PHYSICALLY-BASED MODELING OF ATMOSPHERE-TO-SNOW-TO-FIRN TRANSFER OF H2O2 AT SOUTH-POLE

Quantitative interpretation of ice core chemical records requires a de tailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow, firn, and ice. A unique, 2 year set of year-round surface snow samples at South Pole and snow pits, wi th associated accumulation histories, were used to test a physically b ased model for atmosphere-to-firn transfer of H2O2. The model, which e xtends our previous transfer modeling at South Pole into the snowpack, is based on the advection-dispersion equation and spherical diffusion within representative snow grains. Required physical characteristics of the snowpack, such as snow temperature and ventilation, were estima ted independently using established physical models. The surface snow samples and related model simulations show that there is a repeatable annual cycle in H2O2 in the surface snow at South Pale. It peaks in ea rly spring, and surface snow concentration is primarily determined by atmospheric concentration and temperature, with some dependence on gra in size. The snow pits and associated model simulations point out the impor tance of accumulation timing and annual accumulation rate in und erstanding the deposition and preservation of H2O2 and delta(18)O at S outh Pole. Long-term snowpack simulations suggest that the firn contin ues to lose H2O2 to the atmosphere for at least 10-12 years (similar t o 3 m) after burial at current South Pole temperatures and accumulatio n rates.