Climatic periodicities recorded in lake sediment magnetic susceptibility data: Further evidence for solar forcing on Indian summer monsoon

The Indian summer monsoon exhibits considerable spatio-temporal variability. It is therefore important to understand its dynamics and the inherent periodicities. In this study, we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere (TK)–a small lake in southern India. The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data. Significant periodicities in the TK χ_lf data are centered at 906, 232, 147, 128, 96, 61, 54 and 44 years, which might have a solar origin. The wavelet power spectrum of the raw and detrended χ_lf data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past 3700 cal. years B.P. Positive correlation is documented between sunspot activity and TK χ_lf data; cross-spectral analysis of the reconstructed sunspot data and TK χ_lf data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both. There is a good match between the TK χ_lf and the reconstructed total solar irradiance data for the past 1200 years. However, an out-of-phase relationship is documented at certain time-intervals, which may be attributed to uncertainties in the age-depth model. The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and, like other archives from different regions in India, the TK lake sediments have also recorded these solar signatures.