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Christopher S. Hill

Other affiliations: British Antarctic Survey
Bio: Christopher S. Hill is an academic researcher from Natural Environment Research Council. The author has contributed to research in topics: Subglacial lake & Antarctic ice sheet. The author has an hindex of 3, co-authored 4 publications receiving 184 citations. Previous affiliations of Christopher S. Hill include British Antarctic Survey.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors summarize the scientific protocols and methods being developed for the exploration of Ellsworth Subglacial Lake in West Antarctica, planned for 2012-2013, which they offer as a guide to future subglacial environment research missions.
Abstract: Antarctic subglacial lakes are thought to be extreme habitats for microbial life and may contain important records of ice sheet history and climate change within their lake floor sediments. To find whether or not this is true, and to answer the science questions that would follow, direct measurement and sampling of these environments are required. Ever since the water depth of Vostok Subglacial Lake was shown to be >500 m, attention has been given to how these unique, ancient, and pristine environments may be entered without contamination and adverse disturbance. Several organizations have offered guidelines on the desirable cleanliness and sterility requirements for direct sampling experiments, including the U.S. National Academy of Sciences and the Scientific Committee on Antarctic Research. Here we summarize the scientific protocols and methods being developed for the exploration of Ellsworth Subglacial Lake in West Antarctica, planned for 2012–2013, which we offer as a guide to future subglacial environment research missions. The proposed exploration involves accessing the lake using a hot-water drill and deploying a sampling probe and sediment corer to allow sample collection. We focus here on how this can be undertaken with minimal environmental impact while maximizing scientific return without compromising the environment for future experiments.

153 citations

Book ChapterDOI
01 Jan 2011
TL;DR: A U.K. consortium has planned an extensive logistics and equipment development program that will deliver the necessary resources for direct measurement and sampling of Ellsworth Subglacial Lake and reveal the post-Pliocene history of the West Antarctic Ice Sheet as discussed by the authors.
Abstract: The direct measurement and sampling of Ellsworth Subglacial Lake is a multidisciplinary investigation of life in extreme environments and West Antarctic ice sheet history. The project's aims are (1) to determine whether, and in what form, microbial life exists in Antarctic subglacial lakes and (2) to reveal the post-Pliocene history of the West Antarctic Ice Sheet. A U.K. consortium has planned an extensive logistics and equipment development program that will deliver the necessary resources. This will include hot water drill technology for lake access through approximately 3.2 km of ice, a probe to make measurements with sensors and to collect water and sediment samples, and a percussion corer to acquire an ˜3–4 m sediment core. This chapter details the requirements and early stages of design and development of the probe system. This includes the instrumentation package, water samplers, and a mini gravity corer mounted on the front of the probe. Initial design concepts for supporting equipment required at the drill site to deploy and operate the probe are also described. A review of the literature describing relevant technology is presented. The project will implement environmental protection in line with principles set out by the Scientific Committee on Antarctic Research.

23 citations

Journal ArticleDOI
TL;DR: The Ellsworth Subglacial Lake as mentioned in this paper was first observed in airborne radio echo sounding data acquired in 1978 and is located within a long, deep subglacial trough within the Ellsworth sub-glacial Highlands of West Antarctica.
Abstract: Ellsworth Subglacial Lake, first observed in airborne radio echo sounding data acquired in 1978, is located within a long, deep subglacial trough within the Ellsworth Subglacial Highlands of West Antarctica. Geophysical surveys have characterized the lake, its subglacial catchment, and the thickness, structure, and flow of the overlying ice sheet. Covering 28.9 km2, Ellsworth Subglacial Lake is located below 2.9 to 3.3 km of ice at depths of −1361 to −1030 m. Seismic reflection data have shown the lake to be up to 156 m deep and underlain by unconsolidated sediments. Ice sheet flow over the lake is characterized by low velocities ( 2 m of sediment below the lake floor, (4) water circulation modeling suggesting a melting ice-water interface, and (5) coring that can target the deepest point of the lake floor away from marginal, localized sediment sources.

12 citations

01 Dec 2012
TL;DR: In this article, a formal assessment of the technical risks of the hot-water drilling (HWD) system deployment in Subglacial Lake Ellsworth is presented, where the authors estimate the probability of failure for all components and processes that take part in each phase of the deployment.
Abstract: The exploration of Subglacial Lake Ellsworth is a high profile project funded by the Natural Environment Research Council. Clean access to the lake will be provided by a hot-water drilling (HWD) system developed by the British Antarctic Survey. The HWD system is designed to provide a 36 cm diameter borehole through 3.2 km of ice. Drilling to this depth with the HWD system has never been attempted before. This report aims to quantify the risks of the HWD system deployment. A formal assessment of the technical risks is presented. Our analysis was conducted in two parts. First we estimated the probability of failure for all components and processes that take part in each phase of the deployment. In the second part we estimate the availability of the HWD system in light of all potential failure modes. Availability is the probability of the system being available given that it is needed at a given moment. Seventy five potential failure modes have been identified. The assessments for all these failure modes are presented in this report. The probabilities of failure for the top three critical failure modes are: • Boiler failure at 0.048; • Damaged surface hydraulic pipes at 0.0185; • Driller reeler human error at 0.0168. Our availability analysis concluded that, once water circulation has been established, the probability of successfully creating the main hole is 0.83. This will enable the deployment of the probe. Once the main hole has been created, the probability of successfully reaming the main hole, enabling the deployment of the second probe, is 0.89. This is a very high probability of success. These figures take into account the drilling rate and the uncertainty associated with the effectiveness of the drilling process. The current HWD system design has incorporated design changes to avoid previous weaknesses identified during field campaigns. In particular, the current design does not contain hose couplings. This decision has reduced the risk of not achieving the target depth by 15%.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: This Review summarizes current knowledge of the microbial ecology of frozen waters, including the diversity of niches, the composition of microbial communities at these sites and their biogeochemical activities.
Abstract: The Earth's cryosphere comprises those regions that are cold enough for water to turn into ice. Recent findings show that the icy realms of polar oceans, glaciers and ice sheets are inhabited by microorganisms of all three domains of life, and that temperatures below 0 °C are an integral force in the diversification of microbial life. Cold-adapted microorganisms maintain key ecological functions in icy habitats: where sunlight penetrates the ice, photoautotrophy is the basis for complex food webs, whereas in dark subglacial habitats, chemoautotrophy reigns. This Review summarizes current knowledge of the microbial ecology of frozen waters, including the diversity of niches, the composition of microbial communities at these sites and their biogeochemical activities.

307 citations

Journal Article
TL;DR: The survival rate of Staph. aureus in a standard volume of denbrinated blood is a reliable quantitative measure of the bactericidal power of blood, and the number of viable organisms in the inoculum and in the blood-bacterium mixture may be estimated with the necessary accuracy by counts of colonies developing from measured volumes of the fluids let fall on to the surface of solid media as mentioned in this paper.
Abstract: The survival rate, p , of a measured inoculum of Staph. aureus in a standard volume of denbrinated blood, is a reliable quantitative measure of the bactericidal power of blood. The number of viable organisms in the inoculum and in the blood-bacterium mixture may be estimated with the necessary accuracy by counts of colonies developing from measured volumes of the fluids let fall on to the surface of solid media. Fildes' agar was the most suitable medium for this surface-viable count, and was selected on the basis of four criteria; of the media tested it yielded the highest counts, and the counts conformed most closely to a Poisson series; and on it the mean colony size was maximum, and the coefficient of variation of colony size was minimum. On this medium, the close conformity of the separate count values to a Poisson series enabled the standard error of the survival rate to be determined from a simplification of the general expression for the standard error of a ratio. The number of colonies growing from a sample of a blood-bacterium mixture may be reduced, not by killing of the individual cocci, but as a result of their aggregation either by agglutinins in the blood, or in the cytoplasm of leucocytes that are phagocytic but not bactericidal. It appears that these mechanisms are unlikely to operate in blood-bacterium mixture containing relatively few organisms; in such mixtures the survival rate is a reflexion of the killing power only. The immunological significance of p has not been investigated, but the range of values for healthy human adults differs significantly from that for sufferers from chronic staphylococcal infection. Moreover, by the technique employed differences may be detected between individual values of p that cannot reasonably be attributed to technical or sampling errors.

152 citations

Journal ArticleDOI
TL;DR: Evaluating recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling.

134 citations

Journal ArticleDOI
TL;DR: It is concluded that increased efforts are required to protect the unique ecosystems of Antarctica from microbial and genetic contamination and homogenisation, but that such processes are unlikely to have any immediate gross impact on microbiological community structure or function.

133 citations

Journal ArticleDOI
TL;DR: A review of the links between vegetation-cover and climate with a focus on forests and rain (precipitation) can be found in this article, where the authors highlight advances, uncertainties and research opportunities.

115 citations