The new issue of Scientific Drilling, a multidisciplinary ICDP-IODP program journal delivering peer-reviewed science reports from recently completed and ongoing international scientific drilling projects, is now available online. Deep biosphere-related articles include Microbial diversity of drilling fluids from 3000 m deep Koyna pilot borehole provides insights into the deep biosphere of continental earth crust (Bose et al.) and New Chikyu Shallow Core Program (SCORE): exploring mass transport deposits and the subseafloor biosphere off Cape Erimo, northern Japan (Kubo et al.).
Authors: Man-Yin Tsang, Fumio Inagaki
Below the seafloor are trillions of single-celled microbial life. Marine sediments bury these microorganisms deeper and deeper. Meanwhile, the microorganisms face increasing pressures and temperatures and reduced amounts of food and water. Although they are living in difficult conditions, these microorganisms stay alive and maintain their communities. To date, we know that these microbial communities can survive for millions of years, at 2.5 km below the seafloor, and at temperatures over 100°C. Scientists use multiple approaches to study these fascinating microorganisms.
Authors: T. R. Vonnahme, M. Molari, F. Janssen, F. Wenzhöfer, M. Haeckel, J. Titschack, A. Boetius.
Future supplies of rare minerals for global industries with high-tech products may depend on deep-sea mining. However, environmental standards for seafloor integrity and recovery from environmental impacts are missing. We revisited the only midsize deep-sea disturbance and recolonization experiment carried out in 1989 in the Peru Basin nodule field to compare habitat integrity, remineralization rates, and carbon flow with undisturbed sites. Plough tracks were still visible, indicating sites where sediment was either removed or compacted. Locally, microbial activity was reduced up to fourfold in the affected areas. Microbial cell numbers were reduced by ~50% in fresh “tracks” and by <30% in the old tracks. Growth estimates suggest that microbially mediated biogeochemical functions need over 50 years to return to undisturbed levels. This study contributes to developing environmental standards for deep-sea mining while addressing limits to maintaining and recovering ecological integrity during large-scale nodule mining.
See also the MPI-Bremen press release.
Authors: Shana K. Goffredi, Ekin Tilic, Sean W. Mullin, Katherine S. Dawson, Abigail Keller, Raymond W. Lee, Fabai Wu, Lisa A. Levin, Greg W. Rouse, Erik E. Cordes, Victoria J. Orphan
Deep-sea cold seeps are dynamic sources of methane release and unique habitats supporting ocean biodiversity and productivity. Here, we describe newly discovered animal-bacterial symbioses fueled by methane, between two species of annelid (a serpulid Laminatubus and sabellid Bispira) and distinct aerobic methane-oxidizing bacteria belonging to the Methylococcales, localized to the host respiratory crown. Worm tissue δ13C of −44 to −58‰ are consistent with methane-fueled nutrition for both species, and shipboard stable isotope labeling experiments revealed active assimilation of 13C-labeled methane into animal biomass, which occurs via the engulfment of methanotrophic bacteria across the crown epidermal surface. These worms represent a new addition to the few animals known to intimately associate with methane-oxidizing bacteria and may further explain their enigmatic mass occurrence at 150–million year–old fossil seeps. High-resolution seafloor surveys document significant coverage by these symbioses, beyond typical obligate seep fauna. These findings uncover novel consumers of methane in the deep sea and, by expanding the known spatial extent of methane seeps, may have important implications for deep-sea conservation.
Authors: Sajjad A. Akam, Richard B. Coffin, Hussain A. N. Abdulla and Timothy W. Lyons
Methane transport from subsurface reservoirs to shallow marine sediment is characterized by unique biogeochemical interactions significant for ocean chemistry. Sulfate-Methane Transition Zone (SMTZ) is an important diagenetic front in the sediment column that quantitatively consumes the diffusive methane fluxes from deep methanogenic sources toward shallow marine sediments via sulfate-driven anaerobic oxidation of methane (AOM). Recent global compilation from diffusion-controlled marine settings suggests methane from below and sulfate from above fluxing into the SMTZ at an estimated rate of 3.8 and 5.3 Tmol year–1, respectively, and wider estimate for methane flux ranges from 1 to 19 Tmol year–1. AOM converts the methane carbon to dissolved inorganic carbon (DIC) at the SMTZ. Organoclastic sulfate reduction (OSR) and deep-DIC fluxes from methanogenic zones contribute additional DIC to the shallow sediments. Here, we provide a quantification of 8.7 Tmol year–1 DIC entering the methane-charged shallow sediments due to AOM, OSR, and the deep-DIC flux (range 6.4–10.2 Tmol year–1). Of this total DIC pool, an estimated 6.5 Tmol year–1 flows toward the water column (range: 3.2–9.2 Tmol year–1), and 1.7 Tmol year–1 enters the authigenic carbonate phases (range: 0.6–3.6 Tmol year–1). This summary highlights that carbonate authigenesis in settings dominated by diffusive methane fluxes is a significant component of marine carbon burial, comparable to ∼15% of carbonate accumulation on continental shelves and in the abyssal ocean, respectively. Further, the DIC outflux through the SMTZ is comparable to ∼20% of global riverine DIC flux to oceans. This DIC outflux will contribute alkalinity or CO2 in different proportions to the water column, depending on the rates of authigenic carbonate precipitation and sulfide oxidation and will significantly impact ocean chemistry and potentially atmospheric CO2. Settings with substantial carbonate precipitation and sulfide oxidation at present are contributing CO2 and thus to ocean acidification. Our synthesis emphasizes the importance of SMTZ as not only a methane sink but also an important diagenetic front for global DIC cycling. We further underscore the need to incorporate a DIC pump in methane-charged shallow marine sediments to models for coastal and geologic carbon cycling.
Authors: Jiangtao Li, Paraskevi Mara, Florence Schubotz, Jason B. Sylvan, Gaëtan Burgaud, Frieder Klein, David Beaudoin, Shu Ying Wee, Henry J. B. Dick, Sarah Lott, Rebecca Cox, Lara A. E. Meyer, Maxence Quémener, Donna K. Blackman & Virginia P. Edgcomb
The lithified lower oceanic crust is one of Earth’s last biological frontiers as it is difficult to access. It is challenging for microbiota that live in marine subsurface sediments or igneous basement to obtain sufficient carbon resources and energy to support growth1,2,3 or to meet basal power requirements4 during periods of resource scarcity. Here we show how limited and unpredictable sources of carbon and energy dictate survival strategies used by low-biomass microbial communities that live 10–750 m below the seafloor at Atlantis Bank, Indian Ocean, where Earth’s lower crust is exposed at the seafloor. Assays of enzyme activities, lipid biomarkers, marker genes and microscopy indicate heterogeneously distributed and viable biomass with ultralow cell densities (fewer than 2,000 cells per cm3). Expression of genes involved in unexpected heterotrophic processes includes those with a role in the degradation of polyaromatic hydrocarbons, use of polyhydroxyalkanoates as carbon-storage molecules and recycling of amino acids to produce compounds that can participate in redox reactions and energy production. Our study provides insights into how microorganisms in the plutonic crust are able to survive within fractures or porous substrates by coupling sources of energy to organic and inorganic carbon resources that are probably delivered through the circulation of subseafloor fluids or seawater.
