| Summary: | Degree: Doctor of Philosophy Abstract: Across the circumpolar north, rapid warming and intensifying hydrologic cycles are accelerating permafrost thaw and strengthening land-freshwater linkages. Among the most significant implications of this change is the mobilization of large amounts of previously sequestered organic and inorganic substrate from thawing permafrost into modern aquatic biogeochemical cycles. While microbial oxidation of permafrost organic carbon can produce carbon dioxide (CO2) and methane (CH4) upon thaw, current understanding about the sources and transformation (cycling) of carbon – and thus potential climate feedbacks – in permafrost thaw-affected freshwaters is driven by research in relatively organic-rich terrains. Much less is known about carbon cycling in permafrost terrains containing a relatively greater proportion of inorganic substrate, where the chemical weathering of minerals may shift the direction and magnitude of permafrost carbon-climate feedbacks. This work investigates the summertime (2014–2017) magnitude, drivers, and regional variability in inorganic carbon cycling in a series of northern watersheds in diverse permafrost terrains across the Yukon and Northwest Territories (Canada). Much of this work occurred on the Peel Plateau (Northwest Territories), where terrain subsidence following permafrost thaw (thermokarst) releases tills into fluvial networks. Measurements of dissolved inorganic carbon (DIC, Σ[CO2, HCO3-, CO32-]) showed that the thaw and chemical weathering of carbonate- and sulfide-bearing tills on the Peel Plateau reshaped fluvial inorganic carbon cycling across watershed scales. The substantial thermokarst-driven increase in weathering was reflected by a 100-fold increase in bicarbonate (HCO3–) concentrations between non thermokarst-affected headwaters and the Stony Creek outlet into the Peel River. Ions and stable isotopes of DIC (13CDIC) and CO2 (13CCO2) indicated that carbonate weathering was primarily driven by sulfuric acid from sulfide oxidation, which ...
|
|---|