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Determination of radiocarbon in marine sediment porewater dissolved organic carbon by thermal sulfate reduction
Author(s) -
Johnson Leah,
Komada Tomoko
Publication year - 2011
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2011.9.485
Subject(s) - dissolved organic carbon , seawater , environmental chemistry , sediment , sulfate , total organic carbon , artificial seawater , organic matter , carbon fibers , oxidizing agent , chemistry , mineralogy , environmental science , geology , oceanography , materials science , paleontology , organic chemistry , composite number , composite material
Fractional abundances of 14 C and 13 C in dissolved organic carbon (DOC) in sediment porewaters may hold important clues about organic carbon cycling in sediments. Yet there is a dearth of isotopic signatures for porewater DOC because of the difficulty associated with oxidizing DOC in seawater. At present, marine DOC can be processed for analyses of 14 C and 13 C with high precision and minimal contamination by ultraviolet (UV) oxidation, but this method is resource intensive and could be difficult to implement. To resolve this, a thermal sulfate reduction (TSR) method, previously developed to determine 13 C in seawater DOC (Fry et al. 1996), was modified and tested for 14 C and 13 C determination in porewater DOC. CO 2 yields from six test materials ranged between 90% and 108%. δ 13 C signatures were reproducible within ± 0.4‰ and agreed with independently known values. The 14 C and δ 13 C values of porewater DOC obtained by TSR and UV oxidation showed excellent agreement. Application of TSR to archived porewater DOC samples from a sediment incubation experiment revealed notable changes in isotopic values that were not readily discerned in the DOC concentration data alone. The total uncertainty in the 14 C values after blank correction was ± 0.005 to 0.02 fraction modern (Fm) for sample sizes ranging between 143 and 560 µg C. For systems where precision on the order of ± 0.02 Fm is acceptable, TSR could be a viable alternative to UV oxidation for processing small, concentrated marine DOC samples.