scholarly journals Searching for signatures of life on Mars: an Fe-isotope perspective

2006 ◽  
Vol 361 (1474) ◽  
pp. 1715-1720 ◽  
Author(s):  
M Anand ◽  
S.S Russell ◽  
R.L Blackhurst ◽  
M.M Grady
Keyword(s):  
Low Temperature ◽  
Liquid Water ◽  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Isotope Ratios ◽  
Experimental Investigations ◽  
Form Of Life ◽  
Geological Past ◽  
Martian Meteorites ◽  
Fe Reduction

Recent spacecraft and lander missions to Mars have reinforced previous interpretations that Mars was a wet and warm planet in the geological past. The role of liquid water in shaping many of the surface features on Mars has long been recognized. Since the presence of liquid water is essential for survival of life, conditions on early Mars might have been more favourable for the emergence and evolution of life. Until a sample return mission to Mars, one of the ways of studying the past environmental conditions on Mars is through chemical and isotopic studies of Martian meteorites. Over 35 individual meteorite samples, believed to have originated on Mars, are now available for lab-based studies. Fe is a key element that is present in both primary and secondary minerals in the Martian meteorites. Fe-isotope ratios can be fractionated by low-temperature processes which includes biological activity. Experimental investigations of Fe reduction and oxidation by bacteria have produced large fractionation in Fe-isotope ratios. Hence, it is considered likely that if there is/were any form of life present on Mars then it might be possible to detect its signature by Fe-isotope studies of Martian meteorites. In the present study, we have analysed a number of Martian meteorites for their bulk-Fe-isotope composition. In addition, a set of terrestrial analogue material has also been analysed to compare the results and draw inferences. So far, our studies have not found any measurable Fe-isotopic fractionation in bulk Martian meteorites that can be ascribed to any low-temperature process operative on Mars.

scholarly journals Identifying vital effects in <i>Halimeda</i> algae with Ca isotopes

2014 ◽  
Vol 11 (24) ◽  
pp. 7207-7217 ◽  
Author(s):  
C. L. Blättler ◽  
S. M. Stanley ◽  
G. M. Henderson ◽  
H. C. Jenkyns
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Test Organism ◽  
Isotope Ratios ◽  
First Order ◽  
Geological Past ◽  
Rayleigh Distillation ◽  
Vital Effects ◽  
Specific Factors ◽  
Biogenic Carbonates

Abstract. Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (−0.6‰) appears to be much smaller than that for the algal aragonite (−1.4‰), similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

Using the silica isotope composition of biogenic materials in marine sediments to reconstruct ocean chemistry

2020 ◽  
Author(s):  
Daniel Conley ◽  
Katherine Hendry
Keyword(s):  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Isotope Ratios ◽  
Silicon Isotope ◽  
Skeletal Morphology ◽  
Biological Communities ◽  
Low Concentrations ◽  
Sponge Spicules ◽  
Global Cycles ◽  
Key Events

&lt;div&gt;&lt;span&gt;The silicon isotopic composition of sedimentary biogenic opal can be used to track shifts in the balance between silicon inputs to the ocean and outputs by burial. In addition to biosilicification and opal burial, the global cycles of climate (hydrology, weathering, glaciation, etc.), tectonics (volcanoes, LIPs, mountain building, etc.) and geochemistry (reverse weathering, inorganic Si precipitation, etc.) have driven variations in the global Si cycle over geologic time. Prior to the start of the Phanerozoic it is thought that burial in the global oceans was controlled inorganically through chert formation. The evolution of the Si depositing organisms, radiolarians and sponges, reduced oceanic dissolved Si, but the largest reductions occurred with the evolution of the diatoms bringing dissolved Si to the low concentrations (relative to saturating concentrations) observed today. However, the timing of the depletion of dissolved Si by diatoms is currently under debate.&lt;/span&gt;&lt;/div&gt;&lt;div&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;&lt;span&gt;Our understanding of the biological components of the Si cycle has grown enormously. In the last decade, silicon isotope ratios (expressed as &amp;#948;30Si) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the &amp;#948;30Si of deep-sea sponge spicules has been demonstrated to be a useful proxy for past dissolved Si concentrations. However, more recent studies find anomalies in the isotopic fractionation of sponge spicules that relate to skeletal morphology: reliable reconstructions of past dissolved Si can only be obtained using silicon isotope ratios derived from sponges with certain spicule types. We are applying &amp;#948;30Si proxies from biosiliceous material contained in sediments to generate robust estimates of the timing and magnitude of dissolved Si drawdown. We will provide fundamental new insights into the drawdown of dissolved Si and other key events, which reorganized the distribution of carbon and nutrients in seawater, with implications for productivity of the biological communities within the ancient oceans.&amp;#160;&lt;/span&gt;&lt;/div&gt;

scholarly journals Microbial Isotopic Fractionation of Perchlorate Chlorine

2003 ◽  
Vol 69 (8) ◽  
pp. 4997-5000 ◽  
Author(s):  
Max L. Coleman ◽  
Magali Ader ◽  
Swades Chaudhuri ◽  
John D. Coates
Keyword(s):  
Stable Isotope ◽  
Environmental Samples ◽  
Microbial Respiration ◽  
Isotope Composition ◽  
Isotopic Fractionation ◽  
Stable Isotope Composition ◽  
Biotic Degradation ◽  
Chlorine Stable Isotope

