High-Resolution Paleomonsoon Variability in the Core Monsoon Zone: Multi-Proxy Geochemical Evidence from Recent Holocene Sediments of Lonar Impact Crater Lake, Central India

Abstract

The Indian Summer Monsoon (ISM) exhibits significant variability at multiple timescales, yet high-resolution paleoclimate records from the core monsoon zone capturing centennial-scale monsoon dynamics during climatically critical periods remain limited. This study presents X-Ray Fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) geochemical analysis of a 55 cm post-monsoon sediment core collected from Lonar Lake, a meteorite impact crater lake in central India's core monsoon zone (19.97°N, 76.51°E). The core comprises subsamples analyzed for major elements and trace elements. Integration with published sedimentation rates (50–80 cm/ka) indicates the core represents 900–950 years of recent Holocene history spanning the Medieval Warm Period (~1050–1300 CE), Medieval Warm Period–Little Ice Age transition (~1300–1400 CE), Little Ice Age climax (~1400–1850 CE), and the modern period (~1850–2024 CE). Paleoclimate indices reveal: (1) stable moderate chemical weathering (Chemical Index of Alteration [CIA] = 59.05 ± 1.03) consistent with semi-arid to sub-humid monsoon climate; (2) anomalously elevated Al/Na ratios in the middle core section indicating intensified chemical weathering during the Little Ice Age, contrary to global cooling trends; (3) V/Cr minima and Co maxima in the same interval indicating episodic anoxic conditions and productivity surges linked to enhanced monsoon precipitation; and (4) progressive Ba depletion reflecting long-term evolution toward more oxidizing depositional conditions. These findings challenge simplified global cooling–monsoon suppression paradigms and underscore centennial-scale ISM variability during a climatically critical recent Holocene interval.