well as trace elements (Halbach et al. 1988; Cronan 2000; Glasby 2006). The
nodules, which can reach sizes of 14 cm, often display an alternating growth pattern
reflecting a hydrogenous to diagenetic growth (Glasby 2006). The dominant
minerals found are todorokite, hydrous MnO 2 (dMnO 2 ), as well as hydrous iron
(Thijssen et al. 1985).
In the deep waters, especially of the Pacific Ocean, the concentration of dissolved
oxygen is around 100 mmol kg
À1 (surface region: > 200 mmol kg
À1 ) and therefore
relatively high (Kester 1975). In the depth, the concentration of soluble Mn is
0.1 nmol kg
À1 [10% of the surface water] and that of Fe is 0.4 nmol kg
À1 [like on
the surface] (Bruland et al. 1994). In the oxygen-rich seafloor layers, Mn and Fe
occur in the water mainly as metal oxyhydroxides [MO x OH y ; as Mn(IV)O x OH y or
Fe(III)O x OH y ]. The Mn oxyhydroxides [ß-manganite] are stabilized in the seawater
by binding to other transition elements and by their fine granulation state (Glasby
1974). Those manganite(III)/manganate(IV) minerals represent the precursors for
nodule formation and are formed from Mn(II) via a series of intermediates, partially
autocatalytically (Murray and Brewer 1977). The slow oxidation reactions can be
accelerated substantially in the presence of inorganic interfaces with Mn(IV)oxide
(MnO 2 ) or Fe(III)hydroxide (FeOOH) (Chukhrov et al. 1976), or on bacterial
surfaces (Cowen and Bruland 1985; Hastings and Emerson 1986; Ehrlich 2002).
In the nodules, all three major Mn-oxide crystal structures can be identified, ranging
from todorokite (10 A ˚ manganite), birnessite (7 A ˚ ), and vernadite (d MnO 2 )
(Dymond and Eklund 1978; Post 1999; Glasby 2006). During nodule formation,
Mn oxides tend to incorporate cations [Ni
2+ , Cu
2+ , Zn
2+ ], while the Fe oxyhydroxides scavenge anionic species [P (HPO 4
2À ), V (HVO 4
2À ), Mo (MO 4
2À ),
W (WO 4
2À
), and especially Co (Co 3
2À
) as well as rare earth elements] (Koschinsky
and Halbach 1995).
4.4.2 Growth
The basic reactions responsible for nodule growth are the oxidation of Mn(II) and
Fe(II) to the respective oxyhydroxides that are deposited on already existing seed
crystals. During this process, other metals are incorporated mainly by scavenging
and ionic bond interactions. The Mn and Fe sources are, to a very small extent,
weathering products coming from the continental shelf, but mainly originate from
pore waters released by diagenetic processes (Bonatti and Nayudu 1965). It is not
yet known, if the growth rate on such nodule surfaces that face pore waters is faster
than at surfaces that are directed to the open sea (Moore et al. 1981). However, it is
established that growth of nodules depends on the concentrations of disequilibria of
redox systems of the individual reactants, mainly Mn(II)/Mn(IV) and Fe(II)/Fe(III).
The obvious signs of such alterations are ripple marks within the nodules (Halbach
et al. 1988). A static view of nodule formation alone does not explain those texture
formations and also does not take into consideration the changing chemical reaction
84
X. Wang et al.
nodules, which can reach sizes of 14 cm, often display an alternating growth pattern
reflecting a hydrogenous to diagenetic growth (Glasby 2006). The dominant
minerals found are todorokite, hydrous MnO 2 (dMnO 2 ), as well as hydrous iron
(Thijssen et al. 1985).
In the deep waters, especially of the Pacific Ocean, the concentration of dissolved
oxygen is around 100 mmol kg
À1 (surface region: > 200 mmol kg
À1 ) and therefore
relatively high (Kester 1975). In the depth, the concentration of soluble Mn is
0.1 nmol kg
À1 [10% of the surface water] and that of Fe is 0.4 nmol kg
À1 [like on
the surface] (Bruland et al. 1994). In the oxygen-rich seafloor layers, Mn and Fe
occur in the water mainly as metal oxyhydroxides [MO x OH y ; as Mn(IV)O x OH y or
Fe(III)O x OH y ]. The Mn oxyhydroxides [ß-manganite] are stabilized in the seawater
by binding to other transition elements and by their fine granulation state (Glasby
1974). Those manganite(III)/manganate(IV) minerals represent the precursors for
nodule formation and are formed from Mn(II) via a series of intermediates, partially
autocatalytically (Murray and Brewer 1977). The slow oxidation reactions can be
accelerated substantially in the presence of inorganic interfaces with Mn(IV)oxide
(MnO 2 ) or Fe(III)hydroxide (FeOOH) (Chukhrov et al. 1976), or on bacterial
surfaces (Cowen and Bruland 1985; Hastings and Emerson 1986; Ehrlich 2002).
In the nodules, all three major Mn-oxide crystal structures can be identified, ranging
from todorokite (10 A ˚ manganite), birnessite (7 A ˚ ), and vernadite (d MnO 2 )
(Dymond and Eklund 1978; Post 1999; Glasby 2006). During nodule formation,
Mn oxides tend to incorporate cations [Ni
2+ , Cu
2+ , Zn
2+ ], while the Fe oxyhydroxides scavenge anionic species [P (HPO 4
2À ), V (HVO 4
2À ), Mo (MO 4
2À ),
W (WO 4
2À
), and especially Co (Co 3
2À
) as well as rare earth elements] (Koschinsky
and Halbach 1995).
4.4.2 Growth
The basic reactions responsible for nodule growth are the oxidation of Mn(II) and
Fe(II) to the respective oxyhydroxides that are deposited on already existing seed
crystals. During this process, other metals are incorporated mainly by scavenging
and ionic bond interactions. The Mn and Fe sources are, to a very small extent,
weathering products coming from the continental shelf, but mainly originate from
pore waters released by diagenetic processes (Bonatti and Nayudu 1965). It is not
yet known, if the growth rate on such nodule surfaces that face pore waters is faster
than at surfaces that are directed to the open sea (Moore et al. 1981). However, it is
established that growth of nodules depends on the concentrations of disequilibria of
redox systems of the individual reactants, mainly Mn(II)/Mn(IV) and Fe(II)/Fe(III).
The obvious signs of such alterations are ripple marks within the nodules (Halbach
et al. 1988). A static view of nodule formation alone does not explain those texture
formations and also does not take into consideration the changing chemical reaction
84
X. Wang et al.