See also the NSF press release.
Authors: Rosalind M. Coggon, Jason B. Sylvan, Trevor Williams, Gail L. Christeson, Damon A.H. Teagle, Carlos A. Alvarez Zarikian
The South Atlantic Transect (SAT) is a multidisciplinary scientific ocean drilling project that comprises two International Ocean Discovery Program (IODP) expeditions (390, October–December 2020, and 393, April–June 2021). These expeditions will recover complete sedimentary sections and the upper ~250 m of the underlying oceanic crust along a slow/intermediate spreading rate Mid-Atlantic Ridge crustal flow line at ~31°S. The sediments along this transect were originally spot cored more than 50 y ago during Deep Sea Drilling Project Leg 3 to help verify the theories of seafloor spreading and plate tectonics. Given dramatic advances in drilling technology and analytical capabilities since Leg 3, many high-priority scientific objectives can be addressed by revisiting the transect. The SAT expeditions will target six primary sites on 7, 15, 31, 49, and 61 Ma ocean crust, which will fill critical gaps in our sampling of intact in situ ocean crust with regards to crustal age, spreading rate, and sediment thickness. These sections are required to investigate the history of the low-temperature hydrothermal interactions between the aging ocean crust and the evolving South Atlantic Ocean and quantify past hydrothermal contributions to global geochemical cycles. The transect traverses the previously unexplored sediment- and basalt-hosted deep biosphere beneath the South Atlantic Gyre from which samples are essential to refine global biomass estimates and investigate microbial ecosystems’ responses to variable conditions in a low-energy gyre and aging ocean crust. The drilling operations will include installation of reentry cones and casing to establish legacy boreholes for future basement hydrothermal and microbiological experiments. The transect is also located near World Ocean Circulation Experiment Line A10, providing access to records of carbonate chemistry and deepwater mass properties across the western South Atlantic through key Cenozoic intervals of elevated atmospheric CO2 and rapid climate change. Reconstruction of the history of the deep western boundary current and deepwater formation in the Atlantic basins will yield crucial data to test hypotheses regarding the role of evolving thermohaline circulation patterns in climate change and the effects of tectonic gateways and climate on ocean acidification.
Authors: Jiangtao Li, Paraskevi Mara, Florence Schubotz, Jason B. Sylvan, Gaëtan Burgaud, Frieder Klein, David Beaudoin, Shu Ying Wee, Henry J. B. Dick, Sarah Lott, Rebecca Cox, Lara A. E. Meyer, Maxence Quémener, Donna K. Blackman & Virginia P. Edgcomb
The lithified lower oceanic crust is one of Earth’s last biological frontiers as it is difficult to access. It is challenging for microbiota that live in marine subsurface sediments or igneous basement to obtain sufficient carbon resources and energy to support growth or to meet basal power requirements during periods of resource scarcity. Here we show how limited and unpredictable sources of carbon and energy dictate survival strategies used by low-biomass microbial communities that live 10–750 m below the seafloor at Atlantis Bank, Indian Ocean, where Earth’s lower crust is exposed at the seafloor. Assays of enzyme activities, lipid biomarkers, marker genes and microscopy indicate heterogeneously distributed and viable biomass with ultralow cell densities (fewer than 2,000 cells per cm3). Expression of genes involved in unexpected heterotrophic processes includes those with a role in the degradation of polyaromatic hydrocarbons, use of polyhydroxyalkanoates as carbon-storage molecules and recycling of amino acids to produce compounds that can participate in redox reactions and energy production. Our study provides insights into how microorganisms in the plutonic crust are able to survive within fractures or porous substrates by coupling sources of energy to organic and inorganic carbon resources that are probably delivered through the circulation of subseafloor fluids or seawater.
See also the accompanying Nature news article.
Editors: Andrew McCaig, Peter Kelemen, Gretchen Früh-Green and Damon Teagle
This theme issue brings together international scientists working on all aspects of serpentinisation, a process that may have been important for the origin of life on Earth and perhaps other planets. Serpentine is also a key carrier of water to depth in subduction zones, leading to intermediate depth earthquakes and the formation of island arc volcanoes. This issue is based on a Royal Society discussion meeting held in November 2018.
Authors: T.C. Onstott, B.L. Ehlmann, H. Sapers, M. Coleman, M. Ivarsson, J.J. Marlow, A. Neubeck, P. Niles
Abstract: Here we review published studies on the abundance and diversity of terrestrial rock-hosted life, the environments it inhabits, the evolution of its metabolisms, and its fossil biomarkers to provide guidance in the search for life on Mars. Key findings are (1) much terrestrial deep subsurface metabolic activity relies on abiotic energy-yielding fluxes and in situ abiotic and biotic recycling of metabolic waste products rather than on buried organic products of photosynthesis; (2) subsurface microbial cell concentrations are highest at interfaces with pronounced chemical redox gradients or permeability variations and do not correlate with bulk host rock organic carbon; (3) metabolic pathways for chemolithoautotrophic microorganisms evolved earlier in Earth’s history than those of surface-dwelling phototrophic microorganisms; (4) the emergence of the former occurred at a time when Mars was habitable, whereas the emergence of the latter occurred at a time when the martian surface was not continually habitable; (5) the terrestrial rock record has biomarkers of subsurface life at least back hundreds of millions of years and likely to 3.45 Ga with several examples of excellent preservation in rock types that are quite different from those preserving the photosphere-supported biosphere. These findings suggest that rock-hosted life would have been more likely to emerge and be preserved in a martian context. Consequently, we outline a Mars exploration strategy that targets subsurface life and scales spatially, focusing initially on identifying rocks with evidence for groundwater flow and low-temperature mineralization, then identifying redox and permeability interfaces preserved within rock outcrops, and finally focusing on finding minerals associated with redox reactions and associated traces of carbon and diagnostic chemical and isotopic biosignatures. Using this strategy on Earth yields ancient rock-hosted life, preserved in the fossil record and confirmable via a suite of morphologic, organic, mineralogical, and isotopic fingerprints at micrometer scale. We expect an emphasis on rock-hosted life and this scale-dependent strategy to be crucial in the search for life on Mars.
