A microanalytical oxygen isotopic and U-Th geochronologic investigation of rhyolite petrogenesis at the Krafla Central Volcano, Iceland

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.

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ESTIMATION OF EVAPORATION RATE OF SURFACE WATER USING HYDROGEN AND OXYGEN ISOTOPIC RATIOS

International Journal of Geomate ◽

10.21660/2016.26.5295 ◽

2016 ◽

Author(s):

Masahiro Yamashita

Keyword(s):

Surface Water ◽

Evaporation Rate ◽

Isotopic Ratios ◽

Oxygen Isotopic

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COMPOSITIONAL EVOLUTION OF TORFAJÖKULL CENTRAL VOLCANO, ICELAND: PERSPECTIVES FROM THE APATITE RECORD

10.1130/abs/2019ne-328361 ◽

2019 ◽

Author(s):

Mary Elizabeth Connors ◽

◽

Tamara L. Carley ◽

Adrian Fiege

Keyword(s):

Central Volcano ◽

Compositional Evolution

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Segregation and speciation in the Neogene planktonic foraminiferal clade Globoconella

Paleobiology ◽

10.1017/s0094837300021345 ◽

1999 ◽

Vol 25 (3) ◽

pp. 383-395 ◽

Cited By ~ 6

Author(s):

Cynthia E. Schneider ◽

James P. Kennett

Keyword(s):

Morphological Evolution ◽

Evolutionary Divergence ◽

Clinal Variation ◽

Near Surface ◽

Surface Warming ◽

Isotopic Analyses ◽

Oxygen Isotopic ◽

Morphological Differences ◽

Middle Pliocene ◽

Water Depths

The origin of the Neogene planktonic foraminifer Globorotalia (Globoconella) pliozea in the subtropical southwest Pacific has been attributed to its isolation resulting from intensification of the Subtropical Divergence (Tasman Front). Oxygen isotopic analyses suggest that, although the Subtropical Divergence may have played a role, the evolution of Gr. (G.) pliozea was facilitated by depth segregation of Gr. (G.) conomiozea morphotypes (low and high conical) during an interval of near-surface warming and increasing thermal gradient. Oxygen isotopic analyses suggest that low conical morphotypes of Gr. (G.) conomiozea inhabited greater depths than high conical morphotypes. Low conical forms of Gr. (G.) conomiozea are considered ancestral to the low conical species, Gr. (G.) pliozea. Oxygen isotopes indicate that Gr. (G.) pliozea inhabited greater depths than its ancestor, Gr. (G.) conomiozea.These data are consistent with depth-parapatric and depth-allopatric models, but not with a sympatric model of speciation. In the allopatric model, reproduction at different water depths acts as a barrier between morphotypes. In the parapatric model, clinal variation along a depth gradient acts as a barrier between morphotypes living at the limits of the gradient. Depth segregation in both models results in genetic isolation and evolutionary divergence. Our data support a correlation between morphological evolution and habitat changes in the Globoconella clade, implying separation of populations as a driving force for morphological evolution.Ecological segregation of morphotypes and species may be related to morphology (height of the conical angle), based on the data from Gr. (G.) conomiozea and Gr. (G.) pliozea. However, morphological differences alone do not necessarily produce depth differences. Large morphological differences between Gr. (G.) pliozea and closely related Gr. (G.) puncticulata did not result in isotopic and therefore depth differences between these species. These species coexisted at the same water depths for nearly 1 m.y. Thus, it is unlikely that the extinction of Gr. (G.) pliozea in the middle Pliocene resulted from competition with Gr. (G.) puncticulata, as previously suggested.

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Along-rift propagation of Pleistocene-Holocene faults from a central volcano

Journal of Structural Geology ◽

10.1016/j.jsg.2020.104201 ◽

2020 ◽

Vol 141 ◽

pp. 104201

Author(s):

A. Tibaldi ◽

N. Corti ◽

F.L. Bonali ◽

F. Pasquaré Mariotto ◽

E. Russo

Keyword(s):

Central Volcano ◽

Rift Propagation

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Temperature control on high-resolution SIMS oxygen isotopic compositions in Porites coral skeletons

Solid Earth Sciences ◽

10.1016/j.sesci.2021.02.002 ◽

2021 ◽

Author(s):

Jieqiong Zou ◽

Wenfeng Deng ◽

Xuefei Chen ◽

Xi Liu ◽

Yangrui Guo ◽

...

Keyword(s):

High Resolution ◽

Temperature Control ◽

Coral Skeletons ◽

Isotopic Compositions ◽

Porites Coral ◽

Oxygen Isotopic

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Oxygen isotopes in terrestrial gastropod shells track Quaternary climate change in the American Southwest

Quaternary Research ◽

10.1017/qua.2021.18 ◽

2021 ◽

pp. 1-11

Author(s):

Jason A. Rech ◽

Jeffrey S. Pigati ◽

Kathleen B. Springer ◽

Stephanie Bosch ◽

Jeffrey C. Nekola ◽

...

Keyword(s):

Climate Change ◽

Oxygen Isotopic Composition ◽

American Southwest ◽

Quaternary Climate ◽

San Pedro ◽

Spatial Coverage ◽

Oxygen Isotopic ◽

The Last Glacial Maximum ◽

The Last Glacial ◽

Terrestrial Gastropod

Abstract Recent studies have shown the oxygen isotopic composition (δ18O) of modern terrestrial gastropod shells is determined largely by the δ18O of precipitation. This implies that fossil shells could be used to reconstruct the δ18O of paleo-precipitation as long as the isotopic system, including the hydrologic pathways of the local watershed and the gastropod systematics, is well understood. In this study, we measured the δ18O values of 456 individual gastropod shells collected from paleowetland deposits in the San Pedro Valley, Arizona that range in age from ca. 29.1 to 9.8 ka. Isotopic differences of up to 2‰ were identified among the four taxa analyzed (Succineidae, Pupilla hebes, Gastrocopta tappaniana, and Vallonia gracilicosta), with Succineidae shells yielding the highest values and V. gracilicosta shells exhibiting the lowest values. We used these data to construct a composite isotopic record that incorporates these taxonomic offsets, and found shell δ18O values increased by ~4‰ between the last glacial maximum and early Holocene, which is similar to the magnitude, direction, and rate of isotopic change recorded by speleothems in the region. These results suggest the terrestrial gastropods analyzed here may be used as a proxy for past climate in a manner that is complementary to speleothems, but potentially with much greater spatial coverage.

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δ2Hn-alkane and δ18Osugar biomarker proxies from leaves and topsoils of the Bale Mountains, Ethiopia, and implications for paleoclimate reconstructions

Biogeochemistry ◽

10.1007/s10533-021-00773-z ◽

2021 ◽

Author(s):

Bruk Lemma ◽

Lucas Bittner ◽

Bruno Glaser ◽

Seifu Kebede ◽

Sileshi Nemomissa ◽

...

Keyword(s):

Isotopic Composition ◽

Leaf Growth ◽

Thermal Conversion ◽

Oxygen Isotopic Composition ◽

Leaf Water ◽

Isotope Ratio Mass Spectrometer ◽

Oxygen Isotopic ◽

Calibration Study ◽

Microclimatic Conditions ◽

Paleoclimate Reconstructions

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.

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