
Polymetallic nodules, also called manganese nodules, are mineral
concretion
A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes a ...
s on the sea bottom formed of concentric layers of
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...
s around a core. As nodules can be found in vast quantities, and contain valuable metals,
deposits
A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below.
...
have been identified as a potential economic interest. Depending on their composition and authorial choice, they may also be called ferromanganese nodules. Ferromanganese nodules are mineral
concretion
A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes a ...
s composed of
silicate
A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...
s and
insoluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solub ...
iron and manganese
oxide
An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...
s that form on the ocean
seafloor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
and terrestrial
soil
Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
s. The formation mechanism involves a series of
redox
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...
oscillations driven by both
abiotic
In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them und ...
and
biotic processes.
As a byproduct of
pedogenesis
Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order (anisotropy) within soils. These alterations ...
, the specific composition of a
ferromanganese
Ferromanganese is an alloy of iron and manganese, with other elements such as silicon, carbon, sulfur, nitrogen and phosphorus. The primary use of ferromanganese is as a type of processed manganese source to add to different types of steel, such ...
nodule depends on the composition of the surrounding soil.
The formation mechanisms and composition of the
nodules allow for couplings with
biogeochemical cycle
A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cyc ...
s beyond iron and manganese.
The high relative abundance of
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
,
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
,
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
, and other
rare metals in nodules has increased interest in their use as a mining resource.
Nodules vary in
size
Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to three geometrical measures: length, area, or volume. Length can be generalized ...
from tiny particles visible only under a
microscope
A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...
to large pellets more than across. However, most nodules are between in diameter, about the size of hen's
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...
s. Their
surface textures vary from smooth to rough. They frequently have
botryoidal
A botryoidal ( ) texture or mineral habit, is one in which the mineral has an external form composed of many rounded segments, named for the Ancient Greek (), meaning "a bunch of grapes".Adjective form: ''botruoeidēs'' This is a common form f ...
(mammillated or knobby) texture and vary from
spherical
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
in shape to typically
oblate
In Christianity (specifically the Roman Catholic, Orthodox, Lutheran, Anglican and Methodist traditions), an oblate is a person associated with a Benedictine monastery or convent who is specifically dedicated to God and service.
Oblates are i ...
, sometimes
prolate, or are otherwise irregular. The bottom surface, buried in
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
, is generally rougher than the top due to a different type of
growth.
Occurrence
Nodules lie on the
seabed
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
sediment, often partly or completely buried. They vary greatly in abundance, in some cases touching one another and covering more than 70% of the sea floor surface. The total amount of
polymetallic
nodules on the
sea floor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
was estimated at 500 billion tons by Alan A. Archer of the London
Geological Museum
The Geological Museum (originally the Museum of Economic Geology then the Museum of Practical Geology) was a museum of geology in London. It started in 1835, making it one of the oldest public single science collections in the world. It transfe ...
in 1981.
Polymetallic nodules are found in both shallow (e.g. the
Baltic Sea
The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...
) and deeper waters (e.g. the
central Pacific), even in lakes, and are thought to have been a feature of the seas and oceans at least since the deep oceans were oxygenated in the
Ediacaran
The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
period over 540 million years ago.
Polymetallic nodules were discovered in 1868 in the
Kara Sea
The Kara Sea is a marginal sea, separated from the Barents Sea to the west by the Kara Strait and Novaya Zemlya, and from the Laptev Sea to the east by the Severnaya Zemlya archipelago. Ultimately the Kara, Barents and Laptev Seas are all ...
, in the
Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...
of
Siberia
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
. During the scientific expeditions of
HMS ''Challenger'' (1872–1876), they were found to occur in most oceans of the world.
Their composition varies by location, and sizeable
deposits
A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below.
...
have been found in the following areas:
*
Penrhyn Basin within the
Cook Islands
The Cook Islands is an island country in Polynesia, part of Oceania in the South Pacific Ocean. It consists of 15 islands whose total land area is approximately . The Cook Islands' Exclusive Economic Zone (EEZ) covers of ocean. Avarua is its ...
.
* North central
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
in a region called the
Clarion–Clipperton zone (CCZ) roughly midway between
Hawaii
Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
and
Clipperton Islands.
*
Peru Basin in the southeast Pacific, and
* Southern tropical
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
in a region termed the Indian Ocean Nodule Field (IONF) roughly 500 km SE of
Diego Garcia
Diego Garcia is the largest island of the Chagos Archipelago. It has been used as a joint UK–U.S. military base since the 1970s, following the expulsion of the Chagossians by the UK government. The Chagos Islands are set to become a former B ...
Island.
*In the
Eastern Pacific
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the conti ...
, including the area around
Juan Fernández Islands
The Juan Fernández Islands () are a sparsely inhabited series of islands in the South Pacific Ocean, reliant on tourism and fishing. Situated off the coast of Chile, they are composed of three main volcanic islands: Robinson Crusoe Island, R ...
and the
abyssal plain
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They ...
offshore
Loa River
The Loa River (Spanish: Río Loa) is a U-shaped river in Chile's northern Antofagasta Region. At long, it is the country's longest river and the main watercourse in the Atacama Desert.
Course
The Loa's sources are located on Andean mountain sl ...
.
The largest of these deposits in terms of nodule abundance and metal concentration occur in the
Clarion–Clipperton zone on vast
abyssal plain
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They ...
s in the deep ocean between . The
International Seabed Authority
The International Seabed Authority (ISA; ) is a Kingston, Jamaica-based intergovernmental body of 167 member states and the European Union. It was established under the 1982 UN Convention on the Law of the Sea (UNCLOS) and its 1994 Agreement o ...
estimates that the total amount of nodules in the Clarion–Clipperton zone exceeds 21 billions of tons (Bt), containing about 5.95 Bt of
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
, 0.27 Bt of
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
, 0.23 Bt of
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
and 0.05 Bt of
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
.
All of these deposits are in international waters apart from the Penrhyn Basin, which lies within the
exclusive economic zone
An exclusive economic zone (EEZ), as prescribed by the 1982 United Nations Convention on the Law of the Sea, is an area of the sea in which a sovereign state has exclusive rights regarding the exploration and use of marine natural resource, reso ...
of the
Cook Islands
The Cook Islands is an island country in Polynesia, part of Oceania in the South Pacific Ocean. It consists of 15 islands whose total land area is approximately . The Cook Islands' Exclusive Economic Zone (EEZ) covers of ocean. Avarua is its ...
.
Growth and composition

In both marine and terrestrial environments, ferromanganese nodules are composed primarily of iron and manganese oxide concretions supported by an
aluminosilicate
Aluminosilicate refers to materials containing anionic Si-O-Al linkages. Commonly, the associate cations are sodium (Na+), potassium (K+) and protons (H+). Such materials occur as minerals, coal combustion products and as synthetic materials, of ...
matrix and surrounding a nucleus.
Typically terrestrial nodules are more enriched in iron, while marine nodules tend to have higher manganese to iron ratios, depending on the formation mechanism and surrounding sedimentary composition.
Regardless of where they form, the nodules are characterized by enrichment in iron, manganese,
heavy metals
upright=1.2, Crystals of lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead
Heavy metals is a controversial and ambiguous term for metallic elements with relatively h ...
, and
rare earth element
The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set o ...
content when compared to the Earth's crust and surrounding sediment.
However, organically-bound elements in the surrounding environment are not readily incorporated into nodules.
Marine nodules
On the
seabed
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
the abundance of nodules varies and is likely controlled by the thickness and stability of a
geochemically active layer that forms at the seabed.
Pelagic sediment
Pelagic sediment or pelagite is a fine-grained sediment that accumulates as the result of the settling of particles to the floor of the open ocean, far from land. These particles consist primarily of either the microscopic, calcareous or siliceo ...
type and seabed
bathymetry
Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), river floors, or lake floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of wate ...
(or
geomorphology
Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...
) likely influence the characteristics of the geochemically active layer.
Nodule growth is one of the slowest of all known
geological
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...
phenomena, on the order of a centimeter over several million years. Several processes are hypothesized to be involved in the formation of nodules, including the
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
of metals from
seawater
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximat ...
, the remobilization of manganese in the water column (diagenetic), the
derivation of metals from
hot spring
A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...
s associated with
volcanic activity
Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...
