UCLA

Northern peatlands contain some of the largest terrestrial stores of organic soil carbon (C) which may grow due to increases in productivity, or decline due to higher decay under projected warming and drought scenarios. However, models of peatland growth lack data on basic peatland history for the remote James Bay Lowlands (JBL) region of Canada, as well as the relationships between climate and productivity, and the history of Holocene precipitation. This dissertation presents C accumulation, vegetative macrofossil, and proxy-climate reconstruction data from eight previously unpublished sites in the JBL, as well as synthesizes currently available data. Peatlands in the JBL initiated lagging the retreat of the Laurentide ice sheet, and the drainage of glacial lakes by an average of 2,900 years. Most of the peatlands studied initiated as mineral rich fens, which transitioned to nutrient poor bogs an average of 3,800 years after they initiated. Over the Holocene they have acted as a sink of CO₂, accumulating between 71.5 and 171.2 kgC m^-2, with median long-term apparent C accumulation rates (LARCA) ranging from 13.8 to 31.6 gC m^-2 yr^-1. Peatland C accumulation was variable within and between sites, but was driven by productivity rather than decay during the late-Holocene. The depths of late-Holocene peat deposits correlate positively with growing season length, and photosynthetically active radiation, and were negatively affected by permafrost occurrence. A single site provides evidence for a relatively dry pre-Holocene Thermal Maximum period, and a relatively wet Holocene Thermal Maximum, with a small but positive influence of water table depth on LARCA. Although there was some variation due to site-specific conditions, multiple sites indicate that the warm Medieval Climate Anomaly was a wet period in the JBL, consistent with modern precipitation anomalies, whereas the Little Ice Age was dry. The Little Ice Age may have been locally complex due to precipitation variability, or the formation of permafrost. On the short term, peatland C-stores may grow faster if temperature and seasonality changes occur within their physiological and ecological limitations. However long-term peatland stability in the area will likely be dependent on precipitation, which may fluctuate due to the positions of the Arctic and Pacific fronts, and stochastic interactions between the atmosphere and sea surface temperatures.