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CITATION Hammond, S.R., R.W. Embley, and E.T. Baker. 2015. The NOAA Vents Program 1983 to 2013: Thirty years of ocean exploration and research. Oceanography 28(1):160–173, http://dx.doi.org/​10.5670/​oceanog.2015.17.

DOI http://dx.doi.org/​10.5670/​oceanog.2015.17

COPYRIGHT This article has been published in Oceanography, Volume 28, Number 1, a quarterly journal of The Oceanography Society. Copyright 2015 by The Oceanography Society. All rights reserved.

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DOWNLOADED FROM HTTP://WWW.TOS.ORG/OCEANOGRAPHY REGULAR ISSUE FEATURE 1st 3D plume surveys Gorda Ridge eruption detected over a ridge 1st submarine 1st event Mariana Arc: 1st Ocean Exploration cruise Vents becomes 1986 Cleft 1st EPR eruption plume Earth-Ocean 1st US civilian eruption plume detected tracked 1st arc CO2 vents found 1st back-arc Interactions/ multibeam use verified survey (CoAxial) by float plume survey at NW Eifuku eruption detected Acoustics

1980 1985 1990 1995 2000 2005 2010 2015 1st forcast submarine Vents Megaplume (event Earth- MAPR 1st instrumented submarine 1st deep-sea eruption (Axial Smt.) Program plume) discovery quake program eruption (Axial Smt.) eruption begins monitoring begins observed in situ Ongoing submarine boninite begins NeMO begins eruption discovered 1st Juan de Fuca Ridge 1st Autonomous hydrophone side-scan/plume survey 1st quantification of gas flux The arrays deployed from a submarine volcano NOAA Vents Program 1983 to 2013

Thirty Years of Ocean Exploration and Research

By Stephen R. Hammond, Robert W. Embley, and Edward T. Baker

Eruption of Hades vent, West Mata seamount, taken by Jason remotely operated vehicle in 2009.

160 Oceanography | Vol.28, No.1 1st 3D plume surveys Gorda Ridge eruption detected over a ridge 1st submarine 1st event Mariana Arc: 1st Ocean Exploration cruise Vents becomes 1986 Cleft 1st EPR eruption plume Earth-Ocean 1st US civilian eruption plume detected tracked 1st arc CO2 vents found 1st back-arc Interactions/ multibeam use verified survey (CoAxial) by float plume survey at NW Eifuku eruption detected Acoustics

1980 1985 1990 1995 2000 2005 2010 2015 1st forcast submarine Vents Megaplume (event Earth- MAPR 1st instrumented submarine 1st deep-sea eruption (Axial Smt.) Program plume) discovery quake program eruption (Axial Smt.) eruption begins monitoring begins observed in situ Ongoing submarine boninite begins NeMO begins eruption discovered 1st Juan de Fuca Ridge 1st Autonomous hydrophone side-scan/plume survey 1st quantification of gas flux arrays deployed from a submarine volcano

ABSTRACT. Two seminal advances in the late 1970s in science and technology spurred non-classified multibeam bathymetric the establishment of the National Oceanic and Atmospheric Administration (NOAA) sonar on the Surveyor, one of NOAA’s Vents Program: the unexpected discovery of seafloor vents and chemosynthetic global-class research vessels. In 1980, ecosystems on the Galápagos Spreading Center (GSC), and civilian access to a previously NOAA’s National Ocean Survey (now classified multibeam mapping sonar system. A small team of NOAA scientists Service) began the first systematic, immediately embarked on an effort to apply the new mapping technology to the high-resolution bathymetric mapping of discovery of vents, animal communities, and polymetallic sulfide deposits on spreading seafloor spreading centers. At NOAA’s ridges in the Northeast Pacific Ocean. The addition of interdisciplinary colleagues Pacific Marine Environmental Laboratory from NOAA’s cooperative institutes at Oregon State University and the University (PMEL), interest in the Northeast Pacific of Washington led to the creation of the Vents Program in 1983 at NOAA’s Pacific ridges began with cruises of opportunity in Marine Environmental Laboratory. Within a decade, Vents surveyed the entire Juan 1980–1983 that mapped ridge axial mor- de Fuca and Gorda Ridges for hydrothermal activity, discovered the first “megaplume,” phology, petrology, and tectonic features established multiyear time series of hydrothermal fluid measurements, and, for the first (Malahoff et al., 1982; Fornari et al., 1983) time, acoustically detected and responded to a deep-sea volcanic eruption. With this and found evidence of hydrothermal vent- experience, and partnering with researchers from around the globe, Vents expanded ing in near-bottom waters (Massoth et al., to exploration along the East Pacific and GSC divergent plate boundaries. In 1999, 1982) over the Juan de Fuca and Gorda the Vents Program embarked on systematic surveys along volcanic arcs and back- Ridges (Figure 2). During a span of five arc basins of the Mariana and Kermadec-Tonga subduction zones. For three decades, years, NOAA systematically mapped the the Vents Program focused on understanding the physical, chemical, and biological Northeast Pacific ridges and their inter- environmental consequences of global-scale processes that regulate the transfer of heat vening fracture zones (e.g., Malahoff et al., and mass from Earth’s hot interior into the ocean. As the fourth decade began, the 1981). Relative to the best maps previously Vents Program was restructured into two new programs, Earth-Ocean Interactions and available, the new maps revealed intrigu- Acoustics, that together continue, and broaden, the scope of Vents’ pioneering ocean ing structural complexities. The spread- exploration and research. ing ridges were revealed as a series of off- set segments, and the fracture zones were INTRODUCTION an entirely unanticipated discipline. The found to have a multiplicity of fault zones The 1977 discovery of deep-sea hydro- GSC discoveries, along with the discov- and en echelon pull-apart basins. One of thermal venting and its associated ani- ery of “black smokers” on the East Pacific the most interesting discoveries was that mal communities (Corliss et al., 1979) Rise (EPR) in 1979, quickly became the of an 8 km × 3 km caldera at the summit changed, in a moment, the relationship impetus for collaborative national and of the large volcano that dominates one between researchers and the ocean floor. international studies of spreading centers of the four segments of the Juan de Fuca Before this discovery at the Galápagos throughout the world ocean, an excite- Ridge (JdFR). Now familiarly known as Spreading Center (GSC), marine geol- ment that continues unabated today Axial Seamount, it is the youngest in a ogists and chemists focused predomi- (Figure 1). In this article, we trace the string of large submarine volcanoes, the nantly on questions of broad spatial and three-decade development and impact of Cobb-Eickelberg Seamount Chain, which temporal scale: plate movements, crustal one program whose work spans almost extends westward onto the Pacific plate. properties, and sediment geochemis- the entire history of seafloor hydrother- In 1982, a collaborative expedition try. Within the span of a research cruise, mal discovery and research. between NOAA and academic research- the deep sea acquired a human dimen- Nearly concurrent with the GSC dis- ers surveyed the JdFR using a new deep- sion. Fundamental geological and bio- coveries, the National Oceanic and towed digital 30 kHz side-scan sonar logical processes could be studied during Atmospheric Administration (NOAA) system (Crane et al., 1985). Thermistor the range and duration of a single sub- and the Office of Naval Research had arrays suspended below the side-scan mersible dive. Marine biologists founded the prescience to install the first US unit detected several hydrothermal

