Diel Redox Cycle of Manganese in the Surface Arctic Ocean

Xiang, Yang; Lam, Phoebe J.; Lee, Jong-Mi

doi:10.1029/2021gl094805

Cited by 10 publications

(6 citation statements)

References 49 publications

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“…This phenomenon suggests an unknown formation pathway of OICs in frozen environments under neutral conditions, which is different from the iron(III)-based systems. Manganese species can enter the Arctic Ocean from rivers or coastal erosion and be trapped in frozen media (glacier, sea ice, and atmospheric ice particle) in the Arctic region. , Xiang et al reported that particulate manganese oxidation states were more reduced in the day and more oxidized at night in the surface Arctic Ocean, which indicated that the Mn redox cycle frequently occurred in the polar region. On the other hand, NOM and MnO 2 are more abundant in the terrestrial environments than in the marine environment, and the terrestrial media such as soil and sediments may undergo freezing or freeze–thaw cycles in winter.…”

Section: Resultsmentioning

confidence: 99%

MnO₂-Induced Oxidation of Iodide in Frozen Solution

Du¹,

Kim

Son

et al. 2023

Environ. Sci. Technol.

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Metal oxides play a critical role in the abiotic transformation of iodine species in natural environments. In this study, we investigated iodide oxidation by manganese dioxides (β-MnO 2 , γ-MnO 2 , and δ-MnO 2 ) in frozen and aqueous solutions. The heterogeneous reaction produced reactive iodine (RI) in the frozen phase, and the subsequent thawing of the frozen sample induced the gradual transformation of in situ-formed RI to iodate or iodide, depending on the types of manganese dioxides. The freezing-enhanced production of RI was observed over the pH range of 5.0−9.0, but it decreased with increasing pH. Fulvic acid (FA) can be iodinated by I − /MnO 2 in aqueous and frozen solutions. About 0.8−8.4% of iodide was transformed to organoiodine compounds (OICs) at pH 6.0−7.8 in aqueous solution, while higher yields (10.4−17.8%) of OICs were obtained in frozen solution. Most OICs generated in the frozen phase contained one iodine atom and were lignin-like compounds according to Fourier transform ion cyclotron resonance/mass spectrometry analysis. This study uncovers a previously unrecognized production pathway of OICs under neutral conditions in frozen environments.

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Section: Resultsmentioning

confidence: 99%

MnO₂-Induced Oxidation of Iodide in Frozen Solution

Du¹,

Kim

Son

et al. 2023

Environ. Sci. Technol.

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“…As removal of Cr in subsurface waters at our study sites, where lithogenic suspended particles are abundant, appears to proceed via scavenging of Cr(III) by colloid aggregates that consist of authigenic Fe-(oxyhydr)oxides and/or dust particles (Section 4.2), increased concentrations of dissolved Cr in intermediate waters could be due to re-oxidation of Cr(III) to the less particle reactive Cr(VI), potentially driven by reduction (and dissolution) of manganese (III, IV) oxides (MnO x ) that are present throughout the oxygenated water column (Jones et al, 2020). However, as concentrations of particulate Mn are very low (sub-nanomolar) in oceanic environments (Jones et al, 2020;Xiang et al, 2021), the predicted oxidation rate of Cr(III) is extremely slow, ~2 × 10 -5 nmol kg -1 yr -1 (van der Weijden and Reith, 1982). The residence time of fine lithogenic mineral particles (~1 to 5 mm diameter) in the upper 2000 m of the North Atlantic Ocean water column is months to years (Ohnemus and Lam, 2015;Ohnemus et al, 2019), over which time oxidation of Cr(III) can be expected to increase the Cr concentration of seawater by approximately 10 -5 to 10 -4 nmol kg -1 in the intermediate waters.…”

