n-Alkane analyses from an transect of marine surface sediments off southwest Africa

We found a strong increase in the n-C29-33 weighted mean average d13C values from -33 per mil near the equator to around -26 per mil further south.

Additionally, C25-35n-alkanes reveal a southward trend of increasing average chain length from 30.0 to 30.5. The data reflect the changing contribution of plants employing different photosynthetic pathways (C3 and C4) and/or being differently influenced by the environmental conditions of their habitat. The C4 plant proportions calculated from the data (ca. 20% for rivers draining the rainforest, to ca. 70% at higher latitude) correspond to the C4 plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows.