Nitrate in Greenland and Antarctic ice cores: a detailed description of post-depositional processes

A compilation of nitrate (NO(3)(-)) data from Greenland has shown that recent NO(3)(-) concentrations reveal a temperature dependence similar to that seen in Antarctica. Except for sites with very low accumulation rates, lower temperatures tend to lead to higher NO(3)(-) concentrations preserved in the ice. Accumulation rate, which is closely linked to temperature, might influence the concentrations preserved in snow as well, but its effect cannot be separated from the temperature imprint. Processes involved in NO(3)(-) deposition are discussed and shown to be temperature- and/or accumulation-rate-dependent. Apart from scavenging of nitric acid (HNO(3)) during formation of precipitation, uptake of HNO(3) onto the ice crystal's surface during and after precipitation seems to contribute further to the NO(3)(-) concentrations found in surface snow. Post-depositional loss of NO(3)(-) from the top snow layers is caused by release of HNO(3) and by photolysis of NO(3)(-). It is suggested that photolysis accounts for considerable losses at sites with very low accumulation rates. Depending on the site characteristic, and given that the temperature and accumulation-rate dependence is quantified, it should be possible to infer changes in atmospheric HNO(3) concentrations.