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

Abstract

Natural marine seeps of methane are a small but still important source of a strong greenhouse gas that enters the global environment. Methane emissions from the surface waters of estuaries into the atmosphere arise from a multitude of sources including rivers, benthic production, and simple diffusion from organic-rich sediments and these are poorly constrained on a global scale (Rosentreter et al., 2021).Active methane emissions from coastal margins have been known for over 50 years (Hovland & Judd, 1992 and references therein). Present day methane emission estimates, compiled with large uncertainties, indicate that between 3 and 48 Tg/y of methane is released to the atmosphere from marine seeps, including sources that are both thermogenic and biogenic in origin (Etiope, 2012;Hornafius et al., 1999;Razaz et al., 2020). Globally, the largest known concentrations of marine methane emission sites are on active continental margins that overlie subduction

Reviews and Syntheses: Carbon biogeochemistry of Indian estuaries

“…Further, the abundance of thermogenic sources of CH4 in tectonically active estuarine seafloors remain poorly documented and potentially large positive feedback for climate change (Johnson et al, 2022).The coast of India is home to numerous and diverse estuarine systems facing varying degrees of anthropogenic pressure; to date, studies of Indian estuaries have largely focused on either single estuaries with wide spatial coverage (Mukhopadhyay et al., 2006;Samanta et al, 2015;Dutta et al, 2019aDutta et al, , 2021Gupta et al, 2008;Pattanaik et al, 2017;Bhavya et al, 2017;Bouillon et al, 2003;Sarma et al, 2011), or a large number of estuaries with limited sampling locations (Sarma et al, 2012(Sarma et al, , 2014Krishna et al, 2015Krishna et al, , 2019Rao et al, 2016). Moreover, many of these estuaries have extensive coastal wetlands, particularly mangroves, which are densely distributed in estuaries of the Sundarbans (Saptamukhi, Thakuran, and Matla) and more sparsely scattered along the banks of the Haldia, Mahanadi, Godavari, Krishna, Ponnayaar, Mandovi and Zuari Rivers (Dutta et al, 2015;Rao et al, 2016).…”