| 1. |
- Callac, Nolwenn, et al.
(författare)
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Modes of carbon fixation in an arsenic and CO2-rich shallow hydrothermal ecosystem
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322.
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Tidskriftsartikel (refereegranskat)abstract
- The seafloor sediments of Spathi Bay, Milos Island, Greece, are part of the largest arsenic-CO2-rich shallow submarine hydrothermal ecosystem on Earth. Here, white and brown deposits cap chemically distinct sediments with varying hydrothermal influence. All sediments contain abundant genes for autotrophic carbon fixation used in the Calvin-Benson-Bassham (CBB) and reverse tricaboxylic acid (rTCA) cycles. Both forms of RuBisCO, together with ATP citrate lyase genes in the rTCA cycle, increase with distance from the active hydrothermal centres and decrease with sediment depth. Clustering of RuBisCO Form II with a highly prevalent Zetaproteobacteria 16S rRNA gene density infers that iron-oxidizing bacteria contribute significantly to the sediment CBB cycle gene content. Three clusters form from different microbial guilds, each one encompassing one gene involved in CO2 fixation, aside from sulfate reduction. Our study suggests that the microbially mediated CBB cycle drives carbon fixation in the Spathi Bay sediments that are characterized by diffuse hydrothermal activity, high CO2, As emissions and chemically reduced fluids. This study highlights the breadth of conditions influencing the biogeochemistry in shallow CO2-rich hydrothermal systems and the importance of coupling highly specific process indicators to elucidate the complexity of carbon cycling in these ecosystems.
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| 2. |
- Chi Fru, Ernest, et al.
(författare)
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Arsenic-induced phosphate limitation under experimental Early Proterozoic oceanic conditions
- 2016
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 434, s. 52-63
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Tidskriftsartikel (refereegranskat)abstract
- Comparison of phosphorus concentrations associated with modern hydrothermal Fe(III)(oxyhydr)oxides and ancient Fe(III) oxide-rich iron formations, is used to estimate bioavailable Precambrian marine phosphorus (P) concentrations. This led to the proposition of a low dissolved P budget of similar to 10-25% of present-day levels, before similar to 1.9 billion years ago. Estimates incorporating ancient marine Si levels >= 0.67 mM instead suggested global dissolved P levels greater than today. Here we unite current experimental models that have considered NaCl solutions containing elevated dissolved Fe(II), Si, Ca2+ and Mg2+ ions in the incorporation of P in Precambrian marine Fe(III)(oxyhydr)oxides, in addition to arsenic as a hydrothermal proxy. We show that the coprecipitation of dissolved P and Fe(III)(oxyhydr)oxides from arsenic-rich marine waters produces an average P distribution coefficient of similar to 0.072 (+/- 0.01) mu M-1. This is comparable to the similar to 0.07 mu M-1 predicted for Fe(III)(oxyhydr)oxides in modern arsenic-rich, submarine hydrothermal settings, from which the lower Early Proterozoic dissolved marine P concentrations were predicted. As/P molar ratios below modern seawater ratios removed the negative feedback effect high Si impose on P scavenging by Fe(III)(oxyhydr)oxides. The binding of As(III) to Fe(III)(oxyhydr)oxides exhibits a lower competitive influence on P fixation. As(V) that likely became prominent in the surficially oxidized Early Proterozoic oceans induced dissolved P limitation because of preferential P sequestration at the expense of dissolved As(V) enrichment. The control of As on P scavenging by the precipitating Fe(III)(oxyhydr)oxides is strong regardless of common seawater cations (Mg2+ and Ca2+). The data suggest that the application of Si and Fe(III)(oxyhydr)oxides as an ancient seawater P proxy should consider chemical variability between depositional basins, taking into account the rather strong role hydrothermal arsenic has on the distribution of P in Fe(Ill)(oxyhydr)oxides. We propose that the generalized lower dissolved P budgets estimated from Early Proterozoic iron formations are consistent with oceans thought to be at least 3-4 times more hydrothermally active than at present.
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| 3. |
- Chi Fru, Ernest, et al.
