Using Radiocarbon to Assess the Abundance, Distribution, and Nature of Labile Organic Carbon in Marine Sediments

19 pages, 4 figures, 1 table, supporting information https://doi.org/10.1029/2020GB006676.-- Data Availability Statement: Original analytical data from this study have been submitted to the following FAIR-aligned data repository (US Antarctic Program Data Center; Dataset ID: 601319; DOI: 10.15784/601319). However, all of this information is provided in the Supplemental Data section of this paper as well (Tables S1 and S2 and Figure S1)Positive 14C gradients have recently been observed within the surface mixed layer of several continental-margin sediments. The best explanation for these positive 14C gradients is the occurrence and rapid degradation of labile organic carbon (LOC) in the upper 5–10 cm of the seabed. Based on a two-component model for sedimentary organic matter (i.e., a planktonic labile component and an older refractory component), bulk 14Corg data were used to determine the abundances of LOC within the surface mixed layers of three cores from the West Antarctic Peninsula (WAP) shelf and one core from San Clemente Basin (California Borderland). LOC contents in surface samples from the four stations varied from 0.5 to 1.1 mg/cm3, comprising 20% (San Clemente Basin) to 80% (WAP, Sta. G) of the total organic carbon. By incorporating a steady state diagenetic model and particle-mixing bioturbation coefficients, the LOC profiles were used to determine LOC turnover times (LOC τ) and LOC e-folding depths. The LOC τ values for the West Antarctic Peninsula sediments varied from 0.09 to 0.59 years, whereas the LOC τ value from the San Clemente Basin core was 63 years. The LOC e-folding depths for the WAP stations varied from 0.8 to 3.4 cm, in contrast to the LOC e-folding depth in San Clemente Basin, which was 4.0 cm. LOC characteristics from the four cores examined in this study were compared to LOC data in the literature as a means of substantiating the overall 14Corg-based approach and justifying model assumptionsThe FOODBANCS-2 Project was funded by the National Science Foundation of the USA, Office of Polar Programs (ANT-0636773; C. R. Smith and D. J. DeMaster, PIs, C. J. Thomas, Co-PI). Support for E. Isla was from the Spanish Ministry of Economy and Competitiveness through the project CLIMANT (POL2006-06399/CGL)With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)Peer reviewe