The summer spring–neap variation of the water thermohaline–turbidity structure and its dynamical mechanism in the southern Bohai Strait

• Observation of spring–neap variations in thermohaline and turbidity distribution.
• Special density and turbidity distribution trapped during neap tide.
• Higher turbulence in spring tide led to higher resuspension of the bottom sediment.
• The grain-size of the bottom sediment affected the bottom turbidity distribution.

During summer cruises across the southern Bohai Strait in the spring tide and the neap tide, respectively, the thermohaline–turbidity variations and the mixing–stratification conditions of the water column were analyzed in detail. The thermohaline–turbidity distribution showed both horizontal and vertical variations across the southern Bohai Strait. The suspended sediments across the surveying section were mostly derived from the resuspension of the bottom sediments. A stronger turbulence mixing in the spring tide led to a more intense resuspension of the bottom sediments than that in the neap tide. Moreover, northerly coarsening of the bottom sediments made the sediments more difficult to remain in their resuspended condition in the northern area than in the southern area. The uneven vertical distribution of the resuspended sediments should be considered, when estimating the suspended sediment flux (SSF) across the southern Bohai Strait, for its obvious impact ratio of about 16%, compared with the previous estimation. In addition, the factor of the spring–neap variation in the estimation of SSF should also be involved for its effect on the SSF showed a difference of about 0.06 Mt from the estimation without considering it.