Sediment-redox dynamics in an oligotrophic deep-water lake in Tierra del Fuego: insights from Fe isotopes

IF 1.7 3区 地球科学 Q4 ENVIRONMENTAL SCIENCES
Luis Gabriel Ordoñez Rendón, Ina Neugebauer, Camille Thomas, Massimo Chiaradia, Nicolas Waldmann, Daniel Ariztegui
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引用次数: 0

Abstract

For long time in the history of Earth, ferruginous conditions governed the oceans. With the rise of oxygen during the Proterozoic era and the subsequent evolution of living organisms, worldwide deposition of iron formations occurred. These sedimentary units reveal the transition into oxic oceans, passing by local and transitory euxinic conditions, especially in coastal shelves. Constraining the iron cycle and the biogeochemical processes occurring in present and past ferruginous basins helps answering some of the question regarding global oxygenation, the evolution of life and past climate changes. Therefore, Fe speciation and Fe isotopes in both Proterozoic and recent sedimentary records have been widely used to reconstruct past basin dynamics and redox conditions in the sediment–water interface. However, sedimentation and early diagenesis can alter paleoredox proxies and their primary climate signals. In this work, we disentangled alteration processes occurring at the redox front below the sediment–water interface of a ventilated deep-water lake (Lago Fagnano, Argentina/Chile). A sequential extraction protocol was applied to characterize two reactive Fe pools: Fe oxyhydroxides and reduced iron. Subsequently, Fe isotopes were constrained to determine the main processes mobilizing Fe. At the redox front, ferric minerals reach a δ56Fe value of − 1.3‰ resulting from oxidation of dissolved Fe likely following a Rayleigh distillation effect. Dissolved Fe is produced right below via Fe reduction, as shown by the low ferric Fe content. Our observations delineate a redox cycle and a redox horizon undergoing constant upward migration, initiated by regular sedimentation. However, during events of increased rapid sedimentation (e.g., seismites) this dynamic cycle is interrupted inducing full or partial preservation of the Fe-rich redox front. In such case, oxidation of dissolved Fe is interrupted and can be recycled in ferrous minerals, such as Fe monosulfides and amorphous phases with δ56Fe values down to − 1.7 ‰. These findings have significant implications for the recording of biogeochemical cycles in the geological past, the use of Fe isotopes in freshwater-lake sediments for paleoclimate studies, and the progress of our knowledge regarding the geochemistry of past oceans.

Abstract Image

火地岛寡营养深水湖沉积物氧化还原动力学:铁同位素的启示
在地球历史上的很长一段时间里,铁质环境一直统治着海洋。随着原生代氧气的增加和随后生物的进化,铁质地层在全球范围内沉积。这些沉积单元揭示了向含氧海洋的过渡,经过局部和短暂的富氧条件,特别是在沿海陆架。对现在和过去的铁质盆地中发生的铁循环和生物地球化学过程进行制约,有助于回答有关全球含氧量、生物进化和过去气候变化的一些问题。因此,原生代和近代沉积记录中的铁标本和铁同位素已被广泛用于重建过去的盆地动力学和沉积物-水界面的氧化还原条件。然而,沉积和早期成岩作用会改变古氧化还原代用指标及其主要气候信号。在这项研究中,我们对发生在一个通风深水湖(阿根廷/智利法尼亚诺湖)沉积物-水界面下方氧化还原前沿的变化过程进行了解构。采用顺序萃取协议来描述两个活性铁池的特征:氧化铁和还原铁。随后,对铁同位素进行了限制,以确定铁的主要迁移过程。在氧化还原前沿,铁矿物的δ56Fe值为-1.3‰,这可能是溶解铁在雷利蒸馏效应下被氧化所致。正如较低的铁含量所显示的那样,溶解铁是通过铁还原在水下产生的。我们的观测结果划定了一个氧化还原周期和一个氧化还原层,该氧化还原层在定期沉积作用下不断上移。然而,在沉积速度加快的情况下(如地震带),这种动态循环会被打断,导致富铁氧化还原层全部或部分保留下来。在这种情况下,溶解铁的氧化作用会被打断,并可在亚铁矿物(如单硫化铁和δ56Fe值低至-1.7‰的无定形相)中循环。这些发现对于记录地质过去的生物地球化学循环、利用淡水-湖泊沉积物中的铁同位素进行古气候研究以及我们对过去海洋地球化学的认识具有重要意义。
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来源期刊
Journal of Paleolimnology
Journal of Paleolimnology 地学-地球科学综合
CiteScore
3.70
自引率
9.50%
发文量
44
审稿时长
3 months
期刊介绍: The realization that a historical perspective is often useful, if not essential, to the understanding of most limnological processes has resulted in the recent surge of interest in paleolimnology. The main aim of the Journal of Paleolimnology is the provision of a vehicle for the rapid dissemination of original scientific work dealing with the reconstruction of lake histories. Although the majority of papers deal with lakes, paleoenvironmental studies of river, wetland, peatland and estuary systems are also eligible for publication. The Journal of Paleolimnology, like the subject itself, is multidisciplinary in nature, and papers are published that are concerned with all aspects (e.g. biological, chemical, physical, geological, etc.) of the reconstruction and interpretation of lake histories. Both applied and more theoretical papers are equally encouraged. The Journal of Paleolimnology will continue to be a major repository for papers dealing with climatic change, as well as other pressing topics, such as global environmental change, lake acidification, eutrophication, long-term monitoring, and other aspects of lake ontogeny. Taxonomic and methodological papers are also acceptable provided they are of relatively broad interest. New equipment designs are frequently featured. In addition to original data and ideas, the Journal of Paleolimnology also publishes review articles, commentaries and program announcements. A relevant Book Review Section is also featured.
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