Fluxes of soil organic carbon from eroding permafrost coasts, Canadian Beaufort Sea

Resolving uncertainties about the cycling of organic carbon in the world's oceans is particularly crucial in the Arctic because it is the locus of deep water formation, as well as rapid environmental change. The specific goal of this thesis was to quantify the flux of soil organic carbon (SOC) to the Arctic Ocean due to erosion along the Yukon Coastal Plain. Ground ice and SOC within coastal sediments, and the current and future fluxes of carbon were examined in detail.;Overlooking ground ice resulted in overestimates of SOC and mineral sediment of up to 20%. Corrections were especially important in the upper ice-rich soil layers. Organic carbon contents were related to surficial material and bluff height, and 57% of carbon was located at depths greater than 1 m. SOC fluxes were up to three times higher than previously thought, but comparable to other parts of the Arctic. Eleven per cent of the carbon eroded annually was buried in nearshore sediments, and the carbon in those sediments was overwhelmingly terrigenous.;A morphodynamic model of coastal evolution was used to evaluate future coastal retreat. Low bluffs will retreat more rapidly than higher ones. Ground ice controls the amount of sediment in coastal bluffs and therefore the retreat rates, since bluffs with high ice contents have a lower effective cliff height. SOC fluxes from low coastal bluffs will increase by 29%, but will be offset by a 13% decrease from high bluffs. Regions of low cliffs could become sources of carbon flux to the atmosphere.;By providing insight into the origins and fate of organic matter in a sensitive section of the Arctic coastal system, this study offers valuable input for both current and future studies of regional carbon dynamics.;An evaluation of the volume of ground ice showed it to be a significant constituent of coastal bluffs. The amount of it was related to surficial material and geomorphic history, being lowest in coarse-grained marine deposits and highest in lacustrine materials. It made up almost half the soil volume in formerly glaciated areas where bluffs are high, but only one third the volume in unglaciated portions with low bluffs.