TY  - JOUR
A1  - Sachse, Dirk
A1  - Dawson, Todd E.
A1  - Kahmen, Ansgar
T1  - Seasonal variation of leaf wax n-alkane production and delta H-2 values from the evergreen oak tree, Quercus agrifolia
JF  - Isotopes in environmental and health studies
N2  - In order to understand the timing of leaf wax synthesis in higher plants, we analysed the variability in leaf wax n-alkane concentration, composition (expressed as average chain length (ACL)), and delta H-2(wax) values as well as plant source water delta H-2 values (xylem and leaf water) in the evergreen tree Quercus agrifolia over a period of 9 months, beginning with leaf flush. We identified three distinct periods of leaf development with the first month following leaf flush being characterized by de novo synthesis and possibly removal of n-alkanes. During the following 3 months, n-alkane concentrations increased sevenfold and delta H-2(wax) and ACL values increased, suggesting this period was the major leaf wax n-alkane formation period. During the remaining 4 months of the experiment, stable values suggest cessation of leaf wax n-alkane formation. We find that n-alkane synthesis in Q. agrifolia takes place over 4 months, substantially longer than that observed for deciduous trees.
KW  - leaf wax
KW  - oak tree
KW  - hydrogen-2
KW  - isotope ecology
KW  - n-alkanes
Y1  - 2015
U6  - https://doi.org/10.1080/10256016.2015.1011636
SN  - 1025-6016
SN  - 1477-2639
VL  - 51
IS  - 1
SP  - 124
EP  - 142
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Rach, Oliver
A1  - Kahmen, Ansgar
A1  - Brauer, Achim
A1  - Sachse, Dirk
T1  - A dual-biomarker approach for quantification of changes in relative humidity from sedimentary lipid D/H ratios
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - Past climatic change can be reconstructed from sedimentary archives by a number of proxies. However, few methods exist to directly estimate hydrological changes and even fewer result in quantitative data, impeding our understanding of the timing, magnitude and mechanisms of hydrological changes. Here we present a novel approach based on delta H-2 values of sedimentary lipid biomarkers in combination with plant physiological modeling to extract quantitative information on past changes in relative humidity. Our initial application to an annually laminated lacustrine sediment sequence from western Europe deposited during the Younger Dryas cold period revealed relative humidity changes of up to 15% over sub-centennial timescales, leading to major ecosystem changes, in agreement with palynological data from the region. We show that by combining organic geochemical methods and mechanistic plant physiological models on well characterized lacustrine archives it is possible to extract quantitative ecohydrological parameters from sedimentary lipid biomarker delta H-2 data.
Y1  - 2017
U6  - https://doi.org/10.5194/cp-13-741-2017
SN  - 1814-9324
SN  - 1814-9332
VL  - 13
SP  - 741
EP  - 757
PB  - Copernicus
CY  - Göttingen
ER  -