Impact of the Little Ice Age cooling and recent climate change on peatland vegetation and peat accumulation dynamics in northeastern Alberta, Canada

English Abstract:

Northern peatlands are one of the most important terrestrial sinks of organic carbon (C) and these ecosystems are highly sensitive to human activities and climate change. This study aims at understanding how the climate changes over the last 1000 years have affected peatland vegetation and peat accumulation dynamics in the boreal region of northern Alberta. The past changes in vegetation communities were reconstructed using high-resolution plant macrofossil analyses from multiple peat bogs located at the southern limit of permafrost peatland distribution in the Fort McMurray region (56-57° N). Our data show important changes in peatland vegetation and peat accumulation dynamics that coincide with the Little Ice age cooling period (~AD1600-1850) and the subsequent climate warming. In all the peatlands, the plant macrofossil data suggest a synchronous period of permafrost aggradation characterised by dry ombrotrophic conditions, increased peat decay and high abundance of ericaceous shrubs and black spruce (Picea mariana). In most sites, this period was followed by permafrost thawing characterised by a short-term local shift towards wetter minerotrophic conditions (Sphagnum sect. Cuspidata) and a decline in black spruce on the peatland. Finally, we have observed a subsequent shift to a relatively stable presence of Sphagnum sect. Acutifolia (e.g. Sphagnum fuscum) which indicates the establishment of relatively dry ombrotrophic conditions in all the peatlands. Our data suggest that the recent climate change has been particularly favourable to Sphagnum growth and peat accumulation in northeastern Alberta.