EXPLORATION OF THE PUERTO RICO TRENCH AND MUERTOS TROUGH WITH UNTETHERED FREE-VEHICLES

The Puerto Rico Trench (PRT) and Muertos Trough represent the closest active plate boundary to the U. S. Atlantic seaboard, and of course to Puerto Rico and the U. S. Virgin Islands. Significant seismic and tsunami hazards to U.S. and regional interests are thought to exist, but recurrence rate estimates are largely limited to the spotty historical record. Although twelve people have walked on the Moon and numerous spacecraft are now exploring our solar system and beyond, very little in situ sampling of the Earth’s oceanic trenches has occurred. Their general geographic remoteness and extreme bottom-pressures (>600 atmospheres) have made all sampling techniques difficult. Cable lengths needed (>6.5 km) make tethered sampling cost-prohibitive, and problematic in terms of successful data acquisition. However, developments in the manufacture of glass housings offer scientific investigators and engineers the opportunity to sample the Earth’s deepest trenches at a fraction of the cost of previous methods. In 2006, a team of scientists and engineers began to develop and deploy new instruments to explore the ultra-deep (>8 km) PRT , the deepest part of the Atlantic Ocean and the seventh deepest trench on Earth. This “proof of concept” project laid the groundwork for modern, low-cost, un-tethered free-descent/ascent exploration by obtaining three 60 l water samples (Eloe et al., 2011) and 75 min of acoustic-Doppler current measurements (Schmidt and Siegel, 2011) from the PRT at depths greater than 8.3 km. These low-cost ‘free-vehicles’ are the oceanographic analog to small-satellite space missions, which have been shown to (Baker and Worden, 2008):

1) Be a cost effective method for addressing key scientific questions

2) Have the capability for quick response to targets of opportunity

3) Be a means for the development and demonstration of new technology and design concepts

4) Facilitate opportunity for multi-disciplinary and international collaborations

Free vehicle research payloads in development include sediment samplers and vertebrate/invertebrate traps. Recent tests and deployments will be discussed.