50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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The MCC is bounded by deep-seated transform<br />
faults separating domains in which extension has<br />
been strongly localized on weak, individual faults<br />
(MCC’s) vs. where it is distributed.<br />
ORAL<br />
MAPPING THE DEEP SEA: APPLICATION<br />
<strong>OF</strong> MULTIBEAM DATA TO DEEP SEA<br />
GEOLOGICAL SAMPLING<br />
K. Mackay, Malcolm Clark, Ian Wright,<br />
& Miles Dunkin<br />
NIWA, Private Bag 14 901, Kilbirnie, Wellington,<br />
New Zealand.<br />
(k.mackay*niwa.co.nz)<br />
Multibeam echosounders are becoming<br />
increasingly and routinely used for detailed seafloor<br />
mapping up to several kilometres either side of the<br />
survey vessel. Such multibeam data have been used<br />
to determine seafloor bathymetry and substrate<br />
composition for geological research by accurately<br />
map submarine topography, such as seamounts or<br />
canyons. In addition, the multibeam seafloor<br />
acoustic backscatter data can differentiate between<br />
different substrate types, including sediment and<br />
exposed bedrock, and hence guide successful<br />
geological sampling operations. Multibeam<br />
mapping of the ocean bottom is markedly more<br />
efficient than conventional single-beam<br />
echosounders, and provides greater resolution and<br />
accuracy of both seafloor morphology and<br />
composition.<br />
Since 2001, the Simrad EM300 multibeam system<br />
on NIWA’s research vessel Tangaroa has been used<br />
extensively in support of ocean geology sampling<br />
operations, especially around the east coast of the<br />
North Island, Cook Strait, Kermadec Ridge,<br />
Norfolk Ridge, and Lord Howe Rise.<br />
The existing charts of these regions have generally<br />
proved to be adequate on a large scale, indicating<br />
the approximate position of ridges or seamounts.<br />
However, on the scale of an individual feature, the<br />
depth, size, and shape of a seamount are often<br />
poorly charted. The width of seafloor that can be<br />
mappedisupto4timesthewaterdepth,andsoat<br />
1000 m depth the bathymetry was determined 2 km<br />
either side of the vessel. This enables rapid<br />
evaluation of the shape of the seabed, which was<br />
often very different from the chart.<br />
The seafloor bathymetry is often rugged and<br />
complex, with the multibeam proving essential to<br />
the success of sampling several sites. The acoustic<br />
backscatter intensity gives an indication of<br />
substrate composition, which was used to plan rock<br />
dredging and/or sediment sampling operations. It<br />
also gives us data on the type of sediment and<br />
habitat which may be used later in analyses such as<br />
defining a unique benthic community structure.<br />
POSTER<br />
THE WILD WEST: IMAGING WEST COAST<br />
SEDIMENT CONDUITS<br />
K. Mackay, H.L.Neil&J.Mitchell<br />
NIWA, Private Bag 14 901, Kilbirnie, Wellington,<br />
New Zealand.<br />
(k.mackay*niwa.co.nz)<br />
New Zealand is in a critical location for<br />
reconstructing changes in westerly circulation and<br />
evaluating its role in controlling global climate<br />
change. Surrounded by vast areas of ocean, the<br />
main axial ranges intersect the prevailing<br />
westerlies. The Southern Alps of New Zealand are<br />
an ideal location to understand the history of the<br />
westerly wind system through time as the<br />
interaction between orographic effects and the<br />
westerlies produce significant precipitation on the<br />
West Coast of the South Island.<br />
The first in a probable series of research voyages<br />
projected for the West Coast Canyon region off<br />
South Island, New Zealand was completed in<br />
October <strong>2005</strong>. The aim of this research programme<br />
is to define a history of glaciation during the late<br />
Quaternary in New Zealand, in particular the<br />
relationship with the Westerly Wind system and<br />
correlation with abrupt climate change globally and<br />
to determine the sources and fluxes of sediment<br />
influencing the southern New Zealand region.<br />
The West Coast is supplied by 3 of the 5 largest<br />
rivers in New Zealand with respect to sediment<br />
load. Presently fifty times more sediment is<br />
injected into this system than that into the Bounty<br />
Trough as a consequence of the closer proximity of<br />
the Southern Alps source area and the lack of large<br />
natural lakes that trap up to 15% of the sediment<br />
yield to the east of the Alps. Glacial-Interglacial<br />
changes recorded in sediment sequences in<br />
downslope basins should reflect a switch on with<br />
large sediment flux in peak glacial times and a<br />
switch off during interglacials. At the last glacial<br />
maximum, major valley glaciers reached the open<br />
coast, probably as grounded tidewater glacial fronts<br />
providing voluminous mud, sand and gravel via a<br />
range of processes directly to the continental slope<br />
(Barnes et al., 2001).<br />
Seafloor topography was surveyed using the<br />
Simrad EM300 multibeam sonar, which uses a fan<br />
of 135 sonar beams to simultaneously ensonify and<br />
map a swath of the seafloor up to a width of up to<br />
5-times the water depth. These bathymetric data are<br />
processed within a GIS to form a digital terrain<br />
model (DTM). Using spatial analysis functions of<br />
GIS, the DTM is interrogated to identify, and<br />
50 th <strong>Kaikoura</strong>05 -47- <strong>Kaikoura</strong> <strong>2005</strong>