The role of soil processes in δ18O terrestrial climate proxies. Issue 3 (13th March 2014)

• Record Type: Journal Article
• Authors: Kanner, Lisa C.; Buenning, Nikolaus H.; Stott, Lowell D.; Timmermann, Axel; Noone, David
• Is Part Of: Global biogeochemical cycles. Volume 28:Issue 3(2014:Mar.)
• Page Start: 239
• Page End: 252
• Publication Date: 2014-03-13
• Subjects: Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2013GB004742
• Languages: English
• ISSNs: 0886-6236

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>A paleoclimate interpretation of a terrestrial hydrologic proxy such as the <italic>δ</italic><sup>18</sup>O of tree cellulose or speleothem calcite may be biased or misinterpreted if the isotopic composition of the soil water from which the proxy originated undergoes isotopic exchange or fractionation. In this study, we use a global isotope‐enabled land surface model to investigate how the <italic>δ</italic><sup>18</sup>O of precipitation may be altered in a soil column due to evaporation and vertical moisture transport. In order to assess how precipitation and evaporation contribute to the soil water isotopic variability, we compare seasonal and interannual changes in simulated xylem water <italic>δ</italic><sup>18</sup>O within a control simulation and in a suite of sensitivity experiments where the effects of precipitation <italic>δ</italic><sup>18</sup>O, water vapor <italic>δ</italic><sup>18</sup>O, and soil water evaporation are independently removed. The simulations, carried out for the period 1979 to 2004, reveal that in semiarid regions, such as the southwest United States, the seasonal cycle in xylem water <italic>δ</italic><sup>18</sup>O is strongly affected by evaporative loss during the dry season and evaporation can also constitute as much as 50% of the interannual <italic>δ</italic><sup>18</sup>O variance. Additional simulations, including soil water tagging experiments, indicate that upward fluxes of soil water occur during drier periods. For soil water <italic>δ</italic><sup>18</sup>O profiles that are isotopically more depleted in <sup>18</sup>O at depth, this imparts a low isotopic signature to xylem water <italic>δ</italic><sup>18</sup>O during such dry intervals. Hence, without taking into account vertical moisture transport in the soils, low <italic>δ</italic><sup>18</sup>O years could be misinterpreted as wet conditions (due to decreased evaporative enrichment) when instead drier conditions are equally as likely.</p> </abstract>