25th International Meeting on Organic Geochemistry IMOG 2011

P-192
Climate variability in the Lake Victoria region (East Africa) since
the Late Pleistocene as shown by molecular biomarkers
Melissa Berke 1 , Josef Werne 2 , Thomas Johnson 1 , Kliti Grice 3 , Stefan Schouten 4 , Jaap
Sinninghe Damsté 4
1 Large Lakes Observatory & Department of Geological Sciences, University of Minnesota Duluth, Duluth,
United States of America, 2 Large Lakes Observatory & Department of Chemistry and Biochemistry,
University of Minnesota Duluth, Duluth, United States of America, 3 Department of Chemistry, Curtin
University, Perth, Australia, 4 Royal NIOZ, Department of Marine Organic Biogeochemistry, Den Burg,
Netherlands (corresponding author:berk0135@umn.edu)
Recent organic geochemical advances have
facilitated the comparison between continental
temperature change, hydrologic variability, and
terrestrial vegetation response. TEX86, a proxy based
on the lipids of aquatic Crenarchaeota that show a
positive correlation with growth temperature, was
used to reconstruct surface water temperatures from
Lake Victoria, East Africa during the latest
Pleistocene-Holocene. Hydrologic conditions were
then interpreted using compound specific δD of fatty
acids from sediments and compared to hydrologic
implications from paleoecological data, specifically
pollen and diatom assemblages found in the lake
(Kendall, 1969; Stager et al., 2003). Compound
specific δ 13 C data from terrestrial leaf wax biomarkers
(n-alkanes) was then evaluated in order to determine
how the patterns of rainfall and aridity in this region
have affected the terrestrial vegetation in the
watershed. Initial comparisons of climatic changes
seen in temperature, vegetation, and hydrologic
records appear to show some periods of consistency
between warm/wet intervals and cool/dry intervals,
which is expected for this region, but far less often
shown. This is one of the first studies from a tropical
East African lake to compare all three of these
biomarkers (TEX86, δD, and δ 13 C) in order to
reconstruct a complete regional-scale picture of
climate variability since the Late Pleistocene.
Lake Victoria temperatures show a steady
warming beginning 16 cal ka, with a pause around the
Younger Dryas, dominated by arid conditions and
strong savannah grassland development during this
interval. There is continued warming to a sustained
thermal maximum for this portion of the record at
~10.5-8.5 ka, which generally coincides with the
Northern Hemisphere summer insolation maximum.
This thermal maximum occurs during the most humid
interval of this record (~9.5-8.3 ka), shown by an
increase of humid forest pollen and high diatom
abundance (due to increased water column mixing
and nutrient runoff). Temperatures abruptly cool
~1.5ºC in