Iron and nutrient dynamics along the East Kamchatka Current, western Bering Sea Basin and Gulf of Anadyr

Analysis of observed iron (Fe) and nutrient data from the East Kamchatka Current (EKC) in the western Bering Sea, including the Kamchatka Basin, northeastern shelf slope, and Gulf of Anadyr, in the summers of 2014 and 2018 was conducted. The results indicate the location of the edge of high-nutrient and low-chlorophyll water (Fe-limited subarctic Pacific water), which expands into the EKC area. The supply of Fe was related to the freshwater supply from the Kamchatka Peninsula and caused nutrient depletion along the coast of the Kamchatka Peninsula in the EKC. Consistent with the subarctic Pacific, water with extremely high nitrate (N) and phosphate (P) concentrations and extremely low dissolved oxygen concentrations was observed in a wide density range in the intermediate layer (26.6-27.6 sigma(theta)) in the Kamchatka Basin and formed an intermediate nutrient pool. However, the concentrations of both dissolved Fe (dFe) and silicic acid (Si) were highest in the deep layer below the 27.6 sigma(theta) isopycnal surface in the basin, indicating that the dFe and Si cycles were decoupled from the N and P cycle in the basin intermediate water. The increase in dFe concentration with depth in the deep layer was probably due to a reduction in particulate Fe that occurred in the benthic pore water on the slope or in the settling particulate microenvironment, as indicated by a negative N* index. Based on the observed data around the Kamchatka Strait and EKC in the summer of 2018, the chemical properties of the water in the intermediate layers in the EKC on the Pacific side of the Kamchatka Peninsula were mainly influenced by circulation of the Western Subarctic Gyre, which flows from the southeastern Aleutian Islands, with minor influence from Kamchatka Basin water flowing through the Kamchatka Strait on the coastal side of the EKC. Our results also indicate that nutrient-rich water intrusion occurred from the Aleutian Basin intermediate nutrient pool to the bottom layer of the Gulf of Anadyr. Additionally, nitrate removal by via the denitrification process and the input of sedimentary Fe occurred in the intruding bottom water. The findings from this study are important for understanding the biogeochemical interactions occurring among the subarctic Pacific, Bering Sea, and Arctic Ocean.