Description: We will present the combined results of the French GEOTRACES GEOVIDE cruise in the North Atlantic Ocean and the 2015 German GEOTRACES cruise TransArc II in the central Arctic Ocean. Research vessel "Pourquoi pas?" sailed on May 15th from Lisbon to Greenland to arrive in Newfoundland on June 30th 2014, and icebreaker "Polarstern" sailed on August 17th from Tromsoe to explore the Nansen, the Amundsen and the Makarov basins, to arrive in Bremerhaven on October 15th 2015. Total mercury was sampled using ultra-trace clean rosettes and determined on board. In the Atlantic Ocean, surface waters of the Gulf Stream are cooled down as they travel north, and mix at the same time with waters exiting the Arctic Ocean via Fram Strait. These cool and dense surface waters dive to depth in the Greenland and Labrador seas. The North Atlantic Ocean predominantly receives Hg via atmospheric deposition from Europe and North America where industrial Hg emissions peaked in the 1970s. The Hg inputs to the Arctic Ocean are less well-constrained if not unknown. The current debate opposes a primary atmospheric with a river-dominated scenario. We find consistent surface depleted profiles in the North Atlantic Ocean, while we exclusively observe surface enrichments in the Arctic Ocean, at all sampling stations. We will make use of the combined data sets of both cruises to investigate how climate may impact Hg marine biogeochemical cycle, how anthropogenic Hg makes its way into the deep ocean and whether the temporal evolution of emissions is traceable in water masses of different ages. We will also put our new observations in context with recent numerical model evaluations.

Description: 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.