The Thores Lake proglacial system: remnant stability in the rapidly changing Canadian High Arctic

We describe limnological datasets from Thores Lake, a large ice-contact proglacial lake in northern Ellesmere Island, Nunavut (82.65°N). The lake is formed due to damming by Thores Glacier at its northwest margin, has multi-year ice cover and a cold (< 1.54°C), freshwater column with a layer of < 0°C, high-conductivity water in the deepest basin. Thores Lake is ultra-oligotrophic, with low nutrient and phytoplankton stocks. Accessory pigment data and metagenomics were used to describe the eukaryotic microbial community. Taxonomic composition was homogenous to a depth of 40 m, consistent with density profiles. Surface water at the glacier interface had high turbidity and total phosphorus concentrations, and a distinct phytoplankton community dominated by chlorophytes, whereas the lake water column had higher relative abundances of chrysophytes and photosynthetic dinoflagellates. Thores Lake has a contracted pelagic food-web, with the highest trophic level occupied by phytoplankton-feeding rotifers, and no crustacean zooplankton; profiles showed that omega-3 fatty acids (FA) ranged from < 1% (interface) to 3.6% (lake) of total seston FA. Given the stability of the Thores Glacier and the persistence of cold water capped by perennial ice, Thores Lake provides a baseline to assess the impact of climate change on far northern lakes.