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Indian Ocean high-productivity event (10–8 Ma): Linked to global cooling or to the initiation of the Indian monsoons?

¹ Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721 302, W.B., India
² Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459-0139, USA, and Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, Connecticut 06520-8109, USA

Uplift of the Himalayas and Tibetan Plateau (ca. 10–8 Ma) has been said to be the main cause of the origin or intensification of the Indian monsoon system, because mountains modulate the land-sea thermal contrast. The intensification of the monsoons, in turn, is seen as the cause of major changes in fauna and flora on land (as a result of changing precipitation patterns) as well as in the Indian Ocean, where the monsoons drive increased upwelling and thus increased productivity. We argue that the interactions between the elevation of the Himalayas and Tibetan Plateau, the onset of the monsoons, and their effects on the Indian Ocean biota remain uncertain. The timing of these events (uplift, monsoons, and biotic change) is not well constrained. Neogene deep-sea benthic foraminiferal faunal and isotope records of the Ninetyeast Ridge combined with published data show that a major increase in biogenic productivity occurred at 10–8 Ma throughout the Indian Ocean, the equatorial Pacific, and southern Atlantic. We suggest that this Indian Ocean high-productivity event was not simply the result of monsoon-induced upwelling or nutrient delivery from the weathering of newly uplifted mountains, but may have been caused by strengthened wind regimes resulting from global cooling and the increase in volume of the Antarctic ice sheets.

Key Words: Indian monsoons • Indian Ocean productivity • benthic foraminifera • stable isotopes • Neogene • Ocean Drilling Program • Antarctic ice sheets

This article has been cited by other articles:

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