U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications
Even before the discovery of submarine hydrothermal vents in 1977 [Corliss et al., 1979] and 1979 [RISE Project Group, 1980], a few investigators had recognized large-scale physical and chemical anomalies that were rightly attributed to hydrothermal discharge. Over 30 years ago, Knauss [1962] suggested that abnormally warm water between 3000 and 3500 m over the East Pacific Rise (EPR) near 20°S was probably related to a recently mapped zone of high seafloor heat flow in the same area [Von Herzen, 1959]. Ten years later, Warren [1973] noticed the same feature in data from the SCORPIO expedition at 28°S and 43°S, although he was reluctant to attribute the anomaly to geothermal effects since purely oceanographic effects might also lead to the same temperature distribution. Lonsdale [1976] made perhaps the earliest attempt to quantify the temperature anomaly of a hydrothermal plume when he plotted temperature-salinity curves of profiles west, east, and directly over the EPR at 8°S. The axial stations revealed near-bottom temperature increases of several hundredths of a degree Celsius relative to off-axis water of the same salinity (Figure 2).
Fig. 2. Plot of potential temperature vs. salinity for discrete samples near the East Pacific Rise at 8°S showing hydrothermal heating at the rise crest (reprinted from Lonsdale [1976]).
Measurements of the helium isotopes 3He and 4He in the Kermadec Trench [Clarke et al., 1969] and across the EPR [Craig et al., 1975] provided early evidence that hydrothermal venting could produce widely dispersed chemical anomalies. Shortly thereafter, sampling near the Galapagos Ridge by Klinkhammer et al. [1977] and Bolger et al. [1978] showed that hydrothermal plumes also contain significant anomalies of dissolved and particulate Mn. Since then, plume surveys have contributed to the discovery and characterization of hydrothermal discharge sites on ridges and hotspots throughout the oceans and marginal seas.
Hydrothermal plumes have been mapped in more detail over eastern Pacific ridge
crests than anywhere else in the ocean. Virtually continuous surveys of plume
hydrographic, optical, and/or chemical anomalies have been conducted along much
of the Explorer-Juan de Fuca-Gorda Ridge complex in the northeast Pacific, in
the Gulf of California, and along the EPR from about 9° to 13°N and 13° to 22°S.
Full-rate spreading speeds at these sites range from a medium rate of
Fig. 3. Location map for northeast Pacific spreading centers.
The Explorer-Juan de Fuca-Gorda Ridge complex is an isolated set of spreading
ridges that extend for almost
Plumes emanating from the JDFR have been mapped more intensively and extensively
than those over any other group of ridge-crest segments in the ocean. The first
indication of JDFR hydrothermal plumes came in 1980 from observations of dissolved
Mn [Jones
et al., 1981] and 3He [Lupton,
1990] at five widely spaced stations stretching from 44°31'N to 47°47'N.
In 1982, Crane
et al. [1985] conducted the first large scale, continuous survey of
hydrothermal plumes anywhere on the global midocean ridge (MOR). They attempted
to measure hydrothermally induced temperature anomalies in plumes by hanging
a 50-m-long thermistor chain from a side-scan sonar vehicle while towing it
along the entire JDFR. Their measurements were successful in identifying a few
major thermal anomalies but did not fully reveal the actual plume distribution
because of calibration problems and the very slow
Plume mapping on the JDFR has focused on three areas: the Endeavour segment,
Axial Volcano, and the Cleft segment (Figure 3).
Along the Endeavour segment, Baker
and Massoth [1987] and Thomson
et al. [1992] used transects of temperature and light attenuation anomalies
to characterize the plume and discover vent locations. They combined these anomalies
with concomitantly collected records of plume advection from moored current
meters to estimate mean heat fluxes of 1700 ± 
800 MW
Fig. 4. CTD tow-yo transects of hydrothermal temperature anomaly (°C) along
the Cleft segment axial valley, 1986-1991. Triangles show location of known
venting sites. The lower half of event plume EP86 ("megaplume") is
apparent in the 1986 transect. The anomaly at
The plume distribution over the entire Cleft segment has been mapped one or
more times every year since 1986 [Baker
and Massoth, 1986; Baker
and Massoth, 1987; Baker,
1994], making it a unique source of information about the temporal variability
of hydrothermal venting. Discharge from the Cleft segment is concentrated in
two areas centered at 44°38'-44°43'N and 44°54'-45°N (Figure
4). The first plume survey to estimate hydrothermal fluxes was conducted
at the southern site in 1985 [Baker
and Massoth, 1986; 1987],
finding a heat flux of 580 ±
Fig. 5. (A) Cross-section of EP86 and underlying chronic plume (reprinted
from Baker
et al. [1989]). Contours are isolines of hydrothermal temperature anomaly
(°C). Potential density
Fig. 6. (A) Cross-sections of two event plumes mapped over the CoAxial segment in July, 1993 [Baker et al., 1995]. Both plumes were smaller and had lower temperature anomalies than EP86 or EP87. (B) Plan view of all three CoAxial event plumes showing their relative locations when first discovered. EP93A and EP93B were found directly over the lava eruption mound (solid bead) and warm-water fissure (heavy line) near 46°30'N. EP93C was found two weeks after EP93A and EP93B; its discharge site is unknown.
