EXTRACTING CLIMATE SIGNALS FROM A MODERN ELEPHANT TUSK BY CARBON ISOTOPE AND HISTOLOGICAL ANALYSES

We test the use of serially sampled stable carbon isotope data and histological analysis of Loxodonta africana tusk dentin as a proxy for seasonal climate reconstruction in East Africa. The primary annual variation in East African climate is precipitation, whereas in temperate regions both temperature and precipitation vary. In the latter case, previous studies of serially sampled tusks record seasonal variations in oxygen isotopes. In this study, we expect the dominant climate signal in an elephant tusk from Kenya to be related to the biannual rainy season, which controls vegetative productivity.

Carbon isotope data from the tusk is compared to normalized differential vegetation index (NDVI) data, a proxy for vegetative productivity, collected at 10 day intervals. Multiple radiocarbon dates from collagen sampled along the tusk yield a growth rate of 4 cm yr^-1. This growth rate was used to determine a sampling interval thickness of ~100 microns along growth laminae, which corresponds to ~10 day intervals. Increment thickness of the growth laminae is also evaluated as a climate proxy. The tusk isotope data are compared to contemporaneous tail hair isotope data from the same individual. GPS data from a radio collar provide information on the individual’s location during the time interval recorded in the tusk and tail hair.