Analysis of the redox environment and genesis of surface sediment in the northeast Indian Ocean at the Ninety-East Ridge

The Ninety-East Ridge (NER) is located in the semioceanic to oceanic region of the southern Bengal Fan in the Northeast Indian Ocean. The sedimentary environment, ocean currents, and scientific issues related to climate change have always been the focus of scientists. To well understand the sedimentary environment of the sea area, we studied the modern sedimentary environment of the NER by analyzing the redox-sensitive trace elements (RSEs) and biomarkers in the surface sediments of the northern region and both sides of the NER and the mechanism of their formation. The ratios of Mo/U (average 2.22), (Cu+Mo)/Zn (average 1.51), and the results of δCe<1 of the sediment samples, all indicate the reduction of the sedimentary environment. In addition, the ratio of pristane (Pr) to phytane (Ph), C30 diahopane to C30 hopane, and diasterane to sterane were low in all samples, on average of 1.03, 0.9, and 0.33, respectively. The analysis of RSE and biomarker data revealed that the sedimentary environment on seabed of the NER is generally a rare low-oxygen reduction environment. Through the analysis of sediment characteristics, material sources, and ocean currents, we preliminarily constructed a genetic model for the low-oxygen reducing environment of surface sediments in the NER. We believe that the low-oxygen reduction environment of surface sediment in the NER could be influenced by multiple factors, such as terrestrial input of materials, productivity at sea surface, and sediment particle size.