Plio-Pleistocene reconstruction of East African and Arabian Sea palaeoclimate.
Doctoral thesis, UCL (University College London).
Superimposed upon a long-term trend of aridification, the climate history of Africa was punctuated by episodes of extreme climate variability, characterised by the precessionally-forced appearance and disappearance of large lake systems within the East African Rift Valley. In order to investigate the nature of low-latitude climate variability during the Late Pliocene and Early Pleistocene, this thesis combines high-resolution analyses from one of the lake phases in the Central Kenyan Rift with the reconstruction of long-term changes in the transport of wind-borne terrigenous dust to the Arabian Sea. Climate in both regions is strongly influenced by relative changes in the strength of the Indian Ocean monsoons, which determine rainfall distribution in equatorial East Africa and generate the low-level winds which transport dust offshore from the Arabian Peninsula. In the Baringo-Bogoria basin in the Central Kenyan Rift, a well-dated package of fluvio-lacustrine sediments and diatomite units documents a major humid phase between 2.7 and 2.55 million years ago (Ma), coincident with the intensification of glaciation in the Northern Hemisphere. Stable oxygen isotope measurements of diatom silica, combined with the XRF analysis of whole-sample geochemistry, reveal that the deep lake phase was characterised by wet-dry cycles lasting, on average, 1,400 years. Over longer timescales, variations in the aeolian delivery of lithogenic matter to the Arabian Sea, reflected in normalised flux of titanium, show that monsoonal circulation prior to 2.6 Ma was highly variable and primarily driven by orbitally-forced changes in tropical summer insolation, modulated by the 400,000 year cycle of orbital eccentricity. Millennial-scale fluctuations in the dust record also support the evidence of abrupt wet-dry cycles in East Africa. Such high-resolution cycles are rarely found in older records, thus giving a valuable insight to the nature of short-term fluctuations in Plio-Pleistocene climate.
|Title:||Plio-Pleistocene reconstruction of East African and Arabian Sea palaeoclimate|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences|
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