Application of remote sensing to study nearshore circulation

The research to use remote sensing techniques for studying the continental shelf is reported. The studies reported include: (1) nearshore circulation in the vincinity of a natural tidal inlet; (2) identification of indicators of biological activity; (3) remote navigation system for tracking free drifting buoys; (4) experimental design of an estuaring tidal circulation; and (5) Skylab support work

Evidence of Extensive Gas Venting at the Blake Ridge and Cape Fear Diapirs

Despite the important geologic, geotechnical and biogeochemical implications of seabed fluid escape, the abundance and global distribution of cold seeps remain poorly characterized. Globally, seabed fluid escape is sometimes associated with chemosynthetic communities. Fluid escape on continental margins has also been invoked as a possible trigger for submarine slope failures and seafloor collapse. Along the U.S. Atlantic Margin, acoustic and geochemical water column anomalies have been observed in the Hudson Canyon, the mid-Atlantic shelf break, and the Blake Ridge Diapir (ODP Leg 164 site 996). Of these areas, only the Blake Ridge Diapir site is known to host chemosynthetic communities, a strong seafloor indicator of active seabed fluid flow. In July 2012, NOAA Ocean Exploration Program expedition EX1205L1 identified and characterized cold seeps within the Blake Ridge gas hydrate province, using the platform Okeanos Explorer and the Autonomous Underwater Vehicle (AUV) Sentry. The expedition observed seven spatially distinct water column anomalies using shipboard EM302 30 kHz multibeam and EK60 18 kHz single beam echosounders. These anomalies originate at the seabed and extend up to 900 m above the seafloor. Interpreted as bubble plumes, these anomalies correspond in six locations to Sentry-collected photos documenting chemosynthetic organisms (e.g. mussels and clams). Three plumes are associated with the known Blake Ridge Diapir seep site, while two additional plumes and newly discovered seep communities occur within 2 km of the original site. For the first time, a gas plume and associated seep community were also observed on the main Cape Fear Diapir. Co-located 3.5 kHz subbottom data, including lines that re-occupy a 3D survey conducted in 2003 across the Blake Ridge Diapir (doi:10.1029/2006GL028859), reveal subsurface conduits presently associated with these seeps and should allow us to constrain the plumbing systems in two and three dimensions. No methane seeps were found along 210 km of surveys conducted at the presumed upper edge of gas hydrate stability on the continental slope between Blake Ridge and the head of the Cape Fear slide. Nonetheless, the discovery of new seeps indicates abundant active methane escape along the southern portion of the US Atlantic Margin and calls for a reevaluation of the role of methane venting in regional seafloor processes there. In addition, these results triple the number of known cold seep communities along the US Atlantic margin, thus providing insight into biogeographic connectivity

Evidence for extensive methane venting on the southeastern U.S. Atlantic margin

We present the first evidence for widespread seabed methane venting along the southeastern United States Atlantic margin beyond the well-known Blake Ridge diapir seep. Recent ship- and autonomous underwater vehicle (AUV)–collected data resolve multiple water-column anomalies (\u3e1000 m height) and extensive new chemosynthetic seep communities at the Blake Ridge and Cape Fear diapirs. These results indicate that multiple, highly localized fluid conduits punctuate the areally extensive Blake Ridge gas hydrate province, and enable the delivery of significant amounts of methane to the water column. Thus, there appears to be an abundance of seabed fluid flux not previously ascribed to the Atlantic margin of the United States