Tectonic uplift of mantle rocks along slow- and ultraslow-spreading mid-ocean ridges facilitates diverse styles of hydrothermal circulation. Here, we report on Lucky B, an ultramafic-hosted hydrothermal field on the ultraslow-spreading Lena Trough at 81°N in the ice-covered Arctic Ocean. At the seafloor we observed diffuse, metal-poor fluid discharge with abundant vent fauna alongside sites of massive sulfide deposits and hydrothermal chimneys, extending laterally over at least 1.9 km. The overlying water column exhibited two geochemically distinct plumes, the stronger of which showed strong redox and particle anomalies. We hence identify Lucky B as ‘black smoker’-type system featuring distinct styles of venting from several major fluid sources. The strongest plume also contained high concentrations of dissolved hydrogen (H2) and methane (CH4), distinguishing Lucky B from other ultramafic-hosted systems that primarily emit serpentinization-derived H2. Low H2/CH4 ratios and high CH4 relative to dissolved Mn suggest an involvement of sediment in the subseafloor fluid–rock reactions. Our analysis of the plume microbiology revealed abundant chemoautotrophs that use primarily hydrothermal H2 and sulfide as energy sources. Collectively, these findings reveal multifaceted hydrothermal venting at Lucky B, driven by geological and biogeochemical processes in the subseafloor and extending into the Arctic Ocean water column.

Deep-sea hydrothermal systems are particularly difficult to locate and investigate in the ice-covered Arctic Ocean. Here we report findings of a system in the ultraslow-spreading Lena Trough at 81°22’N, from Expedition PS137 of the icebreaker R/V Polarstern in the summer of 2023. The site, named ‘Lucky B’, was first discovered after the recovery of massive sulfides in a dredge haul in 1999 (Snow et al., 2001) on the western flank of the Lucky Ridge, a 130 km-long ultramafic topographic high.We investigated the buoyant and non-buoyant parts of Lucky B’s hydrothermal plume making use of physical sensors and geochemical hydrothermal tracers. The non-buoyant plume was found at approx. 300–400 m above the seafloor and was characterized by high turbidity and pronounced anomalies in oxidation–reduction potential and temperature (up to ~80 mV and 0.02°C, respectively). In its buoyant part, the plume contained high dissolved H2 (~450 nmol/L) and CH4 (~250 nmol/L).Our seafloor observations, using deep-sea robotics, revealed widespread traces of hydrothermal activity at approx. 3,000–3,300 m water depth. These included hydrothermally discolored rocks and sediment and local outflow of clear hydrothermal fluids with abundant macrofauna. Guided by our discoveries, follow-on operations with the Norwegian icebreaker R/V Kronprins Haakon resulted in ROV dives to a large black smoker vent field with a number of several m-high chimneys. The visual appearance of the suggests vent fluid temperatures similar to those of other high-temperature ultramafic-influenced systems (e.g., 365°C at Rainbow; Charlou et al., 2002).Confirmation awaits comparison with ongoing analyses of hydrothermal plume samples (He isotope signatures, Fe and Mn concentrations, CH4:Mn ratios) and of sulfide chimneys dredged in 1999 (mineral assemblages).In the Arctic, Lucky B is the first hydrothermal system that has been traced to its seafloor source that is associated with ultramafic rocks outcropping at the seafloor. Additional work will be required to conceive its role on biogeochemical cycles in the ice-covered ocean.

