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 degrees 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 x 107 atoms m-2 d-1 (possible range of 1.23 x 107-1.04 x 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 x 107 atoms m-2 d-1 (possible range of 3.87 x 107-1.56 x 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. Half of the Arctic Ocean is composed of shallow seas that extend over the continental shelf, so understanding what controls the chemical composition of the seawater in these regions is imperative to predicting how the Arctic Ocean as a whole may respond to climate change. Radium isotopes are naturally occurring radioactive elements that are produced in seafloor sediments, and they can be used to study the transfer of elements from the continental shelf into the overlying water. Here we combine measurements of radium isotopes with other chemical tracers and physical oceanographic models to study the transport and chemical signature of the Laptev and East Siberian Seas into the open Arctic Ocean. We find that the transport of elements from shelf sediments into the ocean is particularly strong in these seas and in the neighboring Chukchi Sea. Our data indicates that this region has an impact on the chemistry of the broader Arctic Ocean and emphasizes the need to continue to monitor this area for potential climate-driven changes. In 2021, shelf- and river-influenced waters crossed the shelf-basin boundary near 170 degrees E, indicating the likely position of the Transpolar Drift originModels suggest a residence time of similar to 13 months in the Laptev and East Siberian Seas before surface water enters the central Arctic OceanThe Laptev, East Siberian, and Chukchi Shelves contribute a disproportionately high amount of radium to Arctic surface waters