Geochemical and anthropogenic enrichments of Mo in sediments from perennially oxic and seasonally anoxic lakes in Eastern Canada

Chappaz, Anthony; Gobeil, Charles; Tessier, André

doi:10.1016/j.gca.2007.10.014

Cited by 85 publications

(89 citation statements)

References 66 publications

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“…More likely, the high dissolved Fe(III) concentrations are due to oxidation artifacts, the formation of strong organic complexes, the presence of Fe(III) colloids, or some combination of these. While precautions were taken to minimize contamination by oxygen (see The build-up of pore water Fe(II) below the SWI is consistent with Fe redox cycling within the upper centimeters of the sediments, as proposed in previous studies conducted in Basin A (Chappaz et al, 2008;Couture et al, 2010b;Feyte et al, 2010;Feyte et al, 2012 …”

Section: Dissolved Fementioning

confidence: 79%

Iron isotope fractionation in sediments of an oligotrophic freshwater lake

Couture

et al. 2015

Earth and Planetary Science Letters

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Section: Dissolved Fementioning

confidence: 79%

Iron isotope fractionation in sediments of an oligotrophic freshwater lake

Couture

et al. 2015

Earth and Planetary Science Letters

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“…1A), and the modern seawater Mo isotope composition also appears to be reasonably uniform as well (Barling et al, 2001;Siebert et al, 2003). In well-oxygenated sediments of the open ocean, Mo is primarily associated with solid-phase Mn and Fe-oxides (e.g., Bertine and Turekian, 1973;Calvert and Pedersen, 1993;Chappaz et al, 2008). Experimental work and natural samples have shown that Mo adsorption to Mn-oxides results in sediment Mo isotope values that are fractionated relative to parent seawater Mo (Barling et al, 2001;Siebert et al, 2003Siebert et al, , 2006Barling and Anbar, 2004;Wasylenki et al, 2008;Poulson Brucker et al, 2009;Figs.…”

mentioning

confidence: 87%

Molybdenum isotope fractionations observed under anoxic experimental conditions

2012

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Experiments were carried out to determine molybdenum isotope fractionation associated with adsorption to pyrite. Results show that the Mo isotope composition of the aqueous solution becomes progressively heavier as Mo is adsorbed, with a Mo isotope fractionation as large as 2.9‰. This fractionation is larger than observed for typical anoxic continental margin marine sediments (e.g., ~0.7‰), suggesting that Mo adsorption to pyrite is not the dominant process operating in these environments. However, our adsorption results do suggest the possibility that anoxic fractionation processes could impart an isotope signature within the geologic record similar to the isotope fractionation observed under oxygenated conditions. Additional experiments were conducted at high (~100 µM) dissolved Mo concentrations, but at varying pH and ∑H 2 S concentrations, and in each case these experiments promoted Mo-sulfide precipitation. Even though the experiments were conducted under differing conditions and produced different amounts of precipitate, the results suggest a constant fractionation of ~0.9‰ associated with this Mo removal process. This fractionation is more consistent with that inferred for anoxic continental margin marine sediments, suggesting that a process similar to Mo-sulfide precipitation, rather than an adsorption process, may be responsible for the Mo isotope compositions observed in these environments. The findings of this study suggest that, regardless of the geochemical mechanism employed, sediment Mo sequestration under anoxic conditions may impart a significant isotopic fractionation relative to parent seawater.

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“…The transition from Unit II to III is also characterized by elevated Zr/K ratios (Figure 8), pointing to a coarser grain size [68], as well as by an increase in the water content of the sediments ( Figure 5). Mo/Al ratios are low throughout Unit II, indicating oxic conditions at the sediment-water interface [69,70], then increase abruptly at the Unit II-III transition, followed by several minor peaks. From ca.…”

Section: Chemical Sediment Propertiesmentioning

confidence: 99%

“…The Mo/Al peak can be explained by lowered oxygen levels in the interstitial water [69,70], caused by the increased primary production (LOI increase, Figure 5) and consequent oxygen consumption by bacterial respiration. This in turn forced primary biota to reduce sulphate as an energy source, a process with high affinity for Mo enrichment [87].…”

Section: Lake and Catchment Processes During The Holocene (Lithologicmentioning

confidence: 99%

Holocene Hydroclimate Variability in Central Scandinavia Inferred from Flood Layers in Contourite Drift Deposits in Lake Storsjön

et al. 2018

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Despite the societal importance of extreme hydroclimate events, few palaeoenvironmental studies of Scandinavian lake sediments have investigated flood occurrences. Here we present a flood history based on lithological, geochemical and mineral magnetic records of a Holocene sediment sequence collected from contourite drift deposits in Lake Storsjön (63.12 • N, 14.37 • E). After the last deglaciation, the lake began to form around 9800 cal yr BP, but glacial activity persisted in the catchment for~250 years. Element concentrations and mineral magnetic properties of the sediments indicate relatively stable sedimentation conditions during the Holocene. However, human impact in the form of expanding agriculture is evident from about 1100 cal yr BP, and intensified in the 20th century. Black layers containing iron sulphide appear irregularly throughout the sequence. The increased influx of organic matter during flood events led to decomposition and oxygen consumption, and eventually to anoxic conditions in the interstitial water preserving these layers. Elevated frequencies of black layer occurrence between 3600 and 1800 cal yr BP reflect vegetation changes in the catchment as well as large-scale climatic change. Soil erosion during snowmelt flood events increased with a tree line descent since the onset of the neoglacial period (~4000 cal yr BP). The peak in black layer occurrence coincides with a prominent solar minimum~2600 cal yr BP, which may have accentuated the observed pattern due to the prevalence of a negative NAO index, a longer snow accumulation period and consequently stronger snowmelt floods.

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Geochemical and anthropogenic enrichments of Mo in sediments from perennially oxic and seasonally anoxic lakes in Eastern Canada

Cited by 85 publications

References 66 publications

Iron isotope fractionation in sediments of an oligotrophic freshwater lake

Iron isotope fractionation in sediments of an oligotrophic freshwater lake

Molybdenum isotope fractionations observed under anoxic experimental conditions

Holocene Hydroclimate Variability in Central Scandinavia Inferred from Flood Layers in Contourite Drift Deposits in Lake Storsjön

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