HR: 1340h
AN: PP43A-0601    [Abstracts]
TI: Ostracode and Organic Biomarker Evidence for Changes in Lake Productivity and Hydrodynamics Since the Late 19th Century in Central Europe
AU: Schwalb, A
EM: antje.schwalb@tu-bs.de
AF: Institute for Environmental Geology, Technical University Braunschweig, Pockelsstrasse 3, Braunschweig, D-38106 Germany
AU: * Hanisch, S
EM: shanisch@awi-bremerhaven.de
AF: Institute for Environmental Geology, Technical University Braunschweig, Pockelsstrasse 3, Braunschweig, D-38106 Germany
AU: * Hanisch, S
EM: shanisch@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, D-27515 Germany
AU: Mackensen, A
EM: amackensen@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, D-27515 Germany
AU: Wessels, M
EM: martin.wessels@lfula.lfu.bwl.de
AF: Institute for Lake Research, Argenweg 50, Langenargen, D-88085 Germany
AB: Ostracode species assemblages and organic biomarkers from a 87 cm long core taken at 178 m water depth in Lake Constance (southern Germany) reflect the eutrophication history and changes in lake hydrodynamics. Age control is provided by flood layers, magnetic susceptibility, TOC concentrations, and lead and zinc distribution compared to other, well-dated sediment cores from Lake Constance. As in most deep lakes, the profundal ostracode community is comparatively simple; being composed of a few benthonic species living in and on the sediment (Leucocythere, Limnocythere, Fabaeformiscandona, and Cytherissa) and bentho-nektonic species that swim above it (Cypria). Organic biomarkers comprise autochthonous biomarkers such as dinosterol, brassicasterol, and tetrahymanol and allochthonous biomarkers such as sitosterol, amyrenones, and n-alkanes. Eutrophication in Lake Constance started in the 1940's and reached its maximum in the 1970's as shown by the distribution of dinosterol, tetrahymanol and brassicasterol. The ratios of long- to short-chain alkanes display high values in historical flood layers. Land-plant derived sterols and amyrenones also reflect changes in autochthonous and allochthonous sedimentation. Leucocythere shows maximum abundances during the oligotrophic stage, Limnocythere prefers oligotrophic-mesotrophic lake water. During maximum eutrophication, species diversity is reduced to two species, Fabaeformiscandona and Cypria. The return to meso-oligotrophic conditions at the beginning of the 1990's allowed Limnocythere to recolonize the profundal, and provided optimum conditions for Cytherissa. Leucocythere on the other hand has not yet been able to return to the lake bottom. Stable oxygen and carbon isotopes from Limnocythere and Leucocythere are used to reconstruct changes in oxygen supply of the bottom waters that is ultimately controlled by the North Atlantic Oscillation.
DE: 1845 Limnology
DE: 1055 Organic geochemistry
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting