Alpine ice evidence of a three-fold increase in atmospheric iodine deposition since 1950 in Europe due to increasing oceanic emissions

Michel Legrand, Joseph R. McConnell, Susanne Preunkert, Monica Arienzo, Nathan Chellman, Kelly Gleason, Tomás Sherwen, Mat J. Evans, Lucy J. Carpenter

Research output: Contribution to journalArticlepeer-review


Iodine is an important nutrient and a significant sink of tropospheric ozone, a climate-forcing gas and air pollutant. Ozone interacts with seawater iodide, leading to volatile inorganic iodine release that likely represents the largest source of atmospheric iodine. Increasing ozone concentrations since the preindustrial period imply that iodine chemistry and its associated ozone destruction is now substantially more active. However, the lack of historical observations of ozone and iodine means that such estimates rely primarily on model calculations. Here we use seasonally resolved records from an Alpine ice core to investigate 20th century changes in atmospheric iodine. After carefully considering possible postdepositional changes in the ice core record, we conclude that iodine deposition over the Alps increased by at least a factor of 3 from 1950 to the 1990s in the summer months, with smaller increases during the winter months. We reproduce these general trends using a chemical transport model and show that they are due to increased oceanic iodine emissions, coupled to a change in iodine speciation over Europe from enhanced nitrogen oxide emissions. The model underestimates the increase in iodine deposition by a factor of 2, however, which may be due to an underestimate in the 20th century ozone increase. Our results suggest that iodine's impact on the Northern Hemisphere atmosphere accelerated over the 20th century and show a coupling between anthropogenic pollution and the availability of iodine as an essential nutrient to the terrestrial biosphere.

Original languageEnglish
Pages (from-to)12136-12141
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number48
Early online date12 Nov 2018
Publication statusPublished - 27 Nov 2018

Bibliographical note

© 2018 the Author(s). Published by PNAS.


  • Alpine ice core
  • GEOS-Chem
  • iodine
  • trend
  • tropospheric ozone

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