Award: OCE-1829406

The marine iodine cycle is an important component and tracer of the atmospheric ozone and marine oxygen cycles. This project provided constraints necessary to make models of the geochemical iodine and related elemental cycles in seawater. This research was accomplished through a combination of experiments determining rates and pathways of iodine cycling as well as from ocean transects determining the distribution of iodine across biological and geochemical gradients. Specifically, experiments with an iodine isotope tracer were conducted with seawater collected from low oxygen zones of the tropical Pacific and across a south-to-north Atlantic Ocean upper ocean transect to constrain the conditions and rates of iodine reactions. Additional work evaluated the transfer of seawater iodine to and from sediments. Our experiments demonstrate biological and abiotic iodine oxidation and reduction reactions in some oceanic regions while relatively slow or conservative iodine cycling prevails elsewhere. This indicates that some areas of faster reaction rates, such as those generated in low oxygen zones or sediments, may produce changes in iodine distribution that are then sustained and transfered to other areas via physical mixing processes. These constraints were input into models of ocean and sedimentary biogeochemical cycles that can be applied to tracking iodine and related elemental cycles both in the modern ocean and across geologic time. Broader impacts for this award included the training of 3 graduate and 7 undergraduate students. Last Modified: 12/20/2023 Submitted by: DaltonSHardisty