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

Abstract

[1] 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 (nLw(λ)), water diffuse attenuation coefficient at the wavelength of 490 nm (Kd(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 (Kd(490) > 0.3 m−1) showing significant spring-neap tidal variations is ∼4–5 × 105 km2. Similar coverage of moderately turbid waters (0.1 < Kd(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., Kd(490) and TSM, is in the same order as the seasonal variations in the coastal region. Highest Kd(490) and largest turbid water coverage lag the new moon (or full moon) about 2–3 days, while the lowest Kd(490) and smallest turbid water coverage are also ∼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.