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Inorganic carbon-isotope distribution and budget in the Lake Hoare and Lake Fryxell basins, Taylor Valley, Antarctica
- Klaus Neumann, W. Berry Lyons, David J. Des Marais
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- Journal:
- Annals of Glaciology / Volume 27 / 1998
- Published online by Cambridge University Press:
- 15 May 2017, pp. 685-689
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One of the unusual features of Lakes Fryxell and Hnare in Taylor Valley, southern Victoria Land, Antarctica, is their perennial ice cover. This ice cover limits gas exchange between the atmosphere and the lake water, and causesa very stable stratification of the lakes. We analyzed a series of water samples from profiles of these lakes and their tributaries for δ13C of the dissolved inorganic carbon (DIC) in order to qualify the carbon flux from the streams into the lakes, and to investigate the carbon cycling with in the lakes. Isotopic values in the uppermost waters (δ13C = +l.3‰ to 5.3‰ in Lake Hoare, +0.4‰ to +3.0‰ in Lake Fryxell) are close to the carbon-isotope values encountered in the streams feeding Lake Fryxell, but distinctively heavier than in streams feeding Lake Hoare (δ13C= — 2.3%n to 1.4%). These ratios are much heavier than ratios found in the moat that forms around the lakes injanuary February (δC = -10.1%). in the oxic photic zones of the lakes, photosynthesis clearly influences the isotopic composition, with layers of high productivity having enriched carbon-isotope signatures δ13C= +2.7‰ to +6.1‰). in both lakes, the isotopic values become lighter with depth, reaching minima of 3.2‰ and 4.0% in Lakes Fryxell and Hoare, respectively. These minima are caused by the microbial remineralization of isotopically light organic carbon. We present DIC flux calculations that help to interpret the isotopic distribution. For example, in Lake Hoare the higher utilization of CO2aq, and a substantially smaller inflow of CO2 from streams cause the heavier observed isotopic ratios. Differences in the hydrology and stream morphologies of the tributaries also greatly influence the carbon budgets of the basins.
8 - Fraction of suitable planets on which life actually appears, fl, 1961 to the present
- Edited by Douglas A. Vakoch, Matthew F. Dowd, University of Notre Dame, Indiana
- Foreword by Frank Drake
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- The Drake Equation
- Published online:
- 05 July 2015
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- 02 July 2015, pp 145-162
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Summary
Abstract An assessment of fl depends heavily upon perspectives gained from the single known example of our own biosphere. Extrapolating this single data point to a quantitative estimate of fl amounts to sheer speculation. But recent discoveries have identified perspectives about our biosphere and early planetary environments that are quite relevant to fl and that also benefit our search for a second example of life elsewhere. This chapter addresses these topics from the following perspectives: concepts of life, life's environmental requirements, early conditions on rocky planets, and the origins of life. The habitability of a planetary environment is defined by the intrinsic environmental requirements of life, which, in turn, arise from the most universal attributes of life itself. Key environmental requirements include a suitable solvent, the chemical building blocks of life, biologically useful sources of energy, and environmental conditions that favor the survival of key complex molecules and structures. The earliest evidence of our biosphere now extends back to more than 3.7 billion years ago, essentially as old as the oldest rocks that could have preserved recognizable evidence. The most ancestral characteristics of microbial metabolism are broadly consistent with the resources that were likely available as early as 4.4 billion years ago. Organic compounds relevant to prebiotic
chemistry have been discovered in primitive bodies (e.g., meteorites, comets) and in interstellar space, and these might have been delivered intact to planetary surfaces. Thus, life might have begun very soon after habitable conditions were established. Regarding the origins of life, biochemical research is narrowing the knowledge gap between prebiotic chemicals and the first living systems. RNA molecules could have served as both self-replicators and enzymes. The earliest functional protein enzymes might have been much smaller in size and thus perhaps easier to develop than previously imagined. The prebiotic environment could have provided molecules that formed vesicles as precursors of cellular envelopes. Although the evidence certainly cannot prove the notion that another young Earth-like planet probably also sustained an origin of life, the evidence is at least quite consistent with the notion that life can arise early on Earth-like planets. Also, the evolution of stars and planets follows trajectories that allow reasonable estimations to be made of long-term changes in planetary climates and habitability. Thus, although recent discoveries have not yet reduced the enormous uncertainty in estimating fl, they have substantially improved our strategies for seeking a second example of life that would, in turn, substantially reduce that uncertainty.
A spectroscopy and isotope study of sediments from the Antarctic Dry Valleys as analogues for potential paleolakes on Mars
- Janice L. Bishop, Brandy L. Anglen, Lisa M. Pratt, Howell G. M. Edwards, David J. Des Marais, Peter T. Doran
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- Journal:
- International Journal of Astrobiology / Volume 2 / Issue 4 / October 2003
- Published online by Cambridge University Press:
- 09 March 2004, pp. 273-287
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A spectroscopy and isotope study has been performed on igneous sediments from Lake Hoare, a nearly isolated ecosystem in the Dry Valleys region of Antarctica. The mineralogy and chemistry of these sediments were studied in order to gain insights into the biogeochemical processes occurring in a permanently ice-covered lake and to assist in characterizing potential habitats for life in paleolakes on Mars. Obtaining visible/near-infrared, mid-infrared and Raman spectra of such sediments provides the ground truth needed for using reflectance, emittance and Raman spectroscopy for exploration of geology, and perhaps biology, on Mars. Samples measured in this study include a sediment from the ice surface, lake bottom sediment cores from oxic and anoxic zones of the lake and the magnetic fractions of two samples.
These sediments are dominated by quartz, pyroxene, plagioclase and K-feldspar, but also contain calcite, organics, clays, sulphides and iron oxides/hydroxides that resulted from chemical and biological alteration processes. Chlorophyll-like bands are observed in the spectra of the sediment-mat layers on the surface of the lake bottom, especially in the deep anoxic region. Layers of high calcite concentration in the oxic sediments and layers of high pyrite concentration in the anoxic sediments are indicators of periods of active biogeochemical processing in the lake. Micro-Raman spectra revealed the presence of ~5 μm-sized pyrite deposits on the surface of quartz grains in the anoxic sediments. C, N and S isotope trends are compared with the chemistry and spectral properties. The δ13C and δ15N trends highlight the differences in the balance of microbial processes in the anoxic sediments versus the oxic sediments. The biogenic pyrite found in the sediments from the anoxic zone is associated with depleted δ34S values, high organic C levels and chlorophyll spectral bands and could be used as a potential biomarker mineral for paleolakes on Mars.
15 - Flow Chart and Processing Procedures for Rock Samples
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- By Harald Strauss, Ruhr-Universität Bochum, David J. Des Marais, Ames Research Center, J. M. Hayes, Indiana University, Toby B. Moore, University of California, J. William Schopf, University of California
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 695-698
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Summary
Investigation of a large number of samples during this project led to development of the following processing routine.
Curation of samples was performed at the University of California, Los Angeles. As appropriate, subsamples were subsequently distributed to PPRG members for analyses to be carried out at their home institutions. A flow chart outlining the various procedures involved is shown in Figure 15.2 and is summarized below.
The initial curation for every incoming rock sample consisted of assigning a PPRG Sample Number (e.g., “1001”). Pertinent geological information was compiled and entered into the databases “Inventory,” “Site,” and “Strat” (see Chapter 21).
For paleontological and mineralogical studies, petrographic thin sections were prepared of each sample: for microfossil studies, a 150µi-thick “paleo”-section (“1001-1-A”); and for petrographic studies, either a standard 30 µm-thick section for non-carbonates (“1001-1-B”) or a 5 to 15 µm-thick section for carbonates (“1001-1-C”). In addition, large-area thin sections (150 µm-thick, “1001-1-STROM”) were prepared of selected stromatolitic samples.
