ON THE HETEROGENEITY OF PLIO-PLEISTOCENE AFRICAN HYDROCLIMATE: LESSONS FROM NORTH (ODP SITE 659) AND EAST (BARINGO-TUGEN HILLS-BARSEMOI BASIN) AFRICA (Invited Presentation)

The Plio-Pleistocene (5-0 Ma) encompasses several key changes in the frequency, amplitude, and direction of global climate, including the intensification of Northern Hemisphere glaciation (iNHG) (~2.75 Ma) and 41-kyr cycles in temperature / ice volume. Late Pliocene proxy records also inform model simulations of a >400-ppm pCO₂ world. Changes in the trend and periodicity of African climate across the Plio-Pleistocene are particularly important given their potential influence on human evolution, and yet existing records are often short, low-resolution, and / or regionally biased. As a result, many triggers of African hydroclimate have been hypothesized—local insolation forcing, high-latitude teleconnections, Indian Ocean surface temperatures—that are difficult to distinguish with existing data.

Here, we use high-resolution (3-4 kyr) n-alkane-specific leaf wax hydrogen isotope (δ²H_wax) records from Ocean Drilling Program Site 659 (3.6-2.5 Ma) and Kenya’s Baringo Basin (3.3-2.6 Ma) to compare the evolution of East and Northwest African rainfall regimes across the Plio-Pleistocene boundary. At Site 659, δ²H_wax values and n-alkane concentrations vary strongly on 23-kyr timescales, with no significant secular change. Summer insolation cycles, which remain constant across iNHG, is likely the primary driver of North African rainfall. δ²H_wax values are deuterium-depleted relative to the late Pleistocene, implying that drying occurred well after iNHG.

In contrast, Baringo δ²H_wax values display prominent 41-kyr variance and are most spectrally coherent with the north-south insolation gradient. δ²H_wax values decrease by 11.5‰ around 3.05 Ma, indicating the onset of wetter conditions. They and most other long (>200 kyr) East African records covary with the IO zonal surface temperature gradient and West Australian hydroclimate on extra-orbital timescales (>100 kyr), showing that Walker circulation regulates rainfall along the IO rim.

Unlike the last deglaciation, Plio-Pleistocene climate transitions may be regionally heterogeneous across northern and equatorial Africa, with pronounced environmental gradients caused by the differing sensitivity to regional versus remote forcing. This illustrates the need for additional geographically-diverse, high-resolution paleohydrological archives.