Lithogenic flux in the Japan Sea measured with sediment traps

Abstract

Spatial and temporal variations of particulate flux were observed by sediment trap experiments at three locations in the Japan Sea (western Japan Basin, eastern Japan Basin and Yamato Basin) during the period 1999–2002. Annual mean mass flux at 1 km depth was 455 mg/m 2/day in the western Japan Basin, 252 mg/m 2/day in the eastern Japan Basin and 147 mg/m 2/day in the Yamato Basin. In the Japan Sea, the regional differences in mass flux were much larger than the change of mass flux at different depths in each area. At 1 km depth in the Japan Sea, more than 60% of settling particles consisted of lithogenic aluminosilicates and biogenic opal. In order to determine indicators of the origin of aluminosilicates, concentrations of 28 elements in surface sediment at six areas of the Japan Sea were compared. Regional differences in concentration were seen in manganese (Mn), cobalt (Co) and rare earth elements (REEs). The La/Yb and Mn/Al ratios were used as indicators of the origin of aluminosilicates and the “freshness” of particles, respectively. These indicators suggested three sources of lithogenic material for the Japan Sea, (1) atmospheric input of “fresh” Asian loess (i.e. Kosa), (2) lateral transport of “old” Asian loess from the East China Sea by the Tsushima Warm Current (TWC), and (3) lateral transport from the Island arc of the Sakhalin and the Japan Islands. In the western Japan Basin, particles originating from the Asian Continent were observed during winter and spring, and it comprised 84% of annual lithogenic fluxes at 1 km depth in the western Japan Basin. These particles are considered to have been supplied directly to the surface of the Japan Sea by the input of KOSA, because these particles showed the signature of “fresh” particles. On the other hand, “old” Asian loess were found in the Yamato Basin, suggesting that the TWC transported Asian loess from the East China Sea to the southern margin of the Japan Sea. A sporadic current in the southern Japan Sea is considered to play a role in bringing loess particles to the interior of the Yamato Basin. In the eastern Japan Basin, it was calculated that 87% of annual lithogenic flux originated from the Island-arc. These particles likely were transported laterally from the Japanese Islands through the water column.