Special Issue "Tracking the Deep Biosphere through Time"
Deadline for manuscript submissions: 1 September 2019.
Dr. Magnus Ivarsson
Department of Biology, University of Southern Denmark, Odense, DenmarkSwedish Museum of Natural History, Department of Paleobiology, Stockholm, Sweden
Interests: deep biosphere; geobiology; paleobiology; fossilized microorganisms
The oceanic and continental lithosphere constitutes Earth´s largest microbial habitat, yet it is poorly investigated and not well understood. Its physical and chemical properties are distinctly different from the overlaying soils and the hydrosphere, which greatly impacts the microbial communities and associated geobiological and geochemical processes. Fluid-rock interactions, i.e., the serpentinization of ultramafic rocks and the subsequent production of gases and molecular species, are key processes for microbial colonization and persistence in a nutrient-poor and extreme environment. Investigations during recent years have indicated microorganism-related processes, stable isotope variations, and species that are unique to the subsurface crust. Recent advances in geochronology have enabled the direct dating of minerals formed in response to microbial activity, which in turn have led to an increasing understanding of the evolution of the deep biosphere in (deep) time. Similarly, the preservation of isotopic signatures as well as organic compounds within fossilized microcolonies or related mineral assemblages in voids, cements, and fractures/veins in the upper crust provide an archive that can be tapped for knowledge about ancient microbial activity, including both prokaryotic and eukaryotic life. This knowledge sheds light on how lifeforms have evolved in the energy-poor subsurface, but also contributes to the understanding of the boundaries of life on Earth, of early Earth life at times when the surface was inhabitible, and of the preservation of signatures of ancient life, which may have astrobiological implications.
This Special Issue seeks to cover all geobiological aspects of the upper crust (continental and marine) and we invite contributions with relevance to geomicrobiology, isotope geochemistry, microbial-activity-associated geochronology and related geochemical and hydrochemical proxies as well as presentations on new methods, techniques, and experimental approaches in both the modern and ancient crust. We wish to cover a broad spectrum of environments such as ultra-mafic, mafic, and felsic systems, as well as hydrothermal/geothermal areas and sedimentary successions. We encourage contributions related to scientific drilling programs as well as research from underground facilites and deep drillings related to mining activity or nuclear waste disposal, in addition to studies of exposed ancient crust. Astrobiological implications are also encouraged.
Dr. Henrik Drake
Dr. Magnus Ivarsson
Dr. Christine Heim
Manuscript Submission Information
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- deep biosphere
- deep time
The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.
Title: Re-Evaluating the Age of Lockne Deep Biosphere Fossils
Authors: Tillberg, M., Ivarsson, M., Drake, H., Whitehouse, M., Kooijman, E., Hogmalm, J.
Abstract: Impact-generated hydrothermal systems have been suggested as favourable environments for deep microbial ecosystems on Earth, and possibly beyond. Fossil evidence from a handful of impact craters worldwide have been used to support this notion. However, as always with mineralized remains of microorganisms in crystalline rock, certain time constraints with respect to the ecosystems and their subsequent fossilization are difficult to obtain. Here we re-evaluate previously described fungal fossils from the Lockne crater (458 Ma), Sweden. Based on in-situ Rb/Sr dating of secondary calcite-feldspar we conclude that the fungal colonization took place at least 100 Ma after the impact event, thus long after the impact-induced hydrothermal activity ceased. We also present microscale stable isotope data of 13C-enriched calcite suggesting presence of methanogens contemporary with the fungi. Thus, the Lockne fungi fossils are not, as previously thought, related to the impact event, but nevertheless has colonized fractures that may have been formed or/were reactivated by the impact. Instead, the Lockne fossils show similar features as recent findings of ancient microbial remains elsewhere in the fractured Swedish Precambrian basement and may thus represent a more general feature in this scarcely explored habitat than previously known.
Title:Initial formation and long term development of mineralizing biofilms in aquifers in the continental crust
Authors: Christine Heim1, Danny Ionescu2, Tim Leefman3 Klaus Simon1, Joachim Reitner1, Volker Thiel1
Abstract: Biofilms growing within rock fractures exhibit an enormous diversity of aerobic and anaerobic, chemolithotrophic microorganisms. Aquifers in the Precambrian granodioritic rocks of the Baltic Shield have been studied as model systems for this continental subsurface biosphere. To elucidate the metabolic and biomineralization processes occurring therein, flow reactors were installed in the Äspö Hard Rock Laboratory (Äspö HRL, Sweden), connecting to four aquifers that differed in depth, age, and chemical composition. Here we provide an overview about the results obtained during more than a decade of our research at Äspö HRL.
Biofilm development and aquifer composition within the flow reactors were monitored continuously for a time span of about ten years. Initial deposition of salts and organic molecules (‘conditioning films’) in the flow reactors were observed after only 10 minutes. The following biofilm development varied significantly dependent on the available nutrients and energy sources and the water flow. In the shallow, brackish and nutrient-rich aquifers cm-thick biofilms formed already after 2 months and caused partial clogging of the tubings during further vigorous growth. In contrast, in the deepest, more saline and nutrient-poor aquifer (-450 m) it took about 3 years for visible biofilms to develop. Mineral precipitates were formed by direct mineralization, i.e. the biogenic redox conversion of metal ions (e.g. iron hydroxides) but also by indirect mineralization processes due to changes of the chemical equilibrium (e.g. gypsum). Microbial metabolic processes and extracellular polymeric substances (EPS) had a strong influence on cation binding and complex formation. Distinct Ni accumulations were only observed the iron hydroxide containing biofilms but not in the abiotic controls, and may serve as biosignatures in the fossil record. Rare earth element pattern obtained from the iron hydroxide precipitating biofilms mirror the source fluid chemistry, which can also be highly useful for palaeoenvironmental reconstructions. Microscopic and biomarker analyses of the different developmental stages of the mineralized biofilms show an increasing complexity and diversity over the years. Even though biogeochemical processes in the subsurface may be slow, they have a significant influence on aquifer chemistry, mineralogy and fracture permeability over time.