Selenium Isotopes as a Biogeochemical Proxy in Deep Time

Stüeken, Eva E.

doi:10.2138/rmg.2017.82.15

Cited by 44 publications

(45 citation statements)

References 154 publications

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“…The modeled dissolved concentration is ~0.6 nM, and the particulate concentration is 2.5 nmol/g (average log K D of 3.1), which is consistent with values in the literature (Conde & Alaejos, ; Plant et al, ; Table S1). The estimated flux is 3.5 times higher than estimated by Gaillardet et al (; 33 Mmol/a) and more comparable with the estimate of Stueken (; (80 Mmol/a). However, all the estimates are based on limited information and more studies are needed to further constrain this flux.…”

Section: Resultssupporting

confidence: 85%

“…Also, Se (IV) associates more strongly with oxide mineral phases, and adsorption of Se (IV) to oxide mineral phases in the water column close to sediments, or during early diagenesis, could potentially be an important deep ocean sink for Se (Stueken, ). Stueken () estimated burial in the deep ocean to be 90 Mmol/a, somewhat higher but comparable to the model result (72 Mmol/a). Further studies are needed to examine the potential pathways in both the surface and deep ocean in more detail.…”

Section: Resultsmentioning

confidence: 99%

“…There is limited information in the literature on the relative fraction of organic Se in the ocean (Table S1), and the method of determination, which relies on decomposition of this fraction to inorganic Se using strong oxidants (Cutter & Cutter, ; Sherrard et al, ), does not provide information about the specific compounds that make up this fraction. It is assumed to be primarily degraded biochemicals from Se‐containing proteins and other biomolecules (Stueken, ). Clearly, while this fraction is modeled as one pool, the lack of detailed understanding about the chemistry of this pool is a limitation of the study and more research is needed to gain a better understanding of the pathways of degradation of organic Se compounds produced by microorganisms in the ocean.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Atmospheric deposition of Se in both its oxidized forms (Se (IV) and Se (VI)) is the main source to the ocean (Chester & Jickells, ; Cutter, ; Mosher et al, ; Stueken, ; Wen & Carignan, ). The dominant forms in the ocean are inorganic selenite (Se (IV), predominantly as HSeO 3 − ) and selenate (Se (VI), as SeO 4 2− ; Cutter & Cutter, , ; Measures & Burton, ; Sherrard et al, ).…”

Section: Introductionmentioning

confidence: 99%

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The Global Marine Selenium Cycle: Insights From Measurements and Modeling

Mason

Soerensen

DiMento

et al. 2018

Global Biogeochemical Cycles

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Anthropogenic activities have increased the selenium (Se) concentration in the biosphere, but the overall impact on the ocean has not been examined. While Se is an essential nutrient for microorganisms, there is little information on the impact of biological processes on the concentration and speciation of Se in the ocean. Additionally, other factors controlling the distribution and concentration of Se species are poorly understood. Here we present data gathered in the subtropical Pacific Ocean during a cruise in 2011, and we used these field data and the literature, as well as laboratory photochemical experiments examining the stability and degradation of inorganic Se (both Se (IV) and Se (VI)) and dimethyl selenide, to further constrain the cycling of Se in the upper ocean. We also developed a multibox model for the biosphere to examine the impact of anthropogenic emissions on the concentration and distribution of Se in the ocean. The model concurs with the field data indicating that the Se concentration has increased in the upper ocean waters over the past 30 years. Our observational studies and model results suggest that Se (VI) is taken up by phytoplankton in the surface ocean, in contrast to the results of laboratory culture experiments. In conclusion, while anthropogenic inputs have markedly increased Se in the atmosphere (42%) and net deposition to the ocean (38%) and terrestrial landscape (41%), the impact on Se in the ocean is small (3% increase in the upper ocean). This minimal response reflects its long marine residence time.

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Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Global Marine Selenium Cycle: Insights From Measurements and Modeling

Mason

Soerensen

DiMento

et al. 2018

Global Biogeochemical Cycles

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“…Whereas Se can also be sourced to the marine environment by volcanism and hydrothermal activity, oxidative weathering is by far the dominant source on the modern Earth (∼90% of flux to oceans; volcanism ∼10%, hydrothermal input <<1%; ref. 26). Furthermore, the parallel enrichment of U (19), Mo (18), and Se in samples from the Rooihoogte and Lower Timeball Hill formations and the Sengoma Argillite Formation is most parsimoniously explained by enhanced oxidative weathering.…”

Section: Resultsmentioning

confidence: 98%

Selenium isotopes record extensive marine suboxia during the Great Oxidation Event

Kipp

Stüeken

Bekker

et al. 2017

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

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It has been proposed that an "oxygen overshoot" occurred during the early Paleoproterozoic Great Oxidation Event (GOE) in association with the extreme positive carbon isotopic excursion known as the Lomagundi Event. Moreover, it has also been suggested that environmental oxygen levels then crashed to very low levels during the subsequent extremely negative Shunga-Francevillian carbon isotopic anomaly. These redox fluctuations could have profoundly influenced the course of eukaryotic evolution, as eukaryotes have several metabolic processes that are obligately aerobic. Here we investigate the magnitude of these proposed oxygen perturbations using selenium (Se) geochemistry, which is sensitive to redox transitions across suboxic conditions. We find that δ 82/78Se values in offshore shales show a positive excursion from 2.32 Ga until 2.1 Ga (mean +1.03 ± 0.67‰). Selenium abundances and Se/TOC (total organic carbon) ratios similarly show a peak during this interval. Together these data suggest that during the GOE there was pervasive suboxia in near-shore environments, allowing nonquantitative Se reduction to drive the residual Se oxyanions isotopically heavy. This implies O 2 levels of >0.4 μM in these settings. Unlike in the late Neoproterozoic and Phanerozoic, when negative δ 82/78Se values are observed in offshore environments, only a single formation, evidently the shallowest, shows evidence of negative δ 82/78 Se. This suggests that there was no upwelling of Se oxyanions from an oxic deep-ocean reservoir, which is consistent with previous estimates that the deep ocean remained anoxic throughout the GOE. The abrupt decline in δ 82/78 Se and Se/TOC values during the subsequent Shunga-Francevillian anomaly indicates a widespread decrease in surface oxygenation.Paleoproterozoic | trace metals | oxygen | eukaryote evolution

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