The distribution of dissolved cadmium and its isotopes across the subarctic Pacific Ocean

Cadmium (Cd) is a bioactive trace element with a nutrient-type distribution resembling the macronutrient phosphate (PO₄) in the global ocean. At high latitudes, biogeochemical processes generate distinct Cd concentration and isotopic signals in surface waters, which are preserved during formation and advection of high-latitude water masses, exerting a significant control on the deep ocean Cd and dissolved Cd isotope (δ¹¹⁴Cd) distributions. Here, we present the first full depth, cross-basin study of Cd and δ¹¹⁴Cd in the Subarctic Pacific from the Japanese GEOTRACES section GP02, principally along 47˚N. In intermediate and deep waters, δ¹¹⁴Cd values are homogenous (+ 0.24 ± 0.02‰), consistent with previous findings of an isotopically homogenous global deep ocean. However, Cd to PO₄ ratios show clear divergences across the 160˚W meridian, representing increased Cd accumulation relative to PO₄ in Pacific Deep Water in the east. In surface waters, the relationship between Cd and δ¹¹⁴Cd from the Western Subarctic Gyre can be described by closed-system Rayleigh fractionation, consistent with our understanding of Cd systematics in elevated Cd in surface waters linked to upwelling, high-nutrient low chlorophyll environments. In contrast, in the east, where Cd concentrations are lower, an open-system steady state model is more descriptive.