High precision determination of carbon isotope composition and concentration of dissolved inorganic carbon in seawaters

Abstract

Determination of the isotopic composition and concentration of dissolved inorganic carbon (DIC) in sea water requires not only high measurement accuracy, but also the development of unified approaches to data standardization and material collection. In this work, we studied the effect of sampling methods (“in a container” and “in a vial with acid”, with and without the toxin) on the results of determining the values of δ13C(DIC) and the concentration of DIC in sea water. The analytical protocol was described in detail, based on many years of experience in the selection, measurement and standardization of data obtained for a large number of water samples of the Arctic seas. According to this protocol, the values of δ13C(DIC) and [DIC] can be determined with an error of less than 0.05 ‰ (1σ) and 4.5 rel.% respectively. It has been shown that sampling “in a vial with acid” with their storage for 4 months is accompanied by significant contamination by atmospheric carbon dioxide with an underestimation of δ13C(DIC) values by an average of 0.3–0.8 ‰ and an overestimation of [DIC] values by an average of two times. The absence of the toxin that stops biological activity does not lead to significant shifts in the DIC concentration, but it strongly affects the δ13C(DIC) values, which become underestimated by an average of 1 ‰. Using sampling “in a container”, with toxin addition, and following other recommendations, the samples retain the isotope and concentration parameters of DIC for at least year.