Ba, Si, U, Al, Sc, La, Th, C and 13C/ 12C in a sediment core in the western subarctic Pacific as proxies of past biological production

Abstract

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C org) as well as its isotopic ratio ( δ 13C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba ex, showed the best correlation with the Vostok δD ( r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba ex in WSAP were similar to those of Ba ex in the Okhotsk Sea and of other proxies (C org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD ( r = 0.46, p < 0.001) than Ba ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba ex. While both the C org content and U ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ 13C and the Vostok δD ( r = 0.42, p < 0.001), between δ 13C and Ba ex ( r = 0.60, p < 0.001) and between δ 13C and Opal ( r = 0.36, p < 0.01) indicates that δ 13C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba ex in WSAP and Loess ( r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.