Compositions and origins of greenhouse gas species in permafrost ice wedges at the Batagay megaslump, Yana Uplands, Northeast Siberia
Authors: Park Hansu , Ko Na-Yeon , Kim JeongEun , Opel Thomas , Meyer Hanno , Wetterich Sebastian , Fedorov Alexander , Shepelev Andrei , Ahn Jinho 
Published: March 2022

&lt;p&gt;Permafrost has a huge potential as a source for greenhouse gas release under global warming. In this context, it is very important to understand biogeochemical mechanisms of permafrost-related greenhouse gas formation and capacity. As ice wedges are an essential component of ice-rich permafrost and often occupy a large volume fraction of permafrost deposits, it is necessary to study the their gas chemistry. The Batagay megaslump (Yana Uplands, Northeast Siberia) exposes ice-rich permafrost deposits (Ice Complex) that have formed in the Middle and Late Pleistocene. Previous studies suggest the ages of these deposits as MIS 4-2 and at least MIS 16 for the Upper and Lower Ice Complexes, respectively. In this study, we analyzed mixing ratios of gas in air bubbles occluded in ice wedges of both ice complexes. We extracted gas by both, wet and dry extraction methods that connected with a gas chromatography system to analyze CO&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;O, and CH&lt;sub&gt;4 &lt;/sub&gt;concentrations. We observe CO&lt;sub&gt;2&lt;/sub&gt; concentrations of 1.9&amp;#8211;10.3%, N&lt;sub&gt;2&lt;/sub&gt;O of 0.1&amp;#8211;8 ppm, and CH&lt;sub&gt;4&lt;/sub&gt; of 30&amp;#8211;170 ppm for the Lower Ice Complex, and CO&lt;sub&gt;2&lt;/sub&gt; of 0.03&amp;#8211;8.89%, N&lt;sub&gt;2&lt;/sub&gt;O of 0.3&amp;#8211;70 ppm, and CH&lt;sub&gt;4&lt;/sub&gt; of 5&amp;#8211;980 ppm for the Upper Ice Complex. Greenhouse gas mixing ratios higher than atmospheric level indicate active microbial activity. This is supported by the &amp;#948;(O&lt;sub&gt;2&lt;/sub&gt;/Ar) values, which range from &amp;#8211;89.01 to &amp;#8211;67.43% and from &amp;#8211;98.07 to &amp;#8211;47.06% for the Lower and Upper Ice Complexes, respectively. The highly depleted &amp;#948;(O&lt;sub&gt;2&lt;/sub&gt;/Ar) values may indicate strong oxidation reactions by microbial activity and/or non-biological oxidation reactions. Even though there is no significant correlation between CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt;, abiotic CH&lt;sub&gt;4&lt;/sub&gt; formation might be negligible because it is unlikely to occur under permanently frozen conditions. Interestingly, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O show a weak negative correlation in both ice complexes, which can be explained by the nitrogen compounds&amp;#8217; inhibitory effect for methanogenesis. The &amp;#948;(N&lt;sub&gt;2&lt;/sub&gt;/Ar) values range from &amp;#8211;8.06% to 33.86% for the Lower Ice Complex and from &amp;#8211;5.49% to 30.64% for the Upper Ice Complex. Since nitrogen is more soluble in water than argon, this might indicate that ice wedges may have formed without a major contribution of snowmelt but mainly by dry snow compaction, which is also supported by the spherical shape of gas bubbles within the wedge ice. Furthermore, in ice the argon permeation coefficient is higher than that of nitrogen. Thus, high &amp;#948;(N&lt;sub&gt;2&lt;/sub&gt;/Ar) values (&gt;10%) are due to argon&amp;#8217;s diffusion through ice. Our future research will focus on deciphering the biogeochemical process of greenhouse gas formation for both ice complexes by comparison with ice wedges from other Siberian locations which have experienced different biogeochemical conditions in the past.&lt;/p&gt;