9522004 Church Pb isotopes will be used as tracers to quantify the atmospheric inputs to and biogeochemical processes in the surface waters of the Sargasso Sea off Bermuda, and data will be gathered in the South Atlantic as part of a proposed third IOC trace element cruise during the same period. This is a coordinated effort between the University of Delaware Principal Investigators and other institutions. Included are those currently active in studies of the Bermuda atmosphere as part of the AEROCE program in its third phase with support from NSF-ATM, and other scientists investigating the major nutrient cycles, productivity, and associated carbon based flux (JGOFS-BATS and associated activities) in the waters off Bermuda under NSF-OCE support. Existing archived samples of precipitation and oceanic flux particles will be utilized first if they satisfy clean collection criteria. The proposed study will focus on the element Pb and its isotope tracers which include stable Pb (204,206,207,208), and the radioactive nuclide 210Pb with the associated parent/daughter pairs which are part of the series 226 Ra, 222Rn, 210Bi, and 210Po. Lead and its isotopes will be measured in individual and integrated atmospheric samples to be taken at the AEROCE Bermuda site, and on board several cruises off Bermuda. The radioactive lead (210Pb) and its disequilibrium with the daughters 210Bi and 210Po will reveal of atmospheric and surface ocean scavenging. The half lives of these isotopes (5 and 138 days respectively) should be commensurate with processes such as aqueous scavenging of particle reactive elements (such as Bi), and bio-active elements (such as Po). Through modeling of dissolved 210 Po profiles in the surface mixed layer down to the thermocline, eddy diffusion co-efficients in the surface waters will be determined and subsequently used to place constraints on new production rates. Generally, lead isotope modeling will constrain vertical and horizontal contribution s to the surface waters, and calibrate the mixing and particle scavenging of Pb.
