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In light of recent studies that show oxygen isotope fractionation in carbonate minerals to be a function of HCO3 2-; and CO3 2- concentrations, the oxygen isotope fractionation and exchange between water and components of the carbonic acid system (HCO3 2-, CO3 2-, and CO2(aq)) were investigated at 15, 25, and 40 (degrees)C. To investigate oxygen isotope exchange between HCO3 2-, CO3 -2, and H2O, NaHCO3 solutions were prepared and the pH was adjusted over a range of 2 to 12 by the addition of small amounts of HCl or NaOH. After thermal, chemical, and isotopic equilibrium was attained, BaCl2 was added to the NaHCO3 solutions. This resulted in immediate BaCO3 precipitation; thus, recording the isotopic composition of the dissolved inorganic carbon. Data from experiments at 15, 25, and 40 (degrees)C (1 atm) show that the oxygen isotope fractionation between HCO3 2-; and H2O as a function of temperature is governed by the equation: 1000 ;HCO3--H2O = 2.66 + 0.05(106T-2) + 1.18 + 0.52. where is the fractionation factor and T is in kelvins. The temperature dependence of oxygen isotope fractionation between CO32 and H2O is 1000 CO32--H2O = 2.28 + 0.03(106T-2) - 1.50 + 0.29. The oxygen isotope fractionation between CO2(aq) and H2O was investigated by acid stripping CO2(aq) from low pH solutions; these data yield the following equation: 1000 CO2(aq)-H2O = 2.52 + 0.03(106T-2) + 12.12 + 0.33. The kinetics of oxygen isotope exchange were also investigated. The half-times for exchange between HCO3- and H2O were 3.6, 1.4, and 0.25 h at 15, 25, and 40 (degrees)C, respectively. The half-times for exchange between CO2 and H2O were 1200, 170, and 41 h at 15, 25, and 40 (degrees) C, respectively. These results show that the 18O of the total dissolved inorganic carbon species can vary as much as 17 at a constant temperature. This could result in temperature independent variations in the 18O of precipitated carbonate minerals, especially in systems that are not chemically buffered.

Thesis (doctoral)--Faculté des sciences de Paris, (197-?). / Includes bibliographical references (leaves [43]-[46]).

<p> Fractionations of C^13/C^12, O^18/O^16 ratios and Mg between coexisting dolomite and calcite have been determined from rocks of a variety of metamorphic grades in Vermont and the Grenville of Ontario. Working criteria for equilibrium are established. Temperature dependent fractionation expressions are derived (1) for O^18 and C^13 from the C-and O-isotope fractionations concordant with the Mg-calcite solvus thermometer, for T = 130° to 550°C, using natural dolomite-calcite assemblages; (2) for C^13 from hydrothermal partial exchange experiments. Problems with partial exchange reactions are discussed. A thermodynamic analysis of the solvus relations shows that spinodal decomposition probably is important in high Mg-calcites. Quench phenomena in high grade assemblages are complex. The quench temperature may be much lower than the maximum temperature attained. The sizes of some equilibrium systems are delineated.</p> / Thesis / Doctor of Philosophy (PhD)

Xenoliths are pieces from the surrounding bedrock, brought to the surface of the earth by host magma. On Gran Canaria, the largest island in the Canary Islands archipelago, strange xenoliths have been found. They are light in color, porous and very different from the basaltic magma carrying them. By studying petrological features and oxygen isotope content of the xenoliths, the focus of this report will be to investigate their origin. The minerals and texture of 14 samples were studied in thin section, and the δ18O–value was determined for 17 samples. The mineralogical composition of xenolith glass was examined by EPMa. The results show that the xenoliths are rich in silica rich glass, quartz and feldspars, but also have high calcium content. 9 of 14 xenoliths have textures and δ18O–values from 8.1 ‰ to 16.77 ‰, similar to sedimentary rocks. The remaining xenoliths are metamorphosed and exhibit altered phenocrysts, indicating they have been melted and recrystallized. The latter group also has extremely low δ18O–value, which could be explained by the effects of hydrothermal processes. Most likely all the xenoliths originate from the prevolcanic sedimentary deposits beneath Gran Canaria.

