The tidal asymmetry-induced siltation below tidal barriers is a worldwide problem that restricts regional socio-economic and environmental development. The hydrodynamic processes of the small mud estuary also feature ...The tidal asymmetry-induced siltation below tidal barriers is a worldwide problem that restricts regional socio-economic and environmental development. The hydrodynamic processes of the small mud estuary also feature a high uncertainty after estuary restoration measures. In this study, a hydrodynamic model based on the MIKE21 is used to quantify the responses of tidal asymmetry to a two-phase restoration project in Shuanglong Estuary, Bohai Bay, China. According to the numerical modeling results, the tidal flat removal in the upper estuary(first-phase restoration) induces the flood asymmetry switching to the ebb asymmetry in unrestored reach but enhances flood asymmetry in widening restored reach. Although the tidal asymmetry reverts to flood-dominated pattern after full restoration over the estuary, the imbalance between flood and ebb velocities is relieved. A possible net sediment transport pattern based on a comparison of dominant asymmetric current and actual sediment transport period shows net sediments in the upper estuary and inlet transport seaward and landward, respectively, in the first-phase restoration, whereas landward net sediment transport occurs in the whole estuary under the second-phase restoration scenario. Given these results, we assume that a switch from the flood-dominated estuary to ebb-dominated estuary can be caused by redesigning the cross-sectional profile. The quantitative comparison of Lagrangian residual currents also implies that a channel–shoal structure rather than a flat bathymetry can promote the mass transport. Therefore, reshaping the channel–tidal flat system in restoration projects can prevent the sedimentation of the estuary and improve the water environment.展开更多
Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary we...Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that： （1） In recent years （2006-2013）, the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006; （2） The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area; （3） In 2004-2007, the sand-silt boundary in the north part （31 ~30＇N） of the continental shelf area presented no significant changes, while that in the south part （31~30＇S） moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu; （4） The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage.展开更多
The East China Sea(ECS),which is located in the transitional zone between land and ocean,is the main site for the burial of sedimentary organic carbon.Despite good constraints of the modern source to the sinking proce...The East China Sea(ECS),which is located in the transitional zone between land and ocean,is the main site for the burial of sedimentary organic carbon.Despite good constraints of the modern source to the sinking process of organic carbon,its fate in response to changes in climate and sea level since the last deglaciation remains poorly understood.We aim to fill this gap by presenting a high-resolution sedimentary record of core EC2005 to derive a better understanding of the evolution of the depositional environment and its control on the organic deposition since 17.3 kyr.Our results suggest that sedimentary organic carbon was deposited in a terrestrial environment before the seawater reached the study area around 13.1 kyr.This significant transition from a terrestrial environment to a marine environment is reflected by the decrease in TOC/TN and TOC/TS ratios,which is attributed to deglacial sea level rise.The sea level continued to rise until it reached its highstand at approximately 7.3 kyr when the mud depocenter was developed.Our results further indicate that the deposition of the sedimentary organic carbon could respond quickly to abrupt cold events,including the Heinrich stadial 1 and the Younger Dryas during the last deglaciation,as well as‘Bond events'during the Holocene.We propose that the rapid response of the organic deposition to those cold events in the northern hemisphere is linked to the East Asian winter monsoon.These new findings demonstrate that organic carbon deposition and burial on the inner shelf could effectively document sea level and climatic changes.展开更多
The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hour...The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hours of EK application. In the initial tests, high electrokinetic flow potential was achieved;however, high levels of chlorine gas were produced in the high-salinity environments. The process was improved by controlling and maintaining a certain fraction of the chlorine gas (Cl2) in place. The pH was controlled by the chlorine gas maintained in-situ and transported from the anode to cathode. The transports of four heavy metals were evaluated in this study. The chlorine gas can have two impacts on the transport of metals in the system. One is to oxidize the metal ions to a higher oxidation state and the second is to form chloride complexes, which have higher mobility in the system. Determination of oxidation state and the subsequent metal chloride complex are left for future research.展开更多
The Kendeng Basin, the major depocenter of the East Java Basin, has been filled with deep-sea clastic volcanic deposits since the Middle Tertiary, which developed into volcanic deposits in the Quaternary. With thick Q...The Kendeng Basin, the major depocenter of the East Java Basin, has been filled with deep-sea clastic volcanic deposits since the Middle Tertiary, which developed into volcanic deposits in the Quaternary. With thick Quaternary volcanic deposits covering almost the entire basin, outcrops are only found in the north, forming a fold-thrust belt structure. The oldest known stratigraphic unit is the early Miocene Pelang Formation, which was deposited in the lower to the upper bathyal zone. Rocks older than the Pelang Formation have not been identified in this basin either from outcrops or drill-hole data. However, the geochemical analysis of oil seepage proves to be different because the oil source rock in Kendeng Basin was interpreted to be of older lithology than the Pelang Formation, indicating a potentially older stratigraphic unit in the Kendeng Basin that has not been revealed to date. Mud volcanoes transported rock material from the Kendeng Basin to the surface, uncovering the stratigraphy that has been an enigma. The material in question includes Nummulites limestones, conglomerates, and quartz sandstones. Paleontological analysis results on rock fragments indicate that they belong to the Middle Eocene age, so they are older than the Pelang Formation. Mud volcano also carried younger limestones to the surface identified as Miocene Age (equivalent with the Pelang Formation), which were deposited in a middle neritic environment, so they provided information that shallow areas possibly formed a horst-graben structure during the Miocene in the Kendeng Basin. The appearance of Eocene and Miocene rock fragments can be used to complement the stratigraphy and it also provides a potentially new concept of source-reservoir rock in the Kendeng Basin.展开更多
基金financially supported by China Central Government Fund for Marine Usage Program (No. THY-2011)partly supported by the National Natural Science Fundation of China (No. 41776098)
文摘The tidal asymmetry-induced siltation below tidal barriers is a worldwide problem that restricts regional socio-economic and environmental development. The hydrodynamic processes of the small mud estuary also feature a high uncertainty after estuary restoration measures. In this study, a hydrodynamic model based on the MIKE21 is used to quantify the responses of tidal asymmetry to a two-phase restoration project in Shuanglong Estuary, Bohai Bay, China. According to the numerical modeling results, the tidal flat removal in the upper estuary(first-phase restoration) induces the flood asymmetry switching to the ebb asymmetry in unrestored reach but enhances flood asymmetry in widening restored reach. Although the tidal asymmetry reverts to flood-dominated pattern after full restoration over the estuary, the imbalance between flood and ebb velocities is relieved. A possible net sediment transport pattern based on a comparison of dominant asymmetric current and actual sediment transport period shows net sediments in the upper estuary and inlet transport seaward and landward, respectively, in the first-phase restoration, whereas landward net sediment transport occurs in the whole estuary under the second-phase restoration scenario. Given these results, we assume that a switch from the flood-dominated estuary to ebb-dominated estuary can be caused by redesigning the cross-sectional profile. The quantitative comparison of Lagrangian residual currents also implies that a channel–shoal structure rather than a flat bathymetry can promote the mass transport. Therefore, reshaping the channel–tidal flat system in restoration projects can prevent the sedimentation of the estuary and improve the water environment.
