Abstract
In the last two decades, stalagmite oxygen isotope (δ18O) records have been widely used to study the evolution of the paleomonsoon. Nevertheless, interpreting cave δ18O records in eastern monsoonal China as an indicator of East Asian summer monsoon (EASM) rainfall has been intensively debated. This study provides new insights into Chinese cave δ18O records and their paleoclimatic significance, based on recent research progress. The following points are highlighted: (1) Chinese cave δ18O records do not reflect changes in summer rainfall throughout the whole of eastern monsoonal China, which is evident by comparing monitored summer rainfall amount in eastern China and an integrated Chinese cave δ18Osyn proxy. (2) Chinese cave δ18O records can document millennial-scale EASM events, due to the sensitive response to large-scale atmospheric circulation changes. (3) During the early Holocene (before ~7 ka), a decoupled relationship between Chinese cave δ18O records and EASM rainfall (as represented by precipitation in North China) is attributed to the reduction of rainfall in North China, due to the influence of remnant melting ice sheets in the northern high-latitude region. (4) When the ice sheet boundary conditions were stable and ice sheets were small (after ~7 ka), there is an indirect correlation between the Chinese cave δ18O and rainfall changes in North China. (5) The first continuous speleothem δ18O record spanning the entire Holocene is synthesized for the core region of the Indian summer monsoon (ISM)-domain. Comparison of this integrated ISM proxy with Chinese cave δ18O records reveals that in China cave δ18O is primarily a signal of changes in the tropical monsoon and related large-scale circulation. The coupled relationship between rainfall in North China and tropical monsoon (ISM) rainfall is attributed to the response of downstream circulation to changes in circulation upstream, while their decoupled relationship is due to the possible effects of northern high-latitude ice sheets on reducing rainfall in North China. (6) Due to the imprecise definition of monsoon “intensity”, we suggest that cave δ18O can be used as an EASM proxy, if monsoon intensity is defined by changes in atmospheric circulation.
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