Oceanography | March 2015 161 plumes along the ridge. This and other such as iron and sulfur compounds, included appreciable quantities of more information (e.g., Normark et al., 1982) global tracers such as 3He, and biolog- valuable elements, such as gold and silver. enabled discoveries of active hydrother- ically important gases such as carbon These discoveries provided an unam- mal systems along each of the surveyed dioxide (CO2), methane, and hydro- biguous opportunity for NOAA, estab- JdFR segments during the first Alvin sub- gen. Widespread scientific attention was lished with the overarching goal of being mersible dives in the Northeast Pacific in immediately focused on the chemosyn- the United States stewardship agency for 1984 (Figure 2). thetically and microbially sustained eco- Earth’s ocean. This responsibility requires systems that live exclusively in proximity an understanding of natural ocean pro- ESTABLISHING THE NOAA to both the warm and hot chemical-rich cesses and their effects on marine life and VENTS PROGRAM hydrothermal vent fluids. Another prom- resources, both biological and mineralog- Initial studies of the hydrothermal vent inent early interest in hydrothermal vents ical. Consequently, in 1983, NOAA estab- fluids sampled at the GSC and the EPR was the mineral resource potential of the lished the interdisciplinary team of ocean concluded that those discharges must often spectacular chimney-like structures scientists that soon became known as be pervasive along the global network and mounds that form when dissolved the Vents Program. (In an unusual break of seafloor spreading centers, and thus a metals in hot hydrothermal fluids pre- from government tradition, “Vents” has fundamental contributor to the ocean’s cipitate as they exit vent orifices. In addi- always been simply a descriptor, not an geochemical cycle (Edmond et al., 1979). tion to the usually predominant sulfides acronym.) Its mission was to systemat- These fluids introduce ocean nutrients of iron, copper, and zinc, some chimneys ically explore, discover, and, ultimately,

Mercator proj. 180° CM -140°W 180°W 140°E 0km 5000 Vents-Discovered Hydrothermal Sites km 1,000 InterRidge Hydrothermal Sites Database

70°N

70°N 60° N -40°W 0° 40°E NEP 1980-2013

30°N 2003- MA 2013 ° GSC EPR KTA 1991- 1999- 2011

-30° S0 2012 60° S

60°E 120°E 180° 120°W 60°W

FIGURE 1. Confirmed (visually) and inferred (from plume data) vent locations from the InterRidge database. About 50% (red circles) of all sites were discovered with National Oceanic and Atmospheric Administration (NOAA) Vents Program participation, and about half of those were found by var- ious collaborators using Vents Miniature Autonomous Plume Recorders (MAPRs) deployed on conductivity-temperature depth instruments (CTDs), dredges, rock cores, and other deep-towed instruments. The white boxes indicate regions and time intervals of long-term research interest for Vents. NEP = Northeast Pacific. GSC = Galápagos Spreading Center. EPR = East Pacific Rise. KTA = Kermadec-Tonga arc. MA = Mariana arc.

162 Oceanography | Vol.28, No.1 characterize the environmental impacts Faced with the task of finding ship-sized views of hydrothermal plumes could be of submarine volcanism and its associ- vent fields scattered along hundreds of imaged by steaming the NOAA Ship ated hydrothermal activity on the ocean kilometers of oceanic ridges using the Discoverer slowly forward above the at scales from local to global. traditional oceanographic method of axial zone of the Cleft segment of the With a mandate to build a pioneering “drilling holes in the water” with a CTD JdFR while winching a sensor package oceanographic exploration and research (conductivity-​temperature-​depth) sen- up and down in the bottom few hun- program, NOAA set about creating an sor package, the Vents explorers devel- dred meters of the water column (a now achievable and long-term program plan. oped a new technique. Two-dimensional widely used technique commonly known The core team consisted of geological, geo- physical, physical, and chemical ocean- ographers from PMEL, PMEL’s coopera- Hydrothermal tive institutes at Oregon State University Sites (active) (the Cooperative Institute for Marine CANADA Eruption Sites Resources Studies) and the University of Washington (the Joint Institute for the 50° N 0 (km) 200 Mercator projection Study of the Atmosphere and Ocean), Explorer <1000 Explorer Ridge Plate and NOAA’s Atlantic Oceanographic and Pacific Depth (m) Plate Meteorological Laboratory. Additionally, >3500 the program also initiated critical, MV long-standing partnerships with ocean scientists from universities and govern- USA mental agencies, foreign and domestic. Endeavour Recognizing the scale of its mission, e the Vents Program institutionalized sev- WA eral fundamental operating principals. CoAxial C as

One was the need to maintain an inter- c ad

disciplinary approach in which scientific i a

questions were to be designed by consen- Juan de Fuca S u

Plate b sus and studied using complementary Axial d

u

Volcano c tools. Because the objectives were aimed Juan de Fuca Ridg

ti at fundamental planetary-scale pro- o OR n 45° N Cleft cesses, the program required a phased, Z o

n

long-term (initially decadal, eventually e multidecadal) operational approach. And Blanco Fracture Zone finally, given the realities of governmental funding, it would be necessary to lever- age the available resources. In the first North decade, this strategy meant working in American the Northeast Pacific on NOAA vessels. Pacific Plate Plate Later, it meant building collaborations with National Science Foundation (NSF) investigators and international research- Gorda Ridge ers with access to their own ships and Gorda Plate other seagoing assets.

