Active Hydrothermal Vents Research Articles

A data processing method for MAPR hydrothermal plume turbidity data and its application in the Precious Stone Mountain hydrothermal field

Hydrothermal plume is an important constituent of seabed hydrothermal circulation and is also one of the characteristics of active hydrothermal vents. Portable Miniature Autonomous Plume Recorders (MAPR) attached to a towed deep-sea instrument was used to search for hydrothermal plumes and hydrothermal vents. We introduced the basic principle of MAPR based on deep towing technology to detect plumes, then analyzed the factors affecting the quality of the MAPR data and presented a data correction method for MAPR, including instrument location correction, noise reduction processing, system error elimination and seawater background reduction. Finally we applied the method to analyze MAPR data obtained during the Chinese DY115-21 cruise on R/V Dayang I in the “Precious Stone Mountain” hydrothermal field on the Galapagos Microplate. The results provided a better understanding of the distribution of the hydrothermal activity in this field, indicating the presence of a new hydrothermal vent.

The morphotectonics and its evolutionary dynamics of the central Southwest Indian Ridge (49° to 51°E)

The morphotectonic features and their evolution of the central Southwest Indian Ridge (SWIR) are discussed on the base of the high-resolution full-coverage bathymetric data on the ridge between 49 degrees-51 degrees E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topography is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal migration especially in 49 degrees-50.17 degrees E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17 degrees to 50.7 degrees E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA (residual mantle Bouguer anomaly). The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC (oceanic core complex). The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37 degrees 47'S, 49 degrees 39'E is thought to be associated with the detachment fault related to the OCC.

Magmatism and tectonic processes in Area A hydrothermal vent on the Southwest Indian Ridge

The hydrothermal vent in Area A (37.78°S, 49.65°E) is the first active hydrothermal vent discovered on the Southwest Indian Ridge (SWIR). Heat source and adequate bulk permeability are two necessary factors for the formation of a hydrothermal vent. Along the SWIR 49.3°E to 51.2°E, the gravity-derived crustal thickness is up to 9.0 km, much thicker than the average thickness of the global oceanic crust. This characteristic indicates that the magma supply in this area is robust, which is possibly affected by a hotspot. The large-scale residual mantle Bouguer anomalies (RMBA) reveal prominent negative-gravity anomalies between the first-order ridge segment (from Indomed to Gallieni, 46.0°E to 52.0°E) and the Marion-Del Cano-Crozet region. These anomalies indicate the channel of the hotspot-ridge interaction. The tomography data corrected with theoretical thermal model indicate that the low-velocity anomalies corresponding to this channel can reach the base of the lithosphere. Near the hydrothermal vent area, the topography and crustal thickness at the off-axis area are extremely asymmetrical. South of the SWIR, the high topography corresponds to the thinning crustal thickness. The residual isostatic topography anomalies indicate that Area A is a deviation from the local isostatic equilibrium, similar to the characteristics of the transform fault inside corner. The forward profiles of the magnetic data indicate that the thinning magnetic layer at the south side of Area A corresponds to the shallow, high-velocity area revealed by the OBS, which is the result of tectonic extension of a detachment fault. The active tectonic processes in Area A can provide sufficient crustal permeability to the hydrothermal circulation and may form massive sulfide deposits.

Distribution, population structure, reproduction and diet of Ophiolimna antarctica (Lyman, 1879) from Kemp Caldera in the Southern Ocean

A new population of Ophiolimna antarctica (Lyman, 1879) was discovered at 1546m in Kemp Caldera, a topographic feature with active hydrothermal venting at the southern end of the South Sandwich Islands, Southern Ocean. The distribution, population structure, reproduction, and diet of O. antarctica were investigated. O. antarctica were found predominantly on basalt with an over-dispersed distribution. The mean density was 17 individuals m−2 with a range of 9–24 individuals m−2. There was a bimodal population structure, with separate juvenile and adult peaks. Sexes were separate and the sex ratio was not significantly different from equality. The maximum oocyte diameter was 520μm, suggesting direct or lecithotrophic development, whilst individual females reproduced asynchronously. Stomach contents included crustacean fragments, flocculate material, diatoms, forams, fish scales, and ophiuroid tissues and spines, which was indicative of omnivory. There was no apparent influence of hydrothermal vents <500m away on the diet of Ophiolimna antarctica. The ecology of Ophiolimna antarctica is consistent with what is known for other Antarctic and deep-sea ophiuroid species.

The discovery of a natural whale fall in the Antarctic deep sea

Large cetacean carcasses at the deep-sea floor, known as ‘whale falls’, provide a resource for generalist-scavenging species, chemosynthetic fauna related to those from hydrothermal vents and cold seeps, and remarkable bone-specialist species such as Osedax worms. Here we report the serendipitous discovery of a late-stage natural whale fall at a depth of 1444m in the South Sandwich Arc. This discovery represents the first natural whale fall to be encountered in the Southern Ocean, where cetaceans are abundant. The skeleton was situated within a seafloor caldera, in close proximity (<250m) to active hydrothermal vents. We used a DNA barcoding approach to identify the skeleton as that of an Antarctic minke whale (Balaenoptera bonaerensis). The carcass was in an advanced state of decomposition, and its exposed bones were occupied by a diverse assemblage of fauna including nine undescribed species. These bone fauna included an undescribed species of Lepetodrilus limpet that was also present at the nearby hydrothermal vents, suggesting the use of whale-fall habitats as stepping stones between chemosynthetic ecosystems. Using Remotely Operated Vehicle (ROV) videography, we have quantified the composition and abundance of fauna on the whale bones, and tested a hypothesis that varying concentrations of lipids in the bones of whales may influence the microdistribution of sulfophilic whale-fall fauna. Our data supported the hypothesis that more lipid-rich bones support a greater abundance of sulfophilic bacterial mats, which are also correlated with the abundance of grazing limpets (Pyropelta sp.). The abundance of Osedax sp. on bones however, showed a negative correlation with the bacterial-mat percentage cover, and hence greatest abundance on bones predicted to have lowest lipid content.

The Tectonomagmatic Source of Ore Metals and Volatile Elements in the Southern Kermadec Arc

Deciphering the ultimate source of chalcophile metals (e.g., Cu, Zn, Pb) in volcanogenic massive sulfide (VMS) deposits and the volatiles that help drive their formation is critical for understanding where, how, and why VMS deposits form. The southern Kermadec arc volcanic front is known to be highly hydrothermally active and host to at least three VMS deposits, whereas the associated back -arc system is apparently hydrothermally inactive, although this may simply be due to a lack of exploration in this region. We have analyzed major, trace, and volatile element concentrations in a suite of basaltic glasses and olivine-hosted melt inclusions from volcanoes, ridges, and rifts of the southern Kermadec arc volcanic front and Havre Trough back-arc basin. These data indicate clear compositional differences in the mantle beneath the arc front and the back arc, with the arc front having higher extents of prior melt extraction and enrichment in volatile and metal elements from slab-derived aqueous fluids. The magmatic budget of Pb is supplied to the mantle source by these slab-derived fluids, whereas magmatic concentrations of Zn and Cu are primarily controlled by the degree of partial melting, with a Cu-bearing residual phase required in the mantle. Consequently, the relative enrichment of chalcophile metals in the mantle-derived melts is Pb >> Cu > Zn. The magma volatile history recorded by the glasses and melt inclusions indicates that degassing during crystal fractionation is significant and, notably, leads to the reduction of sulfur in the evolving magma as oxidized sulfur degasses preferentially. The apparent absence (or retention) of volatiles (notably CO 2 and SO 3 ) in magma chambers, lack of magmatic activity, and absence of hot, mafic dikes beneath volcanoes may be important factors in inhibiting the formation of active hydrothermal venting, and by extension the potential for VMS deposition.

Controls of faulting and reaction kinetics on serpentinization and double Benioff zones

The subduction of partially serpentinized oceanic mantle may potentially be the key geologic process leading to the regassing of Earth's mantle and also has important consequences for subduction zone processes such as element cycling, slab deformation, and intermediate‐depth seismicity. However, little is known about the quantity of water that is retained in the slab during mantle serpentinization and the pattern of serpentinization that may occur during bending‐related faulting; an initial state that is essential for quantifying subsequent dehydration processes. We present a 2‐D reactive‐flow model simulating hydration processes in the presence of faulting at the trench outer‐rise. We find that the temperature dependence of the serpentinization rate in conjunction with outer‐rise faulting results in plate age and speed dependent patterns of hydration. Serpentinization also results in a reduction in surface heat flux toward the trench caused by advective downflow of seawater into the reaction region. Observed heat flow reductions are larger than the reduction due to the minimum‐water downflow needed for partial serpentinization, predicting that active hydrothermal vents and chemosynthetic communities should also be associated with bend‐fault serpentinization. Our model results agree with previous studies that the lower plane of double Benioff zones can be generated due to dehydration of serpentinized mantle at depth. More importantly, the depth‐dependent pattern of serpentinization including reaction kinetics predicts a separation between the two Benioff planes consistent with seismic observations.

