Elemental distribution of surface sediments around Oki Trough including adjacent terrestrial area: Strong impact of Japan Sea Proper Water on silty and clayey sediments

Abstract

Four-hundred sixty marine sediment samples were collected in the western Sea of Japan and analyzed for 53 elements for a marine geochemical mapping project associated with a nationwide terrestrial geochemical map. Grain size and chemical compositions of marine sediments vary significantly with location of origin (shelf, marginal terrace, slope, or basin). Sandy sediments distributed on the shelf do not likely reflect the geochemical features of river sediments, which are the dominant source of sands in the shelf. Most of the shelf sediments sampled are composed of relict sediments (little contribution of stream sediments) formed between the regression age and the transgression age because they contain a large amount of quartz coated by iron hydroxide and highly enriched in As. The marginal terrace is covered by modern silty sediments that are selectively deposited at the water mass boundary between Tsushima Current (surface water) and Japan Sea Proper Water (deep water). Silty sediments in the western portion of marginal terrace are highly enriched in Nb, rare earth elements, Ta, and Th, which are supplied from Quaternary alkaline volcanic rocks by a denudation process. They are carried eastward by as much as 200 km by oceanic currents. In contrast, the eastern marginal terrace is covered by silty sediments that are highly abundant in Cu, Zn, and Hg, which is attributed to biogenic remains in sediments (organic complex formation). Clayey sediments are widely distributed in the Oki Trough and basin where a hemipelagic environment and highly oxic conditions are found because of the influence of Japan Sea Proper Water. A thin Mn oxide layer in the uppermost 0-4 cm and extreme enrichment of V, Co, Ni, Mo, Sb, and Pb would be caused by an early diagenetic process. Thus, the spatial distribution patterns of elements in marine sediments in the study area are strongly controlled by their depositional environments.

Statistical Analysis of the Spatial Distribution of Multi-Elements in an Island Arc Region: Complicating Factors and Transfer by Water Currents

“…Their spatial distribution can be easily discriminated because they are extremely enriched in silty marine sediments derived from ultramafic rocks in the adjacent terrestrial area. Ohta et al [42] tried to visualize the particle transfer process using the spatial distribution patterns of the other elements. However, many elements are enriched in finer sediments due to the particle size effect, and so in order to highlight the particle transfer process, it is useful to detect outliers using the relationships between elemental concentrations and median diameter or mud content [42].…”

“…The concentrations of all six elements correlate positively and linearly with Cs, and it can be assumed that those samples plotting outside the linear trends are subject to influencing factors in addition to the particle size effect. Ohta et al [42] detected outliers from a scatter diagram according to their best judgment. In this study, the outliers appearing in the scatter diagram are objectively obtained using Mahalanobis' generalized distance (D) [43].…”

“…Silt and clay deposited in deep Pacific basins are typically enriched in MnO, V, Ni, Co, Mo, Sb, Pb, and Bi, as a result of early diagenetic processes in an oxic environment [7,42]. In contrast, Cu, Sb, Cd, Hg, and U are enriched in deep-sea sediments during early diagenesis under anoxic conditions, as they are immobile in reducing waters [52].…”

Influence of different sedimentary environments on multi-elemental marine geochemical maps of the Pacific Ocean and Sea of Japan, Tohoku region

“…Enrichment of As in sandy sediments collected from the southern part of Sendai Bay is also explained by this mechanism, because Nishimura and Saito (2016) found quartz coated with Fe hydroxides (stained quartz) in the sandy sediments of this region. Arsenic is supplied to coastal seas mainly in the dissolved phase through rivers and is precipitated in coastal sediments (Ohta et al, 2015). There are more As-enriched sandy sediments in the Sea of Japan because many major rivers flow into this sea ( Table 1).…”

Evaluation of straightforward and rapid multi-element analyses of stream sediments for geochemical mapping in the remote islands of Japan — Seto Inland Sea region —

“…Although the areas of remote islands are small, they provide important geochemical data that are not available in the main land. For instance, Oki and Iki Islands are covered with alkaline volcanic rocks, which are narrowly or sporadically distributed in the main islands of Japan (Ohta et al, 2015). Furthermore, the geochemical map would also provide fundamental information to conserve the ecosystem indigenous to each isolated island.…”