Effects of aridity and vegetation on plant-wax δD in modern lake sediments

Polissar, P. J.; Freeman, Katherine H.

doi:10.1016/j.gca.2010.06.018

Cited by 166 publications

(126 citation statements)

References 52 publications

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“…Aridity may exert a considerable influence on the apparent fractionation (ε) between plant waxes and meteoric water via evapotranspiration and associated deuterium-enrichment (Polissar and Freeman, 2010;Douglas et al, 2012;Kahmen et al, 2013a, b). It was found that such an effect is less pronounced in lake sediments compared to soils, likely due to the higher potential of lakes to integrate large catchment areas and the small-scale variability of soils related to differences in microclimate and vegetation (Douglas et al, 2012).…”

Section: Other Effects On the Sedimentary δD Wax Signaturementioning

confidence: 99%

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

2018

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Abstract. The Pliocene is regarded as a potential analogue for future climate with conditions generally warmer-thantoday and higher-than-preindustrial atmospheric CO 2 levels. Here we present the first orbitally resolved records of continental hydrology and vegetation changes from West Africa for two Pliocene time intervals (5.0-4.6 Ma, 3.6-3.0 Ma), which we compare with records from the last glacial cycle (Kuechler et al., 2013). Our results indicate that changes in local insolation alone are insufficient to explain the full degree of hydrologic variations. Generally two modes of interacting insolation forcings are observed: during eccentricity maxima, when precession was strong, the West African monsoon was driven by summer insolation; during eccentricity minima, when precession-driven variations in local insolation were minimal, obliquity-driven changes in the summer latitudinal insolation gradient became dominant. This hybrid monsoonal forcing concept explains orbitally controlled tropical climate changes, incorporating the forcing mechanism of latitudinal gradients for the Pliocene, which probably increased in importance during subsequent Northern Hemisphere glaciations.

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Section: Other Effects On the Sedimentary δD Wax Signaturementioning

confidence: 99%

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

2018

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“…Differences in modeled precipitation δ 2 H values are not unexpected; however, mean annual precipitation δ 2 H values are used commonly to model leaf-wax δ 2 H values from plants (19,(33)(34)(35) and sediments (9,36). Often when mean annual precipitation δ 2 H values are used to calculate the apparent fractionation between the δ 2 H values of leaf wax and source waters, the resulting fractionation is smaller than expected (i.e., leaf waxes are more enriched in 2 H than predicted).…”

Section: In Deciduous Species δ 2 H Values Reflect Plant Environment mentioning

confidence: 99%

Leaf-wax n -alkanes record the plant–water environment at leaf flush

Tipple

Berke

Doman

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

173

103

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Leaf-wax n-alkanes 2 H/ 1 H ratios are widely used as a proxy in climate reconstruction. Although the broad nature of the relationship between n-alkanes δ 2 H values and climate is appreciated, the quantitative details of the proxy remain elusive. To examine these details under natural environmental conditions, we studied a riparian broadleaf angiosperm species, Populus angustifolia, growing on water with a constant δ 2 H value and monitored the δ 2 H values of leaf-wax n-alkanes and of stem, leaf, stream, and atmospheric waters throughout the entire growing season. Here we found the δ 2 H values of leaf-wax n-alkanes recorded only a 2-wk period during leaf flush and did not vary for the 19 weeks thereafter when leaves remained active. We found δ 2 H values of leaf-wax n-alkanes of P. angustifolia record conditions earlier in the season rather than fully integrating the entire growing season. Using these data, we modeled precipitation δ 2 H values during the time of wax synthesis. We observed that the isotope ratios of this precipitation generally were 2 H-enriched compared with mean annual precipitation. This model provides a mechanistic basis of the often-observed 2 H-enrichment from the expected fractionation values in studies of broadleaf angiosperm leaf-wax δ 2 H. In addition, these findings may have implications for the spatial and temporal uses of n-alkane δ 2 H values in paleoapplications; when both plant community and growth form are known, this study allows the isolation of the precipitation dynamics of individual periods of the growing season.biomarkers | compound-specific isotope analysis | geographic information system | isoscape | stable isotopes S table isotopes serve as tracers and integrators of both environmental and physiological signals within plant materials. Terrestrial plant leaf waxes (i.e., n-alkanes, n-acids, and others) and their isotope ratios have attracted much interest as a higher plant-specific biomarker for paleoclimate reconstruction (1), because these compounds are easily identified and isolated from a variety of geologic materials and are relatively robust to geologic alteration (2). The environmental information recorded in hydrogen isotope ratios of leaf waxes have become a prevalent proxy to reconstruct ancient climates (3-5), mountain building events (6, 7), and floral transitions (8). However, critical questions related to the interpretation of ancient higher plant biomarkers remain unanswered, especially with respect to the extent of the leaf life cycle recorded by this proxy.Environmental and climate transect studies have shown that δ 2 H values of higher plant n-alkanes and environmental waters are correlated (9, 10), but temporal observations of δ 2 H values of n-alkanes have produced conflicting data on the nature of this relationship (11-15) that require clarification to elucidate how δ 2 H values of ancient n-alkanes can be interpreted. To reconcile these issues and to provide the critical constraints for climate reconstructions using δ 2 H values of n-alkanes, car...

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“…Although propagated uncertainty in « landscape values (SI Appendix) represents a substantial portion of the variability in modern δD rain values across central eastern Africa (approximately 60‰), sedimentary δD 31 values capture space-and time-integrated signals that attenuate variability of individual plants or species (7,31). Thus, uncertainty in « landscape values largely reflects ecosystemscale differences in transpiration and phenology (7), which are at least partially accounted for by « 31/model values, provided living plants are representative of their ancient counterparts.…”

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confidence: 99%

Water, plants, and early human habitats in eastern Africa

Magill

Ashley

Freeman

2012

Proc. Natl. Acad. Sci. U.S.A.

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Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa-Olduvai Gorge. We convert sedimentary leaf-and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water-lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lakewater δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C 4 -dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm·y −1 and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.paleohydrology | plant waxes | carbon isotopes

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Effects of aridity and vegetation on plant-wax δD in modern lake sediments

Cited by 166 publications

References 52 publications

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

Leaf-wax n -alkanes record the plant–water environment at leaf flush

Water, plants, and early human habitats in eastern Africa

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