• Energy Research

Abstract Blooms of dark pigmented microalgae accelerate glacier and ice sheet melting by reducing the surface albedo. However, the role of nutrient availability in regulating algal growth on the ice remains poorly understood. Here, we investigate glacier ice algae on the Greenland Ice Sheet, providing single-cell measurements of carbon:nitrogen:phosphorus (C:N:P) ratios and assimilation rates of dissolved inorganic carbon (DIC), ammonium and nitrate following nutrient amendments. The single-cell analyses reveal high C:N and C:P atomic ratios in algal biomass as well as intracellular P storage. DIC assimilation rates are not enhanced by ammonium, nitrate, or phosphate addition. Our combined results demonstrate that glacier ice algae can optimise nutrient uptake, facilitating the potential colonization of newly exposed bare ice surfaces without the need for additional nutrient inputs. This adaptive strategy is particularly important given accelerated climate warming and the expansion of melt areas on the Greenland Ice Sheet.

The Ancylonema genus includes the most-documented microalgae on glaciers and ice sheets worldwide. There is significant interest in these microalgae in the context of climate change, considering their role in lowering surface ice albedo and acceleration of ice melt. However, currently, no cultures of the two closely related species A. nordenskiöldii or A. alaskanum have been established, restricting our ability to study these globally important species under laboratory conditions. We established and kept cultures of Ancylonema sp. alive for up to 2 years, by testing and optimizing different growth media and parameters. Maximum growth was achieved when using 1:100 diluted media with soil extract and low light intensity (300 µmol m−2s−1). However, as a consequence of incubation in lab conditions, some of the cultures lost their purpurogallin pigmentation and appeared green. Sanger sequencing of the ribulose-1,5 bisphosphate carboxylase/oxygenase large subunit (rbcL) marker gene revealed a large genetic diversity (possibly cryptic) and confirmed the cultures as falling within the same clade as A. nordenskiöldii and A. alaskanum. Growth experiments allowed us to estimate a division rate of between 15 ± 5.2 and 21.9 ± 4.8 days. This is up to 4 times slower than current field-based estimates (3.75–5.5 days) and indicates that, despite the successful growth and long-term maintenance of the cultures, laboratory settings can be further improved to achieve optimal growth conditions.

A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring.