Stewart, G.M., Cochran, J.K., Masqué, P., Armstrong, R.A., Xue, J., Lee, C., Wakeham, S.G., Miquel, J.C., Fowler, S.W. PARTICLE COMPOSITION AND POLONIUM-210 AND LEAD-210 CONTENT IN THE MEDFLUX STUDY: IMPLICATIONS FOR THE USE OF PO AS A TRACER OF PARTICLE FLUX

Abstract: Polonium-210, or the disequilibrium between polonium and its grandparent lead-210, has been proposed as a potential tracer of sinking particulate organic matter in the ocean. It is unclear, however, which specific aspect of organic matter the polonium is tracing. Sinking particles were collected between 200 and 1940 m in the northwestern Mediterranean using IRS sediment traps. We measured trace metals, biogenic and lithogenic minerals, carbon, nitrogen, and the radiotracers ²³⁴Th, ²¹⁰Po, and ²¹⁰Pb in the samples. Biomarkers such as pigments, fatty acids, and amino acids were used to identify the types and sources of material. Multivariate analyses comparing the chemical composition of particles with their polonium and lead content were conducted in order to elucidate which component of sinking particulate matter is traced by Po and/or the Po/Pb ratio. Results indicate that phytoplankton- and zooplankton-derived, nitrogen-rich organic carbon as well as sulfur-containing amino acids and sulfur-seeking metals are the most important factors influencing polonium’s distribution in sinking marine particles. These findings support previous laboratory observations that the distribution of polonium in biota parallels the distributions of both sulfur and protein.