Intensified convection over East Africa during shifts in Walker circulation 140-60 ka BP
Abstract
Thick (up to 5m) diatomite beds deposited during the penultimate interglacial 140-60 ka document intervals where deep freshwater lakes filled large parts of the Central Kenya Rift, East Africa. Palaeohydrological reconstructions of the lake highstands are based on diatom analyses and δ18Odiatom. The chronology of the diatomite deposits is established through precise 40Ar/39Ar dating of intercalated pumice tuffs. The paleolakes experienced multiple hydrological fluctuations on sub-orbital (~1,500 to 2,000 years) time scales. The magnitude of the δ18Odiatom change (±3 permil) and significant changes in the plankton-littoral ratio of the diatom assemblage (±25%) suggest that the paleolake records can be interpreted in the context of long-term climate shifts in East Africa. Using 40Ar/39Ar age control and nominal diatomite-sedimentation rates, we suggest that paleohydrological conditions in equatorial East Africa during the late Pleistocene were primarily influenced by the latitudinal displacement of the inter-tropical convergence zone (ITCZ). Extreme insolation at the eccentricity maximum, and weakened zonal air-pressure gradients in the tropics, favored intensified convection over East Africa and deep freshwater lake conditions. Considering that these scenarios may relate to present-day, ENSO-related shifts in the Walker circulation, we discuss a possible connection between long-term El-Niño-like climate forcing and tropical hydrological change on glacial-Interglacial timescales.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A13B0235B
- Keywords:
-
- 1605 Abrupt/rapid climate change (4901;
- 8408);
- 1616 Climate variability (1635;
- 3305;
- 3309;
- 4215;
- 4513);
- 1620 Climate dynamics (0429;
- 3309);
- 1637 Regional climate change;
- 4522 ENSO (4922)