Lithium isotope systematics in an endorheic saline lacustrine system: Insights from Qinghai Lake, China

IF 3.1 3区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Applied Geochemistry Pub Date : 2024-09-29 DOI:10.1016/j.apgeochem.2024.106190

Yin Li , Yang-Yang Wang , Fancui Kong , Haicheng Wei , Jack Geary Murphy , Dong-Bo Tan , Jing Chen , Jing Lei , Yigan Lu , Cheng-Long Yu , Yilin Xiao

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Abstract

The study of lithium isotopic (δ⁷Li) signatures in sedimentary deposits has become a powerful tool to infer past silicate weathering regimes, thus informing our knowledge of the geological carbon cycle and paleoclimate evolution. Sediments from Qinghai Lake, the largest saltwater lake in China (4625 km²), offer an unparalleled archive for investigating the climatic history of the Qinghai-Tibet Plateau. However, prior to leveraging the δ⁷Li proxy in this context, it is imperative to unravel the mechanisms of lithium (Li) isotope fractionation and elemental cycling within the lake's aqueous and sedimentary systems. In this study, we collected and analyzed samples of Qinghai Lake's water, sediments, and recharge waters (rivers, groundwater, and rainfall) to investigate the processes controlling the δ⁷Li value recorded in Qinghai Lake sediments.

Our data reveal subtle variances in Qinghai Lake water Li concentration ([Li]), ranging from 652 to 873 ng/g, suggesting interactions with iron oxides or suspended matter. The δ⁷Li signature, however, exhibits remarkable uniformity across the lake at 32.1‰ (±0.4‰). Near the estuary of the Buha River, there is a swift homogenization of [Li] and δ⁷Li, stabilizing within just 3 km of the inflow. Lake sediments exhibit δ⁷Li values ranging from 1.5‰ to 6.6‰, exceeding those of the upper continental crust (∼0‰ ± 4‰), yet approximately 30‰ lower than those in lake waters. This significant discrepancy between the δ⁷Li of lake water and sediments is likely due to the preferential incorporation of ⁶Li over ⁷Li during the neoformation of clay minerals.

Lithium mass balance modeling for Qinghai Lake, incorporating inputs from river and groundwater (∼46.5 t/a with δ⁷Li ∼18.3‰) and outputs via clay mineral uptake (∼44 t/a with δ⁷Li ∼5.1‰), indicates that the lake's Li system is currently out of steady state. The model predicts a gradual rise in the lake's Li inventory, estimated to achieve steady state within 1.2 ka and the δ⁷Li value of lake water will increase until reaching ∼45‰ assuming constant climate conditions.

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内生盐湖湖底系统的锂同位素系统学：中国青海湖的启示

对沉积物中锂同位素（δ7Li）特征的研究已成为推断过去硅酸盐风化机制的有力工具，从而有助于我们了解地质碳循环和古气候演变。青海湖是中国最大的咸水湖（4625 平方公里），其沉积物为研究青藏高原的气候历史提供了无与伦比的档案。然而，在利用δ7Li代用指标之前，当务之急是揭示锂（Li）同位素分馏机制以及湖泊水体和沉积体系中的元素循环。在这项研究中，我们采集并分析了青海湖的水、沉积物和补给水（河流、地下水和降雨）样本，研究了青海湖沉积物中记录的δ7Li值的控制过程。然而，整个湖泊的δ7Li特征显示出显著的一致性，为32.1‰（±0.4‰）。在布哈河河口附近，[Li]和δ7Li迅速同质化，在距流入河口仅 3 公里的范围内趋于稳定。湖泊沉积物中的δ7Li值在1.5‰至6.6‰之间，超过了大陆上地壳的δ7Li值（∼0‰ ± 4‰），但比湖水中的低δ7Li值约30‰。湖水和沉积物的δ7Li之间的这一显著差异可能是由于在粘土矿物的新形成过程中，6Li优先于7Li的掺入所致。青海湖的锂质量平衡模型包括来自河流和地下水的输入量（∼46.5 吨/年，δ7Li ∼18.3‰）和通过粘土矿物吸收的输出量（∼44 吨/年，δ7Li ∼5.1‰），表明该湖的锂系统目前处于非稳态。根据模型预测，湖泊的锂存量将逐步上升，估计在 1.2 ka 内达到稳定状态，假定气候条件不变，湖水的 δ7Li 值将增加，直至达到 ∼45‰。

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来源期刊

Applied Geochemistry 地学-地球化学与地球物理

CiteScore

6.10

自引率

8.80%

发文量

272

审稿时长

65 days

期刊介绍： Applied Geochemistry is an international journal devoted to publication of original research papers, rapid research communications and selected review papers in geochemistry and urban geochemistry which have some practical application to an aspect of human endeavour, such as the preservation of the environment, health, waste disposal and the search for resources. Papers on applications of inorganic, organic and isotope geochemistry and geochemical processes are therefore welcome provided they meet the main criterion. Spatial and temporal monitoring case studies are only of interest to our international readership if they present new ideas of broad application. Topics covered include: (1) Environmental geochemistry (including natural and anthropogenic aspects, and protection and remediation strategies); (2) Hydrogeochemistry (surface and groundwater); (3) Medical (urban) geochemistry; (4) The search for energy resources (in particular unconventional oil and gas or emerging metal resources); (5) Energy exploitation (in particular geothermal energy and CCS); (6) Upgrading of energy and mineral resources where there is a direct geochemical application; and (7) Waste disposal, including nuclear waste disposal.