ALBERT

Description: The investigation of microbial ecosystems in permafrost sediments is an important approach to understand the role of microbial organic matter transformation in permafrost sediments for past and future climate changes, and is of high relevance in today’s geoscience research (Wagner, 2008) due to the current debate on the temperature vulnerability of permafrost deposits. Especially, the interplay between the organic substrate and the distribution of the living and past microbial communities in Late Pleistocene (Yedoma) and Holocene permafrost deposits, as well as the substrate potential of the organic matter stored in potentially thawing permafrost deposits are in the focus of the current study. Our investigation is part of the BMBF CarboPerm project an interdisciplinary Russian-German cooperation on the formation, turnover and release of carbon from Siberian permafrost landscapes. Sample material derived from terrestrial permafrost cores drilled at the coast of Bour Khaya in the North-Eastern Siberian Arctic. The gathered core material comprises Late Pleistocene to early Holocene deposits separated by an ice wedge. The microbial life markers (intact phospholipids, PLs) prove the presence of currently living microorganisms in the entire permafrost sequence and show the highest concentration in the uppermost sample indicating an abundant microbial life in the active layer. In comparison, the PL profile is strongly decreased in the underlying permafrost deposits. Nevertheless, the inventory of the Phospholipid fatty acids (PLFAs) suggests that the cell membrane temperature adaptation to cold environmental conditions is mainly regulated via the ratio between iso- and anteiso-fatty acids (FAs) as well as the ratio between saturated and unsaturated FAs. The surface samples show higher proportions of anteiso and unsaturated FAs (adaptation to cooler conditions), which might derive from the fact that surface layers are more affected from the harsh Siberian winter conditions than the deeper constantly cold permafrost deposits, where the above-ground temperature extremes are buffered due to the overlying deposits. Indeed within the deeper permafrost sequence the variations of the ratios are rather small, indicating adaptation to similar constantly cold temperature conditions. Other microbial markers (GDGTs), already partly degraded and, therefore, not indicating microbial life, reveal similarities with the TOC content and an increase especially in Late Pleistocene deposits. This suggests increased microbial life during intervals in the Late Pleistocene presumably caused by periods of moisture and temperature increased environments. Pore water analysis reveals the presence of low molecular weight organic acids (LMWOA) such as acetate, being excellent substrates for microbial metabolism. In the Late Pleistocene deposits below the ice wedge the substrate depth profiles show significant similarities to the TOC content. These points to a link between the organic matter and the LMWOA concentrations solved in the pore water and to the potential of those permafrost layers to provide substrates for microbial greenhouse gas production. In contrast, in the active layer the LMWOA concentrations are low, reflecting an active microbial turnover in the surface layers. Ester cleavage experiments on the residual organic matter resulted in the release of ester linked LMWOAs forming a potential substrate pool when released in future. These bound LMWOA profiles are even better correlated to the TOC content suggesting that the deeper permafrost deposits (older organic material)are not significantly different from those in the surface sediment (fresh organic material). Overall this indicates that the organic matter stored in the permafrost deposits and, therefore, removed from the surface carbon cycle is not much different in terms of organic matter quality than the fresh surface organic material. Considering the discussed increase of permafrost thawing, this might imply a strong impact on the generation of greenhouse gases from permafrost areas in future with its feedback on climate evolution. In a second and ongoing study, four terrestrial permafrost cores spanning from the Eemian interglacial into the Holocene form Bol’shoy Lyakhovsky Island are investigated with the focus on the differences and potential of the organic matter by comparing Eemian, Late Pleistocene and Holocene deposits. First results already reveal similar relations between the living and dead microbial communities with respect to the availability of free substrates, and the quality and amount of the total organic carbon. The results on the future potential of these deposits will also be presented.

Description: 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.

Description: 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 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 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 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.