Browsing by Author "Haslun, Joshua A."

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    Extreme enrichment in atmospheric 15N15N
    (AAAS, 2017) Yeung, Laurence Y.; Li, Shuning; Kohl, Issaku E.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Hu, Huanting; Fischer, Tobias P.; Schauble, Edwin A.; Young, Edward D.
    Molecular nitrogen (N2) comprises three-quarters of Earth’s atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.
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    In Situ Quantification of Biological N2 Production Using Naturally Occurring 15N15N
    (American Chemical Society, 2019) Yeung, Laurence Y.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Sun, Tao; Young, Edward D.; van Kessel, Maartje A.H.J.; Lücker, Sebastian; Jetten, Mike S.M.
    We describe an approach for determining biological N2 production in soils based on the proportions of naturally occurring 15N15N in N2. Laboratory incubation experiments reveal that biological N2 production, whether by denitrification or anaerobic ammonia oxidation, yields proportions of 15N15N in N2 that are within 1‰ of that predicted for a random distribution of 15N and 14N atoms. This relatively invariant isotopic signature contrasts with that of the atmosphere, which has 15N15N proportions in excess of the random distribution by 19.1 ± 0.1‰. Depth profiles of gases in agricultural soils from the Kellogg Biological Station Long-Term Ecological Research site show biological N2 accumulation that accounts for up to 1.6% of the soil N2. One-dimensional reaction-diffusion modeling of these soil profiles suggests that subsurface N2 pulses leading to surface emission rates as low as 0.3 mmol N2 m–2 d–1 can be detected with current analytical precision, decoupled from N2O production.