The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined expo...The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sediments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of nalkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget.展开更多
The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream,midstream,and estuary of the Changjiang River,China,are analyzed.The sources of sediments are discussed co...The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream,midstream,and estuary of the Changjiang River,China,are analyzed.The sources of sediments are discussed concerning their differences in the shape,size,number,gas percentage and genetic type of quartz-hosted fluid inclusions.From upstream to downstream,the characteristics of quartz-hosted fluid inclusions in sediments are different.The fluid inclusion types in the samples from upstream to estuary are gradually enriched.The sediment influx from the tributaries of the Changjiang River makes new types of quartz-hosted fluid inclusions in the downstream and estuary.In terms of the number and size,most quartz-hosted fluid inclusions are concentrated in the range of 2-4μm in diameters and 10-150 in number per 10^-3 mm^3.The number and size ranges of the fluid inclusions from different positions are also different.The fluid inclusions in the sample collected from the Shigu,upstream of the Changjiang River,are 2-18μm in size,with the number of 2-166 per 10^-3 mm^3.Among the samples collected from Yibin,Yichang and Wuhan,the sizes of fluid inclusions are 2-15,2-10,2-12μm,with the number of 1-270,2-220,and 1^-308 per 10^-3 mm^3,respectively.The proportion of primary fluid inclusions in the sample of the upstream(14%)is higher than that of the midstream(6%-8%)and the estuary(5%),suggesting that different types of source rocks have been input into the river by the tributaries.The characteristics of quartz-hosted fluid inclusions in the fluvial sediments could offer a new perspective for exploration of the source of sediments.展开更多
The quantitative analysis of sediment sources in a sink is an important scientific topic and challenge in provenance research.The characteristics of heavy minerals,combined with the geochemical constituents of detrita...The quantitative analysis of sediment sources in a sink is an important scientific topic and challenge in provenance research.The characteristics of heavy minerals,combined with the geochemical constituents of detrital grains,provide a reliable provenance-tracing approach.We developed a mineral identification method to analyze the multiple grain-size fraction of sediments,from which the elemental geochemistry of hornblende was used to compare the characteristics of sediments from the Huaihe River and Huanghe(Yellow)River in eastern China.Elements that were statistically identified as being able to discriminate sediment provenance were employed to perform a quantitative analysis of the sources of sediments of the abandoned Huanghe River.Results reveal that the Huaihe River is characterized by a high amphibole content of>60%and that the Huanghe and abandoned Huanghe rivers have greater abundances of limonite and carbonate minerals compared with those of the Huaihe River.The contents of trace elements and rare earth elements in hornblende show that the sediments of the abandoned Huanghe River are similar to those of the Huanghe River but different from those of the Huaihe River.Furthermore,chemical mass balance was used to calculate the relative contributions of different provenances of sediment from the abandoned Huanghe River,and nine trace elements of hornblende were identified as discriminators of provenance.Approximately 2%of the hornblende in the abandoned Huanghe River is derived from the Huaihe River and 98%from the Huanghe River.Considering the proportion of hornblende in the total sediment,it is inferred that the contribution of Huaihe River sediment to the abandoned Huanghe River is approximately 0.5%.This study shows that mineral analysis using multiple grain-size fractions(within the wide range of 1Φto 6Φ)with assessment in elemental geochemistry of hornblende can characterize the provenance of fluvial material in coastal zones.展开更多
Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to ex...Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to examine the sedimentary successions, describe and analyse these deformation features, discuss their deformation mechanisms and potential triggers. The Maastrichtian Patti Formation is composed of lithofacies interpreted to have been deposited in tidal and fluvial sedimentary environments. Soft sediment deformation structures recognised in the tidal sediments were clastic dykes, load cast, isolated sand balls, dish-and-pillar structures, convolute lamination, diapiric structures and recumbent folds. Severely deformed cross beds, ring structures, associated sand balls, normal folds and recumbent folds were identified in the fluvial sediments. SSDS recognised were interpreted to have been caused by effects of liquefaction and fluidization. Field observations, facies analysis and morphology of the SSDS indicate that there are relationship between the depositional environments and SSDS. Endogenic processes are considered as the trigger agents and they are represented by rapid sedimentation and overloading, impact of breaking waves, pressure fluctuations caused by turbulent water flow, cyclic stress and current generated by storm waves and changes in water table. The present study did not identify exogenic processes as trigger agent. The occurrence of SSDS in southern Bida Basin strongly favoured a non-tectonic origin but a clear relationship high energy processes in tidal and fluvial depositional environments.展开更多
Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity...Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.展开更多
Quantitatively determining the sources of dune sand is one of the problems necessarily and urgently to be solved in aeolian landforms and desertification research. Based on the granulometric data of sand materials fro...Quantitatively determining the sources of dune sand is one of the problems necessarily and urgently to be solved in aeolian landforms and desertification research. Based on the granulometric data of sand materials from the Hulun Buir Sandy Land, the paper employs the stepwise discriminant analysis technique (SDA) for two groups to select the principal factors determining the differences between surface loose sediments. The extent of similarity between two statistical populations can be described quantitatively by three factors such as the number of principal variables, Mahalanobis distance D 2 and confidence level 琢for F-test. Results reveal that: 1) Aeolian dune sand in the region mainly derives from Hailar Formation (Q 3 ), while fluvial sand and palaeosol also supply partially source sand for dunes; and 2) in the vicinity of Cuogang Town and west of the broad valley of the lower reaches of Hailar River, fluvial sand can naturally become principal supplier for dune sand.展开更多
Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface s...Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface sediment samples collected in major rivers of Malay Peninsula and North Borneo in the tropical Southeast Asian region are used to study the present chemical weathering process and its controlling factors of tropical regions.The results indicate that the clay mineral assemblage in Malay Peninsula consists dominantly of kaolinite(average 80%) and minor illite(average 17%),almost without chlorite and smectite,whereas in North Borneo it consists mainly of illite and chlorite,with minor amounts of kaolinite(average 14%) and no smectite.Total contents of illite and chlorite in both Northwest and Northeast Borneo are 84% and 87%,respectively.Major-element geochemical results of both bulk and clay-fraction sediments show intensive chemical weathering degree for both areas.Relatively,the chemical weathering degree is gradually strengthened from Northeast Borneo,Northwest Borneo,to Malay Peninsula,and it is extremely intensive in Malay Peninsula.Our results indicate that,in the tropical Southeast Asian region exampled by Malay Peninsula and Borneo,climatic condition of tropical warm temperature and East Asian monsoon rainfall is the first-order controlling factor on the chemical weathering,resulting in intensive chemical weathering throughout tropical areas,and tectonic activity and lithology of parent rocks are subordinate factors,which still have an important impact on the weathering products,forming completely different clay mineral assemblages between Malay Peninsula and Borneo.展开更多
Studying the grain-size dependent compositional variability in modern river sediments provides a key to decipher the information stored in the sedimentary archive and reconstruct the evolution of the Earth’s surface ...Studying the grain-size dependent compositional variability in modern river sediments provides a key to decipher the information stored in the sedimentary archive and reconstruct the evolution of the Earth’s surface in the past.Bedload sand along the Xigaze cross section of the Yarlung Tsangpo(upper Brahmaputra River)ranges in mean grain size from 0.72Φto 3.21Φ,is moderately to poorly sorted and slightly platykurtic to moderately leptokurtic with sub-angular to sub-spherical grains.Litho-feldspatho-quartzose to feldspatholitho-quartzose sand(Q 43%-65%;F 13%-44%;L 11%-28%)contains 3.4%-14.4%heavy minerals including amphibole(64%-89%),epidote(4%-11%),chloritoid(0-10%),and clinopyroxene(2%-6%).The marked textural and compositional variability observed across the Xigaze transect of the Yarlung Tsangpo mainstem is controlled by both fluvial and aeolian processes,including repeated reworking by westerly and glacial winds,as well as by local contributions from northern and southern tributaries draining the Lhasa Block and the Himalayan Belt,respectively.The modern sedimentary case here will shed new light on interpreting paleogeography and provenance.展开更多
Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology...Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology and ecosystems. However,owing to the lack of detailed quantitative measurements of the bottom boundary layer, the mechanisms and impacts of internal solitary waves in resuspending and transporting seafloor sediments remain poorly understood. In this study, we present highresolution in situ observations of hydrodynamics in the upper layer(14–265 m) and the bottom boundary layer(<1 m) in the continental shelf slope break zone. Our results reveal that strongly nonlinear internal solitary waves, which occur at the peak of semidiurnal tidal currents, trigger benthic storms at the seafloor. Unlike previously proposed global instability mechanisms, the suspended sediment concentration caused by these strongly nonlinear internal solitary waves reaches 60 times higher than the background value and exhibits sudden, transient peaks. The bottom shear stress(τ) is an order of magnitude greater than that in laboratory measurements, and the observed fluctuating pressure is approximately 2.3 to 7 times greater than that in previous coastal observations. The sediments stirred by benthic storms are transported vertically to more than 100 m above the seabed,with lateral transport extending tens of kilometres beyond the study area. This process is driven by the dynamic mechanism of“strongly nonlinear internal solitary waves lifting sediments, weakly nonlinear internal solitary waves assisted by internal tides,and contour currents transporting sediments.” The suspended sediment flux induced by internal solitary waves in the South China Sea is on the same order of magnitude as that of global dust storm emissions, 21.9 times the volume of Asian dust storms entering the sea, and approximately 21 times the fluvial sediment flux entering the northern South China Sea. These findings are significant for evaluating sedimentary processes and ecological–geochemical impacts in the northern South China Sea, offering a novel perspective on marine ecological environments and carbon sequestration processes.展开更多
基金This work was supported by the funding provided by Ventenskapsådet(Grant No.2016-05642)to JR.
文摘The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain.There is an increasing recognition of small mountain rivers(SMRs)to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux.We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers(LMRs)in Nepal.We investigated the organic matter(OM),its compositional variability,and seasonal export using a suite of lipid biomarkers,namely n-alkanes,n-alkanoic acids,n-alkanols,and sterols.The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability.The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments.Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load.Functional lipids(n-alkanoic acids and n-alkanols)were the major constituents in SMR sediments,indicating better preservation.In contrast,n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs.The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs.A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs.Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems.Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs.In LMRs,the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of nalkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool.The differences in lipid concentrations,their distribution,seasonality,and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget.
基金This study was supported by the National Basic Research Program of China(No.2013CB956504).
文摘The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream,midstream,and estuary of the Changjiang River,China,are analyzed.The sources of sediments are discussed concerning their differences in the shape,size,number,gas percentage and genetic type of quartz-hosted fluid inclusions.From upstream to downstream,the characteristics of quartz-hosted fluid inclusions in sediments are different.The fluid inclusion types in the samples from upstream to estuary are gradually enriched.The sediment influx from the tributaries of the Changjiang River makes new types of quartz-hosted fluid inclusions in the downstream and estuary.In terms of the number and size,most quartz-hosted fluid inclusions are concentrated in the range of 2-4μm in diameters and 10-150 in number per 10^-3 mm^3.The number and size ranges of the fluid inclusions from different positions are also different.The fluid inclusions in the sample collected from the Shigu,upstream of the Changjiang River,are 2-18μm in size,with the number of 2-166 per 10^-3 mm^3.Among the samples collected from Yibin,Yichang and Wuhan,the sizes of fluid inclusions are 2-15,2-10,2-12μm,with the number of 1-270,2-220,and 1^-308 per 10^-3 mm^3,respectively.The proportion of primary fluid inclusions in the sample of the upstream(14%)is higher than that of the midstream(6%-8%)and the estuary(5%),suggesting that different types of source rocks have been input into the river by the tributaries.The characteristics of quartz-hosted fluid inclusions in the fluvial sediments could offer a new perspective for exploration of the source of sediments.
