Spatial heterogeneity of monsoon precipitation over the Asian continent during the termination of MIS-9 

Abstract

<p>Understanding the spatial and temporal variability of rainfall which is regulated by the strength of Asian monsoon requires an observational network dispersed across the continental landmass. The operation of monsoonal circulation during the last one million years is possible to be reconstructed using the geochemical and isotopic record available from cave speleothems. The monsoonal circulation brings rain and excess precipitation due to interplay of monsoonal wind strength which is governed by the seasonal movement of Intertropical Convergence Zone (ITCZ) from ocean to the continent. A consensual view is that both the operation of East Asian Summer Monsoon (EASM) and Indian Summer Monsoon (ISM) are in accordance with the orbital forcing. However, the lack of terrestrial records of ISM rainfall variability over glacial interglacial time scales precludes insights into pan-Asian monsoon forcing and related mechanisms. Here, we present independent estimates of temperature change from the clumped isotope record in speleothem from Belum cave, continental India, covering glacial interglacial transition (MIS-9). The palaeo data is used in conjugation with the already reported δ¹⁸O records from Chinese caves and Mean Annual Precipitation from Chinese Loess Plateau (CLP), which are influenced by the EASM, to understand the spatial variability of δ¹⁸O records and its significance in regulation of moisture transport process away from equator. A comparative study across latitudes, particularly at the peak of the interglacial period MIS 9 (after ~320 ka) brings to light the intensification of rainfall accompanied by relatively higher temperature (~35°C in Belum cave- 15.10°N) exhibited by both the ISM system and EASM System (Xiao cave 26.04°N). However, shift in δ¹⁸O record of caves above 30° N (Sanbao and Linzhu caves) is less, though the trend is similar. A recent study of CLP (36.35°N) reported a drop in mean precipitation by ~300mm post 320 ka. Such variation of the mid-latitude precipitation intensity may probably be a consequence of the combined effect of ice volume and snow cover in the Northern hemisphere and low latitude climate changes.</p>