Clumped isotopes in near-surface atmospheric CO<sub>2</sub> over land, coast and ocean in Taiwan and its vicinity
Molecules containing two rare isotopes (e.g., <sup>13</sup>C<sup>18</sup>O<sup>16</sup>O in CO<sub>2</sub>), called clumped isotopes, in atmospheric CO<sub>2</sub> are powerful tools to provide an alternative way to independently constrain...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/5297/2016/bg-13-5297-2016.pdf |
| Summary: | Molecules containing two rare isotopes (e.g., <sup>13</sup>C<sup>18</sup>O<sup>16</sup>O in
CO<sub>2</sub>), called clumped isotopes, in atmospheric CO<sub>2</sub> are powerful
tools to provide an alternative way to independently constrain the sources of
CO<sub>2</sub> in the atmosphere because of their unique physical and chemical
properties. We presented clumped isotope data (Δ<sub>47</sub>) in near-surface
atmospheric CO<sub>2</sub> from urban, suburban, ocean, coast, high mountain
( ∼ 3.2 km a.s.l.) and forest in Taiwan and its vicinity. The primary
goal of the study was to use the unique Δ<sub>47</sub> signature in
atmospheric CO<sub>2</sub> to show the extents of its
deviations from thermodynamic equilibrium due to different processes such as
photosynthesis, respiration and local anthropogenic emissions, which the
commonly used tracers such as δ<sup>13</sup>C and δ<sup>18</sup>O cannot provide. We also explored the potential of Δ<sub>47</sub> to identify/quantify the contribution of CO<sub>2</sub> from various sources. Atmospheric CO<sub>2</sub> over ocean was found to be in thermodynamic equilibrium with the surrounding surface sea water. Respired CO<sub>2</sub> was also in close thermodynamic
equilibrium at ambient air temperature. In contrast, photosynthetic activity
result in significant deviation in Δ<sub>47</sub> values from that expected
thermodynamically. The disequilibrium could be a consequence of kinetic
effects associated with the diffusion of CO<sub>2</sub> in and out of the leaf
stomata. We observed that δ<sup>18</sup>O and Δ<sub>47</sub> do not vary
similarly when photosynthesis was involved unlike simple water–CO<sub>2</sub>
exchange. Additionally we obtained Δ<sub>47</sub> values of car exhaust
CO<sub>2</sub> that were significantly lower than the atmospheric CO<sub>2</sub> but
higher than that expected at the combustion temperature. In urban and
suburban regions, the Δ<sub>47</sub> values were found to be lower than the
thermodynamic equilibrium values at the ambient temperature, suggesting
contributions from local combustion emission. |
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| ISSN: | 1726-4170 1726-4189 |