The Cleft segment time series is proving especially useful in revealing the
linkage between hydrothermal and magmatic activity, because it began simultaneously
with the observation of a new class of plume phenomena: "event plumes."
In 1986, Baker
et al. [1987b] discovered a "megaplume" at the northern end
of the Cleft segment (Figure 5). Analysis of
this and a second megaplume found over the Vance segment in 1987 [Baker
et al., 1989; Gendron
et al., 1993] demonstrate that event plumes are near-instantaneous releases
of enormous volumes of hydrothermal fluid; about
Fig. 7. Summary of hydrothermal temperature anomalies observed along the
crest of the Juan de Fuca Ridge, including Axial Volcano, from 1985 to 1989.
For clarity, segments and the overlying plumes are displayed individually, without
overlap. Triangles show location of known venting sites. Anomalies at the northern
end of the Cobb segment, 47.4°-47.6°N, are believed to mark an intrusion of
geothermally heated bottom water from Cascadia Basin to the east, rather than
axial hydrothermal heating (reprinted from Baker
and Hammond [1992]). Significant hydrothermal plumes 
0.02°C)
In addition to intensive work along the Cleft segment and at other specific sites, the NOAA/VENTS Program also undertook to survey, at least once, as much of the entire JDFR as feasible. As of 1989, about 90% of the ridge from the Cleft to Endeavour segments had been surveyed at least once, and more than 50% at least twice, by a continuous tow-yo transect. The goal of this program was to test the hypothesis that the distribution and intensity of hydrothermal activity are directly related to the variable magmatic budget along the ridge. Baker and Hammond [1992] reported that hydrothermal discharge is strongest on those segments, or portions of segments, where the apparent magmatic budget is highest, as indicated by the degree of along-axis inflation or other morphological characteristics (Figure 7).
Fig. 8. Location map for East Pacific Rise spreading centers. Solid circles indicate locations of axial discontinuities.
Three areas on the EPR, one medium (Gulf of California,
Fig. 9. A 
(3He) section through
the Gulf of California showing evidence of hydrothermal venting in the Guaymas
Basin (reprinted from Lupton
[1979]). Triangle shows location of known venting sites in the Guaymas Basin.
The Gulf of California is a series of en echelon spreading centers opening
at 50-60 mm yr-1 and creating a string of deep, semi-enclosed basins
(Figure 9). Helium isotope profiles in each of
the six major basins [Lupton,
1979] imply that only Guaymas Basin, with
(3He) values of 65-70% ((3He)
=
Plumes over the fast-spreading section of the EPR between 8° and 13°N have been systematically studied since at least 1983. Crane et al. [1988] used the same techniques employed by Crane et al. [1985] on the JDFR to identify perturbations in the temperature field between 8°20' and 13°10'N along the ridge crest, but the results were similarly compromised by the equipment used. This same area has since been resurveyed in detail, by Dynamic Hydrocast and CTD casts from 12°08' to 13°12'N in 1986 [Bougault et al., 1990; Charlou et al., 1991b], and by CTD/transmissometer tows and casts from 8°40' to 11°50'N in 1991 [Lupton et al., 1993; Baker et al., 1994; Feely et al., 1994; Mottl et al., 1995]. These studies precisely mapped the distribution of hydrothermal plumes along the ridge crest, revealing a fine-scale agreement between hydrothermal activity and the apparent magmatic budget, as inferred from ridge morphology and subsurface structure [Bougault et al., 1990; Baker et al., 1994].
Fig. 10. Transects of methane and dissolved manganese along the East Pacific Rise determined from three Dynamic Hydrocast tows [after Bougault et al., 1990]. Connected triangles show area of known venting sites.
