Shallow Antarctic blue ice shows photochemical influence on trapped greenhouse gases

Abstract

Ice cores are archives that preserve past atmospheric greenhouse gases (GHGs). Trapped GHGs can be modified by post-depositional processes, but the mechanisms responsible for such modifications remain incompletely understood. Here, we show that photochemical reactions may contribute to GHG anomalies observed in the Larsen blue-ice area, East Antarctica. CO2 concentrations decrease with depth and stabilize near 4.60 m depth, while CH4 first increase and then gradually decrease. Total air content and various geochemical data indicate that melting, modern air/aerosol intrusion, and microbial activity are less likely to explain the anomalous GHG concentrations. In contrast, the depletion of δ18Oatm observed in the upper 1–2 m of the blue ice is consistent with photochemical influence. Carbon isotope measurements indicate mixed organic and inorganic sources for excess CO2 and an organic source for excess CH4. These findings suggest that photochemical processes can modify trapped GHGs in shallow exposed blue ice and should be considered when interpreting GHG records from blue-ice areas. Photochemical processes may alter trapped greenhouse gases (GHG) in shallow Antarctic blue ice, with implications for interpreting blue-ice GHG records, according to a study combining greenhouse gas, isotopic and geochemical analyses of 11 shallow ice cores from the Larsen blue-ice area.