Yangtze River Mouth Research Articles

Coherence between solar activity and the East Asian winter monsoon variability in the past 8000 years from Yangtze River-derived mud in the East China Sea

AMS 14C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core’s mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called “grain size vs. standard deviation”, we can divide the Core PC-6’s grain-size distribution into two populations at about 28 μm. The fine population (< 28 μm) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon. Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 76-78, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance.

Seasonal change and habitat selection of shorebird community at the South Yangtze River Mouth and North Hangzhou Bay, China

Coastal regions are important habitats for migratory shorebirds. The aim of the study is to understand habitat use by migratory shorebirds and to develop a conservation strategy in the sustainable use of wetlands. From March 2004 to January 2005, we conducted a seasonal shorebirds census in ten coastal habitats along the South Yangtze River mouth and North Hangzhou Bay, simultaneously examining the relative seasonal abundance of shorebirds and their spatial distribution. A total of 25 species were identified, the dominant seasonal species were Great Knot ( Calidris tenuirostris), Sharp-tailed Sandpiper ( Calidris alpine) and Red-necked Stint ( Calidris ruficollis) in spring; Kentish Plover ( Charadrius alexandrinus), Common Greenshank( Tringa nebularia) and Lesser Sand Plover ( Charadrius mongolus) in summer; Kentish Plover, Red-necked Stint and Common Greenshank in autumn; Dunlin( Calidris alpine), Kentish Plover and Marsh Sandpiper ( Tringa stagnatilis) in winter. These species accounted for more than 85% of the total shorebirds. The numbers of shorebirds counted was highest in spring and then in autumn, winter and summer respectively. Among the four seasons, there were few significant differences in the number of bird species between the sites outside the seawall (intertidal mudflat) and the sites inside the seawall (artificial wetland), but the average density of shorebirds was obviously different. The habitat-selection analysis of the environmental factors (outside and inside the seawall) impacting on the shorebird community was made in the 10 study sites with Canonical Correspondence Analysis. The study results indicated that: (1) Outside the seawall, the widths of the total intertidal mudflat and bare mudflat were the key factors affecting the shorebirds; the proportion of bulrush ( Scirpus×mariquete) covering and supertidal mudflat width had a positive correlation with the abundance of birds, while human disturbance and the proportion of both reed ( Phragmites communis) and smooth cord-grass ( Spartina alterniflora) covering in total surveyed areas had negative impacts on bird numbers; (2) Inside the seawall, the proportions of areas with shallow water and mudflats occupying the total surveyed area were key factors influencing the number of birds; the size of the bulrush area should have a positive impact on the appearance of shorebirds. Habitats with heavy human disturbance, dense reed and smooth cord-grass or a high water level were not conducive to be inhabited by shorebirds.

On the Origin of the Radial Sand Ridges in the Southern Yellow Sea: Results from the Modeling of the Paleoradial Tidal Current Fields off the Paleo-Yangtze River Estuary and Northern Jiangsu Coast

The origin of the radial sand ridges (RSR) in the southern Yellow Sea has been a controversial problem since they were discovered. The key to solving this problem is to answer whether the radial tidal current field existed prior to the formation of the RSR. With a two-dimensional tide model over the Bohai Sea, the Yellow Sea, and most of the East China Sea, the M2 tides and tidal currents at around 7000 years BP, 6000 years BP, 3800 years BP, the 8th and 11th centuries AD are simulated. The model results show that, from 7000 years BP to 3800 years BP, tidal currents north of the major longitudinal axis of the Paleo-Yangtze River Estuary (PYRE) converged toward and diverged from the mouth of this river and the distribution pattern of the tidal current field was largely similar to that of the tidal current field over the southern Yellow Sea. Toward the 8th century AD, the PYRE became a delta. The Yangtze River mouth migrated southeastward considerably until the 11th century AD, and the shorelines of the Yangtze River mouth and northern Jiangsu were generally similar in geometry to the present ones. At these two stages (the 8th and the 11th centuries AD), the radial tidal current fields with a focal point in Dongtai area were evident, and the distribution patterns of tidal current fields were much similar than at present. After the 11th century AD, the northern Jiangsu shoreline evolved gradually to the present position under the influence of the shifting Yellow River mouth and the present radial tidal current field, with its focal point in the Qianggang area, was formed eventually over the southern Yellow Sea. In short, the radial tidal current field off the PYRE and northern Jiangsu coast has existed and its distribution pattern has been quite stable since around 7000 years BP, despite the shoreline evolution of the PYRE and northern Jiangsu coast. However, the convergent location of the tidal currents has shifted from the mouth of the PYRE to the Dongtai area and then to the present Qianggang area. This suggests that the radial tidal current field in the RSR area existed before the formation of these sand ridges, and the RSR in the southern Yellow Sea were formed and are maintained by radial tidal current fields with sufficient sediment supply.

