Iodine concentration in ice remained constant during the pre-ozone hole period (1800-1974) but has continuously declined since the onset of the ozone hole era (~1975), closely tracking the total ozone evolution over Antarctic

Polar stratospheric ozone has decreased since the 1970s due to anthropogenic emissions of chlorofluorocarbons and halons, resulting in the formation of an ozone hole over Antarctica. The effects of the ozone hole and the associated increase in incoming UV radiation on the biosphere and on human health have been widely studied; however, the impact on geochemical cycles of ice photoactive elements, such as iodine, remains mostly unexplored. This work combines the first iodine record from the inner Antarctic Plateau that covers the last 212 years (1800-2012 CE), laboratory measurements and chemistry-climate model simulations to show that the “recent” iodine decrease (~1975-present) is caused by enhanced iodine re-emission from snowpack due to the ozone hole driven increase in UV-radiation reaching the Antarctic Plateau. The chemical process behind this effect is that the photooxidation of iodide in ice when exposed to Antarctic sunlight (O2(aq) + 4H+(aq) + 6I−(aq) → 2H2O + 2 I3−(aq); I3−(aq) ↔ I2(g) + I−(aq)) leads to the release of I2(g) to the atmosphere, and proceeds via a charge-transfer complex with oxygen (I−-O2(aq)). This complex has a local absorption maximum between 280 and 330 nm, i.e., encompassing the same spectral range where the largest changes in incoming UV radiation were observed between the pre- and post-ozone hole periods. The resulting increase in ice-to-atmosphere iodine mass transfer has relevant implications for polar tropospheric chemistry and for the Earth’s radiative budget since iodine catalytic cycles play a crucial role in the destruction of tropospheric ozone and can also act as cloud condensation nuclei. Although the Antarctic ozone hole was identified decades ago, these results shed new light on previously unexplored environmental effects caused by its occurrence. Finally, the direct link observed between stratospheric ozone loss and iodine in ice suggests the potential for ice core iodine records from the inner Antarctic Plateau to be as an archive for past stratospheric ozone trends. Andrea Spolaor, Francois Burgay, Rafael P. Fernandez, Clara Turetta, Carlos A. Cuevas, Kitae Kim, Douglas E. Kinnison, Jean-François Lamarque, Fabrizio De Blasi, Elena Barbaro, Juan Pablo Corella, Paul Vallelonga, Massimo Frezzotti, Carlo Barbante and Alfonso Saiz-Lopez. Antarctic ozone hole modifies iodine geochemistry on the Antarctic Plateau. Nature Communications.  DOI: 10.1038/s41467-021-26109-x