Authors: Alice Zhou, Yuki Weber, Beverly K. Chiu, Felix J. Elling, Alec B. Cobban, Ann Pearson, William D. Leavitt
Abstract: Microorganisms regulate the composition of their membranes in response to environmental cues. Many Archaea maintain the fluidity and permeability of their membranes by adjusting the number of cyclic moieties within the cores of their glycerol dibiphytanyl glycerol tetraether (GDGT) lipids. Cyclized GDGTs increase membrane packing and stability, which has been shown to help cells survive shifts in temperature and pH. However, the extent of this cyclization also varies with growth phase and electron acceptor or donor limitation. These observations indicate a relationship between energy metabolism and membrane composition. Here we show that the average degree of GDGT cyclization increases with doubling time in continuous cultures of the thermoacidophile Sulfolobus acidocaldarius (DSM 639). This is consistent with the behavior of a mesoneutrophile, Nitrosopumilus maritimus SCM1. Together, these results demonstrate that archaeal GDGT distributions can shift in response to electron donor flux and energy availability, independent of pH or temperature. Paleoenvironmental reconstructions based on GDGTs thus capture the energy available to microbes, which encompasses fluctuations in temperature and pH, as well as electron donor and acceptor availability. The ability of Archaea to adjust membrane composition and packing may be an important strategy that enables survival during episodes of energy stress.
Authors: Masako Tominaga, Beth N. Orcutt, Peter Blum, and the Expedition 385T Scientists
Abstract: International Ocean Discovery Program (IODP) Expedition 385T aimed to take advantage of a transit of the R/V JOIDES Resolution from Antofagasta, Chile, to San Diego, California (USA), to accomplish new sampling and data collection from legacy borehole observatories in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Holes 504B and 896A on the southern flank of the Costa Rica Rift. In addition, the US Science Support Program organized the participation of 3 Outreach Officers to evaluate the performance of the JOIDES Resolution Outreach Officer program as well as 2 educators and 12 undergraduate students for a shipboard “JR Academy.” Our scientific objectives were to collect (1) new Formation MicroScanner logs from Hole 504B for improving lithologic interpretations of crustal architecture at this archetype deep oceanic crust hole and (2) fluid samples from both holes for evaluating the crustal deep biosphere in deep and warm oceanic crust. These operations in Holes 504B and 896A have direct relevance to Challenges 5, 6, 9, 10, 13, and 14 of the IODP 2013–2023 Science Plan. Accomplishing both of these scientific objectives required the removal of old wireline CORK observatories, including associated inflatable packers that were installed in the cased boreholes in 2001. The fluid sampling plan also included testing a new Multi-Temperature Fluid Sampler. Despite successfully removing the CORK wellhead platforms from both holes, we were unable to remove the packers stuck in casing at both locations after 48 h of milling operations in Hole 504B and 2 h of milling operations in Hole 896A, thus precluding accomplishing any of the scientific objectives of the expedition. We provide an assessment of the final state of the holes and recommendations for possible future operations.
The study of life in extreme environments is a highly interdisciplinary subject, which helps further the understanding of the biological and biogeochemical processes taking place in various environments on the Earth generally considered hostile to life. Life in extreme environments tells us about the limits of life, and in turn, about the possibility of life beyond the Earth. PLOS ONE and PLOS Biology are delighted to announce a Call for Papers on the topic of Life in Extreme Environments, bringing together studies from different disciplines such as biosciences, geosciences, planetary sciences, oceanography and related disciplines in order to shed light on this crucial topic, and to present this research to the broad readership of PLOS ONE and PLOS Biology. This interdisciplinary topic helps us better understand the biodiversity of life on Earth, and the biological processes, geochemistry and nutrient cycling taking place in many of the Earth’s most inhospitable environments, and enables us to make inferences about the potential for life beyond the Earth. Microorganisms and other life in extreme environments are fundamental agents of geochemical and nutrient cycling, in many of the most poorly understood environments on the Earth. A particular set of challenges is present when studying extreme environments, such as the problem of detecting small cell numbers and slow metabolisms, as well as contamination and false positives introduced during sampling and analysis. We particularly welcome submissions with a strong interdisciplinary focus, and papers seeking to improve methodology for sampling and characterizing extreme environments. The submission deadline for this Collection has been extended to October 25, 2019.
Authors: Marianne Quéméneur, Gaël Erauso, Eléonore Frouin, Emna Zeghal, Céline Vandecasteele, Bernard Ollivier, Christian Tamburini, Marc Garel, Bénédicte Ménez and Anne Postec
Rock-hosted subseafloor habitats are very challenging for life, and current knowledge about microorganisms inhabiting such lithic environments is still limited. This study explored the cultivable microbial diversity in anaerobic enrichment cultures from cores recovered during the International Ocean Discovery Program (IODP) Expedition 357 from the Atlantis Massif (Mid-Atlantic Ridge, 30°N). 16S rRNA gene survey of enrichment cultures grown at 10–25°C and pH 8.5 showed that Firmicutes and Proteobacteria were generally dominant. However, cultivable microbial diversity significantly differed depending on incubation at atmospheric pressure (0.1 MPa), or hydrostatic pressures (HP) mimicking the in situ pressure conditions (8.2 or 14.0 MPa). An original, strictly anaerobic bacterium designated 70B-AT was isolated from core M0070C-3R1 (1150 meter below sea level; 3.5 m below seafloor) only from cultures performed at 14.0 MPa. This strain named Petrocella atlantisensis is a novel species of a new genus within the newly described family Vallitaleaceae (order Clostridiales, phylum Firmicutes). It is a mesophilic, moderately halotolerant and piezophilic chemoorganotroph, able to grow by fermentation of carbohydrates and proteinaceous compounds. Its 3.5 Mb genome contains numerous genes for ABC transporters of sugars and amino acids, and pathways for fermentation of mono- and di-saccharides and amino acids were identified. Genes encoding multimeric [FeFe] hydrogenases and a Rnf complex form the basis to explain hydrogen and energy production in strain 70B-AT. This study outlines the importance of using hydrostatic pressure in culture experiments for isolation and characterization of autochthonous piezophilic microorganisms from subseafloor rocks.
Featuring an article about the upcoming IODP Expedition 385: Guaymas Basin Tectonics and Biosphere from co-chiefs Andreas Teske and Daniel Lizarralde!
Authors: P. H. Barry, J. M. de Moor, D. Giovannelli, M. Schrenk, D. R. Hummer, T. Lopez, C. A. Pratt, Y. Alpízar Segura, A. Battaglia, P. Beaudry, G. Bini, M. Cascante, G. d’Errico, M. di Carlo, D. Fattorini, K. Fullerton, E. Gazel, G. González, S. A. Halldórsson, K. Iacovino, J. T. Kulongoski, E. Manini, M. Martínez, H. Miller, M. Nakagawa, S. Ono, S. Patwardhan, C. J. Ramírez, F. Regoli, F. Smedile, S. Turner, C. Vetriani, M. Yücel, C. J. Ballentine, T. P. Fischer, D. R. Hilton & K. G. Lloyd
Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth’s surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth’s deep mantle and shallow crustal reservoirs, as well as Earth’s oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent of carbon released from the slab and mantle beneath the Costa Rican forearc is sequestered within the crust by calcite deposition. Around an additional three per cent is incorporated into the biomass through microbial chemolithoautotrophy, whereby microbes assimilate inorganic carbon into biomass. We estimate that between 1.2 × 108 and 1.3 × 1010 moles of carbon dioxide per year are released from the slab beneath the forearc, and thus up to about 19 per cent less carbon is being transferred into Earth’s deep mantle than previously estimated.
The Northern Pacific, Bering Sea and Western Arctic regions contain important records of linked tectonic and paleoceanographic histories. The primary goal of this workshop was to develop new proposals and reinvigorate existing proposals for scientific ocean drilling in the region. By focusing on regional coordination across scientific themes, our breakout groups and working sessions encouraged new collaborations to develop coordinated drilling strategies.
The UNOLS Logistics Working Group would like to announce the an EoS article entitled “Strategies for Conducting 21st Century Oceanographic Research.” Planning for cruises in/out of foreign ports and applying for marine research clearances takes a lot of time and effort. The UNOLS Logistics Working Group, comprised of scientists, operators and funding agency representatives, reviewed vessel policies and sticking points around working in foreign ports and obtaining marine science research (MSR) clearances. The EoS article builds from the committee’s white paper on “Proposing, Planning, and Executing Logistics involved in Oceanographic Field Operations in Foreign Waters and Ports“ and its appendix in an effort to further awareness of the issues, responsibilities and key topics in planning for these complex cruises. If you will be working in/out of a foreign port or applying for an MSR clearance, we encourage you to read the article and pass it along to anyone else who this might impact.
Authors: Martin R. Fisk, Radu Popa, and David Wacey
We propose a model whereby microscopic tunnels form in basalt glass in response to a natural proton flux from seawater into the glass. This flux is generated by the alteration of the glass as protons from water replace cations in the glass. In our proton gradient model, cells are gateways through which protons enter and alter the glass and through which cations leave the glass. In the process, tunnels are formed, and cells derive energy from the proton and ion fluxes. Proton flux from seawater into basalt glass would have occurred on Earth as soon as water accumulated on the surface and would have preceded biological redox catalysis. Tunnels in modern basalts are similar to tunnels in Archean basalts, which may be our earliest physical evidence of life. Proton gradients like those described in this paper certainly exist on other planetary bodies where silicate rocks are exposed to acidic to slightly alkaline water.
Guaymas Basin Tectonics and Biosphere: feedbacks between continental rifting, magmatism, sedimentation, thermal alteration of organic matter, and microbial activity
Authors: Andreas Teske, Daniel Lizarralde, Tobias W. Höfig
The Guaymas Basin in the Gulf of California is a young marginal rift basin characterized by active seafloor spreading and rapid deposition of organic-rich sediments from highly productive overlying waters. The high sedimentation rates in combination with an active spreading system produce distinct oceanic crust where the shallowest magmatic emplacement occurs as igneous intrusion into overlying sediments. The intrusion of magma into organic-rich sediments creates a dynamic environment where tightly linked physical, chemical, and biological processes regulate the cycling of sedimentary carbon and other elements, not only in a narrow hydrothermal zone at the spreading center but also in widely distributed off-axis venting. Heat from magmatic sills thermally alters organic-rich sediments, releasing CO2, CH4, petroleum, and other alteration products. This heat also drives advective flow, which distributes these alteration products in the subsurface and may also release them to the water column. Within the sediment column, the thermal and chemical gradients created by this process represent environments rich in chemical energy that support microbial communities at and below the seafloor. These communities may play a critical role in chemical transformations that influence the stability and transport of carbon in crustal biospheres. Collectively, these processes have profound implications for the exchange of heat and mass between the lithosphere and overlying water column and may determine the long-term fate of carbon accumulation in organic-rich sediments.
The JOIDES Resolution Assessment Report, representing the results of a multi-phase, year-long community review, is now available on the USSSP website. Thanks to everyone who participated in the community survey and the September ‘17 JR Assessment Workshop, both of which provided crucial input to this report!
Authors: Akira Ijiri, Fumio Inagaki, Yusuke Kubo, Rishi R. Adhikari, Shohei Hattori, Tatsuhiko Hoshino, Hiroyuki Imachi, Shinsuke Kawagucci, Yuki Morono, Yoko Ohtomo, Shuhei Ono, Sanae Sakai, Ken Takai, Tomohiro Toki, David T. Wang, Marcos Y. Yoshinaga, Gail L. Arnold, Juichiro Ashi, David H. Case, Tomas Feseker, Kai-Uwe Hinrichs, Yojiro Ikegawa, Minoru Ikehara, Jens Kallmeyer, Hidenori Kumagai, Mark A. Lever, Sumito Morita, Ko-ichi Nakamura, Yuki Nakamura, Manabu Nishizawa, Victoria J. Orphan, Hans Røy, Frauke Schmidt, Atsushi Tani, Wataru Tanikawa, Takeshi Terada, Hitoshi Tomaru, Takeshi Tsuji, Urumu Tsunogai, Yasuhiko T. Yamaguchi, Naohiro Yoshida
Microbial life inhabiting subseafloor sediments plays an important role in Earth’s carbon cycle. However, the impact of geodynamic processes on the distributions and carbon-cycling activities of subseafloor life remains poorly constrained. We explore a submarine mud volcano of the Nankai accretionary complex by drilling down to 200 m below the summit. Stable isotopic compositions of water and carbon compounds, including clumped methane isotopologues, suggest that ~90% of methane is microbially produced at 16° to 30°C and 300 to 900 m below seafloor, corresponding to the basin bottom, where fluids in the accretionary prism are supplied via megasplay faults. Radiotracer experiments showed that relatively small microbial populations in deep mud volcano sediments (102 to 103 cells cm−3) include highly active hydrogenotrophic methanogens and acetogens. Our findings indicate that subduction-associated fluid migration has stimulated microbial activity in the mud reservoir and that mud volcanoes may contribute more substantially to the methane budget than previously estimated.
