Oxygen-17 anomaly in soil nitrate: A new precipitation proxy for desert landscapes

Abstract

The nitrogen cycle in desert soil ecosystems is particularly sensitive to changes in precipitation, even of relatively small magnitude and short duration, because it is already under water stress. This suggests that desert soils may have preserved past evidence of small variations in continental precipitation. We have measured nitrate (NO 3-) concentrations in soils from the Atacama (Chile), Kumtag (China), Mojave (US), and Thar (India) deserts, and stable nitrogen and oxygen isotope (15 N, 17 O, and 18 O) abundances of the soil NO 3-. 17 O anomalies (Δ 17 O), the deviations from the mass-independent isotopic fractionation, were detected in soil NO 3 from almost all sites of these four deserts. There was a strong negative correlation between the mean annual precipitation (MAP) and soil NO 3-Δ 17 O values (Δ 17 O NO3soil). This MAP-Δ 17 O NO3soil correlation advocated Δ 17 O NO3soil as a new precipitation proxy and was then used to assess precipitation changes in southwestern US at the Pliocene-Pleistocene boundary, in South America during the Miocene, and the Sahara Desert in the past 10 kyr using NO 3-Δ 17 O in paleosols or ancient aquifers. Global and the US maps of surface Δ 17 O NO3soil were also projected with available MAP datasets based on the MAP-Δ 17 O NO3soil model.

A Complete Isotope (δ15N, δ18O, Δ17O) Investigation of Atmospherically Deposited Nitrate in Glacial‐Hydrologic Systems Across the Third Pole Region

“…However, nitrate in desert soils may possess nonzero Δ 17 O values due to limited nitrification in desert ecosystems. The soil nitrate Δ 17 O values are negatively correlated with mean annual precipitation in desert landscapes (Wang et al, 2016). We noted that the mean annual precipitation (1979–2015) at the Western TP, one of major dust sources over the TP (Li et al, 2012), ranged from ~70 to ~180 mm (http://en.tpedatabase.cn/portal/index.jsp).…”

“…We noted that the mean annual precipitation (1979–2015) at the Western TP, one of major dust sources over the TP (Li et al, 2012), ranged from ~70 to ~180 mm (http://en.tpedatabase.cn/portal/index.jsp). Although soil nitrate isotopic compositions over the TP were not determined, soil nitrate Δ 17 O values over the Western TP might be as high as ~15‰ based on the empirical estimation by Wang et al (2016). The potential role of soil nitrate in altering atmospheric nitrate Δ 17 O values should be further investigated by direct isotopic analysis of soil nitrate from the TP.…”

“…Since the TP is an arid region heavily influenced by mineral dust (Li et al, 2012) (Wang et al, 2016). We noted that the mean annual precipitation at the Western TP, one of major dust sources over the TP (Li et al, 2012) ).…”

Isotope Investigation of Nitrate in Soils and Agricultural Drains of the Lower Yakima Valley, Washington

“…A potential mechanism for large quantities of nitrate to be transported into soils is millennial-scale atmospheric deposition, followed by partial biologic processing. A recent study showed that nitrogen cycling in soils depends on mean annual precipitation (MAP) with Δ 17 O values that are increasingly shifted away from the atmospheric value with increasing MAP due to increased biological nitrogen cycling. Wang et al developed an empirical equation to describe this shift: …”

“…A recent study showed that nitrogen cycling in soils depends on mean annual precipitation (MAP) with Δ 17 O values that are increasingly shifted away from the atmospheric value with increasing MAP due to increased biological nitrogen cycling. Wang et al developed an empirical equation to describe this shift: …”