(
hydrothermal
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
), the decomposition of
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic debris by seawater and the
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
of
metal hydroxide
In chemistry, metal hydroxides are a family of compounds of the form where M is a metal. They consist of hydroxide () anions and metallic cations, and are often strong bases. Some metal hydroxides, such as alkali metal hydroxides, ionize comple ...
s through the activity of
microorganism
A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...
s (biogenic). The
sorption
Sorption is a physical and chemical process by which one substance becomes attached to another. Specific cases of sorption are treated in the following articles:
; Absorption: "the incorporation of a substance in one state into another of a d ...
of
divalent
In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Valence is generally understood to be the number of chemica ...
cations
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
such as
Mn2+,
Fe2+,
Co2+,
Ni2+, and
Cu2+ at the surface of
Mn- and
Fe-oxyhydroxides, known to be strong
sorbent
A sorbent is an insoluble material that either absorbs or adsorbs liquids or gases. They are frequently used to remove pollutants and in the cleanup of chemical accidents and oil spills. Besides their uses in industry, sorbents are used in comm ...
s, also plays a main role in the
accumulation of these transition metals in the manganese nodules. These processes (
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
,
sorption
Sorption is a physical and chemical process by which one substance becomes attached to another. Specific cases of sorption are treated in the following articles:
; Absorption: "the incorporation of a substance in one state into another of a d ...
, surface complexation, surface precipitation, incorporation by formation of
solid solution
A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...
s...) may operate concurrently or they may follow one another during the formation of a nodule.
Manganese nodules are essentially composed of hydrated phyllomanganates. These are layered Mn-oxide minerals with interlayers containing water molecules in variable quantities. They strongly interact with trace metals (
Co2+,
Ni2+) because of the octahedral vacancies present in their layers. The particular properties of phyllomanganates explain the role they play in many geochemical concentration processes. They incorporate traces of
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...
s mainly via
cation exchange
Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of ch ...
in their interlayer like
clay minerals
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.
Clay mineral ...
and surface complexation
by formation of
inner sphere complexes at the oxide surface as it is also the case with
hydrous ferric oxides, HFO.
Slight variations in their crystallographic structure and mineralogical composition may result in considerable changes in their chemical reactivity.

The mineral composition of manganese-bearing minerals is dependent on how the nodules are formed;
sedimentary
Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...
nodules, which have a lower Mn
2+ content than
diagenetic, are dominated by Fe-vernadite, Mn-
feroxyhyte
Feroxyhyte is an oxide/hydroxide of iron, δ-Fe3+O(OH). Feroxyhyte crystallizes in the hexagonal system. It forms as brown rounded to concretionary masses. Feroxyhyte is opaque, magnetic, has a yellow streak, and has a relative density of 4.2.
...
, and
asbolane-
buserite while diagenetic nodules are dominated by buserite I,
birnessite,
todorokite
Todorokite is a complex hydrous manganese oxide mineral with generic chemical formula . It was named in 1934 for the type locality, the Todoroki mine, Hokkaido, Japan. It belongs to the prismatic class 2/m of the monoclinic crystal system, b ...
, and asbolane-buserite.
The growth types termed diagenetic and hydrogenetic reflect
suboxic and
oxic
Hypoxia (''hypo'': 'below', ''oxia'': 'oxygenated') refers to low oxygen conditions. Hypoxia is problematic for air-breathing organisms, yet it is essential for many anaerobic organisms. Hypoxia applies to many situations, but usually refers t ...
growth, which in turn could relate to periods of
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...
and
glacial
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
climate. It has been estimated that suboxic-diagenetic type 2 layers make up about 50–60% of the chemical inventory of the nodules from the
Clarion–Clipperton zone (CCZ) whereas oxic-hydrogenetic type 1 layers comprise about 35–40%. The remaining part (5–10%) of the nodules consists of incorporated sediment particles occurring along cracks and
pores.
The chemical composition of nodules varies according to the type of
manganese minerals
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
and the size and characteristics of their core. Those of greatest economic interest contain
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
(27–30 wt. %),
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
(1.25–1.5 wt. %),
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
(1–1.4 wt. %) and
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
(0.2–0.25 wt. %). Other constituents include
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
(6 wt. %),
silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
(5 wt. %) and
aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
(3 wt. %), with lesser amounts of
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
,
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
,
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
,
potassium
Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
,
titanium
Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
and
barium
Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
, along with
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
as well as
water of crystallization
In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is ...
and free water. In a given manganese nodule, there is one part of iron oxide for every two parts of manganese dioxide.
A wide range of trace elements and trace minerals are found in nodules with many of these incorporated from the seabed sediment, which itself includes particles carried as
dust
Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...
from all over the planet before settling to the
seabed
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
.
The size of marine ferromanganese nodules can range from a diameter of 1–15 cm, surrounding a nucleus.
The nucleus itself can be made from a variety of small objects in the surrounding environment, including fragments from previously broken down nodules, rock fragments, or sunken
biogenic
A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...
matter.
