Provenance analysis of late Pleistocene sediment from IODP site U1477 reveals climate and river basin dynamics in the Zambezi river catchment

The provenance of sedimentary material deposited in marginal marine environments offers significant insights into the evolving conditions within adjacent river catchments, thereby revealing the basin dynamics and climate variations. In this study, we used rare earth element (REE) compositions and Sr-Nd-Hf isotope signatures to investigate the provenance of sediments at International Ocean Discovery Program (IODP) Site U1477, located offshore of the Zambezi River mouth, over the past 150 thousand years (ka). These geochemical and isotope proxies indicate that the entire Zambezi River Basin (ZRB) has contributed sediments to the offshore region near the Zambezi River mouth during the last approximately 150 ka. Distinctly unradiogenic ε_Nd and ε_Hf signatures coupled with highly radiogenic ⁸⁷Sr/⁸⁶Sr values are indicative of sediment input from the middle and lower reaches of the ZRB. Conversely, more radiogenic ε_Nd and ε_Hf signatures along with unradiogenic ⁸⁷Sr/⁸⁶Sr values suggest sediment contributions from the upper reaches. The geochemical and isotope data from Site U1477 thus reveal that substantial changes in the sediment provenance occurred during the Late Pleistocene. By integrating our findings with other paleoclimate records from marine sediments and paleolake cores, we infer that the increased contribution of the upper Zambezi sediment sources to the offshore deposits from approximately 40 ka onwards reflects the reestablishment of the sediment supply from both the upper and middle Zambezi at this time. These changes were likely associated with shifts in the regional rainfall patterns across the ZRB, as well as modifications of the drainage divides due to varying sediment loads resulting from active bedrock erosion following the tectonic uplift on the Chobe fault near the Chobe–Zambezi confluence. This study offers novel insights into the Late Pleistocene evolution of the Zambezi drainage system and is essential for accurately reconstructing regional climate and environmental changes.