Understanding Circulation Processes in the Arctic and sub-Arctic Regions Using a Combination of Anthropogenic Chemical Tracers

Nuria Casacuberta1, John Smith2, Anne-Marie Wefing3, Maxi Castrillejo3, Marcus Christl4, Elena Chamizo Calvo5, Mercedes Lopez-Lora5 and William M Smethie Jr6, (1)ETH Zurich, Zurich, Switzerland, (2)Bedford Institute of Oceanography, NS, Canada, (3)ETH Zurich, Switzerland, (4)ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland, (5)Centro Nacional de Aceleradores (CNA), Spain, (6)Lamont -Doherty Earth Observatory, Palisades, NY, United States
Anthropogenic chemical tracers are powerful tools to study ocean circulation timescales, ventilation processes and mixing regimes. On the one hand, the releases of artificial radionuclides from the European nuclear reprocessing plants (e.g. 137Cs, 129I, 236U) have proved to act as suitable water mass tracers for the study of Atlantic water circulation in the Arctic and North Atlantic oceans. On the other hand, the global atmospheric release of both anthropogenic compounds such as CFCs, SF6 and radioactive debris from weapon tests has been extensively used to calculate transit time distributions (TTD) and constrain water circulation and mixing time scales for a wide range of high latitude water masses.

Here we will present the results of a combination of anthropogenic radionuclides (i.e. 129I, 236U, 233U, 14C) measured in the Arctic Ocean (including sub-polar North Atlantic) during several expeditions that took place over the last 6 years. The distribution of 129I and 236U measured in 2015 are a consequence of the anticyclonic atmospheric regime, which shifted the Pacific-Atlantic front towards the North Pole resulting in a weaker boundary current in the Beaufort Sea. The combination of 129I and 236U in a dual tracer approach will be used to revisit the tracer ages of Atlantic waters throughout their transit in the Arctic Ocean (embracing both the Eurasian and Canada basins) and back to the Atlantic Ocean. Additional data on 129I, 236U and 14C in the Fram Strait and sub-polar North Atlantic will be also discussed in the context of the previous results. Finally, the combination of the long-lived 129I and 236U with CFCs and SF6 to extract TTD will be presented as a tool to study parameters associated with mixing and advection.

In this study we therefore highlight the importance of studying the combination of several transient tracers with different historical and regional source inputs, in a holistic approach.