Distribution of Methane Plumes on Cascadia Margin and Implications for the Landward Limit of Methane Hydrate Stability

Abstract

Nearly 3,500 methane bubble streams, clustered into more than 1,300 methane emission sites, have been identified along the US Cascadia margin, derived both from archived published data and 2011, 2016–2018 dedicated multibeam surveys using co-registered seafloor and water column data. In this study, new multibeam sonar surveys systematically mapped nearly 40% of the US Cascadia margin, extending from the Strait of Juan de Fuca in the north to the Mendocino fracture zone in the south, and bounded East–West by the coast and the base of the accretionary prism. The frequency-depth histogram of the bubble emission sites has a dominant peak at the 500 m isobar, which extends laterally along much of the Cascadia margin off Oregon and Washington. Comparisons with published seismic data on the distribution of bottom simulating reflectors (BSR), which is the acoustic impedance boundary between methane hydrate (solid phase) and free gas phase below, correlates the bottom simulating reflectors upward termination of the feather edge of methane hydrate stability (FEMHS) zone and the newly identified bubble emission sites off Oregon and Washington. The Cascadia margin off northern California, where the BSR ends seaward of the FEMHS, has fewer sites centered on the 500 m isobaths, although data are more limited there. We propose that the peak in bubble emission sites observed near the 500 m isobath results from migration of free gas from beneath the solid phase of the BSR upslope to the FEMHS termination zone, and suggest that this boundary will be useful to monitor for a change in methane release rate potentially related to a warming ocean.

Hydrate Formation on Marine Seep Bubbles and the Implications for Water Column Methane Dissolution

“…(2016), Merle and Embley (2016), and Merle et al. (2021). Inset 2: Northern Gulf of Mexico showing the location of GB648, Confetti, Sleeping Dragon, and Horn Dome.…”

“…The Barkley Canyon seep (Figure 1a, panel 1) lies on the northern part of the Cascadia active margin in the Northeast Pacific Ocean. Since 2015, over a thousand previously unknown bubble plumes have been discovered along this margin from offshore Vancouver Island to northern California at water depths of tens of meters to more than 2,500 mbsl (e.g., Embley et al., 2016; Johnson et al., 2015; Merle & Embley, 2016; Merle et al., 2021; Riedel et al., 2018). The seep we focus on here is at the NEPTUNE cabled observatory node referred to as “Barkley Canyon Axis” near the “Barkley Canyon Hydrates” node that is frequently monitored by ROVs (e.g., Juniper et al., 2013) and a remotely operated deep‐sea crawler (Chatzievangelou et al., 2020; Doya et al., 2017; Purser et al., 2013).…”

Saturation sensitivity and influencing factors of marine DC resistivity inversion to submarine gas hydrate

“…Having been viewed as a potential resource, the hydrates are not merely the targets of offshore drilling, infrastructure, and slope stability assessment, but also play a vital role in the study of global climate change and the carbon cycling (Kvenvolden, 2000;Zhang et al, 2020;Kars et al, 2021;Yao et al, 2021;Yu et al, 2022). Therefore, submarine hydrate identification has been of great interest to academic and related industries in recent years (Li et al, 2016;Becker et al, 2020;Merle et al, 2021;Wang et al, 2021).…”

“…The distribution position of natural gas hydrate on land can be judged by the observed abnormal characteristics of seismic reflection and the signs obtained by logging. The distribution of natural gas hydrate on the seabed can be inferred from the abnormal features of seismic acoustic velocity, the bottom simulating reflector (BSR), blank zones, and bright spots on the seismic profile (Hyndman and Spence, 1992;Andreassen et al, 1997;Xu and Ruppel, 1999;Merle et al, 2021).…”

Methane Plume Emissions Associated With Puget Sound Faults in the Cascadia Forearc

“…zones, and the Cascadia margin beneath is an unusually well-studied example (Baumberger, et al, 2018;Embley et al, 2017;Hautala et al, 2014;H. P. Johnson et al, 2019;Merle et al, 2021;Riedel et al, 2018;Salmi et al, 2011). Gas emissions are also identified in abundance on some passive coastal margins, although the mechanism for producing those methane seeps appears to differ from those present on subduction zone margins (Garcia-Tigreros et al, 2020;Mau et al, 2012Mau et al, , 2015Plaza-Faverola & Keiding, 2019;Ruppel & Kessler, 2017;Skarke et al, 2014).…”