Preliminary study on source and sedimentary environment in the Mariana Trench

Hadal trenches (＞6000 m) represent the deepest parts on the Earth’s surface in unique topography and sedimentary processes, and are considered the final sink of sediments. The strontium (Sr) and neodymium (Nd) isotope compositions and clay-mineral assemblages of the detrital fraction of sediments in the southern Mariana Trench, as well as the concentrations of major and trace elements of bulk sediments at water depths of 5800～10954 m were analyzed to trace the sediment provenance and distinguish the changes in the sedimentary redox conditions. The whole Core MBR05 and the interval of 8～20 cm of Core MBR06 are dominated by valve fragments of the giant diatom Ethmodiscus rex, forming laminated diatom mats (LDMs). Both Sr-Nd isotope compositions and clay-mineral assemblages of the detrital fraction reflect a two-component mixing pattern consisting of Luzon Arc volcanic clastics and Asian aeolian dusts, showing greater aeolian dust contribution on the LDMs, indicating that the bloom of E. rex may be related to Asian aeolian dust input. Meanwhile, the rare earth elements (REEs) distribution pattern and weak or absent Ce anomalies in the LDM point to suboxic conditions during the LGM formation, while the non-LDM samples exhibit vey low to zero enrichment of redox-sensitive elements and negative Ce anomalies, indicating the deposition under oxic bottom-water conditions. It is inferred that changes in sedimentary environments is associated with the enhanced mineralization of organic matter caused by the rapid deposition of E. rex giant diatom. The bloom of E. rex giant diatom may be caused by the enhanced input of wind dust during the Last Glacial Maximum. This study is of relevance for understanding the heterogeneity of sediment composition in different water depths of hadal trench and its impact on the distribution, ecology, and activity intensity of benthic microorganisms in the trench areas.