The environmental magnetic record of palaeoenvironmental variations during the past 3100 years: A possible solar influence?

Abstract

Sediments from Pookot Lake (PK) in southern India have provided a record of local environmental changes and catchment processes during the past 3100cal.yearsB.P. Variations in the rock magnetic parameters (χlf, χfd, χARM and IRM's at different field strengths) of sediments from two AMS 14C-dated cores reflect climate-induced changes in the catchment of Pookot Lake. Assuming that rainfall is most likely the dominant driving mechanism behind the rock magnetic variations of PK sediments, the environmental history of the site has been reconstructed. Rock magnetic parameters exhibit significant variations during the past 3100years. The palaeoenvironmental history of the Pookot Lake region may be divided into three phases. During the first phase (~3100 to 2500cal.yearsB.P.), catchment erosion and detrital influx were high, indicating a strong monsoon. The second phase, which lasted from 2500 to 1000cal.yearsB.P., was characterised by low and steady rainfall, resulting in a low and uniform catchment erosion and detrital influx. Phase 2 was interspersed with brief intervals of strong monsoon and characterised by frequent drying up of the lake. During Phase 3 (~1000cal.yearsB.P. to the present), catchment erosion was high, indicating a shift to strong monsoonal conditions. It appears that monsoonal rainfall in the region is influenced by solar activity, with periods of high total solar irradiance being characterised by high rainfall and vice versa; it was relatively low during the Little Ice Age and high during the Medieval Warm Period. The magnetic susceptibility (χlf) data exhibit a number of periodicities which might have a solar origin. The χlf record exhibits similarities with other continental and marine palaeoclimatic records from the region, indicating that regional trends in the monsoon during the Late Holocene are broadly similar.