaimer 2000; Randerson et al. 2002). Therefore, a regional, or even a local,
atmospheric 14C data set is the ideal for calibration of a post-bomb 14C measurement. However, it is
not feasible to develop a local calibration data set in most cases. A number of post-bomb atmo-
spheric 14C records are available (Levin and Kromer 1997; Levin and Kromer, this issue; Manning
and Melhuish 1994; Nydal and Lövseth 1983). These long-term observations provide the best
record of atmospheric 14C values at their respective locations.
Tree rings and other organic material also provide a record of growing season-averaged 14C, pro-
vided mobile carbon compounds are removed during pretreatment (Stuiver and Quay 1981). Hua
and Barbetti (this issue) have compiled zonal averages of 14C data derived from atmospheric, tree-
ring, and organic materials for the Southern Hemisphere and 3 zones in the Northern Hemisphere,
including a zone following the Northern Hemisphere summer Intertropical Convergence Zone
(ITCZ). These compilations, together with the summer means from the atmospheric observations
(Levin and Kromer, this issue), should provide adequate calibration for most purposes. However,
while the Southern Hemisphere is represented by 1 zonal compilation, mixing is likely to have an
influence along the ITCZ. Growing season differences should also be considered especially for the
tropics and for high-latitude sites, and during periods of rapid change in the atmospheric 14C levels.
Subannual measurements may be necessary to capture the rapid response of tree cellulose to atmo-
spheric 14C levels (Grootes et al. 1989).
Marine data sets derived from coral, coraline sponges, fish ootoliths, and shell chronologies are also
available for post-bomb calibration of marine samples, but show higher regional variation (Druffel
1996; Druffel and Griffin 1995; Fallon et al. 2003; Guilderson et al. 2000; Nydal et al. 1984;
Weidman and Jones 1993).
In addition to needing a calibration data set that reflects the 14C content of the atmosphere or ocean
in the locality of the sample growth, it is necessary to consider that some types of samples may have
incorporated carbon from numerous sources. Modern diets and petroleum-based carbon compounds
can introduce additional uncertainty in the calibration. Turnover time of human or animal tissues is
dependent on the type of tissue involved and may be affected by age or health of the organism (Geyh
2001; Harkness and Walton 1972; Lovell et al. 2002; Stenhouse and Baxter 1977). Proximity to dis-
charge from nuclear reactors or medical waste incinerators can introduce additional pulses of 14C,
which may not be observed in the regional or zonal calibration data sets (Cook et al. 1995; Trumbore
et al. 2002), although atmospheric mixing may be rapid enough in some cases to dilute a pulse
beyond detection (McGee et al. 2004).
POST-BOMB CALIBRATION PROGRAMS
Because the 14C content of the atmosphere changed rapidly, especially during the years immediately
preceding the nuclear test ban treaty, computer programs that are used to calibrate post-bomb 14C
data must step through the calibration data set in smaller increments than is normally done in cali-
bration programs, as noted by Puchegger et al. (2000). The resulting calibrated age ranges are thus
given in smaller increments. It must be realized that these narrow ranges may not be completely
realistic given the uncertainties discussed above. The calibration program assumes that the sample
is from a system closed to carbon exchange after its formation. Therefore, it is not appropriate for
use on open systems such as soil carbon, where more complex modeling is required to understand
the carbon dynamics (Trumbore 2000).

1302 P J Reimer et al.
We have constructed a post-bomb calibration program with a graphical user interface for use on
Macintosh OSX or Windows operating systems. The program CaliBomb allows the selection of cal-
ibration data sets or a user-defined local data set. It is up to the user to choose or construct the appro-
priate data set for the region of interest. The data sets and compilations provided have been extended
into the past with tree-ring measurements from the appropriate hemisphere (McCormac et al. 2002;
Stuiver et al. 1998) to provide seamless calibration for modern samples. A moving average of the
data set may be used to approximate the length of time over which the sample accumulated carbon.
