Astronomical climate forcing and tuning of the Baringo core (HSPDP-BTB13-1A), Kenya

Abstract

The core from the Baringo-Tugen Hills-Barsemoi paleolake area in Kenya (called BTB13) provides an excellent opportunity to study east African hydroclimate in relation to human evolution and global climate change during the Pliocene-Pleistocene transition. As age control is critical, a Bayesian age model was previously constructed based on magnetostratigraphy and radio-isotopic dating. In order to improve the existing age model, we astronomically-tune the BTB13 core using the available gamma density (GD) and magnetic susceptibility (MS) records. Spectral analysis and bandpass filtering revealed a dominance of obliquity-related variability, which was used to establish an initial tuning. Significant precession-related variability was subsequently used to tune the records to precession and a standardized obliquity-precession target curve. The precession-paced variability is in very good agreement with precession-obliquity interference, making a shift in the tuning unlikely. Deep lake phases, characterized by diatomites and MS and GD minima, were related to precession minima and obliquity maxima, indicating a link to the intensification of the North African monsoon in response to boreal summer insolation maxima. This is further supported by the simultaneous formation of diatomites with Mediterranean sapropels. The obliquity dominance might be explained by a combination of the cross-equatorial insolation gradient and the seasonal cycle of equatorial insolation, and/or a link to higher latitudes.