Characterizing ancient and modern hydrothermal venting systems

During opening of a new ocean, magma intrudes into the surrounding sedimentary basins. Heat provided by the intrusions matures the host rock, creating metamorphic aureoles potentially releasing large amounts of hydrocarbons. These hydrocarbons may migrate to the seafloor in hydrothermal vent complexes in sufficient volumes to trigger global warming, e.g., during the Paleocene-Eocene Thermal Maximum (PETM). Mound structures at the top of buried hydrothermal vent complexes observed in seismic data off Norway were previously interpreted as sediment volcanoes, and the amount of released hydrocarbon was estimated based on this interpretation. Here, we present new geophysical and geochemical data from the Gulf of California suggesting that such mound structures could in fact be edifices constructed by the growth of black smoker–type chimneys rather than sediment volcanoes. We have evidence for two buried and one active hydrothermal vent systems outside the rift axis. The active vent releases fluids of several hundred degrees Celsius containing abundant methane, mid-ocean ridge basalt–type helium, and precipitating solids up to 300 m high into the water column. Our observations challenge the idea that methane is emitted slowly from rift-related vents. The association of large amounts of methane with hydrothermal fluids that enter the water column at high pressure and temperature provides an efficient mechanism to transport hydrocarbons into the water column and atmosphere, lending support to the hypothesis that rapid climate change such as during the PETM can be triggered by magmatic intrusions into organic-rich sedimentary basins.

The magma plumbing system of large igneous provinces may include emplacement of voluminous sill complexes in sedimentary basins. Key examples include the North Atlantic Igneous Province (NAIP; c. 56 Ma), the Karoo-Ferrar province (c. 183 Ma), and the Siberian Traps province (c. 251 Ma). In these basins, thousands of kilometer-sized hydrothermal vent complexes are associated with the sill complexes. We have interpreted new and legacy 2D and 3D seismic data in the Vøring and Møre basins offshore Norway to characterize the sill and hydrothermal vent complexes in a 100,000 km2 large region. The upper part of one of the hydrothermal vent complexes, the Modgunn Vent, was cored by five boreholes during IODP Expedition 396 in 2021. Saucer-shaped sills and overlying domes at the Top Paleocene level characterize the Jolnir, Tulipan and Infinity sill complexes in the Møre Basin. In contrast, sill complexes in the Vøring Basin display more variable morphologies, including ponding thick sheets and transgressive sheets reflecting the variations in deep basin structure and type of host rocks. The extensive Vivel Sill in the Vigrid Syncline is locally more than 200 m thick in the deeper parts of the basin, with some domal-shaped geometries that crosscut the deep basin stratigraphy and layer-parallel planar geometries at shallow stratigraphic levels. The hydrothermal vent complexes are mainly present as pipe-like disruptive seismic anomalies above transgressive sill segments connecting the contact aureoles with crater- or eye-shaped upper parts of the vent complexes near the Top Paleocene reflection. Scientific and industry drilling samples document that the vent craters were infilled during earliest Eocene times, most likely related to sill emplacement during the Paleocene-Eocene Thermal Maximum (PETM). In conclusion, the current geometries of voluminous igneous sheet intrusions both reflect the pre-emplacement deep basin structure and post-emplacement structural deformation, whereas the contact metamorphic processes triggers pipe-like deformation and focused fluid flow during formation of hydrothermal vent complexes.

Subvolcanic intrusions in sedimentary basins cause strong thermal perturbations and frequently cause extensive hydrothermal activity. Hydrothermal vent complexes emanating from the tips of transgressive sills are observed in seismic profiles from the Northeast Atlantic margin, and geometrically similar complexes occur in the Stormberg Group within the Late Carboniferous-Middle Jurassic Karoo Basin in South Africa. Distinct features include inward-dipping sedimentary strata surrounding a central vent complex, comprising multiple sandstone dykes, pipes, and hydrothermal breccias. Theoretical arguments reveal that the extent of fluid-pressure build-up depends largely on a single dimensionless number ( Ve ) that reflects the relative rates of heat and fluid transport. For Ve >> 1, ‘explosive’ release of fluids from the area near the upper sill surface triggers hydrothermal venting shortly after sill emplacement. In the Karoo Basin, the formation of shallow (< 1 km) sandstone-hosted vents was initially associated with extensive brecciation, followed by emplacement of sandstone dykes and pipes in the central parts of the vent complexes. High fluid fluxes towards the surface were sustained by boiling of aqueous fluids near the sill. Both the sill bodies and the hydrothermal vent complexes represent major perturbations of the permeability structure of the sedimentary basin, and are likely to have long time-scale effects on its hydrogeological evolution.

Spatiotemporal distribution of global mercury enrichments through the Paleocene-Eocene Thermal Maximum and links to volcanism

Introduction: concept of TAIGA.- Geochemical constraints on potential biomass sustained by subseafloor water-rock interactions.- Microbial cell densities, community structures, and growth in the hydrothermal plumes of subduction hydrothermal systems.- Systematics of distributions of various elements between ferromanganese oxides and seawater from natural observation, thermodynamics, and structures.- Evaluating hydrothermal system evolution using geochronological dating and biological diversity analyses.- Quantification of microbial communities in hydrothermal vent habitats of the Southern Mariana Trough and the Mid-Okinawa Trough.- Development of hydrothermal and frictional experimental systems to simulate sub-seafloor water-rock-microbe interactions.- Experimental hydrogen production in hydrothermal and fault systems: Significance for habitability of subseafloor H2 chemoautotroph microbial ecosystems.- Experimental assessment of microbial effects on chemical interaction between seafloor massive sulfides and seawater at 4 .- A compilation of the stable isotopic compositions of carbon, nitrogen, and sulfur in soft body parts of animals collected from deep-sea hydrothermal vent and methane seep fields: variations in energy source and importance of subsurface microbial processes in the sediment-hosted systems.- Tectonic background of four hydrothermal fields along the Central Indian Ridge.- Indian Ocean hydrothermal systems: seafloor hydrothermal activities, physical and chemical characteristics of hydrothermal fluids, and vent-associated biological communities.- Petrology and geochemistry of mid-ocean ridge basalts from the southern Central Indian Ridge.- Petrology of peridotites and related gabbroic rocks around the Kairei-hydrothermal field in the Central Indian Ridge.- Distribution and Biogeochemical Properties of Hydrothermal Plumes in the Rodriguez Triple Junction.- Vent fauna in the Central Indian Ridge.- The mantle dynamics, the crustal formation, and the hydrothermal activity of the Southern Mariana Trough back-arc Basin.- Seismic structure and seismicity in the Southern Mariana Trough and their relation to hydrothermal activity.- Electrical resistivity structure of the Snail site at the Southern Mariana Trough spreading center.- Asymmetric seafloor spreading of the southern Mariana Trough back-arc basin.- Geochemical characteristics of active backarc basin volcanisms at the southern end of Mariana Trough.- Mineralogical and geochemical characteristics of hydrothermal minerals collected from hydrothermal vent fields in the Southern Mariana spreading center.- Dating of hydrothermal mineralization in active hydrothermal fields in the Southern Mariana Trough.- Intra-field variation of prokaryotic communities on and below the seafloor in the back-arc hydrothermal system of the Southern Mariana Trough.- Vent fauna in the Mariana Trough.- Population history of a hydrothermal vent-endemic snail Alviniconcha hessleri in the Mariana Trough.- Hydrothermal activity in the Okinawa Trough backarc basin -geological background and hydrothermal mineralization-.- Active rifting structures in Iheya Graben and adjacent area of the mid-Okinawa Trough observed through seismic reflection surveys.- ESR dating of barite in sea-floor hydrothermal sulfide deposits in the Okinawa Trough.- Fluid geochemistry of high-temperature hydrothermal fields in the Okinawa Trough.- Sediment-pore water system associated with native sulfur formation at Jade hydrothermal field in Okinawa Trough.- Comparative investigation of microbial communities associated with hydrothermal activities in the Okinawa Trough.- In situ determination of bacterial growth in mixing zone of hydrothermal vent field on the Hatoma Knoll, Southern Okinawa Trough.- Vent Fauna in the Okinawa Trough.- Brief report of side-scan sonar observations around the Yokoniwa NTO massif.- Examination of volcanic activity: AUV and submersible observations of fine-scale lava flow distributions along the Southern Mariana Trough spreading axis .- Brief report of side-scan sonar imagery observations of the Archaean, Pika, and Urashima hydrothermal sites.- The Yoron Hole: the shallowest hydrothermal site in the Okinawa Trough.- The Irabu Knoll: Hydrothermal site at the eastern edge of the Yaeyama Graben.- Tarama Knoll: Geochemical and biological profiles of hydrothermal activity.- Petrography and geochemistry of basement rocks drilled from Snail, Yamanaka, Archean, and Pika hydrothermal fields at the Southern Mariana Trough by Benthic Multi-coring System (BMS).- Pore fluid chemistry beneath active hydrothermal fields in the mid-Okinawa Trough: Results of shallow drilling by BMS during TAIGA11 cruise.- The characteristics of the seafloor massive sulfide deposits at the Hakurei Site in the Izena Hole, the Middle Okinawa Trough.- Occurrence of hydrothermal alteration minerals at the Jade hydrothermal field, in the Izena Hole, mid-Okinawa Trough.- Geochemistry of hydrothermal fluids collected from active hydrothermal systems in the southern Mariana Trough backarc spreading center.- Gamma ray doses in water around sea floor hydrothermal area in South Mariana.- 226Ra-210Pb and 228Ra-228Th dating of barite in submarine hydrothermal sulfide deposits collected at Okinawa Trough and South Mariana Trough.- OSL dating of sea floor sediments at the Okinawa Trough.- Immediate change of radiation doses from hydrothermal deposits.- Periodic behavior of deep sea current in the Hatoma Knoll hydrothermal system.- The gelatinous macroplankton community at the Hatoma Knoll hydrothermal vent.

