DeepCHALLA: Analysis of a unique 250,000-year archive of climate and ecosystem history from equatorial Africa

East African lake sediments reveal a uniquely continuous archive of climate and landscape history over the past 250,000 yearst

Long climate records from (sub-)tropical continental regions provide an important counterpoint to the polar ice-core records from Antarctica and Greenland, and are crucial to resolve long-standing questions about the relative importance of tropical and high-latitude climate processes in generating spatial climate variation. Available late-Quaternary climate records show that, on orbital time scales, tropical monsoon rainfall mostly responded to precession-driven changes in low-latitude summer insolation. What has been missing is a long continental climate record from near the equator, where twice-annual passage of the Intertropical Convergence Zone (ITCZ) creates the characteristically inter-tropical, bimodal seasonal rainfall regime of two wet seasons and two dry seasons. Equatorial East Africa is perhaps the most appropriate region to pursue this equatorial record, because here seasonal ITCZ migration spans the widest latitude range in the world, and hence atmospheric dynamics associated with northern and southern hemisphere monsoon systems interact most strongly. DeepCHALLA proposes to exploit the continuous sediment record of Lake Challa, a 92-m deep crater lake near Mt. Kilimanjaro in eastern equatorial Africa. Lake Challa?s proximity to the Indian Ocean ensures its all-season location east of the Congo Air Boundary, the zone of convection between Atlantic and Indian Ocean moisture sources. Consequently the region is not directly impacted by the climatic effects of changes in tropical Atlantic thermohaline circulation, through which signatures of northern hemisphere glaciation are transferred to low-latitude continents. The project?s principal objective is to acquire high-resolution and well-dated proxy records of continental climate and ecosystem dynamics near the equator over the past ca.250,000 years, thus encompassing two complete glacial-interglacial cycles and the entire known existence of modern humans (Homo sapiens) in East Africa. The length of this climate archive, combined with the exquisite temporal resolution provided by finely laminated sediments, provides unique opportunities to increase understanding of tropical climate variability at inter-annual to millennial time scales, including the occurrence of short-lived weather extremes (droughts, floods) with disproportionate impact on regional water resources and economic activity. The project includes a special focus on differentiating the histories of three fundamental aspects of the tropical hydrological cycle: annual rainfall, effective moisture, and the duration/severity of seasonal drought. Documentation of long-term biodiversity patterns and the ecological dynamics of tropical savanna (grassland-woodland) ecosystems in response to changes in atmospheric CO2, temperature, moisture balance, and fire will help explain/predict the present-day/future prevalence of C3 and C4 plant species in tropical grasslands, and the past/future persistence of biodiversity hotspots in eastern Africa.

ICDP Project: 2015- ongoing
Start-Up Funding (Göttingen University for young resaearchers): 7/2016-3/2017
DFG Project: 2017-2020