Climate change and postglacial environmental history of permafrost peatlands in the Mackenzie Delta area, N.W.T

The Holocene environmental histories of two peatlands in the Mackenzie Delta area were reconstructed in order to gain an understanding of how climate change, permafrost and build-up of ground ice affect the processes of peat accumulation in an area of continuous permafrost. Multi-proxy paleoecological analyses, including peat stratigraphy, pollen, plant macrofossils and radiocarbon dating were carried out on cores from Kukjuk peatland, on the Tuktoyaktuk Peninsula 75 km north of present treeline, and Campbell Creek peatland, 20 km south of treeline. Stratigraphy and physical characteristics (bulk density and content of moisture, organic material and inorganic carbon) were analyzed for six cores from Kukjuk peatland and six cores and two peat sections from Campbell Creek peatland. Two cores from each site were selected for pollen and plant macrofossil analyses.; The paleoecological reconstructions are compared with a well established record of regional postglacial environmental history available from previous lake sediment studies, to investigate how past climate changes affected the peatlands. This independent paleoenvironmental record, in combination with the analyses of several cores from each of the peatlands, aids in distinguishing stratigraphic changes in the peat deposits resulting from autogenic succession and local environmental factors from those that are more likely to reflect regional climatic change. An early Holocene period of wanner than present climate has been inferred, based on evidence from lake pollen records and spruce macrofossils that the treeline was further north from 9000-5000 BP, covering at least part of the Tuktoyaktuk Peninsula.; Organic deposition began in Kukjuk peatland by 7200 BP, and in Campbell Creek peatland by at least 9000 BP. Both sites were initially occupied by open water mineral wetlands with emergent and submergent aquatic vegetation. A subsequent fen stage is identified in both peatlands, but with some differences in plant communities. A switch to Sphagnum-dominated ombrotrophic conditions occurred in both peatlands between approximately 4000-5000 BP. This coincides with a deterioration of regional climate and the retreat of treeline to its present position. The changes in the peatland ecosystems may have been an indirect response to this climate change, linked to permafrost aggradation which altered the surface hydrology, allowing the establishment of ombrotrophic vegetation.; A theoretical model of peatland development by terrestrialization in continuous permafrost areas is presented, based on the reconstructed peatland histories. Comparison with published stratigraphical and paleoecological records from other peatlands, mostly in northwestern Canada, suggests that similar peat accumulation processes have occurred at many other sites. However, the model will not apply to all permafrost peatlands, since variations in environmental conditions affecting peat accumulation occur at regional and local scales, and even within a single peatland. The multi-proxy, multi-core approach applied here is recommended for studies aimed at improved understanding of peat accumulation processes, in permafrost or non-permafrost environments. It provides a more complete picture of the history of the entire peatland ecosystem than can be attained by applying a single technique to one core.