Non-stationary response of South Indian hydroclimate to orbital forcing during Marine Isotope Stage 9
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.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP0220009T
- Keywords:
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- 1626 Global climate models;
- GLOBAL CHANGE;
- 1637 Regional climate change;
- GLOBAL CHANGE;
- 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY;
- 4934 Insolation forcing;
- PALEOCEANOGRAPHY