Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean |
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Authors: | Ajai K Rai M S Srinivasan |
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Institution: | (1) Department of Earth and Planetary Sciences, Allahabad University, 211 002 Allahabad, India;(2) Department of Geology, Banaras Hindu University, 221 005 Varanasi, India |
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Abstract: | An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the
northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among
the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence.
The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene
bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears
to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water
(AABW).
Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in
the relative abundance ofU. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic
circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment
accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and
cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by
low abundance ofU. proboscidea and more diverse and equitable benthic fauna.
The lower depth range for the occurrence ofBulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas.B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative
abundance ofStilostomella lepidula occurs close to the Early/Late Pleistocene boundary. |
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Keywords: | Pleistocene benthic foraminifera northern Indian Ocean oceanography |
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