[1] The InterRidge Vents Database is available online as the authoritative reference for locations of active submarine hydrothermal vent fields. Here we describe the revision of the database to an open source content management system and conduct a meta-analysis of the global distribution of known active vent fields. The number of known active vent fields has almost doubled in the past decade (521 as of year 2009), with about half visually confirmed and others inferred active from physical and chemical clues. Although previously known mainly from mid-ocean ridges (MORs), active vent fields at MORs now comprise only half of the total known, with about a quarter each now known at volcanic arcs and back-arc spreading centers. Discoveries in arc and back-arc settings resulted in an increase in known vent fields within exclusive economic zones, consequently reducing the proportion known in high seas to one third. The increase in known vent fields reflects a number of factors, including increased national and commercial interests in seafloor hydrothermal deposits as mineral resources. The purpose of the database now extends beyond academic research and education and into marine policy and management, with at least 18% of known vent fields in areas granted or pending applications for mineral prospecting and 8% in marine protected areas.

Brothers volcano, which is part of the active Kermadec arc, northeast of New Zealand, forms an elongate edifice 13 km long by 8 km across that strikes northwest-southeast. The volcano has a caldera with a basal diameter of ~3 km and a floor at 1,850 m below sea level, surrounded by 290-to 530-m-high walls. A volcanic cone of dacite rises 350 m from the caldera floor and partially coalesces with the southern caldera wall. Three hydrothermal sites have been located: on the northwest caldera wall, on the southeast caldera wall, and on the dacite cone. Multiple hydrothermal plumes rise ~750 m through the water column upward from the caldera floor, originating from the northwest caldera walls and atop the cone, itself host to three separate vent fields (summit, upper flank, northeast flank). In 1999, the cone site had plumes with relatively high concentrations of gas with a ∆pH of-0.27 relative to seawater (proxy for CO2 + S gases), dissolved H2S up to 4,250 nM, high concentrations of particulate Cu (up to 3.4 nM), total dissolvable Fe (up to 4,720 nM), total dissolvable Mn (up to 260 nM) and Fe/Mn values of 4.4 to 18.2. By 2002, plumes from the summit vent field had much lower particulate Cu (0.3 nM), total dissolvable Fe (175 nM), and Fe/Mn values of 0.8 but similar ∆pH (-0.22) and higher H2S (7,000 nM). The 1999 plume results are consistent with a magmatic fluid component with the concentration of Fe suggesting direct exsolution of a liquid brine, whereas the much lower concentrations of metals but higher overall gas contents in the 2002 plumes likely reflect subsea-floor phase separation. Plumes above the northwest caldera site are chemically distinct, and their compositions have not changed over the same 3-year interval. They have less CO2 (∆pH of-0.09), no detectable H2S, total dissolved Fe of 955 nM, total dissolved Mn of 150 nM, and Fe/Mn of 6.4. An overall increase in 3 He/ 4 He values in the plumes from R/RA = 6.1 in 1999 to 7.2 in 2002 is further consistent with a magmatic pulse perturbing the system. The northwest caldera site is host to at least two large areas (~600 m by at least 50 m) of chimneys and subcropping massive sulfide. One deposit is partially buried by sediment near the caldera rim at ~1,450 m, whereas the other crops out along narrow, fault-bounded ledges between ~1,600 and 1,650 m. Camera tows imaged active 1-to 2-m-high black smoker chimneys in the deeper zone together with numerous 1-to 5-m-high inactive spires, abundant sulfide talus, partially buried massive sulfides, and hydrothermally altered volcanic rocks. 210 Pb/ 226 Ra dating of one chimney gives an age of 27 ± 6 years; 226 Ra/Ba dating of other mineralization indicates ages up to 1,200 years. Formation temperatures derived from ∆ 34 Ssulfate-sulfide mineral pairs are 245°to 295°for the northwest caldera site, 225°to 260°C for the southeast caldera and ~260°to 305°C for the cone. Fluid inclusion gas data suggest subsea-floor phase separation occurred at the northwest caldera site. Alteration minerals identified include silicates, ...

Two-thirds of Earth's surface is formed at mid-ocean ridges, yet sea-floor spreading events are poorly understood because they occur far beneath the ocean surface. At 9 degrees 50'N on the East Pacific Rise, ocean-bottom seismometers recently recorded the microearthquake character of a mid-ocean ridge eruption, including precursory activity. A gradual ramp-up in activity rates since seismic monitoring began at this site in October 2003 suggests that eruptions may be forecast in the fast-spreading environment. The pattern culminates in an intense but brief (approximately 6-hour) inferred diking event on 22 January 2006, followed by rapid tapering to markedly decreased levels of seismicity.

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Submarine hydrothermal venting along mid-ocean ridges is an important contributor to ridge thermal structure, and the global distribution of such vents has implications for heat and mass fluxes from the Earth's crust and mantle and for the biogeography of vent-endemic organisms. Previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow-spreading ridges (ridges with full spreading rates <2 cm x yr(-1)-which make up 25 per cent of the global ridge length), and that such vent systems would be hosted in ultramafic in addition to volcanic rocks. Here we present evidence for active hydrothermal venting on the Gakkel ridge, which is the slowest spreading (0.6-1.3 cm x yr(-1)) and least explored mid-ocean ridge. On the basis of water column profiles of light scattering, temperature and manganese concentration along 1,100 km of the rift valley, we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites. Our discovery of such abundant venting, and its apparent localization near volcanic centres, requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow-spreading ridges.

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Although CO2 is generally the most abundant dissolved gas found in submarine hydrothermal fluids, it is rarely found in the form of CO2 liquid. Here we report the discovery of an unusual CO2‐rich hydrothermal system at 1600‐m depth near the summit of NW Eifuku, a small submarine volcano in the northern Mariana Arc. The site, named Champagne, was found to be discharging two distinct fluids from the same vent field: a 103°C gas‐rich hydrothermal fluid and cold (<4°C) droplets composed mainly of liquid CO2. The hot vent fluid contained up to 2.7 moles/kg CO2, the highest ever reported for submarine hydrothermal fluids. The liquid droplets were composed of ∼98% CO2, ∼1% H2S, with only trace amounts of CH4 and H2. Surveys of the overlying water column plumes indicated that the vent fluid and buoyant CO2 droplets ascended <200 m before dispersing into the ocean. Submarine venting of liquid CO2 has been previously observed at only one other locality, in the Okinawa Trough back‐arc basin (Sakai et al., 1990a), a geologic setting much different from NW Eifuku, which is a young arc volcano. The discovery of such a high CO2 flux at the Champagne site, estimated to be about 0.1% of the global MOR carbon flux, suggests that submarine arc volcanoes may play a larger role in oceanic carbon cycling than previously realized. The Champagne field may also prove to be a valuable natural laboratory for studying the effects of high CO2 concentrations on marine ecosystems.

Laboratory calibration of a beam transmissometer by using natural sedimentary particles fractionated into seven size classes demonstrates that slopes of light attenuation vs. particle mass concentration regressions systematically vary with the size distributions of the particles. Suspensions with a mean particle size of 8.5 μm attenuate 660‐nm light 15 times more efficiently than suspensions of similar particles with a mean diameter of 48 μm. Theoretical calculations of attenuation, based on scattering by spherical particles with the measured size distributions, underestimate observed attenuation by factors of 2–4, apparently because the nonspherical shape and roughness typical of natural particles create an effective optical diameter larger than that for a sphere of equal volume. These laboratory results agree with the trend established from a survey of published field data showing that calibration slopes experience a steady increase from inshore high‐energy waters, where large particles are common, to offshore low‐energy waters, where large particles are rare.