Seasonal Variation of Oxygen Isotopic Composition of Firn Cores in the Antarctic Ice Sheet

We have investigated two 30 m cores at two different spots in the most heavy snow-accumulation regions on Mizuho Plateau, East Antarctica. Marked seasonal variations periodically appear in oxygen isotope records of the cores. We analyzed one core with no trace of snow melting and found it had a complete record showing a yearly change of annual net snow accumulations from 1920 through 1980. The analysis shows that a yearly variation of annual net accumulation (N.A.) has some relations with that of the annual maximum value (δmax) of δ18O and that of the annual amplitude (Δδ) of the δ18O-change in an annual snow layer. Power spectral analyses with respect to the variation of N.A., δmax and Δδ also indicate that there is commonly a predominant periodicity of about five years.

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Changes of Ionic and Oxygen Isotopic Composition of the Snowpack at the Glacier Austre Okstindbreen, Norway, 1995

Hydrology Research ◽

10.2166/nh.1998.0001 ◽

1998 ◽

Vol 29 (1) ◽

pp. 1-20 ◽

Cited By ~ 20

Author(s):

Peter Raben ◽

Wilfred H. Theakstone

Keyword(s):

Isotopic Composition ◽

Sea Level ◽

Oxygen Isotopes ◽

Oxygen Isotopic Composition ◽

Isotopic Ratios ◽

Vertical Variations ◽

Oxygen Isotopic ◽

The Difference ◽

Liquid Precipitation ◽

Different Altitudes

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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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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