Seasonal Changes in the Arabian Sea for Last 19 ka: Evidence From δ18O Values of Individual Planktonic Foraminifera Shells

Oxygen and carbon isotope analyses of individual Globigerinoides sacculifer and Neogloboquadrina dutertrei were carried from the ODP Site 723A in the Arabian Sea to unravel the seasonal changes for the last 19 ka. G. Sacculifer is a surface dweller and N. Dutertrei has a deeper depth habitat (100m) and thus it is expected that the range in d18O changes of an individual shells of two species provide seasonal changes in surface and subsurface water through time. δ¹⁸O values of individual G. Sacculifer and N. Dutertrei ranges from 0.54 to 2.09 per mil and from 0.38 to 1.37 per mil respectively. Both species have shown maximum inter-shell δ¹⁸O variability and high standard deviation from 16 to 9 ka suggesting strong seasonal δ¹⁸O changes in surface and subsurface water in the Arabian Sea. Inter-shell δ¹⁸O variations were greater in G. Sacculifer than that of N. Dutertrei, which suggest that seasonal variability is more in the surface water compared to the subsurface water. From 19 to 16 ka and 6 to 1 ka the δ¹⁸O variations in both species were low, which reflects less seasonality during this time. Globigerina bulloides, Pulleniatina obliquiloculata and Uvigerina excellens show sharp depleted δ¹⁸O excursion around 9 ka, ascribed to the distribution of melt water flux of Termination IB to this region. A synchronous δ¹⁸O shift in surface, subsurface and bottom water living foraminifera around 9 ka reveals a rapid transfer of Termination IB signal through the vertical circulation of the Arabian Sea in response to peak monsoon intensity.