Observational and Modeling Evidence of Seasonal Trends in Sediment-Derived Material Inputs to the Chukchi Sea

Benthic inputs of nutrients help support primary production in the Chukchi Sea and produce nutrient-rich water masses that ventilate the halocline of the western Arctic Ocean. However, the complex biological and redox cycling of nutrients and trace metals make it difficult to directly monitor their benthic fluxes. In this study, we use radium-228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sediment-derived tracer to study variability in sediment inputs to the Chukchi Sea. The Ra-228 observations and modeling results are in general agreement and provide evidence of strong benthic inputs to the southern Chukchi Sea during the winter, while the northern shelf receives higher concentrations of sediment-sourced materials in the spring and summer due to continued sediment-water exchange as the water mass traverses the shelf. The highest tracer concentrations are observed near the shelfbreak and southeast of Hanna Shoal, a region known for high biological productivity and enhanced benthic biomass. Plain Language Summary Continental shelf sediments serve as a source of elements, such as carbon and nitrogen, that are important for sustaining life in the ocean. In the shallow Chukchi Sea north of Bering Strait, winter ice cover makes it difficult to collect year-round measurements that would improve our understanding of the shelf source of these elements. Instead, we use a naturally occurring radioactive tracer (radium-228) and a computer model to predict seasonal and spatial trends in the transport of elements from shelf sediments into the overlying Chukchi Sea. Our results suggest an enhanced release of sediment-derived materials to the southern Chukchi Sea during the winter, when there is increased water column mixing due to ice formation. Higher concentrations of the sediment-derived tracers were observed in the northern Chukchi Sea during the spring, likely due to continued additions from sediments as water moved northward over the shelf. Key Points A sediment-derived tracer was incorporated into a circulation model of the Chukchi Sea to investigate trends in benthic inputs The model results compare favorably to water column observations of radium-228, an isotope naturally released from sediments Benthic tracer inputs are highest during early winter in the southern Chukchi Sea and in late winter-early spring in the central Chukchi