Total nodule composition varies based on the formation mechanism, broadly broken down into two major categories: hydrogenetic and
diagenetic.
Hydrogenetic nodules have a higher iron and cobalt enrichment with manganese to iron ratios less than 2.5, while diagenetic nodules are more enriched with manganese, nickel, and copper with manganese to iron ratios typically between 2.5 and 5 but upwards to 30+ in sub-oxic conditions.
The parent mineral for hydrogenetic nodules is vernadite and
buserite for diagenetic nodules.
The majority of observed nodules are a mixture of hydrogenetic and diagenetic regions of growth, preserving the changes in formation mechanisms over time.
Generally, diagenetic layers are found on the bottom where the nodule is either buried in or touching the sea floor sediment and hydrogenetic layers are found towards the top where it is exposed to the overlying water column.
Nodule layers are discontinuous and vary in thickness on micro to nanometer scale with those composed of higher manganese content typically brighter and those with higher iron content dark and dull.
Terrestrial nodules
Terrestrial ferromanganese
nodules form in a variety of soil types, including but not limited to
ultisol
Ultisol, commonly known as red clay soil, is one of twelve soil orders in the USDA soil taxonomy, United States Department of Agriculture soil taxonomy. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate pr ...
s,
vertisol
A vertisol is a Soil Order in the USDA soil taxonomy and a Reference Soil Group in the World Reference Base for Soil Resources (WRB). It is also defined in many other soil classification systems. In the Australian Soil Classification it is c ...
s,
inceptisol
Inceptisols are a soil order in USDA soil taxonomy. They form quickly through alteration of parent material. They are more developed than Entisols. They have no accumulation of clays, iron oxide, aluminium oxide or organic matter. They have a ...
s,
alfisols, and
mollisols.
Similar to the marine nodules, concretion layers are defined based on iron and manganese content as well as their combination.
High iron content nodules appear a red or brown color, while high manganese content appears black or grey.
The dominant metal oxide is related to the elements enriched in the nodule. In manganese-dominated nodules, enriched elements include
barium
Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
,
strontium
Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...
,
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
,
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
,
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
,
cadmium
Cadmium is a chemical element; it has chemical symbol, symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Like z ...
,
lead
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
, and
zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
.
In contrast,
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
-dominated nodules are enriched in
vanadium
Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...
,
phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
,
arsenic
Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...
, and
chromium
Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal.
Chromium ...
.
Formation
Marine origin
Marine ferromanganese nodules form from the
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
of primarily iron, manganese, nickel, copper, cobalt, and zinc around the
nucleus. The mechanism is defined based on the source of the precipitation.
Precipitation sourced from the above
water column
The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...
is referred to as hydrogenetic, while precipitation from the sediment pore water is
diagenetic.
Nodule
growth occurs more readily in oxygenated environments with relatively low
sedimentation
Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...
rates that provide adequate levels of labile
organic matter
Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...
to fuel precipitation.
When sedimentation rates are too high, nodules can be completely covered in sediments, lowering the local oxygen levels and preventing precipitation.
Growth rates for nodules are a current topic for research complicated by the irregular and discontinuous nature of their formation, but average rates have been calculated using
radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...
.
In general hydrogenetic nodules grow slower than diagenetic at approximately 2–5 mm per million years versus 10 mm per million years.
The formation of polynodules from multiple nodules growing together is possible and hypothesized to be facilitated by deposited encrusting organisms.
Terrestrial origin
Formation of terrestrial ferromanganese nodules involves the accumulation of iron and manganese oxides followed by repeated redox cycles of reductive dissolution and oxidative precipitation.
The oscillating redox cycle is controlled by pH, microbial activity, organic matter concentration, groundwater level,
soil saturation, and
redox potential
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
.
Anthropogenic
Anthropogenic ("human" + "generating") is an adjective that may refer to:
* Anthropogeny, the study of the origins of humanity
Anthropogenic may also refer to things that have been generated by humans, as follows:
* Human impact on the enviro ...
activity could influence these cycles through increased nutrient loading via fertilizers. Assessment of the changing paleoclimate conditions during soil evolution can be explored by analyzing the nodule's concretion structure when combined with dating techniques.
Manganese layers typically form at higher redox potentials compared to iron layers, but a period of rapid increase in redox potential can form a mixed layer.
As the nodules are formed,
trace element
__NOTOC__
A trace element is a chemical element of a minute quantity, a trace amount, especially used in referring to a micronutrient, but is also used to refer to minor elements in the composition of a rock, or other chemical substance.
