The Bering Sea is a dynamic high-latitude marginal basin that serves as a key gateway between the North Pacific and the Arctic Ocean, where Pacific-derived waters enter through the Aleutian Passes and are transported along the continental slope before spreading into the basin interior. These inflowing waters provide the primary source of intermediate and deep waters in the Bering Sea, establishing the fundamental hydrographic structure and baseline trace element composition that are subsequently modified by local processes along the slope and basin. However, despite the recognized importance of these processes, their combined influence on trace element distributions remains poorly constrained, particularly with respect to the roles of water mass interaction, boundary inputs, and along-slope transport.

Trace elements, particularly rare earth elements (REEs), provide a powerful tracer system to address this limitation because physical parameters alone cannot resolve non-conservative inputs or chemical modification processes. While temperature and salinity define water mass structure and circulation, REEs exhibit quasi-conservative behavior during transport while remaining sensitive to boundary inputs and particle interactions. In particular, neodymium (Nd) and ytterbium (Yb) are effective tracers for distinguishing between conservative water mass mixing and additional processes such as sediment-derived input and particle-related modification, thereby providing insight into coupled physical–biogeochemical dynamics.

Here, hydrographic observations collected during the R/V Hakuho-Maru cruise KH-25-3 are combined with REE measurements to examine how water mass structure, topographic effects, and mesoscale variability jointly influence the vertical and lateral distribution of trace elements. Seawater samples (50 mL) were filtered onboard and acidified with HCl, then preconcentrated using an InertSep ME-2 chelating resin both onboard and in the laboratory. REE concentrations were determined using Agilent 7700x ICP-MS and Agilent 8900 triple quadrupole ICP-MS/MS systems.
Hydrographic structure reveals a stratified water column consisting of Bering Summer Surface Water (BSSW; S > 33.2), Bering Intermediate Water (BIW; 33.6 < S < 34.2), and deep waters to Bering Deep Water (BDW; S > 34.2), consistent with established classifications. A prominent topographic feature along the transect is associated with deformation of isopycnals, including upward displacement of density surfaces by ~200–300 m, indicating strong interaction between flow and bathymetry.

Nd and Yb concentrations generally increase with depth, from ~2–3 ppt (Nd) and ~1–2 ppt (Yb) in surface waters to ~5–7 ppt (Nd) and ~3–4 ppt (Yb) in deep waters, consistent with typical oceanic behavior. However, localized enrichment is observed near the slope and topographic region, where Yb reaches ~5–6 ppt at depths of ~2000–3000 m. This enrichment coincides with deformation of isopycnals and suggests that interaction between BIW and BDW, together with along-slope transport, contributes to the redistribution of REEs.

Sectional distributions further show that elevated REE concentrations extend beyond the slope region into adjacent waters, indicating that these signals are not confined locally but are redistributed along the slope and into the basin interior. These patterns likely reflect a combination of processes, including the transport of REE-enriched waters along the Aleutian slope and local modification through interaction with underlying deep waters. However, the present dataset does not allow a clear distinction between vertical and horizontal transport mechanisms.

REE concentrations near the slope exceed background deep-water values, suggesting additional input from boundary processes such as sediment–water interaction and particle-related release. PAAS-normalized REE patterns support this interpretation, showing typical heavy REE-enriched signatures in basin waters and relatively elevated concentrations with reduced fractionation near the slope.

Overall, the results indicate that REE distributions in the Bering Sea are governed by the combined effects of Pacific inflow, water mass structure, boundary inputs, and along-slope transport. While the large-scale distribution is controlled by conservative transport within water masses, local deviations reflect interaction between water masses and non-conservative inputs along the continental slope. These findings highlight the importance of integrating physical circulation and geochemical tracers to better understand material transport and transformation in high-latitude marginal seas.
 

Rare Earth Elements,Bering Sea,Topographic Effects,Boundary Inputs,GEOTRACES,Water Mass