The history of Holocene atmospheric iodine over the North Atlantic

Abstract

Atmospheric iodine chemistry has a large influ-ence on the oxidizing capacity and associated radiative im-pacts in the troposphere. However, information on the evo-lution of past atmospheric iodine levels is restricted to theindustrial period while its long-term natural variability re-mains unknown. The current levels of iodine in the atmo-sphere are controlled by anthropogenic ozone deposition tothe ocean surface. Here, using high-resolution geochemicalmeasurements from coastal eastern Greenland ReCAP (REn-land ice CAP project) ice core, we report the first record ofatmospheric iodine variability in the North Atlantic duringthe Holocene (i.e., the last 11 700 years). Surprisingly, ourresults reveal that the highest iodine concentrations in therecord were found during the Holocene Thermal Maximum(HTM;~11 500¿5500 years before-present). These high io-dine levels could be driven by marine primary productivityresulting in an Early Holocene ¿biological iodine explosion¿.The high and stable iodine levels during this past warm pe-riod are a useful observational constraint on projections offuture changes in Arctic atmospheric composition and cli-mate resulting from global warming.