After watching a globular rock shatter under pressure from the manipulator, scientists were convinced they discovered a rare natural asphalt site. Click image for larger view and image credit.
Scientists got more than they bargained for when ROV pilots plucked this single tubeworm specimen from the seafloor. A small reservoir of thick sticky tar was just below the seafloor. Strung out by the current, the tar eventually stuck to the lens of the science camera. Click image for larger view and image credit.
Jason Lowering 280 - Garden Banks 647
June 26, 2007
Matt Frye
Minerals Management Service (MMS)
27° 19.73 N
92° 25.69 W
Scientist discover oozing tar in the chemosynthetic ecosystems of the Gulf of Mexico. (Quicktime, 1.8 Mb.)
Geologists document an accumulation composed of natural asphalt, an exciting find in the northern Gulf of Mexico. (Quicktime, 1.1 Mb.)
During our R/V Atlantis and Alvin cruise last year, we preliminarily explored many of the targets that we’ve been diving on this summer. Having the opportunity to work during two field seasons has been critical for this project. Not only does it allow us to take advantage of the different capabilities provided by Jason and Alvin, but the information from the first field season has been critical to developing detailed sampling plans for each of the sites that we’ve be re-visiting this year. In addition to these ‘known’ locations, we’ve also used remote sensing techniques and 3D seismic data amplitude variations to help identify new targets never previously visited with a submersible. Garden Banks 647 (GB 647) was one of these new exploratory sites. As with any exploratory effort, you are never quite sure what you are going to find........
The feature of interest at GB 647 is a southwest/northeast trending ridge along the seafloor that is underlain by a shallow salt body. The vertical seismic reflection data indicate that the salt comes within several meters of the seafloor. The geophysical maps suggested that several small areas, scattered across the ridge, contained something other than the soft silt and mud that covers most of the Gulf of Mexico seafloor. These anomalous areas often turn out to be carbonate rocks, dense chemosynthetic communities, hydrate accumulations, brine seeps, and in many cases, all of the above.
The Jason ROV landed on the highest point of the ridge, the first of at least 6 geophysical targets in the dive plan that MMS scientists hoped to examine. We immediately noticed a single boulder, no more than one-meter across, resting alone on an otherwise muddy ocean bottom and acting as a host for several species of coral.
This tiny orange sea anemone is growing on a rock near the natural asphalt site. Click image for larger view and image credit.
Due to its unusual nature and rare occurrence, the big asphalt sample attracted a crowd once on deck of the Ron Brown. It has a botryoidally shaped (like a bunch of grapes) hardened outer crust which is very friable, and when pulled apart the rock's interior looks like chewing gum. Click image for larger view and image credit.
The rock was shaped differently than most carbonate rocks that are typically encountered on the seafloor. As the Jason manipulator arm was taking a sample of the rock, it broke apart and floated through the water column. At this point we were certain that this was some sort of natural asphalt and likely contained the residue of a mature petroleum product that had leaked out from below the seafloor. It was an exciting find, as very few asphalt accumulations have been documented on the northern Gulf of Mexico seafloor.
Throughout the remainder of the dive, we continued to see evidence of hydrocarbons at and near the surface. A large exposure of asphalt coincided with our first pre-dive target along the western flank of the topographic feature. This site also contained abundant carbonate rocks, sponges, corals, bacterial mats, and possible brine flows.
Most of the sediment samples collected throughout the day with push cores yielded oily mixtures of mud and silt. At one tubeworm location, an oily liquid dripped from the base of the tubeworm as it was lifted from the seafloor. A similar black fluid, less dense than the surrounding seawater, emerged from the ground where the tubeworm had been located and floated off into the water column
An exploratory site such as GB 647 will always provide new information. During many of our exploratory dives this month, we have found the chemosynthetic tubeworm and mussel communities that we’ve been searching for. In some cases we’ve found little more than silt and mud. In very rare cases like today, we find something completely unexpected! No matter what we come across, in all cases we use our findings to calibrate our pre-dive expectations and enhance our predictive capabilities for the next exploratory effort.
