T01_P09

Assessing radiocarbon blanks associated with solid phase extraction of dissolved organic carbon from sea water

Schlagenhauff S¹,  Grotheer H¹, Niggemann J², Dittmar T², Mollenhauer G^1,3

¹Alfred Wegener Institute, Bremerhaven, Germany, ²Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany, ³Marum Center for Marine Environmental Research and Department of Geosciences, Bremen, Germany

Radiocarbon analysis of marine dissolved organic carbon (DOC) gives insight into mixing timescales and C-storage, but technical challenges make obtaining samples for radiocarbon analysis costly and time consuming. Solid phase extraction (SPE) is a common technique to access not only the radiocarbon age of the SPE-DOC pool but also its molecular composition. The combination of SPE and low mass radiocarbon analysis using the MICADAS is a promising path to increase sample resolution but care must be taken to ensure confidence in the results. The aim of this work is to determine the amount and F¹⁴C value of extraneous carbon (Cex) in solid phase extracted samples to be analyzed on the MICADAS.  The Cex of modified styrene divinyl benzene polymer (PPL) cartridges was investigated indirectly by measuring a ¹⁴C free fossil standard, a modern standard (F¹⁴C =1), as well as fresh water (Suwannee River 2R101N) and marine (NELHA) DOC reference materials. These standards were compared systematically across PPL cartridge sizes and lots. The Cex mass contribution from the SPE ranged from 5.5-17µgC while the F¹⁴C value of the blank was unique to each cartridge lot. Interestingly, no correlation was found between the size of the cartridge used and the amount of Cex introduced into the samples. Since it is not possible to predict or influence the F¹⁴C of blanks in each cartridge lot, when working with low mass SPE samples, it is necessary to incorporate thorough blank assessment procedure.