Yangtze offshore, China: highly laminated sediments from the transition zone between subaqueous delta and the continental shelf

This study examines the deposition of highly laminated muddy sediment in vibrocores recovered from a depth of 40–55 m of water and located 120 km east of the Yangtze River mouth. X-radiographs show numerous sharp-based sedimentary rhythmics with nearly parallel and undulated laminations, interbedded with silty lenses and interbeds. The laminated sediment varies from clayey silt to silty clay. AMS radiocarbon dates on well-preserved bivalves are primarily younger than 5500 y BP, indicating the formation of the laminated sediment under the present sea-level conditions. Macro- and microfossils in the sediments are consistent with the modern offshore sedimentary setting. The laminated sediment originated from the Yangtze estuary, but the sedimentation processes were not deltaic. The highly laminated sediment that lies below the normal wave base of 10 m was deposited on the seaward margin of the Yangtze subaqueous delta, closely associated with submarine tidal and storm-generated currents.

Observed residual currents off the Changjiang (Yangtze) River mouth in wintertime of 1959 and 1982

Data taken in the two large-scale ocean investigations in China in winter 1959 and 1982 are used to analyze the residual current off the Changjiang (Yangtze) River mouth in this paper. The current in wintertime off the river mouth consist of the Changjiang runoff, wind-driven current, coastal current, density-driven current and Taiwan Warm Current (TWC). The TWC occurs in wintertime off the mouth. The surface TWC reaches only to the east side of Dinghai, then turns southeastward. The bottom TWC can flow to the area off the Changjiang mouth along west slop of the submerged river valley (SRV) and to the area off the Subei coast. The simulated currents by 3D model are basically consistent with the observed currents, although the model was run with climatological forces and the observations was done in episodic time manner.

Observed residual currents off the Changjiang (Yangtze) River mouth in summertime of 1959 and 1982

Observed residual currents off the Changjiang (Yangtze) River mouth in summertime of 1959 and 1982

Simulated circulations off the Changjiang (Yangtze) River mouth in spring and autumn

The circulations off the Changjiang mouth in May and November were simulated by a three dimension numerical model with monthly averaged parameters of dynamic factors in this paper. The area covers the East China Sea (ECS), Yellow Sea and Bohai Sea. Simulated results show that the circulation off the Changjiang mouth in spring and autumn is mainly the Changjiang runoff and Taiwan Warm Current (TWC). The Changjiang discharge is much larger in May than in November, and the wind is westward in May, and southward in November off the Changjiang mouth. The runoff in May branches in three parts, one eastward flows, the other two flow northward and southward along the Subei and Zhejiang coast respectively. The Changjiang diluted water expands eastward off the mouth, and forms a strong salinity front near the mouth. Surface circulation in autumn is similar to that in winter, the runoff southward flows along the coast, and the northward flowing TWC becomes weaker compared to that in spring and summer. The bottom circulations in May and November are mainly the runoff near the mouth and the TWC off the mouth, and the runoff and TWC are greater in May than in November.

The characteristics of Quaternary activity of faults in the sea area near the Yangtze River mouth

By shallow seismic prospecting, it is showed that the faults in the sea area near the Yangtze River mouth are mainly the NE and NW-trending faults. The main activity time of fault is Pliocene to Early Pleistocene, and the latest activity is up to Middle Pleistocene. The maximum of fault is generally several tens meters with the throw decreased upward. The dislocation near the bottom of Middle Pleistocene is 12–13 m. The average vertical displacement rate is on a level of 10−3 mm/a.

Distribution characteristics of historical earthquake classes in Jiangsu Province and South Huanghai Sea region

According to the analysis on the characteristics of historic earthquakes in Jiangsu Province and South Huanghai Sea region, the historical earthquakes in the studied area are divided into two kinds of “comparatively safe class” and “comparatively dangerous class”. Then the statistical result of earthquake class, the characteristics of geographical distribution and geological structures are studied. The study shows: a) In Jiangsu Province and South Huanghai Sea region, the majority of historical strong earthquakes belong to “comparatively safe class”, only 13.8% belong to “comparatively dangerous class”; b) Most historical earthquakes belong to “comparatively safe class” in the land area of Jiangsu, eastern sea area of Yangtze River mouth and northern depression of South Huanghai Sea region. However, along the coast of middle Jiangsu Province and in the sea area of South Huanghai Sea, the distribution of historical earthquake classes is complex and the earthquake series of “comparatively dangerous class” and “comparatively safe class” are equivalent in number; c) In the studied area, the statistical results of historical earthquake classes and the characteristics of spatial distribution accord very well with the real case of present-day earthquake series. It shows that the seismic activity in the region has the characteristic of succession, and the result from this study can be used as a reference for early postseismic judgment in the earthquake emergency work in Jiangsu Province.

