Masqué, P., Stewart, G., Cochran, J.K., Miquel, J.C., Rodriguez-Ybaena, A.M., Szlosek, J., Fowler, S.W., Peterson, M.L., and Lee, C. MEDFLUX: POC FLUXES IN THE NORTHWESTERN MEDITERRANEAN SEA DERIVED FROM 210PO/210PB DISEQUILIBRIUM: COMPARISON TO 234TH/238U AND SEDIMENT TRAP PROXIES

Abstract: The disequilibrium between ²¹⁰Po and ²¹⁰Pb in the water column can be used to estimate particulate organic carbon (POC) fluxes from the surface ocean by integrating the deficit of polonium with respect to lead and knowing the POC/Po ratio in sinking particles. Indeed, recent findings have shown that Polonium has a high affinity for organic matter and protein, leading to its bioaccumulation in plankton and suggesting that ²¹⁰Po may be an appropriate tracer of POC in the ocean. The French JGOFS DYFAMED site in the Northwestern Mediterranean Sea was visited several times during 2003. Polonium-210 and Lead-210 were determined in the particulate and dissolved fractions in the water column and in particles collected with in situ pumps and IRS sediment traps (both on sequential fluxes and sinking velocities modes). Derived POC fluxes under steady and non-steady conditions are compared to those obtained using ²³⁴Th/²³⁸U disequilibrium and sediment traps. We also investigate the role of composition and velocities of sinking particles on ²¹⁰Po distributions and export efficiencies and how this can be used to predict POC cycling in the ocean.