Uranium and molybdenum isotope systematics in modern euxinic basins: Case studies from the central Baltic Sea and the Kyllaren fjord (Norway)

Noordmann, Janine; Weyer, Stefan; Montoya-Pino, Carolina; Dellwig, Olaf; Neubert, Nadja; Eckert, Sebastian; Paetzel, Matthias; Böttcher, Michael E.

doi:10.1016/j.chemgeo.2014.12.012

Cited by 131 publications

(102 citation statements)

References 72 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, in the modern Black Sea, U isotope fractionation (Δ 238 U) of ∼0.7‰ between the authigenic U in the sediment and that in the deep water column was observed (10,13,37). As the deep water column provides a maximum value for δ 238 U of sediment pore water (12), this implies that U reduction in the sediment of euxinic basins is dominantly biotic. U(VI) reduction is a relatively common biotic process, as it is carried out by varied metabolic groups of microorganisms-sulfatereducing, iron-reducing, and fermenting bacteria among others (2)-and the biologically driven 238 U/ 235 U fractionation is consistent within these groups (17).…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, permil-level fractionations of the two abundant and primordial uranium isotopes are reported in association with U(VI) to U(IV) redox transitions through the accumulation of the heavy isotope ( 238 U) rather than the light isotope ( 235 U) in the reduced product (8)(9)(10)(11)(12)(13). This isotopic signature has been measured in low-temperature paleo-environments, enabling the use of U isotope fractionation as a proxy for the redox conditions of ancient atmosphere and oceans (14)(15)(16).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

132

147

View full text Add to dashboard Cite

Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

show abstract

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

132

147

View full text Add to dashboard Cite

show abstract

“…The potential of uranium isotopes as a paleo-redox tracer has been investigated by Montoya-Pino et al (2010), Brennecka et al (2011), Kendall et al (2013 and Noordmann et al (2015). Montoya-Pino et al (2010) demonstrated that U isotope variations in black shales can be used to quantify the extent of marine anoxia.…”

Section: Characteristic U Signaturesmentioning

confidence: 97%

Isotope Fractionation Processes of Selected Elements

Hoefs

2015

Stable Isotope Geochemistry

View full text Add to dashboard Cite

“…In addition, Mo is reduced from oxidation state (VI) to (IV) during burial in sediments (Dahl et al, 2013). Under non-euxinic conditions, where H 2 S is only found in pore waters but not in bottom waters, the initial sedimentation of water column Mo often occurs through adsorption to solidphase manganese (Mn) oxides at the sediment-water interface (Scott and Lyons, 2012;Scholz et al, 2013;Noordmann et al, 2015). Upon reduction of Mn oxides, Mo is released into the pore waters, from where it may efflux back to the water column or become sequestered into the sediments in the presence of sufficiently high sulfide levels.…”

Section: Molybdenum Contentmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

View full text Add to dashboard Cite

Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.

show abstract

Uranium and molybdenum isotope systematics in modern euxinic basins: Case studies from the central Baltic Sea and the Kyllaren fjord (Norway)

Cited by 131 publications

References 72 publications

Uranium isotopes fingerprint biotic reduction

Uranium isotopes fingerprint biotic reduction

Isotope Fractionation Processes of Selected Elements

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

Contact Info

Product

Resources

About