| Summary: | The response of Arctic wetland ecosystems and their associated organic carbon stores to future warming is uncertain. For the first time in the Canadian High Arctic I use a multi-proxy palaeoecological approach to test how organic-rich wetlands have responded to pronounced warming since the mid-twentieth century. This approach enables ecological analysis on a timescale beyond that of contemporary studies. An ice-wedge polygon mire was a dual-state system with the raised centre mound showing no response to recent warming, but ~AD 2000 the surrounding trough exhibited a shift to wetter conditions and a transition from sedge and herb-dominated to brown moss-dominated vegetation. The accumulation of this vegetation layer may have the effect of insulating ice-wedges and provide a negative ecological feedback to permafrost degradation, mitigating potential carbon losses. In a valley fen, an increase in growing degree days above 0°C (GDD0) since ~AD 1950 is linked to greater inundation from increased snow and ice melt early in the growing season, coupled with increased drying towards the end of the growing season from elevated evapotranspiration. This may have initiated a pathway to wetland desiccation – although wetland persistence is likely to be determined by future Arctic precipitation patterns. In a coastal fen, greater GDD0 combined with isostatic uplift induced shrubification ~AD 1950 and led to rapid carbon accumulation. After this, increasing bird grazing pressures from ~AD 2000 may have affected vegetation and carbon accumulation. My results illustrate a variety of pathways for change in High Arctic wetlands in response to rapid warming. The results of this study suggest that predictions of the future extent and carbon accumulation rates of northern peatlands should consider the marked, yet complex response of High Arctic wetlands to warming alongside external non-climatic factors such as increased bird grazing pressures.
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