Dissolved inorganic carbon dynamics in a high arctic glacial watershed

In the Canadian Arctic Archipelago, glacial mass loss has accelerated dramatically since the start of the 2000s. While the characterization of the sub-glacial drainage system and its meltwaters have received considerable attention, we know yet little about the quality of these meltwaters as they exit the glacier and flow into receiving freshwater ecosystems. Due to high rates of coupled physical and chemical weathering of geological material, glacial meltwaters could have important consequences for dissolved inorganic carbon (DIC) chemistry in freshwater systems, particularly in determining whether these ultra-oligotrophic freshwaters are sources or sinks of carbon dioxide (CO2). Efforts to quantify CO2 fluxes in the High Arctic at the watershed scale have largely focused on the terrestrial environment, so far leaving the role of large glacier-fed lake ecosystems unresolved. At 540 km2 and 267 m deep, Lake Hazen on northern Ellesmere Island (81°N, 71°W) is the world's largest high arctic lake by volume. Its 7400-km2 watershed is just over a third glaciated and is underlain by permafrost. Since 2005, glacial run-off into the lake has increased 10 fold, as have sedimentation rates. Our objectives were three-fold: 1) to assess temporal variability in pCO2 dynamics during the melt season in glacial rivers; 2) to assess spatial variability in pCO2 in different rivers throughout the watershed; and, 3) to determine the impact of glacial meltwaters on Lake Hazen as a source or sink of CO2 to the atmosphere. During summers 2015 and 2016, we completed detailed DIC, pCO2 and chemical surveys of 7 glacial rivers in the Lake Hazen watershed. From 2013-2016, we also completed DIC, pCO2 and chemical depth profiles in Lake Hazen itself. Spring under ice profiles of the lake indicate the build-up of CO2 and depletion of O2 at depth, suggesting respiration of organic matter at the bottom of the lake over winter. However, dense, turbid glacial rivers form underflow currents upon entering Lake Hazen, transporting waters undersaturated in CO2 to the bottom of the lake. Detailed results of spring and summer watercolumn surveys, along with results from bottle incubation experiments to determine CO2 drawdown rates due to glacial inputs to Lake Hazen, will be presented.