HYDROTHERMAL VENT FLUIDS, CHEMISTRY OF
K. L. Von Damm, University of New Hampshire,
Durham, NH, USA
Copyright & 2001 Elsevier Ltd.
Introduction
It was not until 1977 that we knew that fluids exit
from the seafloor along the global midocean ridge
system. With the first discovery of hydrothermal
venting at the Galapagos Spreading Center, our ideas
on how elements cycle through the oceans and
lithosphere, and even how and where life on our
planet may have originated were fundamentally and
irrevocably changed. Although these fluids were only
a few tens of degrees hotter than ambient sea water
(o301C vs. 21C), on the basis of their chemical
compositions it was immediately clear that these
fluids were derived from reactions at much higher
temperatures between sea water and the oceanic
crust. Less than two years later, spectacular jets of
hot (X3501C) and black water were discovered
several thousand kilometers away on the northern
East Pacific Rise, and ‘black smokers’ and ‘chimneys’
(Figure 1) entered the oceanographic lexicon.
From a chemical oceanography perspective,
hydrothermal venting and hydrothermal vent fluids
provide both new source and sink mechanisms for
elemental cycling in the ocean, and therefore possible
resolutions to a number of the outstanding chemical
flux imbalances. They therefore play a fundamental
role in regulating the chemistry of the oceans
through geological time. From a biological oceanography perspective, hydrothermal vents provide us
with new ecosystems based on chemosynthetic, rather than photosynthetic energy. Of the 4500 new
species discovered at these sites, the archea and other
microbiological components are attracting increasing
interest for both biotechnological applications and
‘origin of life’ questions on our own and other planets. From a physical oceanographic perspective,
hydrothermal vents provide an input of both heat
and materials into the oceanic mid-depth circulation.
From a geological oceanographic perspective they
provide an efficient means of removing heat from
newly formed oceanic crust, as well as a means of
altering the elements recycled into the mantle when
the oceanic crust formed at spreading centers is later
subducted back into the Earth’s interior.
Where are Hydrothermal Vents
Found?
Hydrothermal vents are now known to exist at approximately 30 locations on the global midocean
ridge system (Figure 2). Initially some people had
speculated that venting would only be found on
intermediate- or faster-spreading ridges (i.e., ridges
with full spreading rates of at least 60 mm yr
À1
); we
now know of numerous locations on slow-spreading
ridges (e.g., Mid-Atlantic Ridge) where they occur.
Known sites occur at depths from 800 to 43600 m,
with spreading rates from o20 to 4150 mm y
À1
(full rate), on both bare basalt and sedimented-covered ridges, as well as on seafloor where ultramafic
rock types are known to outcrop, and at temperatures up to 4051C. If one looks at the global distribution of known vent sites, it is obvious that many of
the sites are in relatively close proximity to nations
that operate submersibles, and are clustered disproportionately in the north Atlantic and eastern
Pacific. Although not strictly part of the midocean
ridge system, venting associated with back arc
spreading centers is also known from a number of
sites in the western Pacific. No sites have yet been
discovered in the Indian Ocean, although cruises to
this ocean are now planned. Similarly, no sites are
known in the south Atlantic, or at high latitudes.
This is an exploration issue, not a lack of their existence in these areas.
While initially vents were thought to occur at the
mid-point of ridge segments, this was a largely selffulfilling prophesy, as this is where exploration for
them was focused. There is increasing evidence that
more venting occurs on the magmatically robust
portions of the ridge, rather than on those areas that
are deemed to be magma-starved, on the basis of
their morphological characteristics.
How are they Found?
Vent fields have been discovered in numerous ways,
but surveys of the overlying water column and
camera tows are the most common systematic approaches employed today. The venting of hot/warm
water often forms a plume with unique temperature,
salinity, reduced light transmittance, and other
specific chemical signals several hundred meters
above the ridge. The presence of such a plume
is often the first indication that a given section of
ridge is hydrothermally active. Cameras, or other
81
K. L. Von Damm, University of New Hampshire,
Durham, NH, USA
Copyright & 2001 Elsevier Ltd.
