Accurate seabed sediment classification is essential for mapping marine geological features, assessing benthic habitat, and planning coastal infrastructure. This study investigated the utility of multifrequency multibeam echosounder (MBES) backscatter data for improving seabed sediment classification compared to traditional single-frequency approaches. MBES data were acquired at three frequencies (170, 300, and 450 kHz), and post-processed to produce frequency-specific backscatter mosaics and a composite red–green–blue image. Classification was performed using unsupervised clustering methods, including K-means and isodata clustering, with input vectors composed of normalized backscatter intensities from the three frequencies. The integrated multifrequency approach successfully identified three distinct sediment classes, which were validated using grab samples analyzed for grain size, water content, total organic carbon, and slope. These classes exhibited strong correspondence with underlying geomorphological features and local hydrodynamic regimes, confirming the influence of topography and tidal currents on sediment distribution. Lower-frequency data (170 kHz) were more sensitive to subsurface variability, while higher-frequency data (450 kHz) captured surface texture differences more effectively. The combined use of all three frequencies improved classification performance, particularly in transitional sediment zones where single-frequency methods proved ambiguous. The methodology proved robust across varying water depths, sediment types, and complex seabed terrains, aligning with recent advances in MBES-based sediment mapping and supporting its general applicability for other dynamic coastal systems. These results demonstrate that the use of multifrequency MBES backscatter data enhances the resolution and reliability of sediment classification results, providing a robust framework for high-resolution seabed mapping in dynamic coastal environments.

River discharge depending on the dam gate operation method is an important factor underlying changes in estuarine sedimentation dynamics, but comprehensive studies are limited by data collection constraints. The hydrological operation of Nakdong Dam, designed to prevent seawater intrusion by opening during ebb tides and heavy rains and closing during flood tides, presents an ideal setting for such investigations. This study focused on the Nakdong River Estuary (NRE), utilizing aerial photography, bathymetry data, and sedimentation rate data to determine alterations in sediment transport and deposition patterns within the two tributary estuaries. Spatial discrepancies in sedimentation patterns across the eastern and western regions of the NRE were particularly evident in the spatial variations of textural characteristics and sedimentation rates. An enhanced ebb tidal prism resulting from dam gate opening in the eastern region caused the development of erosional topography and a rough depositional environment, forming a landward migrating (transgressive) barrier island system. Conversely, the predominantly closed dam gates in the western region maintained a consistent deposition pattern due to a regular tidal prism, facilitating the formation of sedimentary topography and fine sediment deposition. Consequently, barrier islands followed a seaward building (prograding) system. Therefore, the results suggested a role of modern dam gate operation as a major sedimentation mechanism, providing valuable insights for the sustainable management of estuarine sediment environments.

Benthic foraminifera are widely used as indicators of marine environmental conditions due to their sensitivity to ecological changes and their excellent preservation in sediments. In this study, benthic foraminiferal assemblages from a sediment core collected in the central Yellow Sea were investigated to document faunal composition and examine temporal changes since the Late Pleistocene. A total of 54 benthic foraminiferal species belonging to 33 genera, 25 families, seven orders, three classes, and one phylum were identified. Among them, 12 species are newly recorded in Korean waters, reflecting the current incompleteness of regional faunal inventories and the importance of detailed taxonomic studies. The assemblages exhibit distinct stratigraphic variations. The lower interval (>30 ka) is characterized by low-diversity assemblages dominated by taxa commonly associated with marginal marine environments. The middle interval (ca. 20–25 ka) shows the occurrence of taxa typically reported from boreal to subarctic environments, suggesting changes in environmental conditions during the Last Glacial Maximum. In contrast, the upper interval (Holocene) is marked by increased species diversity and the dominance of taxa characteristic of normal marine shelf environments. These assemblage changes are interpreted as reflecting long-term responses of benthic communities to sea-level fluctuations, sedimentary conditions, and regional oceanographic variability in the Yellow Sea. In particular, the development of fine-grained deposits in the Central Yellow Sea Mud (CYSM) and the establishment of stable marine shelf conditions during the Holocene likely played important roles in shaping benthic habitats. This study provides new baseline data on benthic foraminiferal diversity in the Yellow Sea and demonstrates the potential of these assemblages as useful, though indirect, indicators for reconstructing past environmental changes. The results highlight the importance of integrating detailed taxonomic analyses with stratigraphic records to improve our understanding of marine biodiversity and paleoenvironmental variability in marginal seas.

Woo, H.J.; Kang, J.; Lee, J.-H., and Jang, S., 2016. Seasonal changes in sediment characteristics on the tidal flat in Geunso Bay, west coast of Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1412 - 1416. Coconut Creek (Florida), ISSN 0749-0208. Geunso Bay, located in Taean, western Korean Peninsula, is a semi-enclosed-type bay with a mean tidal range of about 6 m. Tidal flats are largely developed along the sides of the bay. A digital elevation model showed that 95% of the total area of the bay is tidal flat. Observations in both winter and summer of 2009 revealed that the surface sediments in the bay were mainly muddy sand, and the sediments were classified into five sedimentary facies: sandy silt, slightly gravelly sandy mud/sandy mud, slightly gravelly muddy sand/muddy sand, silty sand, and sand. In the eastern tidal flat, the...

Kang, J.; Koo, B.J.; Jeong, K.-S.; Woo, H.J.; Seo, J.; Seo, H.-S.; Kim, M.-S., and Kwon, K., 2018. Insights into macroinvertebrate burrowing activity and methane flux in tidal flats. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 681–685. Coconut Creek (Florida), ISSN 0749-0208. The CH4 flux was examined preliminarily in tidal flats using a circular closed-chamber method to understand the effects of macroinvertebrate burrowing activity. The chamber was deployed over decapods (mud shrimp, Laomedia astacina and crab, Macrophthalmus japonicus) burrows for ~ 2 h, and the CH4 and CO2 concentrations were continuously monitored using a closed, diffuse CH4/CO2 flux meter. It founds that Laomedia astacina burrow (which is relatively long) site afforded higher-level CH4 production, likely due to diffusive emission of CH4 in deep-layer sediments. In addition, t...

Foraminifera are unicellular protists with external shells (tests) that may be calcareous (porcelaneous or hyaline), agglutinated, or organic-walled. Their test morphology and as-assemblage composition closely track environmental forcing, making them robust bioindicators of marine change. Documenting morphology and faunal composition is therefore essential for interpreting species distributions and their paleoenvironmental significance. Here we provide a systematic account of foraminiferal assemblages from core sediments in the Ulleung Basin, East Sea (Sea of Japan), with accompanying imagery and diagnostic notes. We identify 47 species across 32 genera and 20 families, including 15 planktic and 32 benthic taxa. Seven species are newly recorded for Korean waters: the planktic Tenuitellita fleisheri and Neogloboquadrina atlantica subsp. praeatlantica, and the benthic Islandiella algida, Uvigerina asperula, Pseudonodosaria aequalis, Pseudonodosaria obtusissima, and Astacolus crepidula. The presence of these previously unreported taxa likely reflects historical under-sampling and limited taxonomic emphasis in the region, coupled with the geomorphological challenges of the Ulleung Basin. In addition, the recognition of five distinct morphotypes of Neogloboquadrina pachyderma points to substantial past environmental variability in the basin. Continued evaluation of morphological diversity and distributional patterns in these assemblages will support stratigraphic applications and reconstruction of past marine environments in the East Sea by clarifying depth-wise faunal turnovers that likely record a composite signal of hydrographic variability overprinted by episodic seismic disturbance and slope current reworking.