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

Abstract

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.

Glycerol dialkyl glycerol tetraethers (GDGTs) in high latitude Siberian permafrost: Diversity, environmental controls, and implications for proxy applications

“…4A), implying the presence of methanogenic Euryarchaeota (Blaga et al, 2008). This agrees well with the detection of archaeol in the Bol'shoy Lyakhovsky Island L14 cores by Stapel et al (2018) and archaeol in a drill core from Kurungnakh Island investigated by Bischoff et al (2013). Additionally, mean GDGT-2/crenarchaeol ratios are !0.2 in active layer soils, Holocene fluvial terrace/floodplain sediments, and Yedoma ( Fig.…”

“…Drill cores L14-02, L14-04, and L14-05 were retrieved from Bol'shoy Lyakhovsky Island. L14-02 includes a late Pleistocene Ice Complex sequence (MIS 3) while L14-04 and L14-05 represent interglacial thermokarst sediments from the Eemian (MIS 5) and interstadial deposits from the late Pleistocene (MIS 4 and MIS 3) and Holocene, respectively (Stapel et al, 2018). Each of the Buor Khaya Peninsula and Bol'shoy Lyakhovsky Island drill cores included an uppermost active layer soil.…”

“…Each of the Buor Khaya Peninsula and Bol'shoy Lyakhovsky Island drill cores included an uppermost active layer soil. Detailed descriptions of the drill cores are given by Günther et al (2013), Overduin (2015), Schirrmeister et al (2017), Wetterich (2016, 2015), Stapel et al (2018Stapel et al ( , 2016, and Zimmermann et al (2017aand Zimmermann et al ( , 2017b.…”

Increasing Organic Carbon Biolability With Depth in Yedoma Permafrost: Ramifications for Future Climate Change

“…In a yedoma permafrost core collected from northeast Siberia, sediments deposited during climatic conditions of the late Pleistocene glacial periods had increased aliphatic and acetate concentrations compared to sediments from the same core deposited during interglacial periods and the Holocene (Stapel et al, ). The sediments deposited during glacial periods also had higher abundances of biomarkers for past microbial communities, suggesting that the increased aliphatic and acetate concentrations may have also been influenced by climatic conditions and microbial processing during deposition (Stapel et al, , ). At the VC permafrost tunnel, paleobotanical proxy data from our sampled depths suggest that climatic conditions at the time of sediment deposition were relatively warm, wet, and similar to Holocene conditions (Schirrmeister et al, ).…”

“…Yedoma cores collected from similar depths to our study from near Livengood, AL show increasing acetate concentrations with sediment age (Ewing et al, 2015), suggesting that the variation in WEOM composition we observed at the VC permafrost tunnel may be due to processing following permafrost formation. Each of these studies (this study; Ewing et al, 2015;Stapel et al, 2016Stapel et al, , 2017 point to the importance of OM processing, both during Values are mean (SD) cumulative C mineralization among triplicate vials during the 154-day incubation. a CE = carbon equivalent.…”