Japan Geoscience Union Meeting 2024

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[E] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS03] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

Wed. May 29, 2024 9:00 AM - 10:15 AM 201B (International Conference Hall, Makuhari Messe)

convener:Takuya Sagawa(Institute of Science and Engineering, Kanazawa University), Kenji Matsuzaki(Atmosphere and Ocean Research Institute, The university of Tokyo), Sze Ling Ho(Institute of Oceanography, National Taiwan University), Stephen J Gallagher(University of Melbourne), Chairperson:Kenji Matsuzaki(Atmosphere and Ocean Research Institute, The university of Tokyo), Sze Ling Ho(Institute of Oceanography, National Taiwan University)


9:15 AM - 9:30 AM

[MIS03-02] Hydroclimate Variability in the Andaman Sea during the Last 1.2 Million Years

*Erick Naim1, Masanobu Yamamoto1 (1.Graduate School of Environmental Science, Hokkaido Univ.)

Keywords:Indian summer monsoon, alkenone hydrogen isotopic composition, leaf wax hydrogen and carbon isotopic composition, Mid-Pleistocene Transition

Vegetation on the Indian subcontinent relies on the seasonal monsoon rainfall as the primary source of water. Here we present a 1.2 ma record of alkenone hydrogen (δDalkenone), leaf wax hydrogen (δDwax) and carbon (δ13Cwax) isotopic compositions, pentacyclic triterpene methyl ethers (PTMEs), and polycyclic aromatic hydrocarbons (PAHs) from International Ocean Discovery Program (IODP) Site U1448. δ13Cwax and PTMEs data revealed obvious vegetational shifts that occurred during the observed interval. C3 vegetation dominance over C4 vegetation is observed during Marine Isotope Stage (MIS) 1 and MIS 5, accompanied by low PTMEs signal. Meanwhile, the higher abundance of C4 vegetation over C3 vegetation detected during MIS 2 and MIS 4 occurred synchronously with the increase in PTMEs. The shift in vegetation is thought to be influenced by the seasonality in the study area, as reflected by δDalkenone. The surface salinity record from δDalkenone proxy during Late Pleistocene aligns with δDwax, suggesting that both proxies reflect the precipitation pattern in the Andaman Sea. Interestingly, these records are in mismatch with the global ice volume reconstructed from benthic foraminifera oxygen isotope composition. This observation indicates that in the Andaman Sea region, the Indian summer monsoon responded differently to Milankovitch cycle, i.e. low latitude insolation, a departure from the typical monsoonal response to insolation. Additionally, PAHs data indicate that the occurrence of paleofire is higher during increased C4 plant abundance. In addition to the Late Pleistocene records, we will also present the variability records during the Mid-Pleistocene Transition (MPT) and provide a new insight as to how the Indian summer monsoon respond to climate forcings during this turbulent interval.