In nutr ...
s including but not limited to nickel, cobalt, copper, and zinc are incorporated.
Trace metals composition is a product of three processes: uptake of parent material in surrounding soil, accumulation of the products of microbial iron or manganese-reducing bacteria, and complexation on the nodule's surface.
Proposed mining – history of mining activities
Interest in the potential exploitation of polymetallic nodules generated a great deal of activity among prospective mining consortia in the 1960s and 1970s. Almost half a billion dollars was invested in identifying potential deposits and in research and development of technology for mining and processing nodules. These studies were carried out by four multinational consortia composed of companies from the United States, Canada, the United Kingdom, West Germany, Belgium, the Netherlands, Italy, Japan, and two groups of private companies and agencies from France and Japan. There were also three publicly sponsored entities from the Soviet Union, India and China.
In the late 1970s, two of the international joint ventures collected several hundred-ton quantities of
manganese
Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
nodules from the
abyssal plain
An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They ...
s ( + depth) of the
eastern equatorial Pacific Ocean.
Significant quantities of
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
(the primary target) as well as
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
and
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
were subsequently extracted from this "
ore
Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...
" using both
pyrometallurgical
Pyrometallurgy is a branch of extractive metallurgy. It consists of the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical transformations in the materials to enable recovery of valuable ...
and
hydrometallurgical methods. In the course of these projects, a number of ancillary developments evolved, including the use of near-bottom towed
side-scan sonar array to assay the nodule population density on the abyssal
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...
while simultaneously performing a sub-bottom profile with a derived, vertically oriented, low-frequency acoustic beam. Since then, deep sea technology has improved significantly: including widespread and low cost use of navigation technology such as
Global Positioning System
The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...
(GPS) and
ultra-short baseline (USBL); survey technology such as
multibeam echosounder
A multibeam echosounder (MBES) is a type of sonar that is used to seafloor mapping, map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time of flight, time it takes for the sound waves to reflect off the seabed an ...
(MBES) and
autonomous underwater vehicle
An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring continuous input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification tha ...
s (AUV); and intervention technology including
remotely operated underwater vehicle
A remotely operated underwater vehicle (ROUV) or remotely operated vehicle (ROV) is a free-swimming submersible craft used to perform underwater observation, inspection and physical tasks such as valve operations, hydraulic functions and other g ...
(ROV) and high power
umbilical cable
An umbilical cable or umbilical is a cable and/or hose that supplies required consumables to an apparatus, like a rocket, or to a person, such as a diver or astronaut. It is named by analogy with an umbilical cord. An umbilical can, for example, ...
s. There is also improved technology that could be used in mining including
pump
A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic or pneumatic energy.
Mechanical pumps serve in a wide range of application ...
s, tracked and screw drive rovers, rigid and flexible
drilling risers, and
ultra-high-molecular-weight polyethylene
Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene (HMPE), it has extremely long chains, with a molecular mass typically between 2 and 6 million amu. The l ...
rope. Mining is considered to be similar to the
potato harvest on land, which involves mining a field partitioned into long, narrow strips. The mining support vessel follows the mining route of the seafloor mining tools, picking up the about potato-sized nodules from the seafloor.
In the 2010s, increased demand for
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
and other metals prompted commercial interest in seabed nodules. The
International Seabed Authority
The International Seabed Authority (ISA; ) is a Kingston, Jamaica-based intergovernmental body of 167 member states and the European Union. It was established under the 1982 UN Convention on the Law of the Sea (UNCLOS) and its 1994 Agreement o ...
has granted new exploration contracts and is progressing development of a mining code for the area, with most interest being in the
Clarion–Clipperton zone.
Since 2011, a number of commercial companies have received exploration contracts. These include subsidiaries of larger companies including
Lockheed Martin
The Lockheed Martin Corporation is an American Arms industry, defense and aerospace manufacturer with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta on March 15, 1995. It is headquartered in North ...
,
DEME
In Ancient Greece, a deme or (, plural: ''demoi'', δήμοι) was a suburb or a subdivision of Classical Athens, Athens and other city-states. Demes as simple subdivisions of land in the countryside existed in the 6th century BC and earlier, bu ...
(Global Sea Mineral Resources, GSR),
Keppel Corporation,
The Metals Company, and
China Minmetals, and smaller companies like Nauru Ocean Resources, Tonga Offshore Mining and Marawa Research and Exploration.
