Cross-references
Marine Microfossils
Plate Tectonics
MANGANESE NODULES
James R. Hein
U.S. Geological Survey, Santa Cruz, CA, USA
Synonyms
Fe-Mn nodules; Ferromanganese nodules; Ironmanganese nodules; Polymetallic nodules
Definition
Manganese and iron oxide mineral deposits formed on or
just below the sediment-covered surface of the deep-ocean
seabed by accretion (precipitation) of oxide layers around
a nucleus, thereby forming nodules of various shapes and
sizes and which contain minor but significant amounts of
nickel, copper, cobalt, lithium, molybdenum, zirconium,
and rare earth elements.
Introduction
The existence of manganese (Mn) nodules (Figure 1) has
been known since the late 1800s when they were collected
during the Challenger expedition of 1873–1876. However, it was not until after WWII that nodules were further
studied in detail for their ability to adsorb metals from seawater. Many of the early studies did not distinguish Mn
nodules from Mn crusts. Economic interest in Mn nodules
began in the late 1950s and early 1960s when John Mero
finished his Ph.D. thesis on this subject, which was
published in the journal Economic Geology (Mero,
1962) and later as a book (Mero, 1965). By the
mid-1970s, large consortia had formed to search for and
mine Mn nodules that occur between the Clarion and
Clipperton fracture zones (CCZ) in the NE Pacific
(Figure 2). This is still the area considered of greatest economic potential in the global ocean because of high nickel
(Ni), copper (Cu), and Mn contents and the dense distribution of nodules in the area. While the mining of nodules
was fully expected to begin in the late 1970s or early
1980s, this never occurred due to a downturn in the price
of metals on the global market. Since then, many research
cruises have been undertaken to study the CCZ nodules,
and now 15 contracts for exploration sites have been given
or are pending by the International Seabed Authority
(ISA). Many books and science journal articles have been
published summarizing the early work (e.g., Baturin,
1988; Halbach et al., 1988), and research has continued
to the present day (e.g., ISA, 1999; ISA, 2010). Although
the initial attraction for nodules was their high Ni, Cu, and
Mn contents, subsequent work has shown that nodules
host large quantities of other critical metals needed for
high-tech, green-tech, and energy applications (Hein
et al., 2013; Hein and Koschinsky, 2014).
Occurrence and distribution
Mn nodules are concretions that occur on or near the surface of the sediment that covers abyssal plains throughout
the global ocean, where sedimentation rates are low, less
than 10 centimeters (cm) per thousand years (Figure 2).
Low sedimentation rates occur if the abyssal plain is distant from a continental margin or the margin is adjacent
to a deep-sea trench, has a wide continental shelf, or is
arid. In the open ocean, low sedimentation rates occur
away from regions of strong upwelling and high biological productivity, such as the equatorial zone of high productivity. Nodules are generally about golf ball sized,
most commonly 1–12 cm, but can vary in diameter from
millimeter (mm)-size (micronodules) to as large as
20 cm. The maximum size of nodules increases with
increasing diagenetic input of metals (see next section).
Nodules of greatest economic interest occur in areas of
moderate primary productivity in surface waters (ISA,
2010). The location of nodule growth relative to the calcite
compensation depth (CCD), controlled by productivity in
surface waters, is important because above the CCD, biogenic calcite increases sedimentation rates and dilutes the
organic matter required for diagenetic reactions in the sediment that release Ni and Cu (Verlaan et al., 2004; Cronan,
2006). The most Ni- and Cu-rich nodules form near, but
generally below the CCD.
Most Mn nodules form at water depths of about
3,500–6,500 meters (m), although abyssal plains can have
hills and ridges several hundred meters high and seamounts up to 2 kilometers (km) high rising above the
plains. Nodules can occur on all of those structures if they
are covered by sediment. Mn nodules have been collected
from many of the large seamounts on which Fe-Mn crusts
form, but most of those nodules differ significantly from
abyssal plain nodules since the seamount nodules form
by hydrogenetic accumulation only (see below) and commonly have a large rock fragment as the nucleus. The seamount nodules are mostly Mn- and iron (Fe)-oxide-coated
rock pebbles and cobbles, while abyssal plain nodules
usually have a minute nucleus relative to the thickness of
the accreted Mn- and Fe-oxide layers.
The greatest concentrations of metal-rich nodules occur
in the following regions: in the NE Pacific CCZ (Figure 2)
that extends from the Mexico EEZ to as far west as the longitude of Hawaii, in the SE Pacific Peru Basin, in the central South Pacific Penrhyn Basin, and in the Central Indian
Ocean Basin. In the CCZ, the Mn nodules lie on abyssal
sediments covering an area of about nine million square
kilometers with up to 75 kilograms (kg) of nodules per
square m of seabed, but more commonly average less than
15 kg per square m wet weight. Their high abundance in
this region can be attributed to slow rates of sedimentation, the abundant availability of material for the Mn and
Fe to nucleate around, and moderate productivity in
408
MANGANESE NODULES
Marine Microfossils
Plate Tectonics
MANGANESE NODULES
James R. Hein
U.S. Geological Survey, Santa Cruz, CA, USA
Synonyms
Fe-Mn nodules; Ferromanganese nodules; Ironmanganese nodules; Polymetallic nodules
Definition
Manganese and iron oxide mineral deposits formed on or
just below the sediment-covered surface of the deep-ocean
seabed by accretion (precipitation) of oxide layers around
a nucleus, thereby forming nodules of various shapes and
sizes and which contain minor but significant amounts of
nickel, copper, cobalt, lithium, molybdenum, zirconium,
and rare earth elements.
