| Summary: | Peatlands are an important component of the global carbon (C) cycle. Peak C accumulation rates (CAR) are associated with higher net primary productivity (NPP) and warmer climates. However, warmer conditions could force peatlands close to the moisture limit of development to cross a critical threshold where decay processes exceed NPP gain. The sensitivity of the peatland C stores in regions proximal to such bioclimatic boundaries must be characterised to assess their likely contribution to the global C cycle under projected future climate warming. This thesis investigates the relationship between climate and CAR over the last 2000 years using four peatlands located towards the southern limit of peat growth in eastern North America. Chronologies were developed using tephra and radiocarbon measurements to determine loss-on-ignition inferred carbon accumulation histories. The Alaskan White River Ash eastern lobe (AD 847 ± 1) was detected at all study sites and four previously unidentified cryptotephras of Russian, Japanese, Mexican and Pacific Northwestern origin were detected in Nova Scotia. Investigations into the relationship between CAR and climate reveal that multi-decadal to centennial CAR fluctuations are related to changes in the summer moisture balance, whilst temperature changes become increasingly important over multi-centennial timescales. The most prominent decrease in CAR over the last 2000 years coincided with drier conditions associated with the Medieval Climate Anomaly (MCA). This suggests that the southern moisture limit of peat growth moved northwards during the MCA, suppressing C sequestration in southern sites. Therefore, whilst projected future climate warming may increase peat CAR in more northern regions, peatlands proximal to the southern moisture limit of peat growth may experience a reduction in their C sequestration rates and act as a positive feedback to climate warming.
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