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      Low-frequency orbital variations controlled climatic and environmental cycles, amplitudes, and trends in northeast Africa during the Plio-Pleistocene

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          Abstract

          The eastern Mediterranean sapropels, paced by insolation, provide a unique archive of African monsoon strength over the Late Neogene. However, the longer-term climate of this region lacks characterization within the context of changes in ice volume, sea surface temperature gradients, and terrestrial ecosystems. Here, we examine C 28 n-alkanoic acid leaf wax hydrogen and carbon isotopes in sapropels, sourced from northeast Africa, along with vegetation-corrected precipitation isotopes, derived from astronomically dated sediment cores from ODP 160 Sites 966 and 967 since 4.5 million years ago. Despite sampling only wet-phase sapropels for African monsoon variability, we find a larger range in hydrogen isotopes than previously published data across wet-dry precession cycles, indicating the importance of long-term modulation of Green Sahara phases throughout the Neogene. An influence of orbital properties on regional monsoonal hydroclimate is observed, controlling up to 50% of total hydrogen isotope variance, but large changes outside of these typical frequencies account for at least 50% of the total variance. This secular trend may track changes in ice volume, tropical sea surface temperature, sea surface temperature gradients, or even lower-frequency orbital cycles. Long-term hydroclimate and environmental shifts provide new contexts for milestone events in northeast African hominin dispersal and evolution.

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          A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

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            Stable isotopes in precipitation

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              Leaf epicuticular waxes.

              The external surface of the higher plants comprises a cuticular layer covered by a waxy deposit. This deposit is believed to play a major part in such phenomena as the water balance of plants and the behavior of agricultural sprays. The wax contains a wide range of organic compounds. These complex mixtures are amenable to modern microchromatographic and microspectrometric analytical procedures. The few surveys which have been made of the species distribution of certain classes of constituents indicate that such distribution may be of limited taxonomic value; however, the wax composition of a species may differ for different parts of the same plant and may vary with season, locale, and the age of the plant. This fascinating subject, in which the disciplines of botany, biochemistry, chemistry, and physics overlap and interact, is still in a very active state. Much remains to be learned about the composition and fine structure of the wax deposits, and, for this, experimental study of wax crystallization and permeation through artificial membranes will be required. Enzymic studies, radiolabeling, and electron microscopy will be needed to reveal the mode of biogenesis of the wax constituents and their site of formation and subsequent pathway through the cuticle to the leaf surface.
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                Author and article information

                Contributors
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                Journal
                Communications Earth & Environment
                Commun Earth Environ
                Springer Science and Business Media LLC
                2662-4435
                December 2023
                October 09 2023
                : 4
                : 1
                Article
                10.1038/s43247-023-01034-7
                8982a3b2-1217-4b7f-99cd-5b1b378446cc
                © 2023

                https://creativecommons.org/licenses/by/4.0

                https://creativecommons.org/licenses/by/4.0

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