Authors: Jesse McNichol, Hryhoriy Stryhanyuk, Sean P. Sylva, François Thomas, Niculina Musat, Jeffrey S. Seewald, and Stefan M. Sievert
Below the seafloor at deep-sea hot springs, mixing of geothermal fluids with seawater supports a potentially vast microbial ecosystem. Although the identity of subseafloor microorganisms is largely known, their effect on deep-ocean biogeochemical cycles cannot be predicted without quantitative measurements of their metabolic rates and growth efficiency. Here, we report on incubations of subseafloor fluids under in situ conditions that quantitatively constrain subseafloor primary productivity, biomass standing stock, and turnover time. Single-cell-based activity measurements and 16S rRNA-gene analysis showed that Campylobacteria dominated carbon fixation and that oxygen concentration and temperature drove niche partitioning of closely related phylotypes. Our data reveal a very active subseafloor biosphere that fixes carbon at a rate of up to 321 μg C⋅L−1⋅d−1, turns over rapidly within tens of hours, rivals the productivity of chemosynthetic symbioses above the seafloor, and significantly influences deep-ocean biogeochemical cycling.
Authors: Tiantian Yu, Weichao Wu, Wenyue Liang, Mark Alexander Lever, Kai-Uwe Hinrichs, and Fengping Wang
Members of the archaeal phylum Bathyarchaeota are among the most abundant microorganisms on Earth. Although versatile metabolic capabilities such as acetogenesis, methanogenesis, and fermentation have been suggested for bathyarchaeotal members, no direct confirmation of these metabolic functions has been achieved through growth of Bathyarchaeota in the laboratory. Here we demonstrate, on the basis of gene-copy numbers and probing of archaeal lipids, the growth of Bathyarchaeota subgroup Bathy-8 in enrichments of estuarine sediments with the biopolymer lignin. Other organic substrates (casein, oleic acid, cellulose, and phenol) did not significantly stimulate growth of Bathyarchaeota. Meanwhile, putative bathyarchaeotal tetraether lipids incorporated 13C from 13C-bicarbonate only when added in concert with lignin. Our results are consistent with organoautotrophic growth of a bathyarchaeotal group with lignin as an energy source and bicarbonate as a carbon source and shed light into the cycling of one of Earth’s most abundant biopolymers in anoxic marine sediment.
Axial Seamount is the most magmatically active submarine volcano in the northeast Pacific and has been the focus of inter-disciplinary studies for over two decades. The range of scientific interests includes volcanology, geophysical characterization and monitoring, hydrothermal vent formation and geochemistry, quantification of heat and chemical fluxes, hydrogeology, and the diversity and evolution of microbiological and animal communities. Axial Seamount erupted in January 1998, April 2011, and April 2015, and is likely to erupt again in the coming years. The site, therefore, presents a unique opportunity to study the interaction between volcanic, hydrothermal, and biological responses to magmatic and volcanic events. Primarily for these reasons, Axial Seamount was chosen as one of the key sites on the National Science Foundations’ (NSF) Ocean Observatories Initiative’s (OOI) cabled observatory network, the Cabled Array (CA). The Axial workshop was held to explore how ocean drilling and related studies can complement seafloor-based investigations by gaining access to the subseafloor to expand our understanding of microbiological, geophysical, hydrologic, and geochemical processes, now that the CA is fully operational with data streaming live to shore from a diverse suite of cabled instruments.
We are pleased to announce the release of the JOIDES Resolution Assessment Report, and the accompanying JOIDES Resolution Community Survey Data Report, in support of the National Science Foundation’s request to the National Science Board for the renewal of funding for the JR facility for the next five years. The community overwhelmingly supports the JR and its ability to address high priority objectives of the IODP Science Plan. The Community Survey Data Report documents the responses of 876 of our colleagues, both national and international, and provides significant insights into the IODP community. The Workshop Report reflects the outstanding effort of the 81 attendees of the September 2017 workshop, “Assessment of the JOIDES Resolution in Meeting the Challenges of the IODP Science Plan”. Their tasks included developing expedition results reports in preparation for the workshop, reviewing comments from the Community Survey, and synthesizing the two datasets. The report includes the results of plenary sessions from the workshop that focused on future scientific opportunities that can be addressed in the next five years, as well as discussion surrounding the relationship of the JR to the National Science Foundation’s Sea Change report from 2015, in addition to a list of recommendations and updates for the next five years of JR operations.
Authors: P. Fryer, C.G. Wheat, T. Williams, E. Albers, B. Bekins, B.P.R. Debret, J. Deng, Y. Dong, P. Eickenbusch, E.A. Frery, Y. Ichiyama, K. Johnson, R.M. Johnston, R.T. Kevorkian, W. Kurz, V. Magalhaes, S.S. Mantovanelli, W. Menapace, C.D. Menzies, K. Michibayashi, C.L. Moyer, K.K. Mullane, J.-W. Park, R.E. Price, J.G. Ryan, J.W. Shervais, O.J. Sissmann, S. Suzuki, K. Takai, B. Walter, and R. Zhang
Abstract: Geologic processes at convergent plate margins control geochemical cycling, seismicity, and deep biosphere activity in subduction zones and suprasubduction zone lithosphere. International Ocean Discovery Program Expedition 366 was designed to address the nature of these processes in the shallow to intermediate depth of the Mariana subduction channel. Although no technology is available to permit direct sampling of the subduction channel of an intraoceanic convergent margin at depths up to 19 km, the Mariana forearc region (between the trench and the active volcanic arc) provides a means to access materials from this zone.
Authors: Susan Q. Lang, Gretchen L. Früh-Green, Stefano M. Bernasconi, William J. Brazelton, Matthew O. Schrenk & Julia M. McGonigle
Abstract: Hydrogen produced during water-rock serpentinization reactions can drive the synthesis of organic compounds both biotically and abiotically. We investigated abiotic carbon production and microbial metabolic pathways at the high energy but low diversity serpentinite-hosted Lost City hydrothermal field. Compound-specific 14C data demonstrates that formate is mantle-derived and abiotic in some locations and has an additional, seawater-derived component in others. Lipids produced by the dominant member of the archaeal community, the Lost City Methanosarcinales, largely lack 14C, but metagenomic evidence suggests they cannot use formate for methanogenesis. Instead, sulfate-reducing bacteria may be the primary consumers of formate in Lost City chimneys. Paradoxically, the archaeal phylotype that numerically dominates the chimney microbial communities appears ill suited to live in pure hydrothermal fluids without the co-occurrence of organisms that can liberate CO2. Considering the lack of dissolved inorganic carbon in such systems, the ability to utilize formate may be a key trait for survival in pristine serpentinite-hosted environments.
