EVOLUTION OF THE SOUTH ASIAN MONSOON THROUGH THE LATE QUATERNARY: IMPACTS ON HIMALAYAN GLACIATION AND ASIAN CLIMATE

The south Asian monsoon plays a fundamental role in determining the climatology of the Himalaya and surrounding regions. Temporal variability of the monsoon on timescales associated with Earth's orbital fluctuations has been demonstrated from a variety of proxy data and numerical simulations. In addition, correlation of monsoon strength with tropical Pacific sea surface temperatures (SSTs) exists and has been shown to potentially dominate orbital forcing. Through the late Quaternary both insolation and tropical SST have varied. We examine the monsoon and its impact on Himalayan snow accumulation and on climate in the Asian interior at the Last Glacial Maximum (LGM) and during the mid-Holocene using a coupled atmosphere-ocean general circulation model.

Under LGM conditions, the summer monsoon exhibits stronger westerly winds over the Indian subcontinent, enhanced snow accumulation in the eastern Himalaya, and drier conditions over the rest of the Indian subcontinent and southwest Asia. The mid-Holocene monsoon circulation is stronger than today with greater inland penetration and increased annual mean snow accumulation over the northwestern Himalaya. Both times exhibit more La Nina-like tropical Pacific SST.

These changes in precipitation and snow accumulation are analyzed in terms of the altered atmospheric circulations, which are in turn driven by changes in radiative forcing, sea surface temperatures, and sea surface height. All of these factors are therefore considered to be important in governing the spatio-temporal distribution of snow and ice deposition in the Himalaya during the late Quaternary as well as the evolution of desert margins on the Chinese Loess Plateau. Such factors are therefore likely to have contributed to the observed asynchroneity between Himalayan glaciation and northern hemisphere ice sheet volume.