Rodger Sparks

Bio: Rodger Sparks is an academic researcher from GNS Science. The author has contributed to research in topics: Radiocarbon dating & Accelerator mass spectrometry. The author has an hindex of 7, co-authored 11 publications receiving 414 citations.

Comparison of 14CO2, CO, and SF6 as tracers for recently added fossil fuel CO2 in the atmosphere and implications for biological CO2 exchange

Abstract: [1] We use the nearly ideal tracer 14CO2 to estimate the fossil fuel CO2 enhancement in boundary layer air at two sites in New England and Colorado Improved Δ14C measurement precision of 16–26‰ provides fossil fuel CO2 detection capability of 08–15 ppm Using the indirect tracers CO and SF6, we obtain two additional independent estimates of the fossil fuel CO2 component, and we assess the biases in these methods with respect to the 14CO2-based estimates The SF6-based estimates vary considerably from the 14CO2-based estimates, and are at times implausibly large The CO-based estimates are less variable, but show seasonally coherent biases with respect to the 14CO2 method

The 13C, 14C, and 18O isotopic composition of CO, CH4, and CO2 in the higher southern latitudes lower stratosphere

Abstract: Large air samples were collected in the lower stratosphere (10–12 km) from 43° to 85°S in June 1993, using a special compressor system. For the important trace gases CO, CH4 and CO2, concentration and isotopic analyses were carried out and significant correlations were discovered. The 14CO isotope is considerably in excess of tropospheric levels with very high values from 40 to 120 14CO molecules/cm3 STP (corresponding to 12,500 percent modern carbon, at 30 ppbv), and is negatively correlated with CO. The linear relationship is used to estimate OH to be 2.9×105 cm−3. The 18O/16O ratios for CO are the lowest ever measured and reflect the inverse kinetic isotope effect in the oxidation of CO by OH. The 13C/12C ratios for CO are not much different from tropospheric values and confirm that fractionation is small but also that the in situ contribution from CH4 oxidation is minor. For CH4 a correlation between δ13C and concentration exists from which a fractionation factor for the sink reaction (k12/k13) of about 1.012 is calculated, well in excess of results from laboratory experiments for OH +CH4. The most plausible explanation presently is the removal of approximately 9% of CH4 by Cl atoms, which, as laboratory experiments have just confirmed, induces a very large fractionation. We also reveal a linear correlation between 14CO and 14CO2, precursor and product. Finally, an analysis of potential vorticity shows a structure that seems to give an overall agreement with the trace gas variations.

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

Abstract: We develop a high precision Δ 14 CO 2 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%o (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 Δ 14 CO 2 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. Δ 14 CO 2 at Niwot Ridge decreased by 5.7‰/yr from 2004 to 2006, with a seasonal amplitude of 3-5%o. A comparison with measurements from the free troposphere above New England, USA (41°N, 72°W) indicates that the Δ 14 CO 2 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.

Tropospheric 14CO2 at Wellington, New Zealand: the world’s longest record

Abstract: Measurements of near-sea-level tropospheric Δ14CO2 have been made at Wellington, New Zealand since December 1954; these measurements comprise the longest such record available. The Δ14C rose from −10‰ in 1955 peaking at 695‰ in 1965 as a result of “bomb 14C” production, before falling thereafter to the present day (2005) value of 73‰. The Δ14C 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 14C-enriched CO2 to the biospheric and oceanic pools together with ongoing release of 14C-free CO2 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 Δ14CO2 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 20‰ 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 3.5‰, transitioning to a new seasonal structure after about 1990.

Accelerator and beamline upgrades at the AMS facility of GNS Science, New Zealand

Abstract: This facility report discusses progress and outcomes of three major upgrade projects on the AMS facility at GNS Science, New Zealand. Converting the EN-tandem accelerator from a belt-driven charging system to a Pelletron has reduced the fluctuations on the terminal voltage by at least one order of magnitude. The Pelletron system has been operating for ca . 10,000 h and without problems. Interference-free detection of 26 Al 7+ is now possible with a new beamline that features a Wien velocity filter dispersing perpendicular with respect to the analysing magnet’s bending plane. The detector spectra for 10 Be 3+ and, to a lesser degree, for 14 C 4+ have lower backgrounds than in the old setup. Computer control of ca . half of all parameters along the AMS beamlines is implemented through a distributed network built from a combination of off-the-shelf and in-house built electronic interfaces. Separate from this network is AMS measurement control, for real-time measurement of isotope detector signals and control of the isotope-switching part of the inflection system. Current projects are replacement of the AMS measurement control system and expansion of the parameter control network to all beamlines.