(författare)
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Atmospheric weathering of Scandinavian alum shales and the fractionation of C, N and S isotopes
- 2016
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 74, s. 94-108
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Tidskriftsartikel (refereegranskat)abstract
- Subaerial exposure and oxidation of organic carbon (C-org)-rich rocks is believed to be a key mechanism for the recycling of buried C and S back to Earth's surface. Importantly, processes coupled to microbial C-org oxidation are expected to shift new biomass delta C-13(org) composition towards more negative values relative to source. However, there is scarcity of information directly relating rock chemistry to oxidative weathering and shifting delta C-13(org) at the rock-atmosphere interface. This is particularly pertinent to the sulfidic, C-org-rich alum shale units of the Baltoscandian Basin believed to constitute a strong source of metal contaminants to the natural environment, following subaerial exposure and weathering. Consistent with independent support, we show that atmospheric oxidation of the sulfidic, C-org-rich alum shale sequence of the Cambrian-Devonian Baltoscandian Basin induces intense acid rock drainage at the expense of progressive oxidation of Fe sulfides. Sulfide oxidation takes priority over microbial organic matter decomposition, enabling quantitative massive erosion of C-org without producing a delta C-13 shift between acid rock drainage precipitates and shale. Moreover, C-13 enrichment in inorganic carbon of precipitates does not support microbial C-org oxidation as the predominant mechanism of rock weathering upon exposure. Instead, a Delta S-34 = delta S-34(shale) - delta S-34(precipitates) approximate to 0, accompanied by elevated S levels and the ubiquitous deposition of acid rock drainage sulfate minerals in deposited efflorescent precipitates relative to shales, provide strong evidence for quantitative mass oxidation of shale sulfide minerals as the source of acidity for chemical weathering. Slight delta N-15 depletion in the new surface precipitates relative to shale, coincides with dramatic loss of N from shales. Collectively, the results point to pyrite oxidation as a major driver of alum black shale weathering at the rock-atmosphere interface, indicating that quantitative mass release of C-org, N, S, and key metals to the environment is a response to intense sulfide oxidation. Consequently, large-scale acidic weathering of the sulfide-rich alum shale units is suggested to influence the fate and redistribution of the isotopes of C, N, and S from shale to the immediate environment.
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| 4. |
- Chi Fru, Ernest, et al.
(författare)
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Biogenicity of an Early Quaternary iron formation, Milos Island, Greece
- 2015
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 13:3, s. 225-244
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Tidskriftsartikel (refereegranskat)abstract
- A ~2.0-million-year-old shallow-submarine sedimentary deposit on Milos Island, Greece, harbours an unmetamorphosed fossiliferous iron formation (IF) comparable to Precambrian banded iron formations (BIFs). This Milos IF holds the potential to provide clues to the origin of Precambrian BIFs, relative to biotic and abiotic processes. Here, we combine field stratigraphic observations, stable isotopes of C, S and Si, rock petrography and microfossil evidence from a ~5-m-thick outcrop to track potential biogeochemical processes that may have contributed to the formation of the BIF-type rocks and the abrupt transition to an overlying conglomerate-hosted IF (CIF). Bulk δ13C isotopic compositions lower than -25‰ provide evidence for biological contribution by the Calvin and reductive acetyl–CoA carbon fixation cycles to the origin of both the BIF-type and CIF strata. Low S levels of ~0.04 wt.% combined with δ34S estimates of up to ~18‰ point to a non-sulphidic depository. Positive δ30Si records of up to +0.53‰ in the finely laminated BIF-type rocks indicate chemical deposition on the seafloor during weak periods of arc magmatism. Negative δ30Si data are consistent with geological observations suggesting a sudden change to intense arc volcanism potentially terminated the deposition of the BIF-type layer. The typical Precambrian rhythmic rocks of alternating Fe- and Si-rich bands are associated with abundant and spatially distinct microbial fossil assemblages. Together with previously proposed anoxygenic photoferrotrophic iron cycling and low sedimentary N and C potentially connected to diagenetic denitrification, the Milos IF is a biogenic submarine volcano-sedimentary IF showing depositional conditions analogous to Archaean Algoma-type BIFs.
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| 5. |
- Hemmingsson, Christoffer, et al.
(författare)
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Evaluation of phosphate-uptake mechanisms by Fe(III) (oxyhydr)oxides in Early Proterozoic oceanic conditions
- 2018
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Ingår i: Environmental Chemistry. - 1448-2517 .- 1449-8979. ; 15:1-2, s. 18-28
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Tidskriftsartikel (refereegranskat)abstract
- Banded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III) (oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are (1) surface attachment on pre-formed Fe(III) (oxyhydr)oxides (adsorption), and (2) incorporation of P into actively growing Fe(III) (oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III) (oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations, such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III) (oxyhydr)oxides; however, recent coprecipitation experiments show that DIP is scavenged by Fe(III) (oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In the present study, we show that the DIP uptake onto Fe(III) (oxyhydr)oxides by adsorption is less than 5 % of DIP uptake by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III) (oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, meanwhile the influence of Si on DIP binding is inhibited during coprecipitation when As(III) and As(V) are present. In the Early Proterozoic open oceans, Fe(III) (oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters. Our data imply that, DIP was removed from surface waters through coprecipitation with those Fe(III) (oxyhydr)oxides, rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III) (oxyhydr)oxides, and by the partial release of DIP into the anoxic bottom waters and buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters, both of which would have most likely decreased the productivity of cyanobacteria and O-2 production.
