Reconstruction of environmental changes using a multi‐proxy approach in the Ulleung Basin (Sea of Japan) over the last 48 ka

Abstract

AbstractBased on elemental geochemical data, we reconstructed the sediment provenance, surface productivity and bottom water redox conditions for the last 48 ka in the Ulleung Basin (Sea of Japan) and inferred the factors controlling them. Al2O3/TiO2 ratio and chemical index of alteration (CIA) suggest that sediment provenance changed during the glacial period (48–18 ka) compared to the deglacial (ca. 18–11 ka) and Holocene. Mass accumulation rates of total organic carbon (TOC), CaCO3, phosphorus, cadmium and excess barium reveal low paleoproductivity during low sea stand. During 18–11 ka, productivity increased due to increasing inflow of nutrient‐rich water masses – the Oyashio and the East China Sea coastal water – in tandem with the rising sea level. Maximum productivity occurred during Younger Dryas and Pre‐boreal periods when sea level was at ∼ −60 m and then gradually decreased as the Tsushima Warm Current inflow kicked off at ca. 9.3 ka, consistent with other paleoredox proxies, which reveal the presence of anoxic bottom water during ca. 12–9 ka. With the changes in paleoredox proxies and their ratios (TOC, Mo, U, Mn, C/S ratio and Uauthigenic and Mo contents), we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation‐induced productivity changes. The global climate and sea‐level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection, subsequently driving the oxygenation of bottom water in the Ulleung Basin. Copyright © 2012 John Wiley & Sons, Ltd.