The Dimensions of Oxygen Isotopic Equilibrium Attainment during Prograde Metamorphism

1967 ◽  
Vol 75 (3) ◽  
pp. 323-332 ◽  
Author(s):  
A. T. Anderson
Keyword(s):  
Prograde Metamorphism ◽  
Isotopic Equilibrium ◽  
Oxygen Isotopic

scholarly journals Potential of Stable Carbon and Oxygen Isotope Variations of Speleothems from Andaman Islands, India, for Paleomonsoon Reconstruction

2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Amzad H. Laskar ◽  
S. Raghav ◽  
M. G. Yadava ◽  
R. A. Jani ◽  
A. C. Narayana ◽  
...  
Keyword(s):  
Monsoon Rainfall ◽  
Boreal Summer ◽  
Stable Carbon ◽  
The South ◽  
Isotopic Equilibrium ◽  
The Past ◽  
Carbon And Oxygen Isotope ◽  
Show Evidence ◽  
Oxygen Isotopic ◽  
India Receive

The Indian monsoon activity, coinciding with the Inter-Tropical Convective Zone (ITCZ), progresses from the southern Indian Ocean during the boreal summer and withdraws towards the south in winter. Islands situated to the south of India receive, therefore, the first and last showers of the monsoon; speleothems in such islands have not yet been explored for their potential to reconstruct past monsoon rainfall. Here, we present the first measurements of stable carbon and oxygen isotopic compositions (δ13C and δ18O) of a stalagmite collected from the Baratang Island of Andamans, along with new data on δ18O of modern monsoon precipitation (May to July 2010). The aim was to detect (i) whether these samples are amenable to dating using 14C, (ii) whether their oxygen isotopes indicate precipitation under isotopic equilibrium, and (iii) if (i) and (ii) above are true, can we reconstruct monsoon activity during the past few millennia? Our results indicate that while δ18O of speleothem does show evidence for precipitation under isotopic equilibrium; dating by 14C shows inversions due to varying contributions from dead carbon. The present work highlights the problems and prospects of speleothem paleomonsoon research in these islands.

Chemical and oxygen isotopic properties of ordinary chondrites (H5, L6) from Oman: Signs of isotopic equilibrium during thermal metamorphism

2017 ◽  
Vol 52 (10) ◽  
pp. 2097-2112 ◽  
Author(s):  
Arshad Ali ◽  
Sobhi J. Nasir ◽  
Iffat Jabeen ◽  
Ahmed Al Rawas ◽  
Neil R. Banerjee ◽  
...  
Keyword(s):  
Ordinary Chondrites ◽  
Isotopic Equilibrium ◽  
Thermal Metamorphism ◽  
Oxygen Isotopic

scholarly journals Cryogenic and non-cryogenic pool calcites indicating permafrost and non-permafrost periods: a case study from the Herbstlabyrinth-Advent Cave system (Germany)

2010 ◽  
Vol 4 (4) ◽  
pp. 501-509 ◽  
Author(s):  
D. K. Richter ◽  
P. Meissner ◽  
A. Immenhauser ◽  
U. Schulte ◽  
I. Dorsten
Keyword(s):  
Isotopic Composition ◽  
Isotope Geochemistry ◽  
Isotope Ratios ◽  
Oxygen Isotopic Composition ◽  
Isotopic Equilibrium ◽  
Climate History ◽  
Cave System ◽  
Air Ventilation ◽  
Oxygen Isotopic

Abstract. Weichselian cryogenic calcites collected in what is referred to as the Rätselhalle of the Herbstlabyrinth-Advent Cave system are structurally classified as rhombohedral crystals and spherulitic aggregates. The carbon and oxygen isotopic composition of these precipitates (δ13C = +0.6 to −7.3‰ δ18O = −6.9 to −18.0‰) corresponds to those of known slowly precipitated cryogenic cave calcites under conditions of isotopic equilibrium between water and ice of Central European caves. The carbon and oxygen isotopic composition varies between different caves which is attributed to the effects of cave air ventilation before the freezing started. By petrographic and geochemical comparisons of Weichselian cryogenic calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic calcites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the composition of interglacial speleothems (stalagmites, etc.), isotope ratios of Weichselian non-cryogenic pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend towards low δ18O values with higher carbon isotope ratios reflecting slow freezing of the precipitating solution. In essence, the isotope geochemistry of the Weichselian calcites reflects the climate history changing from overall initial permafrost conditions to permafrost-free and subsequently to renewed permafrost conditions. Judging from the data compiled here, the last permafrost stage in the Rätselhalle is followed by a warm period (interstadial and/or Holocene). During this warmer period, the cave ice melted and cryogenic and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively.

