234Th-derived particulate organic carbon export flux in the western Arctic Ocean

To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean, ²³⁴Th-²³⁸U disequilibrium was applied during the second Chinese National Arctic Research Expedition (July 15–September 26, 2003). The POC export fluxes are estimated from the measured profiles of the ²³⁴Th/²³⁸U activity ratios and the POC/PTh ratios. The average residence times of the particulate and dissolved ²³⁴Th in the euphotic zone are 33 d and 121 d, and their average export fluxes are 480 dpm/m²d and 760 dpm/m²d, respectively. The scavenging and removal processes of particle reactive elements are active in the upper layer of the Chukchi Sea. The average residence time of ²³⁴Th increases from shelf to basin, while the export fluxes of ²³⁴Th decrease. The estimated POC export fluxes from the euphotic zone vary from 2.1 to 20.3 mmol/m²d, indicating that the western Arctic Ocean is an important carbon sink in summer due to efficient biological pump.