Chinese Interstadials 14–17 recorded in a precisely U-Th dated stalagmite from the northern edge of the Asian summer monsoon during the MIS 4/3 boundary

The Marine Isotope Stage (MIS) 4/3 boundary, the so-called unfinished or failed termination, is a time period during which climate shifted from glacial to near-interglacial conditions that is akin to the Termination I. Paleoclimate records on this boundary can provide insights into the mechanisms of abrupt climate change under the circumstances when the global climate system has not reached a full threshold state. However, investigations on this specific climate period are sparse largely due to limited geological records with high temporal resolution. Here, we present a new highly resolved stalagmite record from Wanxiang Cave in western China that provides a detailed evolution of the Asian summer monsoon (ASM) from its northern fringe region. Established with 7 high-precision UTh dates and 647 pairs of isotope data (δ18O and δ13C), this record spans from 59.99 kyr B.P. to 52.94 kyr B.P., and contains the whole MIS 4/3 boundary. Its δ18O reveals three Chinese Interstadials (CISs) on millennial scales, i.e., CISs A.16–17 and 14. Sub-millennial events CIS A.17a and 16a correspond to the Greenland Interstadials 17 and 16 (GISs 16 and 17). The CIS A.17b is related to the ‘precursor events’ (PE 17), while the PEs 14 and 16 events are not evident in our δ18O record, probably due to the gradual change of the CIS A.14b and the lower amplitude of the CIS A.16b. Compared with other climate records, particularly those from the high latitudes, our δ18O record strengthens the notion of the close teleconnection between the ASM and high-latitude climates. Gradual change in δ18O from the CIS A.17b to 17a and the smaller amplitude of the CIS A.16b and 14b are likely coupled to the gradual Antarctic temperature variations, suggesting a dominant role of southern climate process to modulate ASM variability in western China via reorganization of atmospheric circulation. In addition, the westerly jet position relative to the Qinghai-Tibet Plateau may also have suppressed the abrupt 18O-depletion during these periods. At the onset of the MIS 4/3 boundary (at ∼59.82 kyr B.P.), an increase in the Northern Hemisphere summer insolation resulted in rapid ocean-atmospheric reorganizations between the high and low latitudes. This process led to an abrupt increase in precipitation associated with strengthening of ASM circulation, which promoted soil microbial activity and the transition of vegetation type from C4 to C3 as indicated by the δ13C decreasing in the record. After that, centennial-scale variations in δ13C are mainly related to soil humidity change throughout the MIS 4/3 boundary. Our δ18O record further confirms that the MIS 4/3 deglaciation is dominated by a northern-residing forcing, but also involves climate change process from the south. On a regional scale, the δ18O record from Wanxiang Cave may be largely influenced by the Indian summer monsoon, and thus inherits signatures from the south characterized by slightly more negative δ18O than other Chinese stalagmite records on millennial timescales.