Deposition of bomb ¹⁴C in continental slope sediments of the Mid-Atlantic Bight: Assessing organic matter sources and burial rates

As part of the Ocean Margins Program (OMP), organic carbon ¹⁴C measurements have been made on benthic fauna and kasten core sediments from the North Carolina continental slope. These analyses are used to evaluate the nature and burial flux of organic matter in the OMP study area off Cape Hatteras. Despite the fact that surface sediment ¹⁴C contents ranged from -41 to -215 per mil, the benthic fauna (primarily polychaetes) all contained significant amounts of bomb-¹⁴C (body tissue ¹⁴C contents ranging from +20 to +82 per mil). Bomb-¹⁴C clearly is reaching the seabed on the North Carolina slope, and the labile planktonic material carrying this signal is a primary source of nutrition to the benthic ecosystem. The enrichment of ¹⁴C in benthic faunal tissue relative to the ¹⁴C content of bulk surface-sediment organic matter (a difference of ∼ 150 per mil) is attributed to a combination of particle selection and selective digestive processes. Organic carbon burial rates from 12 stations on the North Carolina slope varied from 0.02 to 1.7 mol of Cm^-2yr^-1, with a mean value of 0.7mol of Cm^-2yr^-1. The accumulation of organic matter on the upper slope accounts for <1% of the primary production in the entire continental margin system. The North Carolina margin was deliberately selected because of its potential for offshore transport and high sediment deposition rates, and even in this environment, burial of organic carbon accounts for a very small fraction of the primary production occurring in surface waters.