Estimation of POC and Biogenic silica export fluxes using 234Th/238U disequilibrium in the Amundsen sea, Antarctic (2012)

Seawaters in 14 water columns were collected during February and March 2012, and analyzed for total and dissolved 234Th, and particulate organic carbon and biogenic silica. 234Th activities were analyzed using a gas-flow proportional β-spectrometer manufactured by Risø National Laboratories (Roskilde, Denmark) following methods described in Buesseler et al. (2001). The export fluxes of particulate organic carbon (POC) play an important role in the transfer of carbon between the atmosphere and the ocean. Accurate estimates of POC export fluxes are critical for constraining models of the global carbon cycle. Over the past few decades, the radioisotope pair 238U and 234Th has been increasingly used to estimate POC export fluxes from the euphotic zone. This method is based on the uptake of 234Th onto biogenic particles in the euphotic zone and the subsequent sinking of particles into deep water. The POC export flux is determined by multiplying the depth-integrated 234Th sinking flux by the POC/234Th ratio on sinking particles. This study aims to estimate the POC export fluxes in the Amundsen Sea using 234Th/238U disequilibrium method.