Isotopes of molecular nitrogen, oxygen, and argon in the South Pole ice core document local and global climate change through the last deglaciation.

Ice core gas records are an invaluable paleoclimatic archive. The three most abundant gases in air, nitrogen (N₂), oxygen (O₂), and argon (Ar), provide paleoclimatic information about both global and regional processes including tropical rainfall patterns and local surface temperature changes. We present a large dataset of elemental and isotopic ratios of N₂, O₂, and Ar (O₂/N₂, Ar/N₂, δ¹⁵N, δ¹⁸O, & δ⁴⁰Ar) from the South Pole Ice Core between 0 – 52,000 yr BP, with a focus on high precision δ¹⁵N and δ⁴⁰Ar measurements between 5,000 – 32,000 yr BP. The unprecedented precision of our measurements allows us to use δ¹⁵N_excess (= δ¹⁵N - δ⁴⁰Ar/4) to reconstruct past temperature change at the South Pole. Although this proxy has been widely applied in Greenland, this is the first time it has been successfully applied to Antarctic ice and provides a valuable independent check on the more traditional water isotopes temperature proxy. We find good agreement between the two during the relatively stable climate of the glacial period and the Holocene. However the temperature reconstructions diverge during the deglaciation. We present several hypotheses that could explain the discrepancy and look to other emerging ice core temperature proxies to support our interpretation.