Blue Ice Oases of Microbial Life on the Antarctic Ice Sheet

The East Antarctic Ice Sheet is Earth's largest freshwater ecosystem, containing bacteria, algae, viruses and other microbes transported there by wind and redistributed by ice flow. We have therefore been studying how microorganisms survive in the ice sheet by retrieving samples from some of the oldest surface ice (many thousands of years old) outcropping in the vicinity of Troll Research Station, Antarctica. During a successful field campaign at Troll from December 2019 to January 2020, we collected six glacier ice cores, with the aim of determining whether microbes become active once there is sufficient energy and water to allow for biological production. We found that these conditions were met in the top part of the ice cores, since the sun’s energy could penetrate into the wind-polished blue ice and cause melting at about 0.5 meters depth for much of the summer. In most places, the penetration of the light is strongly reduced by small air bubbles in the near-surface ice and so we have measured the abundance and size of these bubbles in order to predict how light is scattered through this important zone. This work was combined with the mapping of other Antarctic Blue Ice Areas in order to understand the regional distribution of near-surface melting and biological production. About 1% of the ice sheet supports favourable conditions for blue ice ecosystems to develop. We have found that rock particles are critical for allowing microorganisms to live within the blue ice. Their dark colour absorbs much more of the sun’s energy than the bubbles in the ice, leading to meltwater flow and the accumulation of the particles in melt pools known as "cryoconite holes". Mapping showed that the rock particles are derived via two processes: dust deposition from above, and erosion of bedrock near ridges from below. We have found that these holes are far more important hotspots for nutrient enrichment and biological processes than the pure ice, even if water is present. This is quite different to the situation we found in Svalbard, where the ice contains many more living microorganisms. Furthermore, even in the cryoconite holes, rates of biological production seem to be very low compared to both Svalbard and other near-coastal glaciers in Antarctica. Very distinct nutrient and chemical conditions develop in the holes, including high nitrate, phosphate and silica concentrations relative to the neighbouring snow and ice. These conditions most likely reflect efficient recycling of nutrients by a community dominated by bacteria, nutrient release from the rock particles and a lack of “greedier” algae and other, larger organisms. These are signs that the high elevation and great distance to the coast make Troll ideal for examining the limits of life on Earth’s surface. The BIOICE team is performing detailed biological analysis of the microorganisms in the snow, ice and meltwater, as well as the sediment in the cryoconite holes. Results from the molecular (DNA) analyses show almost no detectable cells in the pure ice. In the sediment from the holes, we have found Cyanobacteria are dominant, closely followed by Actinobacteriota, and then Proteobacteria and Bacteroidota. This is surprisingly diverse, especially when compared to the pure glacier ice, where no DNA could be reliably recovered. These communities are now being compared to similar samples from Svalbard. We expect to find that the cryoconite holes are so important because the rock particles provide important nutrients and also a long-lived, stable habitat that survives from one summer to the next.

Almost half of the freshwater bacterial biomass on Earth is stored in the East Antarctic Ice Sheet (EAIS) and ice core studies have shown us that a proportion of it remains viable even after storage for more than 1 million years. However, we have yet to establish what happens to these cells when they emerge at the ice sheet margin and are potentially revived by melt. For example, in the wind polished blue ice areas around the periphery of Antarctica, we have shown that sub-surface melting initiates the southernmost occurrence of photosynthesis on Earth. This study will therefore examine the physical, chemical and biological conditions within these oases and assess the contributions made to ecosystem functioning by older microorganisms transported by ice flow over millennia, and younger microorganisms derived from recent atmospheric deposition. Our project requires that we tackle R&D challenges linked to the sterile analysis of dilute glacier ice, snow and meltwater from extremely remote locations. Therefore, we will use our logistically advantagous location in Svalbard to practise all workflow routines prior to a substantial Antarctic campaign at Troll Station in 2018/19. Use of cores already collected by the Norwegian Polarinstitutt’s Antarctic traverse during the International Polar year in 2007/08 will add significant value to both our project and the legacy of the IPY. Our first exploration of the surface microbiology of the EAIS from its continental interior to the coast is of direct, strategic relevance to the Norwegian Polarintitutt’s mandate from government, and will yield physical, chemical and biological data of great utility to future research in this region. Our collections of microorganisms and genetic information will also be a vital resource for groups involved in the management of Antarctica biodiversity, including the Scientific Committee on Antarctic Research (SCAR) and the Commission for the Conservation of Antarctic Marine Living Resources.