Outokumpu Deep Drill Hole Research Articles

Rock Surface Fungi in Deep Continental Biosphere-Exploration of Microbial Community Formation with Subsurface In Situ Biofilm Trap.

Fungi have an important role in nutrient cycling in most ecosystems on Earth, yet their ecology and functionality in deep continental subsurface remain unknown. Here, we report the first observations of active fungal colonization of mica schist in the deep continental biosphere and the ability of deep subsurface fungi to attach to rock surfaces under in situ conditions in groundwater at 500 and 967 m depth in Precambrian bedrock. We present an in situ subsurface biofilm trap, designed to reveal sessile microbial communities on rock surface in deep continental groundwater, using Outokumpu Deep Drill Hole, in eastern Finland, as a test site. The observed fungal phyla in Outokumpu subsurface were Basidiomycota, Ascomycota, and Mortierellomycota. In addition, significant proportion of the community represented unclassified Fungi. Sessile fungal communities on mica schist surfaces differed from the planktic fungal communities. The main bacterial phyla were Firmicutes, Proteobacteria, and Actinobacteriota. Biofilm formation on rock surfaces is a slow process and our results indicate that fungal and bacterial communities dominate the early surface attachment process, when pristine mineral surfaces are exposed to deep subsurface ecosystems. Various fungi showed statistically significant cross-kingdom correlation with both thiosulfate and sulfate reducing bacteria, e.g., SRB2 with fungi Debaryomyces hansenii.

Response of Deep Subsurface Microbial Community to Different Carbon Sources and Electron Acceptors during ∼2 months Incubation in Microcosms.

Acetate plays a key role as electron donor and acceptor and serves as carbon source in oligotrophic deep subsurface environments. It can be produced from inorganic carbon by acetogenic microbes or through breakdown of more complex organic matter. Acetate is an important molecule for sulfate reducers that are substantially present in several deep bedrock environments. Aceticlastic methanogens use acetate as an electron donor and/or a carbon source. The goal of this study was to shed light on carbon cycling and competition in microbial communities in fracture fluids of Finnish crystalline bedrock groundwater system. Fracture fluid was anaerobically collected from a fracture zone at 967 m depth of the Outokumpu Deep Drill Hole and amended with acetate, acetate + sulfate, sulfate only or left unamended as a control and incubated up to 68 days. The headspace atmosphere of microcosms consisted of 80% hydrogen and 20% CO2. We studied the changes in the microbial communities with community fingerprinting technique as well as high-throughput 16S rRNA gene amplicon sequencing. The amended microcosms hosted more diverse bacterial communities compared to the intrinsic fracture zone community and the control treatment without amendments. The majority of the bacterial populations enriched with acetate belonged to clostridial hydrogenotrophic thiosulfate reducers and Alphaproteobacteria affiliating with groups earlier found from subsurface and groundwater environments. We detected a slight increase in the number of sulfate reducers after the 68 days of incubation. The microbial community changed significantly during the experiment, but increase in specifically acetate-cycling microbial groups was not observed.

CO2 and carbonate as substrate for the activation of the microbial community in 180 m deep bedrock fracture fluid of Outokumpu Deep Drill Hole, Finland.

Microbial communities in deep subsurface environments comprise a large portion of Earth's biomass, but the metabolic activities in these habitats are largely unknown. Here the effect of CO2 and carbonate on the microbial community of an isolated groundwater fracture zone at 180 m depth of the Outokumpu Deep Scientific Drill Hole (Finland) was tested. Outokumpu groundwater at 180 m depth contains approximately 0.45 L L−1 dissolved gas of which methane contributes 76%. CO2, on the other hand, is scarce. The number of microbial cells with intracellular activity in the groundwater was low when examined with redox staining. Fluorescence Assisted Cell Sorting (FACS) analyses indicated that only 1% of the microbial community stained active with the redox sensing dye in the untreated groundwater after 4 weeks of starvation. However, carbon substrate and sulfate addition increased the abundance of fluorescent cells up to 7%. CO2 and CO2 + sulfate activated the greatest number of microbes, especially increasing the abundance of Pseudomonas sp., which otherwise was present at only low abundance in Outokumpu. Over longer exposure time (2 months) up to 50% of the bacterial cells in the groundwater were shown to incorporate inorganic carbon from carbonate into biomass. Carbon recapture is an important feature in this ecosystem since it may decrease the rate of carbon loss in form of CO2 released from cellular processes.