Atmospheric Radiocarbon for the Period 1950–2010

Abstract: We present a compilation of tropospheric 14 CO 2 for the period 1950–2010, based on published radiocarbon data from selected records of atmospheric CO 2 sampling and tree-ring series. This compilation is a new version of the compilation by Hua and Barbetti (2004) and consists of yearly summer data sets for zonal, hemispheric, and global levels of atmospheric 14 C. In addition, compiled (and extended) monthly data sets for 5 atmospheric zones (3 in the Northern Hemisphere and 2 in the Southern Hemisphere) are reported. The annual data sets are for use in regional and global carbon model calculations, while the extended monthly data sets serve as calibration curves for 14 C dating of recent, short-lived terrestrial organic materials. DOI: 10.2458/azu_js_rc.v55i2.16177

An inverse modeling approach to investigate the global atmospheric methane cycle

Abstract: Estimates of the global magnitude of atmospheric methane sources are currently mainly based on direct flux measurements in source regions. Their extrapolation to the entire globe often involves large uncertainties. In this paper, we present an inverse modeling approach which can be used to deduce information on methane sources and sinks from the temporal and spatial variations of atmospheric methane mixing ratios. Our approach is based on a three-dimensional atmospheric transport model which, combined with a tropospheric background chemistry module, is also employed to calculate the global distribution of OH radicals which provide the main sink for atmospheric methane. The global mean concentration of OH radicals is validated with methyl chloroform (CH3CCl3) observations. The inverse modeling method optimizes the agreement between model-calculated and observed methane mixing ratios by adjusting the magnitudes of the various methane sources and sinks. The adjustment is constrained by specified a priori estimates and uncertainties of the source and sink magnitudes. We also include data on the 13C/12C isotope ratio of atmospheric methane and its sources in the model. Focusing on the 1980s, two scenarios of global methane sources are constructed which reproduce the main features seen in the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) methane observations. Differences between these two scenarios may probably be attributed to underestimated a priori uncertainties of wetland emissions. Applying the inverse model, the average uncertainty of methane source magnitudes could be reduced by at least one third. We also examined the decrease in the atmospheric methane growth rate during the early 1990s but could not uniquely associate it with changes in particular sources.

The effect of vertically resolved soil biogeochemistry and alternate soil C and N models on C dynamics of CLM4

Abstract: Soils are a crucial component of the Earth system; they comprise a large portion of terrestrial carbon stocks, mediate the supply and demand of nutrients, and influence the overall response of terrestrial ecosystems to perturbations. In this paper, we develop a new soil biogeochemistry model for the Community Land Model, version 4 (CLM4). The new model includes a vertical dimension to carbon (C) and nitrogen (N) pools and transformations, a more realistic treatment of mineral N pools, flexible treatment of the dynamics of decomposing carbon, and a radiocarbon ( 14 C) tracer. We describe the model structure, compare it with site-level and global observations, and discuss the overall effect of the revised soil model on Community Land Model (CLM) carbon dynamics. Site-level comparisons to radiocarbon and bulk soil C observations support the idea that soil C turnover is reduced at depth beyond what is expected from environmental controls for temperature, moisture, and oxygen that are considered in the model. In better agreement with observations, the revised soil model predicts substantially more and older soil C, particularly at high latitudes, where it resolves a permafrost soil C pool. In addition, the 20th century-C dynamics of the model are more realistic than those of the baseline model, with more terrestrial C uptake over the 20th century due to reduced N downregulation and longer turnover times for decomposing C.

Mass-independent isotope effects in planetary atmospheres and the early solar system.

Abstract: A class of isotope effects that alters isotope ratios on a mass-independent basis provides a tool for studying a wide range of processes in atmospheres of Earth and other planets as well as early processes in the solar nebula. The mechanism for the effect remains uncertain. Mass-independent isotopic compositions have been observed in O3, CO2, N2O, and CO in Earth's atmosphere and in carbonate from a martian meteorite, which suggests a role for mass-independent processes in the atmosphere of Mars. Observed mass-independent meteoritic oxygen and sulfur isotopic compositions may derive from chemical processes in the presolar nebula, and their distributions could provide insight into early solar system evolution.