The Aurora vent field (82 degrees 53.83 ' N, 6 degrees 15.32 ' W) is located in the weakly stratified Arctic Ocean under perennial ice cover at the western edge of the ultraslow-spreading Gakkel Ridge, the slowest spreading mid-ocean ridge on Earth. Here, we report data on the dispersal of the proximal hydrothermal plume in this extreme environment. The hydrothermal plume is of unusual dimensions, with a small horizontal, but large vertical extent, which is caused by the hydrography of the Arctic Ocean. Water column parameters such as turbidity and redox potential show a highly variable but horizontally confined non-buoyant plume. Dissolved iron (dFe), manganese (dMn), delta He-3, and methane (CH4) all show distinct enrichment in the hydrothermal plume relative to background deep-water, but relatively low peak concentrations due to the dilution over a vertical extent of over 500 m. Plume particle samples exhibit elevated Fe/Al ratios consistent with Fe-oxyhydroxide precipitation close to the vent, whereas particulate Mn/Al ratios do not reveal any complementary pMn enrichment in the proximal plume. The positive correlation between Fe/Al, and several other element/Al ratios (e.g., P, V, As) is consistent with scavenging of these elements onto Fe-hydroxide plume particles and removal into the underlying sediments. Surface sediment samples collected close to Aurora reveal highly elevated concentrations of hydrothermally sourced elements in the immediate vicinity of the vent-site. For example, proximal surface sediments contained up to 8,222 mg kg(-1) Cu, whereas Cu concentrations in core tops a few kilometers away from the site were much lower (<50 mg kg(-1)).

The evidence of abundant hydrothermal activity at the Gakkel ridge, the slowest spreading mid-ocean ridge, led scientists to reconsider the relationship between hydrothermal cooling and the spreading rate of mid-ocean ridges. Beneath the year-round ice-cover of the Artic Ocean, images of active hydrothermal vents have now been recorded at the western-most end of this ridge, at the Aurora seamount. The presence of abundant micro-organisms living in hydrothermal vent sites in such extreme conditions has implications for the habitability of other ocean worlds and, hence, the search of life beyond Earth, given the evidence for submarine venting that has been inferred from Enceladus’ ice-covered ocean.A series of deployments of increasingly sophisticated deep-tow camera and ROV systems over the past decade have resulted in the collection of bathymetric, sonar and optical data sets from the Aurora site. Dives have primarily targeted the sampling of rocks and fluids, with platform cameras mainly used for navigation and identification of new vents and species. Nevertheless, the high number of still images and video footage obtained from that work can also be used for 3D reconstruction of this topographically complex environment: an approach that allows for further investigations (e.g., for habitat mapping) which would not be possible using classic ship based multibeam and backscatter technologies.This study highlights the usefulness of opportunistic data, especially when surveying in extreme environments, where data collection requires time consuming operations, expensive devices and experienced operators. We describe the methodological steps undertaken to produce a 3D reconstruction of the recently discovered hydrothermal vents from such opportunistic data.Additionally, the findings of this study highlight the challenges raised by the use of opportunistic data. Regardless of the powerful instrumentation currently available, careful pre-dive planning can help reduce the amount of manual labor required during post-processing steps, which is not only time-consuming but also adds uncertainty and errors to the final product.

The distribution of helium isotopes in the upper kilometer of the water column along the GP15 section in the central Pacific reflects the large-scale patterns of upwelling hydrothermal 3He in the tropics and sub-polar gyre, tracing two important pathways whereby bottom water exits from the deep Pacific. Heavy noble gas saturation anomalies, particularly in the upper two hundred meters of the water column, are more strongly increased by seasonal radiative heating, while lighter noble gas saturation anomalies are increased more by air injection processes. A similar, seasonally persistent radiative heating feature was observed in the Equatorial Undercurrent, and appears to be replicated in climate system model simulations. The origin of this feature, however, remains a mystery. A heuristic component model explains the noble gas saturation anomaly distributions, separating the influences of air injection, barometric pressure and radiative heating/cooling. Results show cohesive spatial patterns consistent with where water masses originate, their circulation, and gas exchange dynamics in relation to their formation regions. Using this model, we diagnose the distribution of "non-atmospheric" 4He in shallow waters, which parallels the helium isotope anomaly and silica distributions.

Active venting at the Aurora hydrothermal field was first located in 2014. In July 2023, the AUV/ROV Nereid Under Ice (NUI) expanded the known size of the Aurora hydrothermal field, discovering 7 ‘black smokers’ together with associated lower-temperature flow. In this study, we present a new high-resolution bathymetric map acquired from NUI which has allowed us to identify morphological features previously undetectable from ship multibeam. All known active vents are aligned along a single 230 m-long ridge, parallel to the Gakkel Ridge strike direction and intersected by a scarp following the general trend of the Lena Trough. The new vents were measured at up to 17 m height from 3D models generated using structure-from-motion techniques applied to opportunistically acquired imaging data collected while in exploration mode. The extent of extinct sulfides present, together with the towering height of vents are consistent with a period of sustained high-temperature venting at Aurora.

