UC Irvine

The standard procedure for storing/preserving seawater dissolved organic carbon (DOC) samples after field collection is by freezing (-20°C) until future analysis can be made. However, shipping and receiving large numbers of these samples without thawing presents a significant logistical problem and large monetary expense. Access to freezers can also be limited in remote field locations. We therefore test an alternative method of preserving and storing samples for the measurement of DOC concentrations ([DOC]), stable carbon (δ13C), and radiocarbon (as δ14C) isotopic values via UV photooxidation (UVox). We report a total analytical reproducibility of frozen DOC samples to be [DOC]±1.3 μM, δ14C±9.4‰, and δ13C±0.1‰, comparable to previously reported results (Druffel et al. 2013). Open Ocean DOC frozen versus acidified duplicates were on average offset by δDOC±1.1 μM, δδ14C± -1.3‰, and δδ13C± -0.1‰. Coastal Ocean frozen vs. acidified sample replicates, collected as part of a long-term (380-day) storage experiment, had larger, albeit consistent offsets of δDOC±2.2 μM, δδ14C±1.5‰, and δδ13C± -0.2‰. A simple isotopic mass balance of changes in [DOC], δ14C, and δ13C values reveals loss of semi-labile DOC (2.2±0.6 μM, δ14C=-94±105‰, δ13C=-27±10‰; n=4) and semi-recalcitrant DOC (2.4±0.7 μM, δ14C=-478±116‰, δ13C=-23.4±3.0‰; n=3) in Coastal and Open Ocean acidified samples, respectively.