An example of the output is given in Figure 1.
Figure 1 Output from the program CaliBomb for the calibration of a hypothetical sample with F14C = 1.220 ± 0.005. The
Southern Hemisphere post-bomb data set from Wellington, New Zealand (Manning and Melhuish 1994) was converted to
F14C for this purpose, assuming the atmospheric samples were measured in the year of collection. The 2-σ calibrated prob-
ability ranges are shown on the calendar axis.
1302 P J Reimer et al.
We have constructed a post-bomb calibration program with a graphical user interface for use on
Macintosh OSX or Windows operating systems. The program CaliBomb allows the selection of cal-
ibration data sets or a user-defined local data set. It is up to the user to choose or construct the appro-
priate data set for the region of interest. The data sets and compilations provided have been extended
into the past with tree-ring measurements from the appropriate hemisphere (McCormac et al. 2002;
Stuiver et al. 1998) to provide seamless calibration for modern samples. A moving average of the
data set may be used to approximate the length of time over which the sample accumulated carbon.
An example of the output is given in Figure 1.
Figure 1 Output from the program CaliBomb for the calibration of a hypothetical sample with F14C = 1.220 ± 0.005. The
Southern Hemisphere post-bomb data set from Wellington, New Zealand (Manning and Melhuish 1994) was converted to
F14C for this purpose, assuming the atmospheric samples were measured in the year of collection. The 2-σ calibrated prob-
ability ranges are shown on the calendar axis.

Reporting and Calibration of Post-Bomb 14C Data 1303
CONCLUSION
It is recommended that F14C be used to report 14C measurements of post-bomb samples. As with all
14C measurements, the measured or estimated δ13C should be reported. The atmospheric post-bomb
calibration data sets and compilations discussed above and the program CaliBomb are available on
the Radiocarbon Web site at http://www.radiocarbon.org or at http://www.calib.org.
ACKNOWLEDGMENTS
This work was funded in part by NSF grant ATM-0407554. A portion of this work was performed
under the auspices of the U S Department of Energy by the University of California, Lawrence Liv-
ermore National Laboratory under Contract Nr W-7405-Eng-48.
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tracer of global carbon cycle dynamics. Radiocarbon
42(1):69–80.
Levin I, Kromer B. 1997. Twenty years of atmospheric
(CO2)-14C observations at Schauinsland station, Ger-
many. Radiocarbon 39(2):205–18.
Levin I, Kromer B. 2004. The tropospheric 14CO2 level
in mid-latitudes of the Northern Hemisphere (1959–
2003). Radiocarbon, this issue.
Levin I, Kromer B, Schmidt M, Sartorius H. 2003. A
novel approach for independent budgeting of fossil
fuel CO2 over Europe by 14CO2 observations. Geo-
physical Research Letters 30: article nr 2194.
Lovell MA, Robertson JD, Buchholz BA, Xie C, Markes-
bery WR. 2002. Use of bomb pulse carbon-14 to age
senile plaques and neurofibrillary tangles in Alzhe-
imer’s disease. Neurobiology of Aging 23:179–86.
Manning MR, Melhuish WH. 1994. Atmospheric ∆14C
record from Wellington. In: Trends: A Compendium of
Data on Global Change. ORNL/CDIAC-65. Carbon
Dioxide Information Analysis Center, Oak Ridge Na-
tional Laboratory, U S Department of Energy, Oak
Ridge. p 173–202.
McCormac FG, Reimer PJ, Hogg AG, Higham TFG,
Baillie MGL, Palmer J, Stuiver M. 2002. Calibration
of the radiocarbon time scale for the Southern Hemi-
sphere: AD 1850–950. Radiocarbon 44(3):641–51.
McGee EJ, Gallagher D, Mitchell PI, Baillie MGL,
Brown D, Keogh SM. 2004. Recent chronologies for
tree rings and terrestrial archives using 14C bomb fall-
out history. Geochimica et Cosmochimica Acta 68:
2509–16.
