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

Abstract

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 228 Ra 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.

The Importance of Benthic Nutrient Fluxes in Supporting Primary Production in the Laptev and East Siberian Shelf Seas

“…Our estimates highlight the important role of benthic fluxes in supporting new primary production in the Siberian sea shelf and possibly serve as a low end of benthic fluxes, as the data were collected in summer. The fluxes have been suggested to be enhanced in winter and thereafter support more primary production in spring using 228 Ra as a sediment‐derived tracer in the Chukchi Sea (Kipp et al., 2020).…”

Size‐Fractionated Compositions of Marine Suspended Particles in the Western Arctic Ocean: Lateral and Vertical Sources

“…We speculate that density‐driven shelf water cascading in winter might be the major source of high lithogenic particles in the central Arctic Basin. Other processes, such as cascading events in different seasons (Ivanov et al, 2004), and the seasonal offset between major convection events and concentrations of suspended shelf sediments (Kipp et al, 2020), however, could also contribute to the lateral lithogenic fluxes.…”

New Constraints on the Physical and Biological Controls on the Silicon Isotopic Composition of the Arctic Ocean

“…The Pacific waters of the UHL are distinguished by a subsurface maximum in silicic acid concentration that reflects both the water's origin in the Pacific and the input of regenerated silicic acid from sediments in the shallow Chukchi Sea (Jones and Anderson, 1986;Nishino et al, 2009Nishino et al, , 2015Kipp et al, 2020). For this study, the UHL defined by potential temperature (θ) and salinity (S) is further subdivided based on silicic acid content, with waters containing >18 µmol kg −1 silicic acid (twice the average silicic acid concentration in the PML) considered representative of the isotopic composition of the Si maximum associated with Pacific waters in the central Arctic Ocean (denoted as UHLP, Table 1).…”