Detailed Asian summer monsoon changes during the Mid Holocene and their teleconnections with the northern high latitudes

Abstract

The Mid Holocene is a period of warm and optimum climate; however, some geological records reveal a climatic instability during this time interval. In East Asia, the detailed characteristics of monsoonal climate change and associated mechanisms remain debated in the Mid Holocene. Here we reconstruct a high-resolution Asian summer monsoon record based on six ²³⁰Th/U dates and 255 stable isotope measurements (δ¹⁸O and δ¹³C) from a stalagmite in Tiechang Cave, Guizhou Province, China, spanning from ∼6.7 to 5.6 ka BP. Both stalagmite TC5 δ¹⁸O and δ¹³C records detect a monsoon weakening event at around 6.5 ka BP, which is supported by speleothem records in the Asian monsoon domain, indicating its regional significance. This 6.5 ka weak monsoon event corresponds to prominent sea ice expansion and surface cooling in the Barents Sea. The expansion of sea ice coverage inhibited the formation of the North Atlantic Deep Water, weakened the Atlantic Meridional Overturning Circulation (AMOC), and induced widespread hemispheric cooling through the AMOC, which led to the Asian summer monsoon weakening. This weak monsoon interval around 6.5 ka BP is also coherent with a relatively high frequency in the El Niño Southern Oscillation (ENSO) variability, supporting the ENSO-monsoon relationship observed during the Late Holocene. In addition, spectral analyses reveal a significant periodicity of ∼60–80 years in TC5 δ¹⁸O and δ¹³C records, which may reflect the primary modulation of the Asian monsoon by the Atlantic multidecadal variability and the secondary influence of the solar activity (the Gleissberg cycle). Our TC5 δ¹⁸O and δ¹³C records suggest that a series of multidecadal oscillations, as well as a weak monsoon event, existed in the Asian monsoon region during the relatively warm and optimum Mid Holocene, and are likely associated with climate changes in the North Atlantic.