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

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.