by Dirk Verschuren, Jaap Sinninghe Damsté, Philip A. Barker, Maarten Blaauw, Daniel Ochieng Olago, Pascal Boeckx, Daniel Joseph Conley, Michel Crucifix, Marc De Batist, Gerald H. Haug, Gerald H. Haug, Christine S. Lane, Melanie J. Leng, Raimund Albert Muscheler, Stephen Mathai Rucina, Walter Salzburger, Nicolas David Waldmann, Pius Zebhe Yanda

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.

• 1) Reconstruct, with high temporal resolution, two glacial-interglacial cycles of tropical monsoon dynamics over the western Indian Ocean. This will allow assessment of the equatorial signatures of i) low-latitude insolation forcing vs. the long-distance impacts of northern hemisphere and Antarctic glaciation;
• ii) the African mega-drought which occurred during MIS5; and iii) inter-annual climate variability and weather extremes under a range of relatively warm and cool mean climate states. Analysis of multiple hydroclimatic and temperature proxies will be accompanied by a range of climate-modeling studies, and proxy validation in the modern climate/lake system.
• 2) Document long-term biodiversity patterns and ecological dynamics of a tropical savanna (grassland-woodland) ecosystem in response to changes in atmospheric CO2, temperature, moisture balance, and fire. Data-generated hypotheses will be tested by vegetation modeling run with ‘snapshot’ climate simulations over the last 120 kyr.
• 3) Reconstruct the long-term dynamics of a tropical freshwater ecosystem (nutrient budget, aquatic productivity) in response to climate-driven changes in hydrology, water-column temperature and stratification; the colonization of this isolated crater lake by cichlid fish; and their morphological response (niche adaptation, and possible evolutionary radiation) to long-term variation in available lake habitat.
• 4) Show exactly how often, when, and how much the East African landscape has changed throughout the entire existence of anatomically modern humans (190 kyr). Specifically, documentation of the magnitude and geographical distribution of severe drought during MIS6 and MIS5 is critical to reconstruct why our ancestors decided to expand from their African homeland into the Middle East and Eurasia ~100,000 years ago.

Africa, CHALLA, Deepchalla, Dynamics, Kenya, Kilimanjaro, Monsoons, Paleoclimate, Tanzania, Tropical Climate

Latitude: -3.31676, Longitude: 37.70403