Time‐series analysis of two hydrothermal plumes at 9°50′N East Pacific Rise reveals distinct, heterogeneous bacterial populations

We deployed sediment traps adjacent to two active hydrothermal vents at 9°50'N on the East Pacific Rise (EPR) to assess the variability in bacterial community structure associated with plume particles on the timescale of weeks to months, to determine whether an endemic population of plume microbes exists, and to establish ecological relationships between bacterial populations and vent chemistry. Automated rRNA intergenic spacer analysis (ARISA) indicated that there are separate communities at the two different vents and temporal community variations between each vent. Correlation analysis between chemistry and microbiology indicated that shifts in the coarse particulate (>1 mm) Fe/(Fe+Mn+Al), Cu, V, Ca, Al, (232) Th, and Ti as well as fine-grained particulate (<1 mm) Fe/(Fe+Mn+Al), Fe, Ca, and Co are reflected in shifts in microbial populations. 16S rRNA clone libraries from each trap at three time points revealed a high percentage of Epsilonproteobacteria clones and hyperthermophilic Aquificae. There is a shift toward the end of the experiment to more Gammaproteobacteria and Alphaproteobacteria, many of whom likely participate in Fe and S cycling. The particle-attached plume environment is genetically distinct from the surrounding seawater. While work to date in hydrothermal environments has focused on determining the microbial communities on hydrothermal chimneys and the basaltic lavas that form the surrounding seafloor, little comparable data exist on the plume environment that physically and chemically connects them. By employing sediment traps for a time-series approach to sampling, we show that bacterial community composition on plume particles changes on timescales much shorter than previously known.

First active hydrothermal vents on an ultraslow-spreading center: Southwest Indian Ridge

The ultraslow-spreading Southwest Indian Ridge is a major tectonic province, representing one of the important end-member mid-ocean-ridge types for its very slow and oblique spreading, and providing the only known route for migration of chemosynthetic deep-sea vent fauna between the Atlantic and Indian Oceans. We report the investigation of the first active high-temperature hydrothermal field found on any ultraslow mid-ocean ridge worldwide. Located on Southwest Indian Ridge at 37°47′S, 49°39′E, it consists of three zones extending ∼1000 m laterally, and it is one of four recently discovered active and inactive vent sites within a 250-km-long magmatically robust section. Our results provide the first direct evidence for potentially widespread distribution of hydrothermal activity along ultraslow-spreading ridges—at least along magmatically robust segments. This implies that the segment sections with excess heat from enhanced magmatism and suitable crustal permeability along slow and ultraslow ridges might be the most promising areas for searching for hydrothermal activities. It is surprising that the special vent fauna appear to indicate some complex affinity to those on the Central Indian Ridge, southern Mid-Atlantic Ridge, and the southwest Pacific Ocean.

ISBA Approval for Exploration for Polymetallic Sulphides in the Southwest Indian Ridge: Beginning of Chinese Ocean Supremacy

International Seabed Authority (ISBA) has recently approved the plans of work in form of contracts to a Chinese company for exploration activities on the active hydrothermal vents in the Southwest Indian Ridge for polymetallic sulphides. This is an indication of the prospects for exploiting submarine mineral resources. On the other hand, it also reflects China’s leapfrog in the technological capabilities. In this sense, acquisition of contract for exploring submarine mineral resources could be described as the beginning of Chinese ocean supremacy in the times to come.

Geophysical characterization of hydrothermal systems and intrusive bodies, El Chichón volcano (Mexico)

[1] The 1982 explosive eruptions of El Chichón volcano (Chiapas, Mexico) destroyed the inner dome and created a 1-km-wide and 180-m-deep crater within the somma crater. A shallow hydrothermal system was exposed to the surface of the new crater floor and is characterized by an acid crater lake, a geyser-like Cl-rich spring (soap pool), and numerous fumarole fields. Multiple geophysical surveys were performed to define the internal structure of the volcanic edifice and its hydrothermal system. We carried out a high-resolution ground-based geomagnetic survey in the 1982 crater and its surroundings and 38 very low frequency (VLF) transects around the crater lake. A 3-D inversion of the ground-based magnetic data set highlighted three high-susceptibility isosurfaces, interpreted as highly magnetized bodies beneath the 1982 crater floor. Inversion of a digitized regional aeromagnetic map highlighted four major deeply rooted cryptodomes, corresponding to major topographic highs and massive lava dome outcrops outside and on the somma rim. The intracrater magnetic bodies correspond closely to the active hydrothermal vents and their modeled maximum basal depth matches the elevation of the springs on the flanks of the volcano. Position, dip, and vertical extent of active and extinct hydrothermal vents identified by VLF-EM surveys match the magnetic data set. We interpret the shallow lake spring hydrothermal system to be mostly associated with buried remnants of the 550 BP dome, but the Cl-rich soap pool may be connected to a small intrusion emplaced at shallow depth during the 1982 eruption.

