New Zealand Journal of Geology and Geophysics abstracts
Occurrence and physical setting of ferromanganese nodules beneath
the Deep Western Boundary Current, Southwest Pacific Ocean
I. C. Wright
National Institute of Water and Atmospheric Research
P.O. Box 14 901
Wellington, New Zealand
I. J. Graham
Institute of Geological & Nuclear Sciences
P.O. Box 31 312
Lower Hutt, New Zealand
S. W. Chang
H. Choi
S. R. Lee
Korea Institute of Geoscience and Mineral Resources
30 Gajung-dong
Yusung-gu, Daejon, 305-350, Korea
Abstract An extensive ferromanganese nodule field
adjacent to the Campbell Plateau in the Southwest Pacific Ocean forms
beneath the Deep Western Boundary Current (DWBC) and Antarctic
Circumpolar Current (ACC). West of c. 174°E, between 59 and
48°S, the field is inferred to be 300–500 km wide, but east of
174°E, where the currents impinge on the eastern slope of the
Campbell Plateau, the field narrows from c. 200 km at 55°S to
c. 120 km at 49°S. This coincides with deflection of current
flow eastward, and consequent reduction in bottom-current velocity and
eddy kinetic energy. Based on seafloor photographs, dredge samples, and
3.5 kHz profile data, five principal nodule facies form broadly
parallel zones eastwards from the lowermost Campbell escarpment. These
are defined based on location, presumed nodule genesis, and seafloor
nodule density: (1) slope hydrogenous, high-density (SHH); (2) abyssal
diagenetic/hydrogenous, low-density (ADHL); (3) abyssal hydrogenous,
high-density (AHH); (4) abyssal diagenetic, high-density (ADH); and (5)
abyssal diagenetic, low-density (ADL). Several nodule morphotypes are
identified including distinctive discoidal forms with overgrowths
possibly resulting from overcrowding and partial sediment burial.
Seafloor abundance, surficial textures, and chemistry indicate a
predominantly hydrogenous nodule growth and very low net sedimentation
beneath the core of the DWBC. Increasing Mn, Ni, and Cu contents, and
decreasing detrital silicate contents from core to rim, reflect
intensifying abyssal DWBC circulation since c. 6 Ma. Because of the
DWBC’s high velocity, the nodules provide no record of an increasing
terrigenous bedload from New Zealand since c. 3 Ma. However, in regions
of reduced flow velocity eastwards from the main DWBC pathway,
relatively higher sedimentation rates prevail, and nodules have a
higher diagenetic component.
Keywords ferromanganese nodules; Deep Western
Boundary Current; Campbell Plateau
G03034; Received 3 October 2003; accepted 5 May 2004; Online
publication date 23 March 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
27–41
0028–8306/05/4801–0027 © The Royal Society of New Zealand 2005
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