In July 2021,
Nauru
Nauru, officially the Republic of Nauru, formerly known as Pleasant Island, is an island country and microstate in the South Pacific Ocean. It lies within the Micronesia subregion of Oceania, with its nearest neighbour being Banaba (part of ...
announced a plan to exploit nodules in this area, which requires the International Seabed Authority, which regulates mining in
international waters
The terms international waters or transboundary waters apply where any of the following types of bodies of water (or their drainage basins) transcend international boundaries: oceans, large marine ecosystems, enclosed or semi-enclosed region ...
, to finalize mining regulations by July 2023. Environmentalists have criticized this move on the grounds that too little is known about seabed ecosystems to understand the potential impacts of deep-sea mining, and some of the major tech companies, including
Samsung
Samsung Group (; stylised as SΛMSUNG) is a South Korean Multinational corporation, multinational manufacturing Conglomerate (company), conglomerate headquartered in the Samsung Town office complex in Seoul. The group consists of numerous a ...
and
BMW
Bayerische Motoren Werke AG, trading as BMW Group (commonly abbreviated to BMW (), sometimes anglicised as Bavarian Motor Works), is a German multinational manufacturer of vehicles and motorcycles headquartered in Munich, Bavaria, Germany. Th ...
, have committed to avoid using metals derived from nodules.
Proposed mining areas of manganese nodules
The
Clarion–Clipperton zone serves as the largest and most popular area for mining manganese nodules. Extending from approximately 120W to 160W, the
Clarion–Clipperton zone can be located in the
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
, lying between Hawaii and Mexico.
According to the
ISA, it covers an area of about four million square kilometers which almost equals the size of the
European Union
The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
.
The huge potential of the
Clarion–Clipperton zone is based on an estimated amount of 21 billion tons of nodules.
Around 44 million tons of cobalt are stored in that area alone, which is around three times more than the land reserves could provide. Manganese nodule fields are not equally distributed on the seafloor within the
Clarion–Clipperton zone but rather occur in patches. Economically interesting patches with a high distribution of manganese nodules can cover an area of several thousand square kilometers. This rather irregular nodule
distribution Distribution may refer to:
Mathematics
*Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations
*Probability distribution, the probability of a particular value or value range of a varia ...
in the South Pacific can be found as a possible result of the greater
topographic
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary scienc ...
and
sedimentological diversity of the South Pacific.
The economic interest of mining manganese nodules
The high natural abundance of
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
,
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
,
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
,
zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
,
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, and manganese in ferromanganese nodules has promoted research into their use as a rare metal resource. The
Clarion–Clipperton zone in the northeastern Pacific Ocean has been observed as an area containing the highest concentration of resource-grade nodules.
A bulk weight greater than 3% for nickel, copper, and cobalt is required to be considered resource-grade.
Nodule formation in oxic waters at or below the carbonate compensation depth produces the most desirable rare metal ratio in hydrogenic nodules.
As the grade of ores from terrestrial mines has decreased over time, ferromanganese nodules may offer a way to meet the growing global demand for rare metals.
However, the low estimated growth rate of hydrogenic nodules of about 2–5 mm per million years categorizes them as a
non-renewable resource
A non-renewable resource (also called a finite resource) is a natural resource that cannot be readily replaced by natural means at a pace quick enough to keep up with consumption. An example is carbon-based fossil fuels. The original organic mat ...
.
Technologies like
electric car batteries, wind turbines and solar panels require rare types of resources that can be found in the seabed.
Manganese nodules provide various sources of these metals, especially
cobalt
Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...
. The ongoing
digitalization, transport and
energy transition
An energy transition (or energy system transformation) is a major structural change to energy supply and consumption in an energy system. Currently, a transition to sustainable energy is underway to limit climate change. Most of the sustainab ...
causes a rising demand for metals such as copper, nickel cobalt and many other metals used in technology. Manganese Nodules are therefore needed for batteries, laptops, and smartphones, in e-bikes and e-cars, solar and wind turbines as well as for the storage of
green electricity. This enormous demand in cobalt sets the ocean into a new light — many countries have already staked their claims. Yet at the same time, mining them might cause even greater damages to the deep-sea ecosystem.
Some scientists question the prime economical interest in manganese nodules. As far as they are concerned, such biological resources could be an untapped value for
biotechnologies and medicines and should therefore be protected at all cost.