Microbial community structure of hydrothermal deposits from geochemically different vent fields along the Mid‐Atlantic Ridge

To evaluate the effects of local fluid geochemistry on microbial communities associated with active hydrothermal vent deposits, we examined the archaeal and bacterial communities of 12 samples collected from two very different vent fields: the basalt-hosted Lucky Strike (37°17'N, 32°16.3'W, depth 1600-1750 m) and the ultramafic-hosted Rainbow (36°13'N, 33°54.1'W, depth 2270-2330 m) vent fields along the Mid-Atlantic Ridge (MAR). Using multiplexed barcoded pyrosequencing of the variable region 4 (V4) of the 16S rRNA genes, we show statistically significant differences between the archaeal and bacterial communities associated with the different vent fields. Quantitative polymerase chain reaction (qPCR) assays of the functional gene diagnostic for methanogenesis (mcrA), as well as geochemical modelling to predict pore fluid chemistries within the deposits, support the pyrosequencing observations. Collectively, these results show that the less reduced, hydrogen-poor fluids at Lucky Strike limit colonization by strict anaerobes such as methanogens, and allow for hyperthermophilic microaerophiles, like Aeropyrum. In contrast, the hydrogen-rich reducing vent fluids at the ultramafic-influenced Rainbow vent field support the prevalence of methanogens and other hydrogen-oxidizing thermophiles at this site. These results demonstrate that biogeographical patterns of hydrothermal vent microorganisms are shaped in part by large scale geological and geochemical processes.

Epibiotic association between filamentous bacteria and the vent-associated galatheid crab,Shinkaia crosnieri(Decapoda: Anomura)

The galatheid crabShinkaia crosnieri, is the sole member of the subfamily Shinkaiinae. It is abundant and forms dense beds around active hydrothermal vents in the Okinawa Trough. Thousands of filamentous bacteria attached to the plumose setae on the ventral surface of this crab were observed using field-emission scanning electron microscopy and transmission electron microscopy. Nucleic acids were extracted from the filamentous bacteria, and the phylotypes of 16S rRNA genes were identified from 81 clones. These phylotypes were divided into three groups: Epsilonproteobacteria (74%); Gammaproteobacteria (20%); and Bacteroidetes (6%). Gamma- and major phylotypes of Epsilonproteobacteria were also detected using fluorescencein situhybridization analysis. These Epsilon- and Gammaproteobacteria were closely related to cultured and uncultured bacteria from hydrothermal vent fields including episymbionts of vent-associated invertebrates such asRimicaris exoculata, Alvinella pompejana, the scaly-foot snail,Kiwa hirsutaetc. The carbon isotopic compositions of the muscle ofS. crosnieriand in filamentous bacteria were similar. The muscle ofS. crosniericontained monounsaturated C16and C18fatty acids, which are known to be characteristic of sulphur-oxidizing bacteria in H2S-rich marine habitats. Through the video images transmitted by a submersible and a remotely operated vehicle,S. crosnieriwas observed to comb out its ventral setae using the third maxilliped and appeared to consume the contents. These evidences suggest the epibiotic association betweenS. crosnieriand the filamentous bacteria attached to the ventral setae of the crab, but the details of role and function are still unclear at the present study.

Preliminary results on the reproduction of a deep‐sea snailfish Careproctus rhodomelas around the active hydrothermal vent on the Hatoma Knoll, Okinawa, Japan

Deep-sea snailfish Careproctus rhodomelas were collected from an active hydrothermal vent using a remotely operated vehicle (R.O.V. Hyper-dolphin) and a pressurized device (Deep-Aquarium). Careproctus rhodomelas exhibited a cystovarian-type ovary containing a small number of developing oocytes at different stages, suggesting that the fish is a batch-spawner that spawns large eggs (c. 6·0 mm) several times within its life span. In vitro culture of the oocytes in the presence of human chorionic gonadotropin showed that oestradiol-17β production fluctuated with oocyte development, suggesting that the oocytes were at the vitellogenic stage.

A novel trigger-based method for hydrothermal vents prospecting using an autonomous underwater robot

In this paper we address the problem of localizing active hydrothermal vents on the seafloor using an Autonomous Underwater Vehicle (AUV). The plumes emitted by hydrothermal vents are the result of thermal and chemical inputs from submarine hot spring systems into the overlying ocean. The Woods Hole Oceanographic Institution’s Autonomous Benthic Explorer (ABE) AUV has successfully localized previously undiscovered hydrothermal vent fields in several recent vent prospecting expeditions. These expeditions utilized the AUV for a three-stage, nested survey strategy approach (German et al. in Deep Sea Res. I 55:203–219, 2008). Each stage consists of a survey flown at successively deeper depths through easier to detect but spatially more constrained vent fluids. Ideally this sequence of surveys culminates in photographic evidence of the vent fields themselves. In this work we introduce a new adaptive strategy for an AUV’s movement during the first, highest-altitude survey: the AUV initially moves along pre-designed tracklines but certain conditions can trigger an adaptive movement that is likely to acquire additional high value data for vent localization. The trigger threshold is changed during the mission, adapting the method to the different survey profiles the robot may find. The proposed algorithm is vetted on data from previous ABE missions and measures of efficiency presented.

Clay alteration of volcaniclastic material in a submarine geothermal system, Bay of Plenty, New Zealand

The Calypso Hydrothermal Vent Field (CHVF) is located along an offshore extension of the Taupo Volcanic Zone (TVZ), an area of abundant volcanism and geothermal activity on the North Island of New Zealand. The field occurs within a northeast-trending submarine depression on the continental shelf approximately 10–15 km southwest of the White Island volcano in the Bay of Plenty. The graben has been partially filled by tephra from regional subaerial volcanic eruptions, and active hydrothermal venting occurs at several locations along its length. The vents occur at water depths of 160 to 190 m and have temperatures up to 201 °C. Recovered samples from the vent field include variably cemented and veined volcaniclastic sediments containing an assemblage of clay minerals, amorphous silica, barite, As–Sb–Hg sulfides, and abundant native sulfur. The volcanic glass has been altered primarily to montmorillonite and mixed-layer illite–montmorillonite; illite, and possibly minor talc and mixed-layer chlorite–smectite or chlorite–vermiculite are also present. A hydrothermal versus diagenetic origin for the smectite is indicated by the presence of both illite and mixed-layer clays and by the correlation between the abundance of clay minerals and the abundance of native sulfur in the samples. The mineralization and alteration of the volcanic host rocks are similar to that observed in near-neutral pH geothermal systems on land in the TVZ (e.g., Broadlands–Ohaaki). However, the clay minerals in the CHVF have a higher concentration of Mg in the dioctahedral layer and a higher interlayer Na content than clay minerals from Broadlands–Ohaaki, reflecting the higher concentrations of Mg and Na in seawater compared to meteoric water. Minerals formed at very low pH (e.g., kaolinite and alunite), typical of steam-heated acid-sulfate type alteration in the TVZ geothermal environment, were not found. Mixing with seawater likely prevented the formation of such low-pH mineral assemblages. The occurrence of illite and mixed-layer illite–smectite close to the seafloor in the CHVF, rather than at depth as in the Broadlands system, is interpreted to reflect the higher pressures associated with submarine venting. This allows hotter fluids to be discharged before they boil, and thus minerals that are encountered mainly at depth in subaerial geothermal systems can form close to the seafloor.

Private rights, public benefits: Industry-driven seabed protection

New Zealand has a large exclusive economic zone (EEZ) that contains a variety of marine habitats and commercially-important species. The commercial fishing industry operating within New Zealand's EEZ is of significant value to the economy and fisheries resources are managed through the extensive use of Individual Transferable Quotas (ITQs). One of the benefits of ITQs has been to better align some of the private incentives of quota owners with the public interest. These incentives contributed to an initiative proposed by the fishing industry to close large areas of New Zealand's EEZ to protect the seabed from trawling. These closed areas are termed benthic protection areas (BPAs) and protect the benthic biodiversity of about 1.1 million square kilometres of seabed—approximately 30% of New Zealand's EEZ. A significant proportion of New Zealand's known seamounts and active hydrothermal vents are protected by these closed areas. We describe and discuss the criteria used to select BPAs and some of the criticism of this marine protection initiative. We argue that the assignment of strong property rights in fishing resources was an important precondition to an industry initiative that has a significant public benefit. Where private and public interests are well aligned, government can adopt an enabling and facilitation role, ceding direct control of processes in order to get the results the align with the public interest.

