Articles | Volume 13, issue 18
Research article
22 Sep 2016
Research article |  | 22 Sep 2016

Clumped isotopes in near-surface atmospheric CO2 over land, coast and ocean in Taiwan and its vicinity

Amzad Hussain Laskar and Mao-Chang Liang

Abstract. Molecules containing two rare isotopes (e.g., 13C18O16O in CO2), called clumped isotopes, in atmospheric CO2 are powerful tools to provide an alternative way to independently constrain the sources of CO2 in the atmosphere because of their unique physical and chemical properties. We presented clumped isotope data (Δ47) in near-surface atmospheric CO2 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 Δ47 signature in atmospheric CO2 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 δ13C and δ18O cannot provide. We also explored the potential of Δ47 to identify/quantify the contribution of CO2 from various sources. Atmospheric CO2 over ocean was found to be in thermodynamic equilibrium with the surrounding surface sea water. Respired CO2 was also in close thermodynamic equilibrium at ambient air temperature. In contrast, photosynthetic activity result in significant deviation in Δ47 values from that expected thermodynamically. The disequilibrium could be a consequence of kinetic effects associated with the diffusion of CO2 in and out of the leaf stomata. We observed that δ18O and Δ47 do not vary similarly when photosynthesis was involved unlike simple water–CO2 exchange. Additionally we obtained Δ47 values of car exhaust CO2 that were significantly lower than the atmospheric CO2 but higher than that expected at the combustion temperature. In urban and suburban regions, the Δ47 values were found to be lower than the thermodynamic equilibrium values at the ambient temperature, suggesting contributions from local combustion emission.

Short summary
We present clumped isotope data in air CO2 over land and ocean in Taiwan and its vicinity. CO2 over ocean is in thermodynamic equilibrium with the surface sea water and deviated significantly in urban and suburban areas due contribution from combustion emission. Photosynthetic activity deviates residual CO2 from thermodynamic equilibrium but respiration does not. Deviations from thermodynamic equilibrium by various interactions in different environments are presented.
Final-revised paper