Contamination tracer testing with seabed drills: IODP Expedition 357

IODP Expedition 357 utilized seabed drills for the first time in the history of the ocean drilling program, with the aim of collecting intact sequences of shallow mantle core from the Atlantis Massif to examine serpentinization processes and the deep biosphere. This novel drilling approach required the development of a new remote seafloor system for delivering synthetic tracers during drilling to assess for possible sample contamination. Here, we describe this new tracer delivery system, assess the performance of the system during the expedition, provide an overview of the quality of the core samples collected for deep biosphere investigations based on tracer concentrations, and make recommendations for future applications of the system

Deeply-Sourced Formate Fuels Sulfate Reducers but Not Methanogens at Lost City Hydrothermal Field

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

Metagenomic Identification of Active Methanogens and Methanotrophs in Serpentinite Springs of the Voltri Massif, Italy

The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12). Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

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

In Search of Life Under the Seafloor

ISSN:0096-3941ISSN:2324-925

Multibeam bathymetry processed data (Kongsberg EM 122 working area dataset) of RRS JAMES COOK during cruise IODP Expedition 357, Atlantis Massif

A Kongsberg EM122 onboard RRS James Cook during IODP Expedition 357 (Früh-Green et al., 2018; doi:10.1016/j.lithos.2018.09.012) was used to acquire the bathymetry data. Data were cleaned and processed using MB System and then gridded at ~20 m in x and y in NETCDF grd grid format (.grd) in geographic coordinates (latitude/longitude)

Searching for life under the seafloor

ISSN:0096-3941ISSN:2324-925

Content and carbon and oxygen isotope composition of total carbon, total non-carbonate carbon, and total inorganic carbon of mafic and ultramafic rocks from the Wadi Tayin Massif, Samail Ophiolite, Oman Drilling Project Phase II

The carbon geochemistry of serpentinized peridotites, and mafic rocks recovered during ICDP Expedition 5057, Oman Drilling Project Phase II (November 2017 to February 2018) on the Wadi Tayin Massif, Samail Ophiolite, was examined to characterize carbon sources, speciation, and the fate of organic and inorganic carbon during natural large-scale hydration and carbonization. The measurements were performed at the ETH Zurich, Geological Institute from 2017 to 2020 using a FlashEA 1112 Elemental Analyzer (EA) interfaced via a Conflo IV to a Delta V Plus Isotope Ratio Mass Spectrometer for total carbon (TC) and total non-carbonate carbon (NCC) content and isotope composition, and a GasBench II connected to a Delta V Mass Spectrometer for the total inorganic carbon (TIC) isotope composition. Results are reported as replicates. Analyzed samples are aliquots of samples used for microbiological studies and were collected under sterile conditions (denoted as MBio samples)

Individual carbon and oxygen isotopes measurements from heterogeneous basement samples from the Atlantis Massif, IODP Expedition 357

The carbon geochemistry of serpentinized peridotites, gabbroic rocks, and sediments recovered during IODP Expedition 357 (October to December 2015) on the Atlantis Massif, Mid-Atlantic Ridge was examined to characterize carbon sources and the fate of dissolved organic (DOC) and inorganic carbon (DIC) in seawater during long-lived hydrothermal circulation and serpentinization. The measurements were performed at the ETH Zurich, Geological Institute from 2017 to 2020 using a GasBench II connected to a Delta V Mass Spectrometer

Clumped and oxygen isotope data of calcite veins from the Atlantis Massif, IODP Expedition 357

The clumped and oxygen isotopes of calcite from serpentinized peridotites recovered during IODP Expedition 357 (October to December 2015) on the Atlantis Massif, Mid-Atlantic Ridge was examined to characterize carbon sources and the fate of dissolved organic (DOC) and inorganic carbon (DIC) in seawater during long-lived hydrothermal circulation and serpentinization. The measurements were performed at the ETH Zurich from 2017 to 2020 using a Kiel IV carbonate device interfaced with a ThermoFisher Scientific MAT253 isotope ratio mass spectrometer