Post-glacial ecological and landscape change in the Eastern Himalayas: Insights from a multi-proxy cirque sediment record

We present a high-resolution multi-proxy sedimentary record from a small alpine cirque lake in the Dibang Valley, Arunachal Pradesh. This is the first high-elevation archive that spans the Holocene within the 900 km long Arunachal Himalayas. A 1.2 m sediment core, retrieved from the lake’s upper shore, captures post-glacial changes in catchment stability, vegetation succession, and regional hydroclimate.<br/>Radiocarbon dating of bulk sediments indicates that deglaciation was underway by 12.7 ± 0.09 cal kyr BP, closely matching in-situ 10Be cosmogenic exposure ages from boulders in the same catchment (13.3 ± 0.7 ka). A suite of multi-proxy analyses—including palynology, ITRAX XRF geochemistry, loss-on-ignition (LOI), particle size distribution, and magnetic susceptibility—captures the full post-glacial trajectory from initial ice retreat through Early Holocene warming and Late Holocene landscape stabilization.<br/><br/>The basal section (&gt; 12.7 cal kyr BP) reflects a cold, geomorphologically unstable landscape with high clastic flux, low organic content, and early herbaceous colonisers. Deglacial instability is followed by early Holocene warming (11.6 ± 0.18 cal kyr BP), initiating a shift in sedimentary and ecological conditions: Expansion in Betula, increase in organic content, and reduction of detrital input as evidenced by declines in Ti, Zr, Fe, K and Ca concentrations, along with lower magnetic susceptibility and reduced sediment density. The mid-Holocene (9.6 to 2.2 cal kyr BP) exhibits high pollen concentrations, fluctuating LOI, and episodic spikes in clastic elements and particle size—which may reflect episodic catchment destabilization or missing sediment, pending further chronological control. The late Holocene (2.2 cal kyr BP to present) shows increasing Tsuga, declining Betula and Artemisia, and organic enrichment, pointing to cooler, wetter conditions and landscape stabilization.<br/><br/>This study fills a critical spatial gap in Himalayan paleoenvironmental archives and highlights the value of integrating pollen and inorganic proxies from small alpine systems. By resolving glacial-interglacial transitions and Holocene variability in this remote region, our record contributes to broader efforts to contextualize present and future change in sensitive mountain environments.