Variability in 210Pb and 210Po partition coefficients (Kd) along the US GEOTRACES Arctic transect

The naturally occurring Po-210 (t(1/2) = 138.3d) and Pb-210 (t(1/2) = 22.3 y) radionuclide pair has been extensively used to study particle scavenging, cycling and transport in the ocean. However, the role of particle composition in the scavenging, sorption and fractionation of Po-210-Pb-210 needs to be better understood to successfully utilize these radionuclides as oceanographic tracers. Here, we measure dissolved and particulate Pb-210 and Po-210 activities for both small (1-51 mu m) and large particles ( > 51 mu m) 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. 21 Po-21 Pb disequilibria were observed throughout the water column for all stations. The Pacific end member had the highest activity of Po-210 and Pb-210 in dissolved samples. The calculated partition coefficients (K-d) of Po-210 and Pb-210 varied between 3.2 x 10(5) to 9.9 x 10(8) L kg(-1) and 7.9 x 10(5) to 6.9 x 10(8) 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 Pb-210 and the lithogenic phase. Both Po-210 and Pb-210 had significant negative correlations with opal. Our results suggest that particle composition alone cannot explain the observed variability in K-d across the different oceanic regime along the transect. Estimated K-d values from an end member mixing model were found to be within the range of observed K-d values and suggest that higher particulate Mn concentration in the Arctic may be partly responsible for the higher K-d observed in the basin compared to Atlantic and Pacific.