Assessments of radiocarbon measurements of dissolved organic carbon for small/ultra-small samples by MICADAS

Abstract The radiocarbon ( 14 C) composition of dissolved organic carbon (DOC) provides critical constraints on its sources, transformation and fates. UV-irradiation is an effective approach to completely oxidize DOC to CO 2 for radiocarbon measurements. In this study, we aimed to evaluate the performance of radiocarbon measurements for small/ultra-small size natural DOC samples using mini carbon dating system (MICADAS) using CO 2 gas as the target. The procedure blank was estimated by the indirect method using two reference standards, oxalic acid II (OXII, modern) and glycine (dead). We modified the UV-generated CO 2 purification and collection approaches for freshwater and marine samples based on the sample salinity. The results showed that the procedure blanks were low and statistically identical for the two approaches, with the carbon mass of 1.65 ± 0.50 µgC and the F 14 C value of 0.4848 ± 0.1455 for freshwater sample processing, and 1.70 ± 0.51 µgC with F 14 C value of 0.4118 ± 0.1235 for marine sample. The UV-generated CO 2 gases in small/ultra-small size (30 – 126 µgC) DOC samples from the Pearl River-Estuary-northern South China Sea continuum were further measured and the data correction was based on those corresponding procedure blank. Our results were comparable to previous studies obtained with large sample size and graphite target for radiocarbon measurements. We concluded that the UV-oxidation system combined with MICADAS gaseous CO 2 measurements at OUC is particularly suitable for small/ultra-small size DOC samples with high throughput, and this system provided powerful tools to acquire radiocarbon data to understand the compositional, spatial and temporal variabilities of DOC.