Variations And Influencing Mechanisms In The Optical Properties Of The Waters In The Yellow Sea And Bohai Sea

Studying the variations of the optical properties of the sea water and its influencing mechanisms is very important for the development of ocean color remote sensing retrieving algorithms with high precision, the research on the transport processes of the suspended particulate matters based on marine optical technique, the development of underwater visibility prediction method and research on the impact of ocean processes and weather processes at short-time scales using optical methods. This research uses the optical properties dataset measured extensively in the Yellow Sea and Bohai Sea (YSBS) to explain the temporal and spatial distribution characteristics of their optical properties; systematically analyzes the influencing mechanisms of the variations of the optical properties in the YSBS in conjunction with synchronously measured chlorophyll concentration, suspended particulate matter characteristics and hydrological data; and develops the parameterized models of inherent optical properties and analyzes the influence of dust storm on the optical properties. The main research results are listed as follows:1. The variations in the optical properties are mainly influenced by the bottom sediments resuspension which induced by tidal currents and waves’friction force, stratification effect determinated by temperature and salinity profiles and vertical mixing function made by wind, and phytoplankton growth process. The detailed influencing mechanisms are listed as follows:in spring, vertical mixing function of the water tends to be weak and the stratification effect emerges. Due to the appearance of stratification effect, vertical mixing function of the water becomes further reduced, which limits moving up of the bottom sediments resuspension that is induced by tidal currents and waves’friction force. Because there exist appropriate conditions needed for phytoplankton to live in spring, phytoplankton starts to grow largely. For the waters with deep depths, the optical properties of the upper layer waters are influenced by the biological process of phytoplankton growth, and the optical properties of the bottom layer waters are influenced by the bottom sediments resuspension process which induced by tidal currents and waves’ friction force; for the waters with shallow depths, vertical mixing function is more powerful and stratification effect is weaker than deep water in the same exterior condition, so that the bottom resuspended sediments are easier to move up to upper layer water. Therefore, the optical properties of the upper layer waters are influenced by the biological process of phytoplankton growth in addition to the bottom sediments resuspension process. In summer, stratification effect of water is enhanced and the optical properties of the majority of the upper layer waters are influenced by the biological process of phytoplankton growth in the YSBS. In autumn and winter, stratification effect of water is weakened and vertical mixing function is enhanced. Because of the powerful vertical mixing function, the depth of the upper mixing layer becomes deeper and the bottom of upper mixing layer is close to the bottom, which makes the bottom resuspended sediments hard to get through the pycnocline to access to the upper mixing layer. Although the upper mixing layer is close to the bottom of sea in some deeper water such as the Yellow Sea Trough, the bottom resuspended sediments are still hard to get through the pycnocline to access to the upper mixing layer because of the strong pycnocline. Therefore, in autumn and winter, the optical properties of the majority of the YSBS waters are influenced by the bottom sediments resuspension process except those of the upper layer waters located in the Yellow Sea Trough which are still influenced by biological process of phytoplankton growth.2. The suspended particulate matters’characteristics directly dominate the variability of optical properties in the YSBS. The optical properties are mainly controlled by the concentration of suspended particulate matters, and the particle type dominates the detailed response relationship between the concentration of suspended particulate matters and optical properties. For the waters with the backscattering ratio with a value greater than 0.015, the optical properties are highly correlated with the concentration of suspended particulate matters, and the mean correlation coefficient is 0.97; and for the waters with the backscattering ratio with a value less than 0.009, the optical properties are highly correlated with the cholorophyll concentration, and the mean correlation coefficient is 0.87.3. For the waters located in the central South Yellow Sea, when a dust storm occurs, dust particles deposited from dust storm with aerosol optical depth of nearly 2.5 into water could induce 0.14 m-1 change of water optical scattering coefficient at 532nm. The influencing time of dust storm on water optical scattering properties is short and the influence disappears rapidly within about 3 hours after the ending of a dust storm. These results are very helpful for understanding the influencing mechanisms of dust storm on optical properties as well as the distribution pattern of dust particles deposited from dust storm into water by means of optical methods. The results also indicate that the contribution of dust particles deposited from atmosphere on particle scattering properties when no dust storm occurs can be approximately equal to 0.