Ecology
Ferromanganese nodules are highly redox active, allowing for interaction with biogeochemical cycles primarily as an electron acceptor. Notably, terrestrial nodules uptake and trap nitrogen, phosphorus, and organic carbon.
The higher rate of organic carbon uptake allows nodules to enhance a soil's ability to
sequester carbon, creating a net sink.
Phosphorus concentration in the nodules ranges from 2.5 to 7 times the value of the surrounding soil matrix.
Microbes in the soil can utilize the nutrient enrichment on the surface of nodules coupled with their redox potential to fuel their
metabolic pathway
In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), cell. The reactants, products, and Metabolic intermediate, intermediates of an enzymatic reaction are known as metabolites, which are ...
s and release the once immobile phosphorus.
Along with nutrients, ferromanganese nodules can sequester toxic heavy metals (lead, copper, zinc, cobalt, nickel, and cadmium) from the soil, improving its quality.
However, similar to the release of phosphorus by microbes, reductive dissolution of the nodules would release these heavy metals back into the soil.
Abiogenesis theory
A recent study hypothesizes that the nodules are a source of "
dark oxygen", oxygen produced without light, which provides the seafloor in the deep ocean with oxygen. However, this study contrasts with many other studies conducted over decades in the deep sea that did not detect oxygen production - and in fact showed only oxygen consumption. If the nodules can produce both
electrical energy
Electrical energy is the energy transferred as electric charges move between points with different electric potential, that is, as they move across a voltage, potential difference. As electric potential is lost or gained, work is done changing the ...
and
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
, they may challenge the conventional theory of
abiogenesis
Abiogenesis is the natural process by which life arises from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single even ...
because, previously only living things such as plants and algae were known to be capable of producing oxygen via
photosynthesis
Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
which requires sunlight.
Environmental impacts of mining manganese nodules
Very little is known about
deep sea ecosystems or the potential impacts of deep-sea mining. Polymetallic nodule fields are
hotspots
Hotspot, Hot Spot or Hot spot may refer to:
Places
* Hot Spot, Kentucky, a community in the United States
Arts, entertainment, and media Fictional entities
* Hot Spot (comics), a name for the DC Comics character Isaiah Crockett
* Hot Spot (Tr ...
of abundance and diversity for a highly vulnerable
abyssal fauna, much of which lives attached to nodules or in the sediment immediately beneath it.
Nodule mining could affect tens of thousands of square kilometers of these deep sea ecosystems, and ecosystems take millions of years to recover.
It causes habitat alteration, direct mortality of
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
creatures, or smothering of
filter feeder
Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...
s by sediment. Due to the complexity and remoteness of the
deep-sea
The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combination of low tempe ...
, environmental scientists work in a knowledge poor situation with many gaps and high uncertainty. Nevertheless, there are several sources of cumulative impacts caused within a mining operation that must be considered. These impacts can be directly caused by the mining activities themselves but also occur as indirect impacts such as
sedimentation plumes and disposition.
Multiple impacts can be caused from the same mining activity but affect the deep-sea environment in different ways.
These could include:
* discharge plumes that have effects of clogging feeding mechanisms of
plankton
Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
* Noise and light pollution that cause reduced visibility for predators
*
Ecotoxicological
Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology ...
or chemical temperature changes in the water quality
Destruction of seabed and habitat
The dump-truck-sized collection vehicles that scour the seafloor for nodule-bearing sediment, do necessarily destroy the top of the seabed at a depth of often more than three kilometers below the surface. Scientists found that collection vehicles can have long-lasting physical and biological effects on the seafloor and cause an altering of various deep-sea ecosystems that scientists are still working to understand.
This mining method leads to an inevitable loss of life among animals while the plow tracks remained visible decades later.
Recent growth estimates suggest that "microbially mediated
biogeochemical functions"
need over 50 years to return to their undisturbed initial state. The DISCOL impact study aimed to reveal the potential long-term impacts of deep-sea mining-related disturbances on seafloor integrity by revisiting 26-year-old plough tracks. While nodules appeared outside the tracks dusted with sediments, the plough tracks themselves were clearly devoid of nodules.
The contracts to explore for manganese nodules are typically for areas up to , but the total area affected by the
extractions is much greater. The extent of physically disturbed seabed area in one mine contract area only can be assumed to be between each year, which equals the size of a large town.
Sediment laden plumes
The mining robots operating on the seabed floor emit plumes of sediment, which could cover
fauna
Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...
in the area around the mining site and therefore have a great impact on the ecosystem of the seabed.
