Late Pleistocene Orbital-Scale Indian Summer Monsoon Hydroclimates Reconstructed Using Leaf Wax Hydrogen and Carbon Isotopes from the Northeast Indian Margin and Andaman Sea

McGrath, Sarah Madeline

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Year:: 2022
Contributor:: McGrath, Sarah Madeline (creator); Clemens, Steven (Advisor); Huang, Yongsong (Advisor); Anand, Pallavi (Reader); Dalton, Colleen (Reader); Russell, James (Reader); Herbert, Timothy (Reader); Brown University. Department of Earth, Environmental, and Planetary Sciences (sponsor)
Genre:: theses
Subject:: Paleoclimatology; hydrogen isotopes; Monsoons; Pleistocene Geologic Epoch; Carbon--Isotopes
Extent:: xv, 106 p.

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Abstract:: The Indian Summer Monsoon (ISM) is vital to over one-fifths of the world’s population who depend upon monsoonal rains. Recently collected marine sediment cores offer an unprecedented opportunity to examine ISM variability by investigating hydrologic and environmental changes surrounding and within the Bay of Bengal, the core convective region of the ISM. IODP Expedition 353 recovered sediment from northeastern Indian margin Site U1446, located near the mouth of the Mahanadi River and Site U1448, located on a rise in the Andaman Sea. I investigate the drivers that influence ISM variability by constructing leaf wax hydrogen isotope (δDwax) and carbon isotope (δ13Cwax) records spanning the past 640,000 years. δDwax records from Sites U1446 and U1448 allow reconstruction of precipitation isotopic composition (δDprecip), which reflects monsoon circulation encompassing changes in precipitation, moisture source, and moisture transport dynamics. I find that ISM isotopic proxies, including speleothems and leaf wax proxies, are quantitatively coherent and show a consistent response to greenhouse gas and ice volume forcing, with light isotopes during greenhouse gas maxima and ice volume minima. U1446 δDwax record shows large core monsoon zone δDprecip variability across the orbital and glacial-interglacial cycles with light isotopes reflective of long cross-continent transport paths and distal moisture sources and heavier isotopes reflective of short transport paths and proximal moisture sources. Compared to U1446 δDwax, U1448 δDwax has half the glacial-interglacial variability, and lacks significant obliquity and precession variability suggesting a relatively stable, proximal moisture source feeds the ISM branch over Andaman Islands, Irrawaddy River, and Salween River basins. The δ13Cwax record at Andaman Site U1448 reflects changes in regional C3/C4 vegetation structure. There is a distinct shift at 250 ka indicating glacial age C4 expansions. The 250 ka shift is tied to the late-Pleistocene submersion of the Sunda Shelf and an enhanced El Niño like climate state that promotes relatively drier ISM during glacial intervals. These results illustrate that the ISM is an integral part of the way in which Earth receives insolation energy and redistributes it among the cryosphere, ocean, atmosphere in complex yet defined circulation patterns that change over time.
Notes:: Thesis (Ph. D.)--Brown University, 2022

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McGrath, Sarah Madeline, "Late Pleistocene Orbital-Scale Indian Summer Monsoon Hydroclimates Reconstructed Using Leaf Wax Hydrogen and Carbon Isotopes from the Northeast Indian Margin and Andaman Sea" (2022). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:fbfccr9r/

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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