Reconstructing atmospheric nitrogen pressure from N2-Ne-Ar systematics in quartz-hosted fluid inclusions

On Earth, atmospheric di-nitrogen partial pressure (pN 2 ) exerts a primary control on surface pressure, climate, and planetary habitability, yet the long-term history of atmospheric pN 2 remains only sparsely constrained and is still characterized by substantial proxy-dependent uncertainties. Quartz-hosted fluid inclusions are recognized archives of paleo-atmospheric gases, but quantitative reconstruction of pN 2 has been limited by radiogenic overprints and post-entrapment modification. Here we present new N 2 -Ne-Ar elemental and isotopic data from ∼20 Ma quartz samples from the Alpine and Himalayan regions to assess the robustness of noble-gas-based approaches for reconstructing pN 2 . Mixing relationships between the N 2 / 22 Ne and 21 Ne/ 22 Ne ratios enable extrapolation to air-saturated water endmembers and isolation of the atmospheric N 2 component largely independent of radiogenic interference. Alpine samples and one Himalayan sample (DK113) yield reconstructed pN 2 values consistent with the modern atmosphere within uncertainty (BEL2: 0−0.69 bar, BEL11: 0.09–1.44 bar, BEL15: 0−1.24 bar, and DK113: 0−0.92 bar), with an average value of 0.34 + 1.50/− 0.34 bar for the BEL + DK113 sample subset. Including JL106 and JL107, gives a higher although less precise apparent pN 2 of 0.98 + 2.84/− 0.98 bar, illustrating the influence of non-atmospheric nitrogen addition and the importance of sample screening. Our results provide a proof-of-concept that N 2 -Ne systematics can be used to recover plausible atmospheric pN 2 values from suitably screened fluid inclusions and establish a promising framework for extending such reconstructions to older geological archives.