Isotope ratio models.pdf (71.96 kB)
Oxygen and hydrogen isotope ratios in tree rings: how well do models predict observed values?
journal contribution
posted on 2023-08-30, 13:30 authored by John S. Waterhouse, V. Roy Switsur, Andrea C. Barker, A. H. C. Carter, Iain RobertsonWe have measured annual oxygen and hydrogen isotope ratios in the α-cellulose of the latewood of oak (Quercus robur L.) growing on well-drained ground in Norfolk, UK. We compare the observed values of isotope ratios with those calculated using equations that allow for isotopic fractionation during the transfer of oxygen and hydrogen from source water taken by the tree to cellulose laid down in the cambium. The equations constitute a model in which isotopic fractionation occurs during evaporative enrichment within the leaf and during isotopic change between carbohydrates and water in the trunk during cellulose synthesis. From the relationship between isotope ratios in precipitation and α-cellulose, we deduce that the source water used by the tree comprises a constant mixture of groundwater and precipitation, chiefly from the months of May, June and July of the growth year. By selection of isotopic fractionation factors and the degree of isotope exchange within the trunk, we are able to model the observed annual values of oxygen isotope ratios of α-cellulose to a significant level (r=0.77, P<0.01). When we apply the same model to hydrogen isotope ratios, however, we find that, although we can predict the average value over the time series, we can no longer predict the year-to-year variation. We suggest that this loss of environmental signal in the hydrogen isotopes is caused by differences in the kinetic isotope effects of the biochemical reactions involved in the fixation of hydrogen in different positions of the glucose molecule. Owing to these effects, the hydrogen isotope ratios of cellulose can vary in a way not anticipated in current models and hence may induce non-climatic ‘noise’ in the hydrogen isotope time series.
History
Refereed
- Yes
Volume
201Issue number
2Page range
421-430Publication title
Earth and Planetary Science LettersISSN
0012-821XExternal DOI
Publisher
ElsevierFile version
- Accepted version
Language
- eng
Official URL
Legacy posted date
2010-11-19Legacy creation date
2020-02-20Legacy Faculty/School/Department
ARCHIVED Faculty of Science & Technology (until September 2018)Usage metrics
Categories
No categories selectedKeywords
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC