Late Holocene vegetation dynamics, hydrological change, and fire history on the Seward Peninsula, Arctic Alaska

Gałka M.; Diaconu A.C.; Kim Y.; Feurdean A.; Kołaczek P.; Obremska M.; Stivrins N.; Swindles G.T.; Wilk K.; Knorr K.H.

Abstract

Recent climate change has significantly impacted Arctic ecosystems, with peatlands being particularly sensitive to shifts in hydrology. A widespread deepening of the water table due to permafrost thaw has driven substantial changes in vegetation composition, accelerated organic matter decomposition, increased carbon emissions, and increased fire activity. However, the complexity of local drivers means that detailed studies on potential peatland trajectories remain limited. To address this gap, we conducted high-resolution, multi-proxy palaeoecological analyses—including plant macrofossils, pollen, testate amoebae, macro- and microcharcoal, and peat stoichiometry—on two radiocarbon-dated peat sequences from Seward Peninsula, Arctic Alaska. Our findings indicate that a deeper water table in recent decades has altered dominant peat-forming species, promoting shrub expansion and a shift from sedge dominance to Sphagnum , brown mosses, and lichens. This water table drop, likely driven by permafrost thaw, has restricted further peat accumulation and led to organic layer degradation. We also document a strong link between increased fire activity following the Little Ice Age—particularly in the second half of 20th century—and periods of deep water tables. Overall, our multi-proxy approach demonstrates that peatlands in this Alaskan region have diverged from the predominantly wet conditions that prevailed before 1850 CE. These hydrological shifts have not only altered plant composition and peat formation but also diminished the ecosystem's carbon storage capacity.