Sea Technology

JUN 2015

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38 st / June 2015 www.sea-technology.com less steel legs ensure that the water just above the seafoor— the bottom boundary layer—fows freely past it. This monitored section of seafoor lies in the northeastern part of the South China Sea. This international effort start- ed with USGS oceanographer Jingping Xu (now a USGS emeritus scientist), who collaborated with Tongji University in Shanghai, China. Xu tapped into expertise in sediment feldwork found at the USGS Pacifc Coastal and Marine Science Center to investigate what has been described as a possible "contourite," or mound of sediment deposited by bottom cur- rents. It's not clear why mounds form in this particular spot or how circula- tion works in this area. Understanding how deep-sea sediment moves can help forecast how potential pollution accumulates in a specifc region or where the most stable area is to bury undersea cables. Other than oil industry in- vestigations, few open, publically available studies exist of the physical characteristics of deep-water sediment dynam- ics near the seabed. Data Collection from FAT This collaboration consisted of designing and testing two tripods that would be jointly de- A fter a piece of U.S. government equipment sat for fve months far away on the seafoor of the South China Sea in roughly 1,900 meters of water, U.S Geological Survey (USGS) instrument specialist George Tate wasn't too worried whether it would return to the surface. "The period of angst was actually the frst week," Tate said. He feared receiving an email from the new instrument, because that would signal it had risen to the surface prematurely. Marine technology with an acronym like FAT likely conjures images of a boxy and heavy piece of gear. But Tate's FAT (free ascending tri- pod) design is much more streamlined. It has to be, because its sole purpose is to sit without disturbing the very section of seafoor it was designed to monitor. Three, 13-foot stain- Trimming the FAT for Seafoor Research in China Constructing a Tripod to Monitor Deep-Sea Sediment Movement By Amy West (Top) Members of Tongji University and USGS reassembling the tripod and at- taching the oceanographic equipment and syntactic foam (orange blocks). Note the square, weighted footpads. (Botom) A bird's eye view of FAT's instrumentation showing the yellow surface recovery foat in the middle and two EdgeTech (West Wareham, Massachusetts) acoustic transpon- ding releases on the left, with a XEOS (Dartmouth, Canada) Sable satellite Iridium beacon mounted between them. (Photo Credit: Joanne Thede Ferreira/USGS) (Photo Credit: Joanne Thede Ferreira/USGS)

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