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https://hdl.handle.net/1912/2981

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Browsing Adminstration by Author "deMenocal, Peter B."
  • Article
    Hydroclimate variability in the equatorial western Indian Ocean for the last 250,000 years
    (American Geophysical Union, 2023-01-21) Windler, Grace ; Tierney, Jessica E. ; deMenocal, Peter B.
    Abstract Indian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean-atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19-193 (2.98°N, 51.47°E) that span the last 250 ky. Sub-surface water temperatures (Sub-T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial-interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo-Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin-wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19-193 indicate that both precession and glacial-interglacial cycles exert control over hydroclimate at this tropical location.
  • Article
    Low-frequency orbital variations controlled climatic and environmental cycles, amplitudes, and trends in northeast Africa during the Plio-Pleistocene
    (Nature Research, 2023-10-09) Lupien, Rachel ; Uno, Kevin ; Rose, Cassaundra ; deRoberts, Nicole ; Hazan, Cole ; deMenocal, Peter B. ; Polissar, Pratigya J.
    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 C28 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.