South Asian monsoon climate change and radiocarbon in the Arabian Sea during early and middle Holocene

Abstract

The 14C ages of planktonic foraminifers Globigerinoides sacculifer bracketing the Younger Dryas in a δ18O record of Globigerinoides ruber from a laminated sediment core on the Pakistani continental margin suggest that surface reservoir ages in the Arabian Sea were in excess of 1000 years during the deglaciation. A least squares error fit of a detailed 14C chronology to the (atmospheric) tree ring record gave variable early Holocene reservoir ages between 780 and 1120 years, well above the prebomb value of 640 years. Mid‐Holocene reservoir ages are less well constrained but were probably closer to the prebomb value. The method used to fit individual core sections to the tree ring record was designed to require only a rough a priori estimate of the time spans, which in the core presented here were taken from each section's range of 14C ages. A significant 220‐year quasi‐oscillation was present in the δ18O record during the early Holocene but not thereafter. This frequency and amplitude pattern resembles an early Holocene 207‐ to 227‐year oscillation previously observed in the atmospheric 14C record, which is generally interpreted as reflecting solar irradiance variability. An early Holocene climate event at 8150–8400 calendar years B.P. observed elsewhere within the Asian‐East African monsoon system was again found in our record, suggesting a reduction in precipitation over NW India and Pakistan.