Two Greenland ice cores reveal that abrupt climate warming and sea ice retreat in the Arctic preceded maximum iodine levels, reaching peak concentrations during interglacial periods.

Iodine has a significant impact on promoting the formation of new ultrafine aerosol particles and accelerating tropospheric and stratospheric ozone loss, thereby affecting radiative forcing and climate. However, iodine´s long-term natural evolution and its coupling with climate variability are unknown. This work combines two Greenland ice cores to report the Arctic iodine variability during the Last Glacial Cycle (last 127000 years). We provide evidence that ocean-ice-atmosphere exchange of biogenic iodine in the Arctic Ocean dominated the atmospheric iodine budget during periods of rapid climatic changes. Arctic iodine levels were highest and lowest during interglacial and glacial periods, respectively, modulated by ocean bioproductivity and sea ice dynamics. Finally, we discuss if iodine levels during past warmer-than-present climate phases can serve as analogues of future scenarios under an expected ice-free Arctic Ocean. We argue that the combination of natural biogenic ocean iodine release (boosted by ongoing Arctic warming and sea ice retreat) and anthropogenic ozone-induced iodine emissions may lead to a near future scenario with the highest iodine levels of the last 127000 years. Juan Pablo Corella, Niccolo Maffezzoli, Andrea Spolaor, Paul Vallelonga, Carlos A. Cuevas, Federico Scoto, Juliane Müller, Bo Vinther, Helle A. Kjær, Giulio Cozzi, Ross Edwards, Carlo Barbante and Alfonso Saiz-Lopez. Climate changes modulated the history of Arctic iodine during the Last Glacial Cycle, Nature Communications, DOI: 10.1038/s41467-021-27642-5