Holocene Evolution of the Indian Summer Monsoon: Insights from Proxy-Model Comparisons on the Thar Desert Margin

The margins of the Thar Desert, which supported dense populations approximately 5000 years ago, are now among the most vulnerable regions to projected future climate change. Paleoclimate records from this region reveal diverse climate histories, reflecting varying sensitivities to monsoonal changes. These variations underscore the importance of comprehensive paleoclimate reconstructions to understand better the complexities of the Indian Summer Monsoon (ISM) at regional scales.

This study investigates the Holocene evolution of the Indian Summer Monsoon (ISM) and its implications for the environmental history of the Thar Desert margin through a comparative analysis of proxy-based reconstructions and simulation results from the Paleoclimate Modelling Intercomparison Project (PMIP). Sediment cores were collected from two lakes at the desert margins, including Karanpura (northern margin) and Raiwasa (eastern margin). For proxy reconstruction using the lake sediments, stable oxygen and carbon isotope analyses of ostracod shells were analysed along with geochemical and sedimentological techniques, including X-ray fluorescence (XRF), Loss on Ignition (LOI), bulk sediment analysis (C/N, TOC), and grain-size analysis to apply a multi-proxy framework to ensure robust findings. Chronologies were established using radiocarbon dating and Optically Stimulated Luminescence (OSL) dating.

Reconstructed monsoon variability was compared with PMIP model outputs, with a focus on key climatic events like the Holocene Climate Optimum, and abrupt climatic events such as the 8.2 ka event, 4.2 ka event, the Little Ice Age (LIA), and the Medieval Climate Anomaly (MCA). Model performance was validated against historical simulation runs (1850–2014 CE) using the Global Precipitation Climatology Centre (GPCC) dataset. Results indicate increased precipitation along the Thar Desert margin during the mid-Holocene, inferred from proxy evidence of high lake levels, intense weathering, and elevated organic matter. However, dry conditions marked by high salinity, coarse grains, and reduced organic input were observed during abrupt events, such as the 8.2 ka and 4.2 ka events. The lake on the eastern margin, Raiwasa Lake, records demonstrates a gradual shift from arid to wetter conditions over time. Comparisons with PMIP model outputs reveal discrepancies between model simulations and proxy data, likely attributable to model biases and limitations in proxy methodologies. Drivers of the ISM variability will be explored to understand the regional differences and differences between model and proxy results.