Sensitivity analysis and quantification of uncertainty for isotopic mixing relationships in carbon cycle research

Zobitz, John M.; Keener, James P.; Schnyder, H.; Bowling, David R.

doi:10.1016/j.agrformet.2006.01.003

Cited by 118 publications

(142 citation statements)

References 36 publications

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“…The applicability of the Keeling plot has been proven in environments where the mixing process between air masses occurs by bulk advection (Bowling and Massman, 2011;Buchmann et al, 1998;Zobitz et al, 2006). However, the assumption of the model for diffusive environments (e.g., from the air-filled porosity of soils to the open atmosphere) could lead to misinterpretation relative to the isotopic ratio of the source (Risk and Kellman, 2008;Nickerson and Risk, 2009).…”

Section: Discussionmentioning

confidence: 99%

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

Garcia-Anton

Cuezva

Fernández-Cortés

et al. 2017

Atmospheric Environment

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This study characterizes the processes involved in seasonal CO 2 exchange between soils and shallow underground systems and explores the contribution of the different biotic and abiotic sources as a function of changing weather conditions. We spatially and temporally investigated five karstic caves across the Iberian Peninsula, which presented different microclimatic, geologic and geomorphologic features. The locations present Mediterranean and Oceanic climates. Spot air sampling of CO 2 (g) and δ 13 CO 2 in the caves, soils and outside atmospheric air was periodically conducted. The isotopic ratio of the source contribution enhancing the CO 2 concentration was calculated using the Keeling model. We compared the isotopic ratio of the source in the soil (δ 13 C s -soil) with that in the soil-underground system (δ 13 C s -system).Although the studied field sites have different features, we found common seasonal trends in their values, which suggests a climatic control over the soil air CO 2 and the δ 13 CO 2 of the sources of CO 2 in the soil (δ 13 C s -soil) and the system (δ 13 C s -system). The roots respiration and soil organic matter degradation are the main source of CO 2 in underground environments, and the inlet of the gas is mainly driven by diffusion and advection. Drier and warmer conditions enhance soil-exterior CO 2 interchange, reducing the CO 2 concentration and increasing the δ 13 CO 2 of the soil air. Moreover, the isotopic ratio of the source of CO 2 in both the soil and the system tends to heavier values throughout the dry and warm season.We conclude that seasonal variations of soil CO 2 concentration and its 13 C/ 12 C isotopic ratio are mainly regulated by thermo-hygrometric conditions. In cold and wet seasons, the increase of soil moisture reduces soil diffusivity and allows the storage of CO 2 in the subsoil. During dry and warm seasons, the evaporation of soil water favours diffusive and advective transport of soil-derived CO 2 to the atmosphere. The soil CO 2 diffusion is enough important during this season to modify the isotopic ratio of soil produced CO 2 (3-6‰ heavier). Drought induces release of CO 2 with an isotopic ratio heavier than produced by organic sources. Consequently, climatic conditions drive abiotic processes that turn regulate a seasonal storage of soilproduced CO 2 within soil and underground systems. The results here obtained imply that abiotic emissions of soil-produced CO 2 must be an inherent consequence of droughts, which intensification has been forecasted at global scale in the next 100 years.

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Section: Discussionmentioning

confidence: 99%

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

Garcia-Anton

Cuezva

Fernández-Cortés

et al. 2017

Atmospheric Environment

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“…Using an ordinary least squares (OLS) regression (Zobitz et al, 2006), the source delta value can be obtained by regressing the difference between the difference in the product of the mole fractions and the isotopic values against the background and observed mole fractions. In this case, the ' obs' value is one of the two polluted towers (Towers 2 or 3), and the 'bg' value is the background tower (Tower 1).…”

Section: Regression Plot Data Analysismentioning

confidence: 99%

Carbon monoxide isotopic measurements in Indianapolis constrain urban source isotopic signatures and support mobile fossil fuel emissions as the dominant wintertime CO source

