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Abstract
Journal of Sedimentary Research, Section
B: Stratigraphy and Global Studies
Vol. 67 (1997)No.
6. (November), Pages 1005-1017
The Sedimentary Regime Beneath the Deep Western Boundary Current Inflow
to the Southwest Pacific Ocean
Lionel Carter (1), I. N. McCave (2)
ABSTRACT
A review of hydrographic sections, single-channel seismic profiles, bottom
photographs, and nephelometer profiles collected by the U.S.N.S. Eltanin,
plus new seismic and sedimentary data from the R.V. Rapuhia, provide
an insight into the sedimentary regime beneath the Pacific deep western
boundary current (DWBC) where it enters the SW Pacific off southernmost
New Zealand at Macquarie Ridge and Campbell Plateau. There the DWBC is
reinforced by the Antarctic Circumpolar Current (ACC) largely through the
generation of deep-reaching eddies formed by interaction of the ACC with
the pronounced bathymetry. It is therefore a region of high eddy kinetic
energy, which induces widespread abyssal erosion. It is also where the
DWBC receives its first major injection of terrigenous se iment, which
is transferred from southern New Zealand along the 450+ km-long Solander
Channel. From Macquarie Ridge the ACC-DWBC travels northeast onto the Subantarctic
Slope of Campbell Plateau. This high, steep, western boundary intensifies
the flow, causing erosion along the slope base. East of the scour the 800
km-long Campbell Drift has been deposited. This drift extends to 51°S,
where the ACC swings east to continue its circum-Antarctic journey, while
the DWBC continues northeast to Bounty Trough, where the combination of
abundant sediment supplied by Bounty Channel, a subdued western boundary,
and a less energetic DWBC, have allowed the Bounty Fan to form directly
across the current path. Apart from localized winnowing near zones of high
relief, evidence for widespread DWBC in luence on the fan is inconclusive.
However, current effects become more apparent north of Bounty Fan, where
the steep western boundary resumes in the form of Chatham Rise. Eroded
fan sediments have contributed to a series of small drifts at 4400-5000
m depth, whereas at 2400-3400 m depth on the flank of Chatham Rise, the
DWBC has molded a sinuous terrace-like drift.
Viewed regionally, sedimentation beneath the boundary current south
of Chatham Rise contrasts strongly with the regime to the north. The southern
current is energetic and terrigenous supply is intermittent, being restricted
to glacial lowstands. Consequently, erosion is common, and drifts are few
and are themselves subject to erosion. By comparison, the current north
of the rise is generally slower and has a more consistent terrigenous supply,
particularly near Hikurangi Channel, which has been active irrespective
of sea level. Thus widespread drift deposition is favored.
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