Accumulation of recent muds associated with coastal circulations, southeastern Korea Sea (Korea Strait)

Abstract

Recent muds accumulating in the southeastern Korea Sea (Korea Strait) are mostly derived from the Nakdong River discharge and can be divided into the Proximal Mud Deposits (PMD) and the Distal Mud Deposits (DMD). The PMD show a relatively well- or weakly stratified subbottom on high-resolution seismic profiles (3.5 kHz and Uniboom), whereas the DMD are acoustically characterized by a transparent subbottom and the extensive occurrence (about 900 km 2 in area) of acoustic turbidity in shallow sediments. 210Pb excess activity profiles of sediment cores yield apparent sediment accumulation rates of 1.8–4.4 mm/yr. On the basis of an average sediment accumulation rate, suspended-sediment budget in the PMD and the DMD was calculated, which provides important information about distribution patterns and transport directions. The PMD are a direct sink of about 35% (1.65×10 6 t/yr) of total fine-grained sediments released from the Nakdong River. The remaining riverine sediments are transported farther to northeastward in response to the strong coastal front between the coastal circulation and the offshore Tsushima Current. An annual sink of sediments in the DMD is estimated to be 2.9×10 6 t/yr that are approximately 63% of the annual discharge of suspended sediments by the Nakdong River. Additionally, average contents of organic carbon and nitrogen in the DMD are about two times of those in the PMD, reflecting high biological productivity associated with coastal upwelling process in this area. The coastal upwelling process is also supported by C/N ratio, sea-surface temperatures and chlorophyll pigment concentrations.