Beyond the treeline: assessing the potential of juniper shrub-ring δ18O for paleoclimatic research in the Himalayas

High-elevation dwarf shrubs above the Himalayan treeline offer a valuable but underexplored archive for paleoclimatic research. This study analyses the stable oxygen isotope composition (δ 18 O) of Juniperus indica dwarf shrub-rings collected above 4000 m a.s.l. on the southern flank of the Himalayan Arc to evaluate their sensitivity to climatic variability. The δ 18 O series demonstrates a clear and coherent response to hydroclimatic conditions during the core summer monsoon season. Daily synoptic-scale analysis reveals that break monsoon weather patterns, rather than active monsoon phases, are the primary drivers of isotopic variability. Break phases are linked either to enhanced northwesterly airflow, leading to suppressed precipitation, or to a northward displacement of the monsoon trough, intensifying precipitation across the Himalayan Arc. Backward air mass trajectory modelling, combined with outgoing longwave radiation data reveal that isotopically enriched δ 18 O values correspond to westerly advection under reduced convective activity, whereas depleted δ 18 O values coincide with enhanced southerly flow and stronger convective activity. Collectively, these synoptic-scale circulation patterns explain up to 30 % of the observed δ 18 O variance. Our findings highlight the central role of break monsoon dynamics in shaping cellulose δ 18 O variability and demonstrate the potential of high-elevation dwarf shrubs as proxies for synoptic-scale paleoclimate in the Himalayas • First δ 18 O chronology from Juniperus indica above 4000 m in the Himalayas. • Shrub-ring δ 18 O reflects hydroclimatic variability, driven by break monsoon phases. • Break monsoons shape δ 18 O via moisture advection and convective activity. • Outgoing Longwave Radiation (OLR) significantly controls variations in δ 18 O. • High-elevation shrubs offer a new archive for Himalayan paleoclimate research.