Abiotic and biotic controls on methane formation down to 2.5 km depth within the Precambrian Fennoscandian Shield

Despite a geological history characterised by high temperature and pressure processes and organic carbon deprived crystalline bedrock, large amounts of hydrocarbons are found in deep groundwaters within Precambrian continental shields. In many sites, methane comprises more that 80% of the dissolved gas phase reaching concentrations of tens of mmoll−1. In this study, we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the Fennoscandian Shield. The main study sites were the Outokumpu Deep Drill Hole and the Pyhäsalmi mine in Finland, both of which allow groundwater sampling down to 2.5km depth and have been previously studied for their groundwater chemistry and microbiology. We show that the differences in the amount and isotopic composition of methane are related to the availability of carbon sources as well as processes behind the incorporation of hydrogen and carbon via abiotic and biotic pathways into hydrocarbon molecules. Supported by previously reported occurrences and isotopic data of deep groundwater methane in lithologically different locations in Finland and Sweden, we show that methane formation is controlled by microbial methanogenesis and abiotic reactions, as well as lithology with the metasedimentary environments being the most favourable for methane occurrence. Rather than a thermogenic relic, crustal methane within the Fennoscandian Shield is more likely the result of low temperature formation from ancient organic compounds or their inorganic intermediates such as graphite. Such crustal gases are characterised by the lack of major amounts of C2+ hydrocarbons and 13C-rich methane. Further, microbiological and isotopic geochemical evidence suggest that microbial methane is more common at depths shallower than 1.5km.

Reorientation of three‐component borehole magnetic data

ABSTRACTThree‐component borehole magnetics provide important additional information compared to total field or horizontal and vertical measurements. These data can be used for several tasks such as the localization of ferromagnetic objects, the determination of apparent polar wander curves and the computation of the magnetization of rock units. However, the crucial point in three‐component borehole magnetics is the reorientation of the measured data from the tool's frame to the geographic reference frame North, East and Downwards. For this purpose, our tool, the Göttinger Borehole Magnetometer, comprises three orthogonally aligned fibre optic gyros along with three fluxgate sensors. With these sensors, the vector of the magnetic field along with the tool rotation can be recorded continuously during the measurement. Using the high–precision gyro data, we can compute the vector of the magnetic anomaly with respect to the Earth's reference frame. Based on the comparison of several logs measured in the Outokumpu Deep Drill Hole (OKU R2500, Finland), the repeatability of the magnetic field vector is 0.8° in azimuthal direction, 0.08° in inclination and 71 nT in magnitude.

Noble gas residence times of saline waters within crystalline bedrock, Outokumpu Deep Drill Hole, Finland

Noble gas residence times of saline groundwaters from the 2516m deep Outokumpu Deep Drill Hole, located within the Precambrian crystalline bedrock of the Fennoscandian Shield in Finland, are presented. The accumulation of radiogenic (4He, 40Ar) and nucleogenic (21Ne) noble gas isotopes in situ together with the effects of diffusion are considered. Fluid samples were collected from depths between 180 and 2480m below surface, allowing us to compare the modelled values with the measured concentrations along a vertical depth profile. The results show that while the concentrations in the upper part are likely affected by diffusion, there is no indication of diffusive loss at or below 500m depth. Furthermore, no mantle derived gases were found unequivocally. Previous studies have shown that distinct vertical variation occurs both in geochemistry and microbial community structuring along the drill hole, indicating stagnant waters with no significant exchange of fluids between different fracture systems or with surface waters. Therefore in situ accumulation is the most plausible model for the determination of noble gas residence times. The results show that the saline groundwaters in Outokumpu are remarkably old, with most of the samples indicating residence times between ∼20 and 50Ma. Although being first order approximations, the ages of the fluids clearly indicate that their formation must predate more recent events, such as Quaternary glaciations. Isolation within the crust since the Eocene–Miocene epochs has also direct implications to the deep biosphere found at Outokumpu. These ecosystems must have been isolated for a long time and thus very likely rely on energy and carbon sources such as H2 and CO2 from groundwater and adjacent bedrock rather than from the ground surface.

