A record of vapour pressure deficit preserved in wood and soil across biomes

• Published in: Scientific Reports
• Main Authors: Broz, Adrian, Retallack, Gregory J., Maxwell, Toby M., Silva, Lucas C. R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Research 2021
• Subjects: Axel Heiberg Island; Canada; Heiberg; Watkins
• Online Access: https://doi.org/10.1038/s41598-020-80006-9; https://scholarsbank.uoregon.edu/xmlui/handle/1794/27841

12 pages The drying power of air, or vapour pressure deficit (VPD), is an important measurement of potential plant stress and productivity. Estimates of VPD values of the past are integral for understanding the link between rising modern atmospheric carbon dioxide (pCO2) and global water balance. A geological record of VPD is needed for paleoclimate studies of past greenhouse spikes which attempt to constrain future climate, but at present there are few quantitative atmospheric moisture proxies that can be applied to fossil material. Here we show that VPD leaves a permanent record in the slope (S) of least-squares regressions between stable isotope ratios of carbon and oxygen (13C and 18O) found in cellulose and pedogenic carbonate. Using previously published data collected across four continents we show that S can be used to reconstruct VPD within and across biomes. As one application, we used S to estimate VPD of 0.46 kPa ± 0.26 kPa for cellulose preserved tens of millions of years ago—in the Eocene (45 Ma) Metasequoia from Axel Heiberg Island, Canada—and 0.82 kPa ± 0.52 kPa—in the Oligocene (26 Ma) for pedogenic carbonate from Oregon, USA—both of which are consistent with existing records at those locations. Finally, we discuss mechanisms that contribute to the positive correlation observed between VPD and S, which could help reconstruct past climatic conditions and constrain future alterations of global carbon and water cycles resulting from modern climate change. We thank Nathan Sheldon, Ilya Bindeman, James Watkins, Josh Roering, and John Roden for useful discussion, Dan Breecker for isotopic data on modern soil carbonate and Hope Jahren for isotopic data on fossil cellulose. Comments and suggestions from four anonymous reviewers greatly improved this work. We also thank the National Science Foundation (AGS#1602958; Convergence Accelerator #1939511). The publication fees for this article were supported by the University of Oregon Libraries Open Access Article Processing Charge Fund.