Wang H.,Ocean University of China |
Wang H.,Key Laboratory of Submarine Geosciences and Prospecting Technology |
Wang H.,CAS Qingdao Institute of Oceanology |
Bi N.,Ocean University of China |
And 6 more authors.
Earth Surface Processes and Landforms | Year: 2010
Few hyperpycnal flows have ever been observed in marine environments although they are believed to play a critical role in sediment dispersal within estuarine and deltaic depositional systems. The paper describes hyperpycnal flows observed in situ off the Huanghe (Yellow River) mouth, their relationship to tidal cycles, and the mechanisms that drive them. Simultaneous observations at six mooring stations during a cruise off the Huanghe mouth in the flood season of 1995 suggest that hyperpycnal flows observed at the river mouth are initiated by high concentrations of sediment input from river and modulated by tides. Hyperpycnal flows started near the end of ebb tides, when near-bottom suspended sediment concentration (SSC) increased rapidly and salinity decreased drastically (an inverse salt wedge). The median grain size of suspended particles within the hyperpycnal layer increased, causing strong stratification of the suspended sediments in the water column. Towards the end of flood tides, the hyperpycnal flow attenuated due to frictions at the upper and lower boundaries of the flow and tidal mixing, which collapsed the stratification of the water column. Both sediment concentration and median grain size of suspended particles within the bottom layer significantly decreased. The coarser sediment particles were deposited and the hyperpycnal flows stopped. The intra-tidal behaviors of hyperpycnal flows are closely associated with the variations of SSC, salinity, and stratification of the water column. As nearly 90% of riverine sediment is delivered to the sea during the flood seasons when hyperpycnal flows are active, hyperpycnal flows at the Huanghe mouth and the river's high sediment loads have caused rapid accretion of the Huanghe delta. © 2010 John Wiley & Sons, Ltd.
Wu X.,Ocean University of China |
Wu X.,Key Laboratory of Submarine Geosciences and Prospecting Technology |
Bi N.,Ocean University of China |
Bi N.,Key Laboratory of Submarine Geosciences and Prospecting Technology |
And 10 more authors.
Journal of Asian Earth Sciences | Year: 2015
The modern Huanghe (Yellow River) delta sedimentary complex has developed since 1855, when the lower river channel migrated northward from the Yellow Sea to the Bohai Sea. As a result, the river-laden sediment accumulated rapidly on the lowlying plain and formed the mega-delta. Here we present high-resolution sedimentary sequences based on 137Cs and 210Pb dating and grain-size parameters of two sediment gravity cores collected near the present river mouth (core A11) and in adjacent Laizhou Bay (core A26). Based on these sedimentary sequences, the different responses of the sediment records to natural and artificial channel shifts are presented. The average sedimentation rates of the two cores A11 (1951-2006) and A26 (1808-2006) were estimated to be 2.25cm/year and 0.80cm/year, respectively. The results indicated that the geometry of the delta (e.g. the location of river mouth and changing coastline) and sediment supply from the river played an important role in the sedimentation of the subaqueous delta. The channel shifts in 1976 and 1996 shortened the distances from the river mouth to the location of core A11, resulting in the local accumulations of relatively coarse particles from the river mouth. The sedimentation of core A26 indicated four major channel shifts in 1855, 1904, 1947 and 1976. When the river mouth approached the core location, the accumulated sediment became finer; otherwise, the active resuspension due to strong hydrodynamics resulted in the accumulation of coarser sediment. The sediment records preserved in the two gravity cores illustrated different sedimentary responses to the lower channel shifts of the Huanghe and sediment supply from the river at centennial scales, which is critical to understanding the evolution of the modern Huanghe Delta in the past and to predicting the future trend. © 2015 Elsevier Ltd.
Sun X.,Ocean University of China |
Sun X.,Key Laboratory of Submarine Geosciences and Prospecting Technology |
Yang Z.,Ocean University of China |
Yang Z.,Key Laboratory of Submarine Geosciences and Prospecting Technology |
And 3 more authors.
Chinese Journal of Oceanology and Limnology | Year: 2014
Suspended particulate substances were sampled in the eastern equatorial Pacific in water column from surface to near bottom in five stations in 2005, from which 868 barite crystals were recovered. The barite crystals were examined under scanning electron microscopy. About 61% of the total barites crystals contained detectable Sr by energy dispersive X-ray spectrometry. Barite crystals could be classified into four groups based on their morphology: 1) bladed; 2) ovoid or rounded; 3) arrow-like; and 4) irregularly shaped. The arrow-like barite crystals in natural environment has never been reported before. In addition, about a half of the studied crystals showed features of dissolution as cavities or holes inside of the crystals or around their edges. We found that differential dissolution of barite crystals is consequence of heterogeneous Sr distribution in barite crystals. Our results would help in understanding the biogeochemical processes of marine barite formation and preservation in seawater and marine sediments. © 2015, Chinese Society for Oceanology and Limnology, Science Press and Springer-Verlag Berlin Heidelberg.