Introduction
It was not until 1977 that we knew that fluids exit
from the seafloor along the global midocean ridge
system. With the first discovery of hydrothermal
venting at the Galapagos Spreading Center, our ideas
on how elements cycle through the oceans and
lithosphere, and even how and where life on our
planet may have originated were fundamentally and
irrevocably changed. Although these fluids were only
a few tens of degrees hotter than ambient sea water
(o301C vs. 21C), on the basis of their chemical
compositions it was immediately clear that these
fluids were derived from reactions at much higher
temperatures between sea water and the oceanic
crust. Less than two years later, spectacular jets of
hot (X3501C) and black water were discovered
several thousand kilometers away on the northern
East Pacific Rise, and ‘black smokers’ and ‘chimneys’
(Figure 1) entered the oceanographic lexicon.
From a chemical oceanography perspective,
hydrothermal venting and hydrothermal vent fluids
provide both new source and sink mechanisms for
elemental cycling in the ocean, and therefore possible
resolutions to a number of the outstanding chemical
flux imbalances. They therefore play a fundamental
role in regulating the chemistry of the oceans
through geological time. From a biological oceanography perspective, hydrothermal vents provide us
with new ecosystems based on chemosynthetic, rather than photosynthetic energy. Of the 4500 new
species discovered at these sites, the archea and other
microbiological components are attracting increasing
interest for both biotechnological applications and
‘origin of life’ questions on our own and other planets. From a physical oceanographic perspective,
hydrothermal vents provide an input of both heat
and materials into the oceanic mid-depth circulation.
From a geological oceanographic perspective they
provide an efficient means of removing heat from
newly formed oceanic crust, as well as a means of
altering the elements recycled into the mantle when
the oceanic crust formed at spreading centers is later
subducted back into the Earth’s interior.
Where are Hydrothermal Vents
Found?
Hydrothermal vents are now known to exist at approximately 30 locations on the global midocean
ridge system (Figure 2). Initially some people had
speculated that venting would only be found on
intermediate- or faster-spreading ridges (i.e., ridges
with full spreading rates of at least 60 mm yr
À1
); we
now know of numerous locations on slow-spreading
ridges (e.g., Mid-Atlantic Ridge) where they occur.
Known sites occur at depths from 800 to 43600 m,
with spreading rates from o20 to 4150 mm y
À1
(full rate), on both bare basalt and sedimented-covered ridges, as well as on seafloor where ultramafic
rock types are known to outcrop, and at temperatures up to 4051C. If one looks at the global distribution of known vent sites, it is obvious that many of
the sites are in relatively close proximity to nations
that operate submersibles, and are clustered disproportionately in the north Atlantic and eastern
Pacific. Although not strictly part of the midocean
ridge system, venting associated with back arc
spreading centers is also known from a number of
sites in the western Pacific. No sites have yet been
discovered in the Indian Ocean, although cruises to
this ocean are now planned. Similarly, no sites are
known in the south Atlantic, or at high latitudes.
This is an exploration issue, not a lack of their existence in these areas.
While initially vents were thought to occur at the
mid-point of ridge segments, this was a largely selffulfilling prophesy, as this is where exploration for
them was focused. There is increasing evidence that
more venting occurs on the magmatically robust
portions of the ridge, rather than on those areas that
are deemed to be magma-starved, on the basis of
their morphological characteristics.
How are they Found?
Vent fields have been discovered in numerous ways,
but surveys of the overlying water column and
camera tows are the most common systematic approaches employed today. The venting of hot/warm
water often forms a plume with unique temperature,
salinity, reduced light transmittance, and other
specific chemical signals several hundred meters
above the ridge. The presence of such a plume
is often the first indication that a given section of
ridge is hydrothermally active. Cameras, or other
81