This study presents a comprehensive paleoecological reconstruction of the Mukhrino peatland, a representative oligotrophic Sphagnum bog within the Middle Taiga zone of Western Siberia—the world's largest peatland region. Utilizing a multidisciplinary approach, the research aims to reconstruct the formation history of the peat deposit, its stratigraphic heterogeneity, and the main stages of ecosystem development throughout the Holocene.

Background and Objectives: As a significant global carbon reservoir, West Siberian peatlands play a crucial role in the carbon cycle. Understanding their long-term development is essential for interpreting contemporary carbon flux monitoring data and forecasting ecosystem responses to ongoing climate change. The goal of this research is to reconstruct the conditions, dynamics and ways that led to the formation of the unified Mukhrino peatland.

Methodology: The research integrates high-precision GPS leveling, digital terrain modeling (DEM), radiocarbon dating (AMS ¹⁴C), and detailed plant macrofossil analysis of peat cores. A dense network of boreholes was established along four stratigraphic profiles (North, South, East, West), enabling spatially explicit analysis. Peat classification follows genetic principles, distinguishing oligotrophic, mesotrophic, and eutrophic types based on macrofossil and trophic status.

Key results: The study reveals that the modern, unified peatland (~75 km²) formed through the coalescence of at least two primary, independent peat-accumulation centers around 9 370 calibrated years before present (cal yr BP). These centers originated via two distinct pathways: terrestrial paludification of dark-coniferous forests on mineral uplands (predominantly in the northern sector) and aquatic paludification (infilling) of primary lakes and paleo-river channels (notably in the western sector).

The internal structure of the peat deposit is highly heterogeneous, directly inherited from the pre-existing relief of the mineral basement (a flat depression with absolute elevations of 28-29 m a.s.l.) and contrasting hydrological regimes. The DEM of the mineral basement shows an inverse topography compared to the current convex bog surface, highlighting the differential peat accumulation rates. Deepest peat depositions (up to 5.5 m) are located in ancient stream and lake basins.

Early Holocene (c. 11 000-8 500 cal yr BP). Peat initiation began around 11 000 cal yr BP in a palaeochannel depression (NE sector) with eutrophic reed-hypnum peat. Shortly after (~10 600 cal yr BP), a second center developed in the south with eutrophic herbaceous (horsetail-menyanthes-fern) and hypnum peats, indicating rich groundwater-fed fen conditions. The merger of the northern and southern centers into a single hydrological system occurred around 9 370 cal yr BP.

Mid-Holocene Transition (c. 8 500-8 000 cal yr BP). The northern sector rapidly transitioned to oligotrophic conditions dominated by Sphagnum fuscum peat by ~8 500 cal yr BP.

Oligotrophic Phase and Late Holocene Dynamics (c. 8 000 – present). The consolidated bog entered a stable oligotrophic stage characterized by rapid peat accumulation (avg. 0.080 cm/yr). The stratigraphy is dominated by alternating layers of Sphagnum fuscum (hummock) peat and Sphagnum balticum/majus/papillosum (hollow) peat, reflecting the establishment of ridge-hollow complexes. A distinct marker horizon of woody-cottongrass peat (~4500 cal yr BP) signals a widespread, relatively dry climatic phase. A continuous layer of elevated ash content across the bog indicates a regional palaeofire event or significant aeolian deposition.

Peat types: Botanical analysis identifies oligotrophic peat as dominant (61.6% of samples). The dominant peat-forming types are: 1) Sphagnum fuscum (oligotrophic) peat (22.4% frequency), forming the peatland domed core; 2) Sphagnum hollow peat (13.9%); and 3) Scheuchzeria-Sphagnum peat (6.5%). Their spatial distribution is closely linked to microtopography and hydrology.

This detailed reconstruction confirms the hypothesis of a polygenetic origin for the Mukhrino peatland. The findings underscore the profound and lasting influence of initial geomorphological and hydrological conditions on peat stratigraphy, even within a seemingly uniform raised bog. This spatial heterogeneity in peat type and formation history is crucial for accurate upscaling of point-based carbon stock and accumulation rate measurements. The research demonstrates the ecosystem's resilience, having undergone significant hydrological and vegetation shifts (e.g., the mid-Holocene dry phase) while maintaining its carbon sequestration function. The study provides an essential paleo-ecological framework for interpreting data from the ongoing carbon monitoring station at the Mukhrino "Carbon Supersite", thereby improving models of carbon budget dynamics and the long-term response of West Siberian peatlands to climate change.