Radium Isotopes as Tracers of Shelf-Basin Exchange Processes in the Eastern Arctic Ocean

Radium isotopes, which are sourced from sediments, are useful tools for studying potential climate-driven changes in the transfer of shelf-derived elements to the open Arctic Ocean. Here we present observations of radium-228 and radium-226 from the Siberian Arctic, focusing on the shelf-basin boundary north of the Laptev and East Siberian Seas. Water isotopes and nutrients are used to deconvolve the contributions from different water masses in the study region, and modeled currents and water parcel back-trajectories provide insights on water pathways and residence times. High radium levels and fractions of meteoric water, along with modeled water parcel back-trajectories, indicate that shelf- and river-influenced water left the East Siberian Shelf around 170°E in 2021; this is likely where the Transpolar Drift was entering the central Arctic. A transect extending from the East Siberian Slope into the basin is used to estimate a radium-228 flux of 2.67 × 10⁷ atoms m⁻² d⁻¹ (possible range of 1.23 × 10⁷–1.04 × 10⁸ atoms m⁻² d⁻¹) from slope sediments, which is comparable to slope fluxes in other regions of the world. A box model is used to determine that the flux of radium-228 from the Laptev and East Siberian Shelves is 9.03 × 10⁷ atoms m⁻² d⁻¹ (possible range of 3.87 × 10⁷–1.56 × 10⁸ atoms m⁻² d⁻¹), similar to previously estimated fluxes from the Chukchi Shelf. These three shelves contribute a disproportionately high amount of radium to the Arctic, highlighting their importance in regulating the chemistry of Arctic surface waters.