The spectral analysis for a lamina thickness series of a stalagmite in Beijing and the climate variation in last 1 ka

The stalagmite lamina is one of the high-resolution records in the paleoclimate research. In order to study the cycles of climate oscillation in Beijing area and their shifts in the last 1 ka, a moving spectral analysis is used to reveal the characteristics of cycles in the lamina thickness sequence of a stalagmite from Shihua Cave. It is found that the dominant cycles in the time series are of 2yr, 3.3yr, 5~6yr, 10~12yr, 16~18yr, 133yr and 194yr. Some of these cycles are close to the cycle of 3.5yr, the cycle of 5~6yr and the cycle of 11yr that are found in many modern climatic record. It means that the dynamic forcing and the climate oscillations in the last 1ka are similar to those of modern climate. The 3.3yr cycle is stronger and continuous before D4 and the 5.8yr cycle is more distinct than the 3.3yr cycle after D4. There are different dominant climate cycles in different periods. Usually, the dominant cycles are stronger and clearer when the laminae are thicker. The dominant cycles are weak when the laminae are thinner. It may reflect that the stronger climate cycles in the wet period could leave much clearer prints in the stalagmite laminae. Therefore the laminae thickness can be used as a proxy of climate oscillation in northern China if the samples are carefully selected. It is noticed that the cycles may merge, branch, replace, abruptly appear, disappear or shift in frequency with the climate evolution. These phenomena demonstrate that the climate oscillation is nonlinear. It is very important for understanding the climatic oscillation of Beijing area in the last 1 ka.