In January/February 2000, the Australian Geological Survey Organisation (AGSO)
completed a 2S-day seabed swath-mapping and geophysical survey off south and
south-east Tasmania and south of Macquarie Island for the National Oceans Office
and Environment Australia. The survey, which is named AUSTREA-2 and designated
as AGSO Cruise 223, used the 8S-m French oceanographic and geoscience research
vessel N/O L 'Atalante, which departed Hobart on January IS and arrived in Bluff,
New Zealand, on February 9. The survey covered about 10,200 km and mapped about
140,000 km2 of seabed. The initial impetus for the work was to map the foot-of-slope
position in several areas to support definition of Australia's legal Continental Shelf
under the United Nations Convention on the Law of the Sea. A significant additional
but complementary aspect was to support marine zone planning and management, and
assessment of seabed living and non-living (petroleum and mineral) resources, as an
important step towards implementation of Australia's Oceans Policy and Australia's
Marine Science and Technology Plan, and, in particular, the development of the
South-east Regional Marine Plan by the National Oceans Office.
Geophysical data collected included Simrad EM12D swath bathymetry and
backscatter, 6-channel GI-gun seismic, 3.S kHz sub-bottom profiling, and gravity and
magnetic profiles. This was augmented by a suite of oceanographic data, such as
seawater temperature, and both current and salinity depth profiles. Weather and sea
conditions were highly favourable, particularly in the more southern latitudes.
Occasional periods of rough weather resulted in higher noise levels, but did not
seriously affect acquisition, and data quality was generally excellent.
The work conducted off Tasmania was mostly to fill in and extend previous swath
coverage, and map the foot-of-slope along the eastern margin of the South Tasman
Rise. It highlighted features such as the major development of slope canyons down
the eastern Tasmanian margin, and the complex character of the Cascade Seamount
and other seamounts adjacent to the South Tasman Rise.
The work conducted over the southern Macquarie Ridge Complex highlighted
features such as: a high-relief axial valley adjoining the deep Hjort Trench; the
broadening to the south of the submerged Hjort Ridge, east of the Hjort Trench; the
development of seafloor spreading tectonic fabric across the Hjort Ridge summit; and
the presence of a linear trough/ridge feature that obliquely truncates the southern end
of the Hjort Trench and adjoining axial valley.
A full set of shipboard maps are held by the National Oceans Office and AGSO, and
copies of the digital data are stored at AGSO. All data from the survey will be
managed jointly by AGSO and the National Oceans Office.