Intercalibration studies of210Po and210Pb in dissolved and particulate seawater samples

Documented is an intercalibration (IC) exercise for both 210 Po and 210 Pb in seawater aliquots distributed between up to eight international laboratories that followed individual protocols. Dissolved and particulate sam ples were provided by GEOTRACES during two IC cruises at baseline stations in the North Atlantic and North Pacific oceans. Included were surface and/or deep dissolved and particulate samples at each site, plus complete profiles analyzed by the laboratory of the lead author. An unspecified solid phase standard was also distributed with 210 Po and 210 Pb in secular equilibrium to confirm spike calibrations. The 210 Po activities reported n = 8) for the standard were very similar with a relative standard deviation (RSD) of 3.6% and mean value indistinguish able from the certified value, confirming accurate calibration of Po spikes. For seawater samples, the agreement was strongly dependent for both nuclides on the activity of the samples. The agreement was relatively good for dissolved seawater samples (RSD = 9% to 29%, n = 4), moderate for the particulate samples (RSD = 12% to 80%, n = 8), and poor for particulate dip blanks (RSD = 50% to 200%, n = 8). Noted is the higher apparent affinity of 210 Po versus 210