Page 251 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

incorporated by default. There is a vital connection between microbiology and climate science which should be stimulated in future research projects and climate reports.
Thermokarst lakes are dynamic key features of a warming Arctic
Thermokarst lakes define rapidly and dynamically changing locations within a warming Arctic. Field observations indicate that they can rapidly form upon thaw, but also quickly drain and disappear (Ruz, Héquette and Hill 1992; Jorgenson and Shur 2007; Grosse et al. 2008; Sannel and Kuhry 2011; Grosse, Jones and Arp 2013). Due to their dynamic nature, thermokarst lakes thus have strong effects on the short term.
In our studies on thermokarst lakes of Alaska, we observed the capacity of thermokarst lakes to rapidly increase GHG production upon warming and increased substrate availability after mineralization of previously frozen organic matter reservoirs (Chapter 7 and 8). An associated issue of increased CH4 production is its poor solubility in water (Walter Anthony et al. 2006; Dean et al. 2018). The supersaturation of the sediment and water column results in the production of gas bubbles that escape the ecosystem, and thus oxidation through ebullition (Lindgren et al. 2016; Wik et al. 2016; Aben et al. 2017). This pathway largely avoids the in situ biological methane filter. Currently, ebullition is estimated to be a major emission pathway of thermokarst lakes with an expected emission of 17-26% (4.1 ± 2.2 Tg CH4 y−1) of the CH4 from northern lakes (Zimov et al. 1997; Walter Anthony et al. 2006; Walter Anthony, Smith and Stuart Chapin 2007; Walter Anthony et al. 2010; Bastviken et al. 2011; Wik et al. 2013; Greene et al. 2014; Wik et al. 2016; Matveev, Laurion and Vincent 2018).
However, most laboratory-based meso- or microcosm studies do not specifically assess ebullitive emissions due to technical limitations. This was also the case for our study set-ups. In closed systems where ebullitive CH4 emissions can be oxidized, the CH4 emission potential is, therefore, likely underestimated in the short term due to oxidative processes with oxygen and alternative electron acceptors. In the field, ebullitive emissions would escape this biological methane filter. Datasets from flux chambers and bubble traps are, therefore, necessary to capture ebullitive emissions and to put these findings into perspective. In addition, laboratory- based meso- or microcosm set-ups are suitable for the assessment of ebullitive CH4 fluxes. For example, microcosm flow chambers allow for controlled set-ups with continuous gas exchanges
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