Mook WG, van der Plicht J. 1999. Reporting 14C activi-
Reporting and Calibration of Post-Bomb 14C Data 1303
CONCLUSION
It is recommended that F14C be used to report 14C measurements of post-bomb samples. As with all
14C measurements, the measured or estimated δ13C should be reported. The atmospheric post-bomb
calibration data sets and compilations discussed above and the program CaliBomb are available on
the Radiocarbon Web site at http://www.radiocarbon.org or at http://www.calib.org.
ACKNOWLEDGMENTS
This work was funded in part by NSF grant ATM-0407554. A portion of this work was performed
under the auspices of the U S Department of Energy by the University of California, Lawrence Liv-
ermore National Laboratory under Contract Nr W-7405-Eng-48.
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the Vienna Environmental Research Accelerator.
Radiocarbon 40(1):273–81.
1304 P J Reimer et al.
ties and concentrations. Radiocarbon 41(3):227–39.
Nydal R, Gulliksen S, Lövseth K, Skogseth FH. 1984.
Bomb 14C in the ocean surface 1966–1981. Radiocar-
bon 26(1):7–45.
Nydal R, Lövseth K. 1983. Tracing bomb 14C in the
atmosphere 1962–1980. Journal of Geophysical Re-
search—Oceans and Atmospheres 88:3621–42.
Puchegger S, Rom W, Steier P. 2000. Automated evalua-
tion of 14C AMS measurements. Nuclear Instruments
and Methods in Physics Research B 172:274–80.
Randerson JT, Enting IG, Schuur EAG, Caldeira K, Fung
IY. 2002. Seasonal and latitudinal variability of tropo-
sphere ∆14CO2: post-bomb contributions from fossil
fuels, oceans, the stratosphere, and the terrestrial bio-
sphere. Global Biogeochemical Cycles 16: article nr
1112.
Reddy CM, Xu L, O’Connor R. 2003. Using radiocarbon
to apportion sources of polycyclic aromatic hydrocar-
bons in household soot. Environmental Forensics 4:
191–7.
Stenhouse MJ, Baxter MS. 1977. Bomb 14C as a biolog-
ical tracer. Nature 267:828–32.
Stuiver M, Polach HA. 1977. Discussion: reporting of
14C data. Radiocarbon 19(3):355–63.
Stuiver M, Quay PD. 1981. Atmospheric 14C changes re-
sulting from fossil-fuel CO2 release and cosmic-ray
flux variability. Earth and Planetary Science Letters
53:349–62.
Stuiver M, Reimer PJ, Braziunas TF. 1998. High-preci-
sion radiocarbon age calibration for terrestrial and ma-
rine samples. Radiocarbon 40(3):1127–51.
Stuiver M, Robinson SW. 1974. University of Washing-
ton GEOSECS North Atlantic carbon-14 results.
Earth and Planetary Science Letters 23:87–90.
Tans P. 1981. A compilation of bomb 14C data for use in
global carbon model calculations. In: Bolin B, editor.
Carbon Cycle Modeling (SCOPE 16). New York:
John Wiley and Sons. p 131–57.
Trumbore S. 2000. Age of soil organic matter and soil
respiration: radiocarbon constraints on belowground
C dynamics. Ecological Applications 10:399–411.
Trumbore S, Gaudinski JB, Hanson PJ, Southon JR.
2002. Quantifying ecosystem-atmosphere carbon ex-
change with a 14C label. Eos Transactions AGU 83:
267–8.
Weidman CR, Jones GA. 1993. A shell-derived time his-
tory of bomb C-14 on Georges Bank and its Labrador
Sea implications. Journal of Geophysical Research-
Oceans 98:14,577–88.
Wild E, Golser R, Hille P, Kutschera W, Priller A, Pu-
chegger S, Rom W, Steier P, Vycudilik V. 1998. First
14C results from archaeological and forensic studies at
the Vienna Environmental Research Accelerator.
Radiocarbon 40(1):273–81.