| Description |
Monterey Bay Aquarium Research Institute,United States Geological Survey, Menlo Park, California. Chief Scientist: Charlie Paull (MBARI). Geological data of field activity W-4-09-WO in Pacific Northwest, Oregon to Canadian border: Hydrate Ridge, Barkley Canyon,and Bullseye Vent from 08/05/2009 to 08/11/2009 |
| Comments |
Our AUV mapping and ROV diving operations associated with MBARIÔøΩs northern expedition this summer are focused on investigatingknown gas vents, chemosynthetic biological communities (CBC), and gas hydrate bearing sites along the North American margin. The plans for the expedition involve collecting a series of AUV mapping surveys from the R/V Zephyr at four sites. This data will then be used to direct Doc Ricketts dives to ground truth the mapping surveys and to help direct the design of other experiments and installations. Among sites include the two summits of Hydrate Ridge (Oregon), Bullseye Vent (Canada), and Barkley Canyon (Canada). These sites continue to be targets for exploration and experimentation by researchers at MBARI and many other institutions. The installation of a seafloor observatory to monitor natural variations in gas and gas hydrate dynamics and to conduct perturbation experiments remains one of the most supported concepts within the various Ocean Observing Initiative efforts. The planned sites for the installation of gas hydrate observatories, as part of NEPTUNE Canada (including future capacity to include an IODP CORK), are Bullseye vent and Barkley Canyon. The other candidate for a cable-connected system is Hydrate Ridge. While an initial deployment of instruments is planned for NEPTUNE Canada in 2009, detailed high-resolution mapping is still lacking in parts of these areas and is necessary for the long-term planning for expansion of hydrate observatory infrastructure. This can be best (and perhaps only) provided with a system like the MBARI mapping AUV. A particular focus of this expedition is the nature and origin of the micro-topography associated with these gas-rich seafloor environments. Visual observations in many such environments have already shown that the seafloor where CBCs are on the surface and gas hydrate are believed to be in the near subsurface is commonly associated with seafloor blisters or mounds of various sizes, shallow depressions (e.g., ~3 m wide and ~1 m deep), as well as an occasional small up-turned ridge of truncated strata. The origin of this topography remains unexplained, yet is potentially critical for assessing the extent to which gas hydrates are geo-hazards and to understand how gas hydrates may shape the seafloor. Moreover, up-to-date maps that document these features do not exist, largely because of the limitations of previously available surveying tools. We are interested in documenting these features and evaluating two possible processes that may play a role in creating these features: (a) The area around these vents may be experiencing seafloor modification because of gas hydrate growth. Subsurface gas hydrate formation may inflate the seafloor producing pingo-like features that range from 1 to 10 m in height and width. When sections of seafloor contain >92% gas hydrate by volume they are buoyant in seawater. Thus, gas hydrate-bearing sediment masses may break loose from the seafloor and float away, leaving depressions on the seafloor (Paull et al., 1996). Repeat visits with an ROV or HOV to vent sites in the Gulf of Mexico (Roberts et al., 2001) and Barkley Canyon (Ross Chapman, personal communication) have shown that gas hydrate mounds observed in previous years have disappeared, apparently leaving holes. Presently, it is unknown whether these changes are of a magnitude that will be within the resolution of the mapping tools on the AUV. (b) We will also focus on documenting the extent and importance of seafloor erosion on the flanks of these structures. Occurrences of carbonate-cemented nodules and concretions exposed on the seafloor that contain cements with light carbon isotopes, indicating a contribution of methane-derived carbon, are commonly interpreted to be indicators of seafloor fluid venting and occur around all these vent systems. However, the fine-grained clastic sediments that typically host these carbonates indicate that many, if not most, of these carbonates were formed within the subsurface, presumably associated with anaerobic oxidation of methane at the sulfate-methane transition zone. We hypothesize that the widespread occurrence of these carbonates on the seafloor may result from persistent seafloor erosion, which preferentially removes the uncemented sediments and leaves the more resistant, cemented sediments standing in relief. Combined multibeam bathymetry, sub-bottom profiling, and side-scan sonar data obtained by the mapping AUV will provide a basic context to understand the nature of these systems and the broad area around them. ROV ground truth sampling also will be required to evaluate these questions. An MBARI mapping AUV survey was conducted at Barkley Canyon in 2007. However, we are interested in returning, in part, to assess whether any changes in the morphology can be quantified and to refine and enlarge the existing survey coverage. The existing schedule allows for up to 7 18-hour long AUV mapping survey missions. We have scheduled this as 2 at Hydrate Ridge (44ÔøΩ 34ÔøΩN 125ÔøΩ 09ÔøΩW); 2 at Bullseye vent (48ÔøΩ 41ÔøΩ N 126ÔøΩ 51ÔøΩW); 2 at Barkley Canyon (48ÔøΩ 19ÔøΩN, 126ÔøΩ 04 W); and one as a contingency. These would be followed by a 10-day Western Flyer expedition out of Newport, Oregon, to ground truth these survey areas. We intend to work with Ross Chapman (University of Victoria) on the Barkley Canyon surveys and Michael Riedel (McGill University) on the Bullseye vent surveys, both as a scientific collaboration and to assist in plans for the installation of Neptune observatories. The day-by-day plan for this trip will be highly dependant on the weather and the results of the AUV surveyÔøΩs. However, it is likely that we will dive on Hydrate Ridge the first day, as it will make logistical sense. On this dive we will focus on sampling up the side of the feature called the Pinnacle which has that has been described as an upward growing chemoherm (e.g., Teicher et al., 2005), but we hypothesis it is an erosional feature (Paull and Ussler, 2008). At Barkley canyon we anticipate picking up some gear of Ross ChapmanÔøΩs. At Bulleye Vent we expect to deploy an Osmo-sampler probe that is to be stuck into the sediment. This probe is designed by Laura Lapham. We believe that this is of a size that will allow it to be carried on the Doc Ricketts.
Staff information imported from InfoBank
Charlie Paull
Bill Ussler
Michael Riedel
Mary McGann
Laura Lapham
Tessie Menotti
Yireng Cho
Non USGS data manager = Kim Fulton (Bennett) |
