REEs and Mn/Al ratio of settling particles: horizontal transport of particulate material in the northern Japan Trench

Time-series sediment traps were arrayed during July of 1996 and June of 1997 in the northern Japan Trench (40°29′N, 144°31′E; water depth 7.6 km). Traps were moored at 1.1-, 4.3- and 7.2-km depths. Concentrations of Al, Ca, Mn, Si and REEs of settling particles were measured. In this region, the mass flux was controlled by opal and clay particles. Opal fluxes steeply increased at 4.3-km depth and clay fluxes increased continuously with depth. To determine the origin of aluminosilicates, the La/Yb ratio of settling particles was applied. Significant seasonal variation of the La/Yb ratio was observed only at 1.1 km. This variation suggests that the origin of aluminosilicates would change seasonally at 1.1 km. The La/Yb ratios of settling particles were 8.24–9.84 at both of 4.3 and 7.2 km, which means that about 90% of the particles originated from the Japan Islands. At 7.2 km, the Mn/Al ratios ranged from 3.0 to 4.8. These values were higher than those of particles collected in the summer at 4.3 km. It is revealed that particles have high Mn/Al ratio load between 4.3 and 7.2 km throughout the year. Loading of high Mn/Al particles is probably caused by the removal of particles from the continental slope to the deep ocean. We named the remobilization of particles “shelf conveyor”. At 7.2 km, the annual organic carbon flux carried by the shelf conveyor was estimated to be 11.5 g C/m2/year. It is shown that the shelf conveyor is important for the transport of organic carbon to the deep ocean in the northern Japan Trench.