Sulfur and oxygen isotopic composition of sulfates at two saline sites in southern Alberta

1993 ◽  
Vol 73 (4) ◽  
pp. 633-637 ◽  
Author(s):  
J. J. Miller ◽  
G. J. Beke ◽  
S. Pawluk ◽  
H. R. Krouse

Possible sources of SO4 in soil, drift and bedrock at two saline sites in southern Alberta were investigated using sulfur and oxygen isotope analyses. Slight differences (0.6–5.2 per mil) between δ34S values of SO4 and insoluble S in the geologic material were attributed to kinetic fractionation during oxidation of organic S. Negative δ18O values of SO4 in the shallow (<6 m) bedrock, drift and soil reflected oxidation of reduced S. In contrast, positive δ18O values in the deep (>6 m) bedrock indicated sulfate reduction. The exact source of SO4 could not be determined in this preliminary study. The isotope approach, however, shows promise and warrants more detailed study. Key words: Salinization, sulfates, sulfur isotopes, oxygen isotopes

1998 ◽  
Vol 29 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Peter Raben ◽  
Wilfred H. Theakstone

Marked vertical variations of ions and oxygen isotopes were present in the snowpack at the glacier Austre Okstindbreen during the pre-melting phase in 1995 at sites between 825 m and 1,470 m above sea level. As the first meltwater percolated from the top of the pack, ions were moved to a greater depth, but the isotopic composition remained relatively unchanged. Ions continued to move downwards through the pack during the melting phase, even when there was little surface melting and no addition of liquid precipitation. The at-a-depth correlation between ionic concentrations and isotopic ratios, strong in the pre-melting phase, weakened during melting. In August, concentrations of Na+ and Mg2+ ions in the residual pack were low and vertical variations were slight; 18O enrichment had occurred. The difference of the time at which melting of the snowpack starts at different altitudes influences the input of ions and isotopes to the underlying glacier.


Author(s):  
Gary S Dwyer ◽  
Mark A Chandler

Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period, ca 3.3–3.0 Ma. Results indicate that, following a low stand of approximately 65 m below present at marine isotope stage (MIS) M2 ( ca 3.3 Ma), sea level generally fluctuated by 20–30 m above and below a mean value similar to present-day sea level. In addition to the low-stand event at MIS M2, significant low stands occurred at MIS KM2 (−40 m), G22 (−40 m) and G16 (−60 m). Six high stands of +10 m or more above present day were also observed; four events (+10, +25,+15 and +30 m) from MIS M1 to KM3, a high stand of +15 m at MIS K1, and a high stand of +25 m at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice.


2021 ◽  
Author(s):  
Bruk Lemma ◽  
Lucas Bittner ◽  
Bruno Glaser ◽  
Seifu Kebede ◽  
Sileshi Nemomissa ◽  
...  

AbstractThe hydrogen isotopic composition of leaf wax–derived n-alkane (δ2Hn-alkane) and oxygen isotopic composition of hemicellulose–derived sugar (δ18Osugar) biomarkers are valuable proxies for paleoclimate reconstructions. Here, we present a calibration study along the Bale Mountains in Ethiopia to evaluate how accurately and precisely the isotopic composition of precipitation is imprinted in these biomarkers. n-Alkanes and sugars were extracted from the leaf and topsoil samples and compound–specific δ2Hn-alkane and δ18Osugar values were measured using a gas chromatograph–thermal conversion–isotope ratio mass spectrometer (GC–TC–IRMS). The weighted mean δ2Hn-alkane and δ18Osugar values range from − 186 to − 89‰ and from + 27 to + 46‰, respectively. Degradation and root inputs did not appear to alter the isotopic composition of the biomarkers in the soil samples analyzed. Yet, the δ2Hn-alkane values show a statistically significant species dependence and δ18Osugar yielded the same species–dependent trends. The reconstructed leaf water of Erica arborea and Erica trimera is 2H– and 18O–enriched by + 55 ± 5 and + 9 ± 1‰, respectively, compared to precipitation. By contrast, Festuca abyssinica reveals the most negative δ2Hn-alkane and least positive δ18Osugar values. This can be attributed to “signal–dampening” caused by basal grass leaf growth. The intermediate values for Alchemilla haumannii and Helichrysum splendidum can be likely explained with plant physiological differences or microclimatic conditions affecting relative humidity (RH) and thus RH–dependent leaf water isotope enrichment. While the actual RH values range from 69 to 82% (x̄ = 80 ± 3.4%), the reconstructed RH values based on a recently suggested coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach yielded a mean of 78 ± 21%. Our findings corroborate (i) that vegetation changes, particularly in terms of grass versus non–grassy vegetation, need to be considered in paleoclimate studies based on δ2Hn-alkane and δ18Osugar records and (ii) that the coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach holds great potential for deriving additional paleoclimatic information compared to single isotope approaches.


2012 ◽  
Vol 18 ◽  
pp. 167-194 ◽  
Author(s):  
Benjamin H. Passey

Carbon isotopes in Neogene-age fossil teeth and paleosol carbonates are commonly interpreted in the context of past distributions of C3 and C4 vegetation. These two plant types have very different distributions in relation to climate and ecology, and provide a robust basis for reconstructing terrestrial paleoclimates and paleoenvironments during the Neogene. Carbon isotopes in pre-Neogene fossil teeth are usually interpreted in the context of changes in the δ13C value of atmospheric CO2, and variable climate-dependent carbon-isotope discrimination in C3 plants. Carbon isotopes in pre-Neogene soil carbonates can be used to estimate past levels of atmospheric CO2. Oxygen isotopes in fossil teeth and paleosol carbonates primarily are influenced by the oxygen isotopic compositions of ancient rainfall and surface waters. The oxygen isotopic composition of rainfall is has a complex, but tractable, relationship with climate, and variably relates to temperature, elevation, precipitation amount, and other factors. Mammal species that rely on moisture in dietary plant tissues to satisfy their water requirements (rather than surface drinking water) may have oxygen isotopic compositions that track aridity. Thus, oxygen isotopes of fossil mammals can place broad constraints on paleoaridity. Carbonate clumped isotope thermometry allows for reconstruction of soil temperatures at the time of pedogenic carbonate mineralization. The method is unique because it is the only thermodynamically based isotopic paleothermometer that does not require assumptions about the isotopic composition of the fluid in which the archive mineral formed. Soil temperature reflects a complex interplay of air temperature, solar radiative heating, latent heat effects, soil thermal diffusivity, and seasonal variations of these parameters. Because plants and most animals live in and/or near the soil, soil temperature is an important aspect of terrestrial (paleo)climate.


2015 ◽  
Vol 68 ◽  
pp. 164-170 ◽  
Author(s):  
S.V. Vysotskiy ◽  
V.P. Nechaev ◽  
A.Yu. Kissin ◽  
V.V. Yakovenko ◽  
A.V. Ignat'ev ◽  
...  

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