Vimont

Turnbull

Petrenko

et al. 2017

Elementa: Science of the Anthropocene

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Vimont, IJ, et al. 2017 Carbon monoxide isotopic measurements in Indianapolis constrain urban source isotopic signatures and support mobile fossil fuel emissions as the dominant wintertime CO source. Elem Sci Anth, 5: 63. DOI: https://doi.org/10.1525/elementa.136 IntroductionUrban carbon monoxide (CO) is a regulated pollutant that impacts human health and influences atmospheric chemistry via its interaction with OH and its role in tropospheric ozone production. Urban emissions are also an important component of the global CO budget (Crutzen, 1973;Crutzen, 1979;Logan et al., 1981;Duncan et al., 2007). Within urban areas of the United States, CO emissions inventories may be inaccurate by as much as a factor of two (e.g. Turnbull et al., 2015;Parrish et al., 2006;Graven et al., 2009;LaFranchi et al., 2013; EPA NEI 2011). In addition to the atmospheric chemistry and health impacts, CO has been explored as a tracer for fossil fuel derived CO 2 (CO 2ff ) (Meijer et al., 1996;Levin and Karstens, 2007;Turnbull et al., 2006;Vogel et al., 2010;Turnbull et al., 2011; Turnbull et al., 2015). This method relies on an assumption that CO is produced entirely by combustion, which is not always true within urban regions (Turnbull et al., 2015). Turnbull et al. (2015) found that during winter at Indianapolis, using CO as a correlate tracer yielded CO 2ff enhancements that were in good agreement with those from 14 CO 2 measurements. This suggested that during the winter at Indianapolis, non-fossil fuel sources of CO do not contribute significantly. In contrast, during the summer, there is weaker correlation between CO and 14 C-derived CO 2ff , suggesting another summertime source of CO in Indianapolis (Turnbull et al., 2015) and in other locations (Turnbull et al., 2006;Miller et al., 2012). Stable isotopic measurements of urban CO can help quantify individual CO sources and sinks and provide an improved understanding of seasonal changes in the urban CO budget (e.g. Stevens et al., 1972;Brenninkmeijer, 1993;Conny, 1998).In order to quantify the sources and sinks of CO via isotopic analysis, the 13 CO and C 18 O isotopic signatures need to be known (Stevens et al., 1972;Brenninkmeijer, 1993;Rockmann and Brenninkmeijer, 1997; O) in air during the winters of 2013-14 and 2014-15 at tall tower sampling sites in and around Indianapolis, USA. A tower located upwind of the city was used to quantitatively remove the background CO signal, allowing for the first unambiguous isotopic characterization of the urban CO source and yielding 13CO of -27.7 ± 0.5‰ VPDB and C 18O of 17.7 ± 1.1‰ VSMOW for this source. We use the tower isotope measurements, results from a limited traffic study, as well as atmospheric reaction rates to examine contributions from different sources to the Indianapolis CO budget. Our results are consistent with earlier findings that traffic emissions are the dominant source, suggesting a contribution of 96% or more to the overall Indianapolis wintertime CO emissions. Our results are also consistent with the hypothesis ...

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“…We used measurements of CO 2 and 18 O taken between 20:00 and 04:00 h and data from four inlets located at 0.05, 1.0, 1.5 and 3.0 m together to examine nightly R . Model I regressions were used to avoid negatively skewed intercepts (Zobitz et al, 2006). To assess the stability of isotopic sources for each night, we compared Keeling intercepts to the isotopic mixing line proposed by Miller and Tans (2003) (Miller and Tans, 2003;Lai et al, 2004).…”

Section: Tunable Diode Laser Systemmentioning

confidence: 99%

“…We employed a two-ended mixing model to estimate δ R (Keeling, 1958;Flanagan et al, 1996;Zobitz et al, 2006). δ R represents the 18 O composition of the net ecosystem flux associated with respiration as well as abiotic invasion flux between leaves and the atmosphere (Francey and Tans, 1987) and soils and the atmosphere (Tans, 1998).…”

Section: Tunable Diode Laser Systemmentioning

confidence: 99%

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

et al. 2013

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We conducted high frequency measurements of the δ¹⁸O value of atmospheric CO₂ from a juniper (Juniperus monosperma) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ¹⁸O value of ecosystem respiration (δ_R). Rain pulses reset δ_R with the dominant water source isotope composition, followed by progressive enrichment of δ_R. Transpiration (E_T) was significantly related to post-pulse δ_R enrichment because the leaf water δ¹⁸O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δ_R enrichment was correlated with both E_T and the ratio of E_T to soil evaporation (E_T/E_S). In contrast, the soil water δ¹⁸O value was relatively stable and δ_R enrichment was not correlated with E_S. Model simulations captured the large post-pulse δ_R enrichments only when the offset between xylem and leaf water δ¹⁸O value was modeled explicitly and when a gross flux model for CO₂ retro-diffusion was included. Drought impacts δ_R through the balance between evaporative demand, which enriches δ_R, and low soil moisture availability, which attenuates δ_R enrichment through reduced E_T. The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δ_R enrichment with increasing drought

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Sensitivity analysis and quantification of uncertainty for isotopic mixing relationships in carbon cycle research

Cited by 118 publications

References 36 publications

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

Abiotic and seasonal control of soil-produced CO2 efflux in karstic ecosystems located in Oceanic and Mediterranean climates

Carbon monoxide isotopic measurements in Indianapolis constrain urban source isotopic signatures and support mobile fossil fuel emissions as the dominant wintertime CO source

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

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