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| 6. |
- Hemmingsson, Christoffer, 1987-
(författare)
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Phosphate and Arsenic Cycling under Experimental Early Proterozoic Marine Conditions
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nutrient dynamics in the Archean-Paleoproterozoic oceans strongly influenced primary productivity and the rise of atmospheric O2. Reconstructing the cycling of key nutrients such as dissolved inorganic phosphate (DIP) at this time is important for our understanding of the timing, rate and extent of atmospheric oxygenation at this time. Banded iron formations (BIF) can be used as proxies for global DIP content in Precambrian marine waters. Estimating Precambrian DIP requires understanding of the mechanisms by which Fe(III)(oxyhydr)oxides scavenge DIP which has come mainly from experimental studies using NaCl solutions that mimick Precambrian marine conditions with for example, elevated Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are 1) Adsorption - surface attachment on pre-formed Fe(III) (oxyhydr)oxides, and 2) Coprecipitation - incorporation of P into actively growing Fe(III) (oxyhydr)oxides. It has been suggested that the elevated Si concentrations suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III)(oxyhydr)oxides. However recent coprecipitation experiments show that DIP is strongly scavenged by Fe(III)(oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In this study we show that the DIP uptake onto Fe(III)(oxyhydr)oxides by adsorption is less than 5% of that by coprecipitation. The data imply that in the Early Proterozoic open oceans, the precipitation of Fe(III)(oxyhydr)oxides during mixing of deep anoxic Fe(II)-rich waters with oxygenated ocean surface waters caused DIP removal from surface waters through coprecipitation rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III)(oxyhydr)oxides, and its partial release into the anoxic bottoms waters and in buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters both of which would have most likely decreased the productivity of Cyanobacteria and O2 production.
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| 7. |
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| 8. |
- Hemmingsson, Oskar, 1975-, et al.
(författare)
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Excision and suture in the midline versus Karydakis flap surgery for pilonidal sinus : randomized clinical trial
- 2022
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Ingår i: BJS Open. - : Oxford University Press. - 2474-9842. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: There are several surgical options for the management of pilonidal disease, including midline and off midline closure, but prospective studies are rare. The study hypothesis was that Karydakis flap surgery would result in shorter wound healing and fewer recurrences than excision of pilonidal sinus and suture in the midline.METHODS: A randomized clinical trial was conducted in two hospitals in Sweden between 2006 and 2015 to compare excision and suture in the midline with Karydakis flap surgery. Adult patients with a chronic pilonidal sinus disease were randomized 1:1 at the outpatient clinic without blinding. Power calculation based on recurrence of 2 per cent for Karydakis flap and 10 per cent for excision and primary closure in the midline required 400 patients with 90 per cent statistical power at 5 per cent significance assuming 10 per cent loss during follow-up. Participants were followed up until complete wound healing; late follow-up after 6-13 years was performed by telephone by two blinded assessors. The two co-primary outcomes were time to complete wound healing and recurrence rate.RESULTS: The study was terminated early at a planned interim analysis due slow recruitment and a significant difference in primary outcome. In total, 125 patients were randomized, of whom 116 were available for the present analysis. Median wound healing time was 49 days (95 per cent confidence interval (c.i.) 32 to 66) for excision with suture in the midline and 14 days (95 per cent c.i. 12 to 20) for Karydakis flap surgery (P < 0.001). There were five recurrences in each group, after a median follow-up of 11 years (P = 0.753).CONCLUSION: Karydakis flap surgery for pilonidal sinus disease led to a shorter wound healing time than excision and suture in the midline but no difference in recurrence rates.Registration number: NCT00412659 (http://www.clinicaltrials.gov).
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| 9. |
- Neubeck, Anna, et al.
(författare)
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Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions
- 2021
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Ingår i: Chemie der Erde. - : Elsevier BV. - 0009-2819 .- 1611-5864. ; 81:1
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Tidskriftsartikel (refereegranskat)abstract
- The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 +/- 0.17 parts per thousand). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5 parts per thousand. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the delta Ni-60 values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry.
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