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

Autor: Amzad Laskar, Mao-Chang Liang
Rok vydání: 2016
DOI: 10.5194/bg-2016-106
Popis: Molecules containing two rare isotopes (e.g., 13C18O16O in CO2), called clumped isotopes, 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 present clumped isotope data (Δ47) in near surface atmospheric CO2 from urban, sub-urban, ocean, coast, high mountain (~3.3 km a.s.l.) and forest in Taiwan and its vicinity. The primary goal of the study is to use the unique Δ47 signature in air CO2 to show the extents of its deviations from thermodynamic equilibrium due to different processes in a variety of environments, which the commonly used tracers such as δ13C and δ18O cannot provide. We also explore the potential of Δ47 in air CO2 to identify/quantify the contribution from various sources. Atmospheric CO2 over ocean is found to be in thermodynamic equilibrium with the surrounding surface sea water. Also respired CO2 is in close thermodynamic equilibrium at ambient air temperature. In contrast, photosynthetic activity results in significant deviation in Δ47 values from that expected thermodynamically demonstrated using CO2 collected from a controlled greenhouse. The disequilibrium could be a consequence of kinetic effects associated with the diffusion of CO2 in and out of the leaf stomata. We also observe that δ18O and Δ47 behave differently in response to photosynthesis unlike simple water-CO2 exchange where the time scale of equilibration of the two is similar. Additionally, the measured Δ47 values in car exhaust CO2 are significantly lower than the atmospheric CO2 but higher than that expected at the combustion temperature. In urban and sub-urban regions, the Δ47 values are found to be lower than the thermodynamic equilibrium values at the ambient temperature, suggesting contributions from local combustion emissions.
Databáze: OpenAIRE