Polygonal peatlands and treed plateau bog in Northwest Hudson Bay Lowlands, Canada: Holocene development and permafrost dynamics

Tiina H. M. Kolari, Laure Gandois, Frédéric Bouchard, Alison E. Cassidy, Nicole K. Sanderson, Rémi Tremouille, Julien Arsenault, Maialen Barret, Adam Collingwood, Lucile Cosyn Wexteen, Sylvain Ferrant, LeeAnn Fishback, Karen Richardson, Michelle Garneau

Since the retreat of the Laurentide Ice Sheet, peatland development in the Hudson Bay Lowlands (HBL) has been mainly influenced by postglacial isostatic rebound and climate. We studied the timing of permafrost aggradation and the successional trajectories of low Arctic and subarctic polygonal peatlands and a boreal plateau bog in Wapusk National Park (WNP), in northwestern HBL. We also explored the timing of peatland initiation and long-term carbon accumulation between peatland types. Peatland initiation in WNP dates to at least 6000 cal BP, and peat thickness and carbon mass were higher in permafrost peat plateaus (mean: 71.7±21.4 (SE) kg C m-2) and intermediate-centred polygons (63.2±7.14 kg C m-2) than in non-permafrost fens (20.4 ±1.75 kg C m-2). In the boreal plateau bog, permafrost may have been present ~2585–1755 cal BP, while the most recent phase of permafrost aggradation likely occurred at the onset of the Little Ice Age (LIA). In the low Arctic and subarctic polygonal peatlands, permafrost likely developed ~1500–1050 cal BP, during the Dark Ages Cold Period (DACP), suggested by rapid declines in peat and carbon accumulation. In three subarctic sites, dry polygons were preceded by treed Sphagnum bogs with Picea mariana and P. glauca, until spruce disappeared ~1330–780 cal BP. These results suggest that in the subarctic HBL, polygons formed in Sphagnum-dominated plateaus after spruce disappeared, during the DACP or at the onset of LIA. In the low Arctic site, dry intermediate-centred polygons formed ~200 cal BP, but the exact successional pathway remained uncertain.