Abstract
Interest in extracting mineral resources from the seafloor through deep‐sea mining has accelerated in the past decade, driven by consumer demand for various metals like zinc, cobalt, and rare earth elements. While there are ongoing studies evaluating potential environmental impacts of deep‐sea mining activities, these focus primarily on impacts to animal biodiversity. The microscopic spectrum of seafloor life and the services that this life provides in the deep sea are rarely considered explicitly. In April 2018, scientists met to define the microbial ecosystem services that should be considered when assessing potential impacts of deep‐sea mining, and to provide recommendations for how to evaluate and safeguard these services. Here, we indicate that the potential impacts of mining on microbial ecosystem services in the deep sea vary substantially, from minimal expected impact to loss of services that cannot be remedied by protected area offsets. For example, we (1) describe potential major losses of microbial ecosystem services at active hydrothermal vent habitats impacted by mining, (2) speculate that there could be major ecosystem service degradation at inactive massive sulfide deposits without extensive mitigation efforts, (3) suggest minor impacts to carbon sequestration within manganese nodule fields coupled with potentially important impacts to primary production capacity, and (4) surmise that assessment of impacts to microbial ecosystem services at seamounts with ferromanganese crusts is too poorly understood to be definitive. We conclude by recommending that baseline assessments of microbial diversity, biomass, and, importantly, biogeochemical function need to be considered in environmental impact assessments of deep‐sea mining.
Abstract
IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences.
New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life.
Abstract
Serpentinization is the process in which ultramafic rocks, characteristic of the upper mantle, react with water liberating mantle carbon and reducing power to potenially support chemosynthetic microbial communities. These communities may be important mediators of carbon and energy exchange between the deep Earth and the surface biosphere. Our work focuses on the Coast Range Ophiolite Microbial Observatory (CROMO) in Northern California where subsurface fluids are accessible through a series of wells. Preliminary analyses indicate that the highly basic fluids (pH 9-12) have low microbial diversity, but there is limited knowledge about the metabolic capabilities of these communties. Metagenomic data from similar serpentine environments [1] have identified Betaproteobacteria belonging to the order Burkholderiales and Gram-positive bacteria from the phylum Clostridiales, as key components of the serpentine microbiome. In an effort to better characterize the microbial community, metabolism, and geochemistry at CROMO, fluids from two representative wells (N08B and CSWold) were sampled during a recent field campaign. The wells selected can be differentiated in that N08B had cell counts ranging from 105 -106 cells mL-1 of fluid, and abundance of the Betaproteobacterium Hydrogenophaga. In contrast, fluids from CSWold have lower cell counts (~103 cells mL-1 ) and an abundance of Dethiobacter, a taxon within the phylum Clostridiales. Geochemical characterization of the fluids includes measurements of dissolved gases (H2, CO, CH4), dissolved inorganic and organic carbon, volatile fatty acids, and nutrients. Microcosm experiments were conducted with the purpose of monitoring carbon fixation and metabolism of small organic compounds, such as acetate, while tracing changes in fluid chemistry and microbial community composition. These experiments are expected to provide insight into the biogeochemical dynamics of the serpentinite subsurface at CROMO and represent a first step for developing RNA based Stable Isotope Probing (RNA-SIP) experiments to trace microbial activity at this site.
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Abstract
Since the days of Darwin, scientists have used the framework of the theory of evolution to explore the interconnectedness of life on Earth and adaptation of organisms to the ever-changing environment. The advent of molecular biology has advanced and accelerated the study of evolution by allowing direct examination of the genetic material that ultimately determines the phenotypes upon which selection acts. The study of evolution has been furthered through examination of microbial evolution, with large population numbers, short generation times, and easily extractable DNA. Such work has spawned the study of microbial biogeography, with the realization that concepts developed in population genetics may be applicable to microbial genomes (Martiny et al., 2006; Manhes and Velicer, 2011). Microbial biogeography and adaptation has been examined in many different environments. Here we argue that the deep biosphere is a unique environment for the study of evolution and list specific factors that can be considered and where the studies may be performed. This publication is the result of the NSF-funded Center for Dark Energy Biosphere Investigations (C-DEBI) theme team on Evolution (www.darkenergybiosphere.org).
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Abstract
I presented a poster at the GRS and GRC titled “Metagenomic evidence for primary production fueled by serpentinization” that summarizes my ongoing work to identify autotrophic organisms in serpentinite-hosted subsurface ecosystems. The particular focus of this poster was to identify intriguing connections between several marine and continental sites of serpentinization in order to gain greater insight into biogeochemical process in ultramafic subseafloor habitats, which are currently inaccessible to the large-scale metagenomic techniques we are employing. This conference represented an opportunity to share my research with a community of researchers who are mostly unaware of our work but share common interests. In addition to the many techniques that we have in common, the questions of microbial biogeography that are inherent to our research direction also drive the work by many other marine microbial ecologists who do not necessarily study the subseafloor.
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Abstract
Genomic investigations of deep biosphere ecosystems have the potential for yielding ground-breaking insights into microbial evolution, but explicitly evolutionary studies are currently limited by technical constraints of environmental sequencing approaches and by the lack of a diverse collection of cultivated model organisms representing subsurface ecosystems (Biddle et al., 2012). This project aimed to study genome evolution in archaeal biofilms inhabiting carbonate chimneys of the Lost City hydrothermal field. The extremely high abundance and low diversity of these biofilms makes them attractive natural models for the study of genome evolution in deep biosphere habitats. The genomic characteristics of this unusual population structure have not yet been explored, so we began to optimize methods for the extraction and sorting of single cells from Lost City chimney biofilms in order to analyze single-cell genomic variability within and between biofilm communities. Our preliminary results indicated that enzymatic digestion of the biofilm extracellular matrix improves recovery of cells compared to typical cell extraction procedures that only utilize physical disruption of samples during cell extraction. We also developed a flow cytometric approach to evaluate the results of cell extraction procedures prior to investing resources into sorting and sequencing of single cells. Future data resulting from these efforts will allow us to pursue our broader goals of measuring the extent of genetic exchange between cells, viruses, and extracellular DNA in this rock-hosted, deep biosphere habitat.