Specific response of earlywood and latewood δ18O from the east and west of Mt. Qomolangma to the Indian summer monsoon

Abstract

This study reports the earlywood and latewood δ18O time series from two hemlock sites located to the east (EQ) and west (WQ) of Mt. Qomolangma (Everest) in the Himalaya. The latewood δ18O series from both sites were highly consistent, whereas the earlywood δ18O values for the two sites show variations over the investigation period. Climate response analysis revealed that the dominant control on latewood δ18O values at both sites was the precipitation amounts of the middle/peak periods of upstream Indian Summer Monsoon (ISM). However, for EQ- and WQ-Earlywood, the main controls were precipitation amounts during the early and middle phases of the upstream ISM, respectively. The upstream amount effect could have accounted for earlywood and latewood δ18O variance. Combined with moisture transport models, we found that source water incorporated into latewood at both sites was derived mainly from the Bay of Bengal and Arabian Sea during middle/peak ISM precipitation. However, during the early ISM, the high ridges of Mt. Qomolangma may block most of the moisture that originates from the Bay of Bengal, which results in a stronger signal of early ISM being recorded in EQ-Earlywood δ18O. The influence of the ISM on WQ-Earlywood is delayed until the middle ISM.