A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Rai, Ajai Kumar
- Influence of Antarctic Bottom Water (AABW) and Monsoonal Activity in the Central Indian Ocean over Past 5 million Years: Benthic . Foraminiferal Record at DSDP Site 238
Authors
1 Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad 211 002, IN
2 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 2 (2007), Pagination: 222-232Abstract
This study quantitatively analyzes Pliocene-Pleistocene benthic foraminifera from DSDP Site 238 in the central Indian Ocean. A Q-mode factor analysis of 28 most abundant species defines three significant faunal assembiages reflecting different environmental characteristics. The Cibicides wuellerstorfi-Oridorsalis umbonatus assemblage (Factor I ) represents well oxygenatcd bottom watcrs with active currents and intermediate to low supply of organic matter. The Uvigerina proboscidea assemblage (Factor 2) indicates a continuously high flux of organic matters to the sea floor in response to increased surface water productivity. The Nuttallides umbonifera assemblage (Factor 3) is associated with Antarctic Bottom Water (AABW) and reflects cold, oligotrophic, increased carbonate corrosiveness and high oxygen concentration.
In most of the past 5 Ma (i.e. 5-4.2 Ma, 2.8-1.8 Ma and 1.2 Ma to Recent) the dominant occurrences of Cibicides wuellerstorfi-Oridorsalis umbonatus assemblage represent active bottom water currents with more ventilation and relatively low trophic levels reflecting the influence of NADW at abyssal depths in the central Indian Ocean. The early Late Pliocene (c. 3.6-2.8 Ma) and Early Pleistocene (c. 1.8-1.2 Ma) are two significant intervals of prominent faunal change, which indicate entirely different deep-sea conditions. The prominent occurrence of Nuttallides umbonifera assemblage during 3.6-2.8 Ma reflects cold, corrosive and well-oxygenated bottom waters possibly in response Lo increased flow of AABW towards the central Indian Ocean at abyssal depths. The Early Plcistocene (c. 1.8-1.2 Ma) is characterized by distinct occurrence of the Uvigerina proboscidea assemblage reflecting higher surface produc6vity. The widespread, intensified monsoon system during Early Pleistocene causes increased upwelling and higher surface productivity, which also enhanced the supply of organic carbon to the ocean floor.Keywords
Benthic foraminiferal record, Antarctic Bottom Water, Monsoonal activity, DSDP Site 238, Central Indian Ocean.- Paleoceanographic Significance of Changes in Miocene Deep-Sea Benthic foraminiferal Diversity on the Wombat Plateau, Eastern Indian Ocean
Authors
1 Department of Earth and Planetary Sciences, Nehru Science Center, University of Allahabad, Allahabad - 21 1 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 70, No 5 (2007), Pagination: 837-845Abstract
In the present work, late Oligocene to latest Miocene (-28 6 5 Ma) Deep-Sea benthic foraminifeia(over 149 μm size fraction) were studied from ODP sites 760A and 761B on Wombat Plateau in the eastern lndian Ocean to understand the faunal diversity pattern. The samples were commonly examined at about 0 75m intelva at both the sites. The bentic foraminifeia species diversity was measured in terms of Shannon-Weaver Index [H(S)] Hurlbe lts Diversity Index (S100), Alpha Index (α) and Equltability (Ε), all of which show almost similar trends with few exceptions. The Miocene section at both the sites show marked fluctuations in the values of various diversity indices of Beep-Sea benthic foraminiteral assemblages. Distinctly low vatues of diversity indices across the Oligocene-Miocene transition correspond well with the higher values of benthic δ180 and δ13c reflecting relatively cold, nutrient depleted, young bottom waters which possibly indicate the influence of Antarctic Circumpolar Current (ACC) in this region Faunal diversity reached to maximum values at both the sites near the end of Miocene climatic optimum at about 15 Ma reflecting warm bottom wateis with low trophic levels. The low bottom water temperature, expansion of East Antarctic Ice Sheet (EATS) and possibly higher trophic level appear to be responsible for less diverse fauna during the middle Miocene 1 e -14Ma and younger. Further, decrease in the values of diversity during latest Miocene (-7 5-6 5 Ma) is suggested to be due to increased surface water productivity in response to the intensified monsoonal activity in the eastern Indian Ocean.Keywords
ODP, Miocene, Benthic Foraminifera, Diversity, Paleoceanography, Wombat Plateau Eastern Indian Ocean.- Pliocene Indonesian Throughflow Change and Planktic Foraminiferal Diversity in the Eastern Subtropical Indian Ocean
Authors
1 Department of Earth and Planetary Sciences, University of Allahabad, Allahabad 211 002, IN
2 Department of Earth Sciences, Indian Institute of Technology, Mumbai 400 076, IN
Source
Current Science, Vol 113, No 05 (2017), Pagination: 955-959Abstract
The opening and closing of seaways due to plate tectonic movement strongly influenced the past oceanic circulation patterns which have their influence on the past climate and faunal record. The considerable restructuring of one such seaway, Indonesian seaway, took place during Pliocene (4–3 Ma). This would have changed the source of Indonesian Throughflow (ITF)from warm and saline south Pacific waters to thenorth Pacific cool and relatively fresh waters. In the present study, three indices of diversity (Shannon-Wiener Index; H(S), equitability; E' and alpha index;α) at ODP sites 762B and 763A in the eastern subtropicalIndian Ocean are calculated to better understand the role of ITF on Pliocene surface hydrography and planktic foraminiferal diversity. A major interval of early Pliocene demonstrates more diverse fauna and low abundance of fertile taxa along with increased planktic Mg/Ca ratios. Strong influence of warm ITF waters due to broad and open seaway until the end of early Pliocene, increased the sea surface temperature(SST) and depth of thermocline in the Leeuwin current area of eastern subtropical Indian Ocean. This would have been responsible for more vertical niche partitioning of surface water and thus, higher planktic foraminiferal diversity. The significant decline in faunal diversity between critical interval of ~3.5 and 3 Ma (beginning of Late Pliocene) is suggested to be the response of fall in SST and increase in surface water productivity possibly due to relatively less influence of ITF waters in the eastern Indian Ocean as a consequence of significant constriction of Indonesian Seaway.Keywords
Diversity, Indian Ocean, Indonesian Throughflow, Pliocene, Planktic Foraminifera.References
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