New molecular proxies of temperature and hydrology are helping to constrain tropical climate change and elucidate possible forcing mechanisms during the Holocene. Here, we examine a ∼14,000 year record of climate variability from Lake Victoria, East Africa, the world's second largest freshwater lake by surface area. We determined variations in local hydroclimate using compound specific δD of terrestrial leaf waxes, and compared these results to a new record of temperature utilizing the TEX 86 paleotemperature proxy, based on aquatic Thaumarchaeotal membrane lipids. In order to assess the impact of changing climate on the terrestrial environment, we generated a record of compound specific δ 13C from terrestrial leaf waxes, a proxy for ecosystem-level C 3/C 4 plant abundances, and compared the results to previously published pollen-inferred regional vegetation shifts. We observe a general coherence between temperature and rainfall, with a warm, wet interval peaking ∼10-9 ka and subsequent gradual cooling and drying over the remainder of the Holocene. These results, particularly those of rainfall, are in general agreement with other tropical African climate records, indicating a somewhat consistent view of climate over a wide region of tropical East Africa. The δ 13C record from Lake Victoria leaf waxes does not appear to reflect changes in regional climate or vegetation. However, palynological analyses document an abrupt shift from a Poaceae (grasses)-dominated ecosystem during the cooler, arid late Pleistocene to a Moraceae-dominated (trees/shrubs) landscape during the warm, wet early Holocene. We theorize that these proxies are reflecting vegetation in different locations around Lake Victoria. Our results suggest a predominantly insolation-forced climate, with warm, wet conditions peaking at the maximum interhemispheric seasonal insolation contrast, likely intensifying monsoonal precipitation, while maximum aridity coincides with the rainy season insolation and the interhemispheric contrast gradient minima. We interpret a shift in conditions at the Younger Dryas to indicate a limited switch in insolation-dominated control on climate of the Lake Victoria region, to remote teleconnections with the coupled Atlantic and Pacific climate system.
Bibliographical noteFunding Information:
We thank LacCore, the National Repository for Lake Sediment Cores at the University of Minnesota for core access and assistance. We thank Ellen Hopmans, Jort Ossebaar, Sarah Grosshuesch, and Julia Halbur for assistance. This research was funded by grant NA-060-AR4310113 from the U.S. Department of Commerce, National Oceanic and Atmospheric Administration . The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement n° [ 226600 ]. Support from the Gledden Fellowship to J.P.W. and European Association of Organic Geochemists to M.A.B. is acknowledged. Work prepared while J.P.W. on leave at the Centre for Water Research, University of Western Australia and the WA-Organic & Isotope Geochemistry Centre, Curtin University of Technology. This work forms contribution 2641-JW at the Centre for Water Research, The University of Western Australia.
Copyright 2012 Elsevier B.V., All rights reserved.
- Compound specific hydrogen and carbon isotopes
- Insolation forcing
- Monsoonal precipitation
- TEX temperatures
- Tropical paleoclimate
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