Isotopic composition of Antarctic Dry Valley nitrate: Implications for NOy sources and cycling in Antarctica

Nitrates minerals from the Dry Valleys of Antarctica have been analyzed for their oxygen and nitrogen isotopic compositions. The ¹⁵N was depleted with δ¹⁵N values ranging from −9.5 to −26.2‰, whereas the ¹⁷O and ¹⁸O isotopes were highly enriched (with excess ¹⁷O) with δ¹⁸O values spanning 62–76‰ and Δ¹⁷O values from 28.9 to 32.7‰. These are the largest ¹⁷O enrichments observed in any known mineral. The oxygen isotopes indicate that nitrate is from a combination of tropospheric transport of photochemically produced HNO₃ and HNO₃ formed in the stratosphere.