Natural radionuclide studies during the GEOTRACES section with Polarstern in the Arctic, Summer 2015

In the summer of 2015 a coordinated pan-arctic GEOTRACES study was executed by the Canadian CCGS Amundsen, the US CGC Healy and the German RV Polarstern. For intercalibration purposes, three cross-over stations were visited, one of them at the North Pole. The Polarstern expedition visited the Nansen, Amundsen and Mendeleev basins. On sections across these basins and the Gakkel and Lomonosov Ridge we collected samples for the full set of GEOTRACES key parameters and many additional analyses. The team of natural radionuclides took samples for U-series nuclides. During earlier work in the central Arctic with Polarstern we have quantified export production with 234Th, studied the interaction between scavenging and deep water ventilation using 230Th and 231Pa, and investigated the shelf-basin exchange with radium isotopes. I will give an overview of these results obtained on earlier expeditions, mention first results of the 2015 expedition, and discuss how these tracers can help us to observe changes in deep water circulation and particle flux that may be related to Arctic Oscillation or caused by sea ice retreat.