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Workshop On 14C Data Reporting

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Abstract

The purpose of the workshop was to clarify any possible confusion related to the reporting 14 C data. Two areas of concern, the use of the new NBS oxalic acid standard (Cavallo and Mann, 1980), and the reporting of marine sample ages, were singled out for detailed discussions.
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Workshop On 14C Data Reporting
Minze Stuiver
Radiocarbon / Volume 22 / Issue 03 / January 1980, pp 964 - 966
DOI: 10.1017/S0033822200010389, Published online: 18 July 2016
Link to this article: http://journals.cambridge.org/abstract_S0033822200010389
How to cite this article:
Minze Stuiver (1980). Workshop On 14C Data Reporting. Radiocarbon, 22, pp 964-966 doi:10.1017/S0033822200010389
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[RADIOGAR1 ON, VOL 22, No. 3, 1980, P 964-966]
WORKSHOP ON 14C DATA REPORTING
MINZE STUIVER
Departments of Geological Sciences and Zoology,
University of Washington, Seattle, Washington 98195
The purpose of the workshop was to clarify any possible confusion
related to the reporting 14C data. Two areas of concern, the use of the
new NBS oxalic acid standard (Cavallo and Mann, 1980), and the report-
ing of marine sample ages, were singled out for detailed discussions.
The 14C activity of the "old" NBS oxalic acid standard has tradi-
tionally been normalized on a S13CpDB value of -19 per mil. This value
is close, but not necessarily identical to the S13CPDB value of CO2 gas
obtained from oxalic acid by a random user. Differences will be small,
however, and if the user does not have a mass spectrometer available for
the 13C measurements, he can, at least for routine work, dispense with
the fine tuning (normalization to -19 per mil) and use his actual oxalic
acid counting rates without 13C correction.
The S13CPDB value of CO2 gas derived from the newly introduced
second NBS oxalic acid standard is closer to -17 per mil. Sentiment was
therefore voiced at the meeting to normalize the new standard to -17
per mil. Others were of the opinion that -19 per mil for both standards
was more appropriate.
Initially, a majority of the attendees in charge of 14C laboratories
expressed an interest in normalizing on a $13CpDB value of -17 for the
new standard. However, during further discussion, normalizing on a
8130 value of -25 per mil was favored because the 13C normalization of
samples and the new oxalic acid standard would then be identical.
To correct for 13C fractionation the oxalic acrd count rate is multi-
2(b13C + b}
plied with the approximate factor 1 - . For the old
1000
oxalic acid, b is 19 per mil. For the new oxalic acid, the discussions cen-
tered around a choice of 17, 19, and 25 per mil. The NBS report gives the
ratio of the oxalic acid counts (Ox for the old, NOX for the new) when
both are normalized to -19 per mil:
NOX(19)/0X(19) =1.2894 ± 0.0005.
The base-line (zero age activity) is obtained for the old oxalic acid
by using the 0.95 0X(19) count rate. The corresponding expression for
the new oxalic acid is X(b) NOX(b). For b = 19 per mil X(19) = 0.7368
when the preliminary NBS value is substituted. Thus, instead of taking
95 percent of the old oxalic acid value, equivalent results are obtained
by taking 73.68 percent of the new oxalic acid count rate (when both
are normalized on a 13C value of -19 per mil). The following relation-
ships apply
964
Workshop on 14C data reporting
Oxalic acid "13CPDB X(b)
965
Old -19 0.95
New -17 0.7338
New -19 0.7368
New -25 0.7457
The issue of normalization thus centers around the -17/0.7338;
-19/0.7368, and -25/0.7457 combination. It is obvious that each labora-
tory can have its preferred 8130 value as long as the appropriate b, X(b)
combination is used.
An ambiguity in the use of radiocarbon ages was discussed also.
Following Stuiver and Polach (1977) the term, conventional radiocarbon
age, would imply 13C normalization of all samples to the base of 613Cp
= -25 per mil. Thus, a conventional radiocarbon age would take into
account 13C fractionation but not differences in 14C specific activity of
reservoirs that arise from effects other than fractionation. A conventional
y
radiocarbon age would be reported without adjustment and a reservoir
corrected age would have to be given separately.
The major difficulty encountered with the above procedure is past
reporting practices for archaeologic and geologic marine samples. The
conventional radiocarbon age for marine materials only takes 13C frac-
tionation into account. Because the corrections for 13C fractionation and
reservoir 14C deficiency cancel each other more or less for shells of mid-
and low-latitude regions, many laboratories have adopted the convenient
practice of deleting correction factors for both isotope fractionation and
14C reservoir deficiency from their calculations. In that instance the radio-
carbon age reported is a reservoir corrected age.
