| Hydrographic and suspended sediment data were collected in 3 synchronic multi-station hydrographic time-series surveys along 4 sections and 24 grid stations off the recent Huanghe (Yellow River) delta and its adjacent Bohai Sea conducted during 3 cruises in low river discharge period in 2003, water-sediment regulation scheme period in 2007 and after storm period in winter of 2006. Based on these data suspended sediment dispersal characteristics, process and its seasonal variation, off the recent Huanghe delta and its adjacent Bohai Sea were studied quantitatively. Its controlling factors and mechanism were analyzed. Based on the bathymetric data of 36 survey transects along the delta in 1976-2003, the effect of the sediment dispersal on the subaqueous Huanghe delta erosion-accumulation were estimated. Additionally, the seasonal variation of the water and sediment fluxes from the Bohai Sea to the Yellow Sea through the southern Bohai Strait were reestimated based on the in-situ time-serious hydrographic data collected in summer of 2007 and in winter of 2006. The major results and conclusions are presented as follows.1. The tidal shear fronts with different mechanisms were found not only in the river mouth area but also in southern and northern area off the Huanghe delta. The tidal shear fronts combined with the tidal currents in the northern and southern delta bared the suspended sediment dispersing to the nearshore area, which was opposite with the function of the tidal shear fronts off the river mouth, resulting in formation of two erosion area off the northern and southern delta .2. Most of the sediment from the river mouth as hypopycnal flow deposited within 5 m isobath due to the jointed effects of tidal shear front and vertical circulation off the river mouth during river low discharge period. Part of suspended sediment was transported northward or southward by the ebb and flood currents through deeper water area but not via shallower area.3. Suspended sediment discharged from the Huanghe to the Bohai Sea was mainly delivered along the coast within the area of about 20 km from the coast during water-sediment regulation scheme period in summer. It was transported southward by the flood current and reach the southwestern sea area of the Laizhou Bay, and was delivered northward by the ebb current but can not extend over 38°N. Most of the river-delivered suspended sediment deposited within 13 m isobath due to the barrier and convergence effects of the tidal shear fronts as well as the trapping effect of the vertical circulation. Moreover, the well-developed pycnocline in the upper water layer in the study area in summer season limited the suspended sediment transport mainly below the pycnocline. Two centers with high suspended sediment concentration were formed in abandoned Diaokou river mouth area and current river mouth area, resulting from resuspension of seabed sediment and river discharged sediment respectively,. There was little sediment exchange between the two centers.4. The suspended sediment concentration, primarily resulted from the resuspension of seabed sediment induced by the waves, was increased substantially in winter in the study area. It was mainly transported southward by strong longshore current induced by wind and waves. The high turbid water mass, originated from the northern delta and river mouth area, was delivered towards to the Bohai Strait through the middle of the Laizhou Bay and the sediment transport along its coast was not significant.5. The suspended sediment dispersal in the study area showed strong seasonal variation. The suspended sediment concentrations and fluxes, mainly directing southward, in winter were 10-25 times and 4-128 times higher than those during river low discharge period in summer, and 2-27 times and 2-123 times those during water-sediment regulation scheme period in summer, except for river mouth area. Therefore, major sediment-transport season off the Huanghe delta was winter, when the marine dynamics was much stronger than that in summer, which was in good agreement with the sediment-transport pattern in East China 6. The suspended sediment transport from the Bohai Sea to the Yellow Sea had a significant seasonal variation resulted from the seasonal variation of the sediment dispersal off the Huanghe delta. The suspended sediment concentrations and fluxes in winter were 4.2 times and 5.0 times higher than those in summer, respectively, which indicated that most of the sediment was transported from the Bohai Sea to the Yellow Sea through the southern Bohai Strait in winter season. Moreover, the water discharge from the Bohai Sea to the Yellow Sea in winter was about 1.2 times that in summer. Based on the method of previous study and in-situ data of this paper, the annual sediment flux was reestimated, which was 30.8 Mt/yr and about 3 times higher than that based on the data collected in August in previous studies. Therefore, it can be concluded that the Bohai Sea basically is the sink of the Huanghe delivered sediment in summer season, and it was transformed to the source of the Huanghe sediment in winter due to the significant difference of the marine dynamics in two seasons.7. The accumulation-erosion pattern of the Huanghe subaqueous delta from 1976 to 2003 showed that there was a water-drop-like accumulation area in the southern delta and two nearshore erosion-accumulation zones in southern and northern delta which was approximately in accordance with our results of fluxes, temporal-spatial process and mechanism of suspended sediment dispersal off the Huanghe delta.
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