The mid-Norwegian margin is regarded as an example of a volcanic-rifted margin formed prior to and during the Paleogene breakup of the northeast Atlantic. The area is characterized by the presence of voluminous basaltic complexes such as extrusive lava and lava delta sequences, intrusive sills and dikes, and hydrothermal vent complexes. We have developed a detailed 3D seismic analysis of fluid- and gas-induced hydrothermal vent complexes in a [Formula: see text] area in the Møre Basin, offshore Norway. We find that formation of hydrothermal vent complexes is accommodated by deformation of the host rock when sills are emplaced. Fluids are generated by metamorphic reactions and pore-fluid expansion around sills and are focused around sill tips due to buoyancy. Hydrothermal vent complexes are associated with doming of the overlying strata, leading to the formation of draping mounds above the vent contemporary surface. The morphological characteristics of the upper part and the underlying feeder structure (conduit zone) are imaged and studied in 3D seismic data. Well data indicate that the complexes formed during the early Eocene, linking their formation to the time of the Paleocene-Eocene thermal maximum at c. 56 Ma. The well data further suggest that the hydrothermal vent complexes were active for a considerable time period, corresponding to a c. 100 m thick transition zone unit with primary Apectodinium augustum and redeposited very mature Cretaceous and Jurassic palynomorphs. The newly derived understanding of age, structure, and formation of hydrothermal vent complexes in the Møre Basin contributes to the general understanding of the igneous plumbing system in volcanic basins and their implications for the paleoclimate and petroleum systems.

Since the discovery of hydrothermal vents 40-years ago, long-term time-series have focused on mid-ocean ridge systems. Based on these studies, hydrothermal vents are widely considered to be dynamic, ephemeral habitats. Under this premise, national, and international regulatory bodies are currently planning for the commercial mining of polymetallic sulfide deposits from hydrothermal vents. However, here we provide evidence of longevity and habitat stability that does not align with historic generalizations. Over a 10-year time-series focused on the back-arc basin systems off the west coast of the Kingdom of Tonga (South Pacific), we find the hydrothermal vents are remarkably stable habitats. Using high-resolution photo mosaics and spatially explicit in situ measurements to document natural changes of five hydrothermal vent edifices, we discovered striking stability in the vent structures themselves, as well as in the composition and coverage of the vent-associated species, with some evidence of microdistribution permanence. These findings challenge the way we think about hydrothermal vent ecosystems and their vulnerability and resilience to deep-sea mining activities.

Putting marine scientific research on a sustainable footing at hydrothermal vents

Doppler wind data obtained over the Indian Ocean during the 1964 Indian Ocean Expedition are analyzed in terms of power spectrum estimates. Peculiarities in the computed distribution of the mean horizontal kinetic energy associated with mesoscale (∼1–100 km) motions are noted in light of energy input from mean wind shear and energy export to the density field in a stably stratified atmosphere. The data indicate that quasi-horizontal eddies 10 km in size derive their energy mainly from mean horizontal wind shear at a wavenumber around 1−2 cycle km−1, and that eddies of a few kilometers in diameter are approximately two-dimensionally isotropic.