scholarly journals Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium

2019 ◽  
Author(s):  
Caroline Thaler ◽  
Amandine Katz ◽  
Magali Bonifacie ◽  
Bénédicte Ménez ◽  
Magali Ader
Keyword(s):  
Oxygen Isotope ◽  
Isotope Composition ◽  
Isotopic Equilibrium ◽  
Oxygen Isotopic ◽  
Vital Effects ◽  
Biogenic Carbonates ◽  
Clumped Isotope ◽  
Interstitial Waters ◽  
Isotopic Disequilibrium ◽  
Paleoenvironmental Reconstructions

Abstract. Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate crystallization occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates, that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water-carbonate δ18O fractionation dependence to temperature at equilibrium can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.

scholarly journals Assessing the relationship between the <i>δ</i><sup>18</sup>O signatures of siliceous sponge spicules and water in a~tropical lacustrine environment (Minas Gerais, Brazil)

2013 ◽  
Vol 10 (8) ◽  
pp. 12887-12918 ◽  
Author(s):  
M. C. Matteuzzo ◽  
A. Alexandre ◽  
A. F. D. C. Varajão ◽  
C. Volkmer-Ribeiro ◽  
A. C. S. Almeida ◽  
...  
Keyword(s):  
Water Temperature ◽  
Pond Water ◽  
Minas Gerais ◽  
Positive Temperature ◽  
Freshwater Species ◽  
Siliceous Sponge ◽  
Isotopic Equilibrium ◽  
Oxygen Isotopic ◽  
Sponge Spicules ◽  
Siliceous Spicules

Abstract. Siliceous sponge spicules constitute an important siliceous component of lacustrine sediments, together with widespread diatom frustules. In contrast to diatom frustules, siliceous spicules are formed in sponges in an enzymatic way. Previous attempts to use their oxygen isotopic signature (δ18Osilica) as a paleoenvironmental proxy have led to contradictory conclusions. These attempts demonstrated the need to further assess whether sponges form their silica in oxygen isotopic equilibrium with water. For this reason, we measured the δ18O signature of sponge spicules from a single freshwater species (Metania spinata) grown on natural and artificial supports over nine months in a small Brazilian pond (Lagoa Verde, northwestern Minas Gerais). The δ18Osilica values were obtained using the infrared (IR) laser-heating fluorination technique following a controlled isotopic exchange (CIE). The δ18O values (δ18Owater) and temperature of the pond water were periodically measured and reconstructed over the course of the sponge growth. Assuming that silica may form continuously in the spicules, temperature and δ18Owater values over the months of growth were weighted using a sponge growth coefficient previously established for Metania spinata. The δ18Osilica values of sponges grown simultaneously and on similar substrates were scattered. No relationships were observed between the Δ18Osilica-water and water temperature when the reconstructed values were considered. Conversely, a positive correlation was obtained, with a coefficient of 0.3‰ °C–1 (R2 = 0.63), when δ18Owater values and water temperature at the time of sample collection were considered. Such a positive temperature coefficient clearly indicates that the freshwater sponge Metania spinata does not form its siliceous spicules in oxygen isotopic equilibrium with the pond water. Instead, one or several biologically controlled kinetic fractionation mechanisms may be in play during the various steps of silica formation. Our results suggest that the latest precipitation gives its δ18O imprint to the entire spicules assemblage. The amplitude of the apparent fractionations increases with temperature, but other controlling parameters, such as dissolved Si concentration and nutrient availability, co-varying with temperature may intervene. These results prevent the use of δ18Osilica values from the spongillites of northwestern Minas Gerais as a direct proxy for past δ18Owater and/or temperature changes.

