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The Water Cycle
Published in Aurèle Parriaux, Geology, 2018
To complement the simulations on the current and future climate status, scientists study paleoclimatic data to understand naturally possible variations and correlations between the climate and the dominant factors (Problem 3.3). Drilling into polar ice sheets and analyzing old ice and air bubbles trapped in the ice lets scientists to “go back in time” several hundred thousand years (Fig. 7.7). They analyze greenhouse gases and oxygen isotope 18, which is an indicator of paleotemperatures; when the climate is warm, the air contains more heavy oxygen than it does during a cool period due to isotopic fractionation during evaporation.
17O
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Oxygen (symbol: O) is the eighth element in the periodic table. It is a member of the chalcogen group (group 16) with a 2s22p4 electronic configuration. The outer shell can hold a total of 8 electrons and is incomplete, which explains oxygen’s tendency to react with other elements. Oxygen is the most abundant element in the Earth’s crust, and the second most abundant in the human body (in atomic percent). Oxygen has three stable isotopes: the most abundant 16O (99.757% natural abundance);17O (only 0.038% natural abundance), which is the only oxygen isotope detectable with NMR; and 18O (0.205%). At room temperature and standard pressure, oxygen is a colorless and odorless diatomic gas O2 (dioxygen), which constitutes about 21% of the gas in the Earth’s atmosphere, and is fundamental to sustain life on the planet, as it is essential for respiration of all plants and animals and for most types of combustion. About 2/3 of the human body weight, and 9/10 of water weight is oxygen. Ozone (O3) can also be formed in the atmosphere from electrical discharges or ultraviolet light acting on O2, and is important for preventing harmful ultraviolet rays of the sun from reaching the earth’s surface. However, aerosols in the atmosphere have a detrimental effect on the ozone layer. The oxygen element is very reactive and can combine to form compounds with almost all other known elements, water H2O being the most abundant and vital. Oxygen is the third most abundant element found in the sun, and plays a part in the carbon-nitrogen cycle responsible for stellar energy production. The basic properties of oxygen are summarized in Table 8.1.
Global Climate Change
Published in John C. Ayers, Sustainability, 2017
Each ice layer in the Greenland ice cores gives us information about the climate in Greenland at the time it formed. The age of the layer can be determined by counting layers from the surface downward, or by using radiometric dating. Historical atmospheric temperatures are estimated using oxygen isotopes. Samples of ancient atmosphere trapped as air bubbles can be analyzed to measure the atmospheric concentration of greenhouse gases at the time the snow contained in the layer was deposited.
Origin of carbonate cements and reservoir evolution of tight sandstone in the Upper Triassic Yanchang Formation, Ordos Basin, China
Published in Australian Journal of Earth Sciences, 2019
S. W. Mao, Z. D. Bao, X. X. Wang, Y. S. Gao, J. Song, Z. C. Wang, W. Liu, L. Zhang, M. Y. Wei, Y. F. Bao
Oxygen isotope values are the primary indicator of the evolution of pore fluids (Land, 1992) and can be influenced by many factors including: (1) the oxygen isotope composition and salinity of sedimentary waters, (2) the temperature of precipitation during the sedimentation, (3) diagenetic fluids during the burial process and (4) diagenetic transformation (Liu et al.,2014). Sedimentary waters are commonly enriched in 18O by evaporation and the δ18O value of carbonates is strongly influenced by the temperature of crystallisation (Friedman & O’Neil, 1977; Liu et al., 2014). The theoretical relationship between precipitation temperature and the oxygen isotope composition of carbonates (Figure 17) can be used to calculate the oxygen isotope composition of diagenetic fluids during precipitation of carbonate cements in the Chang 8 Member sandstones.
Land-sea correlations in the Australian region: 460 ka of changes recorded in a deep-sea core offshore Tasmania. Part 1: the pollen record
Published in Australian Journal of Earth Sciences, 2019
P. De Deckker, S. van der Kaars, M. K. Macphail, G. S. Hope
The new age model presented here is slightly different from the one used by Hiramatsu and De Deckker (1997) that employed tie points linked to the chronostratigraphy of Martinson et al. (1987) and a linear interpolation program (Analyseries; Paillard, Labeyrie, & Yiou, 1996). The oxygen isotope data for both planktic and benthic foraminifera are presented in Figure 4. As we used the tie points for the benthic foraminifera and applied these ages for the planktic foraminifera, it is possible to determine that the signals shown by the isotopic composition of the bottom waters are not always in synchrony with those from the surface waters. Of note is that surface waters are more sensitive to temperature changes than is apparent in the global sea level data seen via the δ18O of the benthic foraminifera (Lisiecki & Raymo, 2005), particularly for the start of deglaciations, and especially prominent for the MIS 12 to 11 transition. It is noteworthy that the benthic curve increases before the planktic one at the end of MIS 8, but this is represented by only one measurement (see Figure 4).
Insights into the evolution of the Thomson Orogen from geochronology, geochemistry, and zircon isotopic studies of magmatic rocks
Published in Australian Journal of Earth Sciences, 2018
A. J. Cross, D. J. Purdy, D. C. Champion, D. D. Brown, C. Siégel, R. A. Armstrong
Discussed below are the results of zircon U–Pb, O, and Hf isotopic studies of 13 igneous samples from the Thomson Orogen (seven volcanic and six intrusive rocks). Zircons considered to have formed from mantle-like sources have δ18O values within error of the normal mantle zircon range 5.3 ± 0.6‰ (2σ) (Valley et al., 2005), and positive εHf(t) values. External uncertainties for oxygen isotope values reported have an upper limit of 0.50‰. We therefore classify zircons with δ18O values between 4.2 and 6.4‰ as normal mantle-like zircon. Also discussed are results of whole-rock geochemistry and Sm–Nd isotopic studies. Table 1 shows the details of the samples and Table 2 is the summary of the zircon, U–Pb, δ18O, and initial εHf(t) and whole-rock εNd values for each of the samples. Geochemistry data are included in the Supplementary papers, Table S14.