GNSS-R is an emerging technology for remote sensing of soil moisture with the advantages of high tempo spatial resolutions at low cost. Most of the current research has been carried out on the basis of space borne observations, and a large number of results have been obtained. Due to the high altitude of satellites, the Fresnel reflection zone is usually a few kilometers in diameter, which does not meet the requirements of fine agriculture. Ground-based and UAV-borne GNSS-R, due to their low altitude, can provide effective observations to address above problem. We have built a ground-based GNSS-R observatory at the Experimental Farm of Weihai Academy of Agricultural Sciences, Shandong Province China. The site is equipped with mainly high gain a downward facing left-handed circularly polarized antenna, an upward facing right-handed circularly polarized antenna, an IF signal collector and a computer platform for running the SDR. Currently the main observables that can be output include: SNR, Power Ratio, DDM, etc. The retrievals were evaluated by the in-suit measurements from TDR and the results show that the accuracy of the solutions can reach 3%. In addition, a UAV-based GNSS-R setups are also built and effective measurements were obtained.

In the past few decades, chemosynthetic ecosystems at deep-sea hydrothermal vents have received attention as plausible analogues to the early ecosystems of Earth, as well as to extraterrestrial ecosystems. These ecosystems are sustained by chemical energy obtained from inorganic redox substances (e.g., H 2 S, CO 2 , H 2 , CH 4 , and O 2 ) in hydrothermal fluids and ambient seawater. The chemical and isotope compositions of the hydrothermal fluid are, in turn, controlled by subseafloor physical and chemical processes, including fluid-rock interactions, phase separation and partitioning of fluids, and precipitation of minerals. We hypothesized that specific physicochemical principles describe the linkages among the living ecosystems, hydrothermal fluids, and geological background in deep-sea hydrothermal systems. We estimated the metabolic energy potentially available for productivity by chemolithotrophic microorganisms at various hydrothermal vent fields. We used a geochemical model based on hydrothermal fluid chemistry data compiled from 89 globally distributed hydrothermal vent sites. The model estimates were compared to the observed variability in extant microbial communities in seafloor hydrothermal environments. Our calculations clearly show that representative chemolithotrophic metabolisms (e.g., thiotrophic, hydrogenotrophic, and methanotrophic) respond differently to geological and geochemical variations in the hydrothermal systems. Nearly all of the deep-sea hydrothermal systems provide abundant energy for organisms with aerobic thiotrophic metabolisms; observed variations in the H 2 S concentrations among the hydrothermal fluids had little effect on the energetics of thiotrophic metabolism. Thus, these organisms form the base of the chemosynthetic microbial community in global deep-sea hydrothermal environments. In contrast, variations in H 2 concentrations in hydrothermal fluids significantly impact organisms with aerobic and anaerobic hydrogenotrophic metabolisms. Particularly in H 2 -rich ultramafic rock-hosted hydrothermal systems, anaerobic and aerobic hydrogenotrophy is more energetically significant than thiotrophy. The CH 4 concentration also has a considerable impact on organisms with aerobic and anaerobic methanotrophic metabolisms, particularly in sediment-associated hydrothermal systems. Recently clarified patterns and functions of existing microbial communities and their metabolisms are generally consistent with the results of our thermodynamic modeling of the hydrothermal mixing zones. These relationships provide important directions for future research addressing the origin and early evolution of life on Earth as well as for the search for extraterrestrial life.

The Paleocene-Eocene Thermal Maximum (PETM) around 56 Ma was associated with 5-6 °C global warming, resulting from massive carbon release into the ocean–atmosphere system. One potential driver of hyperthermal conditions was the North Atlantic Igneous Province (NAIP), as both volcanic degassing and thermogenic volatile release during contact metamorphism during its emplacement were large potential emitters of carbon. Despite a broad temporal correlation between NAIP activity and the PETM, the exact relationship is obscured by multiple climate forcings, imprecise geochronological data, uncertainties in the timing and magnitude of volatile fluxes from volcanic and thermogenic sources, and limited availability from crucial NAIP localities that could constrain these unknowns. Here we present new seismic and borehole data for the Modgunn hydrothermal vent complex in the Northeast Atlantic (IODP Sites U1567-U1568). Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of Apectodinium augustum in the vent crater infill. Modern examples of submarine explosion craters suggest they have filled in within decades to centuries, so the preservation of the PETM onset within the Modgunn vent suggests an extremely close temporal correlation between the crate formation and the onset of hyperthermal conditions. Furthermore, the majority of the craters across the entire NAIP are likely to have vented in very shallow water, implying that the vast majority of emitted CO2 and CH4 gases directly entered the atmosphere during eruptions. These findings add considerable weight to the hypothesis that thermogenic degassing aided the initiation of the PETM. 

Environmental controls on biomineralization and Fe-mound formation in a low-temperature hydrothermal system at the Jan Mayen Vent Fields

Oceanic carbon cycle in a symbiotic zone between hydrothermal vents and cold seeps in the Okinawa Trough

Influence of magma chamber geometry on hydrothermal activity at mid-ocean ridges