Collaborative Research: SNOWpack Photodenitrification from the Antarctic and Arctic Cryosphere (SNOWPAAC)

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The importance of knowing the different sources of atmospheric nitrate to the polar ice sheets of Antarctica and Greenland, along with their transport paths, is of intrinsic interest to the atmospheric chemistry of polar NOx species. In turn, surface photolysis of snowpack nitrate renders these ice sheets as strongly oxidizing surfaces during sunlight. Attempts to derive past conditions or variability of atmospheric NOx (= NO + NO2 +?) species from ice core records will need to take photodenitrification and source transfer function effects into account. The approach willcontinue to use a inverse chemical transfer model (adjoint GEOS-Chem) to test the sensitivity of nitrate deposition to the Antarctic continent from various possible sources. The following questions are posed: 1) what are the important sources of nitrate to Antarctia (and Greenland) in the present and in the pre-industrial Holocene? 2) How does the recycling of reactive nitrogen at the atmosphere-snow interface redistribute nitrate across large polar ice sheets? and 3) are their implications for nitrate preservation in ice cores and their interpretation?Goals being pursued in this modeling study include the reconstruction of past (polar) atmospheric composition and a better contemporary understanding of the variability of atmospheric reactive nitrogen compounds as may be discerned from measurements of nitrate concentrations retained in snow, firn and possibly ice cores in polar regions.