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10. Multiscale Spatio‐Temporal Variations of Suspended Sediment Fronts in the Semi‐Enclosed Bohai Sea, China.

Author

Du, Yunfei, Zhang, Jicai, Bian, Changwei, Fang, Xiaoyu, Cheng, Jun, Wang, Guansuo, Zhu, Jianrong, and Wang, Ya Ping

Subjects
SUSPENDED sediments, SPATIO-temporal variation, EL Nino, SAND waves, TERRITORIAL waters, COASTAL sediments
Abstract

Suspended sediment fronts (SSFs) significantly affect water quality, ecology, and geomorphological evolution of estuarine and coastal waters. Based on 10‐year suspended sediment concentration data derived from satellite images, the multiscale spatio‐temporal variability of SSFs in the Bohai Sea was studied. Frontal probability (FP) was used to quantify the intensity of frontal activity. The 10‐year averaged FP was higher near the coast and decreased with increasing offshore distance. The arc‐shaped distributions of FP near the Yellow River Estuary revealed two tidal shear frontal zones. In the eastern Bohai Sea, 13 finger‐shaped high‐FP areas reflected the spatial pattern and fine structures of tidal sand ridges. The complex topography and strong tidal dynamics provided the essential conditions for frontogenesis. The seasonality of frontal activity was dominantly regulated by the change in wind waves associated with monsoons and stratification. The direct or indirect effects of sediment discharges from the Yellow River and Liaohe River on seasonal and annual variations of frontal activity only existed within close proximity to the estuaries. Frontal activity generally showed an interannual weakening trend, especially in the Laizhou Bay (−0.27%/yr), while an opposite trend was identified in the Liaodong Bay (0.10%/yr). This phenomenon was related to the interannual variations of wind speeds. Meanwhile, wind speed anomalies caused by El Niño‐Southern Oscillation events could explain the significant interannual fluctuations in frontal activity such that, frontal activity was significantly enhanced (suppressed) when El Niño (La Niña) events occurred, especially during 2015–2016 (2017–2018). Plain Language Summary: Suspended sediment fronts, one of the most common phenomena in estuarine and coastal waters, are defined as narrow zones with large spatial changes in suspended sediment concentration over relatively short distances. The Frontogenesis and frontal variability of the Bohai Sea, east coast of mainland China have unique patterns because of its complex hydro‐sedimentary environment, but no relevant studies have been systematically conducted yet. In this study, the intensity of frontal activity in the Bohai Sea was quantified by using satellite observation data spanning 10 years. Our analyses revealed that strong frontal activity mainly occurred in areas with dramatic changes in topography and shoreline and distinct tidal features. The seasonal and year‐to‐year variations of frontal activity were closely related to wind waves, stratification, riverine sediment input, and El Niño‐Southern Oscillation events. Nevertheless, their influence mechanisms varied in different regions. The new findings are of significance to further investigate the sedimentary patterns and the ecological effects of sub‐mesoscale processes in the Bohai Sea, and can also shed light on frontal variability of semi‐enclosed shallow seas worldwide. Key Points: Geostationary Ocean Color Imager remote sensing data were used to quantify suspended sediment front variations in the Bohai SeaSpatial patterns and seasonal‐to‐interannual variability of frontal activity were revealedEffects of dynamic factors on the spatio‐temporal variations of frontal activity were analyzed [ABSTRACT FROM AUTHOR]

Published
2023
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17. The Relationship Between Nitrate and Potential Density in the Ocean South of 30 degrees S

Author

Xu, Dan, Wang, Tao, Xing, Xiaogang, Bian, Changwei, Xu, Dan, Wang, Tao, Xing, Xiaogang, and Bian, Changwei

