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| Titel |
Toward a better δDalkanes paleoclimate proxy; Partitioning of seasonal water sources and xylem-leaf deuterium enrichment according to plant growth form and phenology |
| VerfasserIn |
Lien Wispelaere, Samuel Bodé, Pedro Hervé-Fernández, Andreas Hemp, Dirk Verschuren, Pascal Boeckx |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133473
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| Publikation (Nr.) |
 EGU/EGU2016-14086.pdf |
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| Zusammenfassung |
| The DeepCHALLA consortium is preparing an ICDP (International Continental Drilling
Program) deep-drilling project on Lake Challa, a crater lake near Mt. Kilimanjaro in
equatorial East Africa, where the climate is tropical semi-arid climate and characterized by
two distinct rainy seasons. The main objective of this project is to acquire high-resolution and
accurately dated proxy data of continental climate and ecosystem change near the Equator
over 250,000 years. One of the paleoclimate proxies to be used is the hydrogen-isotopic
composition of sedimentary n-alkanes (δDalkanes) derived from fossil plant leaf wax.
However, this requires a better understanding of seasonal variability in the isotopic
composition of precipitation, and of the fractionation of its hydrogen during incorporation in
the plant waxes. In addition, recent studies have described the existence of “two water
worlds”, resulting in an additional deviation of the isotopic composition of the water taken up
by plants.
In this study, we measured the δD and δ18O of local precipitation, lake water, and xylem and
leaf water from different plant species, seasons and sites with varying distances to Lake
Challa. We use these data to set up a local meteoric water line (LMWL), and to assess spatial
and temporal patterns of water utilization by local plants. Our data show a seasonal
change in water-isotope partitioning with plants tapping water from isotopically
lighter water sources during the dry seasons, as indicated by more negative xylem
δD values and higher offsets from precipitation (i.e. greater distances from the
LMWL), therefore supporting the “two water worlds” hypothesis. Surprisingly,
trees appear to preferentially exploit isotopically more enriched sources of soil
water, suggesting shallower water sources, than shrubs. Plants located at the lake
shore use a mixture of precipitation and lake water, reflected in enriched xylem δD
values and in the intersection of 2H and 18O with the LMWL. Leaf-water deuterium
enrichment, averaged over all plant species, sites and seasons equals 23 ± 27‰.
Several factors influence the isotopic enrichment between xylem and leaf water, but
according to our results, the growth form and phenology of plant species are the primary
factors, while the location (proximity to the lake) and season exert relatively minor
effects. |
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