Introduction
The existence of manganese (Mn) nodules (Figure 1) has
been known since the late 1800s when they were collected
during the Challenger expedition of 1873–1876. However, it was not until after WWII that nodules were further
studied in detail for their ability to adsorb metals from seawater. Many of the early studies did not distinguish Mn
nodules from Mn crusts. Economic interest in Mn nodules
began in the late 1950s and early 1960s when John Mero
finished his Ph.D. thesis on this subject, which was
published in the journal Economic Geology (Mero,
1962) and later as a book (Mero, 1965). By the
mid-1970s, large consortia had formed to search for and
mine Mn nodules that occur between the Clarion and
Clipperton fracture zones (CCZ) in the NE Pacific
(Figure 2). This is still the area considered of greatest economic potential in the global ocean because of high nickel
(Ni), copper (Cu), and Mn contents and the dense distribution of nodules in the area. While the mining of nodules
was fully expected to begin in the late 1970s or early
1980s, this never occurred due to a downturn in the price
of metals on the global market. Since then, many research
cruises have been undertaken to study the CCZ nodules,
and now 15 contracts for exploration sites have been given
or are pending by the International Seabed Authority
(ISA). Many books and science journal articles have been
published summarizing the early work (e.g., Baturin,
1988; Halbach et al., 1988), and research has continued
to the present day (e.g., ISA, 1999; ISA, 2010). Although
the initial attraction for nodules was their high Ni, Cu, and
Mn contents, subsequent work has shown that nodules
host large quantities of other critical metals needed for
high-tech, green-tech, and energy applications (Hein
et al., 2013; Hein and Koschinsky, 2014).
Occurrence and distribution
Mn nodules are concretions that occur on or near the surface of the sediment that covers abyssal plains throughout
the global ocean, where sedimentation rates are low, less
than 10 centimeters (cm) per thousand years (Figure 2).
Low sedimentation rates occur if the abyssal plain is distant from a continental margin or the margin is adjacent
to a deep-sea trench, has a wide continental shelf, or is
arid. In the open ocean, low sedimentation rates occur
away from regions of strong upwelling and high biological productivity, such as the equatorial zone of high productivity. Nodules are generally about golf ball sized,
most commonly 1–12 cm, but can vary in diameter from
millimeter (mm)-size (micronodules) to as large as
20 cm. The maximum size of nodules increases with
increasing diagenetic input of metals (see next section).
Nodules of greatest economic interest occur in areas of
moderate primary productivity in surface waters (ISA,
2010). The location of nodule growth relative to the calcite
compensation depth (CCD), controlled by productivity in
surface waters, is important because above the CCD, biogenic calcite increases sedimentation rates and dilutes the
organic matter required for diagenetic reactions in the sediment that release Ni and Cu (Verlaan et al., 2004; Cronan,
2006). The most Ni- and Cu-rich nodules form near, but
generally below the CCD.
Most Mn nodules form at water depths of about
3,500–6,500 meters (m), although abyssal plains can have
hills and ridges several hundred meters high and seamounts up to 2 kilometers (km) high rising above the
plains. Nodules can occur on all of those structures if they
are covered by sediment. Mn nodules have been collected
from many of the large seamounts on which Fe-Mn crusts
form, but most of those nodules differ significantly from
abyssal plain nodules since the seamount nodules form
by hydrogenetic accumulation only (see below) and commonly have a large rock fragment as the nucleus. The seamount nodules are mostly Mn- and iron (Fe)-oxide-coated
rock pebbles and cobbles, while abyssal plain nodules
usually have a minute nucleus relative to the thickness of
the accreted Mn- and Fe-oxide layers.
The greatest concentrations of metal-rich nodules occur
in the following regions: in the NE Pacific CCZ (Figure 2)
that extends from the Mexico EEZ to as far west as the longitude of Hawaii, in the SE Pacific Peru Basin, in the central South Pacific Penrhyn Basin, and in the Central Indian
Ocean Basin. In the CCZ, the Mn nodules lie on abyssal
sediments covering an area of about nine million square
kilometers with up to 75 kilograms (kg) of nodules per
square m of seabed, but more commonly average less than
15 kg per square m wet weight. Their high abundance in
this region can be attributed to slow rates of sedimentation, the abundant availability of material for the Mn and
Fe to nucleate around, and moderate productivity in
408
MANGANESE NODULES