A majority of the participants felt that for all samples, includin
marine specimens, a conventional radiocarbon age based on the g
normal-
ization to a 8130 value of -25 per mil -
p should be reported. Thus, a con-
ventional radiocarbon age, as well as a reservoir corrected age, would be
given. Although adopted, this proposal sparked strong opposition from
the minority (ca 40 percent of the voting participants).
The various possible ways of correcting for isotope fractionation
were also questioned. The fractionation factor for the distribution of
14C between two compounds should be the square of the fractionation for
13C (Craig, 1957) when possible effects of a molecular asymmetry are
neglected. The use of this rule (Stuiver and Robinson 1974) leads to an.
isotope fractionation corrected i14C (normalized to a 8130 value of -25
per mil) that is given by
Q14C - 1000 1 + 8' 9 C 0.9752
1000 b`13C 2 1 (1)
1+ 1000
where 614C is the relative difference between the 0.95 oxalic acid standard
and sample activity and 613C is the relative difference between the sample'
and PDB 13C/12C ratio.
966 Calibration and Data Reporting
A first order approximation of the above equation results in the
commonly used equation: 614C\
1.4C = 814C - (2 81JC + 50) 1 + 1000 (2)
Another approximation uses the relative 813C deviation (8130 + 25)1
8130
1 + 1000 (hook, 1980) 6C S13C (3)
Q14C = b`14C - 2 (13C + 25) 1 + 1000 1 + 1000
The L14C values derived from equations 2 and 3 differ slightly from
those obtained from equation 1. Equation 2 derived d14C values differ
less than 1 per mil from 014C's derived from equation 1 when 813C ratios
are in the -31 to +3 per mil range. For equation 3 the corresponding
interval is -55 to +6 per mil. Outside this range the discrepancies in-
crease more rapidly for equation 2 derived values than for those derived
from equation 3.
For measuring precisions up to a few per mil, and 8130 values in
the 0 to -30 per mil range, any of the above equations can be used with
good results. However, for high precision work (1 per mil or better), or
when a wide range of 8130 values is encountered, equation 1 is to be
preferred.
In further action, the meeting adopted the AD 1950 absolute NBS
oxalic acid disintegration rate of 14.27 ± 0.07 disintegrations per minute
per gram of carbon. This corresponds with an activity for 95 percent of
oxalic acid of 13.56 ± 0.07 disintegrations per minute per gram carbon,
which gives a 14C/C ratio of (1.176 ± 0.010) 10-12 (Karlen and others,
1968, first reported in 1964). The above activities are normalized on an
oxalic acid 813CPDB value of -19 per mil.
The 14C/C ratio is important for the conversion to total 14C (14C)
of, for instance, ocean water: p14C
"14C = 1.176 10-12 1 + 1000 CO2
where both Lr14C and CO2 are in p mole/kg of sea water.
REFERENCES
Cavallo, L M and Mann, W B, 1980, New National Bureau of Standards contemporary
carbon-14 standards, in Stuiver, Minze and Kra, Renee, eds, Internatl radiocarbon
conf, 10th, Proc: Radiocarbon, v 22, no. 3, p 962-963.
Craig, Harmon, 1957, Isotopic standards for carbon and oxygen and correction factors
for mass-spectrometric analysis of carbon dioxide: Geochim et Cosmochim Acta,
v 12, p 133-149.
Karlen, I, Olsson, I U, Kallberg, P, and Kilici, S, 1968, Absolute determination of the
activity of two 14C dating standards: Arkiv Geofysik, v 4, no. 22, p 465-471.
Mook, W G, 1980, The erect of fossil fuel and biogenic CO2 on the 13C and 14C
content of atmospheric carbon dioxide, in Stuiver, Minze and Kra, Renee, eds,
Internatl radiocarbon conf, 10th, Proc: Radiocarbon, v 22, no. 2, p 392-397.
Stuiver, Minze and Polach, H A, 1977, Discussion: Reporting of 14C data: Radiocarbon,
v 19, p 355-363.
Stuiver, Minze and Robinson, S W, 1974, University of Washington Geosecs North
Atlantic carbon-14 results: Earth and Planetary Sci Letters, v 23, p 87-90.
