210Po/210Pb disequilibria influenced by production and remineralization of particulate organic matter around Prydz Bay, Antarctica

Abstract

Dissolved and particulate 210Po and 210Pb were measured to reveal the particle dynamics around Prydz Bay in the austral summer of 2015. The spatial variations of 210Po activity concentration and 210Po/210Pb disequilibria are mainly controlled by 210Po absorption and particle scavenging, and particulate organic matter (POM) remineralization. Different water masses around Prydz Bay show different characteristics of 210Po/210Pb disequilibria. The activity ratios of total 210Po to total 210Pb (expressed as TPoTPbAR) in Antarctic Surface Water, Winter residual Water, Shelf Water and Thermocline Water are all less than 1.0, indicating that biological absorption and particle adsorption preferentially scavenge 210Po from these waters. Circumpolar Deep Water shows the highest TPoTPbAR characteristics, and the total 210Po is in equilibrium or excess to the total 210Pb, which reflects the effect of POM remineralization. The TPoTPbAR value in the Antarctic Bottom Water is less than 1.0, and it falls between the ratios of Shelf Water and Circumpolar Deep Water, which proves that the formation of Antarctic Bottom Water has an impact on the 210Po/210Pb disequilibria. fretained is defined to represent the proportion of 210Po scavenging from the dissolved phase to the particulate phase but suspended in seawater; we found that there is a linear relationship between fretained and particulate organic carbon (POC), silicic acid and phosphate concentrations, indicating that the balance between input (POM remineralization) and removal (biological absorption and particle adsorption) determines the disequilibrium between 210Po and 210Pb. Based on the 210Po/210Pb disequilibria, the POC export from the euphotic zone is estimated to be 4.11–47.82 mmol C m−2 d−1, showing large spatial variability. The POC export on the shelf is generally higher than that on the slope and basin, which corresponds to the spatial variations of phytoplankton biomass and primary productivity.