Geochemical characteristics of hadal sediment in the northern Yap Trench

Two sediment cores were retrieved in the hadal zone of the Yap Trench, and their concentrations of six major elements Mg, Al, Ca, Ti, Mn and Fe and nine trace elements Sr, Ba, Pb, V, Cr, Co, Ni, Cu and Zn were determined in inductively coupled plasma atomic emission spectrometry (ICP-AES). According to the vertical distribution profiles of the 15 elements, the correlation of their concentrations, the ratios of Ni/Co, V/Cr, Fe/Al, and Ti/Al, and morphological characteristics of the sediment samples, the implications of the depositional environment and the sediment provenance were analyzed. The results show that the ratio of Ni/Co in all depths of the two sediment cores were below 5, and the ratio of V/Cr were lower than 2, indicating that the depositional environment of the hadal zone in the trench was oxidative and might have inflow of the Antarctic bottom oxygen-rich water. The sediment samples on the eastern side of the trench were siliceous mud mainly composed of diatoms, radiolarian, and sponge needles from surface to deep layer. The vertical profile of the elements, the concentration of TOC and the fossil record indicated that the sediment sample from station Dive113 was well mixed from surface to bottom layer. Based on the correlation of concentrations of the elements, the morphological characteristics of the sediment, and the ratios of Fe/Al and Ti/Al, we inferred that the sediment in the hadal zone of the trench had terrestrial, volcanic, biological, and authigenic sources. Major source of the sediment in the eastern side of the trench were terrestrial; whereas the sediment in the western side of the trench received more volcaniclastic input.