Active venting sites on the gas-hydrate-bearing Hikurangi Margin, off New Zealand: ROV measurements and observations
Naudts, L.; Poort, J.; Boone, D.; Linke, P.; Greinert , J.; De Batist, M.; Henriet, J.-P. (2007). Active venting sites on the gas-hydrate-bearing Hikurangi Margin, off New Zealand: ROV measurements and observations. Eos, Trans. (Wash. D.C.) AGU Fall Meet. Suppl. 88(52): F515
In: Eos, Transactions, American Geophysical Union. American Geophysical Union: Washington. ISSN 0096-3941; e-ISSN 2324-9250
During R.V. Sonne cruise SO191-3, part of the New (Zealand Cold) Vents expedition, RCMG deployed a 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 vent locations as well as an extensive BSR, indicating the presence of gas hydrates, have been found at this margin. The aims of the ROV-work were to precisely localise active methane vents, to conduct detailed visual observations of the vent structures and activity, and to perform measurements of physical properties and collect samples at and around the vent locations. The three investigated areas generally have a flat to moderate undulating sea floor with soft sediments alternating with carbonate platforms. The different sites were sometimes covered with dense fields of live clams or shell debris, often in association with tube worms, sponges and/or soft tissue corals. Active bubble-releasing seeps were observed at Faures site and LM-3 site. Bubble-releasing activity was very variable in time, with periods of almost non-activity alternating with periods of violent outbursts. Bubble release occurred mainly from prominent depressions in soft-sediment sea floor. Bottom-water sampling revealed sometimes high concentrations of methane. Sediment-temperature measurements were largely comparable with the bottom-water temperature except for a raindrop site (with dense populations of polychaetes), where anomalous low sediment-temperature was measured. Further analysis of the ROV data together with the integration of other datasets will enable us to produce a model characterising seep structure and environment.
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