Correlated molybdenum and uranium isotope signatures in modern anoxic sediments: implications for their use as paleo-redox proxy

Published on Feb 1, 2020in Geochimica et Cosmochimica Acta4.659
· DOI :10.1016/J.GCA.2019.11.031
Annika Brüske6
Estimated H-index: 6
(Leibniz University of Hanover),
Stefan Weyer35
Estimated H-index: 35
(Leibniz University of Hanover)
+ 6 AuthorsTimothy W. Lyons91
Estimated H-index: 91
(UCR: University of California, Riverside)
Abstract Redox-sensitive trace metals and their isotopes have emerged as important tools that are used to reconstruct the redox-evolution of the ocean-atmosphere system. However, reliability of such reconstructions ultimately depends on a solid understanding of the proxies in the present-day oceanic system and their archival potential in sediments. This study compares isotope fractionation of molybdenum (Mo) and uranium (U) during their removal from seawater and deposition into sediments by investigating sites at various depths of the presently two largest restricted anoxic oceanic basins: The Black Sea and the Cariaco Basin. In support of previous investigations, our data indicate that Mo scavenging and isotope fractionation are mainly controlled by water column sulfide levels. In contrast to Mo, U reduction and immobilization appears to occur mainly at the sediment-water interface and within the uppermost few cm of the sediment pile in both basins. In the Black Sea, decreasing δ238U of surface sediments with increasing water depth correlate with trends for water column δ238U, implying constant U isotope fractionation between water and sediment. However, increasing U concentrations and δ238U within the uppermost few cm of the sediment pile of both basins indicate additional U reduction with depth. Despite the different mechanisms for Mo and U removal and associated isotope fractionations, a similar inverse correlation between δ98Mo and δ238U is observed for sediments of both basins, which translates in a positive correlation of Mo and U isotope fractionation between the sediments and open seawater. The correlation of δ98Mo and δ238U indicates a similar response of isotope fractionation to the efficiency of Mo and U removal that is mainly controlled by sulfate reduction rates. High dissolved sulfide concentrations and sulfate reduction rates are responsible for very effective Mo and U removal and corresponding minor Mo and U isotope fractionation relative to seawater. Further, high dissolved sulfide concentrations also correlate positively with deep water renewal times, resulting in an isotopically fractionated water column with low δ238U (and somewhat higher δ98Mo) in restricted basins with sluggish ventilations, such as the Black Sea. Both mechanisms result in negatively correlated δ98Mo and δ238U with high δ98Mo and low δ238U in sediments under strong euxinic conditions. The particularly strong correlation observed for Cariaco Basin sediments may indicate that its water column was variably stratified in the past. The observed δ98Mo and δ238U correlation of both basins can be reproduced in a simple coupled water column and sediment reactive transport model. Different slopes in δ98Mo and δ238U trends can be linked to varying degree of basin restriction, sulfate reduction rates, and isotope compositions of the respective water columns. The offset towards lower δ98Mo (and δ238U), observed for Cariaco Basin sediments compared to those from the Black Sea, may be the result of inefficient Mo reduction with high Mo isotope fractionation or isotopically light Mo from a particulate Fe-Mn oxide shuttle. The results of this study will help to interpret sedimentary Mo and U isotope values, while showing that coupling of δ98Mo and δ238U in sedimentary archives may be useful for paleo-reconstruction work.
📖 Papers frequently viewed together
89 Citations
6 Citations
41 Citations
#1Michelle L. Abshire (OSU: Oklahoma State University–Stillwater)H-Index: 1
#2Stephen J. Romaniello (UT: University of Tennessee)H-Index: 22
Last. Natascha Riedinger (OSU: Oklahoma State University–Stillwater)H-Index: 21
view all 6 authors...
Abstract In marine sediments, authigenic uranium (U) enrichments and U isotope compositions are important tools for interpreting changes in redox conditions, however, their use as paleoproxies requires a comprehensive understanding of the dominant processes that contribute to sediments becoming enriched or depleted. This study focuses on the U content and 238U/235U ratio of organic-rich surface sediments from the Namibian continental margin, where high productivity results in an expanded oxygen ...
