Fluctuation in Sedimentation of Biogenic Components and Inorganic Elements on the Shatsky Rise in the Western North Pacific During the Late Quaternary

Middle latitude area of the western North Pacific is sensitive for climatic change. Sedimentation of biogenic and abiogenic components was studied in cores NGC108 (36N, 158E; 3390 m) and S2612 (32N, 157E; 2,612 m) from the Shatsky Rise to verify the fluctuation of biogenic sedimentation and the related vertical transport of inorganic elements. Paleo-production, opal/carbonate and Corganic/Ccarbonate ratios have been always higher in core NGC108 than those in core S2612 during the last 180 kyr although the paleo-production in both cores generally increases during glacial times and decreases during interglacial times. These results suggest that the surface water at Site NGC108 has been influenced more by Subarctic water in contrast to Site S2612, which has been more affected by the Central water. The opal/carbonate ratios in core S2612 remain fairly constant relative to those in core NGC108, which suggests that the transition zone between the Subarctic and the Central waters was narrower in latitude during oxygen isotope stage (OIS) 2/3 boundary, OIS 4 and OIS 6. Nine inorganic elements analyzed in this study are divided into three groups based on correlation between each element: 1) terrigenous components (Al, Ti, Fe), 2) biogenic calcareous material (Ca, Sr), and 3) biogenic-scavenged elements (Mg, Zn, Cr, Be). Of these elements, especially sedimentation of particle-reactive Be could be accelerated by both enhanced terrigenous input and biogenic vertical transport. Since its residence time in the ocean is relatively short, regarding Be, ocean reservoir is not under steady state condition but has fluctuated largely in response to climatic change.