Active Hydrothermal Vents Research Articles

A new species of the thorid shrimp genus Lebbeus White, 1847 (Decapoda: Caridea) from the Amami Rift hydrothermal vent field in the Ryukyu region, Japan

A new species of the thorid shrimp genus Lebbeus White, 1847, is described and illustrated on the basis of two specimens collected from the recently discovered Amami Rift hot vent field in the Ryukyu region in southwestern Japan, at a depth of 628 m. Lebbeus parvirostris sp. nov. is morphologically similar to L. microceros (Krøyer, 1841), L. mundus Jensen, 2006, L. saldanhae (Barnard, 1947), L. schrencki (Bražnikov, 1907), L. spongiaris Komai, 2001, and L. tosaensis Hanamura & Abe, 2003, but differs from all of them in the lack of a pterygostomial tooth on the carapace in the female. Other diagnostic characters useful in differentiating the new species from the aforementioned close relatives are also discussed. Genetic analyses using sequences of two mitochondrial markers, including cytochrome c oxidase subunit I (COI) and 16S rRNA, are also presented to provide preliminary support for the status of the new species. Lebbeus parvirostris sp. nov. is the second representative of Lebbeus known from active hydrothermal vents in the Ryukyu region.

Electrochemical survey of electroactive microbial populations in deep-sea hydrothermal fields

Electric discharge in deep-sea hydrothermal fields leads us to expect the existence of electroactive microbial ecosystems in the environments. Electrochemical properties such as electric field distribution on the seafloor and electrical conductivity of the rock can be useful indicators of searching electroactive microbial community in natural environments. We performed electric field measurements in deep-sea hydrothermal fields and collected rock samples by a remotely operative vehicle (ROV) operation. Several spots on the seafloor with strong electric fields were detected, which included both active hydrothermal vent areas and inactive sulfide deposits far from the vents. The electrical conductivity of the rock samples was correlated with the copper and iron sulfide content. Microbial community compositions of the rock samples were characterized by small subunit (SSU) rRNA gene amplicon sequencing analysis. The abundance of several microbial components, which are highly related to electroactive microorganisms such as Geobacteraceae and Thiomicrorhabdus, was affected by the electrical properties of rock samples. The results suggested that electrochemical properties on the seafloor would be related to the abundance of possible electroactive microbial populations, and that the electrochemical survey may be a powerful tool for exploring electroactive ecosystems.

High-resolution decadal-scale eruption age dating of young oceanic basalts at an active hydrothermal vent site

High-resolution decadal-scale eruption age dating of young oceanic basalts at an active hydrothermal vent site

Exploration of hydrothermal venting sites using deep-towed multibeam echosounder data

The Federal Institute for Geosciences and Natural Resources (BGR) obtained a contract for the exploration of polymetallic sulphides from the International Seabed Authority (ISA) in an area of 10,000 km2 located in the southwestern Indian Ocean. Since obtaining this contract of exploration in 2015, BGR has conducted annual research cruises to this area and continuously improves the exploration methods for seafloor sulphides deposits. One of the main instruments is HOMESIDE, a deep-towed multibeam echo sounder (MBES) sled. Its water column data allows to visualize and therefore locate discharge sites of hydrothermal fluid – active hydrothermal venting sites (or commonly also referred to as “black smokers”). Additionally, its bathymetric data is used for geological mapping and therefore greater analysis of the seafloor geomorphology. HOMESIDE is typically towed at an altitude of about 100 m above the seabed in a water depth of approximately 3,000 m, allowing a resolution of the derived digital terrain model (DTM) of 2 m. Due to malfunction of individual positioning sensors or operational errors, the navigation data might need to be further corrected in post-processing. Navigation offsets between adjacent lines are mostly apparent in overlapping swath data. The tool mbnavadjust of the open-source software MB-System showed to be a valuable tool to improve the data quality subsequently in areas with data overlap and systematic navigation offsets. Data mismatches of more than 10 m are processed with this tool and can, therefore, be reduced significantly. In this paper, firstly, the role of deep-towed MBES as exploration tool for hydrothermal sites is presented. Secondly, the importance of post-processing MBES navigation based on the swath data especially for this project is highlighted. The workflow as well as the results are presented and show significant improvement.

