Hydrological and vegetation variability from Mediterranean leaf wax biomarkers before and after the rise of East African C4 grasslands

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Author(s): Meyers, C.; deMenocal, Peter B.; Tierney, J. E.; Polissar, P. J.
Author Affiliation(s): Primary:
Lamont-Doherty Earth Observatory, Nyack, NY, United States
Woods Hole Oceanographic Institution, United States
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Terrestrial and marine paleoclimate records and changes in African fossil mammal taxa indicate that a transition towards more open, C4-dominated grasslands occurred in East Africa near 2 Ma. In contrast, the Mediterranean sapropel record documents pervasive precession-paced wet/dry cycles in the strength of the African monsoon and Nile runoff since at least the late Miocene. This study investigates whether the East African vegetation shift after 2 Ma was accompanied by a change in the monsoonal wet/dry cycle response to orbital precession forcing. We sampled eastern Mediterranean ODP Site 967 at 2-3 ka resolution in two 200 kyr intervals near 3.0 and 1.7 Ma. Nearly identical orbital configurations in these intervals allow us to compare mean conditions and orbital-paced variations before and after the 2 Ma transition. We used leaf wax biomarker concentrations and δD and δ13C compositions as proxies for monsoonal strength and vegetation type, and the δ18O composition of G. ruber as a proxy for Nile River runoff. Leaf wax biomarker concentrations varied over three orders of magnitude, with much higher concentrations in sapropels. During sapropel intervals, large-amplitude negative excursions occur in δDwax, δ13Cwax, and δ18Oruber, corresponding to a strengthened monsoon and less abundant C4 plants. Carbonate-rich intervals have positive isotope excursions indicating a weakened monsoon and more abundant C4 plants. The mean and variance of δDwax and δ13Cwax values are not significantly different between the 3.0 Ma and 1.7 Ma intervals indicating Northern Africa did not experience the vegetation and climate shifts observed in East Africa. While surprising, our finding suggests that the average monsoonal response to precession forcing, and corresponding vegetation variability, did not substantially change across the 2 Ma transition. This implies that North and East Africa exhibited different climate and vegetation behavior since 3 Ma.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Biomarkers; Cenozoic; Climate change; East Mediterranean; Hydrology; Leg 160; Mediterranean Sea; ODP Site 967; Ocean Drilling Program; Paleoclimatology; Paleoecology; Quaternary; Vegetation
Coordinates: N340411 N340411 E0324331 E0324331
Record ID: 2014081866
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