Fig. 11. Transects of light-attenuation anomaly (continuous tow-yo) [Baker
et al., 1994], dissolved Mn, and CH4 (both from discrete
samples) [Mottl
et al., 1995] obtained in November 1991 along the East Pacific Rise
south and north of the Clipperton Transform Zone. Contour intervals are
Between 12°08' and 13°12'N, Bougault
et al. [1990] and Charlou
et al. [1991b] found plumes with dissolved Mn >10 nmol kg-1and
CH4
Plume sampling on the southern EPR has been concentrated along the superfast-spreading
Fig. 12. Tow-yo transects of light attenuation along the East Pacific Rise
just south of the Garrett Transform Zone [Baker
and Urabe, 1994]. Nephelometer data are combined from five tow-yos,
comprising >1000 vertical profiles. Contour interval is 
0.02 m-1
The first large-scale plume survey in this area was completed in 1993 by the
Japanese-NOAA Ridgeflux Expedition using detailed chemical sampling and nearly
continuous CTD/SUAVE/optical tow-yos between 13°50' and 18°40'S [Urabe
et al., 1994; Baker
and Urabe, 1994; Massoth
et al., 1994; Ishibashi
et al., 1994; Feely
et al., 1994; Lupton
et al., 1994]. Preliminary analyses show that hydrothermal plumes covered
~60% of the entire study area (Figure 12). Plumes
were most common south of ~16°30'S, becoming virtually continuous between 17°20'
and 18°40'S. The southern portion of the study area was also characterized by
CH4/Mn ratios as high as 3.9, particulate S/Fe ratios >1, and
Fe/Mn ratios >8. Similarly high CH4/Mn and S/Fe ratios were found
in 1991 in plumes at 9°50'N on the EPR [Lupton
et al., 1993],
The western boundary of the Pacific Ocean is a broad expanse of marginal basins and troughs fragmented by trench-arc systems that mark subduction zones of several tectonic plates [Taylor and Karner, 1983] (Figure 13). Many of these basins contain active spreading centers that likely host hydrothermal activity. Systematic though limited plume sampling has been conducted in the Harve Trough, Lau Basin, North Fiji Basin, Woodlark Basin (Solomon Sea), Manus Basin (Bismark Sea), Mariana Trough, and Okinawa Trough.
Fig. 13. Location map for western Pacific marginal basins. Thin lines are fracture zones, thick lines are spreading centers, and triangled lines are convergent plate edges. 1, Harve Trough; 2, Lau Basin/Valu Fa Ridge; 3, North Fiji Basin; 4, Woodlark Basin; 5, Manus Basin; 6, Mariana Trough; 7, Okinawa Trough.
The 1986 Papatua Expedition [Craig and Poreda, 1987] occupied four hydrocast stations in the Harve Trough, five in the Lau Basin, and three in the Woodlark Basin. Only weak to negligible hydrothermal indications were found in each basin. Subsequent seafloor explorations in the Lau [Fouquet et al., 1991] and Woodlark [Binns et al., 1993] basins, however, have discovered active hydrothermal sites, indicating that sampling during the Papatua Expedition was too sparse to adequately survey these large basins.
Fig. 14. Transects of methane and dissolved Mn along the central spreading
axis in the North Fiji Basin. Data compiled from published and unpublished sources
(see text) spanning several years. Note that the data base is not identical
for each tracer. Contour intervals are
Plumes in the North Fiji Basin have been sampled more intensively than in any
other back-arc basin. Geophysical surveys [Auzende
et al., 1994] indicate two north-south spreading axes: a medium-rate
(3He)
maximum of 71%, confirming its magmatic origin [Craig
et al., 1987]. Nojiri
et al. [1989] interpreted as an event plume a strong plume
Fig. 15. Transects of methane and manganese collected in 1990 along the spreading center in the eastern Manus Basin (reprinted from Gamo et al. [1993] with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington OX5 16B, UK). The Papatua Expedition [Craig and Poreda, 1987] collected samples near stations 37 and 29. Triangle shows location of known venting sites.
The Manus Basin is a fast-spreading (3He) maximum of 58%. The
Papatua Expedition also found CH4 anomalies over the southern ridge,
which was sampled more extensively by Gamo
et al. [1993] in 1990. Gamo
et al. [1993] mapped multiply layered CH4 and Mn plumes between
1000 and
Farther to the north, plumes have been mapped in the Okinawa and Mariana Troughs.
In the Okinawa Trough, a relatively shallow basin behind the deep Ryukyu Trench,
strong CH4, Mn, and 3He (up to a (3He)
of 65%) anomalies at depths between 1300 and 1600 m were found in 1987 [Ishibashi
et al., 1988] and 1988 (J. Ishibashi, personal communication, 1994).
Horibe
et al. [1986] occupied a series of hydrocasts between 18°11'N and 18°15'N
in 1982 in the Mariana Trough, mapping CH4 plumes near-bottom and
700-
Unlike fast-spreading ridge axes such as the EPR, the neovolcanic zone of the
slow-spreading MAR (Figure 16) sits not at a
narrow axial high, but within a broad (5-
Fig. 16. Location map for the northern Mid-Atlantic Ridge and Reykjanes Ridge. Known and suspected hydrothermal sites identified in Figure 19.
