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WP1 Lithosphere - biosphere interaction & resources
WP leader: Walter Roest, IFREMER, France
Multidisciplinary studies at a wide range of sites along the global mid-ocean ridge, back arcs and deep-sea volcanic systems are revealing that the formation and alteration processes of the ocean crust and accompanying biogeochemical processes are far more diverse than previously thought. These systems are areas of intense lithosphere-biosphere interactions, heterogeneous in structure, and are linked to a wide range of mineral-seawater reactions, which locally constitute sinks and sources for many elements. The chemical disequilibria created by these reactions and the transport and mixing of fluids provide chemical energy to sustain diverse communities of microorganisms and invertebrates, which in turn influence mineral-seawater interactions. While they offer some of the most extreme habitats for life, hydrothermal systems are also considered to host some of the most productive marine communities. Key processes sustaining seafloor surface and subsurface chemosynthetic communities on ridges have been highlighted in past studies (e.g., chemolithoautotrophy and dark CO2 fixation and primary production, symbiosis), but the knowledge of driving processes underlying these interactions is still very limited. The variety of redox conditions and the range of biogeochemical pathways supported by hydrothermal systems remain largely undescribed. In addition, the more recent discovery of novel hydrothermal vent systems hosted on ultramafic rocks, located on and away from ridge axes, has opened a completely new area of research, including possible sources of natural hydrogen as a potential energetic resource. As the anthropogenic pressure on these environments increases, energy and carbon transfer mechanisms from mineral compounds to organisms urgently needs to be quantified and modeled in order to estimate impacts on biodiversity and global element cycles, and their potential global significance.
Key objectives of WP1 can be summarised under the following three overarching points: (1) Assessing the importance of lithosphere-biosphere interactions in global element cycles The importance of hydrothermal energy and chemical element transfer from the lithosphere to the biosphere has been reconsidered in the light of recent discoveries. Initially, heat and mass transfer were considered to primarily occur at discrete, isolated, hydrothermally active hotspots around the global ridge system and to have a minor impact on the global ocean carbon cycles. However, recent results suggest that both the local fixation of carbon through chemosynthesis and sequestration of carbon through alteration processes may be much greater than previously recognised. This is particularly true in ridge flank environments and in off-axis hydrothermal systems, in which long-lived convection and fluid-rock interactions have the potential to sustain a diverse deep biosphere over extensive areas of the oceanic crust. Better constraints on fluid pathways, reactions and the regulation of energy and carbon transfer within the lithosphere are required to quantify chemical fluxes and better understand the fundamental processes leading to the formation and evolution of the oceanic lithosphere. In addition, a better understanding of the underlying mechanisms sustaining the high productivity of these ecosystems and their potential impact on global element cycling is needed. As geophysical imaging and geochemical sampling techniques improve, it is essential to combine these data with new numerical and conceptual models of the complex interplay between magmatic, tectonic and alteration process and their consequences and reciprocal influence with biogeochemical systems at various scales, from local to global.
(2) Understanding processes driving the diversity of extremophilic communities on and beneath the seafloor and their biogeochemical feedbacks The habitats created by hydrothermal venting on and beneath the seafloor exhibit tremendous variability in a number of physico-chemical parameters, including temperature, pH, volatiles (H2S, H2, CH4, CO2, CO, O2) and metal concentrations. Associated prokaryotic and eukaryotic organisms have to combine adaptation strategies to face their energy requirements and tolerance to various stressors. Hydrothermal systems are therefore large vast reservoirs of highly specialised species representing unique models for fundamental research and for great potential biotechnological applications. Recent interdisciplinary studies and new analytical capabilities, including metagenomics and other ‘omics’ approaches, have allowed significant advances in estimating vent biodiversity. What is now needed is a better understanding of the links between the diversity of communities and the availability of chemical substrates and energy, underlying the functioning of these ecosystems and their response to disturbance and stresses. The diversity of carbon fixation pathways, metabolic pathways related to detoxification, feedbacks on the biological communities on the export for material to the water column. Experimental strategies and tools to address these questions on the seafloor are now needed.
(3) Deep-sea mineral resources: assessing global distributions and potential environmental impacts of seafloor exploitation The seafloor contains a vast reservoir of renewable and non-renewable mineral resources that are rapidly gaining in scientific as well as economic interest. However, much about the composition and global distribution of mineral resources on and within the seafloor, their quantitative importance for global chemical cycles and biological activity, and the potential impacts of exploitation on ocean chemistry and ecosystems is incompletely understood. As industry interest in resources (such as cobalt crusts, manganese and deep-sea sulphides) increases and before fragile ecosystems are disturbed by mining, there is an increasing need to better understand the geodynamics of ridge systems, the processes leading to mineral resource deposition, the distribution and composition of the communities they sustain and how they are modified with time. For instance, little is known about the volume of sulphide within the oceanic crust, its composition, and mineral-organisms interactions over the lifetime of a hydrothermal system. In addition almost nothing is known about the impact of element remobilization (e.g. sulphur, heavy metals) by physical disturbance and microbial activity and the response of deep-sea vent ecosystems to potential disturbances due to the exploitation of these resources. A better knowledge of the population genetics and biogeography of species would also help understanding the connectivity of populations at larger scales and better assess the effect of disturbance on these populations. Strategies to address these aspects and open questions involve monitoring and sampling both on and below the seafloor. Characterisation of fluids venting on the seabed and the associated biological communities provide insights into the processes occurring deep below the seafloor. Direct drilling projects need to be based on a thorough investigation of the systems using more conventional approaches and multidisciplinary oceanographic investigations. Interdisciplinary integrated studies, modeling and experimental approaches are still a challenge that needs to be met.
Significant and clearly visible outcomes are expected from a coordinated effort at the European level for the definition and implementation of exploration and investigation strategies to study, monitor and model driving and active processes underlying interactions between the lithosphere and biosphere. Benefits that can be expected from enhanced coordination of field and laboratory studies within Europe include facilitating access to ships and submersibles for exploration, observation (monitoring) and sampling, including drilling, encouraging synergies in the development of new mission-specific technologies and coordinating efforts for their design and implementation, developing experimental platforms to elucidate driving and active processes and rates, and promoting the development of (bio)geochemical models (see also WPs 7-8).
List of tentative WP1 participants (Level 3)