Multiple Climate Forcings Decomposed From a Tibetan Plateau Ice Core Isotope Record

Abstract

Due to the impact of various climate systems, including the Asian Summer Monsoon (ASM) and westerlies, it is challenging to identify specific climate variables from the ice core δ¹⁸O records of the Tibetan Plateau (TP). Here, we disentangle the major climate modes by applying the singular spectrum analysis method to a δ¹⁸O time series in a shallow ice core retrieved from central TP. This method allows us to identify three major climate modes: the trend component, the El Niño Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). The trend component mainly reflects warming in the middle and upper troposphere over the south of the TP rather than the low land surface temperature changes. Furthermore, we found that water vapor δ¹⁸O in these upper atmospheric layers positively correlates with temperature. We propose that the up-and-over transport of such water vapor to the TP contributes to the temperature signal in the ice core δ¹⁸O record, which also helps understand the increasing trend in TP ice core δ¹⁸O records during the last deglaciation. ENSO and PDO affect the intensity of the ASM through two phases: warm phases tend to weaken the monsoon, leading to higher δ¹⁸O values, whereas cool phases strengthen the monsoon, resulting in lower δ¹⁸O values. Our findings suggest that multiple climate forcings can have their specific isotopic imprints in isotopic archives and highlight the importance of analyzing the integrated effects of diverse climatic drivers. The analyses also shed light on separating different climate signals from paleoclimate records.