Ice core evidence for an orbital-scale climate transition on the Northwest Tibetan Plateau.

The influences on climate in the Northwest Tibetan Plateau (NwTP) have changed on millennial to precessional timescales and have been dependent on the size of the Northern Hemisphere ice sheets, Northern Hemisphere summer insolation, and the migration of the Intertropical Convergence Zone (ITCZ). All these influences control the position and intensity of the westerlies over Central Asia and the Tibetan Plateau and of the Asian Monsoon over South Asia. The top 187.4 m of a 309.7-m ice core (2015GP) drilled on the plateau of the Guliya ice cap contains a 41-kyr climate history of the NwTP, a region where information on past climate and environment is limited. The oxygen isotope ratio (δ18O), and ammonium (NH 4 +) and dust concentration records from 2015GP show that during the glacial (41–17.5 ka BP) temperature and precipitation in the NwTP were primarily influenced on the precessional timescale by summer insolation, while at millennial resolution the climate was linked to the North Atlantic temperature via the westerlies. During the deglaciation (17.5–12 ka BP) summer insolation remained an important temperature forcing, but the influence of the North Atlantic climate on the NwTP climate weakened as the westerlies shifted northward. The Guliya Holocene δ18O record shows that NwTP climate was no longer in phase with decreasing summer insolation or with North Atlantic climate, perhaps as the moisture source and pathways were more determinative factors in isotopic fractionation than temperature, and/or incoming solar radiation (insolation) forcing was replaced by rising greenhouse gas concentrations as the primary driver of warming in NwTP. • An ice core from the western Kunlun Mts shows orbital to millennial climate changes. • Summer insolation and westerlies influenced glacial stage climate in western Kunlun. • Ice core δ18O variations in NW Tibet and Greenland were similar in last glacial. • Ice core δ18O variations in NW Tibet and Greenland were opposite after 17.5 ka BP. • Mechanisms influencing δ18O in NW Tibet may vary with changing climatic conditions. [ABSTRACT FROM AUTHOR]