variability with the highest grades occurring in the
north.
Atlantic Ocean In the Atlantic Ocean, diagenetic
Mn-, Ni-, and Cu-rich nodules occur most notably
in the Angola Basin and to a lesser extent in the
Cape/Agulhas Basin and the East Georgia Basin.
These three areas have in common elevated
biological productivity and elevated organic carbon
contents in their sediments, which coupled with
their depth near or below the CCD would help to
explain the composition of their nodules. However,
Ni and Cu contents are lower in them than in areas
of diagenetic nodules in the Pacific and Indian
Oceans.
Economic Potential
Interest in manganese nodules commenced around
the mid-1960s and developed during the 1970s, at
the same time as the Third United Nations Law of
the Sea Conference. However, the outcome of that
Conference, in 1982, was widely regarded as unfavorable for the mining industry. This, coupled with
a general downturn in metal prices, resulted in a
lessening of mining company interest in nodules.
About this time, however, several governmentbacked consortia became interested in them and this
work expanded as evaluation of the deposits by
mining companies declined. Part 11 of the 1982 Law
of the Sea Convention, that part dealing with deepsea mining, was substantially amended in an agreement on 28 July 1994 which ameliorated some of the
provisions relating to deep-sea mining. The Convention entered into force in November 1994.
During the 1980s interest in manganese nodules in
exclusive economic zones (EEZs) started to increase.
An important result of the Third Law of the Sea
Conference, was the acceptance of a 200-nauticalmile EEZ in which the adjacent coastal state could
claim any mineral deposits as their own. The nodules
found in EEZs are similar to those found in adjacent
parts of the International Seabed Area, and are of
greatest economic potential in the EEZs of the South
Pacific.
At the beginning of the twenty-first century, the
out-look for manganese nodule mining remains rather unclear. It is likely to commence some time in
this century, although it is not possible to give a
precise estimate as to when. The year 2015 has been
suggested as the earliest possible date for nodule
mining outside of the EEZs. It is possible, however,
that EEZ mining for nodules might commence earlier
if conditions were favorable. It would depend upon
many factors; economic, technological, and political.
Discussion
A model to explain the compositional variability of
nodules in the Penrhyn Basin can be summarized as
follows. Under the flanks of the high productivity
area, reduced sedimentation rates near the CCD due
to calcium carbonate dissolution enhance the content
of metal-bearing organic carbon rich phases (fecal
material, marine snow, etc.) in the sediments, the
decay of which drives the diagenetic reactions that in
turn promote the enrichment of Mn, Ni, and Cu in
the nodules via the sediment interstitial waters. Away
from the CCD, organic carbon concentrating processes are less effective. Further south as productivity
declines, there is probably insufficient organic carbon
supplied to the seafloor to promote the formation of
diagenetic nodules at any depth. Under the equator,
siliceous ooze replaces pelagic clay as the main
sediment builder at and below the CCD, and when
its rate of accumulation is high it dilutes the concentrations of organic carbon-bearing material at all
depths to levels below that at which diagenetic Mn,
Ni, and Cu rich nodules can form.
To a greater or lesser extent, this model can account for much of the variability in nodule composition found in the other South Pacific areas
described, although local factors may also apply. In
the Peru Basin, as in the Penrhyn Basin, diagenetic
Mn-, Ni-, and Cu-rich nodules are concentrated near
the CCD and their Ni and Cu contents reach a
maximum south of the highest productivity waters.
In the Tiki Basin, the greatest diagenetic influences
are also found in the north of the Basin. As the South
Pacific basins deepen to the west, the areas of
diagenetic nodules tend to occur below the CCD as,
for example, in the Nova Canton Trough area. This
may be because the settling rates of large organic
particles are quite fast in the deep ocean. Probably
only limited decay of this material takes place
between it settling through the CCD and reaching
the seafloor, and enough probably gets sedimented
to extend the depth of diagenetic nodule formation
to well below the CCD under high productivity
waters where there is limited siliceous sediment
accumulation.
In the North Pacific, the trends in nodule composition in relation to the equatorial zone are the
mirror image of those in the south. Thus in both the
Central Pacific Basin and the Clarion–Clipperton
Zone the highest nodule grades occur in diagenetic
nodules on the northern flanks of the high
372 MANGANESE NODULES
north.
