Quantitative analysis of the late Cenozoic planktonic foraminiferal record from western Arabian Sea Site 722 revealed long term trends in the history of oceanography and climate. The modern western Arabian Sea surface waters are highly influenced by the monsoonal wind system. Summer upwelling, a result of southwestern winds, occurs along the coast of Somalia which produces distinct foraminiferal assemblages which are dominated by G. bulloides d'Orbigny. Consequently, variations in the distribution record of G. bulloides through time monitor the upwelling history associated with monsoonal activities. G. bulloides was a minor constituent of the foraminiferal fauna from the bottom of the hole (-14.5 Ma) until about 8.6 Ma ago. Then a rapid shift occurred toward higher values, up to 53% at 7.4 Ma. We interpret this rapid increase as a major step in the evolution of the monsoonal history. It is either the establishment of the system or at least a strong intensification of the monsoonal winds. At 5.5 Ma a significant drop of the G. bulloides relative abundance occurred which may indicate less upwelling, or alternatively other biota may have been favored in this period. From 5.0 Ma to Recent the G. bulloides record indicates that upwelling has occurred with minor fluctuations.

Oxygen and carbon isotopes in the tests of Globigerina bulloides and Neogloboquadrina dutertrei from the Indian Ocean provide indicators for the intensity of upwelling and upwelling-related high productivity. The difference in δ 18 O between the surface dwelling G. bulloides and the thermocline dwelling N. dutertrei reflects the mixing of the water column during upwelling situations, and hence the intensity of upwelling. The difference in δ 13 C isotope distribution between the two species is smallest within upwelling areas, indicating that upwelling induced the high productivity. The two parameters are applied to Hole 728A (ODP 117), in the Arabian Sea on the continental margin of Oman. Both upwelling indicators show that from isotopic stage 2 till stage 11 upwelling was stronger during interglacial periods, and that upwelling intensified down core for the same period. In older sediments, stages 12 and 13, the signal from the upwelling indicators is reversed, showing stronger upwelling during glacials.

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