Exploration of Antarctic Subglacial Aquatic Environments Environmental and Scientific Stewardship (2007) / Chapter Skim
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3 Subglacial Environments: Biological Features
3 Subglacial Environments: Biological Features
Pages 62-80
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From page 62... ...
If there are actively growing microbes in subglacial aquatic environments, this will dictate that a specific course of action be taken during the exploration and studies of such environments to ensure that these ecosystems are not profoundly changed or irreversibly altered. While no subglacial aquatic environments have been sampled directly to date, a general understanding of some of the key physiochemical characteristics of these environments has developed (Siegert et al.
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From page 63... ...
to support growth of a co-culture of butyrate-degrading organisms with methanogens in which one species lives off the products of another. Although the ability to measure thermodynamic minima such as BEQ and ME is still very much a work in progress, this result implies that microbial communities could be supported even in extreme subglacial aquatic environments despite ultra-oligotrophic substrate concentrations and the absence of sunlight.
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From page 64... ...
. POTENTIAL IMPEDIMENTS TO LIFE IN SUBGLACIAL AqUATIC ENVIRONMENTS Adverse conditions in the subglacial environment that could inhibit or preclude growth include low temperature, elevated pressure, and any reactive oxygen species favored by high oxygen tensions.
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From page 65... ...
They concluded that this section of the Vostok core consists of ice refrozen from Lake Vostok water. Although the chemical composition of subglacial aquatic environments remains highly speculative, the analysis of glacial and accretion ice from Vostok implies that the elemental requirements for microbial growth could be satisfied in the lake and that there are many possible electron donors and acceptors for biological production by chemotrophic and heterotrophic organisms (Table 3.1)
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From page 66... ...
In addition, some subglacial aquatic environments (e.g., Lake Vostok) may have formed as aerial lakes at a time prior to the cooling of Antarctica.
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From page 67... ...
Oxygen Effects The surface waters of Lake Vostok are inferred to be supersaturated in oxygen given that ice melting into the lake contains air clathrate hydrates while the accretion ice formed during freeze-up of the lake water is gas-free.
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From page 68... ...
. It should also be noted that subglacial aquatic environments may include those in which anoxic conditions or low oxygen tensions prevail, and where even O2-sensitive microbes may survive and grow.
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From page 69... ...
Additional mechanisms include transport by birds and by the increasing presence and activity of humans in Antarctica. Of particular importance to the study of subglacial aquatic environments is their potential connectivity, which may allow the movement of microbes beneath the ice sheet.
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From page 70... ...
. ice sheet originated from the islands and continents of the temperate latitudes of the Southern Hemisphere." EVOLUTION OF LIFE IN SUBGLACIAL AqUATIC ENVIRONMENTS Antarctic subglacial aquatic environments represent potentially rich and largely unexplored storehouses of genetic information.
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From page 71... ...
The exploration of subglacial aquatic environments will provide a unique lens through which to view and study these questions. may have occurred to help these organisms adapt to the cold, dark, oligotrophic environment (Tiedje 1989)
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From page 72... ...
Further, connectivity of subglacial aquatic environments (Chapter 2) will serve to lessen genetic isolation and barriers to gene flow, although it may serve to increase the effective population for recombination (Fraser et al.
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From page 73... ...
CURRENT EVIDENCE FOR LIFE IN SUBGLACIAL AqUATIC ENVIRONMENTS Biogeochemical Evidence for an Active Bacterial Flora in Lake Vostok The total dissolved solids (TDS) in the lake water can be estimated by applying ice-water partition coefficients to the major ion concentrations in the accretion ice (Christner et al.
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From page 74... ...
notes that other reports indicate concentrations less than 10 cells mL–1, but suggests that these disparities may simply reflect sampling error if the microbes are located in veins between the large ice crystals. The bacterial abundance is two- to seven-fold higher in accretion ice than in the overlying glacial ice, implying that Lake Vostok is a source of bacterial carbon beneath the ice sheet.
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From page 75... ...
(2006) state that molecular identification of microbes in Vostok accretion ice by culturing and small subunit rRNA gene amplification, show close agreement with present-day microbiota.
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From page 76... ...
EXPLORATION OF ANTARCTIC SUBGLACIAL AQUATIC ENVIRONMENTS TABLE 3.3 Microbial Diversity, Number of Cells, and Number of Inclusions Observed in Different Horizons of the Vostok 5G Deep Core Accretion Ice Ice Region Total Depth of the Inclusion Numbers of (m Accretion Number Microorganisms (m–1) below Ice Type of Microorganisms Detected surface)
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From page 77... ...
For example, the organic carbon supply from melting ice and subglacial waters entering at the northern end of Lake Vostok could be higher than at the accretion ice end, more than 200 km away, particularly if there are organic inputs from active microbial processes at the ice sheet-rock interface. Many of the aquatic environments may be stratified and organic carbon levels could be higher in the bottom waters of each lake associated with microbial decomposition and release from the sediments.
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From page 78... ...
Subglacial Aquatic Environments and Potential Microbial Communities Two types of evidence have been used to predict what will be found in waters beneath the ice sheet. First, microbes exist in all extreme environments on Earth where there is water, from a depth of 10,000 m in the ocean to surface saline lakes and from subzero temperatures in the brine channels of ocean ice to hot springs.
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From page 79... ...
It is likely that microbial communities, if present and active, will only be able to grow extremely slowly. The growth of accretion ice in Lake Vostok may have created an environment where oxygen concentrations are 50 times higher than in normal lake waters.
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From page 80... ...
. The Possibility of Microbial Evolution If the source population of microbial communities in subglacial aquatic environments is derived from the overlying glacial ice, these populations have been isolated for at least 1 million years, which is the age of the oldest Antarctic ice.
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