ABSTRACT Perchlorate contamination can be microbially respired to innocuous chloride and thus can be treated effectively. However, monitoring a bioremediative strategy is often difficult due to the complexities of environmental samples. Here we demonstrate that microbial respiration of perchlorate results in a significant fractionation (∼−15‰) of the chlorine stable isotope composition of perchlorate. This can be used to quantify the extent of biotic degradation and to separate biotic from abiotic attenuation of this contaminant.

Jarosite in Antarctic deep ice supports the ice-weathering model for jarosite formation on Mars

2021 ◽  
Author(s):  
Giovanni Baccolo ◽  
Barbara Delmonte ◽  
Paul Niles ◽  
Giannantonio Cibin ◽  
Elena Di Stefano ◽  
...  
Keyword(s):  
Low Temperature ◽  
Volcanic Activity ◽  
Liquid Water ◽  
Chemical Weathering ◽  
Ice Core ◽  
Hydrothermal Processes ◽  
Meridiani Planum ◽  
History Of ◽  
Alternative Proposal ◽  
Iron Bearing

&lt;p&gt;On Earth, jarosite is a weathering product forming in acidic-oxidative environments from the alteration of iron-bearing minerals in presence of liquid water. Typical settings where this iron-potassium hydrated sulphate is found, are weathering zones of pyrite-rich deposits, evaporative basins and fumaroles. Jarosite is not only known on Earth, it also occurs on Mars, where it was firstly identified by the Opportunity rover. The mineral was in fact recognized in the finely layered formations outcropping at Meridiani Planum and that were accurately investigated by the rover (Klingelh&amp;#246;fer et al. 2004). Since jarosite requires liquid water to form, its occurrence on Mars has been regarded as an evidence for the presence of liquid water in the geologic past of Mars (Elwood-Madden et al., 2004). Since then, many models have been proposed to describe the environments where the precipitation of Martian jarosite took place. The most accepted ones deal with evaporative basins similar to Earth&amp;#8217;s playas, others concern volcanic activity and hydrothermal processes. An alternative proposal predicted that jarosite may have formed as a consequence of weathering of mineral dust trapped in massive ice deposits, i.e. the ice-weathering model (Niles &amp; Michalsky, 2009). The hypothesis that jarosite formed on Mars because of low-temperature, acidic and water limited weathering, is not new (Burns, 1987), but until now no direct evidences were available to support it.&lt;/p&gt;&lt;p&gt;A potential Earth analogue to investigate such processes is deep Antarctic ice. We present a first investigation of deep ice samples from the Talos Dome ice core (East Antarctica) aimed at the identification of englacial jarosite, so as to support the ice-weathering model. Evidences gathered through independent techniques showed that jarosite is actually present in deep Antarctic ice and results from the weathering of dust trapped into ice. The process is controlled by the re-crystallization of ice grains and the concurrent re-location of impurities at grain-junctions, which both depend on ice depth. This study demonstrates that the deep englacial environment is suitable for jarosite precipitation. Our findings support the hypothesis that, as originally predicted by the ice-weathering model, paleo ice-related processes have been important in the geologic and geochemical history of Mars.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Burns, R. Ferric sulfates on Mars. &lt;em&gt;J. Geophys. Res.&lt;/em&gt; &lt;strong&gt;92&lt;/strong&gt;, E570-E574 (1987).&lt;/p&gt;&lt;p&gt;Elwood-Madden et al., 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. &lt;em&gt;Nature&lt;/em&gt; &lt;strong&gt;431&lt;/strong&gt;, 821-823 (2004).&lt;/p&gt;&lt;p&gt;Klingelh&amp;#246;fer, G. et al. Jarosite and Hematite at Meridiani Planum from Opportunity's M&amp;#246;ssbauer Spectrometer. &lt;em&gt;Science&lt;/em&gt; &lt;strong&gt;306&lt;/strong&gt;, 1740-1745 (2004).&lt;/p&gt;&lt;p&gt;Niles, P. B. &amp; Michalski, J. M. Meridiani Planum sediments on Mars formed through weathering in massive ice deposits. &lt;em&gt;Nat. Geosci.&lt;/em&gt; &lt;strong&gt;2&lt;/strong&gt;, 215-220 (2009).&lt;/p&gt;

scholarly journals Hepatic cryosurgery in experiment and clinic

2003 ◽  
Vol 2 (3) ◽  
pp. 56-61
Author(s):  
B. I. Alperovich ◽  
A. V. Potapov ◽  
V. N. Salo
Keyword(s):  
Low Temperature ◽  
Hepatic Resection ◽  
Morphological Changes ◽  
Hepatic Tissue ◽  
Experimental Investigations ◽  
Original Design ◽  
Hepatic Diseases ◽  
Electron And Light Microscopy ◽  
Design Characteristics ◽  
Sexually Mature

