East Asian Precipitation δ18O Relationship With Various Monsoon Indices

Abstract

AbstractChinese speleothem oxygen isotope (δ18O) variations have been widely interpreted as recording the evolution of the Asian Monsoon. However, calibration of δ18O to monsoon intensity has not yet been carried out in a quantitative way. To understand the climatic significance of δ18O, we measured monthly precipitation δ18O data at Heshang Cave, China, where speleothem δ18O records were previously obtained. We examined the influence of local climate and large‐scale atmospheric circulation on the δ18O by correlating to local meteorological data and various monsoon indices. We find neither a significant amount effect nor temperature effect, and therefore suggest that local climate is not the primary driver of δ18O variability. On seasonal timescales, monthly δ18O is significantly correlated to all monsoon indices, especially the Indian Monsoon (IM) and Western North Pacific Monsoon (WNPM) indices, proving δ18O responds dominantly to the tropical monsoon circulation. On interannual timescales, there are significant negative correlations between annual δ18O and the WNPM and IM monsoon indices defined by zonal winds, reflecting the impact of the El Niño‐Southern Oscillation on δ18O. Similar correlations between δ18O and precipitation amount in these monsoon regions lend further support to this finding. As the driving force of seasonal and interannual monsoon changes can be compared to variations on orbital and suborbital scales, respectively, we argue that speleothem δ18O in southern China is influenced by both external forcing and internal variability. Solar radiation plays an indispensable role on the orbital and seasonal scale δ18O variations, whereas ocean–atmosphere interactions are dominant on suborbital timescales.