Abstract
Coretop sediment samples covering water depth from 247 to 1474 m in the Northwestern Indian Ocean were analyzed. 6 species ofUvigerina among 77 species and 11 species-complexes were found in all 26 samples. They areUvigerina auberiana d’Orbigny,Uvigerina hispida Schwager,Uvigerina peregrina Cushman,Uvigerina proboscidea Schwager,Uvigerina spinicostata Cushman and Jarvis, andUvigerina sp. Characteristics ofUvigerina are (1) high abundance due to rich food supply and less competitors; (2) low diversity because only those eurytopic / opportunistic forms can survive environment of low dissolved oxygen value; (3) various test shapes and ornamentations which are controlled by respiration or gas exchange of the cell; and (4) abundance ofUvigerina is well related with environmental factors such as water depth, oxygen content and productivity or food supply. TheseUvigerina species can be used as paleo-environmental proxy of low oxygen and rich organic matter supply related to high-surface productivity upwelling caused by Indian monsoons. Analysis ofUvigerina in Hole 723B of ODP Leg 117 showed that upwelling was intensified 9, 18, 50, 100, 200, 240, 340, 440, 480, 600 and 700 ka ago, which implies the increasing in global changes effect from the uplift of the Tibetan Plateau.
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