Peat isotopic composition of a deep deposit of palsa mire for the reconstruction of environmental changes in permafrost domain of Northern Siberia

Palsa peatlands are a significant carbon pool in Northern hemisphere which is subjected to change due to accelerated permafrost thaw and peat decomposition with progressing global warming. On the other hand, peat deposits of palsas serve as an important conduit of information about variability of environment conditions in the past millennia and respective vegetation changes. In our study we applied the multi-proxy record to distinguish variation in hydrothermal regimes of palsa peatland in Northern Siberia and to trace the likely diagenetic alteration of accumulated peat.

The study site is located 10 km North-East of Igarka settlement (67^o31’ N, 86^o38’E) within the area underlain discontinuous permafrost. The peat core was obtained in the central intact part of elevated (ca. > 3.5 m above surrounding hollows) dry hummock. The active layer, thawed seasonally layer, at the coring site was about 0.6 m. The entire depth of peat deposit was 8.6 m, but interrupted with several relatively thin (0.1-0.2 m) ice-rich lenses. Thawed and frozen peat samples of 0.5-5.0 cm thickness (mean = 2.8 cm) were collected at 2.5-12.0 cm step (mean =5.4 cm) depending on the amount of peat material. Collected samples (n = 160) after drying at 60^oC for 48 h were subjected to the analysis for C and N content, stable isotopic composition of C and N. These measurements will further accompany radiocarbon dating, loss on ignition, plant macrofossil and macro charcoal analyses.

The analyzed 8.6 m deep peat core demonstrated the large variation of C (17.3-54.7%) and N (0.37-3.26 %) contents as well as C:N ratios (14-134). The isotopic depth profile was in the range from -24.51 to -34.31 ‰ for d¹³C and from -1.77 to 6.96 ‰ for d¹⁵N. The highest enrichment in ¹⁵N (2.69±1.60 ‰ d¹⁵N) was found in seasonally thawed layer (≤0.6 m). A layer close to the bottom (6.9-8.3 m) contained peat the most depleted by ¹³C (<-30 ‰ d¹³C). Meanwhile, along the peat profile depth we detected significant fluctuations in these parameters suggesting the different periods with specific environmental conditions.

Further combined with radiocarbon dating and plant macrofossil analyses we will attempt to capture the changes occurred during the past epochs in an input matter (vegetation changes and/or its productivity), decomposition rates as well as hydrothermal regimes and permafrost processes like aggradation (e.g. hummock uplift and cryoturbation) and degradation (e.g. hummock collapse, shifts from minerotrophic to ombrotrohic conditions and vice versa).

This work was supported by the Russian Science Foundation, project № 20-17-00043.