The Arctic is experiencing warming trends greater than almost any other region on the planet. This is unlocking vast stores of carbon, nutrients and other trace elements present in frozen soils and sediments along the Arctic Ocean margin. It is further leading to shrinking sea ice extent, which is exposing the wide shallow Eurasian Arctic shelves to wind and wave action. We hypothesize that the combination of these processes is resulting in increased material fluxes to the Arctic Ocean and that water column Ra-228 activities will reflect these changes. An interannual Ra isotope time series is required to determine whether (and how fast) the system is changing, and therefore to improve our predictions of how the chemistry and biology of the Arctic may change in the future.

We will measure Ra-228 activities along the Eurasian shelves and in the Transpolar Drift (TPD) on 3 cruises spanning 5 years, extending the existing dataset of Ra-228 in the TPD to an 18-year record that can be used to assess long term changes. The TPD is a surface current that transports river- and shelf- influenced waters from the Laptev and East Siberian Seas across the Arctic basin, thereby serving as a pathway for rapid nutrient, carbon, and trace metal delivery to the central Arctic Ocean.

In addition to monitoring the absolute activities of Ra-228, measurements of Ra-228/Ra-226 and water mass modeling will be employed to help distinguish between the different drivers of change (e.g. increased river discharge vs. rising shelf sediment inputs). Climatological data will be used to help discern changes caused by rising air and water temperatures from those driven by the Arctic Oscillation (AO), which causes natural variability in water circulation and residence times over the shelves. To enhance our spatial coverage of the Arctic, the ARION network includes international collaborators who will collect Ra samples in the nearshore East Siberian and Laptev Seas and the central Arctic, capturing both the up and downstream activities in the TPD.