Whether this is your first or 100th time, planning for a cruise takes a lot of time, good communication and attention to details. Thorough planning is essential to a cruise’s success. To assist cruise participants, the UNOLS Office is pleased to announce the Cruise Planning Page on the UNOLS website. This information covers what you need to know to plan a successful cruise, beginning with the proposal writing phase through post-cruise documentation. The webpage includes a Cruise Planning timeline plus important information
regarding: Vessel-specific cruise planning websites; Working in foreign ports and obtaining Marine Science Research Clearances; Available equipment and services; Conducting isotope work – Radioisotopes, Natural Isotopes and Stable Isotopes. Whether you are a seasoned PI preparing for your next cruise or someone who
is contemplating requesting ship time, this information will help your project get off to the right start. If you have any questions about cruise planning or suggestions for the webpage, please contact the UNOLS office.
Authors: Heuer, V.B., Inagaki, F., Morono, Y., Kubo, Y., Maeda, L., and the Expedition 370 Scientists
Abstract: International Ocean Discovery Program (IODP) Expedition 370 explored the limits of the biosphere in the deep subseafloor where temperature exceeds the known temperature maximum of microbial life (~120°C) at the sediment/basement interface ~1.2 km below the seafloor. Site C0023 is located in the protothrust zone in the Nankai Trough off Cape Muroto at a water depth of 4776 m, in the vicinity of Ocean Drilling Program (ODP) Sites 808 and 1174. In 2000, ODP Leg 190 revealed the presence of microbial cells at Site 1174 to a depth of ~600 meters below seafloor (mbsf), which corresponds to an estimated temperature of ~70°C, and reliably identified a single zone of elevated cell concentrations just above the décollement at around 800 mbsf, where temperature presumably reached 90°C; no cell count data was reported for other sediment layers in the 70°–120°C range because the detection limit of manual cell counting for low-biomass samples was not low enough. With the establishment of Site C0023, we aimed to detect and investigate the presence or absence of life and biological processes at the biotic–abiotic transition utilizing unprecedented analytical sensitivity and precision. Expedition 370 was the first expedition dedicated to subseafloor microbiology that achieved time-critical processing and analyses of deep biosphere samples, conducting simultaneous shipboard and shore-based investigations.
When Lamont-Doherty assumed management of the U.S. Science Support Program (USSSP) in early 2015, one of our main goals was to make the IODP expedition staffing process as transparent as possible. As we approach our fourth year of management, we would like to provide some statistics on U.S. shipboard participation in IODP over the past three years, as well as advice for those aspiring to sail.
Authors: Patricia Fryer, Geoffrey Wheat, Trevor Williams, and the Expedition 366 Scientists
Abstract: Geologic processes at convergent plate margins control geochemical cycling, seismicity, and deep biosphere activity in subduction zones and suprasubduction zone lithosphere. International Ocean Discovery Program (IODP) Expedition 366 was designed to address the nature of these processes in the shallow to intermediate depth of the Mariana subduction channel. Although no technology is available to permit direct sampling of the subduction channel of an intraoceanic convergent margin at depths up to 18 km, the Mariana forearc region (between the trench and the active volcanic arc) provides a means to access this zone.
Authors: Rosalia Trias, Bénédicte Ménez, Paul le Campion, Yvan Zivanovic, Léna Lecourt, Aurélien Lecoeuvre, Philippe Schmitt-Kopplin, Jenny Uhl, Sigurður R. Gislason, Helgi A. Alfreðsson, Kiflom G. Mesfin, Sandra Ó. Snæbjörnsdóttir, Edda S. Aradóttir, Ingvi Gunnarsson, Juerg M. Matter, Martin Stute, Eric H. Oelkers & Emmanuelle Gérard
Abstract: Basalts are recognized as one of the major habitats on Earth, harboring diverse and active microbial populations. Inconsistently, this living component is rarely considered in engineering operations carried out in these environments. This includes carbon capture and storage (CCS) technologies that seek to offset anthropogenic CO2 emissions into the atmosphere by burying this greenhouse gas in the subsurface. Here, we show that deep ecosystems respond quickly to field operations associated with CO2 injections based on a microbiological survey of a basaltic CCS site. Acidic CO2-charged groundwater results in a marked decrease (by ~ 2.5–4) in microbial richness despite observable blooms of lithoautotrophic iron-oxidizing Betaproteobacteria and degraders of aromatic compounds, which hence impact the aquifer redox state and the carbon fate. Host-basalt dissolution releases nutrients and energy sources, which sustain the growth of autotrophic and heterotrophic species whose activities may have consequences on mineral storage.
After recent difficulties working in foreign ports, the funding agencies felt it important for scientists and operators within the U.S. Academic Research Fleet (ARF) to work together to take a closer look at these complex operations. The UNOLS Logistics Working Group, comprised of scientists, operators and funding agency representatives, reviewed current policies and sticking points around working in foreign ports and obtaining marine research clearances (MRC). The summary of their findings and their recommendations can be found in the UNOLS White Paper on Proposing, Planning, and Executing Logistics involved in Oceanographic Field Operations in Foreign Waters and Ports along with its Appendix 1-Detailed Recommendations and Considerations for Working in Foreign Ports and Obtaining Marine Science Research Clearances. These are must-reads for anyone planning to work in a foreign port or apply for an MRC. This includes seasoned PIs, new PIs, future PIs, lab technicians, vessel technicians, schedulers and operators alike. The documents help to outline the issues, responsibilities and key topics to consider when planning these complicated cruises. Please pass this email along. It is important that this information is disseminated throughout the community!
Authors: Roger D. Flood , Roberto A. Violante , Thomas Gorgas , Ernesto Schwarz , Jens Grützner , Gabriele Uenzelmann-Neben , F. Javier Hernández-Molina , Jennifer Biddle, Guillaume St-Onge, and APVCM workshop participants
Abstract. The Argentine margin contains important sedimentological, paleontological and chemical records of regional and local tectonic evolution, sea level, climate evolution and ocean circulation since the opening of the South Atlantic in the Late Jurassic–Early Cretaceous as well as the present-day results of post-depositional chemical and biological alteration. Despite its important location, which underlies the exchange of southern- and northern-sourced water masses, the Argentine margin has not been investigated in detail using scientific drilling techniques, perhaps because the margin has the reputation of being erosional. However, a number of papers published since 2009 have reported new high-resolution and/or multichannel seismic surveys, often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins. There has also been significant progress in studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin. Encouraged by these recent results, our 3.5-day IODP (International Ocean Discovery Program) workshop in Buenos Aires (8–11 September 2015) focused on opportunities for scientific drilling on the Atlantic margin of Argentina, which lies beneath a key portion of the global ocean conveyor belt of thermohaline circulation. Significant opportunities exist to study the tectonic evolution, paleoceanography and stratigraphy, sedimentology, and biosphere and geochemistry of this margin.
