Spatial heterogeneity of Holocene hydroclimatic variations and their driving mechanisms in the South Asian summer monsoon region

Understanding the spatiotemporal variations of the South Asian summer monsoon (SASM) is fundamental for predicting regional water resource availability. On interannual and decadal timescales, precipitation variations in the northeastern Indian Peninsula exhibit an antiphase pattern compared to other SASM-influenced regions, such as the central-western Indian Peninsula, southern Tibetan Plateau and Yunnan-Guizhou Plateau. However, it is unclear whether such heterogeneity existed on the sub-orbital timescale. We synthesized a new Holocene hydroclimatic dataset comprising 88 records from across the SASM region. Contrary to the traditional view of a uniform early Holocene maximum in monsoon precipitation, our results are the first to reveal a pattern of spatial heterogeneity: the northeastern Indian Peninsula experienced a wetting trend, whereas most other SASM regions showed an overall drying trend during the Holocene. This spatial contrast suggests that hydroclimatic variations in the northeastern Indian Peninsula do not represent overall SASM intensity. Notably, stalagmite δ 18 O records show a consistent pattern of the most negative values in the early Holocene followed by a gradual positive shift, contradicting the spatial heterogeneity revealed by moisture-sensitive records. This new finding suggests that not all stalagmite δ 18 O records in the SASM region can be simply interpreted as local precipitation, but rather that they may reflect an integrated signal of precipitation, water vapor sources and transport pathways. PMIP4 simulations corroborate the dipole pattern from hydroclimatic records, capturing the precipitation contrast between the northeastern Indian Peninsula and other SASM-influenced regions. PMIP4 simulations reveal a possible mechanism where the enhanced mid-Holocene land-sea thermal contrast triggered a summer anticyclonic anomaly. This anticyclonic anomaly induced atmospheric subsidence and was accompanied by a reduction in water vapor over the central-eastern Indian Peninsula, thereby suppressing precipitation and driving spatial heterogeneity. However, as simulations provide an atmospheric context rather than precise reconstructions, discrepancies persist between models and records, necessitating future model refinements.