Dinoflagellates frequently cause harmful, large‐scale spring algal blooms in the Changjiang Estuary and adjacent seas of China. However, the population source of some dinoflagellates in this area remains unknown. We deployed an adjoint model and a coupled physical‐biological model to explore the possible nonlocal dinoflagellate population sources to the Changjiang Estuary and adjacent seas. Our simulation results revealed that the Taiwan Strait and the area east of Taiwan are two nonlocal source regions of May dinoflagellate blooms in the study area. Under different hydrodynamic and biochemical conditions, dinoflagellates from the Taiwan Strait directly triggered dinoflagellate blooms from south to north along the coast of China. Dinoflagellates from the area east of Taiwan first concentrated and bred in the offshore temperature frontal area and then spread southwestward, triggering dinoflagellate blooms along the Zhejiang coast. Due to the different influence mechanisms, it took longer for the initial dinoflagellate population in the Taiwan Strait to exert the same impact on dinoflagellate blooms in the study area as that from the area east of Taiwan. Moreover, the density and appearance time of the initial dinoflagellate population in the Taiwan Strait affected their biomass and bloom range in the study area. Even a small initial dinoflagellate population east of Taiwan could trigger a bloom in the study area. This study suggests the target domains for finding nonlocal dinoflagellate cysts and provides a strategy to predict dinoflagellate blooms in the Changjiang Estuary adjacent area by monitoring dinoflagellate biomass in the nonlocal source regions.

The vertical eddy viscosity coefficient (VEVC) is an important parameter used in ocean dynamics studies to describe the intensity of mixing in the vertical direction and the process of momentum transport. In this paper, an adjoint assimilation method was used to invert the VEVC, based on the Ekman model, with the measured wind field and current data. The main purpose was to study the effect of changes in the background wind field on VEVC, and thus investigate the role of wind stress in the inversion process. The results indicated that the inverse vertical eddy viscosity coefficient increased slightly at the surface layer, reaching its maximum at around 10–12 m, and then decreased monotonically with depth. The maximum VEVC value corresponds to different depths for different wind speed ranges. Additionally, wind steering could affect the VEVC inversion curve, causing it to deviate from the general trend. The kinetic energy ratio increased with depth, peaked at 18–20 m, and then rapidly decreased to nearly zero beyond 24 m. The impact of wind field strength and steering on VEVC was observed in the kinetic energy ratio curve, which confirms the speculative wind stress effect. This study revealed the characteristics and mechanisms of VEVC in coastal waters under different wind conditions, which could provide a reference for further research on physical oceanography.

Wan, W.; Feng, X.; Liu, Q.; Yin, B.; Yang, D., and Gao, G., 2018. Study of the tide and tidal currents in the Bay of Bengal based on refined simulations. A high-resolution, two-dimensional, hydrodynamic tidal model of the Bay of Bengal was developed using the Advanced Circulation (ADCIRC) Model to study the tide and tidal currents in the Bay of Bengal. The simulations conformed to the observations, and because of the use of a high-resolution, triangular grid, characteristics of the tide and tidal currents were computed more accurately than in previous studies. The results indicated that tides in most of the Bay of Bengal are semidiurnal, whereas those in the seas SE of Sri Lanka are mixed and predominately semidiurnal. There are two degenerate amphidromic points, one at the NE end of the head of the bay and the other at SE Sri Lanka, whereas there is an amphidromic point at the seas SE of Sri Lanka. The form of the M₂ tidal current is rotary on the continental shelf and rectilinear in coastal areas and seas distant from the continental shelf. Four major tidal currents are in a NW–SE direction, in the western part of the head of the bay, and in a NE–SW direction in river estuary areas. Results from the eastern part are the opposite. The amplitudes and major axes of four tides and tidal currents increase upon entering the head of the bay, whereas those of the M₂ tide are the largest.