25th International Meeting on Organic Geochemistry IMOG 2011

P-461
Miocene to Pliocene environmental changes recorded in South-
West African continental margin sediments
Florian Rommerskirchen 1 , Lydie Dupont 1 , Gesine Mollenhauer 2 , Enno Schefuß 1
1 Marum - Center for Marine Environmental Sciences, University of Bremen, D-28334 Bremen, Germany,
2 Alfred Wegener Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany (corresponding
author:rommerskirchen@uni-bremen.de)
The Miocene epoch is characterized by the
transition from relatively warm greenhouse conditions
to cooler, drier and less stable climates [1,2,3]. During
the late Miocene rapid cooling in mid- to highlatitudes,
surface ocean circulation and enhanced
deep water production were triggered by a permanent
establishment of Antarctic ice-sheets [1,3,4]. On
tropical and subtropical continents plants using the
CO2 concentrating C4 mechanism for photosynthesis
expanded nearly simultaneously at different places in
the world, while temperatures declined and global
CO2 levels exhibited no corresponding decrease [1,5].
Main aim of this study is thus to unravel the climatic
changes in South-West Africa from the Miocene to
Pliocene which led to the expansion of C4 plants in
that area.
We use organic geochemistry combined with
palynology on sediments of ODP Site 1085 to
evaluate the linkage of sea surface temperature
(SST) changes and continental vegetation. The site is
located in the Cape Basin at the south-west African
continental margin, within today‘s Benguela Upwelling
System (BUS). Sea surface and sub-surface
temperatures estimated by U K‘ 37 and TEX86 indicate a
cooling from above approximately 27 to 18°C over a
time period from 13.7 to 2.8 Ma. Differences in rate
and timing between these two temperature proxies
are related to differences in the habitat of the source
organisms, where U K‘ 37 represents surface and TEX86
subsurface temperatures [6]. Increased upwelling led
to lower SSTs and enhanced marine primary
production after 11 Ma. Synchronously, stronger
cooling in sub-surface waters by increased advection
of cold Antarctic intermediate waters is suggested by
TEX86 estimates. Concurrently, the abundance of
marine cysts and terrestrial pollen and spores
increased. The relative contribution of organic river
run-off from the nearby Orange River declined, as
indicated by the decrease in BIT-index from ~0.8 to