Inactive hydrothermal vent microbial communities are important contributors to deep ocean primary productivity.

Active hydrothermal vents are oases for productivity in the deep ocean, but the flow of dissolved substrates that fuel such abundant life ultimately ceases, leaving behind inactive mineral deposits. The rates of microbial activity on these deposits are largely unconstrained. Here we show primary production occurs on inactive hydrothermal deposits and quantify its contribution to new organic carbon production in the deep ocean. Measured incorporation of 14C-bicarbonate shows that microbial communities on inactive deposits fix inorganic carbon at rates comparable to those on actively venting deposits. Single-cell uptake experiments and nanoscale secondary ion mass spectrometry showed chemoautotrophs comprise a large fraction (>30%) of the active microbial cells. Metagenomic and lipidomic surveys of inactive deposits further revealed that the microbial communities are dominated by Alphaproteobacteria and Gammaproteobacteria using the Calvin-Benson-Bassham pathway for carbon fixation. These findings establish inactive vent deposits as important sites for microbial activity and organic carbon production on the seafloor.

Xyloplax princealberti (Asteroidea, Echinodermata): A New Species That Is Not Always Associated with Wood Falls

Xyloplax is a genus of three species of sea stars previously found only on sunken wood in the deep ocean. Their circular and petaloid bodies, which lend them their common name “sea daisy”, and their presumed exclusive diet of wood make them an unusual and rare element of deep-sea ecosystems. We describe here the fourth species of Xyloplax from the eastern Pacific Ocean, Xyloplax princealberti n. sp., which ranges from offshore Canada to the Gulf of California (Mexico) and Costa Rica. Though sampled geographically close to another described species of Xyloplax from the northeastern Pacific, X. janetae, this new species is unique morphologically and according to available DNA data. The short abactinal spines are the most obvious feature that distinguishes X. princealberti n. sp. from other Xyloplax. The minimum distance for mitochondrial cytochrome c oxidase subunit I from Xyloplax princealberti n. sp. to the only other available Xyloplax, X. janetae, was 13.5%. We also describe Ridgeia vestimentiferan tubeworm bushes from active hydrothermal vents as a new Xyloplax habitat, the first record of a non-wood substrate, and a new reproductive strategy, simultaneous hermaphroditism, for this genus. We generated the first mitochondrial genome for a member of Xyloplax and analyzed it with other available asteroid data using nucleotide-coding or amino acid (for protein-coding genes) plus nucleotide coding (for rRNA genes). The nucleotide-coding results place Xylopax as part of the clade Velatida, consistent with a previous phylogenomic analysis that included Xyloplax princealberti n. sp. (as Xyloplax sp.), though the placement of Velatida within Asteroidea differed. The amino acid plus nucleotide coding recovered Velatida to be a grade with X. princealberti n. sp. as sister group to all other Asteroidea.

Strategies of chemolithoautotrophs adapting to high temperature and extremely acidic conditions in a shallow hydrothermal ecosystem

BackgroundActive hydrothermal vents create extreme conditions characterized by high temperatures, low pH levels, and elevated concentrations of heavy metals and other trace elements. These conditions support unique ecosystems where chemolithoautotrophs serve as primary producers. The steep temperature and pH gradients from the vent mouth to its periphery provide a wide range of microhabitats for these specialized microorganisms. However, their metabolic functions, adaptations in response to these gradients, and coping mechanisms under extreme conditions remain areas of limited knowledge. In this study, we conducted temperature gradient incubations of hydrothermal fluids from moderate (pH = 5.6) and extremely (pH = 2.2) acidic vents. Combining the DNA-stable isotope probing technique and subsequent metagenomics, we identified active chemolithoautotrophs under different temperature and pH conditions and analyzed their specific metabolic mechanisms.ResultsWe found that the carbon fixation activities of Nautiliales in vent fluids were significantly increased from 45 to 65 °C under moderately acidic condition, while their heat tolerance was reduced under extremely acidic conditions. In contrast, Campylobacterales actively fixed carbon under both moderately and extremely acidic conditions under 30 − 45 °C. Compared to Campylobacterales, Nautiliales were found to lack the Sox sulfur oxidation system and instead use NAD(H)-linked glutamate dehydrogenase to boost the reverse tricarboxylic acid (rTCA) cycle. Additionally, they exhibit a high genetic potential for high activity of cytochrome bd ubiquinol oxidase in oxygen respiration and hydrogen oxidation at high temperatures. In terms of high-temperature adaption, the rgy gene plays a critical role in Nautiliales by maintaining DNA stability at high temperature. Genes encoding proteins involved in proton export, including the membrane arm subunits of proton-pumping NADH: ubiquinone oxidoreductase, K+ accumulation, selective transport of charged molecules, permease regulation, and formation of the permeability barrier of bacterial outer membranes, play essential roles in enabling Campylobacterales to adapt to extremely acidic conditions.ConclusionsOur study provides in-depth insights into how high temperature and low pH impact the metabolic processes of energy and main elements in chemolithoautotrophs living in hydrothermal ecosystems, as well as the mechanisms they use to adapt to the extreme hydrothermal conditions.4ap83QbxwyKb6GHBwDJLyuVideo

Transient sounds of hydrothermal vents

Transient acoustic signals were recently detected at the Main Endeavour Hydrothermal Vent Field which are believed to be generated by both geological and biological sources, including vent chimney collapse, impulsive geological signals, fish grunts, and snapping. These signals provide an opportunity for long-term passive acoustic monitoring of hydrothermal vent activity and ecology. This method offers advantages of longevity and robustness compared with other monitoring techniques, as the sensor can remain a safe distance away from the high-temperature, caustic vent fluid. Utilizing recordings from a bottom-mounted hydrophone on Ocean Networks Canada’s NEPTUNE observatory, a detector was implemented to identify and classify these signals in more than one year of acoustic data after 2016. While only a single hydrophone is available at this site, an array of three seismic accelerometers also on the NEPTUNE observatory was used to localize transient events when sufficient signal-to-noise ratio was available to provide confidence in the location estimate. Correlation of the transient sounds with seismic activity at the vent field was also evaluated, suggesting that passive acoustic monitoring can augment seismic records to provide additional information regarding geological activity at hydrothermal vent sites.

Identifying Probable Submarine Hydrothermal Spots in North Santorini Caldera Using the Generalized Moments Method

The presence of active hydrothermal vent fields near residential areas and their possible link to volcanic activity poses a potential hazard to the environment, society, and the economy. By capitalizing on Autonomous Underwater Vehicle sampling methodologies and applying the Generalized Moments Method model for geological and physical processes in these environments, we shed light on the underlying dynamics shaping the physicochemical characteristics of the vents. In this study, we focus on the Northern Caldera of Santorini and, more specifically, on the recorded CTD data (Conductivity, Temperature, Depth). The data sets were collected in 2017 in Santorini using an Autonomous Underwater Vehicle during the GEOMAR POS510 mission. Our research shows that the active vent field within the caldera probably follows a multifractal behavior and exhibits a weak memory effect. Depth Profiles and Time Series show similar behavior among conductivity and temperature. The variance and moments of both parameters underline the existence of two different mechanisms governing the behavior of the vent field. Finally, the structure function shows that changes in the time series are described by a Cauchy–Lorentz distribution.

