Dear Zolt,

CO2 may diffuse through PE-bottles and, therefore, will change the
d13C of dissolved inorganic carbonate species. The process should
depend on the pH of the solution but should generally lead to
increasing d13C values in DIC.

Cheers & happy X-mas
Michael

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Dr. Michael E. Boettcher
Biogeochemistry Department
Max Planck Institute for Marine Microbiology
Celsiusstr.1
D-28359 Bremen
Germany