124 D64. Advances in Stable Isotope Geochemistry–Applications to Earth Science Systems

Monday, 5 November 2018
1:30 PM - 5:30 PM
Room 135

PALEOPROXY FOR VAPOR PRESSURE DEFICIT (VPD) FROM FOSSIL CELLULOSE AND PEDOGENIC CARBONATE

Paper number: 124-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Stable 13C and 18O isotope ratios in modern cellulose and pedogenic carbonate are variable (± 4-10 ‰), and yet are surprisingly highly correlated with each other. This correlation may be due to fractionation, mainly by rubisco, but also by leaf conductance, of light isotopologues of carbonyl, incorporated into plant tissue (for cellulose), and then by decay with little fractionation into soil CO2 (for carbonate). Our compilation of data from around the world shows that the slope of the least squares regression of 13C and 18O isotope ratios (S) at each site is correlated with vapor pressure deficit (VPD), throughout the growing season in the case of cellulose (VPD=0.2721∙S+0.3028; r2=0.69; n=14; s.e= ± 0.13 kPa; P < 0.001), and at the end of the growing season in the case of pedogenic carbonate (VPD=0.6609∙S+0.1944; r2=0.67; n=9; ; s.e. = ±; 0.12 kPa; P < 0.007). Thus limited atmospheric and soil water enhances the efficiency of discrimination for light isotopologues of carbonyl by rubisco, and conversely abundant soil and atmospheric water dilutes isotopic discrimination by rubisco. Our new proxy for VPD can be used to estimate vapor pressure deficit of 0.43 kPa ±0.19 kPa for cellulose of Eocene Metasequoia from Axel Heiberg Island, and 0.61 kPa ±0.14 kPa for Eocene pedogenic carbonate from Wyoming. Both estimates are in good agreement with other proxies for these sites.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-317539

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.