A partir de registros de dois testemunhos, KF-12 localizado na Bacia de Campos e KF-18 na Bacia de Santos, ambos na margem continental sudeste brasileira, realizou-se a caracterização do Último Interglacial s.l., de 60 a 130 ka atrás. Primeiramente, estabeleceu-se um Modelo de Idade para o KF-12 tendo como referência a curva do KF-18 que já possuía uma boa cronologia. Com a curva do plexo Menardii, determinou-se as biozonas de Ericson e Wollin (1968) e constatou-se a diferença existente entre os limites da Zona X e do estágio isotópico marinho 5. Os limites inferidos para a biozona X foram 135,6 ka AP (limite inferior), e 82,3 ka AP (limite superior) para o testemunho KF-18 e; para o KF-12, 133,5 ka AP (limite inferior) a 88,4 ka AP (limite superior). O estágio isotópico marinho (MIS) 5, na região de estudo, compreende o intervalo entre 129,5 e 71,1 ka AP, em ambos os testemunhos. Também foram utilizados outros dados, tais como, razão isotópica em foraminífero planctônico, fauna, teor de carbonato, razão Ti/Ca e Fe/Ca através dos quais pôde-se estimar paleotemperaturas da superfície do mar, aporte de material terrígeno de acordo com as condições úmidas/seca da região de estudo durante o intervalo de interesse. Por fim, verificou-se que tanto os dados isotópicos de oxigênio (&#948;18O) do testemunho de gelo da Groenlândia (NGRIP) quanto os da razão de deutério da Antártica variaram de forma semelhante aos &#948;18O de foraminíferos bentônicos do KF-12 e KF-18, confirmando o sincronismo de tais registros. / The Last Interglacial Cycle s.l. (between 60 and 130 ky ago) was characterized through registers of two different cores in the Brazilian continental shelf, KF-12, located in Campos Basin and KF-18, located in Santos Basin. First an \"age model\" was established for KF-12, from the KF-18 curve that already had a good cronology. Using Menardii group curve, the biozones from Ericson e Wollin (1968) were established and the difference between the X Zone and the marine isotope stage 5 edges was noticed. The inferred limits for X biozone were 35,6 ky BP (inferior limit) and 82,3 ky BP (superior limit) for KF-18 core and 133,5 and 88,4 ky BP for KF-12 core. In both cores the marine isotope stage (MIS) 5 was between 129,5 and 71,1 ky BP. Other data were also used in the study, such as isotope ratio in planktonic foraminifera, fauna, carbonate content, Ti/Ca and Fe/Ca ratios whereby humidity/dry conditions and continental runoff were inferred. Lastly, the study showed that both the oxygen isotope data from Greenland ice core (NGRIP) and the Antarctic deuterium ratio ranged in a similar way of the &#948;18O benthonic foraminifera from KF-12 and KF-18, confirming the data synchronism.

A partir de registros de dois testemunhos, KF-12 localizado na Bacia de Campos e KF-18 na Bacia de Santos, ambos na margem continental sudeste brasileira, realizou-se a caracterização do Último Interglacial s.l., de 60 a 130 ka atrás. Primeiramente, estabeleceu-se um Modelo de Idade para o KF-12 tendo como referência a curva do KF-18 que já possuía uma boa cronologia. Com a curva do plexo Menardii, determinou-se as biozonas de Ericson e Wollin (1968) e constatou-se a diferença existente entre os limites da Zona X e do estágio isotópico marinho 5. Os limites inferidos para a biozona X foram 135,6 ka AP (limite inferior), e 82,3 ka AP (limite superior) para o testemunho KF-18 e; para o KF-12, 133,5 ka AP (limite inferior) a 88,4 ka AP (limite superior). O estágio isotópico marinho (MIS) 5, na região de estudo, compreende o intervalo entre 129,5 e 71,1 ka AP, em ambos os testemunhos. Também foram utilizados outros dados, tais como, razão isotópica em foraminífero planctônico, fauna, teor de carbonato, razão Ti/Ca e Fe/Ca através dos quais pôde-se estimar paleotemperaturas da superfície do mar, aporte de material terrígeno de acordo com as condições úmidas/seca da região de estudo durante o intervalo de interesse. Por fim, verificou-se que tanto os dados isotópicos de oxigênio (&#948;18O) do testemunho de gelo da Groenlândia (NGRIP) quanto os da razão de deutério da Antártica variaram de forma semelhante aos &#948;18O de foraminíferos bentônicos do KF-12 e KF-18, confirmando o sincronismo de tais registros. / The Last Interglacial Cycle s.l. (between 60 and 130 ky ago) was characterized through registers of two different cores in the Brazilian continental shelf, KF-12, located in Campos Basin and KF-18, located in Santos Basin. First an \"age model\" was established for KF-12, from the KF-18 curve that already had a good cronology. Using Menardii group curve, the biozones from Ericson e Wollin (1968) were established and the difference between the X Zone and the marine isotope stage 5 edges was noticed. The inferred limits for X biozone were 35,6 ky BP (inferior limit) and 82,3 ky BP (superior limit) for KF-18 core and 133,5 and 88,4 ky BP for KF-12 core. In both cores the marine isotope stage (MIS) 5 was between 129,5 and 71,1 ky BP. Other data were also used in the study, such as isotope ratio in planktonic foraminifera, fauna, carbonate content, Ti/Ca and Fe/Ca ratios whereby humidity/dry conditions and continental runoff were inferred. Lastly, the study showed that both the oxygen isotope data from Greenland ice core (NGRIP) and the Antarctic deuterium ratio ranged in a similar way of the &#948;18O benthonic foraminifera from KF-12 and KF-18, confirming the data synchronism.

