Microbial biogeochemistry and nutrient limitations in cryoconite hole sediments across the Taylor Dry Valley, Antarctica

Abstract:

Despite much work addressing the biology of cryoconite holes on Antarctic glaciers, little is known about potential nutrient limitations in these ice-enclosed ecosystems. We used stable isotope approaches and nutrient and enzyme stoichiometries, to evaluate what nutrients are most limiting to biological activity in cryoconite holes across a nutrient and climatic gradient in the Taylor Dry Valley, Antarctica. Nutrient concentrations (C, N, and P) varied in accordance with previous studies that have shown that the most inland of the three glaciers (Taylor Glacier) is the most oligotrophic. C-to-N ratios of Canada and Commonwealth cryoconite sediments were close to the global mean for biologically-active sediments and soils, whereas Taylor Glacier cryoconite sediments deviated from the global mean and approached high C:N ratios seen in Taylor Valley soils. Stable isotopes (δ¹⁵N and δ¹³C) indicated that high levels of N- and CO₂-fixation are likely occurring in cryoconite sediments on Commonwealth Glacier, but that Taylor Glacier had δ¹⁵N and δ¹³C values that most likely reflect atmospheric deposition of N, and C and N inputs from nearby sediments. Enzyme stoichiometric approaches further support extreme nutrient limitation on Taylor Glacier and indicate that P is the ultimate limiting nutrient across all three glaciers. Extremely high DIN-to-phosphate ratios also indicate P limitation across all three glaciers with Commonwealth Glacier being less severely P-limited that the other two glaciers. Taken together, these results broaden our understanding of nutrient dynamics and limitations in supra-glacial sediments and pave the way for future experimental work to test the relative controls of climate and nutrients on microbial biogeochemistry and diversity of cryoconite holes in one of the most extreme environments on Earth.