Dispersion of a tracer on the East Pacific Rise (9°N to 10°N), including the influence of hydrothermal plumes

On 12 November 2006, 3 kg of sulfur hexafluoride were released in a 1.2 km long streak in the axial summit trough of the East Pacific Rise at 9°30′N to study how circulation and mixing affect larval dispersion. The first half of a tracer survey performed approximately 40 days after the injection found a small percentage of the tracer on the ridge axis between 9°30′N and 10°10′N, with the main concentration near 9°50′N, a site of many active hydrothermal vents. These observations provide evidence of larval connectivity between vent sites on the ridge. The latter half of the survey detected the primary patch of tracer west of the ridge and just south of the Lamont Seamounts, as a majority of the tracer had been transported off the ridge. However, by the end of the survey, the eastern edge of this patch was transported back to within 10 km of the ridge crest at 9°50′N by a reversal in the subinertial flow, suggesting another pathway for larvae between points along the ridge. Both the horizontal and vertical distributions of the tracer were complex and were likely heavily influenced by topography and vents in the area. Elevated tracer concentrations within the axial summit trough and an adjacent depression on the upper ridge flank suggest that tracers may be detained in such depressions. Correlated tracer/turbidity profiles provide direct evidence of entrainment of the tracer into vent plumes from 9°30′N to 10°N. A comparison of the vertical tracer inventory with neutral density vent-plume observations suggests that on the order of 10% of the tracer injected was entrained into vent plumes near the injection site. The results imply that effluent from diffuse hydrothermal sources and larvae of hydrothermal vent fauna can be entrained in significant quantities into plumes from discrete sources and dispersed in the neutrally buoyant plumes.

Shallow Submarine Hydrothermal Systems in the Aeolian Volcanic Arc, Italy

The majority of known high‐temperature hydrothermal vents occur at mid‐ocean ridges and back‐arc spreading centers, typically at water depths from 2000 to 4000 meters. Compared with 30 years of hydrothermal research along spreading centers in the deep parts of the ocean, exploration of the approximately 700 submarine arc volcanoes is relatively recent [de Ronde et al., 2003]. At these submarine arc volcanoes, active hydrothermal vents are located at unexpectedly shallow water depth (95% at &lt;1600‐meter depth), which has important consequences for the style of venting, the nature of associated mineral deposits, and the local biological communities.As part of an ongoing multinational research effort to study shallow submarine volcanic arcs, two hydrothermal systems in the submerged part of the Aeolian arc have been investigated in detail during research cruises by R/V Poseidon (July 2006) and R/V Meteor (August 2007). Comprehensive seafloor video surveys were conducted using a remotely operated vehicle, and drilling to a depth of 5 meters was carried out using a lander‐type submersible drill. This research has resulted in the first detailed, three‐dimensional documentation of shallow submarine hydrothermal systems on arc volcanoes.

Venting sites along the Fonualei and Northeast Lau Spreading Centers and evidence of hydrothermal activity at an off-axis caldera in the northeastern Lau Basin

The regional distribution of hydrothermal vent activity in the northeastern (NE) Lau Basin was recently reported by the Ridge 2000 program; however, active venting sources have yet to be located. Here, we report geological and hydrological evidence that indicates the presence of three active hydrothermal venting sources in the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC), the Northeast Lau Spreading Center (NELSC), and an off-axis caldera (MTJ-1). These examples of hydrothermal activity were recognized by the appearance of hydrothermal plume signals in the water column, including anomalies in light-transmission, methane, adenosine 5'-triphosphate (ATP), and trace metal concentrations (TDMn and TDFe). Three active venting sources were identified by the observation of possible buoyant plumes during conductivity-temperature-depth (CTD) tow-yo surveys and by the recovery of hydrothermal precipitates (chimneys and altered rocks). The strongest light-transmission anomaly, an order of magnitude greater than those at other sites, was observed at the central cone of the MTJ-1 caldera. The recovery of eruption debris at a central volcanic cone, including molten sulfur, volcanic ash, and lapilli, indicates an active volcanic eruption and hydrothermal venting at the MTJ-1 caldera. Our results suggest extensive and various hydrothermal activity in the NE Lau Basin, thereby providing valuable insight into hydrothermal and volcanic processes in back-arc environments.