Browsing by Author "S.K. Bharti"

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Benthic foraminiferal diversity response to the climate induced changes in the eastern Arabian Sea oxygen minimum zone during the last 30 ka BP
(Elsevier Ltd, 2015) A.D. Singh; A.K. Rai; K. Verma; S. Das; S.K. Bharti
A high resolution record of deep sea benthic foraminiferal diversity variations in the eastern Arabian Sea for the last 30kaBP was obtained from two sediment cores (SK17 and MD131) retrieved from the present day Oxygen Minimum Zone (OMZ) in the Indian margin off Goa. The benthic foraminiferal diversity is represented in terms of Sander's rarefaction number (S100), Shannon Wiener Index [H(S)], Equitability (E') and Alpha Index (α). Records of diversity indices exhibit millennial scale changes during the late glacial and deglacial periods, corresponding to the Northern Hemisphere climatic events. We compared the faunal diversity with proxy records of primary productivity (Corg %) and bottom water oxygen (low-O2 taxa %). We suggest that benthic foraminiferal diversity in the eastern Arabian Sea OMZ is largely controlled by the primary productivity induced organic carbon flux and strength of bottom water oxygenation. The less diverse fauna along with increased percentages of Corg and low- O2 taxa during the last glacial maximum (18-22.5kaBP) suggest eutrophic and oxygen-poor benthic environment, attributed mainly to a strong OMZ associated with intense winter monsoon wind induced productivity and a weak deep ocean circulation. The intervals of distinct increase in diversity closely correspond with North Atlantic cold Heinrich events, when eastern Arabian Sea experienced significant declines in monsoon driven productivity and better deep sea ventilation due to enhanced inflow of Antarctic Intermediate Water (AAIW). © 2014 Elsevier Ltd and INQUA.
Late Glacial–Holocene record of benthic foraminiferal morphogroups from the eastern Arabian Sea OMZ: Paleoenvironmental implications
(Springer, 2018) K. Verma; S.K. Bharti; A.D. Singh
The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ) at mid-water depths. The Indian margin where the OMZ impinges provides sediment records ideal to study past changes in the OMZ intensity and its vertical extent in response to the changes of monsoon-driven primary productivity and intermediate water ventilation. Benthic foraminifera, depending upon their adaptation capabilities to variation in sea floor environment and microhabitat preferences, develop various functional morphologies that can be potentially used in paleoenvironmental reconstruction. In this study, we analysed benthic foraminiferal morphogroups in assemblage records of the last 30 ka in a sediment core collected from the lower OMZ of the Indian margin (off Goa). In total, nine morphogroups within two broadly classified epifaunal and infaunal microhabitat categories are identified. The abundance of morphogroups varies significantly during the late Glacial, Deglacial and Holocene. It appears that monsoon wind driven organic matter flux, and water column ventilation governing the OMZ intensity and sea-bottom oxygen condition, have profound influence on structuring the benthic foraminiferal morphogroups. We found a few morphogroups showing major changes in their abundances during the periods corresponding to the northern hemisphere climatic events. Benthic foraminifera with planoconvex tests are abundant during the cold Heinrich events, when the sea bottom was oxygenated due to a better ventilated, weak OMZ; whereas, those having tapered/cylindrical tests dominate during the last glacial maximum and the Holocene between 5 and 8 ka BP, when the OMZ was intensified and poorly ventilated, leading to oxygen-depleted benthic environment. Characteristically, increased abundance of taxa with milioline tests during the Heinrich 1 further suggests enhanced ventilation attributed probably to the influence of oxygen-rich Antarctic Intermediate Water (AAIW). © 2018, Indian Academy of Sciences.
Synthesis, anti-bacterial and anti-fungal activities of some novel Schiff bases containing 2,4-disubstituted thiazole ring
(2010) S.K. Bharti; G. Nath; R. Tilak; S.K. Singh
A series of arylidene-2-(4-(4-methoxy/bromophenyl) thiazol-2-yl) hydrazines (4a-z) and 1-(4-(4-methoxy/bromophenyl) thiazol-2-yl)-2-cyclohexylidene/cyclopentylidene hydrazines (5a-b/6a-b) were synthesized, characterized and screened for their antimicrobial activities. The structures of synthesized compounds were established by spectroscopic (FT-IR, 1H NMR, 13C NMR, Mass) and elemental analyses. Both the anti-bacterial and anti-fungal activities with MIC values of compounds were evaluated. The results of anti-bacterial screening reveal that among all the compounds screened eight compounds showed moderate to good anti-bacterial activity while ten of the newly synthesized compounds displayed good to excellent anti-fungal activity. Among the tested compounds, the most effective compounds with MIC value in the range of 6.25-25 μg/ml are 4a, 4n, 4z, 5a, 5b, 6a and 6b against three fungal strains viz. Candida albicans, Cryptococcus neoformans and Aspergillus flavus. © 2009 Elsevier Masson SAS. All rights reserved.