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 micropaleontolog ical indices, such as the relative abundance or accumulation rate of t he planktonic foraminiferal species Globigerina bulloides or mass accu mulation rate of planktonic foraminifera. We have analyzed the relatio nships between the upwelling history and mean test size variations in the planktonic foraminiferal species Globigerinoides ruber, Globigerin ita glutinata, G, bulloides, and Neogloboquadrina dutertrei through th e last 19,000 years in Ocean Drilling Program hole 723A 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 stron g 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 pro portional to their mean test sizes, indicating that both mean size and productivity of individual species are related to the upwelling inten sity. Therefore we propose that the size variations in G. ruber, G, gl utinata, G. bulloides, and N, dutertrei can be used as an additional m icropaleontological index of upwelling intensity in the Arabian Sea.