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  • Jun 2022
Sand stringers are subtle, aeolian landforms that reach hundreds to thousands of metres in length and lack a slipface. While hundreds of sand stringers exist beyond the Last Glacial Maximum margin in the Upper Midwest, USA, little is known about the timing and nature of their formation. This research characterizes the morphology and stratigraphy and provides geochronological data from two sand stringers in the upper Mississippi River basin in Minnesota and Wisconsin. The sand stringers investigated have similar west–northwest to east–southeast orientations and are located ~100 km from each other on uplands west and east of the Mississippi River valley. The sand stringer in Goodhue County, Minnesota (GC site) is ~870 m long and 50–80 m wide. To the east, the sand stringer in Eau Claire County, Wisconsin (ECC site) is ~925 m long and 30–50 m wide. The main body of the GC sand stringer is characterized by an ~80–270 cm‐thick silt‐rich surface unit overlying a sandy unit that is underlain by a dark brown paleosol, while the main body of the ECC sand stringer is sandier/coarser, stratified, and overlies outwash. ¹⁴ C ages, interpreted as minima, at GC indicate formation began prior to 25–20 cal yr BP, while OSL and ¹⁴ C ages indicate ECC formed ~11.25–8.9 ka. We interpret the main body of GC as equivalent to Peoria Loess, with minor inputs of reworked outwash. We interpret ECC as composed of reworked outwash and local bedrock‐derived sands. Pedogenesis at GC and ECC indicates stabilization with possible minor modification of near‐surface sediments through the Holocene. Differences in stratigraphy and chronology between the two sites highlight the complexity of aeolian systems in the Upper Midwest, interpreted as indicative of the variety of sediment sources contributing to landform development via aeolian processes due to spatial and temporal variability in deglaciation and permafrost melting.
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Discussion-Reporting of 14
Article
Full-text available
  • Jan 1977
  • RADIOCARBON
Count rates, representing the rate of 14 C decay, are the basic data obtained in a 14 C laboratory. The conversion of this information into an age or geochemical parameters appears a simple matter at first. However, the path between counting and suitable 14 C data reporting (table 1) causes headaches to many. Minor deflections in pathway, depending on personal interpretations, are possible and give end results that are not always useful for inter-laboratory comparisons. This discussion is an attempt to identify some of these problems and to recommend certain procedures by which reporting ambiguities can be avoided.
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New National Bureau of Standards Contemporary Carbon-14 Standards
Article
  • Jan 1980
  • RADIOCARBON
In 1957 the National Bureau of Standards (NBS) agreed, at the request of James R Arnold, to store and distribute an oxalic acid contemporary carbon-14 standard. In 1978 stocks of this standard were practically gone. We approached Chas Pfizer and Company, Inc, which had provided the original 1000 pounds of oxalic acid to Dr Arnold to see if they could provide another one-batch lot of 1000 pounds of oxalic acid to replace the old standard. This they did generously, at no cost to NBS. The oxalic acid was prepared by fermentation of French beet molasses from the 1977 spring, summer, and autumn harvest using Aspergillus niger var . The acid was separated from the broth as the insoluble calcium salt and reconverted to free acid using sulfuric acid. The free acid was then crystallized, redissolved, filtered, recrystallized, and dried.
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The Effect of Fossil Fuel and Biogenic CO2 on the 13C and 14C Content of Atmospheric Carbon Dioxide
Article
  • Jan 1980
  • RADIOCARBON
The normalization of a measured δ 14 C value of atmospheric CO 2 to a δ 13 C value of − 25‰ does not take into account the presence of fossil fuel and biogenic CO 2 . In this paper, we try to assess these contaminations as well as the proper 14 C content of “clean air”.
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University of Washington Geosecs North Atlantic carbon-14 results
Article
  • Aug 1974
  • EARTH PLANET SC LETT
The14C activities of North Atlantic water at Geosecs stations 5, 27, and 29 are reported. The influence of the correction for isotope fractionation on the14C results is discussed, and experimental procedures are given.
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Isotopic Standards for Carbon and Oxygen and Correction Factors for Mass Spectrometric Analysis of Carbon Dioxide
Article
  • Dec 1957
  • GEOCHIM COSMOCHIM AC
Seventy-four mass spectrometric analyses have been made on eight isotopic standards for carbon and oxygen. The standards reported on are the National Bureau of Standards limestone, water, and graphite reference samples, the Solenhofen standard used by Niee for absolute measurements, and the carbonate standards used by the Stockholm, Basel, Wellington and Chicago laboratories. The basic measurements are reported as δ values relative to the Chicago PDB standard and as absolute isotope ratios. The absolute ratios are based on new figures for Nier's standard, derived from a reevaluation of his data and new measurements on atmospheric oxygen.The correction factors for instrumental effects and for the nature of the mass spectra have been studied. Simple but precise equations for the mass spectra effects have been derived, which give the correction factors as functions of the measured differences between sample and standard. The oxygen isotopic composition of carbon dioxide produced by combustion of carbon has been studied and the derived correction factors for carbon measurements were checked experimentally by varying the oxygen-18 content of carbon dioxide.
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