The aim of the investigation – to study changes in hepatic tissue resulting from the influence of low temperatures (– 195,8 °C) in experiments and clinic. Hepatic tissue investigations in experiment have been carried out using electron and light microscopy. During the surgery instruments of original design have been used – cryoscalpels and cryodestructors. Experiments have been carried out on 45 sexually mature dogs of both sexes. Animals have been separated into 3 groups. On the first group (consisting of 12 animals), in the acute experiment, there have been studied features of cryoscalpel design characteristics. In the second series of experiment (on 22 dogs) there have been made a comparative study of hepatic resection using cryoultrasonic scalpel and simple surgical scalpel by means of the study of hemorrhage quantity. In 11 cases there have been studied hepatic morphological changes affected by cryoeffect. By the effect of low temperature ice crystals are appeared in hepatic tissue intracellularly and outside the cell, they cause mechanical injury and rupture of hepatic tissue. In 45 days connective tissue elements are formed at the place of cryodestruction. The use of cryoultrasonic scalpel in hepatic resection in the experiment decreases the hemorrhage quantity by 1,26 times as compared to the traditional methods. Positive experimental investigations allowed to use the low temperature with success in clinical practice at 253 patients with different localized hepatic diseases with 13 lethal outcomes (5,1%). Thus, the used cryosurgical technique during surgical operations allows to decrease significantly the hemorrhage, to eliminate parenchymatous bleeding and to prevent relapses of disease both at growths and at parasitic hepatic affection.

scholarly journals Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

2014 ◽  
Vol 14 (23) ◽  
pp. 31813-31841
Author(s):  
S. J. Allin ◽  
J. C. Laube ◽  
E. Witrant ◽  
J. Kaiser ◽  
E. McKenna ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Isotope Ratios ◽  
Gas Chromatography Mass Spectrometry ◽  
Chlorine Isotope ◽  
Site Model ◽  
Tropospheric Measurements ◽  
Single Detector

Abstract. The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (&amp;varepsilon;app) for mid- and high-latitude stratospheric samples are (−2.4 ± 0.5) and (−2.3 ± 0.4)‰ for CFC-11, (−12.2 ± 1.6) and (−6.8 ± 0.8)‰ for CFC-12 and (−3.5 ± 1.5) and (−3.3 ± 1.2)‰ for CFC-113, respectively. Assuming a constant source isotope composition, we estimate the expected trends in the tropospheric isotope signature of these gases due to their stratospheric 37Cl enrichment and stratosphere–troposphere exchange. We compare these model results to the long-term δ(37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978–2010) and tropospheric firn air samples from Greenland (NEEM site) and Antarctica (Fletcher Promontory site). Model trends agree with tropospheric measurements within analytical uncertainties. From 1970 to the present-day, we find no evidence for variations in chlorine isotope ratios associated with changes in CFC manufacturing processes. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes, using a single-detector gas chromatography-mass spectrometry system.

scholarly journals Spatio-temporal stable isotope variation of a benthic primary consumer in a simple food web in a strongly acidic lake

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7890 ◽  
Author(s):  
Hideyuki Doi ◽  
Eisuke Kikuchi ◽  
Shigeto Takagi ◽  
Shuichi Shikano
Keyword(s):  
Stable Isotope ◽  
Temporal Variation ◽  
Food Web ◽  
Isotope Composition ◽  
Isotope Ratios ◽  
Stable Isotope Composition ◽  
Nitrogen Stable Isotope ◽  
Chironomid Larvae ◽  
Carbon And Nitrogen ◽  
Spatio Temporal

Analysis of aquatic food webs is typically undertaken using carbon and nitrogen stable isotope composition of consumer and producer species. However, the trophic consequences of spatio-temporal variation in the isotope composition of consumers have not been well evaluated. Lake Katanuma, Japan, is highly acidic and has only one dominant species of benthic alga and one planktonic microalga, making it a prime system for studying trophic relationships between primary consumers and producers. In this simple lake food web, we conducted a field survey to evaluate spatial and temporal variation in the carbon and nitrogen stable isotope composition of a chironomid larvae in association with a single benthic and planktonic alga. We found a significant correlation between carbon stable isotope ratios of the chironomid larvae and the benthic diatom species in the lake. Thus, chironomid larvae may represent a reliable isotopic baseline for estimating isotope values in benthic diatoms. However, although the correlation held in shallow water, at four m depths, there was no significant relationship between the isotope ratios of chironomids and benthic diatoms, probably because deep-water larvae spend part of their life cycle migrating from the lake shore to deeper water. The differing isotope ratios of deeper chironomid tissues likely reflect the feeding history of individuals during this migration.

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