Linkage between global CO2 concentration and Indian summer monsoon between 309 and 260 kyr BP

Abstract

A speleothem record of oxygen isotope ratios δ¹⁸O) changes from the Bhiar Dhar cave, Uttarakhand suggests sub-millennium scale variability in Indian summer monsoon (ISM) conditions in the northwestern Himalaya during late marine isotope stage (MIS)-9 and early MIS-8. The results indicate the weakening ISM conditions between 309 and 292 kyr BP and from 286 to 264 kyr BP, and strong ISM from 291 to 287 kyr BP. An abrupt surge in ISM-linked precipitation is observed at ∼287 kyr BP, following which the ISM remained weakened. The oxygen isotope ratio suggests a weak ISM with moderate variations from ∼286 to 264 kyr BP when the monsoon was moderately strengthened. The orbital scale changes in the ISM rainfall from 309 to 260 kyr BP in the study area appear to have been driven by the global ice cover and atmospheric CO₂ concentration superimposed by the northern hemisphere solar insolation.