Late Quaternary East Asian Monsoon precipitation dynamics and vegetation response on the Chinese Loess Plateau

Abstract

Research on climate change has intensified after the IPCC warned about more extreme weather events due to global warming, threatening the environment and human life. In East Asia, the climate is influenced by the East Asian Monsoon (EAM), the Indian Monsoon, and the Westerlies. The population from this region relies heavily on rainfall from the EAM for fresh water. However, despite predictions that the EAM would get stronger, it has actually weakened since the 1970s. Understanding past EAM climate is crucial to understand this unexpected behavior. Various methods exist to study past climates. In China, oxygen isotopes from cave formations are used to reconstruct past EAM rainfall. These records show precession cycles and are linked to summer insolation. The Chinese Loess Plateau (CLP) provides records of EAM changes through layers of loess and soil, using magnetic properties and grain size as indicators. Biomarkers, such as plant waxes and bacterial lipids preserved in sediments, give insights into past environmental conditions. This thesis examines the hydrogen and carbon isotopic compositions of plant waxes in different loess-soil sequences on the CLP to understand EAM rainfall and vegetation changes during the Late Quaternary period. The first part of the study focuses on rainfall indicators and evaluates the effectiveness of plant wax isotopes as proxies. It shows that these isotopes and cave records reflect rainfall during the growing season, while magnetic susceptibility contains an additional annual temperature signal. Additionally, it investigates spatial patterns in EAM rainfall and moisture sources over the past 40,000 years. The second part examines how vegetation responded to climate changes, analyzing factors that influenced vegetation on the CLP. This research highlights the importance of using multiple methods to predict future EAM climate behavior accurately.