A Lake Record of Geomagnetic Secular Variations for the Last 23 Ka from Lake Chala: Toward a Composite Directional Lake Record of the Earth's Magnetic Field for Equatorial East Africa

The documentation and understanding of variations in the Earth's magnetic field through time is fundamental for several disciplines, but current geomagnetic models rely on datasets heavily biased toward the mid- and high northern latitudes. The African continent and surrounding islands and oceans are particularly underrepresented. Here, we present a new record of paleo-secular variation (PSV) of the inclinations over the last 23 ka from Lake Chala, situated at 3 degrees S near Mt Kilimanjaro in eastern equatorial Africa. This groundwater-fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well-constrained age model based on 210Pb and 14C dating. The magnetic mineralogy of the sediments is tested with rock magnetic analyses. The Lake Chala inclination record shows four highs and lows over 20 ka and compares well with that of Lake Malawi (10 degrees S) between 20 and 16.2 ka, and from 9.8 to 2.6 ka. This record is linked to PSV records at Lakes Victoria and Malawi using a sequence slotting technique to generate a composite PSV model for east Africa. Analyzed at best-possible resolutions up to 200 years, the Lake Chala PSV record not only represents an important contribution to improve our understanding of local and global features of the Earth's magnetic field. It also expands the utility of paleomagnetism as a key tool for dating and correlation both for archeological sites throughout East Africa and the many volcanoes, active or dormant, of the East African Rift System. The understanding of the behavior of the Earth's Magnetic field in the geological past is based on an even spatial and temporal distribution of data collections. Nonetheless, data from large areas, such as from the African continent, remain sparse. In this study, we present new data from Lake Chala in equatorial East Africa, near Mount Kilimanjaro. The new inclination data are measured in lacustrine sediments covering the last 23 ka. We combine the data from Lake Chala with other data from Lake Victoria and Lake Malawi to produce a composite record for east African Lakes, using sequence slotting which improves the coherence between the records, whilst still constrained by the sediment age models. The composite record, centered on Lake Chala, improves our understanding of how the Earth's magnetic field changed in the recent past and can serve as an independent tool for dating nearby archeological sites as well as volcanic deposits from the African Rift emplaced in the last 23 ka. Lake Chala contains an exceptionally well-dated paleosecular variation record for east Africa Sequence slotting is used to refine a match to other secular variation records from east African lakes A composite paleosecular variation for equatorial east Africa is produced utilizing the combined set of control dates and magnetic records