A new high precision ¹⁴CO₂ time series for North American continental air

Abstract

We develop a high precision Δ14CO2 measurement capability in 2‐5 L samples of whole air for implementation within existing greenhouse gas flask sampling networks. The long‐term repeatability of the measurement is 1.8‰ (1‐sigma), as determined from repeated analyses of quality control standards and replicate extraction and measurement of authentic field samples. In a parallel effort, we have begun a Δ14CO2 measurement series from NOAA/ESRL’s (formerly NOAA/CMDL) surface flask sampling site at Niwot Ridge, Colorado, USA (40.05°N, 105.58°W, 3475 masl) in order to monitor the isotopic composition of carbon dioxide in relatively clean air over the North American continent. Δ14CO2 at Niwot Ridge decreased by 5.7‰/yr from 2004 to 2006, with a seasonal amplitude of 3‐5‰. A comparison with measurements from the free troposphere above New England, USA (41°N, 72°W) indicates that the Δ14CO2 series at the two sites are statistically similar at timescales longer than a few days to weeks (i.e., those of synoptic scale variations in transport), suggesting that the Niwot Ridge measurements can be used as a proxy for North American free tropospheric air in future carbon cycle studies.

Estimation of continuous anthropogenic CO<sub>2</sub>: model-based evaluation of CO<sub>2</sub>, CO, δ<sup>13</sup>C(CO<sub>2</sub>) and Δ<sup>14</sup>C(CO<sub>2</sub>) tracer methods

“…4m) and 14 C(CO 2 ) bg (Fig. 4n) as has already been described in Turnbull et al (2007). Thus, precise and accurate 14 C(CO 2 ) measurements are important for fuel CO 2 determination.…”

Modern Radiocarbon Levels for Northwestern Mexico Derived from Tree Rings: A Comparison with Northern Hemisphere Zones 2 and 3 Curves

“…Yet in this case, the fossil fuel effect cannot be ruled out as the reported sampling site is indeed very close to Mexico City, inside the Valley of Mexico. (Levin and Kromer 2004), and Niwot Ridge, Colorado USA (gray line) (Turnbull et al 2007). Vertical error bars correspond to ±1 horizontal error bars reflect the number of years comprising samples analyzed by LSC (see Table 1).…”

“…The common interval time span of the chronology was 1829 to 2005 and had a mean sensitivity of 0.25, a correlation of 0.537 among all radii, 0.534 between trees, 0.719 within trees, signal-to-noise ratio of 30.9, and variance in the first eigenvector of 55.5%. In the last decade, several dendrochronologies have been constructed for northern Mexico using Douglas-fir (Therrell et al 2002;Cleaveland et al 2003;González-Elizondo et al 2005;Villanueva-Diaz et al 2007), including the master tree-ring chronology for the sampling site (Villanueva-Diaz et al 2008). …”

Atmospheric measurement of point source fossil CO<sub>2</sub> emissions

“…In the case of grass samples, pieces of grass were acid washed (0.5 M HCl at 85 • C for 30 min) to remove any adhering material, then rinsed to neutral and freeze dried, prior to sealed tube combustion with copper oxide and silver wire at 900 • C. The resulting CO 2 was cryogenically purified. CO 2 from either sample type was then reduced to graphite with hydrogen over an iron catalyst, using methods adapted from Turnbull et al (2007). The 14 C content was measured using accelerator mass spectrometry at GNS Science .…”

“…In the current atmosphere, 1 ppm of added CO 2 ff decreases 14 CO 2 by about 2.6 ‰ 14 CO 2 can be determined directly from measurements of 14 C in CO 2 extracted from flask samples of air (e.g. Turnbull et al, 2007;Graven et al, 2007). The 14 C content of CO 2 is also maintained in carbon assimilated by plants so that the average 14 C of the assimilated CO 2 , and hence the overlying atmosphere at the time of uptake, can be determined from the 14 C content of plant materials (e.g.…”