Spatial Variability in Depositional Environments Along an Outer-to-Inner Transect in Jinhae Bay, South Korea

Coastal environments have been increasingly affected by the combined influences of fluvial and marine processes. Understanding how these factors interact to control sedimentary environments is critical for evaluating the sensitivity of coastal systems to changing environmental conditions, particularly in bays where multiple freshwater and marine inputs overlap under complex geomorphological settings. Jinhae Bay, a semi-enclosed embayment with restricted water exchange on the southeastern coast of Korea, provides a representative setting for examining the interplay between fluvial and marine processes. We investigated dominant sediment sources using high-resolution multi-proxy analyses (grain size, LOI, XRF, pollen, dinoflagellate cysts) on three 50-cm-long sediment cores collected along an outer-to-inner transect. The outer bay exhibits higher Zr concentrations and coarser grain size, reflecting strong hydrodynamic energy and mixed marine-fluvial inputs, whereas the inner bay contains finer-grained and organic-rich sediments with elevated Fe/Mn ratios and abundant dinoflagellate cysts, indicating deposition under low-energy and reducing conditions. These contrasting spatial patterns demonstrate that sedimentation in Jinhae Bay is controlled by external inputs from the Nakdong River and open sea as well as internal hydrodynamic and redox processes. The results highlight distinct sedimentary gradients and provide a robust framework for proxy interpretation and management of semi-enclosed bays.