Atlantic Ocean In the Atlantic Ocean, diagenetic
Mn-, Ni-, and Cu-rich nodules occur most notably
in the Angola Basin and to a lesser extent in the
Cape/Agulhas Basin and the East Georgia Basin.
These three areas have in common elevated
biological productivity and elevated organic carbon
contents in their sediments, which coupled with
their depth near or below the CCD would help to
explain the composition of their nodules. However,
Ni and Cu contents are lower in them than in areas
of diagenetic nodules in the Pacific and Indian
Oceans.
Economic Potential
Interest in manganese nodules commenced around
the mid-1960s and developed during the 1970s, at
the same time as the Third United Nations Law of
the Sea Conference. However, the outcome of that
Conference, in 1982, was widely regarded as unfavorable for the mining industry. This, coupled with
a general downturn in metal prices, resulted in a
lessening of mining company interest in nodules.
About this time, however, several governmentbacked consortia became interested in them and this
work expanded as evaluation of the deposits by
mining companies declined. Part 11 of the 1982 Law
of the Sea Convention, that part dealing with deepsea mining, was substantially amended in an agreement on 28 July 1994 which ameliorated some of the
provisions relating to deep-sea mining. The Convention entered into force in November 1994.
During the 1980s interest in manganese nodules in
exclusive economic zones (EEZs) started to increase.
An important result of the Third Law of the Sea
Conference, was the acceptance of a 200-nauticalmile EEZ in which the adjacent coastal state could
claim any mineral deposits as their own. The nodules
found in EEZs are similar to those found in adjacent
parts of the International Seabed Area, and are of
greatest economic potential in the EEZs of the South
Pacific.
At the beginning of the twenty-first century, the
out-look for manganese nodule mining remains rather unclear. It is likely to commence some time in
this century, although it is not possible to give a
precise estimate as to when. The year 2015 has been
suggested as the earliest possible date for nodule
mining outside of the EEZs. It is possible, however,
that EEZ mining for nodules might commence earlier
if conditions were favorable. It would depend upon
many factors; economic, technological, and political.
Discussion
A model to explain the compositional variability of
nodules in the Penrhyn Basin can be summarized as
follows. Under the flanks of the high productivity
area, reduced sedimentation rates near the CCD due
to calcium carbonate dissolution enhance the content
of metal-bearing organic carbon rich phases (fecal
material, marine snow, etc.) in the sediments, the
decay of which drives the diagenetic reactions that in
turn promote the enrichment of Mn, Ni, and Cu in
the nodules via the sediment interstitial waters. Away
from the CCD, organic carbon concentrating processes are less effective. Further south as productivity
declines, there is probably insufficient organic carbon
supplied to the seafloor to promote the formation of
diagenetic nodules at any depth. Under the equator,
siliceous ooze replaces pelagic clay as the main
sediment builder at and below the CCD, and when
its rate of accumulation is high it dilutes the concentrations of organic carbon-bearing material at all
depths to levels below that at which diagenetic Mn,
Ni, and Cu rich nodules can form.
To a greater or lesser extent, this model can account for much of the variability in nodule composition found in the other South Pacific areas
described, although local factors may also apply. In
the Peru Basin, as in the Penrhyn Basin, diagenetic
Mn-, Ni-, and Cu-rich nodules are concentrated near
the CCD and their Ni and Cu contents reach a
maximum south of the highest productivity waters.
In the Tiki Basin, the greatest diagenetic influences
are also found in the north of the Basin. As the South
Pacific basins deepen to the west, the areas of
diagenetic nodules tend to occur below the CCD as,
for example, in the Nova Canton Trough area. This
may be because the settling rates of large organic
particles are quite fast in the deep ocean. Probably
only limited decay of this material takes place
between it settling through the CCD and reaching
the seafloor, and enough probably gets sedimented
to extend the depth of diagenetic nodule formation
to well below the CCD under high productivity
waters where there is limited siliceous sediment
accumulation.
In the North Pacific, the trends in nodule composition in relation to the equatorial zone are the
mirror image of those in the south. Thus in both the
Central Pacific Basin and the Clarion–Clipperton
Zone the highest nodule grades occur in diagenetic
nodules on the northern flanks of the high
372 MANGANESE NODULES