Spring-neap tidal effects on satellite ocean color observations in the Bohai Sea, Yellow Sea, and East China Sea

Eight-year ocean color observations between 2002 and 2009 from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite are used to quantitatively assess the spring-neap tidal effects on variability of ocean optical and biogeochemical properties in the Bohai Sea, Yellow Sea, and East China Sea. We demonstrate that spring-neap tidal variation is one of important ocean processes that drive both the synoptic-scale and mesoscale changes of the ocean optical, biological, and biogeochemical properties in the coastal region. Normalized water-leaving radiance spectra (nL(w)(lambda)), water diffuse attenuation coefficient at the wavelength of 490 nm (K-d(490)), and total suspended matter (TSM) concentration show significant spring-neap variations in the coastal region within a lunar cycle of 29.53 days. In the open ocean, however, spring-neap tidal effects on ocean color data are negligible. The entire areal coverage of the turbid waters (K-d(490) > 0.3 m(-1)) showing significant spring-neap tidal variations is similar to 4-5 x 10(5) km(2). Similar coverage of moderately turbid waters (0.1 < K-d(490) <= 0.3 m(-1)) is also impacted by the spring-neap tides. The magnitude of the spring-neap tidal effects on the variations of the satellite ocean color properties, e. g., K-d(490) and TSM, is in the same order as the seasonal variations in the coastal region. Highest K-d(490) and largest turbid water coverage lag the new moon (or full moon) about 2-3 days, while the lowest K-d(490) and smallest turbid water coverage are also similar to 2-3 days behind the one-quarter (or three-quarter) moon. This is attributed to the seawater inertia and the friction against the seabed as well as the sediment resuspension process.