Ingalls¹, A.E., R.F. Anderson², A. Pearson¹ and C. Lee³

¹Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, Tel: 617 496-4297, Fax: 617 496-4387, E-mail: ingalls@eps.harvard.edu, ²Lamont-Doherty Earth Observatory, Columbia University, Route 9W Palisades, NY 10964 and ³Marine Sciences Research Center, Stony Brook University, Stony Brook, NY 11794-5000

Prospects for radiocarbon dating diatom-bound organic compounds

Obtaining accurate radiocarbon chronologies for sedimentary deposits lacking calcium carbonate has been an obstacle to understanding biogeochemical cycling in several oceanic regions including the North Pacific and the Southern Ocean. Attempts to use organic carbon instead of calcium carbonate have been unsuccessful due to problems with contamination and diagenesis. Here we apply compound-specific radiocarbon dating of diatom frustule-bound organic compounds toward the goal of developing age chronologies for sediment cores from the Southern Ocean. Diatom frustules-bound organic carbon is both from a known phytoplankton source and is relatively unaltered by diagenesis on thousand year time-scales.

Sediment samples are acid hydrolyzed and solvent extracted to remove non-diatom-bound organic matter. The cleaned sediment is digested in HF. Diatom-bound organic compounds are identified and isolated using liquid chromatography-mass spectrometry (LC-MS) and collected using an automated fraction collector. LC-MS and NMR analyses suggest that a major component of diatom-bound organic matter is present as polyamines. Individual fractions of polyamines are then radiocarbon dated using Accelerator Mass Spectrometry. We will present data comparing the radiocarbon age of diatom-bound polyamines to that of calcium carbonate from a Southern Ocean sediment core. Our results suggest that radiocarbon dating of diatom-bound organic matter will lead to a better understanding of sediment dynamics in diatom-rich locations.