Two Decades of Environmental Isotope Records in Croatia: Reconstruction of the Past and Prediction of Future Levels
Issue Date
1998-01-01Keywords
ecologyatmospheric precipitation
biosphere
future
deuterium
prediction
O 18 O 16
hydrogen
tritium
oxygenO 18Croatiastatistical analysisatmosphereSouthern Europetree ringsisotope ratiosEuropesample preparationC 14carbonisotopesradioactive isotopesstable isotopes
Metadata
Show full item recordCitation
Krajcar-Bronić, I., Horvatinčić, N., & Obelić, B. (1998). Two decades of environmental isotope records in Croatia: Reconstruction of the past and prediction of future levels. Radiocarbon, 40(1), 399-416.Journal
RadiocarbonDescription
From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.Additional Links
http://radiocarbon.webhost.uits.arizona.edu/Abstract
A two-decade-long record of environmental isotopes (2H, 3H, 14C, 18O) in Croatia is presented and the data are statistically analyzed. The atmospheric 14C activity for the period before the actual measurements started is reconstructed by measuring tree rings from the clean-air sites, and the past tritium activity in precipitation is estimated by the correlation of our data with the Vienna station record. The long-term 3H record helped to determine a locally contaminated sampling site, and new clean sites are put into operation. The 14C data were fitted by an analytical function and the prediction of future levels is given assuming that the rate of the 14C releases remains constant. From the long-term stable isotope data record, the local meteoric water line and the temperature gradient of delta-18O in precipitation are determined.Type
Proceedingstext
Language
enISSN
0033-8222Scopus Count
Collections
Related items
Showing items related by title, author, creator and subject.
-
Iron-Manganese System for Preparation of Radiocarbon AMS Targets: Characterization of Procedural Chemical-Isotopic Blanks and FractionationWe report a practical system to mass-produce accelerator mass spectrometry (AMS) targets with 10-100 micrograms carbon samples. Carbon dioxide is reduced quantitatively to graphite on iron fibers via manganese metal, and the Fe-C fibers are melted into a bead suitable for AMS. Pretreatment, reduction and melting processes occur in sealed quartz tubes, allowing parallel processing for otherwise time-intensive procedures. Chemical and isotopic (13C, 14C) blanks, target yields and isotopic fractionation were investigated with respect to levels of sample size, amounts of Fe and Mn, pretreatment and reduction time, and hydrogen pressure. With 7-day pretreatments, carbon blanks exhibited a lognormal mass distribution of 1.44 micrograms (central mean) with a dispersion of 0.50 micrograms (standard deviation). Reductions of 10 micrograms carbon onto targets were complete in 3-6 h with all targets, after correction for the blank, reflecting the 13C signature of the starting material. The 100 micrograms carbon samples required at least 15 h for reduction; shorter durations resulted in isotopic fractionation as a function of chemical yield. The trend in the 13C data suggested the presence of kinetic isotope effects during the reduction. The observed CO2-graphite 13C fractionation factor was 3-4% smaller than the equilibrium value in the simple Rayleigh model. The presence of hydrogen promoted methane formation in yields up to 25%. Fe-C beaded targets were made from NIST Standard Reference Materials and compared with graphitic standards. Although the 12C ion currents from the beads were one to two orders of magnitude lower than currents from the graphite, measurements of the beaded standards were reproducible and internally consistent. Measurement reproducibility was limited mainly by Poisson counting statistics and blank variability, translating to 14C uncertainties of 5-1% for 10-100 micrograms carbon samples, respectively. A bias of 5-7% (relative) was observed between the beaded and graphitic targets, possibly due to variations in sputtering fractionation dependent on sample size, chemical form and beam geometry.
-
On Correcting 14C Ages of Gastropod Shell Carbonate for FractionationCorrecting the 14C age of a sample for fractionation is straightforward if the measured carbon was derived entirely from the atmosphere, either directly or through chemical and/or biological reactions that originated with atmospheric carbon. This correction is complicated in the case of gastropods that incorporate carbon from limestone or secondary carbonate (e.g. Soil carbonate) during shell formation. The carbon isotopic composition of such gastropod shells is determined by fractionation, as well as mixing of carbon from sources with different isotopic values. Only the component of shell carbonate derived from atmospheric carbon should be corrected for fractionation. In this paper, the author derives a new expression for correcting the measured 14C activity of gastropod shells for fractionation, and describe an iterative approach that allows the corrected 14C activity and the fraction of shell carbonate derived from atmospheric carbon to be determined simultaneously.
-
Comparison of Vanadium Oxide Catalysts for Synthesis of Benzene: Benzene Purity, Yields and Reconditioning MethodsThis study compares vanadium oxide catalysts from three different sources: Noakes (N), Harshaw Chemical (H) and Kh. Arslanov at the St. Petersburg State University, Russia (R). The catalysts are used to convert acetylene to benzene in the last step of benzene synthesis. The organic purity of benzene in all three catalysts is high; 99.91-99.93% for (N) and (H) and 99.87% for (R). The benzene yields range from 90.0 to 94.3%. (N) averaged 92.6%, (H) averaged 91.1% and (R) averaged 92.0%. A conversion residue in the catalysts was analyzed for delta-13C and found to be isotopically lighter relative to acetylene by -2.2 per mil for (N) and (H) and -3.9 per mil for (R). Benzene yields were studied on different reconditioning methods applied to all catalysts: heating to 400 degrees C in air averaged 92.3%; the same temperature with a half and half mixture of O2 and Ar averaged 91.9%, adding a half and half mixture of H2 and Ar at 200 degrees C to the end of this treatment averaged 91.8%. Based on this research, the obvious difference seen between the catalysts is in their trace by-products.
