Holocene climate variability deciphered from Chilika Lagoon sediments: Implication for anthropogenic activity or paleocyclones?

Coastal lagoons, acting as a link between land and sea, serve as valuable archives for past climate variations, human activities, and paleo-cyclonic events. In this study, we employ a multi-proxy approach to analyze sedimentary records and uncover climatic shifts influenced by both monsoonal and non-monsoonal factors. Our analysis incorporates sediment characteristics such as grain size, magnetic susceptibility (MS), and clay mineralogy to infer high-energy conditions within the Chilika Lagoon. Additionally, we utilize Rock-Eval pyrolysis and deconvolution of flame ionization detector (FID) signals to determine the type of organic matter (OM) present.

Findings reveal that during the Early Holocene, a high sand percentage and elevated MS indicate an intensified monsoon, coinciding with a dominance of terrestrial OM. However, as monsoonal intensity declined after the Early Holocene, marine OM became more prevalent, likely linked to the formation of an estuary around ∼7.7 Ka. Despite a weakening monsoon around ∼4 Ka, MS values remained high, possibly due to increased aeolian input, which transported titanomagnetite, contributing to elevated MS in the sediment record. After ∼4 Ka, the sedimentary record indicates a greater influx of terrestrial OM, likely due to the formation of a barrier spit that limited marine influence. From this period onward, monsoonal intensity gradually increased, peaking around ∼1.1 Ka, coinciding with the Medieval Warm Period. Following ∼1.1 Ka, sedimentation rates rose, accompanied by low magnetic susceptibility (MS) and high sand content. This phase also shows an increase in both terrestrial and marine OM, along with higher CaCO₃ and illite concentrations, suggesting the impact of high-energy events, possibly cyclones. The intensification of cyclonic activity after ∼1.1 Ka may be associated with a weakening of El Niño–Southern Oscillation (ENSO) intensity during this period.