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

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.