Canyon processes that transport material through submarine canyons can result in distinctive sediment deposits. Major transport events produce thick deposits of sediments along the canyon floor. These deposits can either be poorly sorted or contain relatively thick beds of coarse sand, depending upon the sediment source. By sampling these deposits we can obtain independent data for assessing which sediment transport processes are most important. Moreover, by integrating observations from the physical sensors and material sampling we can document the response of the canyon floor to measured physical conditions. MBARI scientists take sediment cores in order to obtain this information.
MBARI’s ROVs provide access to the seafloor. However, to productively use the ROVs to address many scientific questions require that they are also able to collect appropriate samples. Core samples are one of the most basic sources of geologic information. For more than 30 years, scientific submersibles and ROVs have routinely collected push cores which are typically only about 25 cm long, which is about the limit that a neutrally buoyant underwater vehicle can push into the bottom. While many scientific questions have been resolved using with this sampling technique, the resolution of numerous other problems has been hampered by the lack of longer and larger samples.
ROV Vibracoring system
Vibracoring is a common technique used to obtain samples from water saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance. Vibracorers are the best systems for collecting modest length cores in sandy sediments, like those that are common along the axis of the Monterey canyon.
MBARI Scientists Charlie Paull and
Bill Ussler prepare for ROV vibracore dive
ROV Ventana with vibracoring device.
Charlie Paull and Bill Ussler inspect core.
An ROV- operated vibracoring system has been constructed by mounting a rigid frame onto the bow of the Ventana. It usually takes only 2-3 minutes before the weight of the motor drives the vibrating core liner fully into the sediment. The core is then pulled back out of the sediment using a winch mounted on the same frame. The cores are 7.6 cm I.D. aluminum tubes. These thin- walled aluminum tubes are easily cut open longitudinally to expose the sediment core, which can be up to 2.5 meters long.
The initial coring efforts in the canyon floor indicate that there is a great deal of horizontal and vertical facies variation. In some places we have encountered deposits that suggest deposition in a high-energy environment, such as coarse gravel layers and sand horizons that are more than a meter thick. However, other cores contain thick sequences (>2 m) of finely laminated mud, suggesting continuous deposition in a calm environment.
Closer Look at Vibracores
- This vibracore is approximately 127 inches in length. The sediment is uniformly sand.
- This vibracore shows a sequence of variability and oscillations between sand and clay.
- This vibracore contains a slump deposit, which is indicative of high energy deposition events.