Paleohydrology of a Canadian Shield lake inferred from 18O in sediment cellulose

1989 ◽  
Vol 26 (9) ◽  
pp. 1850-1859 ◽  
Author(s):  
T. W. D. Edwards ◽  
J. H. McAndrews
Keyword(s):  
Lake Water ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Cellulose Synthesis ◽  
Isotopic Enrichment ◽  
Oxygen And Carbon Isotope ◽  
The Past ◽  
Two Factors ◽  
Isotope Analyses ◽  
Isotope Content

Oxygen- and carbon-isotope analyses on cellulose in the postglacial sediment of Weslemkoon Lake, southern Ontario, show that the cellulose came mainly from aquatic plants or algae, rather than from terrestrial sources. If a wholly aquatic source is assumed, the oxygen-isotope content permits inferences of lake-water δ18O values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis. Chronological control is provided by pollen analysis and six 14C dates. Our reconstruction shows lake-water δ18O fluctuated from about 5‰ lower than present in the early postglacial to 5‰ or more above present values during the mid-postglacial. These broad, secular shifts reflect a combination of fluctuating mean annual δ18O of local precipitation, evaporative isotopic enrichment of surface waters, and snowmelt-bypass effects. The first two factors reflect the changing paleotemperature and paleohydrology, respectively, whereas the third factor is a more speculative interpretation of isotope effects during snowmelt delivery to the lake. The snowmelt-bypass mechanism is supported by parallel changes in the overall abundance and seasonal distribution of precipitation. This effect is probably responsible for pronounced isotopic enrichment of the water throughout the moist climate of the past 6000 years.

scholarly journals Can Adsorption on Graphene be Used for Isotopic Enrichment? A DFT Perspective

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2981 ◽  
Author(s):  
Mateusz Pokora ◽  
Piotr Paneth
Keyword(s):  
Aromatic Compounds ◽  
Model Compound ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Adsorbed Molecule ◽  
Polar Compounds ◽  
Isotopic Enrichment ◽  
Reliable Prediction ◽  
Computational Procedures ◽  
Nonpolar Molecules

We have explored the theoretical applicability of adsorption on graphene for the isotopic enrichment of aromatic compounds. Our results indicate that for nonpolar molecules, like benzene, the model compound used in these studies shows a reasonable isotopic fractionation that is obtained only for the deuterated species. For heavier elements, isotopic enrichment might be possible with more polar compounds, e.g., nitro- or chloro-substituted aromatics. For benzene, it is also not possible to use isotopic fractionation to differentiate between different orientations of the adsorbed molecule over the graphene surface. Our results also allowed for the identification of theory levels and computational procedures that can be used for the reliable prediction of the isotope effects on adsorption on graphene. In particular, the use of partial Hessian is an attractive approach that yields acceptable values at an enormous increase of speed.

scholarly journals Islam dan Budaya Masyarakat Gayo, Provinsi Aceh: Kajian Sejarah dan Sosial

2020 ◽  
Vol 1 (1) ◽  
pp. 1-31 ◽  
Author(s):  
Arfiansyah
Keyword(s):  
Collective Memory ◽  
Historical Analysis ◽  
Community Practice ◽  
Religious Texts ◽  
Post Colonial ◽  
The Past ◽  
Islamic Tradition ◽  
Colonial Time ◽  
Two Factors ◽  
The Impact

This article argues that Gayonese community practice Islam through the culture and less concern with religious texts. Although the wave of islamization since the colonial time and post-independence was high, the process does not succeed in introducing what the local scholars called as Islamic tradition. Such situation forces the following ulama to defend culture by finding justification for every practice instead of abolishing it. There are two factors leading to the situation. First, ulama of colonial and post-colonial time did not succeed in finding what they called as Islamic tradition replacing the existing tradition. second, lacking of regeneration of reformer Ulama that drive the living reformer ulama to support culture by inserting Islamic values and norms into the culture. This effort is crucial as the Gayonese refers more to the culture than the religious texts. This Article historically studies the development of Islam in Gayonese community. It frames its historical analysis from the Dutch colonial period to post independence of Indonesia Republic. It generally observes the impact of islamization in the past to the current situation. This article brings back the fundamental question in socio-anthropological studies about Islam that why do Muslim who refer to same source of text understand and practice Islam in widely various expression. The question is applied to this research exploring the development of Islam in Gayonese community inhabiting Central Aceh and Bener Meriah District. Thus, this research questions how did Islam develop in colonial time and its impact to the local culture? did there a debate about religion and culture take place during the colonial time and post-independence of Indonesia?  How does the past event affect the current practice of Islam in Gayonese community? the questions are explored historically by collecting relevant literatures and collective memory of the local people. The collective memory data were collected from 2015 to 2019

Hydrogen and Oxygen Isotopic Fractionation During Heterotrophic Cellulose Synthesis

1992 ◽  
Vol 43 (1) ◽  
pp. 47-50 ◽  
Author(s):  
YAO-HUA LUO ◽  
LEONEL DA SILVEIRA LOBO STERNBERG
Keyword(s):  
Isotopic Fractionation ◽  
Cellulose Synthesis ◽  
Oxygen Isotopic

scholarly journals Spectra of Southern Radio Sources

1977 ◽  
Vol 74 ◽  
pp. 85-97 ◽  
Author(s):  
J. G. Bolton
Keyword(s):  
Time Scale ◽  
Galactic Plane ◽  
Complete Sample ◽  
High Frequencies ◽  
The Past ◽  
Average Accuracy ◽  
Sky Survey ◽  
Two Factors ◽  
Optical Identifications ◽  
One Year

Surveys of the sky between declinations +25° and −90° at 2700 MHz (11 cm) have been in progress for the past 10 years. Excluding some regions close to the galactic plane the whole sky south of +25° has been surveyed to a flux density limit of 0.6 Jy at 2700 MHz and within this area surveys to limits of 0.35, 0.25 or 0.1 Jy have been made covering 3.5 sr. Flux densities have been measured at 5000 MHz for all sources stronger than 0.35 Jy at 2700 MHz. The source positions have an average accuracy of 10″ arc in both coordinates and the positions have been examined for optical identifications on Palomar, ESO or SRC sky survey plates, which now cover 95% of the area. The first part of this paper concerns the relationships between the spectral indices α(2700 to 5000 MHz) and the identifications of the 2300 sources with galactic latitudes greater than 10°. It is a statistically significant sample, since the sources stronger than 0.35 Jy cover 3.5 sr. It is also a representative sample, since no selection was made on the basis of spectral index or identification. It cannot however be claimed as a complete sample, for two reasons. A substantial fraction of sources found in radio surveys at high frequencies are variable - variations of up to a factor of three can occur on a time scale of a year - thus the various sections of the survey are complete only for the relevant epoch. Many of their optical counterparts are also variables - variations of up to a factor of 100 can occur on a time scale of one year. It is hoped to make some assessment of the effect of these two factors in the next two years, when second-epoch Parkes surveys will begin and SRC Schmidt plates will overlap the Palomar Sky Survey.

Assessment of Changes in Lake Water Chemistry in Sudbury Area Lakes since Preindustrial Times

1992 ◽  
Vol 49 (S1) ◽  
pp. 8-16 ◽  
Author(s):  
Sushil S. Dixit ◽  
Aruna S. Dixit ◽  
John P. Smol
Keyword(s):  
Lake Water ◽  
Acidic Ph ◽  
Prevailing Wind ◽  
Alkaline Ph ◽  
Sediment Samples ◽  
Ion Concentrations ◽  
The Past ◽  
Lake Water Chemistry ◽  
Water Ph ◽  
Inferred Ph

Surface (recent) and bottom (pre-1880s) sediment samples from each of 72 Sudbury area lakes were analyzed for diatom valves and chrysophyte scales, and using these microfossils, we inferred changes in lake water pH, [Al], [Ni], conductance, and [Ca]. The study shows that extensive acidification has occurred in presently acidic (pH < 6.0) Sudbury lakes. Inferred [Al] has also increased in these lakes. The region also contains a few naturally acidic lakes; however, even these lakes have acidified further since the bottom sediments were deposited. Lakes that have current measured pH between 6.0 and 7.0 have either declined or increased in inferred pH in the past, whereas all lakes that are presently alkaline (pH > 7.0) have become more alkaline. The increase in inferred [Ni] in most of the study lakes indicates that Ni inputs are mainly atmospheric. Our data suggest that, in general, ion concentrations have increased in Sudbury lakes. The extent of acidification or alkalification in Sudbury lakes was primarily a function of proximity of the lakes to the smelters, orientation of prevailing wind patterns, and differences in watershed geology.

scholarly journals 2H/1H variation in microbial lipids is controlled by NADPH metabolism

2019 ◽  
Vol 116 (25) ◽  
pp. 12173-12182 ◽  
Author(s):  
Reto S. Wijker ◽  
Alex L. Sessions ◽  
Tobias Fuhrer ◽  
Michelle Phan
Keyword(s):  
Metabolic Flux ◽  
Isotope Effects ◽  
Full Range ◽  
Isotopic Fractionation ◽  
Flux Analysis ◽  
Organic Substrates ◽  
Nadph Metabolism ◽  
Highly Correlated ◽  
Geologic Record ◽  
Ancient Ecosystems

The hydrogen-isotopic compositions (2H/1H ratios) of lipids in microbial heterotrophs are known to vary enormously, by at least 40% (400‰) relative. This is particularly surprising, given that most C-bound H in their lipids appear to derive from the growth medium water, rather than from organic substrates, implying that the isotopic fractionation between lipids and water is itself highly variable. Changes in the lipid/water fractionation are also strongly correlated with the type of energy metabolism operating in the host. Because lipids are well preserved in the geologic record, there is thus significant potential for using lipid 2H/1H ratios to decipher the metabolism of uncultured microorganisms in both modern and ancient ecosystems. But despite over a decade of research, the precise mechanisms underlying this isotopic variability remain unclear. Differences in the kinetic isotope effects (KIEs) accompanying NADP+ reduction by dehydrogenases and transhydrogenases have been hypothesized as a plausible mechanism. However, this relationship has been difficult to prove because multiple oxidoreductases affect the NADPH pool simultaneously. Here, we cultured five diverse aerobic heterotrophs, plus five Escherichia coli mutants, and used metabolic flux analysis to show that 2H/1H fractionations are highly correlated with fluxes through NADP+-reducing and NADPH-balancing reactions. Mass-balance calculations indicate that the full range of 2H/1H variability in the investigated organisms can be quantitatively explained by varying fluxes, i.e., with constant KIEs for each involved oxidoreductase across all species. This proves that lipid 2H/1H ratios of heterotrophic microbes are quantitatively related to central metabolism and provides a foundation for interpreting 2H/1H ratios of environmental lipids and sedimentary hydrocarbons.

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