Award: OCE-0961351

Trace element cycling in the ocean has an important control on marine ecosystem functioning and the carbon cycle. Pb-210 and Po-210 are daugter products in the U-238-decay chain and has contrasting biogeochemical behavior in marine system. Po-210 preferentially bioaccumulates within organic tissues, in addition to the removal by terrigenous and biogenic particulate matter. Pb-210 is predominantly removed by terrigenous particulate matter. Their overall geochemical behavior in marine system is relevant to export of particulate organic carbon from the upper ~200 m, export fluxes of sinking particulate matter, sediment mixing and deposition rates. As a part of our group (Tom Church, University of Delaware - dissolved phase; Gillian Stewart, Queens College - >51 um particulate matter and Mark Baskaran, Wayne State University - 0.8-51 um), we measure particulate and dissolved activities of Po-210 and Pb-210. The primary objective is to improve our understanding of processes that control the distribution of Po-210 and Pb-210 nuclide cycles in the North Atlantic and its interfaces. We collected and analyzed seawater samples from 7 super stations and include: a well-developed bottom nepheloid layer from 2900 m depth to bottom, a station with oxygen minimum zone and at the Mid-Atlantic ridge where the Trans-Atlantic Geotraverse (TAG) hydrothermal plume was observed. Based on our results, we report the following: i) There is no disequilibrium between Po-210 and Pb-210 in oligotrophic station; ii) Remineralization of particulate matter could redistribute Po-210 and Pb-210 in the whole water column; iii) What we find at the interfaces (upper 300 m, bottom 300 m) seem to reflect the partitioning of nuclides in the overall water column; and iv) Interfaces provides clue on the extent of redistribution of Po-210 and Pb-210 - mechanistic linkages between interfaces and the whole water column needs to be reassessed. Last Modified: 01/05/2015 Submitted by: Mark Baskaran