INTRODUCTION
Leg 181 will drill
sites located in the key Southwest Pacific Gateway because:
- The
Pacific Deep Western Boundary Current (DWBC) is the
largest single contributor today to the deep waters of
the world's oceans (20 Sverddrups [1 Sv = 106 m3s-1];
Fig. 1), and
deciphering its history is, therefore, of fundamental
importance to global and Pacific ocean hydrography.
- The
stratigraphic record of the eastern New Zealand Plateau
and its abyssal margins is the best one available for
deciphering the development history of Pacific Southern
Ocean water masses, and of the sediment drifts they
deposited. Recent publications (Carter and Carter, 1993,
1996; Lewis, 1994; Carter and McCave, 1994, in press; L.
Carter et al., 1996; McCave and Carter, 1997) delineate
the region between the Solander Trough and the Kermadec
Trench, east of the modern Australian-Pacific plate
boundary, as an integrated sediment source-transport-sink
area, termed the Eastern New Zealand Oceanic Sedimentary
System (ENZOSS). Since ~10 Ma, sediment from mountains
along the New Zealand plate boundary has been transported
through deep-sea channel/fan systems, delivered into the
path of the DWBC, entrained northwards within this
current system and finally consumed by subduction at the
same plate boundary after a transport path of up to 3500
km. The stratigraphic record from the ENZOSS, and in
particular any new high-resolution, Neogene Ocean
Drilling Program (ODP) sections from its deep-sea parts,
are directly relevant to one of the most important
unresolved problems of Cenozoic climatology, namely the
timing and precise nature of the development of
widespread glaciation on the Antarctic continent
(Barrett, in press). In turn, the same glacial events
that contribute source water to the DWBC and its
companion flow, the Antarctic Circumpolar Current (ACC),
force the boundary current south of 49°S.
- The
gateway region includes two major oceanic fronts, the
Subtropical Convergence and the Subantarctic Front, and
is proximal to a third, the Antarctic Convergence (Figs. 2, 3). Thus, the
region is in a prime position to allow determination of
the migration of these boundaries, the forcing processes
that cause them to move, and the environmental response
to their movement.
To 181 Background
To 181 Table of
Contents