| Summary: | The nutrient-type distribution of dissolved cadmium concentrations (dCd) reflects a biological control in the global ocean, with uptake of dissolved Cd into biogenic particles in surface waters and regeneration of particulate Cd at depth. Depth profiles of dissolved Cd stable isotope composition ((d delta Cd-114/110), while sparse in coverage, exist for most of the major ocean basins, with spatial coverage improving through the efforts of the GEOTRACES program. However, a dearth of similarly resolved particulate delta Cd-114/110 (delta Cd-114/110) distributions limits our ability to use stable Cd isotopes to better understand Cd cycling in the global ocean. Here we present two p delta Cd-114/110 depth profiles from the subarctic northeast Pacific which demonstrate more complex delta Cd-114/110 cycling than dissolved profiles would suggest. Surface p delta Cd-114/110, while lighter than surface d delta Cd-114/110, is heavy relative to Pacific deepwater and crustal p delta Cd-114/110 components. Surface particulate and dissolved delta Cd-114/110 distributions are not well explained by closed-system Rayleigh fractionation following a single fractionation factor, in agreement with other recent studies in the Atlantic and Pacific Oceans. These variable fractionation trends in surface waters complicate the potential utility of delta Cd-114/110 as a paleoproductivity proxy. Particulate delta Cd-114/110 becomes lighter as particulate Cd is remineralized in the nutricline, reaching a minimum p delta Cd-114/110 of around -0.5 parts per thousand, among the lightest values reported in natural telluric samples. This p delta Cd-114/110 trend within the nutricline might be explained by (1) multiple pools of particulate Cd with different isotopic compositions and labilities, or (2) by fractionation during particulate Cd remineralization. The observed shallow loss of heavy p delta Cd-114/110 above the winter mixed layer, rather than the formation of especially light surface p delta Cd-114/110, may help to maintain the observed ...
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