Palaeoredox reconstruction in the eastern Arabian Sea since the late Miocene: Insights from trace elements and stable isotopes of molybdenum (δ98/95Mo) and tungsten (δ186/184W) at IODP Site U1457 of Laxmi Basin

Abstract

The present study investigates the oxygenation history of the northeastern Arabian Sea since the late Miocene using redox sensitive elemental and metal stable isotopic signatures in the deep-sea sediments. To achieve this, the sediment core samples collected at Site U1457 (67°55.80′E, 17°9.95′N, water depth 3534 m) of Laxmi Basin in the northeastern Arabian Sea during the International Ocean Discovery Program (IODP) Expedition 355 were analysed for a suite of elemental (Mo, W, U, V, Ba, Cd and P) and stable molybdenum (Mo) isotope (δ 98/95 Mo relative to NIST SRM 3134 lot No. 130418) as well as stable tungsten (W) isotope (δ 186/184 W relative to NIST SRM 3163 lot No. 080331) composition. Sedimentary δ 98/95 Mo values (−0.70‰ to +1.18‰) at IODP Site U1457 in the northeastern Arabian Sea indicated partial authigenic Mo component. In contrast, the sedimentary δ 186/184 W values (−0.02‰ to +0.21‰) were in the range similar to that of lithogenous material suggesting dominance of detrital composition. The study reveals that the water column in the eastern Arabian Sea was oxic during the late Miocene and Pliocene while oxic to suboxic condition prevailed during the Pleistocene. The study also explores that under oxic to suboxic condition with limited particle shuttling, the W isotopes do not undergo significant fractionation, and their isotope ratios reflect the detrital source signature. This study reports the first results on isotopic compositions of Mo and W in sediments of the northeastern Arabian Sea since the late Miocene to investigate the palaeoredox conditions on a million-year time scale. • First results of δ 98/95 Mo and δ 186/184 W in the late Miocene Arabian Sea sediments. • Oxic condition during late Miocene & Pliocene, and suboxic during Pleistocene. • δ 98/95 Mo values (−0.70 to +1.18‰) exhibits partial authigenic component. • δ 186/184 W values (−0.02 to +0.21‰) exhibit dominant detrital control. • Under oxic setting with limited particle shuttling, tungsten isotopes do not fractionate.