CA THE NORTHEAST PACIFIC: Mendocino Fracture Zone A NATURAL LABORATORY FOR 40° N MID-OCEAN RIDGE STUDIES 130°W 125°W In 1984, the new Vents Program began FIGURE 2. Northeast Pacific hydrothermal and submarine eruption sites. White stars are known systematically searching the water col- hydrothermal sites, more than half of which were discovered by Vents researchers. Red stars indicate umn above Northeast Pacific ridge axes submarine eruptions detected and verified by the Vents Program. Some sites (e.g., Axial Seamount for evidence of hydrothermal venting. and Endeavour Segment) have multiple sites that cannot all be resolved at the scale of the map.

Oceanography | March 2015 163 as a “tow-yo”; Baker et al., 1985). This been active for decades, were a hallmark the world (Baker et al., 2011). The erup- strategy greatly improved the efficiency of Vents and a key factor in the success tion hypothesis had been confirmed, but of hunting for new vent sites, which had of the program. a convincing explanation of how such previously depended on using geological immediate and immense transfers of evidence and intuition. Discovery of Megaplume heat and chemicals from crust to ocean The mineral potential of hydro- Leads to Research on Seafloor occur remains unknown (e.g., Rubin thermally emplaced sulfide deposits Volcanic Events et al., 2012). This transference remains an spurred interest in the Gorda Ridge. The In 1986, during a Vents survey for hydro- important gap in our understanding of a only North American spreading cen- thermal activity along the Cleft segment, fundamental Earth process: the creation ter within the newly created (1984) US scientists encountered an unanticipated of ocean crust by dike injections. Exclusive Economic Zone, Gorda Ridge hydrothermal plume some 20 km in Concurrently with geological map- was chosen for coordinated exploration diameter and more than 1 km thick. The ping at the eruption site (Figure 3c,d), and research by the Gorda Ridge Task signal was so unusual that the scientists Vents was building a unique multiyear Force, staffed by scientists from NOAA, on board initially thought their instru- database of plume and vent fluid chem- the United States Geological Survey, and ments were faulty! This, the first of a new istry to document changes that could be Oregon State University. In 1985, water class of plumes (Figure 4), was dubbed related to local geologic activity. A nine- column profiles, multibeam sonar map- a “megaplume” or “event plume” to dis- year time series (1983–1991) of vent ping, and dredging were used in one of the tinguish it from the familiar “chronic” and plume samples from the Cleft seg- first systematic geologic and hydrother- plumes caused by (more or less) steady- ment yielded the first estimates of annual mal investigations of an entire first-order state hydrothermal discharge. This ser- average flux of hydrothermal Mn and Fe (i.e., bounded by fracture zones) spread- endipitous discovery was hypothesized (Massoth et al., 1994). Four years of vent ing center segment. to result from a seafloor-spreading event, fluid sampling (1988, 1990–1992) by sub- Between 1984 and 1989, Vents that is, the magmatic injection of a verti- mersibles and remotely operated vehi- mapped the overall distribution of vent- cal dike of magma at the mid-ocean ridge cles (ROVs) yielded data indicating that ing on the entire JdFR with a series of and subsequent eruption of lava onto the the 1986 eruption caused a boiling event, along-axis tow-yos. New deep-tow side- seafloor (Baker et al., 1987; Lavelle, 1995). which released vapor-enriched fluids scan sonar vehicles provided the high- To test the eruption hypothesis, during through 1988 followed by a transition to est resolution seafloor imagery and 1987–1989, Vents deployed deep-towed brine-enriched fluids by 1990 (Butterfield resolved volcanic features such as lava camera surveys to search for recent lava and Massoth, 1994). This discovery was flows, fractures, faults, and craters. flows. Shiny black lavas devoid of sedi- the first report of major changes in vent Complementary finer-scale explorations ment, circumstantial evidence of a recent fluid composition over the time scale of used a deep-sea camera system designed eruption, were imaged. But had this erup- years (Figure 5). Over time, this system- and constructed by the Engineering tion occurred at the time of the event atic process of vent fluid evolution was Development Division of PMEL. This plume? Comparing the various cam- confirmed at other places where mag- advanced package included an inte- era and sonar tracks over the new lava matic events were discovered. grated CTD, real-time low-light video, a zone revealed another important puz- 35 mm film camera, and high-resolution zle piece—some patches of the new lava New Technology Leads to Event downward-looking and forward-looking imaged by the camera system were actually Detection and Rapid Response (obstacle avoidance) sonars (Figure 3a). small pillow lava mounds that appeared The event plume discovery was an The manned submersiblesPISCES IV on a few “swaths” of a 1987 multibeam important catalyst in creating a new per- and Alvin provided opportunities to fur- map but not on the original map com- spective on ridge-crest processes. Ridges ther ground truth the sonar imagery and pleted in 1982/1983 (Figure 3b). This were now seen as dynamic environments, collect samples for biologic and chemical evidence constrained the lava emplace- shaped not only by processes occur- analyses. During this period, Vents began ment to between 1983 and 1987, and thus ring on the time scale of seafloor spread- to develop a strong interdisciplinary strongly favored the eruption hypothe- ing but also over days. Consequently, team of collaborators, including special- sis (Chadwick et al., 1991). Since 1986, to fully understand the ocean environ- ists in basalt geochemistry, sulfide min- an additional 14 confirmed event plumes mental impacts of submarine volcanism eralization, gas chemistry, benthic ecol- have been observed at four separate erup- would require detection and observation ogy, and microbiology, to complement tion sites, (three in the Northeast Pacific of episodic volcanic events while they PMEL’s in-house expertise (Johnson and and one in the Northeast Lau Basin), with are active. Because of the detection lim- Embley, 1990; Embley et al., 1994). These less-​conclusive evidence for event plumes its of land-based seismometers, the small collaborations, a number of which have at as many as five other locations around earthquakes associated with submarine

