Precession-forced changes in South West African vegetation during Marine Isotope Stages 101–100 (2.56–2.51 Ma)

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 δ¹³C 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 C₃₁ n-alkane δ¹³C 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 C₃ photosynthesis or subtle changes in the proportion of C₃ and C₄ 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 pCO₂ or temperature change, forced changes in southern African vegetation during this period.     

Serological evidence for Encephalitozoon cuniculi infection (nosemiasis) in gnotobiotic guineapigs

Encephalitozoon cuniculi infection (nosemiasis) was serologically diagnosed in hysterectomy-derived gnotobiotically reared guineapigs. The probability of vertical transplacental transmission is discussed.