Holocene hydroclimatic variations on the Tibetan Plateau: An isotopic perspective

There is much debate regarding the temporal and spatial pattern of hydroclimate variations on the Tibetan Plateau during the Holocene, focusing especially on the dipolar pattern of precipitation and moisture between the southern and northern regions, on multiple timescales. Modern observations reveal that the delta O-18 in precipitation is an integrated tracer of the atmospheric processes of the Indian summer monsoon (ISM), the East Asian summer monsoon (EASM), and the westerlies, which dominate the climate of the Tibetan Plateau. Here, we summarize and compare 20 Holocene lacustrine authigenic carbonate delta O-18 records from lakes distributed across the Tibetan Plateau. After carefully considering the potential effects of temperature, evaporation, site elevation, meltwater supply, and moisture sources, we eliminate their influences on the isotopic composition of Tibetan lakes, and suggest that the long-term variations of the lacustrine delta O-18 records were dominated by the moisture sources. The delta O-18 values of the lake sediments in the central and western Tibetan Plateau increased since the early Holocene, which agrees with the trend of delta O-18 in speleothem records from the plateau, as well as with the variations of monsoon precipitation reconstructions for the region. Overall, this evidence indicates the substantial influence of the monsoon in the abovementioned regions. However, the delta O-18 records from lakes in the northeastern Tibetan Plateau show a decreasing trend during the second half of the Holocene (after similar to 5 ka), highlighting the operation of a different hydrological process, with enhanced moisture availability, in the regions. It has been suggested that the increased contribution from westerlies-derived moisture in the nonmonsoon season, with depleted delta O-18 (e.g., from melting snow or frozen soil in spring), is responsible for such variations. We propose that the interplay between the Asian summer monsoon and the westerlies was the major control of the hydroclimatic variations on the Tibetan Plateau during the Holocene, which led to the dipolar pattern of moisture variation between the northeastern Tibetan Plateau and other parts of the plateau, on the multi-millennial timescales during the Holocene.

Automated summary

This article summarizes and compares 20 Holocene lacustrine carbonate δ^18O records from lakes across the Tibetan Plateau and investigates the factors and trends of hydroclimate variations. The study finds that long-term variations of lake δ^18O records are primarily influenced by moisture sources, and different regions show distinct trends in variations.