164 Oceanography | Vol.28, No.1 FIGURE 3. Selected photos of seafloor sites and instruments used by the Vents Program. (a) Towed camera system with real-time imagery developed by NOAA Pacific Marine Environmental Laboratory (PMEL) engineers and used from 1987 to 1995 to map hydrothermal systems on Juan de Fuca Ridge. (b) Presumptive lava mounds from the 1986 North Cleft eruption, photo taken with Alvin’s still camera. (c) Vigorous black smoker (Pipe Organ vent) at North Cleft, taken with Alvin submersible still camera. (d) Eruptive fissure, North Cleft, taken with Alvin still camera 1988. (e) ROPOS remotely oper- ated vehicle (ROV) on deck of the NOAA Ship Discoverer, ~1992. (f) Vivid yellow microbial mats stained by iron precipitation, photographed by ROPOS about three weeks after an eruption in July 1993. (g) Black glassy lava from a 1996 Gorda Ridge eruption contrasts with older sediment-coated lavas, taken with Woods Hole Oceanographic Institution towed camera system. (h) First view of ASHES vent field on Axial Seamount, 1984 Alvin photograph. (i) Tubeworm field photographed in 1997 by ROPOS before its destruction during the 1998 eruption. (j) Pressure gauge and hydrophone package (VSM) stuck in 1998 lava flow, photographed by ROPOS. (k) El Guapo vent photographed by Jason ROV in Axial caldera; white color is from light reflected through boiling, vapor-rich fluids (~350°C). (l) One of the first observations of ash and gas plumes erupting from the submarine volcano NW Rota-1 (Mariana arc), photo by Jason ROV digital still camera. (m) Champagne vent with vigorous flow of supersaturated CO2 fluid and liquid CO2, NW Eifuku Seamount, Mariana arc, taken in 2004 by ROPOS digital still camera (DSC). (n) Thick carpet of iron-rich microbial mat being sampled from summit of NW Eifuku Seamount by ROPOS DSC in 2004. (o) Dense mussel beds near Champagne vent, NW Eifuku Seamount, taken in 2004 by ROPOS DSC. (p) Crab “fossilized” in elemental sulfur, Nikko Seamount, sampled by Jason ROV in 2006. (q) Five Towers vent field, shallowest black smoker (345 m) discovered to date, East Diamante Seamount, Mariana arc, ROPOS DSC photo 2004. (r) Explosive eruption of boninite lava at West Mata Seamount, NE Lau basin, Jason ROV photo, 2009. (s) A 360°C black smoker, Mata Ua Seamount, NE Lau basin, taken with QUEST 4000 ROV digital still camera in 2012. (t) Miniature Autonomous Plume Recorder (MAPR) on cable and close-up of the instrument.

Oceanography | March 2015 165 eruptions could only be detected by sub- observations that confirmed the presence the Northeast Pacific Ocean on NOAA marine hydrophones. In 1991, Vents was of an event plume (Figure 4). The era of vessels (Figure 3e). By 1993, ROPOS successful in its request to use military ridge-crest “detection and response” was ready for a challenge no one had hydrophone data, and in 1993, the data efforts had begun. expected: the first-ever submarine erup- began to be acquired in real time. Fortuitously, the CoAxial erup- tion detection and response cruise. Amazingly, in June 1993, only a week tion coincided with the availabil- The first dive at the CoAxial erup- after acquiring the real-time data link, a ity of a new seafloor asset. For almost a tion site immediately discovered a pris- swarm of earthquakes was detected on decade, Vents had depended primarily tine lava flow still venting warm water the CoAxial segment, a little known sec- on Alvin for conducting seafloor explo- (Figure 3f). The successful series of ROV tion of the JdFR (Fox, 1995). Over the ration and sampling. As Alvin’s avail- dives that followed demonstrated, for the next 23 days, more than 676 events of ability declined, Vents looked to alterna- first time, that a rapid-response cruise magnitude M ≤4 were recorded. During tive submarine vehicles, such as ROVs. offered a means for addressing previ- the course of the swarm, the locations A team of Canadian colleagues had pur- ously unknown global-scale processes of the events were observed to migrate chased a high payload, deep-diving ROV, and their impacts on ocean environ- to the north, presumably as magma was but did not have access to a suitable ves- ments. A follow-up expedition with NSF progressively intruded along the strike sel. In 1992/1993, Vents entered into a collaborators using Alvin then collected of the rift. A hastily arranged diversion partnership to help develop the vehicle, direct evidence of a subsurface micro- of an underway Canadian cruise while known as ROPOS (Remotely Operated bial biosphere in the upper portion of the seismic swarm was active provided Platform for Ocean Sciences), for use in the ocean crust, an idea long conceptual- ized (e.g., Deming and Baross, 1993) but scarce in support (Butterfield et al., 2004). Transect lines cross Access to real-time hydrophone data 1.5 South North East West was a singular technological advance >30 that led directly to the discovery and >90 the beginning of previously hypothe- >150 2.0 sized deep-ocean geological processes >210 (Dziak et al., 2007). Utilization of hydro- Depth (km) >270 phone data continues to the present and Dissolved Mn (nmol/L) 2.5 now also incorporates systematic efforts focused on detection and study of marine 1.5 >30 mammals (Mellinger et al., 2007). >90 The success of the CoAxial response >150 galvanized the ridge crest community 2.0 >210 to create a formal “time-critical stud- Depth (km) >270 ies” program. The NSF RIDGE Program Dissolved Fe (nmol/L) >330 2.5 committed to funding “rapid-response” efforts as soon as possible upon the detec- 1.5 >0.02 tion of the next eruption in the Northeast >0.06 Pacific. Vents agreed to provide ship time >0.10 and to provide the staging facility for sea- 2.0 >0.14 going gear. This agreement proved timely,

Depth (km) >0.18 as the next event was detected and located

Temperature anomaly (°C) >0.22 in February 1996 on the northern Gorda 2.5 Ridge, off southern Oregon (Figures 2 46°15’ 46°20’ 46°25’ 46°30’N 126°30’ 126°36°W Latitude along towpath Longitude and 3g). A large earthquake swarm trig- FIGURE 4. Juan de Fuca megaplumes. South-north and east-west perpendicular transects (verti- gered an event response that included cal black lines show their intersection points) of plume chemistry (dissolved Mn and Fe) and hydro- a week on the NOAA Ship MacArthur thermal fluid temperature anomalies mapped by CTD tows (paths shown by white lines in bottom and additional time on Oregon State panel) about two weeks after the 1993 eruption on the CoAxial segment of the Juan de Fuca Ridge. University’s research vessel Wecoma The plume chemistry was measured by a continuous in situ analyzer (SUAVE) developed at PMEL. (Cowen and Baker, 1998). Red bars near 46°32'N, 126°34'W denote the location of the 1993 lava flow. Two megaplumes (event plumes), rising approximately 1 km above the lava flow, were created by the eruption. Figure after A unique experiment conducted Massoth et al. (1995) during this response was the first

