Stüeken Eva E, Tino Christopher, Arp Gernot, Jung Dietmar, Lyons Timothy W
School of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, Fife, KY16 9AL Scotland, UK.
Virtual Planetary Laboratory, University of Washington, Seattle, WA 98195, USA.
Sci Adv. 2020 Feb 26;6(9):eaay3440. doi: 10.1126/sciadv.aay3440. eCollection 2020 Feb.
High-pH alkaline lakes are among the most productive ecosystems on Earth and prime targets in the search for life on Mars; however, a robust proxy for such settings does not yet exist. Nitrogen isotope fractionation resulting from NH volatilization at high pH has the potential to fill this gap. To validate this idea, we analyzed samples from the Nördlinger Ries, a Miocene impact crater lake that displayed pH values up to 9.8 as inferred from mineralogy and aqueous modeling. Our data show a peak in δN of +17‰ in the most alkaline facies, followed by a gradual decline to around +5‰, concurrent with the proposed decline in pH, highlighting the utility of nitrogen isotopes as a proxy for high-pH conditions. In combination with independent mineralogical indicators for high alkalinity, nitrogen isotopes can provide much-needed quantitative constraints on ancient atmospheric co (partial pressure of CO) and thus climatic controls on early Earth and Mars.
高pH值的碱性湖泊是地球上生产力最高的生态系统之一，也是在火星上寻找生命的主要目标；然而，目前还没有适用于此类环境的可靠替代指标。在高pH值条件下，由NH挥发导致的氮同位素分馏有可能填补这一空白。为了验证这一想法，我们分析了来自诺德林格里斯（Nördlinger Ries）的样本，这是一个中新世撞击坑湖，根据矿物学和水相模拟推断，其pH值高达9.8。我们的数据显示，在最碱性的相中，δN峰值为+17‰，随后逐渐下降至约+5‰，这与推测的pH值下降同时发生，突出了氮同位素作为高pH值条件替代指标的作用。结合高碱度的独立矿物学指标，氮同位素可以为古代大气co（CO的分压）提供急需的定量限制，从而为早期地球和火星的气候控制提供依据。
