Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet

Abstract

Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment?water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciationPeer reviewe

Glacier Biogeochemistry

“…Along similar lines, a 2017 study of methane cycling in subglacial Lake Whillans in West Antarctica (led by Alexander Michaud et al, 2017) found evidence of both hydrogenotrophic methanogenesis and aerobic methanotrophy, and concluded that most of the methane produced in the lake sediments was converted to carbon dioxide and biomass before it had any opportunity to reach the atmosphere.…”

“…Alex Michaud found that CH 4 was being produced in the sediments beneath Subglacial Lake Whillans (Michaud et al, 2017) (Fig. 10.3).…”

“…Figure 10.3 Concentration and carbon isotope composition of CH 4 in the sediment beneath Subglacial Lake Whillans. The distribution and relative abundance of methane oxidising and methane producing microbes is also shown (modified from Michaud et al, 2017).…”

“…It is my guess that crushing of bedrock by glacier erosion is the source (Telling et al, 2015), and that this will be a big research theme in the future (Tranter, 2015). Figure 10.4 Differing mechanisms of CH 4 formation, as differentiated by δD and δ 13 C isotopes (modified from Michaud et al, 2017).…”

A Brief History of Biochemical Genetics’ 50 Years and a Reflection About Past and Present Research Directions

“…Curiously, phages are presently viewed as having an important role in bacterial ecology and evolution (Obeng et al 2016). The different metabolic pathways occurring in different types of bacteria and other prokaryotes, such as sulfur bacteria, methane bacteria, cyanobacteria, and heterotrophic bacteria, among many others, also caused an impact on my interest in the field, the genetic basis and evolution of which are still a fascinating subject (Fani and Fondi 2009), as are their possible implications in more global topics, including climate change (Michaud et al 2017). During my biology studies in the late 1980s, classical experiments with Drosophila melanogaster were still common, en route to all the developments that made it a global model organism in genetics (Attrill et al 2016).…”