Particulate organic carbon export fluxes and validation of steady state model of 234Th export in the Chukchi Sea

To evaluate the efficiency of biological pump and carbon sequestration content on Arctic shelf, estimations of POC export fluxes derived from 234Th/238U disequilibrium were made during the 3rd Chinese National Arctic Research Expedition (CHINARE-3) from July 12 to September 22, 2008. The 234Th analysis was based on small volume MnO2 co-precipitation and β-counting method. Great deficits of 234Th to 238U were observed widely over Chukchi shelf, with an average 234Th/238U activity ratio of 0.64±0.28, resulting from intense particle scavenging. The average POC export fluxes in the entire study area, shelf and slope area were 24.9±23.3, 29.5±23.0 and 2.1±0.5 mmol C m−2 d−1, respectively, resulting in that 21% of the primary production on average was exported to the benthos. Comparing with steady state model, non-steady-state model was recommended to derive a more accurate particulate 234Th export flux in a rapidly changing environment in the high latitude areas.