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Biomarkers and their Stable Isotope Composition
13C, D/H) as Recorders of Ancient Ecosystems and Changes in the Hydrological Cycle

Funding: Deutsche Forschungsgemeinschaft
Starting date: November 2007

Gerald Haug (PI), Dirk Sachse (co-PI)

Collaborating researchers (PI’s only)

A. Brauer (GFZ Potsdam), H. Wilkes (GFZ Potsdam), G. Gleixner (MPI-BGC Jena), A. Kahmen (UC Berkeley), U. Kienel (Universität Potsdam/GFZ Potsdam)

Description

Specific organic compounds in sediments are sometimes termed „molecular fossils“ or biomarkers, because their presence can be used to infer the relative contributions of, for instance, algae, bacteria or land plants into the sedimentary record (1, 2). Through advances in analytical methods, it has become possible to measure the stable isotopic composition (the ratio of carbon 13 and carbon 12, δ13C; and the ratio of deuterium and protium, dD or D/H) of these biomarkers from which additional source and climatic information about the time of deposition can be derived.

Especially the D/H composition of lipids has developed into a promising new proxy for paleohydrology, as every photosynthetic organism uses (environmental) water as their hydrogen source. Recent research has shown that the isotopic composition of source water (lake water, ocean water, precipitation), in which climatic information such as evaporation, is encoded, is recorded in the D/H composition of lipid biomarkers from algae, bacteria and plants (3, 4, see figure 1).

BiomarkersFig1

Fig 1: Relationship between the hydrogen isotopic composition of lake water and the nC17 alkane (a biomarker for cyanobacteria) for different European lakes (3). A mean difference of -157‰ between lake water and lipid is observed, attributed to isotope fractionation during biosyhthetisis.


While the D/H composition of lipid biomarkers has been used to reconstruct paleoclimatic changes (5), a number of open questions regarding the (biosynthetic) transfer of hydrogen from water into organic material, especially in higher plants, remain. If these questions can be answered, this new proxy has the potential to significantly increase our understanding of how the hydrological cycle reacts in relation to climate change. Exact knowledge about past changes in hydrology is essential in predicting the future response of the hydrological cycle to anthropogenically induced climate change.

Therefore, we propose to:

  1. Identify the environmental and physiological forcing parameters determining the D/H composition of higher plant lipids, to be able to use their D/H ratio as a paleo-evaporation proxy (see figure 2).
  2. Apply lipid D/H measurements to reconstruct changes in the hydrology in the catchments of European lakes throughout the Holocene, to determine the response of the hydrological cylcle to climatic changes.

 

/research/researchBiomarkers/imagesBiomarkers/BiomarkersFig2

Fig 2: Conceptual scheme of the isotopic relationships between the different compartments of a lake system, after (4). If aquatic and terrestrial organisms use the same water as their hydrogen source (which is the case in small-catchment lake systems), the difference between aquatic and terrestrial lipid D/H is solely due to evaporation processes in soil and within the leaf - therefore this difference can potentially be used to reconstruct evaporation and evapotranspiration.


Dirk Sachse has obtained funding through the Emmy-Noether Program of the DFG to further work on the application of organic geochemical proxies to reconstruct paleohydrological conditions.

References:

(1) Eglinton, G. and Hamilton, R. J., 1967. Leaf Epicuticular Waxes. Science 156, 1322-1334.

(2) Meyers, P. A., 2003. Applications of organic geochemistry to paleolimnological reconstructions: a summary of examples from the Laurentian Great Lakes. Org Geochem 34, 261-289.

(3) Sachse, D., Radke, J., and Gleixner, G., 2004. Hydrogen isotope ratios of recent lacustrine sedimentary n-alkanes record modern climate variability. Geochimica et Cosmochimica Acta 68, 4877-4889.

(4) Sachse, D., Radke, J., and Gleixner, G., 2006. delta D values of individual n-alkanes from terrestrial plants along a climatic gradient - Implications for the sedimentary biomarker record. Org Geochem 37, 469-483.

(5) Pagani, M., Pedentchouk, N., Huber, M., Sluijs, A., Schouten, S., Brinkhuis, H., Damste, J. S. S., Dickens, G. R., and Scientists, E., 2006. Arctic hydrology during global warming at the Palaeocene/Eocene thermal maximum. Nature 442, 671-675.


Dirk Sachse (co-PI) in the Lab

Dirk Sachse (co-PI) in the Lab

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