A Multi-frequency Look at Gas Seeps on the Eastern Siberian Margin
Thursday, 17 December 2015
Poster Hall (Moscone South)
The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean. In 2014 SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN (12 kHz EM122 multibeam echo sounder, 2-8 kHz SBP120 subbottom profiler, and an 18 kHz EK60 split-beam sonar). On Leg 2 of the 2014 expedition, a new wideband transceiver (EK80) was added to the split-beam echo sounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30 kHz). While the broader bandwidth unquestionably provides higher target resolution a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg 2 approximately 34 seeps were mapped, mostly in the vicinity of Herald Canyon. The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp sub-bottom profiling (from the SBP120 multibeam sub-bottom profiler) combined with water column imaging of seeps collected at both 12 kHz (from the EM122) and 15-30 kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transport from the seeps.