Spatial Association of Methane Seeps and Seafloor Geomorphic Classification on the Northern US Atlantic Margin

Methane seeps are a common feature on continental margins around the world. Dissociation of subsurface methane hydrate often exerts first order control on the location of seeps on continental margins. Seeps are typically found clustered along a depth contour coincident with the very upper limit of the Methane Hydrate Stability Zone (MHSZ), where minor variations in pressure or temperature can drive instability, hydrate dissociation, and gas release. Observations of widespread methane discharge from the northern US Atlantic margin indicate substantial variability in the depth of seeps, with methane exiting the seafloor well above and below the upper limit of the MHSZ. This depth variability exceeds that of other mid-latitude margins and suggests additional processes are involved in mediating the location of methane discharge on this margin. Examination of seeps and coincident seafloor bathymetric data on the northern US Atlantic margin suggests that seep locations may be spatially associated with specific geomorphic features. To investigate this association, we used geomorphon (Jasiewicz & Stepinski, 2013) and bathymetric position index (Wright et al., 2005) approaches to quantitatively segment and classify seafloor geomorphic features based upon gridded bathymetric data. We then quantified the degree of spatial association between methane seeps and resultant geomorphic classes as well as measured seafloor slope gradient, and aspect. Results indicate that seeps above the MHSZ are most commonly associated with slopes and spur features, while seeps below the MHSZ are most commonly associated with ridge features. The results of this research hold the potential to enhance understanding of the geological and physical oceanographic processes that mediate gas release, provide insight into the non-uniform spatial distribution of the seeps along the margin, and better predict the location of seeps on margins that have not yet been surveyed.