(A) Time series of iodine in Col du Dome ice core in summer (red) and winter (blue). (A) Time series of iodine in Col du Dome ice core in summer (red) and winter (blue). Dots are yearly values; solid lines are the first component of a single spectra analysis with a 7-y time window (summer) and robust spline (winter). Vertical bars show the modeled mean deposition for summer (brown) and winter (purple) for 1850 (shown at 1890), 1950, 1980, 1995, and 2005. The dashes and arrow on the bars show the deposition of inorganic iodine minus HOI (lower dash) and minus half of HOI deposition (middle dash), and the total (top arrow). (B and C) Modeled seasonality of surface iodine species mixing ratio in 1850 (PI) and 2005 (PD); other iodine is composed of HI, I2, IxOy, IBr, ICl, IONO, and aerosol phase iodine. (D and E) Modeled seasonality of iodine species deposition. (F–H) Seasonal cycle of iodine measured in the CDD ice cores averaged for three time periods: 1930–1950, 1965–1980, and 1980–1995. Outlier values in winter 1994/1995 were not considered, as well as values observed in the 1948 summer layers (SI Appendix). Data obtained in firn layers were also not considered (SI Appendix). Michel Legrand et al. PNAS 2018;115:48:12136-12141 ©2018 by National Academy of Sciences