Sea Water Turbidity Variability and Relation to Tides and Environmental Factors in the Korean Coastal Region of the Yellow Sea

This study analyzes sea surface water turbidity variability in the coastal region of the Yellow Sea and investigates the relationships with environmental factors. By applying spectral analysis, harmonic analysis, wavelet transformation, and multivariate linear regression to in situ measurements of seawater turbidity data, we examined the temporal turbidity variability and the fractional contributions of tidal currents and atmospheric components to turbidity variations. A multivariate linear regression was used to determine the daily variations in the fractional contributions of tidal currents and atmospheric components to turbidity. The results showed that seawater turbidity exhibited dominant fluctuations corresponding to major tidal harmonics (M₂, S₂, K₁, and O₁), along with shallow-water tides (MS₄ and M₄) and the M₂ variation-related semi-diurnal tides (H₁ and H₂). The amplitudes of turbidity variations associated with these shallow-water tides and semi-diurnal tides demonstrated a linear relationship with those of the tides, with a rate of 0.24 NTU cm⁻¹. This rate was four times greater than the rate of 0.06 NTU cm⁻¹ observed for the major tides, addressing the important roles of non-linear tidal processes in shallow regions. In addition, an inertial motion in coastal turbidity (19.56 h) was detected when external forces were relatively weak. The impact of tidal currents on turbidity fluctuations was significantly reduced during typhoon periods due to pronounced atmospheric influences. Investigations of high-resolution Sentinel-2 turbidity over the past 6 years (2018–2023) illustrated more distinctive responses to extreme environmental conditions. This study is expected to enhance the comprehensive understanding of turbidity fluctuations and their linkages to tidal currents and atmospheric conditions in the Yellow Sea.