Author
Max Coleman
Other affiliations: Jet Propulsion Laboratory, University of Tulsa, NASA Astrobiology Institute ...read more
Bio: Max Coleman is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Pyrite & Stable isotope ratio. The author has an hindex of 47, co-authored 125 publications receiving 8560 citations. Previous affiliations of Max Coleman include Jet Propulsion Laboratory & University of Tulsa.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, a 1-10 mg portion of water is reduced with Zn metal in a sealed tube at 450 /sup 0/C to prepare hydrogen for isotopic analysis.
Abstract: A 1-10 mg portion of water is reduced with Zn metal in a sealed tube at 450 /sup 0/C to prepare hydrogen for isotopic analysis. After reaction the tube is attached directly to the mass spectrometer without further processing. Replicate analyses of water samples give reproducibility of 0.2-0.4% (1sigma); fluid inclusion samples, 1.9%; and water of hydration of gypsum, released and reduced in the sealed tube, 1.1%. A batch of 10 samples can be prepared in 1 h.
1,234 citations
TL;DR: In this article, the relative dominance of different burial diagenesis processes within specific depth intervals is given by the isotopic composition of incorporated oxygen which is temperature dependent (1) 0 to −2‰, (2) −1.5 to −5'
Abstract: Organic matter is modified by several processes operating at different depths during burial diagenesis: (1) sulphate reduction; (2) fermentation; (3) thermally-induced decarboxylation, and so on. CO2, one common product of each, can be distinguished by its carbon isotope composition: approximately (1) −25‰, (2) +15‰, (3) −20‰ relative to PDB. These values are preserved in diagenetic carbonates of the Upper Jurassic Kimmeridge Clay. Independent corroboration of the relative dominance of each process within specific depth intervals is given by the isotopic composition of incorporated oxygen which is temperature dependent (1) 0 to −2‰, (2) −1.5 to −5‰,(3) −3.5 to −7.0‰.
1,232 citations
TL;DR: Geochemical and microbiological studies suggest that contemporary formation of siderite concretions in a salt-marsh sediment results from the activity of sulphate-reducing bacteria, which may be an important and previously unrecognized agent for Fe(III) reduction in aquatic sediments and ground waters.
Abstract: REDUCTION of ferric iron (Fe(III)) to ferrous iron (Fe(II)) is one of the most important geochemical reactions in anaerobic aquatic sediments because of its many consequences for the organic and inorganic chemistry of these environments1. In marine environments, sulphate-reducing bacteria produce H2S, which can reduce iron oxyhydroxides2 to form iron sulphides. The presence of siderite (FeCO3) in marine sediments is anomalous, however, as it is unstable in the presence of H2S. Previous work3,4 has suggested a bacterial origin of siderite. Here we describe geochemical and microbiological studies which suggest that contemporary formation of siderite concretions in a salt-marsh sediment results from the activity of sulphate-reducing bacteria. We find that, instead of reducing Fe(III) indirectly through the production of sulphide, some of these bacteria can reduce Fe(III) directly through an enzymatic mechanism, producing siderite rather than iron sulphides. Sulphate-reducing bacteria may thus be an important and previously unrecognized agent for Fe(III) reduction in aquatic sediments and ground waters.
450 citations
TL;DR: The early stages of burial diagenesis involve the reactions of various oxidizing agents with organic matter, which is the only reducing agent buried with the sediment as discussed by the authors, and thermodynamic principles indicate that, inter alia, manganese, iron and sulphate should each be consumed successively to give rise to a clearly characterized vertical zonation.
