Substrate potential of last interglacial to Holocene permafrost organic matter for future microbial greenhouse gas production

• Published in: Biogeosciences
• Main Authors: Stapel, Janina, Schwamborn, Georg, Schirrmeister, Lutz, Horsfield, Brian, Mangelsdorf, Kai
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: COPERNICUS GESELLSCHAFT MBH 2018
• Subjects: Global warming; permafrost; Siberia
• Online Access: https://epic.awi.de/id/eprint/47301/; https://epic.awi.de/id/eprint/47301/1/Stapel_Lyakhovsky_bg2017_89.pdf; https://hdl.handle.net/10013/epic.605c1e6e-ba00-4027-8244-692b1e37738f

. In this study the organic matter (OM) in several permafrost cores from Bol´shoy Lyakhovsky Island in NE Siberia was investigated. In context of the observed global warming the aim was to evaluate the potential of freeze-locked OM from different depositional ages to act as a substrate provider for microbial production of greenhouse gases from thawing permafrost. To assess this potential, exemplarily the concentrations of free and bound acetate, which form an appropriate substrate for methanogenesis, are determined. The largest free (in pore water) and bound (organic matrix linked) acetate substrate pools are present in layers that cover interstadial MIS 3 and stadial MIS 4 Yedoma permafrost deposits. In contrast, deposits from the last interglacial MIS 5e (Eemian) contain only a small pool of substrates. The Holocene (MIS 1) deposits reveal a significant bound acetate pool, representing a future substrate potential upon release during OM degradation. Additionally, pyrolysis experiments on the OM allocate an increased aliphatic character to the MIS 3 and 4 Late Pleistocene deposits, which might indicate less decomposed and presumably better degradable OM. Biomarkers for past microbial communities including those for methanogenic archaea show also highest abundance during MIS 3 and 4, which indicates that the OM stimulated microbial degradation and presumably greenhouse gas production during time of deposition. On a broader perspective, Arctic warming will increase and deepen permafrost thaw and favour substrate availability from freeze-locked older permafrost deposits. Therefore, especially the Yedoma deposits show a high potential for providing substrates relevant for microbial greenhouse gas production