Authors: Tiantian Yu, Qianyong Liang, Mingyang Niu, Fengping Wang
The archaeal phylum Bathyarchaeota, which is composed of a large number of diverse lineages, is widespread and abundant in marine sediments. Environmental factors that control the distribution, abundance and evolution of this largely diversified archaeal phylum are currently unclear. In this study, a new pair of specific primers that target the major marine subgroups of bathyarchaeotal 16S rRNA genes was designed and evaluated to investigate the distribution and abundance of Bathyarchaeota in marine sediments. The abundance of Bathyarchaeota along two sediment cores from the deep-sea sediments of South China Sea (SCS, each from the Dongsha and Shenhu area) was determined. A strong correlation was found between the bathyarchaeotal abundance and the content of total organic carbon (TOC), suggesting an important role of Bathyarchaeota in organic matter remineralisation in the sediments of SCS. Furthermore, diversity analysis revealed that subgroups Bathy-2, Bathy-8 and Bathy-10 were dominant bathyarchaeotal members of the deep-sea sediments in the SCS. Bathy-8 was found predominantly within the reducing and deeper sediment layers, while Bathy-10 occurred preferentially in the oxidizing and shallower sediment layers. Our study lays a foundation for the further understanding of the ecological functions and niche differentiation of the important but not well-understood sedimentary archaeal group.
Authors: Martin Krüger and Axel Schippers
Integrated Ocean Drilling Program (IODP) Expedition 347 to the Baltic Sea in 2013 was in line with the IODP Science Plan main research theme “Deep biosphere responses to glacial–interglacial cycles,” addressing questions such as deep biosphere evolution, its biogeochemical processes, and how the postglacial diffusive penetration of conservative seawater ions may alter the chemical composition and microbial physiology in the subseafloor biosphere. Consequently, we tried to enrich indigenous microorganisms at in situ conditions using a broad range of electron acceptors (for fermenters; Fe, Mn, and sulfate reducers; and methanogens), simple and complex carbon substrates (in mixtures or as single compounds), and a wide range of culture conditions (temperature and salinity) to cover varying environmental conditions and metabolic requirements. The most successful were enrichment cultures with a mix of polymeric substrates, which proved to be successful for all samples investigated. Also, iron- and manganese-reducing organisms could be enriched from all sites, whereas nitrate as an electron acceptor did not work well. Methanogenic enrichments were only successful for a few of the samples investigated. In these cases, different monomeric as well as complex substrates were converted to methane, indicating a metabolically versatile indigenous microbial community in the sediments.
Authors: Katrina I. Twing, William J. Brazelton, Michael D. Y. Kubo, Alex J. Hyer, Dawn Cardace, Tori M. Hoehler, Tom M. McCollom and Matthew O. Schrenk
Serpentinization is a widespread geochemical process associated with aqueous alteration of ultramafic rocks that produces abundant reductants (H2 and CH4) for life to exploit, but also potentially challenging conditions, including high pH, limited availability of terminal electron acceptors, and low concentrations of inorganic carbon. As a consequence, past studies of serpentinites have reported low cellular abundances and limited microbial diversity. Establishment of the Coast Range Ophiolite Microbial Observatory (California, U.S.A.) allowed a comparison of microbial communities and physicochemical parameters directly within serpentinization-influenced subsurface aquifers. Samples collected from seven wells were subjected to a range of analyses, including solute and gas chemistry, microbial diversity by 16S rRNA gene sequencing, and metabolic potential by shotgun metagenomics, in an attempt to elucidate what factors drive microbial activities in serpentinite habitats. This study describes the first comprehensive interdisciplinary analysis of microbial communities in hyperalkaline groundwater directly accessed by boreholes into serpentinite rocks. Several environmental factors, including pH, methane, and carbon monoxide, were strongly associated with the predominant subsurface microbial communities. A single operational taxonomic unit (OTU) of Betaproteobacteria and a few OTUs of Clostridia were the almost exclusive inhabitants of fluids exhibiting the most serpentinized character. Metagenomes from these extreme samples contained abundant sequences encoding proteins associated with hydrogen metabolism, carbon monoxide oxidation, carbon fixation, and acetogenesis. Metabolic pathways encoded by Clostridia and Betaproteobacteria, in particular, are likely to play important roles in the ecosystems of serpentinizing groundwater. These data provide a basis for further biogeochemical studies of key processes in serpentinite subsurface environments.
Topic Editors: Anke Marianne Herrman, Doug LaRowe, Alain F. Plante. Energy is continuously transformed in the environment through the metabolic activities of organisms. These transformations of energy, i.e. bioenergetics, underpin most biogeochemical cycles on Earth and allow the delivery of a wide range of life-supporting ecosystem services. The aim of this Research Topic is to gather contributions from scientists working in diverse disciplines who have a common interest in evaluating bioenergetics at various spatial and temporal scales in a variety of different environments. The spatial scales range from the process and organismal level up to ecosystems, the temporal scales range from the near-instantaneous to the millennial, and the scientific disciplines involved include: soil scientists, biogeochemists, organic geochemists, microbial and ecosystem ecologists etc. Articles can be original research, techniques, reviews or synthesis papers. We encourage manuscripts focusing on interdisciplinary interactions addressing both basic and applied research as well as associated theoretical work. The overarching goal of this Research Topic is to demonstrate the environmental breadth of bioenergetics, and foster understanding between different scientific communities who may not always be aware of one another’s work. Abstract submission deadline: June 30, 2017.