Abstract: The early stages of burial diagenesis involve the reactions of various oxidizing agents with organic matter, which is the only reducing agent buried with the sediment. In a system in which a local equilibrium is established, thermodynamic principles indicate that, inter alia , manganese, iron and sulphate should each be consumed successively to give rise to a clearly characterized vertical zonation. However, ferric iron may not react fast enough and the relative rates of reduction of Fe III and sulphate not only control the formation of iron sulphide and associated carbonate but also may lead to extreme chemical and isotopic dis-equilibrium. This produces kinetically controlled ‘micro -environments’. On a larger scale, sulphide will diffuse upward to a zone in which its oxidation leads to a reduction of pH. The various dramatic changes in chemical environment across such an interface cause both dissolution and precipitation reactions. These explain common geological observations: the occurrence of flint nodules (and their restriction to chalk hosts) and the association of phosphate with glauconite.
247 citations
TL;DR: In the Central Pennine Region of England, three different types of concretions (calcite/pyrite, dolomite, pyrite and siderite) occurring spatially quite close together in the central Pennine region of England vary widely in carbon isotope composition (+10.35% >δ13C > −21.49% as mentioned in this paper.
225 citations
Cited by
More filters
TL;DR: The physiological characteristics of Geobacter species appear to explain why they have consistently been found to be the predominant Fe(III)- and Mn(IV)-reducing microorganisms in a variety of sedimentary environments.
2,633 citations
TL;DR: It is completely unclear how important microbial diversity is for the control of trace gas flux at the ecosystem level, and different microbial communities may be part of the reason for differences in trace gas metabolism, e.g., effects of nitrogen fertilizers on CH4 uptake by soil; decrease of CH4 production with decreasing temperature.
1,622 citations
TL;DR: In this article, the authors provide an overview of isotope dendroclimatology, explaining the underlying theory and describing the steps taken in building and interpreting isotope chronologies.
1,531 citations
TL;DR: Biological iron apportionment has been described as one of the most ancient forms of microbial metabolism on Earth, and as a conceivable extraterrestrial metabolism on other iron-mineral-rich planets such as Mars.
Abstract: Iron (Fe) has long been a recognized physiological requirement for life, yet for many microorganisms that persist in water, soils and sediments, its role extends well beyond that of a nutritional necessity. Fe(II) can function as an electron source for iron-oxidizing microorganisms under both oxic and anoxic conditions and Fe(III) can function as a terminal electron acceptor under anoxic conditions for iron-reducing microorganisms. Given that iron is the fourth most abundant element in the Earth's crust, iron redox reactions have the potential to support substantial microbial populations in soil and sedimentary environments. As such, biological iron apportionment has been described as one of the most ancient forms of microbial metabolism on Earth, and as a conceivable extraterrestrial metabolism on other iron-mineral-rich planets such as Mars. Furthermore, the metabolic versatility of the microorganisms involved in these reactions has resulted in the development of biotechnological applications to remediate contaminated environments and harvest energy.
1,440 citations
Journal Article•
TL;DR: This chapter discusses zinc Nutrition, which focuses on dietary requirements and recommended intakes for zinc, and causes of zinc deficiency and groups at high risk.
Abstract: Chapter 1: Overview of Zinc Nutrition ............................................................................................................... S99 1.1 Biological functions of zinc ............................................................................................................................. S99 1.2 Tissue zinc distribution and reserves .............................................................................................................. S99 1.3 Zinc metabolism ........................................................................................................................................... S100 1.4 Importance of zinc for human health........................................................................................................... S101 1.5 Human zinc requirements............................................................................................................................. S105 1.5.1 Adult men ............................................................................................................................................. S106 1.5.2 Adult women......................................................................................................................................... S109 1.5.3 Children ................................................................................................................................................ S110 1.5.4 Pregnancy.............................................................................................................................................. S111 1.5.5 Lactation ............................................................................................................................................... S112 1.6 Dietary sources of zinc and suggested revisions of Recommended Daily Intakes .................................... S112 1.6.1 Dietary sources of zinc and factors affecting the proportion of zinc available for absorption ........ S112 1.6.2 Revised estimates of dietary requirements and recommended intakes for zinc ............................... S114 1.7 Zinc toxicity.................................................................................................................................................... S118 1.8 Causes of zinc deficiency and groups at high risk ....................................................................................... S121 1.9 Summary ........................................................................................................................................................ S123
1,280 citations