New Zealand Journal of Marine and Freshwater Research abstracts
Subantarctic oceanography around New Zealand: preliminary results from an
ongoing survey
MICHELE MORRIS
BASIL STANTON
HELEN NEIL
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 14 901, Kilbirnie
Wellington, New Zealand
email: b.stanton@niwa.cri.nz
Abstract An ongoing observational program focused on
variability in the subantarctic currents and water masses around southern New
Zealand was initiated in May 1998. This paper describes the preliminary results
deduced from CTD (conductivity, temperature, depth) data collected during three
hydrographic surveys, and moored current and temperature records between 1998
and 1999. An extensive archived data set has also been analysed to provide a
hydrographic climatology of the region. The low-frequency circulation within
the subantarctic zone is described, revealing previously unreported flow
features: persistent but weak anticyclonic and cyclonic circulations over the
Campbell Plateau and a strong cyclonic flow around the western edge of the
Bounty Trough. Flow within the Subantarctic Front (SAF) is strongly constrained
by the New Zealand bathymetry; diverting to follow the south-eastern flanks of
the Campbell Plateau and crossing to the Bounty Plateau, before separating to
join the basin-scale circulation. The flow features deduced from recent data
are consistent with the hydrographic climatology as well as mid-depth float
trajectories. Subantarctic Mode Water (SAMW) is observed year-round over an
extensive fraction of the subantarctic zone: along the equatorward side of the
SAF, over the Campbell Plateau, and flowing within the cyclonic circulation
around the Bounty Trough. There is a marked cooling and freshening of SAMW
between the deep water along the western flanks of Campbell Plateau and waters
further east, consistent with a blocking of the eastward flow carrying warm and
salty SAMW by the plateau. Earlier ideas that a substantial volume of SAMW is
formed over the Campbell Plateau by deep vertical mixing (Heath 1981) are not
substantiated by our data, which include seasonal observations of the upper
water column.
Keywords Subantarctic Front; Subantarctic Mode Water;
currents; water masses; hydrographic climatologies; seasonal cycle; water
column stability; heat balance
New Zealand Journal of Marine and Freshwater Research, 2001, Vol. 35:
499-519
0028-8330/01/3503-0499 $7.00 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (5054K); (scanned from paper original: notes about this process)
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