EPSS Colloquium fall-2015

Zinc and cadmium are important micronutrients in the ocean, where biological productivity draws down Zn and Cd concentrations in surface waters and fractionates Zn and Cd stable isotopes. New global datasets of seawater dissolved stable isotope ratios (?66Zn and ?114Cd) provide unique insight into biogeochemical cycling of these elements. Cd is governed by simple nutrient dynamics, with preferential uptake of lighter Cd isotopes in the surface ocean and remineralization in the deep. A combination of observations, experiments, and modeling suggest that Zn cycling is more complicated, with an ‘inverse’ isotope profile caused by preferential adsorption of heavier Zn isotopes onto sinking particles. With a more complete understanding of Zn and Cd isotope cycling in the modern ocean, we can begin to use them as tracers in the geological record. For example, ?66Zn and ?114Cd in a post-snowball Earth cap carbonate hint at weak surface-ocean productivity during deglaciation.