Distributed natural gas venting offshore along the Cascadia margin

Riedel, Michael, Scherwath, Martin, Römer, M., Veloso, Mario, Heesemann, M. and Spence, G. D. (2018) Distributed natural gas venting offshore along the Cascadia margin Nature Communications, 9 (3264). DOI 10.1038/s41467-018-05736-x.

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Abstract

Widespread gas venting along the Cascadia margin is investigated from acoustic water column data and reveals a nonuniform regional distribution of over 1100 mapped acoustic flares. The highest number of flares occurs on the shelf, and the highest flare density is seen around the nutrition-rich outflow of the Juan de Fuca Strait. We determine similar to 430 flow-rates at similar to 340 individual flare locations along the margin with instantaneous in situ values ranging from similar to 6 mL min(-1) to similar to 18 L min(-1). Applying a tidal-modulation model, a depth-dependent methane density, and extrapolating these results across the margin using two normalization techniques yields a combined average in situ flow-rate of similar to 88 x 10(6) kg y(-1). The average methane flux-rate for the Cascadia margin is thus estimated to similar to 0.9 g y(-1) m(-2). Combined uncertainties result in a range of these values between 4.5 and 1800% of the estimated mean values.

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