History of monsoon-induced upwelling and associated productivity based on planktic foraminiferal assemblage since the Last Glacial Maximum in the eastern Arabian Sea

Relative abundance of planktic foraminifera from Eastern Arabian Sea (EAS) deep-sea sediment Core SK291/GC17 suggests surface water palaeoceanographic shifts in the EAS during ~25–3.5 calibrated kilo years before present (cal ky BP). The chronology of the studied core is established based on fifteen AMS 14 C dates derived from a mixed planktic foraminiferal assemblage and using the ‘Bacon R’ statistical package. Between ~21 and 19 ky BP, the mixed-layer oligotrophic planktic foraminifera, such as Globigerinoides ruber and Trilobatus spp. show higher abundance, whereas eutrophic species like Globigerina bulloides and Globigerinita glutinata show a decreasing trend. Pulleniatina obliquiloculata , which thrives in the deeper segment of the thermocline, shows consistently low abundance in the same interval. These changes in planktic foraminiferal abundance imply that upwelling-related productivity declined due to a subdued Indian Summer Monsoon (ISM) during the Last Glacial Maximum. Following the LGM, a significant shift in monsoon-induced productivity occurs at ~11.0 kyr BP, overlapping with the onset of the early Holocene. The low relative abundances of oligotrophic planktic foraminifera and an increase in eutrophic species, including P. obliquiloculata , indicate an increasing influence of the strong ISM in the EAS during the early Holocene. Another significant change in planktic foraminifera is observed from ~6.0 to 3.5 kyr BP, where the abundance of G. bulloides and P. obliquiloculata drastically reduces in this interval, suggesting a weakening of ISM winds and thermocline deepening/or a possible shifting of the upwelling centre due to sea-level rise. A decrease in G. bulloides mean abundance—from ~11.3% in the early Holocene to ~6.9% in the mid-late Holocene—indicates a regional contrast. Correlation with other Arabian Sea datasets suggests that spatial hydrographic variability in the EAS is linked to changes in ISM intensity.