R.V. Sonne New Vent Survey SO191. Multi-Channel Seismic Reflection Regional Survey

German Research Vessel R.V. Sonne visited New Zealand early this year to initiate a large collaborative research program involving IFM-GEOMAR (Germany), GNS Science and a number of New Zealand university. The aim of the project is to study gas hydrates in the offshore region of the North Island east coast, and in particular, to investigate local and regional processes of methane transport and the characterization of facies at cold vents and gas hydrate deposits along the Hikurangi margin. The survey included three legs from 11 January to 23 March 2007, during which a variety of geophysical, geochemical, biological and environmental data where acquired. The geophysical data will help investigate the structures, fluid flow conduits and possible connections to deeper fluid sources of vent sites

Introduction to special issue on gas hydrate in porous media: linking laboratory and field-scale phenomena

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(8), (2019): 7525-7537, doi: 10.1029/2019JB018186.The proliferation of drilling expeditions focused on characterizing natural gas hydrate as a potential energy resource has spawned widespread interest in gas hydrate reservoir properties and associated porous media phenomena. Between 2017 and 2019, a Special Section of this journal compiled contributed papers elucidating interactions between gas hydrate and sediment based on laboratory, numerical modeling, and field studies. Motivated mostly by field observations in the northern Gulf of Mexico and offshore Japan, several papers focus on the mechanisms for gas hydrate formation and accumulation, particularly with vapor phase gas, not dissolved gas, as the precursor to hydrate. These studies rely on numerical modeling or laboratory experiments using sediment packs or benchtop micromodels. A second focus of the Special Section is the role of fines in inhibiting production of gas from methane hydrate, controlling the distribution of hydrate at a pore scale, and influencing the bulk behavior of seafloor sediments. Other papers fill knowledge gaps related to the physical properties of hydrate‐bearing sediments and advance new approaches in coupled thermal‐mechanical modeling of these sediments during hydrate dissociation. Finally, one study addresses the long‐standing question about the fate of methane hydrate at the molecular level when CO2 is injected into natural reservoirs under hydrate‐forming conditions.C. R. was supported by the U.S. Geological Survey's Energy Resources Program and the Coastal/Marine Hazards and Resources Program, as well as by DOE Interagency Agreement DE‐FE0023495. C. R. thanks W. Waite and J. Jang for discussions and suggestions that improved this paper and L. Stern for a helpful review. J. Y. Lee was supported by the Ministry of Trade, Industry, and Energy (MOTIE) through the Project “Gas Hydrate Exploration and Production Study (19‐1143)” under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM). Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government

CO2 Release from Pockmarks on the Chatham Rise‐Bounty Trough at the Glacial Termination

Seafloor pockmarks of varying size occur over an area of 50,000 km2 on the Chatham Rise, Canterbury Shelf and Inner Bounty Trough, New Zealand. The pockmarks are concentrated above the flat‐subducted Hikurangi Plateau. Echosounder data identifies recurrent episodes of pockmark formation at ~100,000yr frequency coinciding with Pleistocene glacial terminations. Here we show that there are structural conduits beneath the larger pockmarks through which fluids flowed upward toward the seafloor. Large negative Δ14C excursions are documented in marine sediments deposited next to these subseafloor conduits and pockmarks at the last glacial termination. Modern pore waters contain no methane and there is no negative δ13C excursion at the glacial termination that would be indicative of methane or mantle‐derived carbon at the time the Δ14C excursion and pockmarks were produced. An ocean general circulation model equipped with isotope tracers is unable to simulate these large Δ14C excursions on the Chatham Rise by transport of hydrothermal carbon released from the East Pacific Rise as previous studies suggested. Here we attribute the Δ14C anomalies and pockmarks to release of 14C‐dead CO2 and carbon‐rich fluids from subsurface reservoirs, the most likely being dissociated Mesozoic carbonates that subducted beneath the Rise during the Late Cretaceous. Because of the large number of pockmarks and duration of the Δ14C anomaly, the pockmarks may collectively represent an important source of 14C‐dead carbon to the ocean during glacial terminations

Submarine mass movements and their consequences

This sixth edition of the Submarine Mass Movements and Their Consequences volume, coincident with the seventh eponymous conference includes 61 papers that span a variety of topics and are organized into nine parts as follows: (1) Submarine mass movement in margin construction and economic significance; (2) Failure dynamics from landslide geomorphology; (3) Geotechnical aspects of mass movement; (4) Multidisciplinary case studies; (5) Tectonics and mass move- ment processes; (6) Fluid flow and gas hydrates, (7) Mass transport deposits in modern and outcrop sedimentology; (8) Numerical and statistical analysis; and, (9) Tsunami generation from slope failure. The breath and quality of this body of work underpins a positive outlook and our enthusiasm for the future direction of research in this area of science as it moves towards ever more detailed analysis and monitoring. We also emphasize in this volume the need to look at mountain-scale outcrops to better understand our seismic imaging, to carry out statistical studies that draw on global data sets to better constrain broad behavioural characteristics, and to undertake numerical modelling to understand the sensitivity of a range of natural slopes.peer-reviewe

Porewater Geochemical Assessment of Seismic Indications for Gas Hydrate Presence and Absence: Mahia Slope, East of New Zealand’s North Island

We compare sediment vertical methane flux off the Mahia Peninsula, on the Hikurangi Margin, east of New Zealand’s North Island, with a combination of geochemical, multichannel seismic and sub-bottom profiler data. Stable carbon isotope data provided an overview of methane contributions to shallow sediment carbon pools. Methane varied considerably in concentration and vertical flux across stations in close proximities. At two Mahia transects, methane profiles correlated well with integrated seismic and TOPAS data for predicting vertical methane migration rates from deep to shallow sediment. However, at our “control site”, where no seismic blanking or indications of vertical gas migration were observed, geochemical data were similar to the two Mahia transect lines. This apparent mismatch between seismic and geochemistry data suggests a potential to underestimate gas hydrate volumes based on standard seismic data interpretations. To accurately assess global gas hydrate deposits, multiple approaches for initial assessment, e.g., seismic data interpretation, heatflow profiling and controlled-source electromagnetics, should be compared to geochemical sediment and porewater profiles. A more thorough data matrix will provide better accuracy in gas hydrate volume for modeling climate change and potential available energy content

A new depositional model for the Tuaheni Landslide Complex, Hikurangi Margin, New Zealand

The Tuaheni Landslide Complex (TLC) is characterised by areas of compression upslope and extension downslope. It has been thought to consist of a stack of two genetically linked landslide units identified on seismic data. We use 3D seismic reflection, bathymetry data, and IODP core U1517C (Expedition 372), to understand the internal structures, deformation mechanisms and depositional processes of the TLC deposits. Unit II and Unit III of U1517C correspond to the two chaotic units in 3D seismic data. In the core, Unit II shows deformation whereas Unit III appears more like an in situ sequence. Variance attribute analysis shows that Unit II is split in lobes around a coherent stratified central ridge and is bounded by scarps. By contrast, we find that Unit III is continuous beneath the central ridge and has an upslope geometry that we interpret as a channellevee system. Both units show evidence of lateral spreading due to the presence of the Tuaheni Canyon removing support from the toe. Our results suggest that Unit II and Unit III are not genetically linked, that they are separated substantially in time and they had different emplacement mechanisms, but fail under similar circumstances