Persistence of bubble outlets in soft, methane‐generating sediments. Issue 6 (3rd June 2017)

• Record Type: Journal Article
• Authors: Scandella, Benjamin P.; Delwiche, Kyle; Hemond, Harold F.; Juanes, Ruben
• Is Part Of: Journal of geophysical research. Volume 122:Issue 6(2017)
• Page Start: 1298
• Page End: 1320
• Publication Date: 2017-06-03
• Subjects: methane venting -- sediment -- methanogenesis -- incubation -- experiment; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2016JG003717
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Sediments submerged beneath many inland waterways and shallow oceans emit methane, a potent greenhouse gas, but the magnitude of the methane flux to the atmosphere remains poorly constrained. In many settings, the majority of methane is released through bubbling, and the spatiotemporal heterogeneity of this ebullition both presents challenges for measurement and impacts bubble dissolution and atmospheric emissions. Here we present laboratory‐scale experiments of methane ebullition in a controlled incubation of reconstituted sediments from a eutrophic lake. Image analysis of a 0.14 m 2 sediment surface area allowed identification of individual bubble outlets and resolved their location to ∼1 cm. While ebullition events were typically concentrated in bursts lasting ∼2 min, some major outlets showed persistent activity over the scale of days and even months. This persistence was surprising given the previously observed ephemerality of spatial structure at the field scale. This persistence suggests that, at the centimeter scale, conduits are reopened as a result of a drop in tensile strength due to deformation of sediments by the rising bubbles. The mechanistic insight from this work sheds light on the spatiotemporal distribution of methane venting from organic‐rich sediments and has important implications for bubble survival in the water column and associated biogeochemical pathways of methane. Key Points: Our novel incubation experiment allows direct imaging of bubble releases with centimeter‐scale resolution Bubble outlets are reused both within ebullition events and over the scale of days to months Hydrostatic pressure plays a determinant role in enhancing and inhibiting ebullition