基金Supported by the National Natural Science Foundation of China(Nos.41576057,41876092)。
文摘The quantitative analysis of sediment sources in a sink is an important scientific topic and challenge in provenance research.The characteristics of heavy minerals,combined with the geochemical constituents of detrital grains,provide a reliable provenance-tracing approach.We developed a mineral identification method to analyze the multiple grain-size fraction of sediments,from which the elemental geochemistry of hornblende was used to compare the characteristics of sediments from the Huaihe River and Huanghe(Yellow)River in eastern China.Elements that were statistically identified as being able to discriminate sediment provenance were employed to perform a quantitative analysis of the sources of sediments of the abandoned Huanghe River.Results reveal that the Huaihe River is characterized by a high amphibole content of>60%and that the Huanghe and abandoned Huanghe rivers have greater abundances of limonite and carbonate minerals compared with those of the Huaihe River.The contents of trace elements and rare earth elements in hornblende show that the sediments of the abandoned Huanghe River are similar to those of the Huanghe River but different from those of the Huaihe River.Furthermore,chemical mass balance was used to calculate the relative contributions of different provenances of sediment from the abandoned Huanghe River,and nine trace elements of hornblende were identified as discriminators of provenance.Approximately 2%of the hornblende in the abandoned Huanghe River is derived from the Huaihe River and 98%from the Huanghe River.Considering the proportion of hornblende in the total sediment,it is inferred that the contribution of Huaihe River sediment to the abandoned Huanghe River is approximately 0.5%.This study shows that mineral analysis using multiple grain-size fractions(within the wide range of 1Φto 6Φ)with assessment in elemental geochemistry of hornblende can characterize the provenance of fluvial material in coastal zones.
文摘Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to examine the sedimentary successions, describe and analyse these deformation features, discuss their deformation mechanisms and potential triggers. The Maastrichtian Patti Formation is composed of lithofacies interpreted to have been deposited in tidal and fluvial sedimentary environments. Soft sediment deformation structures recognised in the tidal sediments were clastic dykes, load cast, isolated sand balls, dish-and-pillar structures, convolute lamination, diapiric structures and recumbent folds. Severely deformed cross beds, ring structures, associated sand balls, normal folds and recumbent folds were identified in the fluvial sediments. SSDS recognised were interpreted to have been caused by effects of liquefaction and fluidization. Field observations, facies analysis and morphology of the SSDS indicate that there are relationship between the depositional environments and SSDS. Endogenic processes are considered as the trigger agents and they are represented by rapid sedimentation and overloading, impact of breaking waves, pressure fluctuations caused by turbulent water flow, cyclic stress and current generated by storm waves and changes in water table. The present study did not identify exogenic processes as trigger agent. The occurrence of SSDS in southern Bida Basin strongly favoured a non-tectonic origin but a clear relationship high energy processes in tidal and fluvial depositional environments.
基金funded by the N atural Science Foundation of China (G rants No. 11172217, 51279144 and 11432015)Chinese Academy of Sciences (G rant No. KZZDEW -05-01-03)
文摘Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.
文摘Quantitatively determining the sources of dune sand is one of the problems necessarily and urgently to be solved in aeolian landforms and desertification research. Based on the granulometric data of sand materials from the Hulun Buir Sandy Land, the paper employs the stepwise discriminant analysis technique (SDA) for two groups to select the principal factors determining the differences between surface loose sediments. The extent of similarity between two statistical populations can be described quantitatively by three factors such as the number of principal variables, Mahalanobis distance D 2 and confidence level 琢for F-test. Results reveal that: 1) Aeolian dune sand in the region mainly derives from Hailar Formation (Q 3 ), while fluvial sand and palaeosol also supply partially source sand for dunes; and 2) in the vicinity of Cuogang Town and west of the broad valley of the lower reaches of Hailar River, fluvial sand can naturally become principal supplier for dune sand.
基金supported by National Natural Science Foundation of China (Grant Nos. 40925008,40876024,and 40776027)National Basic Research Program of China (Grant No. 2007CB815906)+1 种基金Shanghai Shuguang Program (Grant No. 07SG23)Shanghai Subject Chief Scientist Program (Grant No. 10XD1406300)
文摘Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface sediment samples collected in major rivers of Malay Peninsula and North Borneo in the tropical Southeast Asian region are used to study the present chemical weathering process and its controlling factors of tropical regions.The results indicate that the clay mineral assemblage in Malay Peninsula consists dominantly of kaolinite(average 80%) and minor illite(average 17%),almost without chlorite and smectite,whereas in North Borneo it consists mainly of illite and chlorite,with minor amounts of kaolinite(average 14%) and no smectite.Total contents of illite and chlorite in both Northwest and Northeast Borneo are 84% and 87%,respectively.Major-element geochemical results of both bulk and clay-fraction sediments show intensive chemical weathering degree for both areas.Relatively,the chemical weathering degree is gradually strengthened from Northeast Borneo,Northwest Borneo,to Malay Peninsula,and it is extremely intensive in Malay Peninsula.Our results indicate that,in the tropical Southeast Asian region exampled by Malay Peninsula and Borneo,climatic condition of tropical warm temperature and East Asian monsoon rainfall is the first-order controlling factor on the chemical weathering,resulting in intensive chemical weathering throughout tropical areas,and tectonic activity and lithology of parent rocks are subordinate factors,which still have an important impact on the weathering products,forming completely different clay mineral assemblages between Malay Peninsula and Borneo.
