APRI members Klemens Weisleitner and Birgit Sattler (University of Innsbruck) joined a scientific expedition team to study the impact of a glacier on a unique Antarctic lake ecosystem.
A glimpse behind the scenes of the Antarctic expedition that led to the featured scientific publication (© Klemens Weisleitner).
The perennially ice-covered (2-4m) and 170m deep Lake Untersee is one of the largest freshwater surface lakes in Antarctica. It harbors so-called giant stromatolites which are living structures that are found nowhere else on Earth and they hold clues how life on Earth might have evolved. The expedition aimed to identify environments outside Lake Untersee that could serve as a microbial source for this unique Antarctic lake ecosystem.
The location of Lake Untersee (Google).
A lake with a peculiar history
Lake Untersee was first discovered in 1939 during a German reconnaissance flight. Disguised as a whaling expedition, aerial pictures were recorded with the aim to map the area and later lay claim to the territory. It took until 1969 – the year of the moon landing – until the first humans walked across the 2-4m thick lake ice cover. Later, mainly German-Soviet expeditions took place in this area to learn more about Lake Untersee and the surrounding mountains. Since 2008, annual expeditions under U.S. leadership have taken place. As experts in microbial ecology of glaciers, the APRI members were invited to join the expedition team for multiple seasons. Not many researchers had the opportunity to study Lake Untersee.
Overview of the study site. The Anuchin Glacier (left) dams Lake Untersee (right). The lake is surrounded by the Gruber Mountains (© Klemens Weisleitner).
The absence of infrastructure at the study site forced the expedition teams to sleep and work in tents while coping with extreme Antarctic conditions. Preparations for such expeditions exceeds planning experiments and sampling strategies. Physical examinations and trainings were crucial as well. Also, the expedition team had to cope with isolation from civilization for up to two months with limited possibilities for communication with the outside world.
“Despite its thick perennial ice cover, Lake Untersee is not an isolated system. The adjacent Anuchin Glacier serves as important water, nutrient and microbial source.”
Microbial source tracking
Previous biological studies from Lake Untersee described microbial communities within the lake. However, potential microbial sources outside the lake were discussed but never identified. To tackle this gap of knowledge, the researchers collected samples from the lake environment (sediments, water, lake ice) and from the adjacent surroundings including soils, air, glacial ice and so-called cryoconite holes. The latter are depressions on the surface of glaciers that form when dark particulate matter accumulates and melts into the ice. All samples were transported back to Austria to identify the microbial communities from the above-mentioned environments.
(A) Schematic illustration of Lake Untersee [illustration based on (Wand et al., 2006)]. (B) Soil sample. (C) Stromatolites, pinnacle mats and flat mats at a depth of about 24 m. (D) Pigmented microbial benthic mats. (E) “White Ice Patch” -glacial ice integrated in the lake ice containing cryoconite holes that are aligned from NE to SW; (F) Aerial image of a pressure ridge. (G) Typical morphology of an Antarctic ice-lidded cryoconite hole (© Weisleitner et al.).
Cryoconite holes on glaciers as major microbial source for Lake Untersee
Based on a microbial source tracking analysis, cryoconite holes from the Anuchin Glacier were identified as most important microbial source for Lake Untersee. These findings suggest that the glacier serves as important source for the perennially ice-covered lake. Compared to the volumetric input of melting glacial ice, cryoconite holes contribute a very small fraction to the lake which emphasizes the importance of these glacial features. According to the authors, logistical constraints at the study site hampered sampling of potential microbial sources beneath the glacier. Future expeditions may tackle this challenge. Until then, life beneath the glacier remains a mystery.
View through an ice core barrel towards the glacier surface that features a cryoconite hole (© Klemens Weisleitner).
Written by Klemens Weisleitner and Birgit Sattler.
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