A joint electromagnetic and seismic study of Arctic hydrates and fluid escape features, offshore Svalbard

• Main Author: Goswami, Bedanta
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: Arctic; Svalbard
• Online Access: https://eprints.soton.ac.uk/396590/; https://eprints.soton.ac.uk/396590/1/Goswani%252C%2520Bedanta_PhD_May_16.pdf

The west Svalbard continental margin has been in the spotlight since 2008, when more than 200 active methane seeps were reported near the landward edge of the gas hydrate stability zone (GHSZ). Several additional seeps have since been reported in the continental shelf area, some of which are likely to be associated with shallow hydrate dissociation and ocean warming. In addition, active seeps and seafloor pockmarks were also reported along the crest of the deep water Vestnesa Ridge area, which is also a known area of gas hydrate presence. However, the seeps at the ridge are unlikely to be related to ocean warming. Nevertheless, improved estimates of the amount of methane trapped within hydrate and gas in the west Svalbard continental margin are necessary to evaluate seafloor methane fluxes and its impact on future climate. Hydrate presence in the two study areas, the Vestnesa Ridge and the continental slope of the margin were traditionally inferred from the presence of bottom simulating reflectors (BSR) in seismic reflection data and high seismic velocity anomalies observed within the GHSZ. Bulk resistivity estimates obtained from marine controlled source electromagnetic (CSEM) data are highly sensitive to the presence of both hydrate and free gas within the sediment pore spaces. The presence of hydrate leads to an increase in the bulk resistivity and seismic velocity, whereas the presence of free gas leads to an increase in bulk resistivity but decrease in seismic velocity. These complementary attributes, combined with seismic reflection data provide a unique opportunity to obtain improved constraints on hydrate and free gas saturations in the margin. Therefore, CSEM data were acquired in 2012 at the two locations, to complement coincident seismic reflection and seismic refraction data. The CSEM data were acquired using a 100 m long horizontal electric dipole antenna that transmitted a 81 A, 1 Hz pseudo-square wave current. It was recorded using two sets of CSEM receivers: ocean bottom electric-field (OBE) ...