A multi-proxy paleoclimate record from a peat soil of interior Alaska: insight on mechanisms of Holocene peatland formation and landscape development

Arctic and subarctic regions are warming at an alarming rate, with consequences for permafrost degradation, greenhouse gas emission, ecosystem destabilization, and infrastructure deterioration. Despite high latitude sensitivity to modern climate change, a substantial gap remains in our understanding of high latitude environmental response to past episodes of climatic change. Peat soils, common across the high latitudes, provide a valuable archive for paleoclimate reconstruction to address this knowledge gap. Many such records exist across interior Alaska and have high potential as paleoclimate archives.

Here we develop a multi-proxy paleoclimate record from a peat bog soil (Terric Hemistel) in the Delta River Valley of interior Alaska to explore mechanisms of peatland initiation and evolution. We aim to develop a comprehensive record related to the formation and evolution of this peat bog and test the hypothesis that increased moisture availability and water perching within the soil, rather than warmer temperatures, initiated peatland development. We evaluate key physical and chemical properties of organic and mineral soil materials from pedon descriptions and samples collected by horizon with depths defined according to organic matter content, bulk density, pH, carbon (C), nitrogen (N), and the carbon to nitrogen (C/N) ratio. We use radiocarbon dates to build an age-depth model and analyze stable isotopic signatures (δ¹³C) of bulk material for moisture and habitat changes, while also evaluating compound-specific isotopic trends (δ¹³C, δD) of plant waxes to track hydrological fluctuations. Finally, we perform analyses of bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) to enable temperature reconstruction.

Our preliminary chronological framework demonstrates the initiation of the peat bog during the Middle Holocene (ca. 6800 cal yr BP) with a consistent growth rate of ~0.15 mm/yr.  At the landscape scale, there is relative stability indicated by pedogenesis through the Holocene, but at the pedon scale there is a shift from concurrent aeolian deposition and mineral soil development to accumulation of organics. This shift in predominant parent material is likely due to a changing moisture regime, inferred to be the result of feedbacks between increased summer precipitation and increased soil water holding capacity. We hypothesize that brGDGTs will show relatively flat temperatures through the Holocene, following other work in the area, while C/N ratios and stable isotope data will indicate pronounced changes in moisture. This multi-proxy approach will help improve models of peatland formation and resolve debate over the response of peatlands to varying climatic conditions (e.g., drier vs. wetter). Such work is particularly important for contextualizing peatland development under ongoing and future climate change.