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. (June 2017)

• Record Type: Journal Article
• Authors: Pattan, J.N.; Parthiban, G.; Garg, Anita; Moraes, N.R. Cesar
• Is Part Of: Marine and petroleum geology. Volume 84(2017)
• Page Start: 243
• Page End: 256
• Publication Date: 2017-06
• Subjects: Eastern arabian sea sediments -- Oxygen minimum zone -- Redox-sensitive elements -- Non-euxinic -- Reducing conditions -- Last deglaciation -- Heinrich events (H1, H2 -- H3) -- Ventilation -- Lanthanide fractionation; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2017.03.034
• Languages: English
• ISSNs: 0264-8172

Abstract

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. Highlights: Sediments from EAS are of non-euxinic environments where hydrogen sulfide is restricted to sediment pore-waters. Productivity may not have control on the development of reducing conditions. Intense reducing conditions during LDG & HEs could be due to ventilation of the oxygen depleted bottom waters from SAIW-AAIW. There is distinct lanthanide fractionation [La(n)/Yb(n)] in Holocene, Younger dryas, Bǿlling-Allerǿd and last deglaciation events.