Diffuse reflectance spectroscopy of a tropical southern Indian lake sediment core: A window to environmental change

Pookot is a small freshwater lake situated in the Sahyadri (the Western Ghat) of southern India. We used diffuse reflectance spectroscopy (DRS) and magnetic parameters to characterize the sediment components present in a core dating back to ~3000 cal. years B.P. DRS data indicate the presence of CaCO₃, goethite, hematite/goethite, clay minerals and organic carbon in the lake sediments. Based on the down-core variations of the four components, and the values of x_lf (low-field magnetic susceptibility indicative of detrital magnetite) and DRS parameter redness %, we reconstructed the paleoenvironmental history of the region surrounding the lake. The down-core variations of DRS-determined sediment composition and of data obtained from independent analyses (CaCO₃, S-ratio, clay % and C_org %) are similar. The pre-2500 cal. years B.P. period was characterized by a stronger monsoon compared to the Present. From 2500-1000 cal. years B.P., the monsoon was weak and steady, but interspersed with brief periods of strong monsoon, whereas from 1000 cal. years B.P. to the Present, rainfall exhibited a fluctuating trend. Rainfall was relatively high during the Medieval Warm Period (1000-600 cal. years B.P.), low during the Little Ice Age (600-350 cal. years B.P.) and from 350 cal. years B.P. to the Present, it exhibited an increasing trend.