Publication Date:
2019
Description:
Abstract
Several post‐depositional processes impact snow nitrate, however, only the isotopic effects of nitrate photolysis have been quantified. Here, we discuss results from experiments in Antarctic snow investigating isotopic fractionation of nitrate due to volatilization. At ‐35oC, concentration and isotopic composition of nitrate remained constant during the 16‐day experiment. At ‐24oC, 7.5% of nitrate was lost, synchronous with 1.5‰ decrease in δ18O and a constant δ15N. At ‐4oC, 38% of nitrate was lost, and δ15N and δ18O decreased by 3.1‰ and 1.8‰, respectively. Results at ‐4oC yield calculated fractionation constants close to theoretical estimates including equilibrium isotopic exchange between nitric acid and nitrate and the desorption of nitric acid from water in quasi‐liquid layers. It suggests that isotopic fractionation associated with nitrate volatilization across most of Antarctica, especially at sites with temperatures 〈‐24oC, should be minor, but the isotopic effects at warmer sites should be considered in interpreting archived nitrate records.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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