Monitoring methane emissions at Southern Hydrate Ridge using an OOI Cabled Array Acoustic Doppler Current Profiler

Gas hydrate deposits along continental margins are commonly associated with overlying methane seeps, which support extensive biological communities on and within the sediments. In addition, the rising methane-rich plumes may be responsible for increased biological productivity within the overlying ocean. The extent to which methane seeps contribute to oceanic and atmospheric carbon is thought to be relatively minor, but this conclusion is largely based on infrequent observations of bubble release over short timescales. Here, we present initial results of bubble plume variability from a cabled Acoustic Doppler Current Profiler (ADCP) deployed for 2 years at Southern Hydrate Ridge (SHR), a well-studied hydrate-bearing seep site off the coast of Oregon. This area is characterized by extensive bacterial mats, focused venting of bubble plumes, and rare exposed gas hydrate on the seafloor. The upward-looking ADCP is a part of NSF's Ocean Observatories Initiatives Cabled Array infrastructure at SHR. Live data from eleven cabled instruments and three un-cabled sensors at SHR for which data are collected post annual Operations and Maintenance cruise enable long-term monitoring of process linkages at SHR seeps. Preliminary results indicate that bubble plumes extend over much of the water column at SHR, though further analysis is required to determine whether seepage is forced over tidal periods. Future studies involving the incorporation of data from proximal instrumentation at SHR would provide a comprehensive understanding of the link between subsurface gas transport and gas distribution throughout the overlying water column.