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Intense reducing conditions during the last deglaciation and Heinrich events (H1, H2, H3) in sediments from the oxygen minimum zone off Goa,eastern Arabian Sea
Institution:1. CSIR, National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India;2. CSIR, National Institute of Oceanography, Dona Paula, Goa 403004, India;3. Department of Geological Oceanography, Xiamen University, Xiamen, China;4. High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan, ROC;5. Center for Marine Environmental Sciences (MARUM), Bremen, Germany;1. Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, 721302, India;2. School of Earth, Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, 751007, India;3. Department of Applied Geology, Indian Institute of Technology (Indian School of Mines) Dhanbad, 826004, India;1. Department of Earth Science, University of CA, Santa Barbara 93106, USA;2. Museum für Naturkunde, Leibniz-Institut für Biodiversity and Evolutionsbiologie, Invalidenstrasse 43, 10115 Berlin, Germany;3. Institute of Geoscience, Christian-Albrechts Universitaet, Kiel, Germany
Abstract:Two sediment cores, ABP-32/GC-01R and ABP-32/GC-03 were collected at a water depth of 642 m and 1086 m off Goa from the present day Oxygen Minimum Zone (OMZ) of eastern Arabian Sea (EAS) cover time span of last 18 ka and 32 ka respectively were analysed for multi-proxy redox-sensitive elements to understand the variation in the redox conditions and factors responsible for its development.Redox-sensitive elements concentration and their normalized ratios (Mn/Al, U/Th, Mo/Al and Ce/Ce*) suggest that sediment core ABP-32/GC-01R is under more reducing conditions due to its location within the centre of OMZ compared to core ABP-32/GC-03 which is at the base of OMZ. Sediments from the EAS are of non-euxinic environments where dissolved sulfide is present but restricted to the sediment pore-waters. Lack of significant correlation (r=< 0.1) of organic carbon with U and Mo suggest that productivity may not have control on the development of reducing conditions. The lowest Mn/Al ratio, strong negative Ce/Ce* anomaly and remarkable enrichment of U/Th and Mo/Al ratios during the last deglaciation, and Heinrich events (H1, H2, H3) indicate intense reducing conditions probably due to poor ventilation by oxygen depleted bottom waters from Subantarctic Mode Waters (SAMW) - Antarctic Intermediate waters (AAIW). There is a distinct lathanide fractionation in the sediment cores where, La(n)/Yb(n) ratio is <1, ≈1 and >1 during the last 10 ka (Holocene), 14–10 ka (includes-Younger Dryas and Bǿlling-Allerǿd), 18–14 ka (last deglaciation) and Heinrich events suggesting less reducing, terrigenous dominated and intense reducing condition respectively.
Keywords:Eastern arabian sea sediments  Oxygen minimum zone  Redox-sensitive elements  Non-euxinic  Reducing conditions  Last deglaciation  Heinrich events (H1  H2  H3)  Ventilation  Lanthanide fractionation
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