The role of hydrodynamics for the spatial distribution of high-temperature hydrothermal vent-endemic fauna in the deep ocean environment

Active hydrothermal vents provide the surrounding submarine environment with substantial amounts of matter and energy, thus serving as important habitats for diverse megabenthic communities in the deep ocean and constituting a unique, highly productive chemosynthetic ecosystem on Earth. Vent-endemic biological communities gather near the venting site and are usually not found beyond a distance of the order of 100 m from the vent. This is surprising because one would actually expect matter ejected from high-temperature vents, which generate highly turbulent buoyancy plumes, to be suspended and carried far away by the plume flows and deep-sea currents. Here, we study this problem from a fluid dynamics perspective by simulating the vent hydrodynamics using a numerical model that couples the plume flow with induced matter and energy transport. We find that both low- and high-temperature vents deposit most vent matter relatively close to the plume. In particular, the tendency of turbulent buoyancy plumes to carry matter far away is strongly counteracted by generated entrainment flows back into the plume stem. The deposition ranges of organic and inorganic hydrothermal particles obtained from the simulations for various natural high-temperature vents are consistent with the observed maximum spatial extent of biological communities, evidencing that plume hydrodynamics exercises strong control over the spatial distribution of vent-endemic fauna. While other factors affecting the spatial distribution of vent-endemic fauna, such as geology and geochemistry, are site-specific, the main physical features of plume hydrodynamics unraveled in this study are largely site-unspecific and therefore universal across vent sites on Earth.

Taxonomic diversity of microbial communities in sub-seafloor hydrothermal sediments of the active Santorini-Kolumbo volcanic field.

Active hydrothermal vents of volcanic origin provide a remarkable manifestation of life on Earth under extreme conditions, which may have consequences for our understanding of habitability on other terrestrial bodies as well. Here, we performed for the first time Illumina sequencing of bacterial and archaeal communities on sub-seafloor samples collected from the Santorini-Kolumbo volcanic field. A total of 19 (3-m long) gravity corers were collected and processed for microbial community analysis. From a total of 6,46,671 produced V4 sequences for all samples, a total of 10,496 different Operational Taxonomic Units (OTUs) were identified that were assigned to 40 bacterial and 9 archaeal phyla and 14 candidate divisions. On average, the most abundant phyla in all samples were Chloroflexi (Chloroflexota) (24.62%), followed by Proteobacteria (Pseudomonadota) (11.29%), Firmicutes (Bacillota) (10.73%), Crenarchaeota (Thermoproteota) (8.55%), and Acidobacteria (Acidobacteriota) (8.07%). At the genus level, a total of 286 known genera and candidate genera were mostly dominated by members of Bacillus, Thermoflexus, Desulfatiglans, Pseudoalteromonas, and Pseudomonas. In most of the stations, the Chao1 values at the deeper layers were comparable to the surface sediment samples denoting the high diversity in the subsurface of these ecosystems. Heatmap analysis based on the 100 most abundant OTUs, grouped the sampling stations according to their geographical location, placing together the two hottest stations (up to 99°C). This result indicates that this specific area within the active Kolumbo crater create a distinct niche, where microorganisms with adaptation strategies to withstand heat stresses can thrive, such as the endospore-forming Firmicutes.

REE-bearing minerals in sediment-hosted stratiform pyrite mineralization zones of the Wiśniówka area (Holy Cross Mts., Poland)

