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Abstract

The S-ratio is a rock magnetic parameter employed to provide a relative measure of the contributions of soft and hard magnetic minerals, such as magnetite and hematite, respectively. We demonstrate the applicability of the S-ratio as a palaeomonsoon proxy in monsoon-dominated Indian lake sediments of the Deccan Traps that are investigated across a large rainfall gradient of about 100–4000 mm yr^–1. This is despite of the fact that no such possibility exists in weathered material in the catchment of Deccan Trap basalt rocks¹. Inferences based on magnetic susceptibility (κ) alone do not provide a direct manifestation of the changes in monsoon intensity², and can at times be misleading. However, our data indicate that a more reliable interpretation of palaeomonsoon rainfall can be achieved when κ is used jointly with the S-ratio. Specifically, our study on (titano-)magnetite and its weathering products, i.e., low-temperature oxidized (titano-)magnetite and hematite, shows that the S-ratio in the lake sediments responds sensitively to the reduction of monsoon rainfall associated with Northern latitude climate variabilities such as during the Last Glacial Maximum, Younger Dryas, and Little Ice Age. References:1, Zhang Q., et al. (2021), Is alteration of magnetite during rock weathering climate‐dependent? J. Geophysical Research, 126 (10), 1-20. DOI: 10.1029/2021JB0226932, Basavaiah N., et al. (2022), Holocene environmental magnetic records of Indian monsoon fluctuations. In Holocene Climate Change and Environment; Kumaran, K.P.N. & Padmalal, D., Eds., Elsevier: London, UK, pp. 229–246. DOI: 10.1016/B978-0-323-90085-0.00004-8