13 CitationsSource
#1George R. Helz (UMD: University of Maryland, College Park)H-Index: 42
#2Trent P. Vorlicek (MSU: Minnesota State University, Mankato)H-Index: 7
Abstract Molybdenum preserved in organic-rich shales is a key archive employed in studying Earth's past oxygenation and Life's evolution. In these shales, positive correlations between Mo and Corg are common and have been attributed to Mo scavenging from seawater by organic shuttles. Here, we argue that known organic ligands are too weak or too scarce to capture more than minor amounts of Mo from seawater, especially in competition with sulfide. Alternatively, we demonstrate that Mo-Corg correla...
31 CitationsSource
#1Morten B. Andersen (ETH Zurich)H-Index: 25
#2Alan Matthews (HUJI: Hebrew University of Jerusalem)H-Index: 42
Last. G. F. de Souza (ETH Zurich)H-Index: 6
view all 6 authors...
Abstract Present-day Mediterranean deep-waters are well oxygenated, but the episodic formation of organic-rich sediments (sapropels) indicates that this pattern was frequently perturbed in the past. Both high export productivity and disruption of the thermohaline circulation, leading to reduced deep-water ventilation, have been proposed to account for sapropel deposition and anoxia. The last interglacial sapropel S5 is considered one of the most strongly developed. Here, we apply the redox-sensi...
18 CitationsSource
#1Shaun T. Brown (University of California, Berkeley)H-Index: 18
#2Anirban Basu (University of California, Berkeley)H-Index: 13
Last. Donald J. DePaolo (University of California, Berkeley)H-Index: 102
view all 5 authors...
Significant uranium (U) isotope fractionation has been observed during abiotic reduction of aqueous U, counter to the expectation that uranium isotopes are only fractionated by bioassociated enzymatic reduction. In our experiments, aqueous U is removed from solution by reductive precipitation onto the surfaces of synthetic iron monosulfide. The magnitude of uranium isotopic fractionation increases with decreasing aqueous U removal rate and with increasing amounts of neutrally charged aqueous Ca–...
32 CitationsSource
#1Duc Huy Dang (Trent University)H-Index: 11
#2R. Douglas Evans (Trent University)H-Index: 30
Last. Cédric Garnier (AMU: Aix-Marseille University)H-Index: 24
view all 9 authors...
Abstract By assessing U geochemistry in marine sediments of Toulon Bay (NW Mediterranean Sea), authigenic U accumulation was found to be tightly linked to that of Mo and V with slight differences in accumulation rate depending on sediment redox conditions. In sediments collected on a transect along a river plume, the authigenic accumulation of these redox-sensitive elements appears to be linked to sediment grain size which probably drives the redox status of the sediments. A typical U loss in re...
5 CitationsSource
#1Elvira Bura-Nakić (ETH Zurich)H-Index: 15
#2Morten B. Andersen (ETH Zurich)H-Index: 25
Last. Derek Vance (ETH Zurich)H-Index: 63
view all 6 authors...
Abstract Sedimentary molybdenum (Mo) and uranium (U) abundances, as well as their isotope systematics, are used to reconstruct the evolution of the oxygenation state of the surface Earth from the geological record. Their utility in this endeavour must be underpinned by a thorough understanding of their behaviour in modern settings. In this study, Mo-U concentrations and their isotope compositions were measured in the water column, sinking particles, sediments and pore waters of the marine euxini...
41 CitationsSource
#1Antje Wegwerth (Leibniz Institute for Baltic Sea Research)H-Index: 9
#2Sebastian Eckert (University of Oldenburg)H-Index: 4
Last. Hans J. Brumsack (University of Oldenburg)H-Index: 7
view all 11 authors...
Abstract The Black Sea repeatedly experienced major hydrographic changes during glacial-interglacial transitions, with alternating limnic and brackish stages. While the redox conditions during the present Holocene brackish period (since ~ 9,000 yr BP) have been intensively studied, the redox evolution during the last interglacial, the Eemian (~ 128,000-120,000 yr BP), remains largely unexplored. With its at least 3 °C warmer climate and an up to 10 m higher global sea level, the Eemian could ope...
19 CitationsSource
#1Devon B. Cole (Yale University)H-Index: 11
#2Shuang Zhang (Yale University)H-Index: 9
Last. Noah J. Planavsky (Yale University)H-Index: 56
view all 3 authors...
