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1000
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Abstract/Summary
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The 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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1000
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Hinweis
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DeepGreen-ID: 4551a42a4fe1429c82641f581e3cc259 ; metadata provieded by: DeepGreen (https://www.oa-deepgreen.de/api/v1/), LIVIVO search scope life sciences (http://z3950.zbmed.de:6210/livivo), Crossref Unified Resource API (https://api.crossref.org/swagger-ui/index.html), to.science.api (https://frl.publisso.de/), ZDB JSON-API (beta) (https://zeitschriftendatenbank.de/api/), lobid - Dateninfrastruktur für Bibliotheken (https://lobid.org/resources/search)
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