A terrestrial permafrost core from Buor Khaya in northern Siberia comprising deposits of Late Pleistocene to Early Holocene age has been investigated to characterize living and past microbial communities with respect to modern and paleoclimate environmental conditions and to evaluate the potential of the organic matter (OM) for greenhouse gas generation. Microbial life markers—intact phospholipids and phospholipid fatty acids—are found throughout the entire core and indicate the presence of living microorganisms also in older permafrost deposits. Biomarkers for past microbial communities (branched and isoprenoid glycerol dialkyl glycerol tetraether as well as archaeol) reveal links between increased past microbial activity and intervals of high OM accumulation accompanied by increased OM quality presumably caused by local periods of moister and warmer environmental conditions. Concentrations of acetate as an excellent substrate for methanogenesis are used to assess the OM quality with respect to microbial degradability for greenhouse gas production. For this purpose two acetate pools are determined: the pore water acetate and OM bound acetate. Both depth profiles reveal similarities to the OM content and quality indicating a link between the amount of the stored OM and the potential to provide substrates for microbial greenhouse gas production. The data suggest that OM stored in the permafrost deposits is not much different in terms of OM quality than the fresh surface organic material. Considering the expected increase of permafrost thaw due to climate warming, this implies a potentially strong impact on greenhouse gas generation from permafrost areas in future with positive feedback on climate variation.
Abstract. In this study the organic matter (OM) in several permafrost cores from
Bol'shoy Lyakhovsky Island in NE Siberia was investigated. In
the 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, the concentrations of free and bound
acetate, which form an appropriate substrate for methanogenesis, were
determined. The largest free-acetate (in pore water) and bound-acetate
(organic-matrix-linked) substrate pools were present in interstadial
marine isotope stage (MIS) 3 and stadial MIS 4 Yedoma permafrost deposits. In
contrast, deposits from the last interglacial MIS 5e (Eemian) contained only
a small pool of substrates. The Holocene (MIS 1) deposits revealed a
significant bound-acetate pool, representing a future substrate potential
upon release during OM degradation. Additionally, pyrolysis experiments on
the OM allocated an increased aliphatic character to the MIS 3 and 4 Late
Pleistocene deposits, which might indicate less decomposed and presumably
more easily degradable OM. Biomarkers for past microbial communities,
including those for methanogenic archaea, also showed the highest abundance
during MIS 3 and 4, which indicated 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
favor substrate availability from older freeze-locked permafrost deposits.
Thus, the Yedoma deposits especially showed a high potential for providing
substrates relevant for microbial greenhouse gas production.
Abstract. Multiple permafrost cores from Bol´shoy Lyakhovsky Island in NE Siberia comprising deposits from Eemian to modern time are investigated to evaluate the stored potential of the freeze-locked organic matter (OM) to serve as substrate 10 for the production of microbial greenhouse gases from thawing permafrost deposits. Deposits from Late Pleistocene glacial periods (comprising MIS 3 and MIS 4) possess an increased aliphatic character and a higher amount of potential substrates, and therefore higher OM quality in terms of biodegradation compared to interglacial deposits from the Eemian (MIS 5e) as well as from the Holocene (MIS 1). To assess the potential of the individual permafrost deposits to provide substrates for microbially induced greenhouse gas generation, concentrations of free and bound acetate as an excellent substrate for 15 methanogenesis are used. The highest free (in pore water and segregated ice) and bound (bound to the organic matrix) acetate-substrate pools of the permafrost deposits are observed within the interstadial MIS 3 and stadial MIS 4 period deposits. In contrast, deposits from the last interglacial MIS 5e show only poor substrate pools. The Holocene deposits reveal a significant bound-acetate pool, representing at least a future substrate potential upon release during OM degradation.Biomarkers for past microbial communities (branched and isoprenoid GDGTs) show also highest abundance of past 20 microbial communities during the MIS 3 and MIS 4 deposits, which indicates higher OM quality with respect to microbial degradation during time of deposition. On a broader perspective, Arctic warming will increase permafrost thaw and favour substrate availability from freeze-locked older permafrost deposits. Therefore, especially those deposits from MIS 3 and MIS 4 show a high potential for providing substrates relevant for methanogenesis.
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