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WaxPSM: A Forward Model of Leaf Wax Hydrogen Isotope Ratios to Bridge Proxy and Model Estimates of Past Climate
Author(s) -
Konecky Bronwen,
Dee Sylvia G.,
Noone David C.
Publication year - 2019
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004708
Subject(s) - wax , proxy (statistics) , environmental science , climate change , paleoclimatology , evapotranspiration , climate model , physical geography , precipitation , climatology , atmospheric sciences , geology , chemistry , ecology , geography , mathematics , meteorology , oceanography , statistics , organic chemistry , biology
The D/H ratio of epicuticular plant waxes ( δ D wax ) preserved in sedimentary archives is a powerful tool for paleoclimate reconstruction, but comparisons to other proxy records or to climate model simulations requires a proxy system model (PSM) that accounts for transformations between δ D precip and δ D wax . Here we present a new, publicly available PSM for plant waxes, WaxPSM. WaxPSM predicts δ D wax from observational data or any isotope‐enabled modern, paleo, or future climate model experiment. δ D values of the C 29   n ‐alkane are calculated based on precipitation or soil water δ D and observed apparent fractionation values, adjusted for plant‐type differences. Using WaxPSM, we assess three key uncertainties in δ D wax records: the degree to which variations in δ D may reflect changes in vegetation rather than climate, structural uncertainties that arise from limited water isotopic observations, and the impacts of land cover change on climate reconstructions during the Last Glacial Maximum and the Preindustrial period. Parametric and structural uncertainties can cause δ D wax variations up to 50‰, but in most cases, the differences are ∼10–30‰. The drier subtropics are additionally impacted by the incorrect structural assumption that plants' source water, δ D soil , is isotopically similar to the climate variable of interest, δ D precip . We recommend a coordinated, systematic effort to elevate observational constraints on δ D precip , δ D soil , and the δ D of multiple compound classes, which would dramatically reduce parametric and structural uncertainties and allow further complexity to be built into the model.

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