East–West similarities and differences in the surface and deep northern Arabian Sea records during the past 21 Kyr

This study analyses monsoon proxy Globigerina bulloides from Ocean Drilling Program (ODP) Hole 723A (western Arabian Sea) and Hole ABP-25, 02 (northeastern Arabian Sea) as well as dominant benthic foraminifera, pteropods, total organic carbon (TOC), Inorganic Carbon (IC) and stable isotope values of benthic foraminifera from Hole ABP-25, 02 to understand summer monsoon-driven changes in the western and eastern Arabian Sea and their impacts on deep-sea ventilation during the past 21 Kyr. We have also combined published TOC data from ODP Hole 724B to understand if deep-sea conditions in the Arabian Sea were same throughout the region during the studied interval. The summer monsoon was generally weaker during cold intervals including the Last Glacial Maximum, the Younger Dryas and the Bond events of the Holocene. From 20 to 10 Kyr, the deep northeastern Arabian Sea was better oxygenated with less organic carbon supply except during 14–12.5 Kyr when TOC values increased, indicating a weaker summer monsoon and a weak oxygen minimum zone (OMZ). The TOC values and the abundance of the eutrophic benthic foraminiferal species Bulimina aculeata, Melonis barleeanum and Uvigerina peregrina increased during the late Holocene whereas well-oxygenated, low organic carbon benthic species Sphaeroidina bulloides as well as pteropods decreased, indicating an intense OMZ and an increased supply of refractory organic material to the Arabian Sea. It is important to note that although the surface response to monsoon variability was more or less similar in the western and northeastern Arabian Sea, the deep-sea conditions show a marked contrast in the two regions during the past 21 Kyr.

► This is the first attempt to analyze and compare results from the eastern and western Arabian Sea using foraminifera, stable isotopes, total organic carbon and calcium carbonate to understand if changes in the Indian monsoon were contemporaneous in both eastern and western parts of the Arabian Sea since the Last Glacial Maximum.
► Our study suggests that although the surface response to monsoon variability was more or less similar in the western and eastern Arabian Sea, the deep-sea conditions show a marked contrast in the two regions during the past 21 Kyr.
► We also identified D–O cycles, Younger Dryas, B-A interstadials and Last Glacial Maximum in the paleomonsoon record from the two regions.