基金supported by the Fundamental Research Funds for Central Welfare Research Institutes(Grant No.TKS160103)the National Key Research and Development Program of China(Grant No.2016YFC0402106)the National Natural Science Foundation of China(Grant Nos.51579123 and 41331174)
文摘Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that： （1） In recent years （2006-2013）, the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006; （2） The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area; （3） In 2004-2007, the sand-silt boundary in the north part （31 ~30＇N） of the continental shelf area presented no significant changes, while that in the south part （31~30＇S） moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu; （4） The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage.
基金the National Natural Science Foundation of China(No.41976053)and the Shandong Province Funds for Excellent Young Scholars(No.ZR2021YQ26)。
文摘The East China Sea(ECS),which is located in the transitional zone between land and ocean,is the main site for the burial of sedimentary organic carbon.Despite good constraints of the modern source to the sinking process of organic carbon,its fate in response to changes in climate and sea level since the last deglaciation remains poorly understood.We aim to fill this gap by presenting a high-resolution sedimentary record of core EC2005 to derive a better understanding of the evolution of the depositional environment and its control on the organic deposition since 17.3 kyr.Our results suggest that sedimentary organic carbon was deposited in a terrestrial environment before the seawater reached the study area around 13.1 kyr.This significant transition from a terrestrial environment to a marine environment is reflected by the decrease in TOC/TN and TOC/TS ratios,which is attributed to deglacial sea level rise.The sea level continued to rise until it reached its highstand at approximately 7.3 kyr when the mud depocenter was developed.Our results further indicate that the deposition of the sedimentary organic carbon could respond quickly to abrupt cold events,including the Heinrich stadial 1 and the Younger Dryas during the last deglaciation,as well as‘Bond events'during the Holocene.We propose that the rapid response of the organic deposition to those cold events in the northern hemisphere is linked to the East Asian winter monsoon.These new findings demonstrate that organic carbon deposition and burial on the inner shelf could effectively document sea level and climatic changes.
文摘The removal efficiency of heavy metals from offshore muds is enhanced in the presence of generated chlorine gas (Cl2). The tests showed a high removal efficiency of heavy metals at the anode end of cores after 24 hours of EK application. In the initial tests, high electrokinetic flow potential was achieved;however, high levels of chlorine gas were produced in the high-salinity environments. The process was improved by controlling and maintaining a certain fraction of the chlorine gas (Cl2) in place. The pH was controlled by the chlorine gas maintained in-situ and transported from the anode to cathode. The transports of four heavy metals were evaluated in this study. The chlorine gas can have two impacts on the transport of metals in the system. One is to oxidize the metal ions to a higher oxidation state and the second is to form chloride complexes, which have higher mobility in the system. Determination of oxidation state and the subsequent metal chloride complex are left for future research.
文摘The Kendeng Basin, the major depocenter of the East Java Basin, has been filled with deep-sea clastic volcanic deposits since the Middle Tertiary, which developed into volcanic deposits in the Quaternary. With thick Quaternary volcanic deposits covering almost the entire basin, outcrops are only found in the north, forming a fold-thrust belt structure. The oldest known stratigraphic unit is the early Miocene Pelang Formation, which was deposited in the lower to the upper bathyal zone. Rocks older than the Pelang Formation have not been identified in this basin either from outcrops or drill-hole data. However, the geochemical analysis of oil seepage proves to be different because the oil source rock in Kendeng Basin was interpreted to be of older lithology than the Pelang Formation, indicating a potentially older stratigraphic unit in the Kendeng Basin that has not been revealed to date. Mud volcanoes transported rock material from the Kendeng Basin to the surface, uncovering the stratigraphy that has been an enigma. The material in question includes Nummulites limestones, conglomerates, and quartz sandstones. Paleontological analysis results on rock fragments indicate that they belong to the Middle Eocene age, so they are older than the Pelang Formation. Mud volcano also carried younger limestones to the surface identified as Miocene Age (equivalent with the Pelang Formation), which were deposited in a middle neritic environment, so they provided information that shallow areas possibly formed a horst-graben structure during the Miocene in the Kendeng Basin. The appearance of Eocene and Miocene rock fragments can be used to complement the stratigraphy and it also provides a potentially new concept of source-reservoir rock in the Kendeng Basin.
