| 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. |
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| 3. |
- Chi Fru, Ernest, et al.
(författare)
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Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments
- 2018
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 141:1, s. 41-62
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Tidskriftsartikel (refereegranskat)abstract
- The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing<2.0ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.
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| 4. |
- Chi Fru, Ernest, et al.
(författare)
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Arsenic stress after the Proterozoic glaciations
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Protection against arsenic damage in organisms positioned deep in the tree of life points to early evolutionary sensitization. Here, marine sedimentary records reveal a Proterozoic arsenic concentration patterned to glacial-interglacial ages. The low glacial and high interglacial sedimentary arsenic concentrations, suggest deteriorating habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago. A similar intensification of near continental margin sedimentary arsenic levels after the Cryogenian glaciations is also associated with amplified continental weathering. However, interpreted atmospheric oxygen increase at this time, suggests that the marine biosphere had widely adapted to the reorganization of global marine elemental cycles by glaciations. Such a glacially induced biogeochemical bridge would have produced physiologically robust communities that enabled increased oxygenation of the ocean-atmosphere system and the radiation of the complex Ediacaran-Cambrian life.
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| 5. |
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| 6. |
- Chi Fru, Ernest, et al.
(författare)
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Fossilized iron bacteria reveal pathway to biological origin of banded iron formation.
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4:2050, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Debates on the formation of banded iron formations in ancient ferruginous oceans are dominated by a dichotomy between abiotic and biotic iron cycling. This is fuelled by difficulties in unravelling the exact processes involved in their formation. Here we provide fossil environmental evidence for anoxygenic photoferrotrophic deposition of analogue banded iron rocks in shallow marine waters associated with an Early Quaternary hydrothermal vent field on Milos Island, Greece. Trace metal, major and rare earth elemental compositions suggest that the deposited rocks closely resemble banded iron formations of Precambrian origin. Well-preserved microbial fossils in combination with chemical data imply that band formation was linked to periodic massive encrustation of anoxygenic phototrophic biofilms by iron oxyhydroxide alternating with abiotic silica precipitation. The data implicate cyclic anoxygenic photoferrotrophy and their fossilization mechanisms in the construction of microskeletal fabrics that result in the formation of characteristic banded iron formation bands of varying silica and iron oxide ratios.
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| 7. |
- Chi Fru, Ernest, et al.
(författare)
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Proterozoic arsenic dynamics controlled by glaciations
- 2015
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Ingår i: Abstracts of the 25<sup>th</sup>Goldschmidt Conference, Prague. ; , s. 537-537
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Konferensbidrag (refereegranskat)abstract
- Increased chemical weathering of trace elements from land to ocean after the Great Oxidation Event is often correlated to biological stimulation near the ocean margins. However, life had to develop strategies to combat the sudden bioavailability of a range of toxic/redox-sensitive elements that became widely accessible because of the GOE. Here, sedimentary As marine records reveal a cyclic Proterozoic arsenic concentration pattern influenced by glacial-interglacial cycles. Postglacial sedimentary arsenic concentrations suggest deterioration of habitable marine conditions may have coincided with atmospheric oxygen decline after ~2.1 billion years ago (Ga). This changed after ~0.58 Ga when marine biota developed widespread stress responses against postglacial reorganization of global marine elemental cycles, producing physiologically robust communities that enabled increased oxygenation of the atmosphere-ocean system and radiation of complex life.
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| 8. |
- Chi Fru, Ernest, et al.
(författare)
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Sedimentary mechanisms of a modern banded iron formation on MIlos Island, Greece
- 2018
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Ingår i: Solid Earth. - : European Geosciences Union (EGU). - 1869-9510 .- 1869-9529. ; 9, s. 573-598
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Tidskriftsartikel (refereegranskat)abstract
- An early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Field-wide stratigraphic and biogeochemical reconstructions show two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggests the presence of a photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on a basement consisting of andesites in a ∼ 150m wide basin in the SW margin of the basin. A banded nonfossiliferous IF (NFIF) sits on top of the Mn-rich sandstones at the transition to the renowned Mn-rich formation, capping the NFIF unit. Geochemical data relate the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions predominated by anoxia, similar to the MFIF. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average δ13Corg signature of ∼ −25‰. A similar δ13Corg signature in the MFIF could not be directly coupled to hematite by mineralogy. The NFIF, which postdates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO2 ⋅ nH2O) while crystalline quartz (SiO2) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity, and abiotic Si precipitation are proposed to have collectively formed the unmetamorphosed BIF-type deposits in a shallow submarine volcanic center. Despite the differences in Precambrian ocean–atmosphere chemistry and the present geologic time, these formation mechanisms coincide with those believed to have formed Algoma-type BIFs proximal to active seafloor volcanic centers.
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| 9. |
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| 10. |
- Ivarsson, Magnus, et al.
(författare)
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Exceptional Preservation of Fungi as H2-Bearing Fluid Inclusions in an Early Quaternary Paleo-Hydrothermal System at Cape Vani, Milos, Greece
- 2019
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 9:12, s. 1-33
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Tidskriftsartikel (refereegranskat)abstract
- The production of H-2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H-2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H-2-production, of which anaerobic fungi have been put forward as a potential source of H-2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H-2. A biological origin of the H-2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H-2 by micro-eukaryotes is an unrecognized source of H-2 in hydrothermal systems that may support communities of H-2-dependent prokaryotes.
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