Sample processing for geochemical and/or palynological studies was initiated by discarding any weathered surface or secondarily emplaced vein material and generating a mass of clean interior rock chips ≤ 1 cm in diameter (“1001-1-RC”). Chipping of small samples was performed using a geologic hammer; larger samples were chipped with a jawbone (i.e., “chipmunk”) crusher. In order to remove any organic contaminants, the chips were etched in a 20% HF-10% HC1 solution, then rinsed with large volumes of distilled water and dried in a drying oven at 75° C.
6 - Modern Mat-Building Microbial Communities: a Key to the Interpretation of Proterozoic Stromatolitic Communities
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- By Beverly K. Pierson, University of Puget Sound, John Bauld, Bureau of Mineral Resources, Richard W. Castenholz, University of Oregon, Elisa D'Amelio, Ames Research Center, David J. Des Marais, Ames Research Center, Jack D. Farmer, University of California, John P. Grotzinger, Massachusetts Institute of Technology, Bo Barker Jørgensen, University of Aarhus, Douglas C. Nelson, University of California, Anna C. Palmisano, Ivorydale Technical Center, J. William Schopf, University of California, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd, David M. Ward, Montana State University
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 245-342
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Summary
Introduction
Modern microbial mats are structurally coherent macroscopic accumulations of microorganisms. Mats are widely distributed on earth. They are found in a surprisingly large number of diverse environments from the equatorial zones to both polar regions. They vary in size from extensive terrestrial and hypersaline mats that cover areas several square kilometers in extent to minute mats only a few square centimeters in area found in small thermal springs. They vary in thickness from massive accumulations measured in meters, such as those in the Persian Gulf and the Red Sea region, to thin films less than a few millimeters in thickness. In addition to being highly varied in size, modern microbial mats are also very diverse in morphology, community structure, and physiological characteristics. What do such mats have in common? Under what conditions do they form? What is the basis of their diversity? What insight do they provide, if any, to the interpretation of the widespread stromatolites of the Proterozoic?
A Terminology
Microbial mats are accretionary cohesive microbial communities which are often laminated and found growing at the sediment-water (occasionally sediment-air) interface. Most mats stabilize unconsolidated sediment. The mats are comprised of the various microorganisms that accumulate along with their metabolic products. The most conspicuous of these products is usually a copious amount of extracellular polysaccharide which helps hold the cells together to form a cohesive structure.
3 - Proterozoic Biogeochemistry
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- By J. M. Hayes, Indiana University, David J. Des Marais, Ames Research Center, Ian B. Lambert, Resource Assessment Commission, Australia, Harald Strauss, Ruhr-Universität Bochum, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 81-134
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Biogeochemistry encompasses the study of chemical fossils. It includes and draws on knowledge of the biochemical activities of contemporary organisms in modern sedimentary environments, including their roles in the biogeochemical cycling and isotopic fractionation of important elements such as carbon, oxygen, sulfur, and nitrogen, and their production of taxonomically distinctive organic compounds. This Section deals with the chemical entities preserved in the Proterozoic sedimentary record that may carry information about the biology and evolution of early life.
Chemical fossils can be discerned at the atomic level, in the occurrence of anomalous concentrations of a particular element or an isotope; at a molecular level, in the structure and stereochemistry of hydrocarbons derived from membrane lipids or pigments; and at a macromolecular level by way of the preservation of detailed chemical structures in kerogen and morphologically distinct microfossils. Paleobiochemical information is encoded in the nucleic acids of extant organisms and in their comparative biochemistry; this topic is treated in Chapter 9. Here we examine and discuss the occurrence of isotopic and molecular fossils. A considerable and consistent body of information derived, in part, from techniques developed during exploration for petroleum and minerals is now available. Rapid expansion of this knowledge is presently taking place, particularly with regard to chemical processes in early preservation of organic matter, structures of kerogen, isotopic composition of individual biomarkers, and global secular variations in organic and inorganic isotopic abundances.
16 - Procedures of Whole Rock and Kerogen Analysis
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- By Harald Strauss, Ruhr-Universität Bochum, David J. Des Marais, Ames Research Center, J. M. Hayes, Indiana University, Ian B. Lambert, Resource Assessment Commission, Australia, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
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- 26 June 1992, pp 699-708
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