166 Oceanography | Vol.28, No.1 successful placement of a ballasted float The monitoring program at Axial of hydrothermal venting. This broader in an event plume (Lupton et al., 1998). Seamount, conducted by cruises and approach was necessary because hypoth- Tracking of the float enabled plume sam- with deployed instruments, continued eses formulated on the JdFR could not be pling only days after its inception and after the 1998 eruption. In 2011, just over tested without surveys and samples from then 60 days later. Negligible decay of the 13 years later, Axial Seamount erupted a globally diverse set of geological envi- plume occurred, suggesting that event again, this time forecast by continuing ronments. Three new exploration and plumes might have lifetimes on the order reinflation of the caldera (Chadwick et al., research fronts were identified: diver- of a year, permitting broad dispersal of 2012). Monitoring at Axial Seamount gent ridges of varying spreading rates, their entrained chemical and biological has a bright future because the summit the as yet unexplored submarine volca- cargoes. Other Vents studies of current has now been instrumented with a new nic arcs and back-arc ridges, and culti- and plume flow along seafloor spreading fiber-optic cable network and is part of vation of a global program by engaging centers provided insights into how phys- NSF’s Ocean Observatories Initiative. US and foreign colleagues and sharing ical oceanographic factors exert major Event responses occurred after several resources and data. influences on the dispersal of the larvae serendipitously discovered eruptions on of hydrothermal vent animals (Cannon other portions of the mid-ocean ridge, Divergent Plate Boundaries: et al., 1995; Lavelle et al., 2012). but the Northeast Pacific remains the The Effects of Varying only place on the deep seafloor where it Magmatic Budgets The First Instrumented has been feasible to detect, locate, and, To explore the influence of fluctuations Submarine Eruption at NeMO: most importantly, quickly respond to epi- in the magmatic budget on the distribu- The New Millennium Observatory sodic volcanic events when they occur tion and composition of hydrothermal Buoyed by successes in responding to (Baker et al., 2012). venting, Vents began to look for oppor- submarine eruptions, Vents next aimed tunities to work on the faster spreading at a more difficult task: gathering data EXPANSION TO A GLOBAL ridges of the EPR, where spreading rates before and during an eruption. Axial PERSPECTIVE vary from ~80 to 150 mm yr–1. Between Seamount, the most magmatically robust After a decade working on the JdFR, 1991 and 2005, Vents participated in four site on the JdFR, was chosen for this the Vents Program had developed tools cruises that strengthened the correlation effort (Figure 3h–k). After deploying and techniques to address a global view between spreading rate (or magmatic instruments on the seafloor during the 1996–1997 field seasons, the array was Time (years) christened NeMO (the New Millennium -1 0 2 4 6 8 Observatory), the world’s first in situ sub- Heat flux JdFR, N Cleft marine volcanic observatory. The wait for EPR, 9°N an eruption was breathtakingly short. In EPR,18°26'S late January 1998, a strong earthquake EPR,17°25'S swarm at Axial Seamount’s summit her-

alded the onset of a volcanic event (Dziak y Brine and Fox, 1999). A response cruise 18 days 2 S later on Wecoma sampled a large plume Decay / Cl Fe H2S over the caldera. Two moorings that sur- V Cl vived the eruption documented the for- 1 Vapor mation of a hydrothermal plume two Relative intensit hours after the first earthquake and min- Cl utes after the onset of caldera deflation Time (Figure 6). Remarkably, the instruments Event tracking deflation of the seafloor were par- FIGURE 5. The hypothetical response of hydrothermal discharge chemistry to a volcanic event, pro- tially engulfed in the lava, yet survived to posed by Butterfield et al. (1997). Immediately after an eruption, a vapor-rich, but low-chlorinity (Cl) record unique data (Figure 3j). An inno- phase produces high heat flux and a spike in dissolved Fe, followed some time later by a rise in 2H S vative engineering effort using ROPOS accompanied by a decline in Fe. After the vapor-phase is depleted, a brine-rich phase emerges, enabled recovery of the instruments. with increased Cl and Fe. Eventually the system decays to the pre-eruption chemistry. Cl measure- ments for a variety of eruption-affected vent fluids (cyan symbols) suggest a time scale of several Vents scientists had, for the first time, years duration for the vapor and brine phases (upper time scale), during which the ratio of vent fluid measured the geological and thermal Cl (Clv) to seawater Cl (Cls) can vary from <0.5 to almost 2 (right-hand scale) (D. Butterfield, NOAA, characteristics of a submarine eruption! pers. comm., 2014).

Oceanography | March 2015 167 budget) and the spatial density of venting ridge are more frequent, and thus per- confirmed at other ridges influenced by sites (Figure 7), and showed that plume haps smaller volumetrically, than those the Amsterdam-St Paul and Ascension chemistry was strongly influenced by the on more slowly spreading ridges (Urabe hotspots (Baker et al., 2008). The appar- magmatic state of a ridge segment. et al., 1995; Baker et al., 2002). The ent deficit in high-temperature venting Working with various US and for- 28°–32°S study also demonstrated the remains an enigma. eign colleagues between 1991 and 1998, first rigorous correlation between hydro- Vents explored for hydrothermal vent- thermal plumes and ridge areas where Convergent Plate Boundaries: ing on three cruises at fast-spreading axial inflation was relatively high and Arcs and Back-Arcs ridges: the northern EPR 8°40'–11°50'N fracture density was relatively low. These Through the first two decades of hydro- (100 mm yr–1), and the southern correlations suggested that hydrothermal thermal exploration, little attention was EPR at 14°–19°S and 28°–32°S (up to venting is most active where the apparent paid to sources on convergent mar- 150 mm yr–1). The northern EPR cruise magmatic budget is greatest, and recent gins, even though those plate boundar- occurred only six months after the 1991 eruptions have largely paved over the ies extend for some 23,000 km and host eruption, discovered during earlier Alvin pre-eruption fracture network. volcanic arcs, forearc rifts, and back- dives, and found that plumes in the vicin- To further the relationship between arc basin spreading ridges (Figure 1). ity of the eruption were derived from a venting and spreading rate (a proxy Hydrothermal discharge along volca- young, evolving hydrothermal system for the magmatic budget), Vents was nic arcs fundamentally differs from that

with high ratios of volatile components funded by NSF and the NOAA Office along mid-ocean ridges and1998 lava back-arc flow boundaries (such as hydrogen and hydrogen sulfide) of Exploration and Research (OER) to basin spreading centers 100min contourits reflection interval

1600 46°0' N 0(km)4 to heat and metals (Lupton et al., 1993). study an entirely different sort of mid- of the complex source historyTM proj. CM 130°of Wfluids This observation was important because ocean ridge, one where the magmatic arising from subduction zones. This vari-

1500 2000 it afforded a way to identify sites of budget is strongly increased because of ability notably 1500includes vent fields, con- 45°58' N on­going or recent eruptions by means of interaction with a mantle “hotspot.” This sideredVSM the1 best modern analogues of water column measurements. Cruises on cruise, in 2005/2006, and a follow-up volcanogenic massive sulfide deposits 97T41

the superfast-spreading EPR confirmed cruise in 2011, found that the GSC has currently1400 exploited on land, particularly VSM2 this finding. Areas with a high proportion significantly fewer high-temperature45°56' N vent the gold-rich97T42 variety. Additionally, hydro- of volatile-rich plumes coincided with sites than mid-ocean ridges with simi- thermal vent sites in volcanic arc settings the occurrence of recent magmatic activ- lar spreading rates, a characteristic first range from depths of thousands of meters

ity, implying that magmatic intrusions suggested by work along45°54' N the Reykjanes to the sea surface, thereby broadening the 0 and eruptions on a superfast-spreading Ridge (near the Iceland hotspot) and200 later reach of their environmental impact well

1400 45°52' N 1998 lava flow boundaries 100m contour interval 130°8'W 130°6'W 130°4'W 130°2'W 130°0'W 129°58'W 129°56'W 129°54'W

1600 46°0' N 0(km)4 3.2 TM proj. CM 130°W

3.0 Subsidence (m )

2000 1500 0 1500 2.8 1 45°58' N VSM1 2.6 2

Temperature (°C) 2.4

97T41 150 3 1400 VSM2 45°56' N 97T42 100

50 T-wave events/hr 45°54' N 0 0 200 1/22 1/26 1/30 2/3 2/7 2/11 2/15 Date (1998) 1400 45°52' N

130°8'W 130°6'W 130°4'W 130°2'W 130°0'W 129°58'W 129°56'W 129°54'W

3.2FIGURE 6. Seafloor deflation, near-bottom water temperature, and T-phase swarms recorded during the 1998 Axial eruption, the first submarine erup- tion monitored by in situ instrumentation. The map shows locations of volcanic system monitors (VSMs, red), temperature moorings (blue), and the black 3.0 Subsidence (m ) outline of the lava flow. The graph shows the numbers of earthquakes recorded as T-wave events (black line), the subsidence (deflation) of the seafloor 0 2.8(blue line), and the temperature signal (red line) during and following the eruption. 1 2.6 2

Temperature (°C) 2.4168 Oceanography | Vol.28, No.1 150 3

100

50

T-wave events/hr 0 1/22 1/26 1/30 2/3 2/7 2/11 2/15 Date (1998) beyond that typical of spreading ridges. back-arc spreading centers, and multi- to ~1% of that from all subaerial volca- In 1999, Vents teamed with the ple discrete volcanoes between the arc noes (Dziak et al., 2012a). New Zealand research institute GNS and back arc. During cruises between Another, non-erupting, volcano on the Science to conduct the first systematic sur- 2008 and 2012, Vents discovered at least Mariana arc, NW Eifuku, is also a major vey of the hydrothermal state of subma- 22 active hydrothermal systems, includ- CO2 source, venting a blizzard of liquid rine arc volcanoes. Only two submarine ing active eruptions on a back-arc ridge CO2 droplets directly from the seafloor arc volcanoes, both on the Izu-Bonin arc, (where event plumes were observed; (Lupton et al., 2006; Figure 3m–o). This had been previously sampled for vent flu- Baker et al., 2011) and at West Mata discharge provides an ideal laboratory for ids. The 1999 cruise covered only 260 km Volcano (Resing et al., 2011; Figure 3r,s), studying the effect of CO2 acidification on of the Kermadec arc, yet found seven of defining this area as perhaps the most the local ecosystem. Another completely 13 volcanoes to be hydrothermally active. concentrated region of volcanic activity unexpected discovery was pools of liq- As deduced from plume samples, the on the planet (Figure 3r,s). uid sulfur ringed by lush animal commu- arc volcanoes showed remarkable chem- The Vents Program’s work along vol- nities found on Daikoku and Nikko vol- ical diversity ranging from metal-rich canic arcs has provided glimpses into canoes of the Mariana arc and Macauley to gas-rich, demonstrating that volca- a diversity of seafloor volcanic activity Cone of the Kermadec arc. These pools, nic arcs could be an abundant, yet unex- far greater than seen along mid-ocean up to several meters in diameter, act as plored, source of hydrothermal discharge, ridges (Embley et al., 2008; Figure 3l–s). condensers of gases that derive from the chemosynthetic ecosystems, and mineral Eruptions lasting for years have been underlying magmas (de Ronde et al., resources (de Ronde et al., 2001). imaged and monitored at volcanoes on 2015). The volcanic vents beneath these Subsequent cruises conducted during the Mariana (NW Rota-1; Figure 3l; lakes provide a steady outflow of hot 2002–2007 along the Kermadec-Tonga Chadwick et al., 2008) and Tofua (West gases that continuously generate molten arc with New Zealand and Australian Mata; Embley et al., 2014) arcs (Figures 1 sulfur. Further exploration along other scientists and ships brought the total and 3r). Acoustic monitoring, visual interoceanic arcs and the longer length to 57 volcanic centers surveyed, 30 of observations, and plume sampling by (14,800 km) of island arcs (whose volca- which were found to be hydrothermally Vents at NW Rota-1 has led to the char- noes are largely subaerial) will ultimately active. These discoveries spurred Vents acterization of a submarine pyroclastic be needed to refine the global chemi- to begin exploration of the Mariana eruption (Chadwick et al., 2008; Figure 9) cal and thermal contribution of arcs, as arc (Figure 8), the second longest (after and the first estimate of annual CO2 sup- well as their role in the biogeography of Kermadec-Tonga) interoceanic arc ply from a submarine volcano, amounting vent-endemic animals. (Embley et al., 2007). Supported by

