| Popis: |
High-quality paleoclimate records are rare in the dry eastern branch of the East African Rift System, due to frequent desiccation of lakes which form the major source of paleoenvironmental information in the region. In this study, we present a 1,300-year history of hydrological change at hypersaline, alkaline Lake Bogoria (Central Rift Valley, Kenya), which has survived more recent destructive episodes of drought. Multi-proxy analyses on sediment cores from five key positions, supplemented with seasonal sediment-trap data, resulted in a detailed characterization of lacustrine deposits in Lake Bogoria’s three basins and on the two sills separating them. Variability in sedimentation dynamics at the different core sites allowed a semi-quantitative reconstruction of historical lake-level fluctuations over the past 1,300 years, constrained in time by a robust chronological framework. Moisture-balance variability throughout this period greatly exceeded the 20th-century range known from historical records. Between ca. AD 690 and 1100, drought isolated Lake Bogoria’s central and southern basins as separate, shallow brine pools with intense evaporation leading to the deposition of sodium carbonates and other evaporative minerals. A pronounced highstand between ca. AD 1100 and 1350 was followed by another lake-level decline, and the northern basin was disconnected from the joint central and southern basins for most of the time until ca. AD 1800. During the last two centuries, lake level has uninterruptedly been relatively high. With the sedimentological framework in place, new stable-isotope and XRF analyses currently underway will translate the sediment archive from Lake Bogoria into a unique, high-resolution hydroclimate record of the past millennium in equatorial East Africa. |