Fig. 17. Along-axis maxima in total reactive (~dissolved) Mn [Klinkhammer et al., 1985] and CH4 [Charlou and Donval, 1993] from vertical casts on the Mid-Atlantic Ridge. High values in parentheses at 26°N and 29°N are representative samples over the TAG [Klinkhammer et al., 1986] and Broken Spur [Elderfield et al., 1993] hydrothermal fields, respectively. Thin dashed line on each plot marks the regional background value of Mn and CH4.
Until 1984 it was widely predicted that hydrothermal activity might be restricted to fast-spreading ridges and that at slow-spreading ridges, such as the MAR, heat flow would be insufficient to support active high-temperature black smoker vent fields. It is now clear that this is not the case. In 1984, Klinkhammer et al. [1985] carried out systematic discrete sampling and shipboard Mn analysis of seawater samples from stations occupied throughout the MAR rift valley between 11°N (the Vema Fracture Zone) and 26°N (Figure 17). Nine discrete segments were occupied during this survey and dissolved Mn anomalies--interpreted as the product of active hydrothermal venting--were found at every station. As a conservative estimate, Klinkhammer et al. [1985] concluded that a minimum of at least five discrete hydrothermal fields must characterize this section of the MAR.
Fig. 18. Geochemical plume transect for total reactive Mn at the TAG hydrothermal site in 1985 (reprinted from Klinkhammer et al. [1986] with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kiddington 0X5 16B, UK). Solid circles indicate sample positions.
These predictions were confirmed in 1985 when a series of CTD-nephelometer hydrocasts (Figure 18) and deep-tow video camera deployments confirmed the first active black-smoker hydrothermal field at the northernmost station occupied by Klinkhammer et al. [1985], the TAG hydrothermal field at 26°N [Rona et al., 1986]. In 1986, black-smoker hydrothermal venting was also found at the Snakepit hydrothermal field at 23°N [Ocean Drilling Program Leg 106 Scientific Party, 1986], close to where Klinkhammer et al. [1985] had reported water column dissolved Mn anomalies.
Between 1985 and 1988 another series of cruises mapped the distribution of CH4 between 12° and 26°N [Charlou and Donval, 1993] (Figure 17). High CH4 concentrations were found over the TAG and Snakepit sites, as well as the 15°20' fracture zone. Because of very low Mn in the plumes near the 15°20' fracture zone, and the occurrence of local outcrops of serpentinized ultrabasic diapirs, Charlou and Donval [1993] hypothesized that CH4 anomalies there arise from fluid circulation in ultrabasic rocks rather than basalt-seawater interactions typical of faster-spreading ridges. The changes of mechanical properties and density caused by the serpentinization of deep crustal rocks, as inferred from these CH4 anomalies, may play an influential role in the construction of slow-spreading ridges [Charlou et al., 1991a; Charlou and Donval, 1993; Bougault et al., 1993].
Fig. 19. Summary of evidence for hydrothermal venting along the Mid-Atlantic Ridge compiled from water-column investigations between 11° and 40°N [German et al., 1995]. Only four segments or segment portions have confirmed active venting.
In 1992, as part of a joint FARA (French American Ridge Atlantic) cruise aboard
the R/V Atlantis II, Project FAZAR, systematic water-column sampling was carried
out along a more northerly section of the Mid-Atlantic Ridge between 32°N and
the Kurchatov Fracture Zone close to 40°N [e.g.,
Wilson et al., in press; Klinkhammer
et al., in press]. Stations were occupied approximately every
German
et al. [1994] carried out a systematic survey of the Reykjanes Ridge
between 57°45'N and 63°09'N. Approximately 120 stations were occupied at
Fig. 20. 38 kHz echo-sounder trace from a transect along the axis of the Reykjanes Ridge between 63°06.04'N and 63°06.10'N, indicating the presence of gas-rich hydrothermal plumes rising from the seabed close to 63°06.06'N (reprinted from German et al. [1994] with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington OX5 1GB, UK).
Very few studies of hydrothermal activity have been carried out in the Indian
Ocean, even though sediments exhibiting hydrothermal metal enrichments along
the Indian Ocean ridge system have been known for almost thirty years [Boström
et al., 1969]. To date, however, discovery of evidence for hydrothermal
activity along the ridges of the Indian Ocean has been limited to three specific
studies. The Central Indian Ridge between 21°S and 24°S, close to the Rodriguez
Triple Junction, was investigated between 1983 and 1988 by cruises of the R/V
Sonne. A series of CTD hydrocast stations occupied between 21°15'S and
21°30'S in 1986 found distinct plumes of dissolved Mn and CH4 anomalies
at several stations, with concentrations up to
In 1993, a group of Japanese investigators conducted water-column observations
around the Rodriguez Triple Junction [Gamo
et al., 1994]. Hydrothermal optical and chemical (CH4 and
dissolved Mn and Fe) anomalies were found centered around the
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