Preservation of Hydrogen Peroxide and Formaldehyde in Snow and Firn in West Antarctica: Implications for a Potential Deep Ice-core Record.

Ice-core records of formaldehyde (HCHO) and hydrogen peroxide (H2O2) yield the potential to assess how the atmospheric oxidation capacity has changed in the past due to natural and anthropogenic causes. Atmospheric and shallow-core measurements of formaldehyde (HCHO) and hydrogen peroxide (H2O2) from a transantarctic traverse (ITASE) were used to test air-snow transfer models at a variety of different locations in West Antarctica. Snow pit profiles (1-2 m depth) of H2O2 from 9 sites show with one exception a clear seasonal signal, with absolute concentrations in the summer of 35-265 ppbw and in the winter of 0-85 ppbw. HCHO measured down to a depth of 1 m is on the order of 1.0-5.5 ppbw at the surface, and up to a factor of 3 higher in the layer of the previous winter, consistent with thermal release of HCHO from the near surface snow in spring and summer. Calculated profiles derived with existing physical transfer models are consistent with measurements. Spot measurements of the respective atmospheric mixing ratios in summer were used to constrain the model calculations and are also presented. At warm, low-accumulation sites little H2O2 is present below 75 cm due to reemission to the atmosphere. In contrast, shallow cores in the vicinity of a prospective inland deep drilling site show that the annual accumulation rate is sufficiently high and the average temperature sufficiently low so that H2O2 is preserved at depth. Based on these findings, ice core records of formaldehyde and hydrogen peroxide at the prospective inland deep drilling site would be suitable to investigate past changes in atmospheric composition of reversibly deposited species.