Radar measurements of subterranean Antarctica have revealed that a massive network of rivers, streams and lakes exist beneath the ice sheet in Antarctica. These regions are host to a number of Antarctic aquatic environments beneath the Antarctic ice sheet.
Subglacial Lakes in Antarctica
The radar measurements used include both surface and airborne radar measurements that have managed to identify greater than 400 Antarctic subglacial lakes (Seigert et al., 2016). The largest of these is Lake Vostok, which has a total area of about 10,000 sq km and is buried under greater than about 3.7 km of the Antarctic ice sheet. Lake Vostok once was a large surface lake in Antarctica now covered by a layer of ice for over a millennia and is believed to be one of the world’s most extreme environments for any life form supposed to live beneath the ice sheet. Antarctic aquatic environments overall exist as among the world’s most extreme environments for life to thrive and prosper.
However, in the 1990s an international team supposedly discovered microbes in the accretion ice just above the lake that could derive energy from minerals in the lake and in the surrounding rocks. The results however, are largely speculative as of now as obtaining completely pristine samples is difficult given that one would need to drill through a deep layer of ice to get to the lake, with lubricating fluids being the usual culprit. Other subterranean lakes in Antarctica present similar challenges in terms of determining Antarctic aquatic environments.
Fig: A Drainage Map of Antarctica
Source: Zina Deretsky / National Science Foundation, USA
The reason for the ubiquity of subglacial lakes in Antarctica is mainly because ice is a good insulator of heat. While the ice bed undergoes geothermal heating, the maintenance of a certain degree of pressure melting temperature allows liquid water to form at the bottom, provided that the ice bed is thick enough to insulate the liquid water at the bottom. These deposits of liquid water are called hydrological sinks, with water accumulated there due to the action of gravity and the pressure exerted by the ice sheet. It was in the 1960s that subglacial lakes in Antarctica were first discovered with the help of ice-penetrating radar and noting the difference in the radio-wave reflections propagated between liquid water and ice.
These subglacial lakes can exist in terms of great diversity (Wright & Siegert, 2011). Antarctic subglacial lakes can vary in size in terms of area and depth. They can also vary according to where they are located, which can influence the amount of ice sheet deposits above, to variance in terms of the nature of the hydrological system, in which there can be long isolated lakes containing ancient water to those at the edge of the ice sheet cover which could sometimes be ephemeral lakes. There can also be a variety of topographical and geological settings, from valleys to flat sediment lake beds. Ice sheet dynamics can also influence Antarctic subglacial lakes in terms of ice flow for example. Finally, there can also be variability in terms of the thickness of the ice sheet (Siegert, 2016).
Studying Antarctic Subglacial Lake Environments
What invigorates the curiosity of scientists and the public towards Antarctic aquatic environments is the possibility that these extreme environments could harbour life that could exist in habitats that have not been previously observed on Earth. Thus much international attention has its lens on the challenges posed by how science is practiced over Antarctic aquatic environments. Many isolated ancient lakes need environmental protection against the agency of improper research practices. In this proper planning of the exploration of Antarctic aquatic environments is required, and also proper establishment and functioning of environmental protocols and more dynamic and sensitized international co-operation are necessary.
In this regard, the Subglacial Lake Exploration Group of Specialists (SALEGOS) has made headway in terms of coming up with a plan for studying Antarctic aquatic environments in subglacial lakes. The SALEGOS was set up by the Scientific Committee on Antarctic Research (SCAR) in 2000 in a multilateral approach as an international group of scientists whose credentials could possibly address all aspects of research programs.
The SALEGOS has been established by SCAR in a bid to encourage international co-operation in studying Antarctic aquatic environments in the case of subglacial lakes. The objectives of the SALEGOS include understanding subglacial environments and their impacts on life (if present) beneath the ice sheets; ascertaining the form, distribution and functioning of biological and geological systems in subglacial environments; and recovering information on past climate change contained in Antarctic marine environments and their corresponding ice sheets. The plan needs a commitment of human and logistical resources that could extend over many years (Priscu, 2005).
Subglacial Antarctic aquatic environments have not been fully explored till now, with in situ observatories not present for a majority of subterranean Antarctic lakes. In the case of Lake Vostok, which has received a fair bit of attention, lake water is being gradually removed from the lake due to the melting of the ice sheet at the northern end of Lake Vostok. At the same time the water in the lake is freezing towards the base of the glacial portion in the remainder of the lake due to changes in the pressure melting temperature. This is contributing to the removal of lake water.
Such principles could mean that with the melting of the ice sheet due to climate change, Antarctic aquatic environments under the ice sheet could experience water loss. Climate change in this perspective does not bode well thus in the case of the water volume of water bodies deep within Antarctica’s ice sheet.
Possibilities for Life in Subglacial Lakes
In Lake Vostok in the 1990s an international team discovered microbes in frozen lake water above the surface of the principal lake water in the form of accretion ice. This was present in the frozen top of the lake’s water. On analysis of the microbes it was found that their unique characteristics could suggest a unique ecosystem in isolation for millions of years. The microbes found revealed on analysis that they could possibly derive energy from minerals in the lake and from the surrounding rocks.
However, completely pristine samples of water from the lake have not as yet been recovered with evidence of life existing in the water of lake Vostok in Antarctica (B. Oskin, 2015). The Russians have made attempts at reaching the water’s surface but their results are suspect as the samples were contaminated with fluid used to facilitate the drilling process (C. Brahic, 2015). The best bet is samples of accreted ice recovered from Lake Vostok.
Although immersion in the lake has not yet occurred, samples have been taken of accretion ice. Limitations such as the nature of the samples, unknowns of the accretion process including the possibility of finding frozen microbes from a much older period, and contamination due to human intervention during the drilling process have led to differing opinions on the possibilities for life in these environments. The exciting part is that their DNA signatures indicate that these are as yet unclassified phylotypes that are thermophilic. Also found are mesophilic bacteria with diverse physiologies. Also, the geochemical composition of the accreted ice samples indicates a hydrothermal signature in Lake Vostok.
Over two decades since the 1990s, the notion of Antarctica as a lifeless and barren wasteland has been overturned into that of an icy wonderland for scientists and enthusiasts. Antarctica beneath its ice sheet has numerous subglacial lakes and extensive drainage by subterranean rivers.
SCAR began with the possibilities for exploring Lake Vostok, Lake Ellsworth and Lake Whillans. In a major breakthrough in January 2013, scientists from the US successfully accessed and sampled the subglacial Lake Whillans and found a thriving microbial ecosystem in the lake water and in the sediments (Siegert, Priscu & Alekhina, 2015). With the coming of hot water drilling and a variety of instruments now available, scientists are optimistic about being able to explore and observe Antarctic aquatic environments in water under deep ice sheets more carefully.