There are two arsenical pyrite (As-FeS 2 ) mineralization zones cropping out in the Podwiśniówka and Wiśniówka Duża quarries where quartzites and quartzitic sandstones have been extracted for over a century. A large amount of pyrite in the Wiśniówka siliciclastics is unusual in the hard rock mining throughout the world. The pyritiferous beds contain a variety of REE-bearing minerals, including a crandallite series of aluminum-phosphate-sulfate (APS) minerals, e.g., predominant goyazite SrHAl 3 [(PO 4 ) 2 (OH) 6 ] with subordinate gorceixite BaHAl 3 [(PO 4 ) 2 (OH) 6 ] and very occasional crandallite CaHAl 3 [(PO 4 ) 2 (OH) 6 ]. By contrast, the other REE-phosphate minerals, e.g., xenotime YPO 4 , bur particularly monazite CePO 4 occur in a lesser amount. Goyazite prevails somewhat in the Podwiśniówka beds whereas xenotime in the Wiśniówka Duża beds. Of the other REE-bearing minerals, bastnäsite REECO 3 (F,OH), florencite (REE)Al 3 (PO 4 ) 2 (OH) 6 and synchysite CaCe[CO 3 ] 2 F occur in trace amounts. Interestingly, the quite common phosphate minerals, i.e., wavellite (Al 3 [(OH,F) 3 |(PO 4 ) 2 ]×5H 2 O and variscite Al[PO 4 ]×2H 2 O) are depleted in REEs with only Ce attaining 0.09 wt.% as documented by an electron-probe microanalysis. In contrast to quartzites/quartzitic sandstones, carbonaceous clayey-silty shales and bentonites/tuffites are distinctly enriched in REE-bearing minerals. This diversity is also mirrored in the mean total REE concentrations varying from 204 to 314 mg/kg, in clayey-silty shales and bentonites, attaining 457 mg/kg in some Podwiśniówka shale beds. Results of this and the previous petrographic, mineralogical and geochemical studies have indicated that REE-bearing minerals formed generally along with As-rich pyrite, nacrite/dickite and probably TiO 2 polymorphs as a result of multiphase hydrothermal vent activity that took place in the Wiśniówka Late Cambrian sedimentary basin. This evidence is also backed up by the values of LREE NASC /HREE NASC (1.44–1.75) and Eu/Eu NASC (1.24–1.30) coefficients in the clayey-silty shales. This positive Eu anomaly (³1.20) points to the formation of REE-bearing minerals in a reducing environment.

Near-Bottom Magnetic Anomaly Features and Detachment Fault Morphology in Tianxiu Vent Field, Carlsberg Ridge, Northwest Indian Ocean

As a product of hydrothermal mineralization at spreading centers, seafloor massive sulfides (SMS) have become a research hotspot in the field of prospecting and exploring deep-sea mineral resources owing to their enrichment of various strategic metals. Since hydrothermal circulation changes the magnetic properties of host rocks and can generate magnetic anomalies, near-bottom magnetic surveying is an effective method to determine magnetic anomaly features of the seafloor. This technology has been applied to the detection of SMS deposits, in addition to its use in understanding hydrothermal fluid flow conduits and associated hydrothermal alterations. The Tianxiu Vent Field (TVF) is a detachment-fault-controlled, ultramafic-associated hydrothermal system located on the Carlsberg Ridge, Northwest Indian Ocean. During China’s DY57th cruise in 2019, near-bottom magnetic data were collected by an autonomous underwater vehicle. In this paper, we use bathymetric and magnetic data, as well as rock sampling information, to analyze and discuss the magnetic anomaly features of the TVF region. Then, we apply 2.5D magnetic anomaly profile forward modeling to determine the shallow magnetic structure and the pattern of detachment faults in the subsurface. Our results show that TVF is characterized by a significant positive magnetic anomaly, where stronger magnetization exists in the area with active hydrothermal vent clusters. The detachment fault has a dip of less than 30° at shallow depths, which steepens to a dip of ~70° at depths of around 300 m.

Ambient Noise Tomography of the Lipari Volcanic Island (Southern Italy) From a Dense Nodal Array

AbstractWe applied ambient noise tomography to continuous data recorded by a dense seismic array deployed on the volcanic island of Lipari in the southern Tyrrhenian Sea. Since most of Lipari's seismicity occurs offshore and is not evenly distributed, this technique allowed us to obtain the first high‐resolution images beneath the island down to ∼2.5 km depth. Results show a complex seismic structure related to the various ages and compositions of the volcanic products characteristic of the different regions of the island. High shear wave velocities are found in western Lipari, where active hydrothermal vents and N‐S faults are mapped. Low wave speeds are revealed beneath southern and northeastern Lipari, where more recent volcanic activity developed along N‐S dike‐like structures that are aligned with rhyolitic vents. We suggest these dikes likely represent the probable pathways of future volcanic eruptions.

Active hydrothermal vent ecosystems in the Indian Ocean are in need of protection

Deep-sea hydrothermal vent fields are among the most pristine and remarkable ecosystems on Earth. They are fueled by microbial chemosynthesis, harbor unique life and can be sources of precipitated mineral deposits. As the global demand for mineral resources rises, vent fields have been investigated for polymetallic sulfides (PMS) and biological resources. The International Seabed Authority (ISA) has issued 7 contracts for PMS exploration, including 4 licenses for vent fields in the Indian Ocean. Here, we provide a summary of the available ecological knowledge of Indian vent communities and we assess their vulnerability, sensitivity, ecological and biological significance. We combine and apply scientific criteria for Vulnerable Marine Ecosystems (VMEs) by FAO, Particular Sensitive Sea Areas (PSSAs) by IMO, and Ecologically or Biologically Significant Areas (EBSAs) by CBD. Our scientific assessment shows that all active vent fields in the Indian Ocean appear to meet all scientific criteria for protection, and both the high degree of uniqueness and fragility of these ecosystems stand out.

Biogeochemical cycling of dissolved manganese in the Arabian Sea

The study of marine biogeochemical cycling of Mn, a bio-essential trace metal, is crucial to decipher its relative role in controlling the production and diversity of marine phytoplankton. Furthermore, Mn oxides and oxyhydroxides act as sinks for other trace elements in the water column, and Mn redox cycling may exert a major control on the vertical distribution of these elements. Dissolved Mn (dMn) concentrations are measured along two GEOTRACES-India (GI) transects, GI05 and GI10, for a basin-wide investigation of biogeochemical controls on the dMn distribution in the Arabian Sea (AS). Surface dMn distribution shows a strong spatial gradient, with relatively dMn-rich levels in the eastern AS (3.4–5.7 nmol kg−1) compared to the central and western AS (1.2–2.3 nmol kg−1). This correlates with the higher model estimates of soluble Mn input from the atmospheric dust deposition in the eastern AS (∼1.5–2.0 times of input in the western and central AS), and probable additional Mn input from riverine discharge and shallow shelf region of the eastern AS. In the south-eastern AS, a correlated increase in surface dMn with a decrease in salinity indicates the Mn input by the advection of dMn-rich, low-salinity Bay of Bengal (BoB) surface waters to the AS under the influence of the Northeast Monsoon Current. Our mass balance estimates for dMn in the euphotic waters (upper 100 m) suggest important contributions from atmospheric Mn deposition (14–99% of the total estimated input flux), and dMn input/dilution (13–74% of the total estimated input or removal flux) due to lateral/vertical advective-eddy diffusive mixing. Mn-oxidation and passive scavenging are determined to be the dominant processes for the dMn removal (61–99%) from the euphotic zone (upper 100 m), while export via Mn bio-assimilation is comparatively negligible.In the AS denitrification zone, the observed dMn maxima in the upper thermocline depths (∼200–400 m) result from the in situ reductive dissolution of Mn oxides and oxyhydroxides, and lateral advective-eddy diffusive Mn flux from the reducing sediments of the western Indian margin. Outside the denitrification zone, in the northern and western AS, a shift of dMn maxima to the lower thermocline waters (∼500 m) indicates the change in the source region and dMn input from the reducing margins of the north (Pakistan Margin) and north-western AS (Oman Margin), intersecting the core of the oxygen minima at the depth range of 400–600 m.Deep water (>1500 m) dMn concentrations are low (<0.3 nmol kg−1) in most of the AS regions. Anomalous dMn enrichment in the deep waters is observed in the southern and western AS, presumably indicating the influence of hydrothermal plumes emanating from the active hydrothermal vents over the Carlsberg Ridge and spreading ridges in the Gulf of Aden. A correlated and localized increase in dMn and dAl levels close to the Murray Ridge hints at dMn input from the sediment resuspension over the ridge and subsequent Mn dissolution in low-oxygen waters (DO < 20 µM) and/or diffusive flux from the Mn-rich pore waters.

Arsenic and Mercury Distribution in an Aquatic Food Chain: Importance of Femtoplankton and Picoplankton Filtration Fractions.

Arsenic (As) and mercury (Hg) were examined in the Yellowstone Lake food chain, focusing on two lake locations separated by approximately 20 km and differing in lake floor hydrothermal vent activity. Sampling spanned from femtoplankton to the main fish species, Yellowstone cutthroat trout and the apex predator lake trout. Mercury bioaccumulated in muscle and liver of both trout species, biomagnifying with age, whereas As decreased in older fish, which indicates differential exposure routes for these metal(loid)s. Mercury and As concentrations were higher in all food chain filter fractions (0.1-, 0.8-, and 3.0-μm filters) at the vent-associated Inflated Plain site, illustrating the impact of localized hydrothermal inputs. Femtoplankton and picoplankton size biomass (0.1- and 0.8-μm filters) accounted for 30%-70% of total Hg or As at both locations. By contrast, only approximately 4% of As and <1% of Hg were found in the 0.1-μm filtrate, indicating that comparatively little As or Hg actually exists as an ionic form or intercalated with humic compounds, a frequent assumption in freshwaters and marine waters. Ribosomal RNA (18S) gene sequencing of DNA derived from the 0.1-, 0.8-, and 3.0-μm filters showed significant eukaryote biomass in these fractions, providing a novel view of the femtoplankton and picoplankton size biomass, which assists in explaining why these fractions may contain such significant Hg and As. These results infer that femtoplankton and picoplankton metal(loid) loads represent aquatic food chain entry points that need to be accounted for and that are important for better understanding Hg and As biochemistry in aquatic systems. Environ Toxicol Chem 2023;42:225-241. © 2022 SETAC.

Emplacement and impacts of lava flows and intrusions on the sediment-buried Escanaba Segment of the Gorda mid-ocean ridge

The Escanaba Segment, the southernmost of the Gorda mid-ocean ridge segments, contains thick sandy to silty turbidite deposits that are Pleistocene to Recent in age. Dozens of deep laccoliths and shallower sills intrude into these sediments. The intrusions uplifted hills of the unconsolidated turbidites and some fed surface lava flows supplied along steeply dipping reverse faults that surround some of the tallest uplifted hills. Multibeam bathymetric mapping at 1-m resolution and chirp subbottom profile (SBP) lines at ~150 m spacing show that the uplifted sediment hills have complex patterns of surface deformation and experienced debris avalanche landslides on over-steepened slopes formed by uplift along reverse faults. The uplifted hills are spatially associated with 262 hydrothermal chimneys that are several-m-tall and abundant at two main areas named NESCA and SESCA (for northern and southern Escanaba). Chimneys are more abundant and widespread than previously mapped. The uplifted hills are also spatially associated with over 600 previously unrecognized pockmarks that range from a few to over 100 m in diameter and are up to 24 m deep. The hydrothermal deposits and pockmarks are associated with oily sediment, oily sulfide deposits, and tar mounds on the seafloor. The intrusions provide the heat to mature hydrocarbons from organic carbon in the sediment and to drive hydrothermal circulation that deposits sulfides and sulfates on the seafloor, mostly surrounding the tallest hills overlying thick laccoliths. The frequency sweep (chirp) subbottom profiles show that most sills and all the laccoliths are deeper than the ~60 m penetration of the system. However, the thicknesses and depths of numerous shallow sills are mapped from the bathymetry and SBP data. The deepest intrusions are all domed or punched laccoliths, those of intermediate depth are thick inflated sills, and the shallowest are the thinnest sills, as determined from the height of the uplifted hills. For most intrusions, depth to the top of the intrusion is roughly 3 times the thickness of the intrusion. The dome laccolith under Central Hill, in the NESCA vent field, is the only laccolith with well-constrained thickness (from the height of the uplifted Central Hill) and depth (from ODP drill 1038H through the hill that bottomed in the upper part of the laccolith. Sediment thicknesses on top of lava flows that pre- and postdate emplacement of the laccolith that uplifted Central Hill, coupled with an average sediment accumulation rate of 17.8 cm/kyr over the past almost 8800 years indicated that active hydrothermal venting on Central Hill began before ~225 years ago (the inferred age of the NESCA Young lava flow) but after ~1685 years ago (the average inferred age of NESCA #1 lava flow).

Metagenomic Features Characterized with Microbial Iron Oxidoreduction and Mineral Interaction in Southwest Indian Ridge.

The Southwest Indian Ridge (SWIR) is one of the typical representatives of deep-sea ultraslow-spreading ridges, and has increasingly become a hot spot of studying subsurface geological activities and deep-sea mining management. However, the understanding of microbial activities is still limited on active hydrothermal vent chimneys in SWIR. In this study, samples from an active black smoker and a diffuse vent located in the Longqi hydrothermal region were collected for deep metagenomic sequencing, which yielded approximately 290 GB clean data and 295 mid-to-high-quality metagenome-assembled genomes (MAGs). Sulfur oxidation conducted by a variety of Gammaproteobacteria, Alphaproteobacteria, and Campylobacterota was presumed to be the major energy source for chemosynthesis in Longqi hydrothermal vents. Diverse iron-related microorganisms were recovered, including iron-oxidizing Zetaproteobacteria, iron-reducing Deferrisoma, and magnetotactic bacterium. Twenty-two bacterial MAGs from 12 uncultured phyla harbored iron oxidase Cyc2 homologs and enzymes for organic carbon degradation, indicated novel chemolithoheterotrophic iron-oxidizing bacteria that affected iron biogeochemistry in hydrothermal vents. Meanwhile, potential interactions between microbial communities and chimney minerals were emphasized as enriched metabolic potential of siderophore transportation, and extracellular electron transfer functioned by multi-heme proteins was discovered. Composition of chimney minerals probably affected microbial iron metabolic potential, as pyrrhotite might provide more available iron for microbial communities. Collectively, this study provides novel insights into microbial activities and potential mineral-microorganism interactions in hydrothermal vents. IMPORTANCE Microbial activities and interactions with minerals and venting fluid in active hydrothermal vents remain unclear in the ultraslow-spreading SWIR (Southwest Indian Ridge). Understanding about how minerals influence microbial metabolism is currently limited given the obstacles in cultivating microorganisms with sulfur or iron oxidoreduction functions. Here, comprehensive descriptions on microbial composition and metabolic profile on 2 hydrothermal vents in SWIR were obtained based on cultivation-free metagenome sequencing. In particular, autotrophic sulfur oxidation supported by minerals was presumed, emphasizing the role of chimney minerals in supporting chemosynthesis. Presence of novel heterotrophic iron-oxidizing bacteria was also indicated, suggesting overlooked biogeochemical pathways directed by microorganisms that connected sulfide mineral dissolution and organic carbon degradation in hydrothermal vents. Our findings offer novel insights into microbial function and biotic interactions on minerals in ultraslow-spreading ridges.

Discovery of active off-axis hydrothermal vents at 9° 54′N East Pacific Rise

Comprehensive knowledge of the distribution of active hydrothermal vent fields along midocean ridges is essential to understanding global chemical and heat fluxes and endemic faunal distributions. However, current knowledge is biased by a historical preference for on-axis surveys. A scarcity of high-resolution bathymetric surveys in off-axis regions limits vent identification, which implies that the number of vents may be underestimated. Here, we present the discovery of an active, high-temperature, off-axis hydrothermal field on a fast-spreading ridge. The vent field is located 750 m east of the East Pacific Rise axis and ∼7 km north of on-axis vents at 9° 50'N, which are situated in a 50- to 100-m-wide trough. This site is currently the largest vent field known on the East Pacific Rise between 9 and 10° N. Its proximity to a normal fault suggests that hydrothermal fluid pathways are tectonically controlled. Geochemical evidence reveals deep fluid circulation to depths only 160 m above the axial magma lens. Relative to on-axis vents at 9° 50'N, these off-axis fluids attain higher temperatures and pressures. This tectonically controlled vent field may therefore exhibit greater stability in fluid composition, in contrast to more dynamic, dike-controlled, on-axis vents. The location of this site indicates that high-temperature convective circulation cells extend to greater distances off axis than previously realized. Thorough high-resolution mapping is necessary to understand the distribution, frequency, and physical controls on active off-axis vent fields so that their contribution to global heat and chemical fluxes and role in metacommunity dynamics can be determined.