Thermodynamic Predictions of Hydrogen Generation during the Serpentinization of Harzburgite with Seawater-derived Brines

IF 3.8 Q2 ASTRONOMY & ASTROPHYSICS
Sanjoy M. Som, Serhat Sevgen, Adam A. Suttle, Jeff S. Bowman and Britney E. Schmidt
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Abstract

Salty aqueous solutions (brines) occur on Earth and may be prevalent elsewhere. Serpentinization represents a family of geochemical reactions where the hydration of olivine-rich rocks can release aqueous hydrogen, H2(aq), as a byproduct, and hydrogen is a known basal electron donor for terrestrial biology. While the effects of lithological differences on serpentinization products have been thoroughly investigated, effects focusing on compositional differences of the reacting fluid have received less attention. In this contribution, we investigate how the chemistry of seawater-derived brines affects the generation of biologically available hydrogen resulting from the serpentinization of harzburgite. We numerically investigate the serpentinization of ultramafic rocks at equilibrium with an array of brines at different water activities (a proxy for salt concentration in aqueous fluids and a determinant for habitability) derived from seawater evaporation. Because the existing supersaturation of aqueous calcium carbonate, a contributor to dissolved inorganic carbon (DIC) in natural seawater, cannot be captured in equilibrium calculations, we bookend our calculations by enabling and suppressing carbonate minerals when simulating serpentinization. We find that the extent of DIC supersaturation can provide an important control of hydrogen availability. Increased DIC becomes a major sink for hydrogen by producing formate and associated complexes when the reacting fluids are acidic enough to allow for CO2. Indeed, H2(aq) reduces CO2(aq) to formate, leading to a hydrogen deficit. These conclusions provide additional insights into the habitability of brine systems, given their potential for serpentinization across diverse planetary bodies such as on Mars and ocean worlds.
海水卤水蛇床子化过程中氢气生成的热力学预测
地球上存在含盐水溶液(盐水),其他地方也可能普遍存在。蛇纹石化是地球化学反应的一种,富含橄榄石的岩石在水化过程中会释放出水溶液氢(H2(aq))作为副产品,而氢是已知的陆地生物的基本电子供体。虽然岩性差异对蛇纹石化产物的影响已得到深入研究,但反应流体成分差异的影响却较少受到关注。在这篇论文中,我们研究了海水衍生盐水的化学性质如何影响哈兹堡垒岩蛇纹石化过程中产生的生物可用氢。我们用数值方法研究了超基性岩在与一系列不同水活度的盐水(水流中盐浓度的代表和可居住性的决定因素)达到平衡时的蛇纹石化过程。碳酸钙是天然海水中溶解无机碳(DIC)的成因之一,由于平衡计算无法捕捉到碳酸钙水溶液的过饱和度,因此我们在模拟蛇化过程中通过启用和抑制碳酸盐矿物来对计算进行补充。我们发现,DIC 过饱和的程度可以对氢的可用性起到重要的控制作用。当反应流体的酸性足以允许二氧化碳进入时,DIC的增加会产生甲酸盐和相关的络合物,从而成为氢的主要吸收汇。事实上,H2(aq)会将 CO2(aq)还原成甲酸盐,从而导致氢气不足。考虑到盐水系统在火星和海洋世界等不同行星体中的蛇床子化潜力,这些结论为盐水系统的宜居性提供了更多启示。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
The Planetary Science Journal
The Planetary Science Journal Earth and Planetary Sciences-Geophysics
CiteScore
5.20
自引率
0.00%
发文量
249
审稿时长
15 weeks
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