Abstract In this study, we have analyzed systematically the oxygen isotopic compositions of South China Sea (SCS) and Luzon Strait (LS) seawater so that a comprehensive interpretation of their temporary and spatial variability can be delineated. The oxygen isotopic compositions of the samples collected in the two areas were determined using the Epstein-Mayeda technique, and the overall precision of the d18OSMOW measurements is +0.1 ?. Our data suggest that LS seawater is a mixture of SCS and Kuroshio waters. The precipitation (1.5 mm) on SCS in April 1998 (during ORI517 cruise) is much less than that (169.5 mm) in April 1999 (during ORI546 cruise). As LS and SCS waters are concerned, the profiles of d18OSMOW generally share the same trend as those of salinity. The d18OSMOW values of the SCS surface water decrease toward the south, while those of the LS surface water decrease toward the west. These suggest that the effect of the Kuroshio water decreases are it moves from northeast toward southwest after its intrusion through LS. The salinity of Kuroshio water reaches the maximum at 34.92 with the corresponding d18OSMOW value of 0.42 ?, whereas the salinity of the representative SCS surface water is 33.34 and the corresponding d18OSMOW is -0.25 ?. As these two data were selected as end members, the estimated proportion of the intruding Kuroshio water in the composition of LS water could be high up to 80 % at 121.5o E. The plot of d18OSMOW versus salinity for cruises OR517 and 546 shows a difference between the slopes of the two regression lines, indicating the effect of variability in precipitation and the depth of the mixed layer. The average d18OSMOW value for surface water decreases toward the west as the water moves from Western Philippine Sea (WPS) to LS and SCS. The average d18OSMOW values for the surface, subsurface, intermediate, and deep waters are listed in the corresponding order in parentheses preceded by the studied area as follows: WPS (0.29 ?, 0.25 ?, -0.06 ?, -0.10 ?); LS (0.15 ?, 0.17 ?, -0.02 ?, -0.08 ?); SCS (-0.03 ?, 0.18 ?, -0.05 ?, -0.08 ?).

Thesis (Ph. D.)--University of Chicago, Dept. of Geophysical Sciences, December 2000. / Includes bibliographical references. Also available on the Internet.

Isotopic investigations of speleothem CR1 from Cristal Cave in southeastern Brazil have established a high-resolution record of climate change extending 4,100 years prior to sample collection in 2007. A total of 14 subsamples were collected from CR1 for U/Th age determination. ICP-MS analysis yielded very precise ages with analytical errors (2σ) averaging ± 13 years. An initial growth rate of .062 mm y-1 for the first 2860 years is followed by a rate of .08 mm y-1 for the remaining growth period allowing for sampling of δ18O at sub-decadal resolution. Stable isotope analyses show a large range of δ18O values between -7.5 ‰ to -4 ‰. The data show a trend of steadily decreasing values over the past 4,000 y BP. The exception to this trend is the last 150 years BP when some of the least negative and most variable values for the record are observed. Variations in speleothem δ18O in southern Brazil have been shown to reflect changes in rainfall δ18O, which in turn indicate changes in rainfall source or rainfall amount (Cruz et al., 2006). In Southeastern Brazil, δ18O is controlled mainly by moisture source location, in particular South American monsoonal versus extratropical sources (Cruz et al., 2005). The relative contribution of monsoonal and extratropical moisture help to define the δ18O of regional precipitation via the mean location and southward extent of Hadley cell convective activity associated with the South American summer monsoon (Cruz et al., 2005). For example, decreases in precipitation δ18O are often interpreted as a decreased contribution of winter versus summer precipitation (Cruz et al., 2005). Assuming that the modern (observed) relationship between the seasonality and moisture source location effect occurring in southeastern Brazil have functioned for the past ~ 4,100 years, trends of more negative values towards modern day are likely due to increased summer precipitation and/or an overall increase in total yearly precipitation. The more enriched values of the past 100 years suggest a recent decrease in summer and/or total rainfall.