Seasonal changes of sedimentary environment at the macrotidal flat in Gomso Bay, west coast of Korea

Abstract

The sedimentary processes in the tidal flats on the west coast of Korea are directly influenced by monsoons, resulting seasonal deposition and/or erosion of sediments. Gomso bay on the mid-west of Korea is composed of a main channel to the north and the wide tidal flat with abundant tidal creeks to the south. The sedimentary analyses were investigated to understand seasonal sedimentary processes of tidal flats in Gomso bay. The surface sediments in the tidal flat were classified into three sedimentary facies. Generally, sandy sediments were dominated in the outer tidal flat of the bay in spring 2011, but the area of silty sand sediments extended from middle to the outer tidal flat of the bay in summer 2012. The short-term sedimentation rates were obtained from three lines by burying a plate at sub-bottom depth from May 2011 to May 2012. In the tidal flat at inner bay (KB- Line), the annual sedimentation rates were ranged -8.91 to 41.58 mm/year with the net deposition rate of 16.04 mm/year. The deposition on KB-Line occurred in autumn, winter and spring. The erosion was dominated on the tidal flats at middle (KH-Line) and outer bay (KM-Line) during autumn and winter with an annual erosion rate of -1.71 mm/year and -11.98 mm/year, respectively. The 12.5 hours anchoring survey at the bay mouth was revealed a large amount of suspended sediments were transported into the bay during a tidal cycle in spring 2012. Based on REE geochemistry, the tidal flat could receive resuspended sediments by tidal erosion at southern muddy coastal area during spring and summer. Additionally, Jujin Stream also supplied silt-dominated sediments at middle bay around KH-Line after summer rainfall. The seasonal variations of sedimentation on tidal flats showed that the deposition occurred with an inflow of muddy sediments by tidal current and rainfall in spring and summer, whereas the erosion was dominated by wave in autumn and winter.