Authors: Céline Pisapia, Emmanuelle Gérard, Martine Gérard, Léna Lecourt, Susan Q. Lang, Bernard Pelletier, Claude E. Payri, Christophe Monnin, Linda Guentas, Anne Postec, Marianne Quéméneur, Gaël Erauso and Bénédicte Ménez
Despite their potential importance as analogs of primitive microbial metabolisms, the knowledge of the structure and functioning of the deep ecosystems associated with serpentinizing environments is hampered by the lack of accessibility to relevant systems. These hyperalkaline environments are depleted in dissolved inorganic carbon (DIC), making the carbon sources and assimilation pathways in the associated ecosystems highly enigmatic. The Prony Bay Hydrothermal Field (PHF) is an active serpentinization site where, similar to Lost City (Mid-Atlantic Ridge), high-pH fluids rich in H2 and CH4 are discharged from carbonate chimneys at the seafloor, but in a shallower lagoonal environment. This study aimed to characterize the subsurface microbial ecology of this environment by focusing on the earliest stages of chimney construction, dominated by the discharge of hydrothermal fluids of subseafloor origin. By jointly examining the mineralogy and the microbial diversity of the conduits of juvenile edifices at the micrometric scale, we find a central role of uncultivated bacteria belonging to the Firmicutes in the ecology of the PHF. These bacteria, along with members of the phyla Acetothermia and Omnitrophica, are identified as the first chimneys inhabitants before archaeal Methanosarcinales. They are involved in the construction and early consolidation of the carbonate structures via organomineralization processes. Their predominance in the most juvenile and nascent hydrothermal chimneys, and their affiliation with environmental subsurface microorganisms, indicate that they are likely discharged with hydrothermal fluids from the subseafloor. They may thus be representative of endolithic serpentinization-based ecosystems, in an environment where DIC is limited. In contrast, heterotrophic and fermentative microorganisms may consume organic compounds from the abiotic by-products of serpentinization processes and/or from life in the deeper subsurface. We thus propose that the Firmicutes identified at PHF may have a versatile metabolism with the capability to use diverse organic compounds from biological or abiotic origin. From that perspective, this study sheds new light on the structure of deep microbial communities living at the energetic edge in serpentinites and may provide an alternative model of the earliest metabolisms.
Authors: Janelle J. Sikorski and Brandon R. Briggs
Microbial processes in the deep biosphere affect marine sediments, such as the formation of gas hydrate deposits. Gas hydrate deposits offer a large source of natural gas with the potential to augment energy reserves and affect climate and seafloor stability. Despite the significant interdependence between life and geology in the ocean, coverage of the deep biosphere is generally missing in most introductory oceanography textbooks, so there is a need for instructional materials on this important topic. In response to this need, a course module on the deep biosphere with a focus on gas hydrate deposits was created. The module uses Google Earth (Google, Mountain View, CA) to support inquiry-based activities that demonstrate the interaction of the deep biosphere with geology. The module was tried as both a series of in-class exercises and as an out-of-class assignment in an introductory, undergraduate oceanography course. The students took short, preactivity and postactivity quizzes to determine the effectiveness of the module in improving student knowledge about gas hydrates. The module was effective at increasing student knowledge about the basic environmental and biological controls on the formation of gas hydrates on the seafloor. Students showed a consistently low initial comprehension of the content related to gas hydrates, but most (>80%) of the students increased their quiz scores for all module activities. This module on gas hydrate deposits increases the available teaching resources focused on the deep biosphere for geoscience educators.
Authors: André Friese, Jens Kallmeyer, Jan Axel Kitte, Ivan Montaño Martínez, Satria Bijaksana, Dirk Wagner, the ICDP Lake Chalco Drilling Science Team and the ICDP Towuti Drilling Science Team
Subsurface exploration relies on drilling. Normally drilling requires a drilling fluid that will infiltrate into the drill core. Drilling fluid contains non-indigenous materials and microbes from the surface, so its presence renders a sample unsuitable for microbiological and many other analyses. Because infiltration cannot be avoided, it is of paramount importance to assess the degree of contamination to identify uncontaminated samples for geomicrobiological investigations. To do this, usually a tracer is mixed into the drilling fluid. In past drilling operations a variety of tracers have been used, each has specific strengths and weaknesses. For microspheres the main problem was the high price, which limited their use to spot checks or drilling operations that require only small amounts of drilling fluid. Here, we present a modified microsphere tracer approach that uses an aqueous fluorescent pigment dispersion with a similar concentration of fluorescent particles as previously used microsphere tracers. However, it costs four orders of magnitude less, allowing for a more liberal use even in large operations. Its applicability for deep drilling campaigns was successfully tested during two drilling campaigns of the International Continental Drilling Program (ICDP) at Lake Towuti, Sulawesi, Indonesia, and Lake Chalco, Mexico. Quantification of the tracer requires only a fluorescence microscope or a flow cytometer. The latter allowing for high-resolution data to be obtained directly on-site within minutes and with minimal effort, decreasing sample processing times substantially relative to traditional tracer methods. This approach offers an inexpensive, rapid, but powerful alternative technique for contamination assessment during drilling campaigns.
International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge (MAR) to study the links between 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. The primary goals of this expedition were to (1) examine the role of serpentinization in driving hydrothermal systems, sustaining microbial communities, and sequestering carbon; (2) characterize the tectonomagmatic processes that lead to lithospheric heterogeneities and detachment faulting; and (3) assess how abiotic and biotic processes change with variations in rock type and progressive exposure on the seafloor. To accomplish these objectives, we developed a coring and sampling strategy centered on the use of seabed drills—the first time that such systems have been used in the scientific ocean drilling programs. This technology was chosen in the hope of achieving high recovery of the carbonate cap sequences and intact contact and deformation relationships. The expedition plans also included several engineering developments to assess geochemical parameters during drilling; sample bottom water before, during, and after drilling; supply synthetic tracers during drilling for contamination assessment; acquire in situ electrical resistivity and magnetic susceptibility measurements for assessing fractures, fluid flow, and extent of serpentinization; and seal boreholes to provide opportunities for future experiments.
The Integrated Ocean Drilling Program (IODP) Expedition 337 was the first expedition dedicated to subseafloor microbiology that used riser-drilling technology with the drilling vessel Chikyu. The drilling Site
C0020 is located in a forearc basin formed by the subduction of the Pacific Plate off the Shimokita Peninsula,
Japan, at a water depth of 1180 m. Primary scientific objectives during Expedition 337 were to study the relationship between the deep microbial biosphere and a series of ∼ 2 km deep subseafloor coalbeds and to explore the limits of life in the deepest horizons ever probed by scientific ocean drilling. To address these scientific objectives, we penetrated a 2.466 km deep sedimentary sequence with a series of lignite layers buried around 2 km below the seafloor. The cored sediments, as well as cuttings and logging data, showed a record of dynamically changing depositional environments in the former forearc basin off the Shimokita Peninsula during the late Oligocene and Miocene, ranging from warm-temperate coastal backswamps to a cool water continental shelf. The occurrence of small microbial populations and their methanogenic activity were confirmed down to the bottom of the hole by microbiological and biogeochemical analyses. The factors controlling the size and viability of ultra-deep microbial communities in those warm sedimentary habitats could be the increase in demand of energy and water expended on the enzymatic repair of biomolecules as a function of the burial depth. Expedition 337 provided a test ground for the use of riser-drilling technology to address geobiological and biogeochemical objectives and was therefore a crucial step toward the next phase of deep scientific ocean drilling.