Precession-forced changes in South West African vegetation during Marine Isotope Stages 101-100 (~2.56-2.51 Ma) [An article from: Palaeogeography, Palaeoclimatology, Palaeoecology]

This digital document is a journal article from Palaeogeography, Palaeoclimatology, Palaeoecology, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
The intensification of Northern Hemisphere Glaciation (iNHG) is one of the critical climate thresholds in the Cenozoic. This study focuses on marine sediments recovered from Marine Isotope Stages 101/100 at the Ocean Drilling Program Site 1083 to assesses the impact of the iNHG on continental southern African vegetation through n-alkane (straight-chain hydrocarbon) abundance and @d^1^3C values. The n-alkane abundance data yield a convoluted signal due to the number of controlling factors such as the source area, transportation routes and vegetation type. The C"3"1n-alkane @d^1^3C values, however, exhibit a cyclic pattern with a periodicity of c. 20 ka, and are not correlated to the abundance data. It is inferred that the signal does not represent a change in the geographical source of n-alkanes. Instead, we suggest that the variations are caused by water-stress-induced changes in either carbon isotope fractionation during C"3 photosynthesis or subtle changes in the proportion of C"3 and C"4 plants. These changes, unlike variations in oceanographic proxies, closely track precessional forcing factors and are independent of the prevailing obliquity-forced glacial/interglacial cycles. We conclude that the varying monsoon strength, rather than pCO"2 or temperature change, forced changes in southern African vegetation during this period.