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The paths of the Amur River discharge on the continental shelf in the Sea of Okhotsk are still unknown despite their significance in transporting dissolved and particulate iron. In this study, we conduct a coupled ice-ocean simulation for the northern Sea of Okhotsk from June 1998 to September 2000 to answer the question: Does the Amur River discharge deposit materials to the pathway of the dense shelf water? In a series of numerical experiments, we identified two routes (the western and eastern routes) that could transport the river water more than 100km offshore over the northwestern continental shelf. The two routes share the clockwise gyre in the Sakhalin Gulf and the northeastward flow on the northwestern continental shelf. These features are connected through the westward jet along the slope from the Sakhalin Gulf (the western route) and the northward transport over the shelf break canyon (the eastern route). The river water, the dense shelf water, and the easterly wind are in a fine geophysical balance for those features, and all are required for the formation of the two routes. The model results show that these unique joint effects in the Sea of Okhotsk allow the Amur River discharge to be effectively transported over the northwestern continental shelf, unlike a general river discharge that flows along the coast, and deposit materials into the pathway of the dense shelf water. [ABSTRACT FROM AUTHOR]

An ocean general circulation model coupled with a simple biogeochemical model was developed to simulate iron circulation in and around the Sea of Okhotsk. The model has two external sources of iron: dust iron at the sea surface and sedimentary iron at the seabed shallower than 300m. The model represented characteristic features reasonably well, such as high iron concentration in the dense shelf water (DSW) and its mixing, which extends southward in the intermediate layer from the northwestern shelf along Sakhalin Island and finally flows into the Pacific. Sensitivity experiments for the solubility of dust iron in seawater suggest that a solubility of 1% is appropriate in our simulation. Higher solubilities (5% and 10%) result in too low phosphate in the northwestern North Pacific in summer as well as too high iron concentrations at the sea surface, compared with observations. Besides, these experiments show that dust iron hardly contributes to the high iron concentration in the intermediate layer. To investigate locations from which the iron in the intermediate layer originates, the fate of sedimentary iron input from four regions in the Okhotsk Sea was examined. Results suggest that the western and central parts of the northern shelf are important. [ABSTRACT FROM AUTHOR]

• We revealed the water chemical properties in the Kamchatka Basin in the western Bering Sea. • Decoupling of Si from N and P in the intermediate water occurred, and higher dissolved Si concentrations and sedimentary-sourced Fe accumulated in the deep water in the Kamchatka Basin. • The WSG water circulation flowing along the southern side of the Aleutian Islands had a strong influence on the chemical properties of the intermediate water in the East Kamchatka Current. • Nutrient-rich water intrusion occurred from the Aleutian Basin intermediate nutrient pool to the bottom layer of the 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 σ θ) 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 σ θ 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. [ABSTRACT FROM AUTHOR]