Can phytoliths provide an insight into past vegetation of the Middle Kalahari palaeolakes during the late Quaternary?

Abstract

The Middle Kalahari is characterised by significant regional scale geomorphic activity and landscape change during the late Quaternary period. Very little however, is known about vegetation dynamics over this period due in part to the absence of well-preserved organic records. Here we test the application of phytolith analyses to sandy shoreline deposits of megalake Makgadikgadi, one of the sumps of the Okavango delta, routinely sampled and dated as part of a separate systematic geomorphological analysis. We confirm the presence of both an abundant and diverse assemblage of diagnostic phytoliths within these sand-dominated samples. The phytolith record reveals significant differences in the savanna vegetation through time with the composition of shoreline vegetation during different lake high-stand events was found to vary. Lake high stands are characterised by a coherently grassland dominated signal as well as a general trend towards more mesic and C3 prominent taxa during lake events after ∼40 ka. We suggest that phytolith analyses, whilst far from a perfect proxy, provide the potential to offer an important insight into long-term changes in Kalahari savanna, critical for understanding the response of regional vegetation to climatic and hydrological change both in the past and under future climate change scenarios.