Late Pleistocene Paleoclimates of North America as Inferred from Stable Isotope Studies of Speleothems

1978 ◽  
Vol 9 (1) ◽  
pp. 54-70 ◽  
Author(s):  
Russell S. Harmon ◽  
Peter Thompson ◽  
Henry P. Schwarcz ◽  
Derek C. Ford
Keyword(s):  
Climate Changes ◽  
Temperature Fluctuations ◽  
Radiometric Dating ◽  
Isotopic Equilibrium ◽  
Climatic Fluctuations ◽  
Cave Deposits ◽  
Oxygen Isotopic ◽  
Isotope Studies ◽  
Temperature Records ◽  
Continental Climate

Some speleothems (CaCO3 cave deposits) can be demonstrated to have been formed in oxygen isotopic equilibrium with their parent seepage waters and thus a record of relative fluctuations in depositional temperature can be obtained from the δ18O variations in successive growth layers of such deposits. These temperature fluctuations reflect variations in the average annual air temperature at the surface above the cave, and therefore permit inference of past continental climate changes. Equilibrium deposits have been obtained from caves in San Luis Potosi, Bermuda, Kentucky, West Virginia, Iowa, and Alberta, ranging in age from 200,000 years BP to the present, as determined by 230Th/234U dating of the speleothems. The δ18O time curves for the six sites show the following synchronous climatic fluctuations: warm periods from 190 to 165 and from 120 to 100 Ka, at 60 and 10 Ka, and cold periods from 95 to 65 and from 55 to 20 Ka. The periods of thermal maxima correspond in time to the interglacial periods of the marine foraminiferal isotopic and faunal temperature records and to periods of high sea stand as observed from radiometric dating of raised coral reefs. Maxima and minima in insolation appear to be synchronous with this record as well.

scholarly journals Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium

2020 ◽  
Vol 17 (7) ◽  
pp. 1731-1744 ◽  
Author(s):  
Caroline Thaler ◽  
Amandine Katz ◽  
Magali Bonifacie ◽  
Bénédicte Ménez ◽  
Magali Ader
Keyword(s):  
Oxygen Isotope ◽  
Isotope Composition ◽  
Carbonate Precipitation ◽  
Isotopic Equilibrium ◽  
Oxygen Isotopic ◽  
Vital Effects ◽  
Biogenic Carbonates ◽  
Clumped Isotope ◽  
Isotopic Disequilibrium ◽  
Paleoenvironmental Reconstructions

Abstract. Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate precipitation occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited, and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water–carbonate δ18O fractionation dependence on temperature at equilibrium, can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.

EFFECT OF PROPYLTHIOURACIL ON THE IODINATION AND MATURATION OF RAT THYROGLOBULIN

1966 ◽  
Vol 53 (2) ◽  
pp. 271-285 ◽  
Author(s):  
Claude Simon ◽  
Marie Roques ◽  
Janine Torresani ◽  
Serge Lissitzky
Keyword(s):  
Single Injection ◽  
Freezing And Thawing ◽  
Isotopic Equilibrium ◽  
Sedimentation Constant

ABSTRACT The effect of propylthiouracil on the maturation of rat thyroglobulin in vivo has been investigated. Newly iodinated thyroglobulin dimer is labile to freezing and thawing. This observation has been used to interpret the findings in the present experiments. From experiments using rats in isotopic equilibrium with 125I, and treated with propylthiouracil or propylthiouracil and tri-iodothyronine and also given a single injection of 131I, the following conclusions were formulated 1) the appearance of iodinated S12 thyroglobulin monomer is due to the dissociation of labile iodinated thyroglobulin dimer and appears more readily if the dimer is poorly iodinated, 2) uniodinated thyroglobulin dimer is the most probable substrate for iodination in vivo, 3) maturation of thyroglobulin dimer (as shown by increasing sedimentation constant from 16—17 to 19) is accompanied by increasing amounts of iodine in the molecule, 4) it is not possible to say at present if iodination and iodothyronine formation is the cause or the consequence of thyroglobulin dimer maturation, 5) propylthiouracil might inhibit thyroglobulin maturation by decreasing iodine organification.

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