Characterisation and isotopic evolution of saline waters of the Outokumpu Deep Drill Hole, Finland – Implications for water origin and deep terrestrial biosphere

The isotopic composition of water and dissolved Sr as well as other geochemical parameters at the 2516m deep Outokumpu Deep Drill Hole, Finland were determined. The drill hole is hosted by Palaeoproterozoic turbiditic metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granitoids. Sodium–Ca–Cl and Ca–Na–Cl-rich waters (total dissolved solids up to ca. 70gL−1) containing significant amounts of gas, mainly CH4 (up to 32mmolL−1), N2 (up to 10mmolL−1), H2 (up to 3.1mmolL−1) and He (up to 1.1mmolL−1) discharge from fracture zones into the drill hole. This water is distinct from the shallow fresh groundwater of the area, and has an isotopic composition typical of shield brines that have been modified during long-term water–rock interaction. Based on water stable isotopes and geochemistry, the drill hole water profile can be divided into five water types, each discharging from separate fracture systems and affected by the surrounding rocks. The δ2H varies from −90‰ to −56‰ (VSMOW) and δ18O from −13.5‰ to −10.4‰ (VSMOW), plotting clearly above the Global and Local Meteoric Water Lines on a δ2H vs. δ18O diagram. The 87Sr/86Sr ratios range between 0.72423 and 0.73668. Simple two-component mixing between 2H and 18O rich end-member brine and meteoric water cannot explain the water stable isotopic composition and trends observed. Instead, hydration of silicates by ancient groundwaters recharged under different climatic conditions, warmer than at present, is the most likely mechanism to have caused the variation of the δ2H and δ18O values. Water types correlate with changes in microbial communities implying that different ecosystems occur at different depths. The different water types and microbial populations have remained isolated from each other and from the surface for long periods of time, probably tens of millions of years.

Geothermal studies of the Outokumpu Deep Drill Hole, Finland: Vertical variation in heat flow and palaeoclimatic implications

Detailed geothermal studies of deep drill holes provide insights to heat transfer processes in the crust, and allow separation of different factors involved, such as palaeoclimatic and structural conductive effects as well as advective fluid flow effects. We present high resolution geothermal results of the 2516 m deep Outokumpu Deep Drill Hole in eastern Finland drilled in 2004–2005 into a Palaeoproterozoic formation with metasedimentary rocks, ophiolite-derived altered ultramafic rocks and pegmatitic granite. The down-hole temperatures have been logged five times after end of drilling and extend to day 948 after drilling. The hole is completely cored (79% core coverage) and thermal conductivity measurements were done at 1 m intervals. The geothermal results on temperature gradient, thermal conductivity and heat flow density yield an exceptionally detailed data set and indicate a significant vertical variation in gradient and heat flow density. Heat flow density increases from about 28 – 32 mW m −2 in the uppermost 1000 m to 40–45 mW m −2 at depths exceeding 2000 m. The estimated undisturbed surface heat flow value is 42 mW m −2. We present results on forward and inverse transient conductive models which suggest that the vertical variation in heat flow can mostly be attributed to a palaeoclimatic effect due to ground surface temperature (GST) variations during the last 100,000 years. The modeling suggests that the average GST was about −3 to −4 °C during the Weichselian glaciation. Holocene GST values are within ±2° from the present average GST in Outokumpu (5 °C). The topographic hydraulic heads and hydraulic conductivity of crystalline rocks are low which suggests that advective heat transfer in the formation is not significant. The slow replacement of fresh flushing water by saline formation fluids is observed in the hole, but it does not generate significant thermal disturbances in the logs. On the other hand, free sluggish thermal convection is present in the large diameter (22 cm) borehole, and temperature variations in the range of few mK to 0.01 K occur over times of minutes to tens of minutes. Theory suggests that convection cells are about as tall as the drill hole diameter, and thus the free convection is expected to generate only local thermal ‘noise’ not affecting the general geothermal results.

Ultrasonic velocity of the upper gneiss series rocks from the Outokumpu deep drill hole, Fennoscandian shield — Comparing uniaxial to triaxial loading

Abstract P- and S-wave propagation velocities in dry mica schist samples obtained from the Outokumpu deep drill hole in Eastern Finland were measured under uniaxial compression in a custom built measurement device. At 300 MPa pressure the obtained velocities (5520 ± 130) m/s and (3270 ± 60) m/s, for P- and S-waves, respectively, agreed with those measured under triaxial compression, (5530 ± 200) m/s and (3300 ± 90) m/s. The increase in Vp with uniaxial pressure was steeper, whereas this was not the case with Vs. These results indicate that ultrasound velocity measurements can be performed under uniaxial compression without the need to alter the cylindrical geometry of a borehole sample. Results obtained with the device can improve the interpretation of seismic crustal structure maps by providing seismic velocity data of the Outokumpu drill core as well as seismic impedances and reflection coefficients measured under crustal conditions.