Hydrothermal vents emit hot fluids enriched in energy sources for microbial life. Here, we compare the ecological and biogeochemical effects of hydrothermal venting of two recently discovered volcanic seamounts, Polaris and Aurora of the Gakkel Ridge, in the ice-covered Central Arctic Ocean. At both sites, persistent hydrothermal plumes increased up to 800 m into the deep Arctic Ocean. In the two non-buoyant plumes, rates of microbial carbon fixation were strongly elevated compared to background values of 0.5–1 μmol m−3 day−1 in the Arctic deep water, which suggests increased chemoautotrophy on vent-derived energy sources. In the Polaris plume, free sulfide and up to 360 nM hydrogen enabled microorganisms to fix up to 46 μmol inorganic carbon (IC) m−3 day−1. This energy pulse resulted in a strong increase in the relative abundance of SUP05 by 25% and Candidatus Sulfurimonas pluma by 7% of all bacteria. At Aurora, microorganisms fixed up to 35 μmol IC m−3 day−1. Here, metal sulfides limited the bioavailability of reduced sulfur species, and the putative hydrogen oxidizer Ca. S. pluma constituted 35% and SUP05 10% of all bacteria. In accordance with this data, transcriptomic analysis showed a high enrichment of hydrogenase-coding transcripts in Aurora and an enrichment of transcripts coding for sulfur oxidation in Polaris. There was neither evidence for methane consumption nor a substantial increase in the abundance of putative methanotrophs or their transcripts in either plume. Together, our results demonstrate the dominance of hydrogen and sulfide as energy sources in Arctic hydrothermal vent plumes.

Some ocean worlds may sustain active, seafloor hydrothermal systems, but the characteristics and controls on fluid‐heat transport in these systems are not well understood. We developed three‐dimensional numerical simulations, using a ridge‐flank hydrothermal system on Earth as a reference, to test the influence of ocean world gravity on fluid and heat transport. Simulations represented the upper ∼4–5 km below the seafloor and explored ranges of: heat input at the base, aquifer thickness, depth, and permeability, and gravity values appropriate for Earth, Europa, and Enceladus. We tested when a hydrothermal siphon could be sustained and quantified consequent circulation temperatures, flow rates, and advective heat output. Calculations illustrate a trade‐off in energy between the reduction of buoyancy at lower gravity, which tends to reduce the primary forces driving fluid circulation, and the concomitant reduction in secondary convection, which consumes available energy. When a siphon was sustained under lower gravity, circulation temperatures tended to increase modestly (which should lead to more extensive geochemical reactions), whereas mass flow rates and advective heat output tended to be reduced. Deeper subseafloor circulation resulted in higher temperatures and flow rates, with a deeper, thin aquifer being more efficient in removing heat from the rocky interior. Water‐rock ratios were lower when gravity was lower, as was the efficiency of heat extraction, whereas the time required to circulate the volume of an ocean‐world's ocean through the seafloor increased. This may help to explain how small ocean worlds could sustain hydrothermal circulation for a long time despite limited heat sources.

Precise measurements of dissolved noble gases along the GP15 GEOTRACES Pacific Meridional Transect reveal the oldest northern bottom waters equilibrated with the atmosphere at a higher barometric pressure than more recent waters. Here, using a radiocarbon-calibrated multi-tracer-based diagnostic model, we reconstruct the magnitude and timing of this palaeo-barometric pressure anomaly. We hypothesize this multi-millennial trend in sea-level pressure results from local and regional processes extant in Antarctic Bottom Water formation regions.

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers and hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured microbial eukaryotic cell abundance and predation pressure in low-temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show cell abundances and grazing rates higher than those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between the protistan grazing rate, prey cell abundance, and temperature of end-member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. Our results show substantial protistan biomass at hydrothermally fueled microbial food webs, and when coupled with improved grazing estimates, suggest an important contribution of grazers to the local carbon export and supply of nutrient resources to the deep ocean.