基金supported financially by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP,Grant No.2019QZKK0204)the National Natural Science Foundation of China Project(Grant No.4200020124)the Jiangsu Shuangchuang(Mass Innovation and Entrepreneurship)Talent Program(Grant No.JSSCBS20210014)。
文摘Studying the grain-size dependent compositional variability in modern river sediments provides a key to decipher the information stored in the sedimentary archive and reconstruct the evolution of the Earth’s surface in the past.Bedload sand along the Xigaze cross section of the Yarlung Tsangpo(upper Brahmaputra River)ranges in mean grain size from 0.72Φto 3.21Φ,is moderately to poorly sorted and slightly platykurtic to moderately leptokurtic with sub-angular to sub-spherical grains.Litho-feldspatho-quartzose to feldspatholitho-quartzose sand(Q 43%-65%;F 13%-44%;L 11%-28%)contains 3.4%-14.4%heavy minerals including amphibole(64%-89%),epidote(4%-11%),chloritoid(0-10%),and clinopyroxene(2%-6%).The marked textural and compositional variability observed across the Xigaze transect of the Yarlung Tsangpo mainstem is controlled by both fluvial and aeolian processes,including repeated reworking by westerly and glacial winds,as well as by local contributions from northern and southern tributaries draining the Lhasa Block and the Himalayan Belt,respectively.The modern sedimentary case here will shed new light on interpreting paleogeography and provenance.
基金the National Natural Science Foundation of China for supporting open scientific expeditions in the northern South China Sea (NORC2020-05, NORC2022-05)supported by the National Natural Science Foundation of China (Grant Nos. 41831280, 42207173)the Natural Science Foundation of Shandong Province (Grant No. ZR2022QD002)。
文摘Internal solitary waves can generate intense bottom currents and turbulent mixing over continental slopes, influencing the redistribution of sediments and pollutants, as well as driving changes in marine geomorphology and ecosystems. However,owing to the lack of detailed quantitative measurements of the bottom boundary layer, the mechanisms and impacts of internal solitary waves in resuspending and transporting seafloor sediments remain poorly understood. In this study, we present highresolution in situ observations of hydrodynamics in the upper layer(14–265 m) and the bottom boundary layer(<1 m) in the continental shelf slope break zone. Our results reveal that strongly nonlinear internal solitary waves, which occur at the peak of semidiurnal tidal currents, trigger benthic storms at the seafloor. Unlike previously proposed global instability mechanisms, the suspended sediment concentration caused by these strongly nonlinear internal solitary waves reaches 60 times higher than the background value and exhibits sudden, transient peaks. The bottom shear stress(τ) is an order of magnitude greater than that in laboratory measurements, and the observed fluctuating pressure is approximately 2.3 to 7 times greater than that in previous coastal observations. The sediments stirred by benthic storms are transported vertically to more than 100 m above the seabed,with lateral transport extending tens of kilometres beyond the study area. This process is driven by the dynamic mechanism of“strongly nonlinear internal solitary waves lifting sediments, weakly nonlinear internal solitary waves assisted by internal tides,and contour currents transporting sediments.” The suspended sediment flux induced by internal solitary waves in the South China Sea is on the same order of magnitude as that of global dust storm emissions, 21.9 times the volume of Asian dust storms entering the sea, and approximately 21 times the fluvial sediment flux entering the northern South China Sea. These findings are significant for evaluating sedimentary processes and ecological–geochemical impacts in the northern South China Sea, offering a novel perspective on marine ecological environments and carbon sequestration processes.
