| Summary: | Accelerated glacier ice mass loss and intensified meltwater fluxes are among principal vectors of change affecting northern latitudes in a warming climate. Aquatic systems impacted by glacier ice meltwater are vulnerable to hydrologic shifts in flow conditions that may render consequences to sources, and biogeochemical processes, controlling carbon cycling. Whereas the Canadian high Arctic is the third most extensively glacier covered region on Earth, it is relatively understudied with respect to carbon chemistry in glaciers, and meltwaters traversing proglacial freshwater systems (Chapter 2). To fill this knowledge gap, intensive multi-year (2015-19) sampling expeditions of the Lake Hazen watershed were completed, spanning various meltwater flow conditions. Lake Hazen is Canada’s most northern large lake, located within the Quttinirpaaq National Park, on Northern Ellesmere Island, Nunavut, and is hydrologically dominated by seasonal pulses of glacier ice meltwaters that rapidly navigate the proglacial environment along glacial rivers. Overarching research objectives were to assess carbon chemistry in glacial runoff, whether proglacial river continua were simple pipelines for organic and inorganic carbon pools, and the sources and sinks of carbon in Lake Hazen. Dissolved organic carbon (DOC) has a heterogeneous chemical composition in glacial headwaters that is a confluence of supraglacial meltwater sources (Chapter 3). However, abundant polycondensed aromatic “black carbon” molecules identified in a glacier snow sample were only sparingly detected in glacial headwaters, suggesting that this organic material is removed in the supraglacial environment either via adsorption to sinking particles (i.e., cryoconite), or long-term processing. DOC in glacial headwaters is 14C-ancient, often pre-dating the most recent deglaciation (~ 5 ka BP), which provided compelling evidence that older sources of organic carbon must also be present. In fact, the δ13C and Δ14C of extremely low concentration DOC in glacial headwaters ...
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