The 2-week, virtual Future of the Search for Life science and engineering workshop brought together more than 100 scientists, engineers, and technologists in March and April 2022 to provide their expert opinion on the interconnections between life-detection science and technology. Participants identified the advances in measurement and sampling technologies they believed to be necessary to perform in situ searches for life elsewhere in our Solar System, 20 years or more in the future. Among suggested measurements for these searches, those pertaining to three potential indicators of life termed "dynamic disequilibrium," "catalysis," and "informational polymers" were identified as particularly promising avenues for further exploration. For these three indicators, small breakout groups of participants identified measurement needs and knowledge gaps, along with corresponding constraints on sample handling (acquisition and processing) approaches for a variety of environments on Enceladus, Europa, Mars, and Titan. Despite the diversity of these environments, sample processing approaches all tend to be more complex than those that have been implemented on missions or envisioned for mission concepts to date. The approaches considered by workshop breakout groups progress from nondestructive to destructive measurement techniques, and most involve the need for fluid (especially liquid) sample processing. Sample processing needs were identified as technology gaps. These gaps include technology and associated sampling strategies that allow the preservation of the thermal, mechanical, and chemical integrity of the samples upon acquisition; and to optimize the sample information obtained by operating suites of instruments on common samples. Crucially, the interplay between science-driven life-detection strategies and their technological implementation highlights the need for an unprecedented level of payload integration and extensive collaboration between scientists and engineers, starting from concept formulation through mission deployment of life-detection instruments and sample processing systems.

The noble gas signature of incoming Pacific Bottom Water (PBW), when compared to North Atlantic Deep Water, indicates the addition of 450 ± 70 GT a −1 glacial melt water to form AABW and subsequently PBW. The downstream evolution of this signature between the southern (20°S to equator) and northern (25°–45°N) bottom waters indicates a decrease in sea level pressure around Antarctica over the past two millennia. Vertical profiles of noble gases in the deep Pacific show exponential relationships with depth with scale heights identical to temperature and salinity. Unlike the other noble gases, helium isotopes show evidence of mid‐depth injection of non‐atmospheric helium. Using observed deviations from exponential behavior, we quantify its magnitude and isotope ratio. There is a clear latitude trend in the isotope ratio of this added helium that decreases from a high exceeding 9 R A (atmospheric 3 He/ 4 He ratio) in the south to around 8 R A near the equator. North of 30–40°N, it systematically decreases northward to a low of ∼2 R A north of 50°N. This decline results from a combination of northward decline in seafloor spreading, release of radiogenic helium from increased sediment thickness, and the possible emission of radiogenic helium through cold seeps along the Alaskan and North American margins. Finally, we derive an improved method of computing the excess helium isotope concentrations and that the distributions of bottom water 3 He XS / 4 He XS are consistent with what is known about bottom water flow patterns and the input of low 3 He/ 4 He sedimentary helium.

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers, hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured cell abundances and predation pressures of vent-associated microbial eukaryotes in low temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show higher cell abundances and grazing rates compared to those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between protistan grazing rate, prey cell abundance, and temperature of end member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. The quantification of protistan biomass and grazing pressure shows that hydrothermally-fueled microbial food webs play a significant role in the broader deep-sea carbon budget by contributing to local carbon export and supply of nutrient resources to the deep ocean.

Several moons in the outer solar system host liquid water oceans. A key next step in assessing the habitability of these ocean worlds is to determine whether life’s elemental and energy requirements are also met. Phosphorus is required by all known life and is often limited to biological productivity in Earth’s oceans. This raises the possibility that its availability may limit the abundance or productivity of Earth-like life on ocean worlds. To address this potential problem, here we calculate the equilibrium dissolved phosphate concentrations associated with the reaction of water and rocks—a key driver of ocean chemical evolution—across a broad range of compositional inputs and reaction conditions. Equilibrium dissolved phosphate concentrations range from 10 −11 to 10 −1 mol/kg across the full range of carbonaceous chondrite compositions and reaction conditions considered, but are generally > 10 −5 mol/kg for most plausible scenarios. Relative to the phosphate requirements and uptake kinetics of microorganisms in Earth’s oceans, such concentrations would be sufficient to support initially rapid cell growth and construction of global ocean cell populations larger than those observed in Earth’s deep oceans.

