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19Lake high-stand sediments are found in three onshore terraces at Lake Donggi Cona, north-eastern 20Tibetan Plateau, and reveal characteristics of hydrological changes on lake shorelines triggered by 21 climate change, geomorphological processes, and neo-tectonic movements. The terraces consist of 22 fluvial, alluvial to littoral-lacustrine facies. End-member modeling of grain size distributions allowed 23 quantification of sediment transport processes and relative lake levels during times of deposition. 24Radiocarbon dating revealed higher than modern lake levels during the early and mid-Holocene. Lake 25 levels follow the trend of Asian monsoon dynamics, and are modified by local non-climatic drivers. 26Site-specific impacts explain fluctuations during the initial lake level rise ~11 cal ka BP. Maximum lake 27 extension reached ~9.2 cal ka BP, at ~16.5 m above present lake level (a.p.l.l.). Littoral and lacustrine 28 sediment deposition paused during a phase of fluvial activity and post-depositional cryoturbations at 29 ~8.5 cal ka BP, when the lake level fell to ~8 m a.p.l.l. After a second maximum at ~7.5 cal ka BP, lake 30 level declined slightly at ~6.8 cal ka BP, probably due to a non-climatic pulse that caused lake 31 opening. The level remained high until a transition towards drier conditions of ~4.7 cal ka BP. Though 32 discontinuous, high-stand sediments provide a unique, high-resolution archive.

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The buried China-Russia Crude Oil Pipeline (CRCOP) across the permafrost-associated cold ecosystem in northeastern China carries a risk of contamination to the deep active layers and upper permafrost in case of accidental rupture of the embedded pipeline or migration of oil spills. As many soil microbes are capable of degrading petroleum, knowledge about the intrinsic degraders and the microbial dynamics in the deep subsurface could extend our understanding of the application of in-situ bioremediation. In this study, an experiment was conducted to investigate the bacterial communities in response to simulated contamination to deep soil samples by using 454 pyrosequencing amplicons. The result showed that bacterial diversity was reduced after 8-weeks contamination. A shift in bacterial community composition was apparent in crude oil-amended soils with Proteobacteria (esp. α-subdivision) being the dominant phylum, together with Actinobacteria and Firmicutes. The contamination led to enrichment of indigenous bacterial taxa like Novosphingobium, Sphingobium, Caulobacter, Phenylobacterium, Alicylobacillus and Arthrobacter, which are generally capable of degrading polycyclic aromatic hydrocarbons (PAHs). The community shift highlighted the resilience of PAH degraders and their potential for in-situ degradation of crude oil under favorable conditions in the deep soils.

The response of methanogens to thawing permafrost is an important factor for the global greenhouse gas budget. We tracked methanogenic community structure, activity, and abundance along the degradation of sub-Arctic palsa peatland permafrost. We observed the development of pronounced methane production, release, and abundance of functional (mcrA) methanogenic gene numbers following the transitions from permafrost (palsa) to thaw pond structures. This was associated with the establishment of a methanogenic community consisting both of hydrogenotrophic (Methanobacterium, Methanocellales), and potential acetoclastic (Methanosarcina) members and their activity. While peat bog development was not reflected in significant changes of mcrA copy numbers, potential methane production, and rates of methane release decreased. This was primarily linked to a decline of potential acetoclastic in favor of hydrogenotrophic methanogens. Although palsa peatland succession offers similarities with typical transitions from fen to bog ecosystems, the observed dynamics in methane fluxes and methanogenic communities are primarily attributed to changes within the dominant Bryophyta and Cyperaceae taxa rather than to changes in peat moss and sedge coverage, pH and nutrient regime. Overall, the palsa peatland methanogenic community was characterized by a few dominant operational taxonomic units (OTUs). These OTUs seem to be indicative for methanogenic species that thrive in terrestrial organic rich environments. In summary, our study shows that after an initial stage of high methane emissions following permafrost thaw, methane fluxes, and methanogenic communities establish that are typical for northern peat bogs.