Subglacial methane cycling under the Greenland Ice Sheet 

<p>Glaciers and ice sheets cover around 10% of the Earth&#8217;s surface and the Greenland Ice Sheet (GrIS) is the largest ice mass in the Northern hemisphere, but is melting at an increasing rate, losing ~400 km³ annually. There have been recent studies linking subglacial environments of the GrIS with methane (CH₄) production and release, presenting a possible positive climate feedback. Previous work has linked organic carbon in subglacial environments with significant CH₄ export via methanogenesis. It has been hypothesised that the GrIS overlies a methanogenically active wetland environment, and thus needs to be included in the global CH₄ budget.</p><p>However, the subglacial system of the GrIS is complex and highly heterogenous, hosting oxic and anoxic ecosystems, which have developed over a range of timescales. There are still questions outstanding surrounding the ubiquity of CH₄ release from the GrIS, mainly because of the limited understanding of subglacial carbon cycling and the potential sources of CH₄ in these environments. &#160;</p><p>We present the first data from two new, complimentary projects investigating CH₄ release from the GrIS margin, where we aim to quantify the production and release of CH₄ into the atmosphere from the GrIS. We have developed an ambitious temporal and spatial sampling regime to evaluate the CH₄ release along the western margin of the GrIS. We present the first radiocarbon (¹⁴C) dated CH₄ samples from Greenland, helping to shed light on the carbon cycling processes occurring under the ice sheet. We analyse a mixture of atmospheric CH₄ exported from subglacial ice caves and dissolved CH₄ from proglacial rivers draining subglacial portals to explore the age of subglacially sourced CH₄.</p><p>We can combine the carbon age of exported CH₄ with microbial analysis and stable isotope data to improve our understanding of the environmental controls on and microbial sources of subglacial CH₄ production and export. Understanding the mechanisms behind subglacial CH₄ export is crucial when attempting to upscale the point source data that is available currently and we consider whether the GrIS could be a potentially important source of CH₄, leading to a substantial, yet currently understudied climatic feedback.</p>