HR: 1340h
AN: B43E-1656    [Abstracts]
TI: Multi-frequency Hydro-acoustic Imaging of Cold Seeps on the Hikurangi Margin Offshore New Zealand
AU: * Weinrebe, W
EM: wweinrebe@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148, Germany
AU: Klaucke, I
EM: iklaucke@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148, Germany
AU: Greinert, J
EM: j.greinert@gns.cri.nz
AF: GNS Sciences, 1 Fairway Drive, Avalon, Lower Hutt, 5010, New Zealand
AU: Linke, P
EM: plinke@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148, Germany
AU: Bialas, J
EM: jbialas@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148, Germany
AB: The subduction of the Pacific plate underneath the Australian plate along the Hikurangi margin leads to intense fluid venting along the southeastern margin of New Zealand's North Island. In the framework of the NewVents project several areas, where active fluid venting was known or expected, have been mapped using shipborne multibeam bathymetry as well as deep-towed sidescan sonar. Among the areas investigated the area known as Wairarapa, located just north of the southern end of Cook Strait, is one of the most interesting because several sites showing different degrees of fluid venting have been identified on 75 kHz sidescan sonar data. The Wairarapa area is located in roughly 1000-m water depth on a southwest-northeast trending ridge that has a distinct cone-shaped elevation at its northern end. Relief on the ridge is rather small and erosive sediment pathways separate the area from direct input of coarse sediment. Sedimentation in the Wairarapa area is dominated by hemipelagic sedimentation together with probably only very fine-grained turbidite spill-over deposition. Distinct high backscatter features showing a rough surface on the ridge are consequently most likely the result of carbonate cementation and precipitation of authigenic carbonates, as ground-truthing by video observation and coring show. A minimum of seven such high backscatter patches with maximum diameters of several hundreds of meters can be distinguished. Active fluid venting in these areas is demonstrated by very distinct acoustic flares in the water column. Due to narrow spacing of mapping profiles and an increased swath width of the deep-tow sidescan sonar system several high backscatter patches have been surveyed several times within the space of a few hours. Interestingly the outline of the flares change over time as viewed in different profiles indicating the activity of the seeps.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3004 Gas and hydrate systems
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting