Award: OPP-1435376

The naturally occurring 210Po (t1/2=138.3d) and 210Pb (t1/2=22.3 y) radionuclide pair has been extensively used to study particle scavenging, cycling and transport of carbon as well as other metals in the ocean. 210Pb and 210Po are both particle reactive but have different particle affinities and, often, removal mechanisms. 210Pb is adsorbed to all particle surfaces, which include both lithogenic and biogenic particles whereas 210Po can also be incorporated via biological activity into the cytoplasm and cell wall of some species of phytoplankton, more like a nutrient element. However, the role of particle composition in the scavenging, sorption and fractionation of 210Po-210Pb needs to be better understood to successfully utilize these radionuclides as oceanographic tracers. In this research we measure dissolved and particulate 210Pb and 210Po activities for both small (1-51μm) and large particles (> 51μm) with abundance of major phases of suspended particulate matter (SPM) from the US GEOTRACES Arctic transect to examine the role of the concentration and composition of SPM in scavenging and fractionation of these radionuclides along the coastal, Canada Basin and interior stations. 210Po-210Pb disequilibria were observed throughout the water column for all stations. The Pacific end member had the highest activity of 210Po and 210Pb in dissolved samples. The calculated partition coefficients (Kd) of 210Po and 210Pb varied between 3.2 x 105 to 9.9 x 108 L kg-1 and 7.9 x 105 to 6.9 x 108 L kg-1 respectively and followed a log-linear trend with SPM for particle size fractions. Principal Component Analysis (PCA) and correlation analysis for six major particle phases indicated a significant positive correlation between 210Pb and the lithogenic phase. Both 210Po and 210Pb had significant negative correlations with opal. Our results suggest that particle composition alone cannot explain the observed variability in Kd across the different oceanic regime along the transect. Estimated Kd values from an end member mixing model were found to be within the range of observed Kd values and suggest that higher particulate Mn concentration in the Arctic may be partly responsible for the higher Kd observed in the basin compared to Atlantic and Pacific. Last Modified: 03/16/2020 Submitted by: Kanchan Maiti