conditions on the surfaces of the spheroidal nodules and finally also their mechanical rolling/movement on the seafloor. It is quite conceivable that simple mechanical
movement, bioturbation, of the nodules is one determining parameter for the
formation of their spheroidal/concretionary shapes (Somayajulu 2000).
Chemical analyses of the nodules did not reveal any marked differences between
the center and the surface of the nodules even after their long growth history
(Glasby 2006). Likewise, only little information on the dynamics of growth of the
spheric nodules (Fig. 4.4a) could be gathered from polished cuts through nodules.
They revealed a layered and lamellar structures, but did not allow a resolution of
globular units at the mm-scale (Fig. 4.4b–d). Progress came recently from analyses
of small, broken, unpolished nodule samples that were studied by high-resolution
scanning electron microscopy (HR-SEM) and high-resolution energy dispersive
X-ray (HR-EDX) techniques; e.g., samples of polymetallic nodules collected from
the Clarion-Clipperton Zone in the Eastern Pacific Ocean basin (see: Wang and
M€ uller 2009). Their fracture planes revealed a distinct sub-composition of the
nodules into blackish drops, termed micronodules (Fig. 4.4e–h) that are prominent
in the outer lamellae/regions. The diameters of the spheroidal to ellipsoid
micronodules vary between 100 and 450 mm (Fig. 4.4d and f). Between the darkmetallic micronodules, an interstitial whitish, non-shiny material is seen which
apparently glues the micronodules together (Fig. 4.4e and f). In the nodules studied
by us, 2–5 individual lamellae are found, which might reflect the same number of
different, consecutively uniform growth periods, each with an own distinct
hydrogenetic history (Halbach et al. 1988), as shown in Fig. 4.4b and c. A closer
view of the individual lamellae displays their dendritic and ornamental pattern,
which is unraveled to single blackish drops, termed micronodules (Fig. 4.4e and f).
The micronodules are especially dominant in the surface lamellae. In addition, they
are also found, to a lesser degree, in the sublamellar layers (Fig. 4.4g and h).
4.4.3 Microorganisms
HR-SEM analyses were performed to identify bacteria/microorganisms within the
Mn nodules. In micronodules, dense accumulations of microorganisms were seen
(Fig. 4.5a and d). Only two morphotypes can be distinguished: round-shaped,
spherical microorganisms, which were operationally term cocci, and elongated
microorganisms, which were termed rods. In most areas, the cocci were predominant with surprisingly uniform diameters of about 2.5–4 mm and a mean of 3.5 mm
(Fig. 4.5b). The surface of the cocci was smooth, covered with small-sized platelets,
presumably consisting of Mn oxides (Fig. 4.5b). Occasionally, the cocci were
arranged in bead-like chains, as in the genus Streptococcus (Ryan and Ray 2004);
Fig. 4.5c. This chained growth form indicated cellular division along a single axis.
The rods on the other side were especially prevalent on the surfaces of the
micronodules (Fig. 4.5d). Two growth forms could be distinguished for the rods;
(1) either arranged in a palisade-like pattern, in which the rods were attached to
4 Biogenic origin of nodules and crusts
85
movement, bioturbation, of the nodules is one determining parameter for the
formation of their spheroidal/concretionary shapes (Somayajulu 2000).
Chemical analyses of the nodules did not reveal any marked differences between
the center and the surface of the nodules even after their long growth history
(Glasby 2006). Likewise, only little information on the dynamics of growth of the
spheric nodules (Fig. 4.4a) could be gathered from polished cuts through nodules.
They revealed a layered and lamellar structures, but did not allow a resolution of
globular units at the mm-scale (Fig. 4.4b–d). Progress came recently from analyses
of small, broken, unpolished nodule samples that were studied by high-resolution
scanning electron microscopy (HR-SEM) and high-resolution energy dispersive
X-ray (HR-EDX) techniques; e.g., samples of polymetallic nodules collected from
the Clarion-Clipperton Zone in the Eastern Pacific Ocean basin (see: Wang and
M€ uller 2009). Their fracture planes revealed a distinct sub-composition of the
nodules into blackish drops, termed micronodules (Fig. 4.4e–h) that are prominent
in the outer lamellae/regions. The diameters of the spheroidal to ellipsoid
micronodules vary between 100 and 450 mm (Fig. 4.4d and f). Between the darkmetallic micronodules, an interstitial whitish, non-shiny material is seen which
apparently glues the micronodules together (Fig. 4.4e and f). In the nodules studied
by us, 2–5 individual lamellae are found, which might reflect the same number of
different, consecutively uniform growth periods, each with an own distinct
hydrogenetic history (Halbach et al. 1988), as shown in Fig. 4.4b and c. A closer
view of the individual lamellae displays their dendritic and ornamental pattern,
which is unraveled to single blackish drops, termed micronodules (Fig. 4.4e and f).
The micronodules are especially dominant in the surface lamellae. In addition, they
are also found, to a lesser degree, in the sublamellar layers (Fig. 4.4g and h).
4.4.3 Microorganisms
HR-SEM analyses were performed to identify bacteria/microorganisms within the
Mn nodules. In micronodules, dense accumulations of microorganisms were seen
(Fig. 4.5a and d). Only two morphotypes can be distinguished: round-shaped,
spherical microorganisms, which were operationally term cocci, and elongated
microorganisms, which were termed rods. In most areas, the cocci were predominant with surprisingly uniform diameters of about 2.5–4 mm and a mean of 3.5 mm
(Fig. 4.5b). The surface of the cocci was smooth, covered with small-sized platelets,
presumably consisting of Mn oxides (Fig. 4.5b). Occasionally, the cocci were
arranged in bead-like chains, as in the genus Streptococcus (Ryan and Ray 2004);
Fig. 4.5c. This chained growth form indicated cellular division along a single axis.
The rods on the other side were especially prevalent on the surfaces of the
micronodules (Fig. 4.5d). Two growth forms could be distinguished for the rods;
(1) either arranged in a palisade-like pattern, in which the rods were attached to
4 Biogenic origin of nodules and crusts
85