Abstract The enrichment and depletion of redox sensitive trace metals in marine sediments have been used extensively as paleoredox proxies. The trace metals in shale are comprised of both detrital (transported or particulate) and authigenic (precipitated, redox-driven) constituents, potentially complicating the use of this suite of proxies. Untangling the influence of these components is vital for the interpretation of enrichments, depletions, and isotopic signals of iron (Fe), chromium (Cr), ur...
52 CitationsSource
#1Xinze Lu (UW: University of Waterloo)H-Index: 3
#2Brian Kendall (UW: University of Waterloo)H-Index: 27
Last. Jan Ove R. Ebbestad (Uppsala University)H-Index: 15
view all 7 authors...
The final publication is available at Elsevier via © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
26 CitationsSource
#1John M. Rolison (University of Otago)H-Index: 9
#1John M. Rolison (University of Otago)H-Index: 4
Last. Micha J.A. Rijkenberg (UU: Utrecht University)H-Index: 18
view all 4 authors...
The isotopic compositions of redox-sensitive metals, including uranium (U), in marine sediments have recently emerged as powerful diagnostic tracers of the redox state of the ancient ocean–atmosphere system. Reliable interpretation of sedimentary isotopic information requires a thorough understanding of the environmental controls on isotopic fractionation in modern anoxic environments before being applied to the paleo-record. In this study, the relationship between ocean anoxia and the isotopic ...
48 CitationsSource
Cited By28
#1Linsong Liu (CUMT: China University of Mining and Technology)H-Index: 1
#2Hao Zhang (CUMT: China University of Mining and Technology)H-Index: 1
Last. Qinfu Liu (CUMT: China University of Mining and Technology)H-Index: 26
view all 7 authors...
Abstract null null In order to investigate the genesis of different types of claystones and facies-related variations in clay mineralogy, a mineralogical and geochemical investigation of the coal-bearing Upper Carboniferous Taiyuan Formation of North China was undertaken in the Wangping and Xiaoyu mines of the SE Datong Basin. This formation contains both kaolinitic and mixed-layer illite/smectite (I/S) claystones having distinctly different compositions. The former is composed of kaolinite with...
#1Wen Pan (China University of Geosciences (Wuhan))H-Index: 3
#2Mengchun Cao (UCPH: University of Copenhagen)H-Index: 2
Last. Tais W. Dahl (UCPH: University of Copenhagen)H-Index: 16
view all 11 authors...
Abstract The delayed diversification of early animals until the middle Ediacaran Period, despite their likely origin in the Cryogenian Period or earlier, has been attributed to low levels of dissolved O2 in global seawater. To provide more robust constraints on the extent of global-ocean oxygenation during the mid-Cryogenian Period, we analyzed paired U (δ238U) and Mo (δ98Mo) isotope compositions of organic-rich shale in the basal Datangpo Formation from two separate drillcores in South China. T...
#1Meng Cheng (China University of Geosciences (Wuhan))H-Index: 14
#2Zihu Zhang (China University of Geosciences (Wuhan))H-Index: 8
Last. Chao Li (China University of Geosciences (Wuhan))H-Index: 52
view all 11 authors...
Abstract In order to explore Cryogenian seawater chemistry and its underlying controls, we present an integrated study of iron speciation, major and trace elements, and carbon isotopes of Mn‑carbonates and their host black shales in the Datangpo Formation from three drillcores (Gaodi, Xixibao and Changxingpo) in the Nanhua Basin, South China. A key aspect of this analysis was use of the B/Ga, Sr/Ba, and S/TOC proxies to evaluate paleosalinity variation in this marginal-marine basin. Our results ...
#1Christopher Siebert (Leibniz Institute of Marine Sciences)H-Index: 22
#2Florian Scholz (Leibniz Institute of Marine Sciences)H-Index: 24
Last. Wolfgang Kuhnt (CAU: University of Kiel)H-Index: 54
view all 3 authors...
Abstract null null Extreme periods of global warming in Earth's history have been strongly associated with declining oxygen concentrations in the ocean, a scenario not unlike the current evolution of oxygen concentrations in the oceans. One of the most intense Phanerozoic deoxygenation events (so called Ocean Anoxic Events (OAE)) is the late Cretaceous OAE2 approximately 94 Ma ago. Although several studies have investigated the evolution of redox sensitive proxies during the OAE2 event, geochemi...
