Vertical-change index for the particulate transport of chemical and isotopic components in the ocean.

Abstract

Data obtained by recent sediment-trap experiments were compiled to discuss the mechanism for the removal of trace metals from the ocean. The vertical-change index (IM), or the rate constants of first order change with depth, were estimated. The results and the IM values in km-' shown in parentheses are as follows. The total particulate matter flux(-0.05) is nearly constant with depth due to rapid sinking of its major components of tests of biogenic silica(-0.03) and calcium carbonate( 0.05) to the bottom. The organic fraction(-0.27) of settling particles reduces with depth together with components contain ed in soft tissue of organisms such as Cd(-0.23). The fluxes of the lithophile components of Al(+ 0 .22), Fe(+0.17), and 232Th(+0.19) largely increase with depth due to the lateral transport of particles from the continental margin. The large index of Mn(+0.47) is due to the early diagenetic process in the sur face sediment in addition to the simple resuspension. The flux of short-lived 234Th(-0 .01) is saturated, but that of 228Th(-0.14) having no substantial source in the pelagic ocean is the smallest among radiogenic nuclides in seawater. The largest index is found for the long-lived radionuclides such as 230Th(+0 .50) and 231Pa(+0.56). The effect of radioactive decay is somewhat reflected in the indices of 210Pb(+0 .41) and 210Po(+0.43). These results support the train-passengers model proposed by Tsunogai (1987) for the behavior of chemical elements in the ocean.

Copper and nickel in settling particle collected with sediment trap in the western North Pacific.

“…Regenerated Mn from the anoxic coastal sediment is oxidized to the insoluble oxide in the oxic bot tom water, and is transported to the open ocean (Kato et al, 1995). Mn/Al ratios of settling par ticles in intermediate and deep waters were larger than that in surface water due to the association of Mn onto aluminosilicate materials (Tsunogai et al, 1990). These facts show that lithogenic and manganese oxide particles are laterally and verti cally transported from shallow coastal regions to the deep open ocean.…”

“…However, there was a slight minimum in the Cu/ Al ratio of the settling particle around 2 km depth in the open ocean (Tsunogai et al, 1990). These facts suggest that Cu is regenerated from settling particles in the upper 2 km depth water column, and scavenged from the seawater in the deep wa ter.…”

“…These facts suggest that Cu is regenerated from settling particles in the upper 2 km depth water column, and scavenged from the seawater in the deep wa ter. On the other hand, the Ni/Al ratio of settling particles decreased with depth, due to the regen eration of Ni in the deep water (Tsunogai et al, 1990).…”

“…Masuzawa et al (1989) reported a fourth category of biogenic-scavenged elements in which the ele ment concentration remained almost constant or increased a little with depth and the element to Al ratio decreased with depth. Tsunogai et al (1990) and Noriki and Tsunogai (1992) revealed vertical and spatial variations of concentrations and fluxes of some trace metals in the Pacific Ocean.…”

Sedimentation of natural radionuclides on the seabed across the northern Japan Trench.

“…Based on the sediment trap data, Tsunogai et al (1990a) have defined the vertical change index, which is the first order increase rate of particulate flux with increasing depth in the water column. The vertical change indices predict that the par ticulate fluxes of 210Pb and 230Th increase by factors of 2.3 and 2.7, respectively, during sinking through 2 km water column in a usual oceanic basin.…”