High Resolution Climate (Monsoon) Record of the Last Three Millennia Reconstructed from a Multi-Proxy Analysis of an Organic Rich Sediment Deposit (Ladakh-NW Himalaya)

Ladakh is a region where the northern front of monsoon and the westerlies interact having annual peak rainfall during monsoon seasons. A chronologically well-constrained organic sediment deposit from Upshi (Ladakh) was studied using a multi-proxy approach namely palynology, environmental magnetism, total organic carbon (TOC), total nitrogen (TN), stable isotopes of carbon and nitrogen. The record constrained by five ¹⁴C AMS dates provides a continuous vegetation and paleo-environmental history spanning from the last ~2700 years with a temporal resolution of ~43 year. Pollen assemblage shows non-arboreal pollen (NAP) and non-pollen palynomorph (NPP) were dominant around Upshi from ~2646 to 2431 cal. yr BP, indicating warmer conditions. Arboreal pollen (AP) and NAP gradually increased from ∼2431 to 1860 cal. yr BP in the study area, under warm and wet conditions, corresponding to the Rowan Warm Period (RWP). This phase also witnessed enhanced sediment δ¹⁵N and χlf values. From ~1860 to ~1154 cal. yr BP increased Chenopodiaceae/Amaranthaceae and substantial spread of NPP suggest decreased temperature and prevalence of cold-dry climate. This period also records declining trends of χlf, δ¹⁵N, δ¹³C_org, TOC and TN contents. From ~1154 to 293 cal. yr BP, the vegetation type reversed to a mixed conifer and broadleaved forest with significant increase in herbaceous taxa, rising δ¹⁵N, δ¹³C_org, TOC and TN suggesting warm and wet conditions in the study area. This period broadly correspond to the Medieval Warm Period (MWP). Amongst all the proxies employed, depth profiles of TOC and TN (wt.%) appear to respond best against external climate forcings showing remarkable correlation(s) with residual Δ¹⁴C in atmosphere, indicating dominance of intrinsic solar variability on regional climate/environment. δ¹³C and δ¹⁵N analysis also gives us a perspective on how photosynthetic capability of plants influenced by soil moisture drives carbon sequestration and the temporal variation of sub-surface denitrification respectively all driven by climate. The record is also comparable to the historical events of India, China, South East Asia and Europe. This can perhaps be inferred as climatic(monsoonal) variability played an important role in modulating anthropogenic changes and developments in the Late Holocene.