Multi-proxy study of soil organic matter dynamics in permafrost peat deposits reveal vulnerability to climate change in the European Russian Arctic

Abstract

Soil organic carbon (SOC) in permafrost terrain is vulnerable to climate change.Perennially frozen peat deposits store large amounts of SOC, but we know little about its chemical composition and lability. We used plant macrofossil and biomarker analyses to reconstruct the Holocene paleovegetation and paleoenvironmental changes in two peat plateau profiles from the European Russian Arctic. Peat plateaus are the main stores of permafrost soil C in the region, but during most of the Holocene peats developed as permafrost-free rich fens with woody vegetation, sedges and mosses. Around 2200 cal BP, permafrost aggraded at the site resulting in frost heave and a drastic reduction in peat accumulation under the drier uplifted surface conditions. The permafrost dynamics (aggradation, frost-heave and thaw) ushered changes in plant assemblages and carbon accumulation, and consequently in the biomarker trends too. 2Detailed biomarker analyses indicate abundant neutral lipids, which follow the general pattern: n-alkanols > sterols ≥ n-alkanes ≥ triterpenols. The lignin monomers are not as abundant as the lipids and increase with depth. The selected aliphatic and phenolic compounds are source specific, and they have different degrees of lability, which is useful for tracing the impact of permafrost dynamics (peat accumulation and/or decay associated with thawing). However, common interpretation of biomarker patterns, and perceived hydrological and climate changes, must be applied carefully in permafrost regions. The increased proportion (selective preservation) of n-alkanes and lignin is a robust indicator of cumulative decomposition trajectories, which is mirrored by functional compounds (e.g. n-alkanol, triterpenol, and sterol concentrations) showing opposite trends. The distribution of these compounds follows first order decay kinetics, and concurs with the downcore diagenetic changes. In particular, some of the biomarker ratios (e.g. stanol/sterol and higher plant alkane index) seem promising for tracing SOC decomposition despite changes in botanical imprint, and sites spanning across different soil types and locations. Carbon accumulation rate calculated at these sites varies from 18.1 to 31.1 gC m -2 yr -1 , and it is evident selective preservation, molecular complexity of organic compounds, and freezing conditions enhance the long-term stability of SOC. Further, our results suggest permafrost dynamics strongly impact the more undecomposed SOC that could be rapidly remobilized through ongoing thermokarst expansion.

Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic

“…However, low n-alkane concentrations do not reflect degradation from fatty acids into alkanes, indicative of degradation (Routh et al, 2014). For the peat intrusion this is different.…”

“…For the peat intrusion this is different. The HPA, which gives an indication of the relative amount of fatty acids remaining in a sample (Routh et al, 2014), shows that buried peat was probably highly degraded. Low n-fatty acids correlate with high n-alkanes, indicating OM degradation in the buried peat in the slump floor, which most likely originated from the cryoturbated upper permafrost layer and is subject to humification in the disturbed zone (Andersson and Meyers, 2012).…”

Warming of subarctic tundra increases emissions of all three important greenhouse gases – carbon dioxide, methane, and nitrous oxide

“…The landscape in our study region comprises upland tundra with mineral soil overlain by a shallow organic layer (thickness 2-9 cm), as well as large peat plateau complexes with up to 4-m-thick peat deposits (Hugelius et al, 2012). Additional site information can be found in studies by Hugelius et al (2011Hugelius et al ( , 2012 and Routh et al (2014). Vegetation on the upland soils is lichen-rich, dry shrub tundra dominated by Betula nana L., Vaccinium uliginosum L., Salix sp., Empetrum nigrum subsp.…”

A combined biogeochemical and palaeobotanical approach to study permafrost environments and past dynamics

“…A study by Routh et al . () at same site on a vegetated peat plateau surface dated the permafrost initiation to as late as ca . 2200 cal a BP.…”