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Accueil du site → Doctorat → États-Unis → 1992 → Pliocene-Pleistocene evolution of tropical aridity

Columbia University (1992)

Pliocene-Pleistocene evolution of tropical aridity

deMenocal, Peter Bedloe

Titre : Pliocene-Pleistocene evolution of tropical aridity

Auteur : deMenocal, Peter Bedloe

Université de soutenance : Columbia University

Grade : Doctor of Philosophy (PhD) 1992

The goal of this research has been to determine the nature and origin of low-latitude terrestrial climate variability prior to and after the rapid expansion of high -latitude ice sheets near 2.4 Myr to understand the interactions between high- and low-latitude climate systems since the late Pliocene (ca. 3.5 Myr). Records of eolian dust variability were reconstructed from whole-core magnetic susceptibility data at Ocean Drilling Project Site 661 in the eastern equatorial Atlantic and Site 721 on the Owen Ridge in the Arabian Sea. Susceptibility is a rapidly-measured and conservative indicator of terrigenous (eolian) variations at both sites. Susceptibility correlations were used to construct well-dated, composite sequences extending to 3.5 Myr. Evolutive spectral analysis of the two susceptibility records demonstrate that prior to 2.4 Myr both eolian records are dominated by variance at the 23-19 kyr precessional periodicities, whereas after 2.4 Myr the records exhibit strong increases in 41 kyr power. Dominant 23-19 kyr variations at Site 721 extend from 2.4 Myr to at least the late Miocene (ca. 6 Myr). The increase in 41 kyr power after 2.4 Myr and the subsequent increase in 100 kyr power after 0.7 Myr are interpreted to reflect the onset of glacial aridity in African and Arabian dust source areas. We also present a 0.9 Myr record of eolian accumulation from ODP Site 663 in the tropical Atlantic ; concentrations of two terrestrial eolian components, opal phytoliths (grass cuticles) and freshwater diatom (Melosira) valves from desiccated lake beds, were also measured. General circulation model (GCM) sensitivity tests were used to examine physical linkages between high and low latitude climate. These results demonstrate that the African and Asian monsoon circulations are very responsive to precessional insolation forcing in the absence of significant ice volume variability. However, full glacial ice cover caused significant precipitation and temperature decreases in monsoon dust source areas in Arabia and northeast Africa. The paleoclimate data and modeling results are combined to develop a generalized model for the Pliocene -Pleistocene evolution of low-latitude terrestrial climate

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