The produced plumes contain a mixture of dissolved material and suspended particles of a range of sizes. Dissolved material is transported inextricably by the water that contains it, whereas suspended particles tend to sink.
The contained area can be estimated much bigger than the actual mined area, since finer particles and dissolved material will be transported greater distances away from the actual mined area.
Seabed
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
accumulations of plume material will therefore be thicker and contain larger particles close to the source of the plume.
In addition to the plumes created by mining activities on the seabed, discharge plumes should also be considered, that will be created by the return of excess water. Excess water occurs during the dewatering process on board of the surface vessel as well as when
ore slurries are transported from the mothership to the transport barges.
Predictions of the net impact of plumes should therefore consider a range of scenarios.
A lot of unknowns remain, scientists warn that there might be
toxic impacts.
Noise pollution
Human-generated sound can cause direct damage to
marine animals
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
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, as many of them use sound as their primary mode of communication. The extreme background noise caused by the mining machines can interfere with the communication between animals and limit their ability to detect prey. Furthermore, noise and vibration can affect auditory senses and systems of marine animals.
Noise can be caused during different processes of deep-sea mining:
* noise and vibration from seabed production tools
* midwater plumes used to transfer ores to the surface ship
* the surface ship itself
The surface vessel produces several high intensities sounds for example caused by the propellers, engines, generators, and hydraulic pumps. It is also important to consider the fact that the ship will operate almost continuously for many years during the mining contract which usually lasts for 20–30 years.
Light pollution
Mining activities could impair the feeding and reproduction of
deep-sea species through the creation of intense noise and light pollution in a naturally dark and silent environment.
Light pollution is another important factor that causes environmental impacts on sea life. The light that is used to make mining work undersea possible could attract or repel some animal species, bright lights can also blind certain marine animals. Strong lights used at the vessel and ships can influence birds as well as near surface animals.
Reduced oxygen content
If these nodules are shown to produce a significant quantity of oxygen, removal of this oxygen source may impact communities.
Mitigation of environmental impacts
There is still a gap in research of how to reduce these environmental impacts. This is partly because the entire ocean ecosystem still needs to be discovered and researched much more. Some scientists suggest that one possibility would be to reduce the weight of mining vehicles. This could reduce compaction and lessen the amount of disturbed sediment at the rear of the vehicle.
Since many deep seas are extremely dependent on the hard substrate of manganese nodules in their food chain, another option would be to leave at least a few tracks of nodules left and to not harvest them. Due to the extremely long growth rate, the mined manganese nodules will not return for millions of years. To combat this, distributing manufactured replacement nodules could be an option. But these possibilities also need to be further explored. The most beneficial mitigation effect would bring a reduction of the sediment plumes and their spreading, as these not only affect the immediate surroundings, but also affect the ecosystem at considerable distances from the nodule harvesting sites
.Experimental studies in the 1990s concluded in part that trial mining at a reasonable scale would likely help best constrain real impacts from any commercial mining.
Recovery potential of seabed ecosystems
The slow recovery potential of ecosystems can be seen as one of the major concerns of nodule mining. Seabed areas that contain nodules will be massively disturbed and the recovery of
epifauna is exceptionally slow within the mined areas. A significant proportion of the animals are dependent on the nodules, which create a hard substrate for them. These substrates will not return for millions of years until new nodules are formed.
Nodules grow from a few to a few tens of millimeters per million years. Their extreme slow growth rate is not continuous or regular and differs regarding the environment and surface. They may also not grow at all or be completely buried for periods of time.
Altogether, manganese nodules grow with an average of 10–20 mm per million years and usually have an age of several million years – if they are not mined.
Because many
deep-sea species are rare, long-lived and slow to reproduce, and because polymetallic nodules (which may take millions of years to develop to a harvestable size) are an important
habitat
In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
for deep-sea species, scientists can not rule out that some species would face extinction from habitat removal due to mining. The affected ecosystems would require extremely long time periods to recover, if ever.
Nodule mining could affect tens of thousands of square kilometers of
deep-sea ecosystems, and ecosystems take millions of years to recover.
See also
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* – A list of different manganese minerals
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References
Further reading
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* Abramowski, T. (2016)
Value chain of deep seabed mining Book: Deep sea mining value chain: organization, technology and development, pp 9–18, Interoceanmetal Joint Organization
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External links
Report on a World Almanac 1997 documentary Universe Beneath the Seaclaiming evidence of rapid formation
The International Seabed Authority
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