Post-glacial paleoenvironmental changes of sedimentary processes recorded in the contourite drifts of Hupo Basin in the eastern margin of Korean Peninsula, East Sea

The Hupo Basin is a slope-perched half-graben bounded on the east by the Hupo Bank in the eastern margin of Korean Peninsula. In the western slope of the Hupo Bank, moats, formed by bottom current activity, occur along the base of slope at water depths ranging from 208 to 238 m. Associated drift deposits with the moats which fills the Hupo Basin, thin out as they extend from the moat toward the coast. This study aims to understand post-glacial changes of sedimentary processes in the Hupo Basin, influenced both by transgression and variations in the along-slope bottom current activity based on the sedimentary characteristics of three piston cores acquired along an east-west transect from the drift deposit. 

The core sediments consist of bioturbated mud, bioturbated sandy mud, or muddy sand, which show abrupt upward fining trends after the Last glacial Maximum to about 8 ka, indicating progressively deepening offshore environments during the post-glacial sea-level rise. The overall mean grain sizes of the core sediments exhibit a fining trend towards the Hupo Bank decreasing from 51 μm at the shallowest (161 m) western-most site (P02), to 7 μm at the deepest (182 m) eastern-most site (P01), while the sedimentation rates since ca. 8 ka drastically increase towards the Hupo Bank, ranging from 38 to 104 cm/kyr. Moreover, the mean grain size of the P01 site slightly coarsens since ca. 2.3 ka, exhibiting significant cyclic fluctuations with ca. 100 – 200 yr periods and around 4 μm amplitude.

The spatial temporal variations of grain sizes and sedimentation rates demonstrate how the sedimentary characteristics of shallow water contourites, such as the moat-drift system in the Hupo Basin, can be influenced by an interplay between variations in offshore-directed hydrodynamic conditions and associated along-slope bottom current activity due to sea-level changes. The sedimentary records of the contourite drifts of the Hupo Basin indicate initiation of vigorous bottom current activity in the western slope of the Hupo Bank by the East Korean Warm Current, a branch of Tsushima Warm Current flowing northward along the eastern margin of the Korean Peninsula since ca. 8 ka, with increased variability since ca. 2.3 ka.