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We analyzed the deuterium composition of individual plant-waxes in lake sediments from 28 watersheds that span a range of precipitation D/H, vegetation types and climates. The apparent isotopic fractionation (εa) between plant-wax n-alkanes and precipitation differs with watershed ecosystem type and structure, and decreases with increasing regional aridity as measured by enrichment of 2H and 18O associated with evaporation of lake waters. The most negative εa values represent signatures least affected by aridity; these values were −125 ± 5‰ for tropical evergreen and dry forests, −130‰ for a temperate broadleaf forest, −120 ± 9‰ for the high-altitude tropical páramo (herbs, shrubs and grasses), and −98 ± 6‰ for North American montane gymnosperm forests. Minimum εa values reflect ecosystem-dependent differences in leaf water enrichment and soil evaporation. Slopes of lipid/lake water isotopic enrichments differ slightly with ecosystem structure (i.e. open shrublands versus forests) and overall are quite small (slopes = 0–2), indicating low sensitivity of lipid δD variations to aridity compared with coexisting lake waters. This finding provides an approach for reconstructing ancient precipitation signatures based on plant-wax δD measurements and independent proxies for lake water changes with regional aridity. To illustrate this approach, we employ paired plant-wax δD and carbonate-δ18O measurements on lake sediments to estimate the isotopic composition of Miocene precipitation on the Tibetan plateau.
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Plant Wax Isotopic Reconstructions Reveal Thermodynamic Drivers of Hydroclimate Over the Last Two Glacial Cycles at Great Salt Lake and Bear Lake, Utah
Abstract The growth and decay of the Laurentide ice sheet altered the hydrological cycle over southwestern North America. While it is well‐documented that the last glacial was wetter and had isotopically lighter precipitation, much less information is available for prior glacials. Increased proxy coverage is needed to test climate models' ability to reconstruct these changes and to assess their predictive power for water availability in response to future climate change. Here, we present parallel precipitation isotope records spanning the last two glacial cycles from two large, proximal lakes in Utah, USA: Great Salt Lake and Bear Lake. We use plant waxn‐alkane δD as a proxy for precipitation δD (δDprecip) and find coherent glacial‐interglacial fluctuations in δDprecip, with a ∼30‰ D‐depletion during glacial maxima relative to interglacials. We find similar δDprecipvalues between the Holocene and Eemian, but at the lower‐pCO2MIS 7 interglacial, D‐enrichment is only weakly recorded at Great Salt Lake and absent at higher elevation Bear Lake. Comparison to regional proxy archives finds large‐scale coherence in regional hydroclimate change over the last two glacial cycles is best explained by thermodynamic processes, with increased rainout efficiency, isotopic fractionation, and snow in a colder atmosphere. Comparison of proxies to climate model experiments showed models considerably underestimate glacial lowering of precipitation isotopic values, but overestimate inland Rayleigh distillation. New and assembled proxy reconstructions provide greater temporal and spatial coverage as targets for model skill in capturing hydroclimate variations across the past two glacial cycles.
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- PAR ID:
- 10662512
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 41
- Issue:
- 2
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025PA005357
