Timing of the Indian Summer Monsoon onset during the early Holocene: Evidence from a sediment core at Linggo Co, central Tibetan Plateau

The spatial and temporal variability, effects, and mechanisms of the Indian Summer Monsoon (ISM) have been investigated intensively during the past few decades. The pattern of a relatively strong ISM during the early to middle Holocene, and a relatively weak ISM in the late Holocene, has been widely demonstrated in both marine and continental records. However, the timing of the ISM onset during the early Holocene remains controversial. Here, we present oxygen isotope record from ostracods and hydrogen isotope record from sedimentary leaf waxes from a sediment core at Linggo Co, a glacier-fed lake on the central Tibetan Plateau, in order to investigate the onset of the ISM. The ostracod δ18O record indicates an early ISM onset at ~11.7 ka, whereas the leaf wax δD record indicates a later ISM onset at ~10 ka. This apparent two-step development of the ISM revealed by aquatic and terrestrial records is confirmed by principal component analysis of nine marine records from the ISM domain. The comparison between isotope records from Linggo Co and the marine records implies that the early ISM onset was likely linked to elevated temperatures in the Northern Hemisphere, while the later ISM onset may be related to intensified precipitation.