Solar influence on Millennial-scale variability of Indian Winter Monsoon during mid-late Holocene: Evidence from coastal sediments from Southeastern Sri Lanka

Sun-climate connection is a well-documented expression of earth´s climate system. Higher sensitivity to solar forcing is evident in many paleoclimate records, ranging from decadal to millennial time scales. Considering the Indian monsoon domain, Summer Monsoon show asynchronous variations with energy output of the Sun throughout Holocene, however the response of its winter counterpart is not well understood. This study aims to explore the variability of the Indian Winter Monsoon in association with solar activity during Holocene. Monsoon reconstruction was based on trace elements and lanthanide geochemistry of lagoon sediments from south-eastern Sri Lanka.  A 5.1 m sediment core acquired from Pottuvil Lagoon was logged for concentrations of K, Rb, Mg, Al, Ti and rare earth elements at a 5cm interval using ICP-MS. The chronology of the core was established by Bacon 2.2 age-depth modelling based on calibrated AMS ¹⁴C dates. Reconstructed monsoon signal was compared with Holocene records of ¹⁴C and ¹⁰Be nuclide production rates which are considered as proxies for solar activity. Results revealed a distinct millennial scale variability of Indian Winter Monsoon during mid-late Holocene with three strong monsoon activity phases at 2553-2984 yrs BP, 3899-5021 yrs BP, and at 5244-5507 yrs BP. Further, the millennial-bands detected in Pottuvil monsoon record are closely matched with shifts in cosmogenic nuclide production rates, showing coherence with solar output. The existence of millennial scale variability is further reinforced by occurrence of dominant 1600 and 1000-year periodicities in Lomb-Scargle power spectra of element proxies. In particular, 1000-year periodic band is consistent with Eddy solar cycle. Thus, this study suggests a possible link to solar influence on millennial scale variability of Indian winter monsoon from mid to late Holocene.