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T9
Biome dynamics in the Ohrid Basin (Albania, Macedonia) revealed by biomarkers
and compound-specific isotopes ( 13 C, D)
J. Holtvoeth 1 *, H. Vogel 2,3 , V. Valsecchi 4 , M.J. Leng 5 , S. Schouten 6 , B. Wagner 2 , T.
Wagner 7 and G.A. Wolff 1
1 University of Liverpool, School of Environmental Sciences, Liverpool
2 University of Cologne, Institute of Geology and Mineralogy, Cologne, Germany
3 University of Bern, Institute of Geological Sciences, Bern, Switzerland
4 University of Montpellier, Institut des Sciences de l’Evolution de Montpellier, France
5 British Geological Survey, NERC Isotope Geosciences Laboratory, Nottingham
6 Royal Netherlands Institute for Sea Research, Department of Marine Organic Biochemistry, Den Burg,
Texel, The Netherlands
7 University of Newcastle, School of Civil Engineering and Geosciences, Newcastle-upon-Tyne
Currently, biome reconstructions using marine or lacustrine sedimentary archives are
overwhelmingly based on pollen data. As such, they are principally reconstructions of the
vegetation cover in the catchment of the study site. This approach, however, neglects the
dynamics of the soil cover. Attempts to incorporate soil dynamics into paleoenvironmental
studies have been made only recently and are generally based on the geochemical
differences between soils, terrestrial vegetation and sediments.
In order to better understand the dynamics of the soil carbon pool and its contributions to
sedimentary organic matter (OM), we have investigated sediments of Lake Ohrid
(Albania/Macedonia), one of the oldest lakes in the World (~1.6Ma). Sediment core
Co1202 has been taken near the eastern shores of the lake and covers the past 136,000
years. Our multi-proxy approach focussed on the period from 130 to 97ka and included
elemental analysis (TOC, CaCO 3 ), biomarker analysis (TEX 86 /surface water temperature,
lipid composition), carbonate carbon isotope (13Ccalcite) and compound-specific carbon
and hydrogen isotope analysis ( 13 C and D of fatty acids) as well as palynology. For an
improved knowledge of the organic geochemical fingerprints of the main contributors to
sedimentary OM we also investigated modern materials such as leaf litter, soils, water
plants and phytoplankton.
Lipid distributions and compound-specific isotopes of modern materials reveal that midchain
C 22 and C 24 n-fatty acids (FA) and n-alcohols (OH) are biosynthesised during litter
degradation and increase relative to long-chain compounds from litter to soil. Furthermore,
long-chain OH appear more resistant to degradation than FA. Ratios of mid-chain over
long-chain compounds and of long-chain FA over OH in the sediments are thus recording
changing overall contributions from the soil carbon pool as well as the level of degradation
of the terrestrial plant matter. While carbonate sedimentation and surface water
temperature appear closely linked to North Atlantic climate, these new lipid-based proxies
provide valuable additional information as they incorporate basin-specific biome
responses to climate change such as soil build-up and maturation lagging behind
vegetation expansion. Abrupt shifts in several proxies can now be related to lake-level rise
and the rapid inundation of marshy areas that led to a change in OM supply from forest
vegetation and low-land soils in the catchment of Co1202. Finally, the correlation of
carbonate carbon isotopes with soil OM degradation (long-chain FA/OH ratio) under stable
humid conditions confirms that dissolution of the underlying limestone is influenced by the
presence of substantial soils and enhanced soil respiration.
Keywords: Lake Ohrid; biome reconstruction; biomarkers; Marine Isotope Stage 5; soil
organic matter