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WP3 Deep biosphereWP leader: Bo Barker Jørgensen, Arhus University, Denmark Marine sediments hold the largest organic carbon reservoir and the majority of all microorganisms on our planet. Up to one third of the living biomass on Earth is thriving beneath the seafloor, and microbial cells are recorded down to a sediment depth of 1.6 kilometers with an age of up to 116 million years. The discovery of a diverse and active sub-seafloor microbial community, both in deep sediments and in crustal rocks, has fundamentally changed our perception of life on Earth. This research is, however, only at its beginning and it is not yet clear which of the two domains of prokaryotic life, bacteria or archaea, predominate in the sub-surface or what the exact role of eukaryotic microorganisms or viruses may be. Microorganisms are the most abundant and diverse life forms on the planet and are key drivers of global biogeochemical cycles. Exploration of sub-seafloor life thus offers an unmatched opportunity to explore the fundamental processes and mechanisms that have determined and continue to drive the evolution and dispersal of life on Earth. For instance, microorganisms are known to horizontally exchange genes, a process that provides rapid genome adaptation and diversification. The deep ocean subsurface biosphere of the Earth represents a unique habitat in which to address questions regarding fundamental evolutionary biology and ecology that will yield insights into the contributions of horizontal gene flow to deep biosphere microbial community structure and function. There is little information available about the role of viral infection in horizontal gene transfer processes in the deep biosphere, or of gene flow and evolutionary processes in general, in part because of low microbial biomass, low microbial activity and possibly limited and/or significantly restricted community interactions in the deep biosphere. Resource availability deep beneath the seafloor may impose constraints on microbial growth and dispersal patterns that differ greatly from the surface world. Processes that mediate microbial evolution and diversity may also be very different in these habitats, which approach and probably pass the extreme limits of life. Communities in parts of the deep subsurface may resemble primordial microbial ecosystems, and may serve as analogues of life on other planetary bodies such as Mars or Europa that have, or once had water. The deep sub-seafloor biosphere has been discovered only within the past two decades and comprises the last major frontier for biological exploration. We lack fundamental knowledge of microbial community composition, diversity, distribution and metabolism in sub-seafloor environments. Exploration of this system presents a rich opportunity to understand microbial communities at Earth’s extremes. Microbes in different sub-seafloor environments must survive conditions of high pressure, high temperature, and extreme starvation. The limits of subsurface life are not yet known in terms of any environmental properties, including depth, temperature, energy availability, and geologic age. However, it is known that sub-seafloor microbes play a significant role in chemical reactions that were previously thought to have been abiotic, such as ethane and propane generation. The microorganisms are active in processes which affect the chemistry of the oceans on both a short and a long time scale, such as the degradation of oil and gas, the release or sequestration of carbon dioxide, and the oceanic cycling of major and trace elements, including nutrients and metals. The first high-capacity meta-genomic screening of sub-seafloor microbial communities has indicated that they possess equally great phylogenetic diversity as marine surface communities. This diversity may conceal an equally great diversity of functional genes and metabolic potentials, which could be of importance for the discovery of new bio-catalytic capacities or of bioactive compounds. Deep drilling of marine sediments and igneous crust offers a unique opportunity to explore how life persists and evolves in the Earth’s deepest subsurface ecosystems. The exploration of the deep biosphere has been recognised as one of the three main focus areas of the Integrated Ocean Drilling Program, IODP (see their Initial Science Plan, Appendix 2). European research groups are among the leading pioneers in deep biosphere research of the IODP, yet these groups have not been well organised and have therefore not had the optimal impact to direct its program and drive its science. This work package will help to coordinate the European deep biosphere research and ensure its strong representation in future international ocean drilling.
List of tentative WP3 participants (Level 3) |
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