Biogeochemical nitrogen cycle response to Middle Permian climate warming in Northwest China paleolake

IF 4 1区地球科学 Q1 GEOGRAPHY, PHYSICAL

Global and Planetary Change Pub Date : 2025-09-11 DOI:10.1016/j.gloplacha.2025.105069

Xueqi Song , Ruining Hu , Wenquan Xie , Jinqi Xu , Xin Liu , Haibo Xu , Jingqiang Tan , Thomas J. Algeo

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引用次数: 0

Abstract

The response of nitrogen cycling in lake systems to icehouse-to-greenhouse climate transitions remains essentially uninvestigated, even though similar responses are imminent in modern lakes. Here, we examine the biogeochemical nitrogen cycle in Paleolake Junggar, a saline lacustrine system in the Jimsar Sag (Junggar Basin, NW China) through analysis of elemental, isotopic, and biomarker proxies in the Middle Permian Lucaogou Formation. The study section comprises three depositional intervals (Intervals A, B, and C) based on variations in organic matter abundance and lithofacies associations. Our results document a climatic shift from cold-arid in Interval A (oldest) to warm-humid conditions in Interval C (youngest), promoting terrestrial nutrient influx. Salinity and redox proxies suggest higher salinity and stronger anoxia in Intervals A and C compared to Interval B. Biomarkers show an abundance of halotolerant green algae in Interval A, with increased cyanobacterial inputs in Intervals BC. A decrease in nitrogen isotopic compositions (δ¹⁵N) records a climate-driven reduction in lake water pH, defining three biogeochemical nitrogen cycling stages. Under the initially arid climate conditions of Interval A, anoxic and alkaline conditions were favorable to halotolerant green algae and methanogens, and ammonia volatilization was strong (δ¹⁵N > +10 ‰). Climate warming and increased chemical weathering in Interval B led to cyanobacterial blooms in a nutrient-rich watermass along with incomplete denitrification accompanied by possible biological nitrogen fixation (+8 ‰ < δ¹⁵N < +10 ‰). Following development of a wetter climate in Interval C, the stratified and neutral-pH lake was marked by increased productivity and bottom-water anoxia, facilitating the enrichment of organic matter and triggering a shift to dominance of denitrification (+5 ‰ < δ¹⁵N < +8 ‰). These findings demonstrate that nitrogen isotopes can serve as an effective proxy for climate change in alkaline lakes, especially offering insights into the response of biotic community structures to Middle Permian climate warming.

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西北古湖泊生物地球化学氮循环对中二叠世气候变暖的响应

湖泊系统中氮循环对冰窖到温室气候转变的响应基本上尚未被研究，尽管类似的响应即将在现代湖泊中出现。通过对中二叠统芦草沟组元素、同位素和生物标志物等指标的分析，研究了准噶尔盆地吉木萨尔凹陷古咸化湖系准噶尔湖的生物地球化学氮循环。根据有机质丰度变化和岩相组合，研究段分为3个沉积层段（A、B、C）。我们的研究结果记录了气候从间隔a（最古老）的寒冷干旱到间隔C（最年轻）的温暖潮湿条件的转变，促进了陆地营养物质的流入。盐度和氧化还原指标表明，与区间b相比，区间A和C的盐度更高，缺氧程度更强。生物标志物显示，区间A耐盐绿藻丰富，而区间BC的蓝藻输入增加。氮同位素组成（δ15N）的减少记录了气候驱动的湖水pH降低，定义了三个生物地球化学氮循环阶段。在A段初始干旱气候条件下，缺氧和碱性条件有利于耐盐绿藻和产甲烷菌生长，氨挥发强（δ15N > +10‰）。B段气候变暖和化学风化作用增强导致富营养化水体蓝藻大量繁殖，并伴有不完全反硝化作用，可能伴有生物固氮作用（+8‰< δ15N < +10‰）。随着C段湿润气候的发展，层状和中性ph湖泊以生产力增加和底部缺氧为特征，促进了有机质的富集，引发了反硝化为主的转变（+5‰< δ15N < +8‰）。这些发现表明，氮同位素可以作为碱性湖泊气候变化的有效指标，特别是为生物群落结构对中二叠世气候变暖的响应提供了新的见解。

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来源期刊

Global and Planetary Change 地学天文-地球科学综合

CiteScore

7.40

自引率

10.30%

发文量

226

审稿时长

63 days

期刊介绍： The objective of the journal Global and Planetary Change is to provide a multi-disciplinary overview of the processes taking place in the Earth System and involved in planetary change over time. The journal focuses on records of the past and current state of the earth system, and future scenarios , and their link to global environmental change. Regional or process-oriented studies are welcome if they discuss global implications. Topics include, but are not limited to, changes in the dynamics and composition of the atmosphere, oceans and cryosphere, as well as climate change, sea level variation, observations/modelling of Earth processes from deep to (near-)surface and their coupling, global ecology, biogeography and the resilience/thresholds in ecosystems. Key criteria for the consideration of manuscripts are (a) the relevance for the global scientific community and/or (b) the wider implications for global scale problems, preferably combined with (c) having a significance beyond a single discipline. A clear focus on key processes associated with planetary scale change is strongly encouraged. Manuscripts can be submitted as either research contributions or as a review article. Every effort should be made towards the presentation of research outcomes in an understandable way for a broad readership.