Abstract The deep biosphere is one of the least understood ecosystems on Earth. Although most microbiological studies in this system have focused on prokaryotes and neglected microeukaryotes, recent discoveries have revealed existence of fossil and active fungi in marine sediments and sub-seafloor basalts, with proposed importance for the subsurface energy cycle. However, studies of fungi in deep continental crystalline rocks are surprisingly few. Consequently, the characteristics and processes of fungi and fungus-prokaryote interactions in this vast environment remain enigmatic. Here we report the first findings of partly organically preserved and partly mineralized fungi at great depth in fractured crystalline rock (−740 m). Based on environmental parameters and mineralogy the fungi are interpreted as anaerobic. Synchrotron-based techniques and stable isotope microanalysis confirm a coupling between the fungi and sulfate reducing bacteria. The cryptoendolithic fungi have significantly weathered neighboring zeolite crystals and thus have implications for storage of toxic wastes using zeolite barriers.
The production of H2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H2 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 H2-production, of which anaerobic fungi have been put forward as a potential source of H2 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 H2. A biological origin of the H2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H2 by micro-eukaryotes is an unrecognized source of H2 in hydrothermal systems that may support communities of H2-dependent prokaryotes.
The Anthropocene has been framed around humanity's impact on atmospheric, biologic, and near-surface processes, such as land use and vegetation change, greenhouse gas emissions, and the above-ground hydrologic cycle.Groundwater extraction has lowered water tables in many key aquifers but comparatively little attention has been given to the impacts in the deeper subsurface.Here, we show that fluid fluxes from the extraction and injection of fluids associated with oil and gas production and inflow of water into mines likely exceed background flow rates in deep (>500 m) groundwater systems at a global scale.Projected carbon capture and sequestration (CCS), geothermal energy production, and lithium extraction to facilitate the energy transition will require fluid production rates exceeding current oil and co-produced water extraction.Natural analogs and geochemical modeling indicate that
A growing literature of deep but also surficial fossilized remains of lithobiological life, often associated with igneous rocks, necessitates the unfolding of a sub-discipline within paleobiology. Here, we introduce the term paleolithobiology as the new auxiliary sub-discipline under which fossilized lithobiology should be handled. We present key criteria that distinguish the paleolithobiological archive from the traditional one and discuss sample strategies as well as scientific perspectives. A majority of paleolithobiological material consists of deep biosphere fossils, and in order to highlight the relevance of these, we present new data on fungal fossils from the Lockne impact crater. Fungal fossils in the Lockne drill cores have been described previously but here we provide new insights into the presence of reproductive structures that indicate the fungi to be indigenous. We also show that these fungi frequently dissolve and penetrate secondary calcite, delineating the role lithobionts plays in geobiological cycles. We hope that the formalization of the sub-discipline paleolithobiology will not only highlight an overlooked area of paleobiology as well as simplify future studies of endo- and epilithic fossil material, but also improve our understanding of the history of the deep biosphere.
Biotite dissolution, the main Fe-bearing mineral in granitic bedrock, is of particular importance for the remediation of reducing conditions after the ingress of oxygen, such as after mining activities or the construction of deep repositories for toxic waste. This study investigated the leaching of biotite of size fraction 0.053–0.075 mm under anaerobic conditions at room temperature and pH 4 and 6.5 for a maximum of 160 days. The changes in the concentrations of the major elements in the leaching solutions were monitored. In addition, Fe(II) was analysed separately. pH-independent rate coefficients kH+ were 4.8∙10−10, 6.9∙10−10, 6.3∙10−11, and 1.0∙10−12 mol1-n m−2 s-1, for Fe, Fe(II), Mn, and Si, respectively. The corresponding proton reaction orders nH+ were 0.61, 0.63, 0.33, and 0.09, respectively. The corresponding parameters for Al were not evaluated because of a suspected gibbsite precipitation at pH 6.5. The dissolution of biotite was found to be incongruent (non-stoichiometric) with respect to both the dissolving elements and the pH value. At pH 4, the dissolution was dominated by the octahedral layer element Fe, whereas at pH 6.5, the dissolution of the tetrahedral element Si dominated. There was no evidence of secondary phase formation, and the biotite leaching rates were consistent with those reported in previous studies conducted under aerobic conditions. In addition, the Fe(III)/Fetot ratio of biotite remained essentially unchanged before and after the experiment. This indicates that the anaerobic conditions alone have little effect on the rate and nature of biotite dissolution, although they may influence vermiculite formation. Therefore, biotite dissolution rates previously obtained under aerobic conditions may also be valid under anaerobic conditions.
Precipitation of exceptionally 13C-depleted authigenic carbonate is a result of, and thus a tracer for, sulphate-dependent anaerobic methane oxidation, particularly in marine sediments. Although these carbonates typically are less depleted in 13C than in the source methane, because of incorporation of C also from other sources, they are far more depleted in 13C (δ13C as light as -69‰ V-PDB) than in carbonates formed where no methane is involved. Here we show that oxidation of biogenic methane in carbon-poor deep groundwater in fractured granitoid rocks has resulted in fracture-wall precipitation of the most extremely 13C-depleted carbonates ever reported, δ13C down to -125‰ V-PDB. A microbial consortium of sulphate reducers and methane oxidizers has been involved, as revealed by biomarker signatures in the carbonates and S-isotope compositions of co-genetic sulphide. Methane formed at shallow depths has been oxidized at several hundred metres depth at the transition to a deep-seated sulphate-rich saline water. This process is so far an unrecognized terrestrial sink of methane.
Detailed geochemical investigations of calcite veins, genetically related to intrusions and vein-hosting bedrock, have been used to indicate fluid evolution during intrusion-related hydrothermal mineralization, involving fluid mixing and water rock interaction. The area of investigation is located in the southeast of Sweden. The 1.85 Ga granitoid country rocks and the 0.9 Ga dolerite vein-related intrusions differ in chemical, geochemical, and stable isotope composition. The variation in rare earth and stable isotope composition across calcite veins and the presence of two groups of fluid inclusions suggests mixing of two types of fluids. Light rare earth enrichment and increasing 87Sr/86Sr-ratios suggest water rock interaction of one/both fluids.
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