381
turbidity flows and volcanic ash are low. They therefore occur in highest abundances on red clay and
siliceous ooze far from land. They occur worldwide
and are found in most major oceanic basins. Their
distribution is also related to the patterns of oceanic
bottom water flow and, to a lesser extent, to the
availability of potential nuclei on which they grow such
as weathered volcanic rock, pumice, whales’ ear-bones,
sharks’ teeth, fragments of older nodules and indurated
sediment. Antarctic Bottom Water (AABW) is the
major oceanic bottom current in the Pacific. Its influence is seen in the lowered sedimentation rates, and
therefore increased nodule abundance, along its flow
path. A huge literature on deep-sea nodules has developed over the last 30 years, including a number of
standard texts on the subject (Mero 1965; Horn 1972;
Glasby 1977; Anon 1979; Bischoff and Piper 1979;
Sorem and Fewkes 1979; Cronan 1980; Varentsov and
Grasselly 1980; Roy 1981; Teleki et al. 1987; Baturin
1988; Halbach et al. 1988; Nicholson et al. 1997;
Cronan 2000).
In the Pacific Ocean, the distribution of manganese
nodules has been mapped as part of the Circum-Pacific
Map Project using data from 2,500 bottom camera
stations and from sediment cores (Piper et al. 1987)
(Fig. 11.8). Although considerable variability in nodule
abundance within individual stations was observed,
high coverage of nodules was recorded in five main
regions: between the Clarion and Clipperton Fracture
Zones (C-C F.Z.) in the equatorial North Pacific and
extending westwards into the northern sector of the
Central Pacific Basin, in the abyssal plain area around
the Musicians Seamounts in the Northeast Pacific
Basin, in the central sector of the Southwestern Pacific
Basin, in an E-W trending belt in the Southern Ocean
coincident with the Antarctic Convergence, and in the
northern sector of the Peru Basin. Andreev and
Gramberg (2004) have recently published a more
detailed map of the mineral resources of the world ocean
including manganese nodules.
In discussing the composition of deep-sea manganese nodules, it should be born in mind that the composition of nodules varies within individual nodules
as seen in the discrete micro-banding in the nodules,
locally (on the scale of hundreds of meters) and
regionally (over thousands of km) (e.g von Stackelberg
and Marchig 1987). In spite of this, regional patterns
in the composition of nodules are commonly observed
such that we can reasonably compare and contrast
the characteristics of nodules from different physiographic provinces of the world ocean as attempted
here (cf. Cronan 1977; Piper and Williamson 1977;
Sorem and Fewkes 1979).
In the following section, the distribution,
mineralogy and composition of manganese nodules
from three of these regions is considered in order to
illustrate the different modes of formation of nodules
in different settings. A detailed comparison of the
characteristics of the nodules from these three regions
has already been presented by Glasby et al. (1983).
Southwestern Pacific Basin
The Southwestern Pacific Basin has an area of 10·10
6
km
2
. It is bounded by New Zealand-Tonga-Kermadec
Arc, the East Pacific Rise and the Polynesian island
chain and has a maximum depth 5,800 m. It lies beneath
subtropical anticyclonic gyre which is a low productivity area. Two cruises of R.V. Tangaroa were undertaken in 1974 and 1976 to study the distribution and
mode of formation of nodules in the Southwestern
Pacific and Samoan Basins (Glasby et al. 1980). On a
transect from New Zealand to Rarotonga in the Cook
Islands, it was shown that the maximum abundance of
nodules (>20 kg m
-2
) occurs on the dusky brown clays
in the region 220-745 km S.W. of Rarotonga. The
western sector of the basin, particularly N.E. of New
Zealand, was largely devoid of nodules. This was
attributed to the influx of terrigenous sediments from
the New Zealand landmass which raised the sedimentation rate above the threshold for nodule formation.
The morphology of the nodules in the Southwestern
Pacific Basin is somewhat variable but those taken
S.W. of Rarotonga are 40% s[S]m, 17% m[S]m and 16%
s[E]m (see box for explanation). 72% of these nodules
are small (<30 mm), 26% medium (30-60 mm) and 2%
large (>60 mm). The nodules are dominantly spheroidal
with smooth surface texture when small but become
more ellipsoidal and develop equatorial rims with
increasing size. The larger nodules also tend to exhibit
differences in the surface texture between the upper
and lower surfaces. This reflects the fact that the larger
nodules have been static at the seafloor for longer
than is necessary to form the external layer of the
nodule (i.e. their rate of rolling is slower than the rate
of growth). Mineralogically, the nodules consist of
δMnO 2 , quartz and feldspar. Table 11.4 lists the average
composition of nodules from S.W. Pacific Basin and
the adjacent Samoan Basin. The average Ni+Cu+Co
content of the nodules on the transect from New
Zealand to Rarotonga is 1.00%. This is well below the
level considered necessary for economic exploitation
even though the Southwestern Pacific Basin is thought
to contain 10·10
9
t of nodules. A subsequent E-W
transect across the Southwestern Pacific Basin at 42°S
undertaken during cruise SO-14 of R.V. Sonne showed
11.4
Manganese Nodules and Crusts
turbidity flows and volcanic ash are low. They therefore occur in highest abundances on red clay and
siliceous ooze far from land. They occur worldwide
and are found in most major oceanic basins. Their
distribution is also related to the patterns of oceanic
bottom water flow and, to a lesser extent, to the
availability of potential nuclei on which they grow such
as weathered volcanic rock, pumice, whales’ ear-bones,
sharks’ teeth, fragments of older nodules and indurated
sediment. Antarctic Bottom Water (AABW) is the
major oceanic bottom current in the Pacific. Its influence is seen in the lowered sedimentation rates, and
therefore increased nodule abundance, along its flow
path. A huge literature on deep-sea nodules has developed over the last 30 years, including a number of
standard texts on the subject (Mero 1965; Horn 1972;
Glasby 1977; Anon 1979; Bischoff and Piper 1979;
Sorem and Fewkes 1979; Cronan 1980; Varentsov and
Grasselly 1980; Roy 1981; Teleki et al. 1987; Baturin
1988; Halbach et al. 1988; Nicholson et al. 1997;
Cronan 2000).
In the Pacific Ocean, the distribution of manganese
nodules has been mapped as part of the Circum-Pacific
Map Project using data from 2,500 bottom camera
stations and from sediment cores (Piper et al. 1987)
(Fig. 11.8). Although considerable variability in nodule
abundance within individual stations was observed,
high coverage of nodules was recorded in five main
regions: between the Clarion and Clipperton Fracture
Zones (C-C F.Z.) in the equatorial North Pacific and
extending westwards into the northern sector of the
Central Pacific Basin, in the abyssal plain area around
the Musicians Seamounts in the Northeast Pacific
Basin, in the central sector of the Southwestern Pacific
Basin, in an E-W trending belt in the Southern Ocean
coincident with the Antarctic Convergence, and in the
northern sector of the Peru Basin. Andreev and
Gramberg (2004) have recently published a more
detailed map of the mineral resources of the world ocean
including manganese nodules.
In discussing the composition of deep-sea manganese nodules, it should be born in mind that the composition of nodules varies within individual nodules
as seen in the discrete micro-banding in the nodules,
locally (on the scale of hundreds of meters) and
regionally (over thousands of km) (e.g von Stackelberg
and Marchig 1987). In spite of this, regional patterns
in the composition of nodules are commonly observed
such that we can reasonably compare and contrast
the characteristics of nodules from different physiographic provinces of the world ocean as attempted
here (cf. Cronan 1977; Piper and Williamson 1977;
Sorem and Fewkes 1979).
In the following section, the distribution,
mineralogy and composition of manganese nodules
from three of these regions is considered in order to
illustrate the different modes of formation of nodules
in different settings. A detailed comparison of the
characteristics of the nodules from these three regions
has already been presented by Glasby et al. (1983).
Southwestern Pacific Basin
The Southwestern Pacific Basin has an area of 10·10
6
km
2
. It is bounded by New Zealand-Tonga-Kermadec
Arc, the East Pacific Rise and the Polynesian island
chain and has a maximum depth 5,800 m. It lies beneath
subtropical anticyclonic gyre which is a low productivity area. Two cruises of R.V. Tangaroa were undertaken in 1974 and 1976 to study the distribution and
mode of formation of nodules in the Southwestern
Pacific and Samoan Basins (Glasby et al. 1980). On a
transect from New Zealand to Rarotonga in the Cook
Islands, it was shown that the maximum abundance of
nodules (>20 kg m
-2
) occurs on the dusky brown clays
in the region 220-745 km S.W. of Rarotonga. The
western sector of the basin, particularly N.E. of New
Zealand, was largely devoid of nodules. This was
attributed to the influx of terrigenous sediments from
the New Zealand landmass which raised the sedimentation rate above the threshold for nodule formation.
The morphology of the nodules in the Southwestern
Pacific Basin is somewhat variable but those taken
S.W. of Rarotonga are 40% s[S]m, 17% m[S]m and 16%
s[E]m (see box for explanation). 72% of these nodules
are small (<30 mm), 26% medium (30-60 mm) and 2%
large (>60 mm). The nodules are dominantly spheroidal
with smooth surface texture when small but become
more ellipsoidal and develop equatorial rims with
increasing size. The larger nodules also tend to exhibit
differences in the surface texture between the upper
and lower surfaces. This reflects the fact that the larger
nodules have been static at the seafloor for longer
than is necessary to form the external layer of the
nodule (i.e. their rate of rolling is slower than the rate
of growth). Mineralogically, the nodules consist of
δMnO 2 , quartz and feldspar. Table 11.4 lists the average
composition of nodules from S.W. Pacific Basin and
the adjacent Samoan Basin. The average Ni+Cu+Co
content of the nodules on the transect from New
Zealand to Rarotonga is 1.00%. This is well below the
level considered necessary for economic exploitation
even though the Southwestern Pacific Basin is thought
to contain 10·10
9
t of nodules. A subsequent E-W
transect across the Southwestern Pacific Basin at 42°S
undertaken during cruise SO-14 of R.V. Sonne showed
11.4
Manganese Nodules and Crusts