Long‐term sensitivity of a High Arctic wetland to Holocene climate change

Summary1 The response of peat‐rich permafrost soils to human‐induced climate change may be especially important in modifying the global C‐flux. We examined the Holocene developmental record of a High Arctic peat‐forming wetland to investigate its sensitivity to past climate change and aid understanding of the likely effects of future climate warming on high‐latitude ecosystems. 2 The microhabitat of mosses was quantified in the present‐day polygon‐complex at Bylot Island (73° N, 80° W) and used to interpret the radiocarbon‐dated macrofossil record of three cores, comprising c.  3500 years of wetland development. Recurrent wet and dry phases in the reconstructed palaeohydrological record indicated pronounced temporal variability. Wet and dry phases were compared between cores and with palaeoclimatic proxy values, measured as percentage melt and δ 18 O in nearby ice cores. 3 Periodic wet and dry phases appear unrelated to past climate over c.  50% of the combined stratigraphic records, and are attributable instead to geomorphological mechanisms. At other times, association of wet and dry phases with significantly lower and higher values of percentage melt and δ 18 O indicate a possible effect of past climate change on polygon hydrology and vegetation, although inconsistencies between cores suggest that local geomorphological processes continued to modify a regional climatic effect. However, during a period incorporating the Little Ice Age ( c.  305–530 cal. years bp ), reconstructed moisture and vegetation change is pronounced and consistent among all three cores. 4 The results provide strong evidence for the sensitivity of a High Arctic terrestrial ecosystem to past climate change during the Holocene. The estimated magnitude of changes in soil moisture between wet and dry phases is sufficient to imply recurrent shifts in wetland function, periodically impacted upon by pronounced climatic variability, although controlled principally by autogenic processes. The structure and function of such wetlands may therefore be susceptible to predicted, human‐induced climate warming.