Southern hemisphere forced millennial scale Indian summer monsoon variability during the late Pleistocene

Abstract

Peninsular India hosts the initial rain-down of the Indian Summer Monsoon (ISM) after which winds travel further east inwards into Asia. Stalagmite oxygen isotope composition from this region, such as those from Belum Cave, preserve the vital signals of the past ISM variability. These archives experience a single wet season with a single dominant moisture source annually. Here we present high-resolution δ18O, δ13C and trace element (Mg/Ca, Sr/Ca, Ba/Ca, Mn/Ca) time series from a Belum Cave stalagmite spanning glacial MIS-6 (from ~ 183 to ~ 175 kyr) and interglacial substages MIS-5c-5a (~ 104 kyr to ~ 82 kyr). With most paleomonsoon reconstructions reporting coherent evolution of northern hemisphere summer insolation and ISM variability on orbital timescale, we focus on understanding the mechanisms behind millennial scale variability. Finding that the two are decoupled over millennial timescales, we address the role of the Southern Hemisphere processes in modulating monsoon strength as a part of the Hadley circulation. We identify several strong and weak episodes of ISM intensity during 104–82 kyr. Some of the weak episodes correspond to warming in the southern hemisphere associated with weak cross-equatorial winds. We show that during the MIS-5 substages, ISM strength gradually declined with millennial scale variability linked to Southern Hemisphere temperature changes which in turn modulate the strength of the Mascarene High.

Variation in Dynamics, Controls, and Impacts of Agulhas Leakage through Late Pleistocene: A Review

“…Recent observations suggest that variations in the intensity and location of the SISH, influenced by the low latitude insolation gradient, are associated with changes in the Southeast trade winds, which in turn impact the strength and leakage of the Agulhas Current (Backeberg et al, 2012;Beck et al, 2018). Band et al (2022) recently conducted a study and found that warmer sea surface Additionally, a more prominent low-pressure system over the Asian landmass contributed to the stronger monsoon patterns (Beck et al, 2018). The enhanced Asian Summer Monsoon resulted in a more robust flow of southeast trade winds, which bolstered the South Equatorial Current (SEC).…”