PP022-0009
Non-stationary response of South Indian hydroclimate to orbital forcing during Marine Isotope Stage 9

Thursday, 10 December 2020
Poster
Kaustubh Thirumalai, University of Arizona, Department of Geosciences, Tucson, AZ, United States, Judson Wiley Partin, University of Texas at Austin, Institute for Geophysics, Austin, TX, United States, Madhusudan G Yadava, Physical Research Laboratory, Geosciences Division, Ahmedabad, India, Chuan-Chou Shen, National Taiwan University, Research Center for Future Earth, Taipei, Taiwan, Steven C Clemens, Brown University, Earth, Environmental, and Planetary Sciences, Providence, RI, United States, Mahjoor Ahmad Lone, National Taiwan University, High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC) , Department of Geosciences, Taipei, Taiwan, Tsai-Luen Yu, National Taiwan University, High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geoscience, Taipei, Taiwan, Prosenjit Ghosh, Indian Institute of Science, Centre for Earth Sciences, Bangalore, India, Rachana Subba, Indian Institute of Science, Bangalore, India, Narayana Chinna Allu, University of Hyderabad, Hyderabad, India and Rengaswamy Ramesh, National Institute of Science Education and Research Bhubaneswar, School of Earth and Planetary Sciences, Bhubaneswar, India
Abstract:
Paleoclimate records suggest significant fluctuations in the Indian Summer Monsoon (ISM) phenomenon over the Pleistocene. Yet, delineating the phasing and magnitude of the ISM response to orbital forcing has proven to be complex due to substantial spatial variability in the monsoon subsystem and continues to be a subject of intense debate. Here we present a record of monsoon hydroclimate variability from peninsular India spanning Marine Isotope Stage 9 (MIS9; ~340-300 ka), an interglacial period where precession-induced changes in seasonal insolation were greater than those during the Holocene. Towards this, we use the stable oxygen isotope (δ¹⁸O) composition of a stalagmite from Belum Cave, Andhra Pradesh, India, a location where cave-dripwater δ¹⁸O is found to be negatively and significantly correlated with present-day rainfall amount above the cave. We find that the Belum Cave record documents disparate responses of South Indian hydroclimate to precession-driven insolation forcing over MIS9. First, in spite of a full cycle of changes in boreal summer insolation (~60 W/m²), we observe no orbital-scale trends in Belum Cave δ¹⁸O across the MIS 10-9 transition (and deglaciation) from ~340-330 ka. Essentially, the record shows little-to-no changes in the orbital-scale mean over this period and remains subdued for ~10,000 years. In striking contrast, after ~320 ka, under fully-developed interglacial conditions, the δ¹⁸O record shifts in concert with local summer insolation and displays a pronounced orbital-scale excursion (~6‰) towards the most-negative δ¹⁸O values (~10‰) of the record at ~312 ka, indicative of intensified monsoonal activity. Throughout MIS9, the stalagmite δ¹⁸O record exhibits persistent and considerable millennial-scale variability with swings on the order of 2-2.5‰. In this presentation, we discuss the potential influence of Northern Hemisphere ice-sheets on South Indian hydroclimate variations and speculate on their role in buffering concomitant responses to orbital forcing. Our findings do not lend support to the (“zero-phase”) hypothesis that monsoon intensity varies in-phase with changes in boreal summer insolation and instead point to more diverse controls on Pleistocene variability of the ISM.
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