Imprint of solar activity on Nanjing stalagmite annual layer thickness sequence during the Last Glacial Maximum

A 3000-year-long stalagmite chronology from Hulu Cave near Nanjing was established by counting annual layers under microscope. Based on the 230Th age, this chronology covers the period 24-21 kaBP, within the Last Glacial Maximum (LGM). Two proxies, annual layer thickness and gray level were measured along the growth axis of the stalag-mite profile in order to establish a high-resolution East Asian monsoon history during the LGM. The high correlation coefficient (r = 0.55) between the two proxies suggests that both of them were controlled by a common factor, possibly reflecting changes in the strength of summer monsoon circulation and its pre-cipitation. Low frequency variations of the annual layer thickness, ranging from centennial to millennial scales, are approximately in agreement with the 10Be-flux recorded in the Greenland ice core, indi-cating that changes in East Asian monsoon strength might be forced by solar outputs during the LGM pe-riods. In support of this, Fourier power spectrum analysis of the annual layer thickness showed certain decadal to centennial-scale cycles that agree well with the periodicities of solar activity.