OER, in 2003 the first comprehensive 6 exploration of the Mariana arc covered 1,370 km and identified 76 volcanic edi- 5 fices grouped into 60 “volcanic centers,” including at least 26 (20 submarine) that are hydrothermally or volcanically 4 (#/100 km) active (Figures 3l–q and 8). Follow-up y cruises with ROV assets were conducted 3 between 2004 and 2010. Based on work in the Kermadec-Tonga and Mariana 2 arcs, Vents estimated that intraoceanic nt field frequenc

arcs could contribute ~10% of the global Ve 1 hydrothermal budget. Chemically, how- ever, the impact may be even more sig- 0 nificant. Many important volatile species, 0 20 40 60 80 100 120 140 160 –1 for example CO2, are often more highly Full spreading rate (mm yr ) concentrated in arc fluids than in mid- FIGURE 7. Scatter plot of vent field frequency, sF (number of vent fields per 100 km of ridge axis), –1 ocean ridge fluids (Lupton et al., 2008). versus spreading rate, us (mm yr ). Open squares give values for 20 ridge segments (335–2,060 km In 2008, Vents commenced explora- long). Colored diamonds show the average values from ridge segments binned in five spreading length categories (colored bars on rate axis) from ultra slow to superfast. Solid black line is the lin- tion of the northern Lau Basin, which ear regression fit of Fs = 0.85 + 0.021 us. Dashed curved lines enclose the 95% confidence intervals hosts the volcanically active Tofua arc for the slope. Vent field frequencies were determined from the InterRidge database, http://vents- (offset to the west from the Tonga arc), data.interridge.org (Beaulieu et al., 2013).

Oceanography | March 2015 169 Global Studies Complement crust spurred the long-term deployment until 2008. The region includes EPR, Site Studies of hydrophones in the equatorial Pacific, GSC, Middle America and Peru-Chile The successful monitoring of earth- piggybacking on ship time used to ser- trench systems, and the Easter and Juan quakes by Vents in the Northeast Pacific vice the NOAA equatorial buoy array Fernandez microplates. This effort was since 1993 and the emerging realization (Fox et al., 2001). The eastern equato- the first regional acoustic monitoring of that eruptions cause profound changes rial Pacific was continually monitored seafloor tectonic/volcanic activity, later in hydrothermal circulation within the by autonomous hydrophones from 1996 expanded to the northern Mid-Atlantic Ridge, Bransfield Strait (Antarctica), the northern Lau Basin, and the southern Vents-Discovered Indian Ocean (Dziak et al., 2012b). Hydrothermal Sites 24° N Vents has also participated in Other Hydrothermal Sites global programs to map the distribu- Back-arc Spreading Nikko Center tion of hydrothermal plumes on the Mariana T ocean-basin scale. Beginning in the 0km200 Transverse mercator proj. 1970s, the Geochemical Ocean Sections CM 145°E rench Study (GEOSECS) and World Ocean 22° N Circulation Experiment (WOCE) pro- NW Eifuku grams used 3He measurements to map Daikuku hydrothermal plumes. These plumes identify sources of concentrated and persistent volcanic activity and provide Maug insight into patterns of ocean circulation 20° N and mixing. In the Pacific, plumes thou- Philippine Plate sands of kilometers long emanate from

W the EPR between 10°N and 20°S, the

est Mariana Ridge Backarc Basi JdFR, Loihi Seamount in the Hawaiian

Mariana Islands, and the northern end of the Lau 900 0 Basin (Lupton, 1998). In 2013, another

18° N −1000

Arc global program, GEOTRACES, resam- −2000 3 −3000 pled the He plume that spreads west- −4000 n −5000 ward from the EPR at ~15°S to mea- −6000 sure concentrations of trace metals. Depth (meters) −7000 Resing et al. (in press) unexpectedly found that hydrothermal dissolved iron,

16° N E Diamante −10900 manganese, and aluminum travel west- ward in 3He-enriched plumes for at least 4,000 km across the South Pacific. Using the ratio of dissolved iron to 3He appli- NW Rota-1 cable to mid-ocean ridge hydrothermal emissions, the estimated global hydro- 14° N thermal 3He flux of 530 mol yr–1 yields –1 Guam an iron input of 4 Gmol yr to the ocean interior, or ~20% of the riverine supply. No individual laboratory possesses the resources to fund a global explora- tion program. Vents interest in explor-

12° N Mariana Trench Pacific Plate ing ridge and volcanic arc sections around the world depended upon collab-

142°E 144°E 146°E 148°E orations with US and foreign research- ers. In the mid-1990s, Vents recognized FIGURE 8. Subaerial and submarine volcanoes along the Mariana arc. Islands are solid green shading. White stars are hydrothermal sites discovered by the Vents Program during the period another untapped resource: vessels work- 2003–2006. Red stars are other hydrothermal sites. ing along ridges and arcs (e.g., collecting

170 Oceanography | Vol.28, No.1 petrological samples) but not collect- private organizations such as the Ocean of seafloor environments and their liv- ing data in the water column. PMEL Exploration Trust and the Schmidt Ocean ing and nonliving resources. Over the Engineering developed a simple plume Institute. New technologies already on past decade, for example, collaborative sensor, the Miniature Autonomous Plume the horizon hold the promise of dramat- exploration in the Mariana arc, located Recorder (MAPR; Figure 3t), which ically improving subsea navigation and within the United States Exclusive allows any researcher using any wire low- long-term autonomy of subsea vehicles, Economic Zone, revealed an unexpected ered to the seafloor—such as rock cores, making large-scale exploration of the myriad of diverse ecosystems and signif- dredges, side-scan sonars—to explore for ocean more practical, and diminishing icant submarine sources of CO2, all pro- hydrothermal activity at no cost to the pri- the traditional reliance on surface ships. duced and sustained by volcanic activity. mary cruise objectives. Since then, some Beyond science and the promise of These discoveries fostered establishment 50 partners in the United States and nine new technologies, it will be essential for of the Mariana Trench Marine National foreign countries have conducted over governments to provide wise stewardship Monument in 2009. Without a doubt, 100 cruises using MAPRs supplied and maintained by PMEL. These cruises have collected data in every ocean by means Hi of some 2,000 vertical profiles and along 300 14,000 km of towed track line, creating new collaborations to expand the reach 200 of hydrothermal research (Figure 1). Frequency (Hz) About one-quarter of all the vent loca- 100 tions in the InterRidge database (http:// vents-data.interridge.org) were discov- 0 Lo ) ered using MAPRs. 4 3

