States of element occurrence of sediments in the southern Okinawa Trough and its hydrothermal activity

To understand the element occurrence states of sediments in the southern Okinawa Trough and the influence of hydrothermal activity on the elemental composition of the sediments, the whole-sample and sequential extraction of core HOBAB4-S2 from the southern Okinawa Trough were analyzed and the occurrence state of Al, Ti, K, Fe, Mn, Cu, Zn, Pb, Co, Ni, and rare earth elements in the sediment core. The results show that the residual phase and carbonate phase are the important forms of elements in the sediments, and the typical clastic components Al, K, and Ti have a high proportion in the residual phase. The contents of elements in Fe-Mn oxide and organic bound phases are relatively low, but in the Fe-Mn oxide phase, the extraction rates and contents of metallic elements associated with hydrothermal activity in the cores are consistent with depth, and anomalously high values appear in four layers, indicating that the significant influence of hydrothermal activity on elemental compositions occurred in the corresponding period of the layer. The same trend can be seen in the total amount of rare earth elements. The chondrite-normalized rare earth element distribution patterns of the sediments show evidence of light rare earth element enrichment relative to heavy rare earth elements, with very small positive Ce anomalies and obvious negative Eu anomalies. The case is similar to the distribution pattern of the Fe-Mn oxide phase of the sediments in the South Atlantic Ocean, showing that it was less affected by hydrothermal activity, but affected by hydrothermal fluids, which is the result of rare earth elements absorption by Fe-Mn particles in seawater and hydrothermal fluids.