Monsoon upwelling effects on test size of some planktonic foraminiferal species from the Oman Margin, Arabian Sea

Variation in upwelling may be monitored using various micropaleontological indices, such as the relative abundance or accumulation rate of the planktonic foraminiferal species Globigerina bulloides or mass accumulation rate of planktonic foraminifera. We have analyzed the relationships between the upwelling history and mean test size variations in the planktonic foraminiferal species Globigerinoides ruber, Globigerinita glutinata, G. bulloides, and Neogloboquadrina dutertrei through the last 19,000 years in Ocean Drilling Program hole 723 A from the Oman Margin, Arabian Sea. The study reveals that these species were larger on average between 11 and 5 ka, which coincides with a period of strong upwelling. On the other hand, these species showed smaller mean test sizes during the last glacial period and late Holocene when upwelling was weaker. Mass accumulation rates of these species are linearly proportional to their mean test sizes, indicating that both mean size and productivity of individual species are related to the upwelling intensity. Therefore we propose that the size variations in G. ruber, G. glutinata, G. bulloides, and N. dutertrei can be used as an additional micropaleontological index of upwelling intensity in the Arabian Sea.