Radium isotopes and 228Th in surface water samples collected on POLARSTERN expedition PS78

228Ra is strongly enriched in shelf waters and its half-life (5.8 years) is well suited to study the fate of shelf-derived water in the central Arctic. During PS78 (TRANSARC I) we studied the distribution of 228Ra in surface waters of the central Arctic to investigate how this 228Ra signal is transported in the Transpolar Drift. Water from the ships' seawater intake (Sta 196, 205) or from a submersible pump lowered to 10m depth on hydrographic stations (from station 209 onwards) was filtered and passed over MnO2-coated cartridges to absorb Radium and Thorium. Short-lived 224Ra, as analog for the total concentration of its parent 228Th, was determined on board with RaDeCC counting. In the lab, the cartridges were leached and long-lived Radium isotopes were measured by gamma spectroscopy.