#1Yvonne Roebbert (Leibniz University of Hanover)H-Index: 3
#2Chris Daniel Rosendahl (Leibniz University of Hanover)
Last. Stefan Weyer (Leibniz University of Hanover)H-Index: 35
view all 6 authors...
Uranium (U) isotopes are suggested as a tool to trace U reduction. However, noncrystalline U(IV), formed predominantly in near-surface environments, may be complexed and remobilized using ligands under anoxic conditions. This may cause additional U isotope fractionation and alter the signatures generated by U reduction. Here, we investigate the efficacy of noncrystalline U(IV) mobilization by ligand complexation and the associated U isotope fractionation. Noncrystalline U(IV) was produced via th...
#1Lucile Roué (University of Tübingen)
#2Florian Kurzweil (University of Cologne)H-Index: 6
Last. Ronny Schoenberg (University of Tübingen)H-Index: 35
view all 7 authors...
Abstract The scavenging of dissolved trace metals such as chromium (Cr), molybdenum (Mo) and tungsten (W) and their authigenic enrichment in sedimentary archives mainly occur by particle shuttling that cause resolvable isotope fractionation. Because their scavenging is also dependent on the local marine redox potential and the overall marine chemical environment, the stable isotope composition of these elements in Archean sediments is widely used as paleoredox proxy. Tungsten, a new element in t...
#1Simon V. Hohl (Tongji University)H-Index: 8
#2Sebastian Viehmann (University of Vienna)H-Index: 10
Abstract Understanding the origin and evolution of life on Earth and potentially other planets in our solar system is of fundamental interest for humanity. For the longest time in Earth's history, life evolved in microbial communities. It is, however, still incompletely understood how, when and where such habitable environments formed and how microbial communities adopted to the drastic changes of the atmosphere-hydrosphere-lithosphere systems through deep time. Stromatolites, i.e., lithified mi...
#1Alexander J. Dickson (RHUL: Royal Holloway, University of London)H-Index: 20
#2Marie-Laure Bagard (University of Cambridge)H-Index: 4
Last. Anthony S. Cohen (OU: Open University)H-Index: 33
view all 6 authors...
Abstract A multi-million-year decrease in global temperatures during the Eocene was accompanied by large reorganisations to ocean circulation, ocean chemistry and biological productivity. These changes culminated in the rapid growth of grounded ice on Antarctica during the Eocene–Oligocene climate transition (EOT), ∼34 million years ago. However, while it is likely that environmental perturbations of this magnitude altered the oceanic oxygen inventory, the sign and magnitude of the response is p...
#1Florian Kurzweil (University of Cologne)H-Index: 6
#2Corey Archer (ETH Zurich)H-Index: 13
Last. Olaf Dellwig (Leibniz Institute for Baltic Sea Research)H-Index: 28
view all 6 authors...
Free oxygen represents an essential basis for the evolution of complex life forms on a habitable Earth. The isotope composition of redox-sensitive trace elements such as tungsten (W) can possibly trace the earliest rise of oceanic oxygen in Earth's history. However, the impact of redox changes on the W isotope composition of seawater is still unknown. Here, we report highly variable W isotope compositions in the water column of a redox-stratified basin (δ186/184W between +0.347 and +0.810 ‰) tha...
3 CitationsSource
#1Ji Shen (USTC: University of Science and Technology of China)H-Index: 7
#2Yingnan Zhang (USTC: University of Science and Technology of China)H-Index: 3
Last. Huaiwei Ni (USTC: University of Science and Technology of China)H-Index: 18
view all 8 authors...
Abstract Molybdenum (Mo) isotopes can be fractionated during redox-related hydrothermal and Earth’s surface processes. Distinct Mo isotope features of different reservoirs, thus, make Mo isotopes as a potential tracer for the recycling of crustal materials, particularly subduction sediments. Here, we report the Mo isotope compositions of 61 early Cretaceous high-K calc-alkaline rocks (defined as adakitic rocks) with distinct source affinities from central-eastern China, including low-Mg adakitic...