Linking glacial melt to downstream ecosystem function and health in the Canadian High Arctic

Abstract:

The Lake Hazen watershed (7516 sq. km), located in northern Nunavut (Canada, 81.8N, 71.4W), is ~40% glacierized and underlain by continuous permafrost, making it particularly susceptible to the dramatic warming predicted for the Arctic. Since 2012, we have conducted detailed surveys of freshwater quality (contaminants, nutrients, carbon) and aquatic communities (microbes, phytoplankton) across the land-to-ocean aquatic continuum within the watershed: from glacial headwaters through Lake Hazen (544 sq. km, 267 m deep) and out to nearshore waters along the eastern coast of Ellesmere Island. Combining data collected in spring (2012-15, 17) and summer (2015-16, 18-19), we found that glacial runoff annually transformed ultra-oligotrophic Lake Hazen during the summer months, strongly influencing the physical and chemical structure of the water column. Upon entering Lake Hazen, the glacial rivers formed turbidity currents, transporting sediment-laden, oxygenated, low CO₂ surface waters to the lake depths. Glacial rivers were annually an important source of nutrients (e.g., major cations and anions), but also contaminants (mercury), to Lake Hazen. Lake water column microbial communities were more or less stable despite fluctuating environmental conditions, but phytoplankton communities within the lake exhibited distinct seasonality, driven largely by differences in inferred nutrient limitation. Thus, given its size and long residence time (>25 years), Lake Hazen acts as an important physical and chemical intermediary between the glacial rivers and the Ruggles River outflow to the ocean, significantly modifying glacial exports to Arctic marine waters. We highlight the importance of studying glacial systems at the watershed scale in the context of climate change predicted for high latitude and altitude regions.