A multiscale numerical framework has been developed to investigate the dispersion of deep-sea hydrothermal plumes that originate from the Endeavour Segment of the Juan de Fuca Ridge located in the Northeast Pacific. The analysis of simulation outputs presented in this study provides insights into the influences of tidal forcing and the buoyancy flux associated with hydrothermal venting on ocean circulation and plume dispersion in the presence of pronounced seafloor topography. The results indicate that tidal forcing drives anti-cyclonic circulation near the ridge-axis, while hydrothermal venting induces cyclonic circulation around vent fields within the axial rift valley. Tidal forcing has a notable impact on plume dispersion, particularly near the large topographic features to the north of the Endeavour Segment. Furthermore, plume dispersion exhibits notable inter-annual variability, with a northbound trajectory in 2016 and a southbound trajectory in 2021. The study also reveals that both buoyancy fluxes and tidal forcing enhance the mixing of hydrothermal plumes with ambient seawater.

Water parcels close to their freezing point contract and become heavy on warming if they are sufficiently fresh, but expand and become buoyant when salty. We explore the resulting divergent behavior of hydrothermal plumes in fresh verses salty icy ocean worlds, with particular emphasis on Enceladus and Europa. Salty oceans develop buoyant plumes which rise upwards in the water column when energized by localised hydrothermal vents. Fresh oceans, instead, develop bottom-hugging gravity currents when heated near the freezing point, because of the anomalous contraction of fluid parcels on warming. The contrasting dynamics are highlighted and the implications discussed.

Submarine massive sulfide deposits on slow-spreading ridges are larger and longer-lived than deposits at fast-spreading ridges, likely due to more pronounced tectonic faulting creating stable preferential fluid pathways. The TAG hydrothermal mound at 26∘N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 yrs and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of possibly up to 1700 MW remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment but that circulation mode is thermodynamically unfavorable and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with vertical discharge and recharge along the detachment. The numerical simulations reveal that the high-temperature circulation system at TAG may be confined to a vertical zone of enhanced permeability that channelizes upflow and a recharge system that is hosted by the detachment surface with a high permeability of 2×10−13 to 10−12m2. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and allows to identify the prerequisites for generating substantive seafloor mineral systems.

Systematic surveys of the distribution of epibenthic megafaunal species relative to one another and to environmental variables in the deep sea can lead to inferences and testable hypotheses regarding factors that influence their distributions. Here we use a seascape approach to provide insight into the character and spatial extent of the influence of a chemosynthetic seep on the distribution of epibenthic megafauna and the nature of transition zones (ecotones). Faunal distributions were determined from georeferenced images of the seabed collected during a systematic survey (~ 400 m x 400 m) by the Autonomous Underwater Vehicle Sentry in the vicinity of a newly discovered methane bubble plume on the Blake Ridge Diapir. The survey area was found to include both seep and non-seep habitats. The sphere of influence of seep productivity on the surrounding benthic megafaunal assemblage was limited—on the order of 10’s of meters—based on ecotone analysis. Small but detectable redox anomalies in the water column (5 m above bottom) in the study area occurred on a similar horizontal scale. Distributions of background megafaunal taxa were non-random for many morphotypes and included both positive and negative associations between morphotypes and the seep habitat. Subtle variations in depth (<6 m) correlated with distributions of seep-associated vesicomyid clams, which occupy shallow depressions in the seabed. The seep habitat itself, comprising a patchy mosaic of megafaunal sub-communities (e.g., clam bed, mussel bed, background soft-sediment bathyal taxa) and transition zones, was at least as diverse as the surrounding non-seep habitat and contributes seep endemic morphotypes to regional biodiversity. While seep productivity may support prey fields for deep-diving beaked whales, any relationship between the seeps and whale feeding areas remains intriguing speculation. Like many other regions of the deep sea, Blake Ridge South has accumulated marine litter, including litter likely originating from scientific endeavors. The suite of observations and analyses deployed here underscore the importance of seep habitats in enriching regional biodiversity, provide a glimpse of the non-random complexity of species distributions from a seascape perspective, and establish ecological baselines against which future studies may measure natural and anthropogenic changes in the seascape.