La/Yb and Th/Sc in settling particles: Vertical and horizontal transport of lithogenic material in the western North Pacific

Abstract

In order to understand the origins and transport processes of lithogenic aluminosilicate in the western North Pacific, time-series sediment traps were deployed at Stn. KNOT at 44∞N 155∞E (water depth: 5320 m). Annual mean content of aluminum (Al) which is a proxy of lithogenic material in settling particles was 0.38% at 1 km depth, 0.78% at 3 km depth and 1.14% at 5 km depth, respectively. Mass fluxes were corrected by 230 Th and 231 Pa activities in particles and seawater. Annual mean corrected Al fluxes at 1, 3 and 5 km depths were calculated to 0.45, 0.46 and 0.33 g/m 2 /year, respectively. Lanthanum/ytterbium (La/Yb) and thorium/scandium (Th/Sc) ratios were used as proxies for estimating the origin of lithogenic aluminosilicate in settling particles. Both La/Yb and Th/Sc ratios in settling particles increased with depth, and the seasonal variation was the smallest at 5 km depth. It was considered that variations of La/Yb and Th/Sc ratios in settling particles reflected the change of source material of lithogenic aluminosilicates. Origins of lithogenic materials in the settling particles were summarized using two end-members, loess from central Asian continent (AL) and basalts from the Kurile-Kamchatka Islands (KK). Contributions of end-members in settling particles were estimated from the La/Yb and Th/Sc ratios. The contribution of KK particles in lithogenic materials was calculated to be 84% at 1 km depth, and 61% at 3 and 5 km depths, respectively. Although the KK material was the dominant constituent of the terrigenous component in settling particles at Stn. KNOT, the KK flux decreased with depth. On the other hand, the AL flux increased with depth and the significant increase of the AL flux was presumably due to the lateral import of AL particles to the deep layer at Stn. KNOT. From these results we conclude that the distribution of lithogenic materials recorded in sediments in the western North Pacific are influenced by the northward transport of AL within the deep layer.

Eolian dust input to the Subarctic North Pacific

“…A major source is volcanic ash from the surrounding Kurile, Aleutian, Kamchatka, Alaska and Japan volcanic arcs (Bailey, 1993;Jones et al, 1994Jones et al, , 2000Maeda et al, 2007;Nakai et al, 1993;Olivarez et al, 1991;Otosaka et al, 2004;Shigemitsu et al, 2007;Weber et al, 1996). Also contributing to the lithogenic fraction are hemipelagic material (Jones et al, 1994(Jones et al, , 2000, ice-rafted debris (IRD;McKelvey et al, 1995;St.…”

“…3, 4). As the surrounding land is of volcanic origin, the hemipelagic and riverine input as well as IRD have a geochemical signature similar to the fine-grained volcanic ash (Jones et al, 1994;McKelvey et al, 1995;Otosaka et al, 2004;Shigemitsu et al, 2007) and are therefore accounted for by the volcanic endmembers.…”

“…The other dominant lithogenic component in this region is interpreted to represent volcanic input (e.g., Bailey, 1993;Maeda et al, 2007;Nakai et al, 1993;Olivarez et al, 1991;Otosaka et al, 2004;Shigemitsu et al, 2007;Weber et al, 1996). Volcanic ashes from subduction-related volcanic arcs are known to be effectively helium-free in comparison to continental dust (Patterson et al, 1999; Supplementary Information, Section 2.3).…”

Grain size, La/Yb and Th/Sc of settling particles in the western North Pacific: Evidence for lateral transport of small Asian loess

“…based on mineralogy (Griffin et al, 1968), the isotopic composition of neodymium and strontium (Nakai et al, 1993;Jones et al, 1994), and the elemental composition of sediment and settling particles (Weber et al, 1996;Otosaka and Noriki, 2000;Otosaka et al, 2004). These studies revealed that the source materials of lithogenic particles in sediment and settling particles in the north Pacific are Asian loess and volcanic materials from the Kurile-Kamchatka Islands.…”

“…The behavior of settling lithogenic particles in the ocean has been studied using sediment traps (e.g., Honjo et al, 1982;Walsh et al, 1988;Saito et al, 1992;Otosaka et al, 2004). Previous studies have concluded that lithogenic particle fluxes increase with depth and that the increases were caused by laterally transported particles.…”