RRS James Clark Ross Cruise 253, 26 Jul -25 Aug 2011. Arctic methane hydrates

Abstract

The cruise built on the successful geophysical and geochemical mapping, undertaken during the 2008 IPY voyage JCR211 (Westbrook et al., 2009) that made the first comprehensive survey of methane bubble plume venting along the western Svalbard margin. The main achievements of JCR253 included the recovery of the ESONET demonstration mission AOEM - MASOX seafloor lander (with recovery of 10 months of physical and biogeochemical parameters from a vigorous bubble plume site) and its deployment for a further 12 months at the same site (for recovery in August 2012), completion of 23 HyBIS ROV dives, totaling 35 hr. Seafloor video and photographs, were completed along transects in both 420 – 380 m and 80-90 m water-depths, but additionally HyBIS was used to sample bubble plume fluids at seafloor “vents” for geochemical analysis, and bubble imaging to measure bubble sizes and ascent rates. A suite of 14 piston / gravity cores were acquired along three transects perpendicular to both the interpreted position of the hydrate stability zone outcropping at the seafloor and general linear band of bubble plumes emitting from the seafloor around ~ 390 m. A comprehensive suite of 28 CTD stations were completed for physical / chemical sensing and water-sampling along the three transects (co-located with sediment and box cores) and the shallow-water sites. Additionally, the active acoustic bubble BOB imaging system was deployed to record active methane bubble release at a representative bubble stream at 390 m for an 18-day deployment. A major “discovery” of the cruise is the observation of active methane bubble release in shallow- ater (80-90 m water-depth) landward of the previously described edge of the hydrate stability zone outcropping near the seafloor at water-depths of 420 – 380 m.

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