PS 41-123 - Recent Sphagnum expansion into the tundra on the North Slope of Alaska

Abstract: Ecological changes associated with recent high-latitude warming have raised concerns about potential climate feedbacks, given the abundance of carbon-rich ecosystems in these regions. Observations on the North Slope of Alaska have revealed patches of Sphagnum peat occurring within the widespread matrix of tussock tundra and mineral soils. However, little is known about the establishment history of these peat patches and whether they represent incipient peatlands that possibly formed in response to environmental changes associated with recent warming. Previous paleoecological work near Toolik Lake indicated that peat patches may represent relatively recent landscape features, developing over the past century; however, it is unclear whether this is representative of other areas on the North Slope. We conducted a multi-site paleoecological study on peat cores collected from nine peat patches spanning an approximately 300-km longitudinal gradient on the North Slope to determine 1) when Sphagnum became a significant component of the vegetation and 2) when Sphagnum became dominant like it is on modern peat patches. Stratigraphically constrained cluster analysis, applied to plant macrofossil, C:N, and total organic matter data, was used to delineate developmental phases in these records, and ¹⁴C dating was used to estimate the timing of Sphagnum establishment and expansion. We then compared our data to paleoclimate and instrumental temperature records, as well as testate amoeba-inferred water-table depth estimates from the same peat cores, to assess relationships to recent warming and associated hydrological changes. Results confirm that Sphagnum peat patches on the North Slope are a recently developed feature. Although Sphagnum was present in the cores for at least the past 350 years, and was variably abundant at many sites prior to the 1960s, it abruptly became dominant at 8 of the 9 locations after the 1970s. Most of this expansion occurred in the 1990s and 2000s (6 out of 9 sites). Sphagnum peat patch development occurred in association with the pronounced warming of the last several decades, and was associated with increased rates of carbon storage. Testate amoebae from the cores also indicate a general drying trend over the past century, but particularly since the 1960s. Additional research is needed to explore whether similar changes are happening in other regions of the arctic tundra, and the potential implications of these changes to carbon cycling and storage.