Submeter mapping of methane seeps by ROV observations and measurements at the Hikurangi Margin, New Zeeland
Naudts, L.; Greinert, J.; Poort, J.; Belza, J.; Vangampelaere, E.; Boone, D.; Linke, P.; Henriet, J.-P.; De Batist, M. (2008). Submeter mapping of methane seeps by ROV observations and measurements at the Hikurangi Margin, New Zeeland. Geophys. Res. Abstr. 10(2107)
In: Geophysical Research Abstracts. Copernicus: Katlenburg-Lindau. ISSN 1029-7006; e-ISSN 1607-7962
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Naudts, L.; Greinert, J.; Poort, J.; Belza, J.; Vangampelaere, E.; Boone, D.; Linke, P.; Henriet, J.-P.; De Batist, M. (2008). Submeter mapping of methane seeps by ROV observations and measurements at the Hikurangi Margin, New Zeeland. Eos, Trans. (Wash. D.C.) AGU Fall Meet. Suppl. 89(53): F1690, more
During R.V. Sonne cruise SO191-3, part of the "New (Zealand Cold) Vents" expedition, RCMG deployed their CHEROKEE ROV "Genesis" on the Hikurangi Margin. This accretionary margin, on the east coast of New Zealand, is related to the subduction of the Pacific Plate under the Australian Plate. Several cold seep locations as well as an extensive BSR, indicating the presence of gas hydrates, have been found at this margin. The aim of the ROV-work were to precisely localize active methane seeps, to conduct detailed visual observations of the seep structures and activity, and to perform measurements of physical properties and collect samples at and around the seep locations. The ROV allowed first ever visual observations of bubble-releasing seeps at the Hikurangi Margin. Seeps were observed at Faure Site and LM-3 in the Rock Garden area, at a flat to moderately undulating sea floor where soft sediments alternate with carbonate platforms. Bubble-releasing activity was very variable in time, with periods of almost non-activity (5 bubbles/second) alternating with periods of violent outbursts (190 bubbles/second). Bubbles sizes ranged from less than 5 mm to more than 20 mm. At Faure Site, bubble release was monitored over a period of 20 minutes, resulting in the observation of 6 outbursts, each lasting 1 minute at a 3 minute interval. These violent outbursts were accompanied by the displacement and resuspension of sediment grains and the formation of small depressions showing what is possibly an initial stage of pockmark formation. At the LM-3 site only some small bubble seeps were observed near a large carbonate platform covered by Bathymodiolus mussels, Calyptogena shells and tube worms. Sediment-temperature measurements, in both areas, were largely comparable with the bottom-water temperature except at LM-3, at a site densely populated by polychaetes, where anomalous low sediment-temperature was measured. Overall, both seep areas are very confined in space and bottom-water sampling revealed that the released methane has a microbial signature.
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