A LOOK TO THE FUTURE 0 Seafloor research during the past three

Amplitude (x 10 –3 decades has produced many, often star- 010 20 30 tling, discoveries. Still, we remain at the Time (minutes) threshold of understanding how Earth’s c most widespread and prevalent volca- nic activity affects the physical, chemical, ab d and biological environments of the global ocean. Sadly, the ocean remains largely unexplored in both space and time, despite the fact that it makes life on Earth possible. New technologies, especially autonomous sensors and sampling sys- tems, are needed to acquire knowledge of critical ecosystems before environmental changes occurring in many ocean regions overtake our ability to respond to or mit- igate them. Bringing the value and excite- ment of ocean exploration and research to the public, to educators, and to the worldwide community of ocean scientists FIGURE 9. Submarine eruption at NW Rota-1 Seamount, Mariana arc. (top) Hydrophone data during is an urgent task. an active eruption in 2006. Data displayed as both a time series (in digital units, bottom) and NOAA has begun this task by ini- spectrogram (in frequency, top). (bottom) Diagrammatic model for the eruptive activity observed tiating a science and technology col- at NW Rota-1 in 2006 (red = magma. White = magmatic gases. Blue = seawater. Black = solidified laboration between PMEL and OER. lava. Gray = older lavas). (a) Between bursts, seawater cools the top of the magma column, forming a solidified cap. (b) When the next gas-rich pocket reaches the cap, it immediately starts to escape. Extramural collaborations include excit- (c) The gas pocket forces the lava cap upward in the vent where explosions destroy it. (d) With the ing opportunities with NSF, NASA, the vent uncapped, the eruptive burst proceeds at a higher level until all the gas in the pocket is vented Navy, NOAA Cooperative Institutes, and and the activity abruptly ceases, returning to the initial state. Figure from Chadwick et al. (2008)

Oceanography | March 2015 171 other places and processes yet to be dis- H. Milburn and C. Meinig were the principal engineer- possible relationship to recent volcanism. Journal ing leads for the Vents Program’s many technical inno- of Geophysical Research 99:4,951–4,968, covered will have similar, or even greater vations. A multitude of organizations, programs, agen- http://dx.doi.org/10.1029/93JB02798. import, and will therefore stand in need cies, and universities, both domestic and international, Butterfield, D.A., K.K. Roe, M.D. Lilley, J. Huber, also provided intellectual and material support that J.A. Baross, R.W. Embley, and G.J. Massoth. 2004. of informed governance. directly contributed to the success of Vents. We are Mixing, reaction and microbial activity in sub-sea- In its fourth decade, the Vents especially grateful for long-term support of the NOAA floor revealed by temporal and spatial variation in Office of Ocean Exploration and Research and NSF. diffuse flow vents at Axial Volcano. Pp. 269–289 Program is also evolving to address such Thanks are due as well to the crews of the ships of in The Subseafloor Biosphere at Mid-Ocean challenges. In place of a single program, the NOAA and UNOLS fleets as well as those of our Ridges. W.S.D. Wilcock, E.F. DeLong, D.S. Kelley, international partners. Without all of these assets, we J.A. Baross, and S.C. Cary, eds, Geophysical Vents has been restructured and repur- would not have been able to make the sustained year- Monograph Series, vol. 144, American Geophysical posed through division into two dis- to-year observations that are at the scientific heart of Union, Washington, DC. the program. This paper was materially improved by Cannon, G.A., D.J. Pashnski, and T.J. Stanley. tinct but complementary programs. An the reviews of R. Koski, M. Perfit, and V. Tunnicliffe. 1995. Fate of event hydrothermal plumes Acoustics Program continues broad-scale Financial support for the paper was supplied by NOAA’s on the Juan de Fuca Ridge. Geophysical Office of Ocean Exploration and Research and NOAA’s Research Letters 22:163–166, http://dx.doi.org/​ monitoring of ocean seismic events, nat- Pacific Marine Environmental Laboratory (S.R.H.), 10.1029/94GL02280. ural and anthropogenic ocean noise, and NOAA’s Earth-Ocean Interactions Program (R.W.E.), Chadwick, W.W. Jr., K.V. Cashman, R.W. Embley, and the University of Washington’s Joint Institute for H. Matsumoto, R.P. Dziak, C.E.J. de Ronde, T.K. Lau, marine mammal distributions. An Earth- the Study of the Atmosphere and Ocean through N.D. Deardorff, and S.G. Merle. 2008. Direct video Ocean Interactions Program builds on NOAA Cooperative Agreement NA10OAR4320148 and hydrophone observations of submarine explo- (E.T.B). S. Merle and K. Birchfield provided graphics sive eruptions at NW Rota-1 Volcano, Mariana Arc. the foundation of Vents pioneering sub- support for many of the paper’s figures. Journal of Geophysical Research 113, B08S10, marine volcanic exploration and research This is PMEL contribution 4214, and JISAO contri- http://dx.doi.org/10.1029/2007JB005215. bution 2321. Chadwick, W.W. Jr., R.W. Embley, and C.G. Fox. 1991. and continues to address both natu- Evidence for volcanic eruption on the south- rally occurring processes and those that REFERENCES ern Juan de Fuca ridge between 1981 and 1987. Nature 350:416–418, http://dx.doi.org/​ Baker, E.T., W.W. Chadwick Jr., J.P. Cowen, R.P. Dziak, impact the ocean environment as a con- 10.1038/350416a0. K.H. Rubin, and D.J. Fornari. 2012. Hydrothermal Chadwick, W.W. Jr., S.L. Nooner, D.A. 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Deep-Sea Research Part II 45:2,503–2,511, Hydrothermal venting along Earth’s fastest spread- resulted in international recognition of their discover- http://dx.doi.org/10.1016/S0967-0645(98)00080-0. ing center: East Pacific Rise, 27.5°–32.3°S. Journal ies and scientific breakthroughs. Crane, K., F. Aikman, R. Embley, S. Hammond, of Geophysical Research 107(B7), http://dx.doi.org/​ We are especially grateful for the efforts of indi- A. Malahoff, and J. Lupton. 1985. The distribution 10.1029/2001JB000651. viduals with whom we worked for a decade or more: of geothermal fields on the Juan de Fuca Ridge. Baker, E.T., J.W. Lavelle, and G.J. Massoth. 1985. PIs include D. Butterfield, G. Cannon, W. Chadwick, Journal of Geophysical Research 90(B1):727–744, Hydrothermal particle plumes over the south- R. Dziak, R. Feely, C. Fox, W. Lavelle, J. Lupton, http://dx.doi.org/10.1029/JB090iB01p00727. ern Juan de Fuca Ridge. Nature 316:342–344, G. Massoth, H. Matsumoto, J. Resing, and P. Rona. 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