Oxygenation and Alkalinity Drive the Lacustrine Nitrogen Isotope Record Throughout the Past 3.2 Billion Years

IF 3.4 2区 地球科学 Q2 BIOLOGY
Geobiology Pub Date : 2025-09-18 DOI:10.1111/gbi.70033
Diana Velazquez, Nathan D. Sheldon, Michael T. Hren, Jenan J. Kharbush
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引用次数: 0

Abstract

The widespread, stepwise oxygenation of Earth's atmosphere in the Precambrian led to a transformation of the global carbon (C) and nitrogen (N) cycles. While the temporal evolution of these nutrient cycles has been studied extensively in marine environments, lacustrine environments are understudied. This study first examines how water column oxygen conditions impact sedimentary carbon (δ13Corg) and nitrogen (δ15N) isotope signals in modern lakes. Subsequently, we use these patterns to interpret past changes in the geological record of lacustrine δ15N during atmospheric oxygenation. The compiled modern lake sediment dataset reveals average (± standard deviation) δ15N values of +2.9‰ ± 3.2‰ and δ13Corg values of −25.99‰ ± 3.77‰, as well as thresholds in δ13Corg for oxic versus anoxic conditions, and in δ15N for circumneutral versus alkaline pH conditions. In contrast to the stepwise oxygenation of the atmosphere, the lacustrine δ15N record does not directly reflect major oxygenation events, but instead increases gradually in response to the evolution of new aerobic N metabolic pathways, with a notable shift in the Phanerozoic. While we found that intrasite variability at a single modern anoxic lake is expected to remain within ~5‰ for δ15N, alkaline lakes in both the ancient and modern deviate from this range. We observe δ15N > +10‰ for approximately half of total ancient alkaline lake sediments and some modern lake sediments. This is consistent with previous applications of enriched δ15N as a basicity proxy. The lacustrine δ15N record aligns well with the evolution of microbial metabolic pathways in addition to providing information pertaining to environmental conditions of the depositional setting.

Abstract Image

32亿年来,氧合和碱度驱动湖泊氮同位素记录。
在前寒武纪,地球大气的广泛、逐步的氧化作用导致了全球碳(C)和氮(N)循环的转变。虽然这些营养循环在海洋环境中的时间演化已经得到了广泛的研究,但对湖泊环境的研究还不够。本研究首先考察了水柱氧条件对现代湖泊沉积碳(δ13Corg)和氮(δ15N)同位素信号的影响。随后,我们利用这些模式来解释大气氧化过程中湖泊δ15N地质记录的过去变化。现代湖泊沉积物数据集的δ15N平均值(±标准差)为+2.9‰±3.2‰,δ13Corg平均值(±标准差)为-25.99‰±3.77‰,δ13Corg值为缺氧与缺氧条件下的阈值,δ15N值为环中性与碱性条件下的阈值。与大气的逐步氧合作用不同,湖相δ15N记录并不直接反映主要的氧合作用事件,而是随着新的有氧N代谢途径的演化而逐渐增加,在显生宙发生了显著的变化。虽然我们发现单个现代缺氧湖的岩内变率在δ15N值范围内保持在~5‰,但古代和现代碱性湖的岩内变率都偏离了这一范围。近一半的古碱性湖泊沉积物和部分现代湖泊沉积物δ15N > +10‰。这与以往富δ15N作为碱度代表的应用一致。湖相δ15N记录与微生物代谢途径的演化具有较好的一致性,并提供了沉积环境条件的相关信息。
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来源期刊
Geobiology
Geobiology 生物-地球科学综合
CiteScore
6.80
自引率
5.40%
发文量
56
审稿时长
3 months
期刊介绍: The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time. Geobiology invites submission of high-quality articles in the following areas: Origins and evolution of life Co-evolution of the atmosphere, hydrosphere and biosphere The sedimentary rock record and geobiology of critical intervals Paleobiology and evolutionary ecology Biogeochemistry and global elemental cycles Microbe-mineral interactions Biomarkers Molecular ecology and phylogenetics.
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