Publications (2)5.91 Total impact
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Article: Tropospheric 14CO2 at Wellington, New Zealand: the world's longest record
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ABSTRACT: Measurements of near-sea-level tropospheric Delta(14)CO(2) have been made at Wellington, New Zealand since December 1954; these measurements comprise the longest such record available. The Delta(14)C rose from -10aEuro degrees in 1955 peaking at 695aEuro degrees in 1965 as a result of "bomb (14)C" production, before falling thereafter to the present day (2005) value of 73aEuro degrees. The Delta(14)C peak occurred about 1 year later in the southern hemisphere than in the northern hemisphere. The post-1965 fall is due to the transfer of (14)C-enriched CO(2) to the biospheric and oceanic pools together with ongoing release of (14)C-free CO(2) from fossil fuel combustion, during an era without major atmospheric nuclear-weapon tests. Time series analysis of the data using Loess decomposition and filtering indicates an approximately exponential decline in excess Delta(14)CO(2) over 1967-2005 with an e-folding time of 18 years. The seasonal cycle from 1954 until 1980 had a maximum in the late (austral) summer, a minimum in winter, with peak-to-trough amplitude that peaked at 20aEuro degrees in 1966. For the period 1980-1989, a new seasonal cycle emerged, with a maximum in winter and a minimum in late summer/early autumn and peak-to-trough amplitude of 3.5aEuro degrees, transitioning to a new seasonal structure after about 1990.Biogeochemistry 07/2011; 104(1-3):5-22. · 3.07 Impact Factor -
Article: A new method for analyzing (14)C of methane in ancient air extracted from glacial ice
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ABSTRACT: We present a new method developed for measuring radiocarbon of methane ((14)CH(4)) in ancient air samples extracted from glacial ice and dating 11,000-15,000 calendar years before present. The small size (similar to 20 mu g CH(4) carbon), low CH(4) concentrations ([CH(4)], 400-800 parts per billion [ppb]), high carbon monoxide concentrations ([CO]), and low (14)C activity of the samples created unusually high risks of contamination by extraneous carbon. Up to 2500 ppb CO in the air samples was quantitatively removed using the Sofnocat reagent. (14)C procedural blanks were greatly reduced through the construction of a new CH(4) conversion line utilizing platinized quartz wool for CH(4) combustion and the use of an ultra-high-purity iron catalyst for graphitization. The amount and (14)C activity of extraneous carbon added in the new CH(4) conversion line were determined to be 0.23 +/- 0.16 pg and 23.57 +/- 16.22 pMC, respectively. The amount of modern (100 pMC) carbon added during the graphitization step has been reduced to 0.03 mu g. The overall procedural blank for all stages of sample handling was 0.75 0.38 pMC for similar to 20-mu g, (14)C-free air samples with [CH(4)] of 500 ppb. Duration of the graphitization reactions for small (<25 mu g C) samples was greatly reduced and reaction yields improved through more efficient water vapor trapping and the use of a new iron catalyst with higher surface area. (14)C corrections for each step of sample handling have been determined. The resulting overall (14)CH(4) uncertainties for the ancient air samples are similar to 1.0 pMC.Radiocarbon 11/2008; 50(1):53-73. · 2.84 Impact Factor
