Gas escape features off New Zealand: Evidence of massive release of methane from hydrates

Multibeam swath bathymetry data from the southwest margin of the Chatham Rise, New Zealand, show gas release features over a region of at least 20,000 km(2). Gas escape features, interpreted to be caused by gas hydrate dissociation, include an estimated a) 10 features, 8-11 km in diameter and b) 1,000 features, 1-5 km in diameter, both at 800-1,100 m water depth. An estimated 10,000 features, similar to 150 m in diameter, are observed at 500-700 m water depth. In the latter depth range sub-bottom profiles show similar gas escape features (pockmarks) at disconformities interpreted to mark past sea-level low stands. The amount of methane potentially released from hydrates at each of the largest features is similar to 7*10(12) g. If the methane from a single event at one 8-11 km scale pockmark reached the atmosphere, it would be equivalent to similar to 3% of the current annual global methane released from natural sources into the atmosphere. Citation: Davy, B., I. Pecher, R. Wood, L. Carter, and K. Gohl (2010), Gas escape features off New Zealand: Evidence of massive release of methane from hydrates, Geophys. Res. Lett., 37, L21309, doi:10.1029/2010GL045184.