Drivers of Indian vegetation and summer monsoon dynamics during MIS 11

Oliveira, Dulce Martinez, Philippe Yin, Qiuzhen [UCL] Krishnamurthy, Anupama Prasad, Srinivasan Schneider, Ralph Zorzi, Coralie Clément, Charlotte Deb, Ankur Desprat, Stéphanie et al.[show all]

Asian monsoon variations dramatically affect nearly half of the world’s population as the ecosystems, agriculture and economy in Asia are intrinsically linked to monsoon rainfall. The Indian Summer Monsoon (ISM) is the dominant Asian summer monsoon subsystem concerning energy flux, being considered as one of the strongest hydrological regimes on Earth. It brings up to 90% of the annual rainfall into the Indian Core Monsoon Zone (CMZ), where the ISM has its most representative expression. Alarmingly, the uncertainty in ISM precipitation projections is still high due to the complexity of simulating its various interconnections. High-fidelity ISM proxy records of past interglacials, warm periods of reduced ice volume as the Holocene, are thus critical to address important questions regarding the role of the primary forcings (insolation, ice volume and CO2) in driving ISM natural variability. Based on pollen analysis at IODP Site U1446 strategically retrieved from the CMZ, this study focuses on the Indian monsoon-induced vegetation changes during MIS 11 (425-374 ka), a key analogue of the current interglacial owing to its similar astronomical configurations, higher than present-day sea-level and greenhouse gas-driven climate warming. On orbital timescales, our results show a first major forest phase during the peak of MIS 11 (MIS 11c) followed by two forest phases separated by open vegetation periods (MIS 11b-a) indicating a shift to drier conditions due to reduced ISM. The forest maximum development occurs during the highest insolation level of MIS 11c which reveals the dominant influence of this forcing on the ISM hydroclimate under interglacial conditions, i.e., relatively high sea-level and atmospheric CO2 concentrations. However, the forest declines during MIS 11b-a while insolation remains high suggest that the insolation forcing is overshadowed by the influence of increasingly large ice caps and lower atmospheric CO2 concentrations, as well as the interaction of orbital and millennial scale variability. Our results highlight, therefore, the complex interplay between the forcings in driving hydroclimate and vegetation change under the distinct boundary conditions of MIS 11.