Section: Regeneration Of Cr In Deeper Watersmentioning

confidence: 99%

Biogeochemical cycling of chromium and chromium isotopes in the sub-tropical North Atlantic Ocean

et al. 2023

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Chromium (Cr) is a redox-sensitive element and because Cr isotopes are fractionated by redox and/or biological processes, the Cr isotopic composition of ancient marine sediments may be used to infer changes in past seawater oxygenation or biological productivity. While there appears to be a ‘global correlation’ between the dissolved Cr concentration and Cr isotopic composition of seawater, there is ongoing debate about the relative importance of external sources and internal cycling on shaping the distribution of dissolved Cr that needs to be resolved to validate the efficacy of using Cr isotopes as a paleo proxy. Here, we present full water column depth profiles of total dissolved Cr (Cr(VI)+Cr(III)) and dissolved Cr isotopes (δ53Cr), together with ancillary data, for three stations along a transect (GEOTRACES GApr08) across the sub-tropical North Atlantic. Concentrations of dissolved Cr ranged between 1.84 and 2.63 nmol kg-1, and δ53Cr values varied from 1.06 to 1.42‰. Although atmospheric dust, hydrothermal vents and seabed sediments have the potential to modify the distribution of Cr in the oceans, based on our observations, there is no clear evidence for substantial input of Cr from these sources in our study region although benthic inputs of Cr may be locally important in the vicinity of hydrothermal vents. Subsurface waters (below the surface mixed layer to 700 m water depth) were very slightly depleted in Cr (by up to ~0.4 nmol kg-1), and very slightly enriched in heavy Cr isotopes (by up to ~0.14‰), relative to deeper waters and the lowest Cr concentrations and highest δ53Cr values coincided with lowest concentrations of colloidal (0.02 to 0.2 μm size fraction) Fe. We found no direct evidence for biological uptake of dissolved Cr in the oligotrophic euphotic zone or removal of Cr in modestly oxygen depleted waters (O2 concentrations ~130 μmol kg-1). Rather, we suggest removal of Cr (probably in the form of Cr(III)) in subsurface waters is associated with the formation of colloid aggregates of Fe-(oxyhydr)oxides. This process is likely enhanced by the high lithogenic particle load in this region, and represents a previously unrecognized export flux of Cr. Regeneration of Cr in deeper waters leads to subtly increased levels of Cr alongside decreased δ53Cr values at individual sites, but this trend is more obvious at the global scale, with δ53Cr values decreasing with increasing radiocarbon age of deep waters, from 1.16 ± 0.10‰ (1SD, n=11) in deep Atlantic waters to 0.77 ± 0.10‰ (1SD, n=25) in deep Pacific waters. Removal of relatively isotopically light Cr from subsurface waters onto particulate material and regeneration of this Cr back into the dissolved phase in deep waters partly accounts for the systematic relationship between δ53Cr and Cr concentrations in seawater discussed by other studies.

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“…Bulk measurements can also be used on heterogeneous samples to determine average speciation or redox states of the area illuminated. This can be a good strategy for determining large-scale changes in the environment (Lam and Bishop, 2008;Lee et al, 2021;Xiang et al, 2021).…”

Section: Guidance For Successful Synchrotron Analysismentioning

confidence: 99%

Characterization and Speciation of Marine Materials Using Synchrotron Probes: Guidelines for New Users

Jones¹,

Nicholas²,

Northrup³

et al. 2022

Oceanog

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Synchrotron instruments are useful for marine studies because they make nondestructive measurements of chemical composition and speciation on small sample volumes and at low concentrations. Synchrotron beamtime is available without cost using a peer-reviewed proposal system. New users do not have to be synchrotron radiation experts to design a good experiment, but some guidance is needed to design and propose appropriate experiments. Here we present some of that guidance to encourage and increase access to synchrotron facilities for marine science. We provide advice and examples from experts on how to access these instruments, choose the optimal sample preparation, and avoid common pitfalls. We then present some examples of successful marine studies that use these techniques.

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Diel Redox Cycle of Manganese in the Surface Arctic Ocean

Cited by 10 publications

References 49 publications

MnO₂-Induced Oxidation of Iodide in Frozen Solution

MnO₂-Induced Oxidation of Iodide in Frozen Solution

Biogeochemical cycling of chromium and chromium isotopes in the sub-tropical North Atlantic Ocean

Characterization and Speciation of Marine Materials Using Synchrotron Probes: Guidelines for New Users

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Diel Redox Cycle of Manganese in the Surface Arctic Ocean

Cited by 10 publications

References 49 publications

MnO2-Induced Oxidation of Iodide in Frozen Solution

MnO2-Induced Oxidation of Iodide in Frozen Solution

Biogeochemical cycling of chromium and chromium isotopes in the sub-tropical North Atlantic Ocean

Characterization and Speciation of Marine Materials Using Synchrotron Probes: Guidelines for New Users

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Product

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MnO₂-Induced Oxidation of Iodide in Frozen Solution

MnO₂-Induced Oxidation of Iodide in Frozen Solution