Modelling The Magnitude of Climatic Changes In East Africa During The Last 150 Kyr
Abstract
In order to assess the links between hydrology and climate in continental basins, water- balance modelling of lakes is a useful tool, because lakes are sensitive recorders of hydrologic fluctuations due to regional climate change. In the Central Kenya Rift, 40Ar/39Ar- dated lake sediments from the Naivasha and Nakuru-Elmenteita basins provide detailed information on extent and chronology of environmental changes and their effect on paleo-lakes. Mapping of lake deposits in surface outcrops and boreholes suggests that the extent of the lakes was comparable during highstands at 9 and 138 kyr BP, respectively, but significantly different compared to present conditions. Whereas the present Lake Naivasha (180 km2), Nakuru (40 km2) and Elmenteita (26 km2) have a water volume < 1 km3, paleo-lake areas were larger by factor of 3 to 4, and lake volumes increased by factor of 50 to 60. Simultaneously, these lakes were subject to considerable hydrochemical changes. For example, diatom and authigenic mineral assemblages indicate pH fluctuations between 7 and 11 for Lake Naivasha during the last 150 kyr, in contrast to a pH of 8.2.
Hydroclimatic lake-balance modelling of the most prominent lake phases of Lake Naivasha and Lake Nakuru-Elmenteita were performed in order to compare past and present-day climate conditions. Our results show that a +15% increase in precipitation compared to modern values may have been responsible for a lake-level highstand at 9 kyr BP. In addition, the increase in precipitation may reach as much as +30% if a change in vegetation due to increased humidity in the catchment is taken into account. Preliminary modelling results for an earlier highstand of Lake Naivasha at 138 kyr BP suggests hydroclimatic conditions comparable to the Holocene highstand. From the analysis of lake sediments we infer that Lake Nakuru-Elmenteita also experienced significant lake highstands at 138 kyr BP most probably caused by the same wetter cli- mate conditions. Our paleoclimate reconstructions from long-term sediment archives of the Naivasha and Nakuru-Elmenteita basins combined with hydrologic modelling suggest that this methodology provides important constraints for future large-scale climate modelling.- Publication:
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EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.4065B