MARINE OXYGEN ISOTOPE RECORDS OF INDIAN MONSOON DURING THE HOLOCENE

Abstract

To understand the significance of δ18Osw in Indian monsoon in Indian Ocean, researchers have studied the sea surface temperatures (SSTs) and salinity from paired δ18O and Mg/Ca measurements in planktonic foraminifera namely Globigerinoids ruber from the Indian Ocean. From the already published δ18OSW datasets collected for this study, it was seen that in the Pre-Holocene period, the Indian Ocean seawater was generally enriched in δ18Osw compared to the Holocene time inferring more saline waters induced by weakened monsoon, suggesting a drier climate over the Indian Ocean region including the Arabian Sea and the Bay of Bengal. Depletion in δ18Osw was observed during the transition from Last Glacial period to Early Holocene which suggests freshening due to massive rainfall and river discharges resulting from the intensification of Indian monsoon, also causing a more humid climate. Within this period, it was possible to observe in some records that there was a stronger monsoon during Bolling-Allerod (BA; 14.7-12.8 ka) while weaker during the Younger Dryas (12.8-11.7 ka) period. δ18Osw values during the Holocene Period are found to be inconsistently variable even within the same basin/region suggesting the complex spatial and temporal heterogeneity of the monsoon variations. However, REDFIT spectral and wavelet analyses, using PAST program, performed on the datasets have yielded periodicities mostly linked with thermohaline circulation and solar insolation cycles, suggesting that the Indian monsoon variability is heavily influenced by the solar and North Atlantic Deep Water circulation interplaying at different time periods and different timescales.