Development of a Self Triggering Submarine Canyon Event Detector

Instruments to detect the occurrence of energetic sediment transport events within submarine canyons are being developed. Submarine canyons are known to act as conduits for transporting sediment from the continents into the deep sea. Because the sediment primarily moves in discrete energetic events, determining the occurrence of events and the quantity of sediment involved in these transports has been difficult. Instruments placed at sites known to experience transport events are frequently lost, along with their data. In an effort to address this problem, the Monterey Bay Aquarium Research Institute (MBARI) has developed a Self Triggering Event Detector (STED). This presentation will deal specifically with the design, development, testing, and initial deployments of the proto-type STED system. The STEDs are placed in the axis of the Monterey Canyon at locations known to experience frequent sediment transport events. A combination of MBARI (Paull et al, 2003) and USGS (Xu et al, 2004) experiments demonstrate that the maximum currents on the floor of the canyon are less than 60 cm/sec under normal conditions. However, during sediment transport events, current velocities of over 200 cm/sec are sustained for several minutes. When a STED platform experiences currents in excess of 200 cm/sec, one meter above the sea bed, a positive buoyant science package is released to the surface. Included in this science package is an ARGOS Pop-off satellite transmitter that will time stamp the event and can be adapted to provide essential scientific data. Elements of the STED system include: a benthic platform, current detecting/triggering mechanism, Argos satellite transmitter, Homer Pro beacon, and instrument suite. The base is a robust structure constructed of heavy gauge steel which rests on the seafloor. An aluminum tower one meter in height is attached to the base and supports the triggering/release mechanism. The triggering/release mechanism rotates and functions as does a wea- - ther vane, always pointing into the prevailing current. When a current velocity exceeds the 200 cm/sec threshold, a trigger plate, forced to face into the current by the vane assembly, triggers the release, permitting the positive buoyant instrument suite to float upwards through the water column to the surface. Upon reaching the surface the ARGOS transmitter establishes satellite contact and down loads the acquired data. The unique identification of each ARGOS transmitter establishes the time and location in the canyon where an event/s has occurred. The Homer Pro beacons will allow these sites to be surveyed by ROV after an event has been detected. Requirements include: ease of manufacture (expendable), deployable and serviceable by ROV, remain functional for up to three years, survive currents up to the 200 cm/sec release threshold, and reliably release and deliver the instrument package to the surface. A goal of this project is to deploy several on these systems within the Monterey Canyon. To accomplish this it is necessary to design a system that is simple, affordable, and relatively easy to manufacture. These systems will be deployed by ROV, driving weight constrains of 91 kg in air and 45 kg in sea water. In the event of a release and the survival of the platform, the system can be rearmed by ROV intervention. To validate the system, significant testing was conducted in the MBARI 1,500.000 liter test tank. Two STED devices were deployed in depths of 290 and 520 m on May 30, 2006. On June 19, 2006 a release occurred at the 550 m site. Investigation revealed an event had taken place resulting in the transport of this platform 500 m down canyon