The failure propagation of weakly stable sediment:A reason for the formation of high-velocity turbidity currents in submarine canyons

The long-distance movement of turbidity currents in submarine canyons can transport large amounts of sediment to deep-sea plains.Previous studies show obvious differences in the turbidity current velocities derived from the multiple cables damage events ranging from 5.9 to 28.0 m/s and those of field observations between 0.15 and 7.2 m/s.Therefore,questions remain regarding whether a turbid fluid in an undersea environment can flow through a submarine canyon for a long distance at a high speed.A new model based on weakly stable sediment is proposed(proposed failure propagation model for weakly stable sediments,WS S-PFP model for short)to explain the high-speed and long-range motion of turbidity currents in submarine canyons through the combination of laboratory tests and numerical analogs.The model is based on two mechanisms:1)the original turbidity current triggers the destabilization of the weakly stable sediment bed and promotes the destabilization and transport of the soft sediment in the downstream direction and 2)the excitation wave that forms when the original turbidity current moves into the canyon leads to the destabilization and transport of the weakly stable sediment in the downstream direction.The proposed model will provide dynamic process interpretation for the study of deep-sea deposition,pollutant transport,and optical cable damage.

Boosting spring runoff into the sea by reservoir regulation and its potential for estuarine fishery recovery

With global surge in reservoir construction over the past decades,river systems worldwide have been profoundly fragmented.Consequently,flow manipulation by reservoirs has altered the natural hydrological processes,resulting in extensive modifications of fluvial-marine ecosystems.Mitigating the adverse ecological consequences of reservoirs has become a global concern and has garnered increasing attention.The Yellow River,as one of the most extensively manipulated river systems globally,has experienced substantial changes in the amount and timing of water discharge due to the presence of numerous reservoirs scattered throughout its catchment area.These alterations have caused physicochemical changes in the estuary and subsequent modifications to the estuarine ecosystem.In recent years,the Yellow River Conservancy Committee initiated the release of water through the Xiaolangdi Dam during the major spawning period of fisheries,specifically in the spring,with the aim of improving the estuarine ecological environment.From 2011 to 2020,a total of 84.05 km^(3)of water was discharged from the Xiaolangdi Reservoir during spring seasons,of which 40%(33.16 km^(3))constituted water impounded within the reservoir during preceding months.Correspondingly,the spring water discharge from the Yellow River to the sea increased significantly from 1.50 km^(3)/yr to 3.46 km^(3)/yr in the past decade,leading to a decrease in estuarine salinity by 1.6 PSU.The estuarine fishery resources,such as fish eggs in the Yellow River estuary,have demonstrated evident improvement.The reservoir regulation in the Yellow River,which has successfully enhanced spring water discharge and subsequently restored estuarine fishery resources,presents an effective attempt for mitigating the adverse ecological effects associated with reservoirs.

Microbial Sulfate Reduction and Its Role in Carbon Sequestration in Marine Sediments

0 INTRODUCTION The carbon buried in marine sediments in the form of organic carbon or carbonate minerals represents the largest pathway for carbon removal from Earth's surface environments(Sun and Turchyn,2014).Microbial sulfate reduction(MSR)is a fundamental biogeochemical process occurring in marine sediments,where sulfate-reducing bacteria(SRB)reduce sulfate(SO42-)to sulfide(S2-)using organic matter or methane as electron donors(Jorgensen,2021).

黄河下游与河口对2015~2017年调水调沙中断的沉积响应

受流域内降水波动和小浪底库容变化的影响,2015~2017年期间黄河调水调沙中断.本研究系统收集了2015~2017年黄河主要水文站水沙数据、下游河道高程资料和冲淤数据、河口测深和粒度资料,研究了调水调沙中断导致的黄河入海泥沙来源和通量变化,探讨了下游河道和河口地貌演化对调水调沙中断的快速响应.2015~2017年,上中游来沙完全被小浪底水库拦截,黄河首次出现全年进入下游的泥沙量为0.水库下泄清水,引起下游河道全线冲刷,累积冲刷量达1.8亿m^(3),高村以上河段是主要冲刷区,高村向下冲刷量逐渐降低,下游河道断面发生展宽和下切,断面形态向宽深方向演化.下游河道起动的泥沙成为黄河入海泥沙的唯一来源,由于缺少中游泥沙供应,黄河入海沙量进一步降低,2017年,黄河全年入海泥沙仅为770万t,是1950年黄河利津站有连续观测记录以来的最低值.黄河行水河口陆域面积开始萎缩,水下三角洲冲刷强烈,最大冲刷量高达1.8 m/a,导致表层沉积物粗化明显.