Abstract

As a main source of nitrate for the pycnocline in the global ocean, the ocean south of 30 degrees S plays a pivotal role in the global marine biogeochemical cycle. Nitrate in the pycnocline often shows a more stable relationship with density than with depth. Hence, it is important to understand the nitrate structure and its relationship with density in the ocean south of 30 degrees S. In the present study, the nitrate-density relationship and the mechanisms for its variability are studied based on the data from more than 60,000 profiles. Through analysis, we find that nitrate is approximately linearly correlated with potential density in the nitracline, except for the western boundary current zones. The upper bounds of the nitracline depend on the mixed layer and euphotic layer depth. The lower bounds are related to the depth of maximum nitrate, which mainly vary meridionally with sharp changes near the Subantarctic Front. The diapycnal gradients of nitrate also show meridional variability, with large magnitudes corresponding to thick Subantarctic Mode Water, low diapycnal mixing in the nitracline, and high biological uptake in the euphotic layer. The nitrate-density relationship can be applied to predict nitrate concentrations based on the observed temperature and salinity profiles and support some detailed studies on the physical-biogeochemical interactions. Two examples show that the predicted nitrate data could help better resolve the effects of ocean circulations and mesoscale eddies on nitrate than the existing observed nitrate profiles.

Published
2022
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34. An exploratory model study of sediment transport sources and deposits in the Bohai Sea, Yellow Sea, and East China Sea

Author

Bian, Changwei, Jiang, Wensheng, and Greatbatch, Richard John

Subjects
parasitic diseases
Abstract

A regional ocean circulation model (ROMS) is used to simulate the Chinese land-derived sediment transport in the Bohai Sea, Yellow Sea, and East China Sea (BYECS). The model includes the effect of currents, tides, and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine-grain sediment transport from the Huanghe River (Yellow River), the Old Huanghe Delta, and the Changjiang River (Yangtze River) in the BYECS. The seasonal variability of the sediment transport in the BYECS and the sources of the Yellow Sea Trough mud patch, the mud patch southwest of Cheju Island, the mud patch offshore from the Zhejiang and Fujian provinces and the Okinawa Trough mud patch are discussed. The results show that the Huanghe River sediment can be transported to the Yellow Sea Trough, but little makes it to the outer shelf while the Old Huanghe Delta sediment is mainly transported to the Yellow Sea Trough. Most of the sediment from the Changjiang River mouth is carried to the mud patch off the coast of the Zhejiang and Fujian provinces but with part of this sediment also transported to the Yellow Sea Trough. The model shows that it is difficult to transport land-derived sediment to the Okinawa Trough mud patch under normal conditions. The model also has difficulty accounting for the deposition of sediment in the region to the southwest of Cheju Island and offshore from the Zhejiang and Fujian provinces, an issue requiring further study.

Published
2013

36. Distributions of suspended sediment concentration in the Yellow Sea and the East China Sea based on field surveys during the four seasons of 2011

Author

Bian, Changwei, Jiang, Wensheng, Quan, Qi, Wang, Tao, Greatbatch, Richard John, Li, Wei, Bian, Changwei, Jiang, Wensheng, Quan, Qi, Wang, Tao, Greatbatch, Richard John, and Li, Wei

Abstract

The seasonal and spatial variation of the suspended sediment concentration (SSC) in the Yellow Sea and the East China Sea (YSECS) is studied using turbidity, temperature and velocity field data from all seasons of 2011. The important hydrodynamic factors affecting the SSC distribution are discussed, based on the field data. The data provide a picture of the seasonal evolution of the SSC in the YSECS in a single year. The results show that the highest surface layer SSC was measured in spring and winter, while the summer had the lowest surface layer SSC. In the bottom layer, the SSC distribution patterns were similar in all seasons except that a much higher SSC water plume extended from the Subei Shoal to the East China Sea shelf in winter survey. The vertical SSC gradient was stronger in the shallow water area than the deep water area, and it was stronger in summer and autumn than in winter and spring. We argue that wind-induced vertical mixing dominated the SSC distribution in the surface layer while the tidal currents played an important role in the bottom layer and sub-tidal currents dominated the horizontal pattern of the SSC distribution pattern over the shelf area. In particular, the presence of the summer thermocline limited the vertical mixing in summer, decreasing the SSC in the surface layer. The front between the East China Sea Coastal Current and the Taiwan Warm Current appears to prevent the high SSC water from being transported to the shelf. The sediment discharged by the Changjiang River was found to be concentrated in the estuary area and influenced the shelf SSC distribution only through the action of the subtidal currents.

Published
2013
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