Effects of Reduced Yangtze River Discharge on the Circulation of Surrounding Seas

A regional model of the western Pacific Ocean with 1/6o resolution is used to investigate possible effects of reduced Yangtze River discharge on the circulation of surrounding seas. To the extent of data availability, the model is mostly driven by monthly climatological winds and inflows/outflows through open-ocean boundaries. With climatological discharge rate, the Yangtze River plume disperses to the northeast in summer but follows the China Coastal Current (CCC) to the south in winter. While a substantial amount of the summer plume is retained in the southern Yellow Sea and northern East China Sea until the arrival of winter northerly monsoon, the winter Yangtze River discharge is able to escape freely to the south through advection by the CCC. The source water of the CCC is mainly comprised of winter discharge from Yangtze River, remnants of Yangtze River plume water retained in areas northeast of the river mouth from the preceding summer, Yellow Sea water and even some of the Bohai water. The effect of reduced Yangtze River discharge is highly asymmetric between summer and winter. Summer reduction produces an expansive, positive salinity anomaly northeast of the Yangtze River mouth. The response is rather swift and directly proportional to the reduction of freshwater supply. Winter reduction of freshwater discharge from the Yangtze River leads to higher salinity in the CCC south of the river mouth. The winter insensitivity of the CCC to reduced Yangtze outflow arises because the CCC is fed by multiple sources, some of which are not related to winter discharge from Yangtze River. In the highly unlikely event that the Yangtze River discharge is terminated for multiple years, the source water of the CCC will be dominated by the Yellow Sea and even Bohai waters.

Morphological response of tidal marshes, flats and channels of the Outer Yangtze River mouth to a major storm

Systematic morphological changes of the coastline of the outer Yangtze River mouth in response to storms versus calm weather were documented by daily surveys of tidal marshes and flats between April 1999 and May 2001 and by boat surveys offshore during this and earlier periods. The largest single event during 1999 to 2001 was Typhoon Paibaian, which eroded the unvegetated tidal flat and lower marsh and led to accretion on the middle-to-upper marsh and in the subtidal channel. The greatest erosion of 21 cm occurred at the border between the marsh and the unvegetated flat due to the landward retreat of the marsh edge during the storm. Strong waves on the flats increased suspended sediment concentration by 10-20 times. On the upper marsh, where the frequency of submergence by astronomical tides is only 3%, Typhoon Paibian led to 4 cm of accretion, accounting for 57% of the net accretion observed over the 2-yr study. Typhoon Paibian and other large storms in the 1990s caused over 50 cm of accretion along the deep axis of the river mouth outlet channel. During calm weather, when hydrodynamic energy was dominated by tides, deposition was centered on the unvegetated flats and lower marsh with little deposition on the high marsh and erosion in the subtidal channel. Depositional recovery of the tidal flat from typhoon-induced erosion took only several days, whereas recovery of the subtidal channel by erosion took several weeks. A conceptual model for the morphological responses of tidal marshes, flats, and subtidal channels to storms and calm weather is proposed such that sediment continually moves from regions of highest near-bed energy towards areas of lower energy.

Intensity distribution and effect of the Nov. 9, 1996 earthquake of M S=6.1 in offshore outside the Yangtze River Mouth on the South Korea

Intensity distribution and effect of the Nov. 9, 1996 earthquake of M S=6.1 in offshore outside the Yangtze River Mouth on the South Korea

Sediment provenance and province of the southern Yellow Sea: Evidence from light mineral

The distribution for percent content of light mineral is divided in detail to emphasize distributional trends of higher and lower contents by using 222 samples of light mineral in the southern Yellow Sea. 5 mineral provinces are divided, and they are I-north mineral province of the southern Yellow Sea, the sediment dominantly derived from the Yellow River; II-mixed mineral province, the sediment derived from both the Yellow River and Yangtze River; III-middle mineral province, the sediment derived mainly from the Yellow River and a part of sediment derived from Yangtze River; IV-province east of Yangtze River mouth, the sediment derived dominantly from Yangtze River; and V south mineral province, sediment was affected by relict sediment and modern sediment of Yangtze River. In this paper, the assemblage of dominant mineral and diagnostic mineral for the five provinces are discerned.

Hydrological Regime and Morphodynamics of the Yangtze River Mouth Area

The features of the hydrological regime, modern morphological structure, fluviomorphological processes, and the history of formation of the Yangtze River mouth area are discussed. The influence of the huge river water and sediment runoff and tides on the hydrological and morphological processes in the Yangtze River mouth is shown. The possible impact of construction of the large waterworks “Three Gorges” on the hydrological and morphological processes in the Yangtze River mouth is roughly evaluated.

Sedimentary processes on an estuarine marsh island within the turbidity maximum zone of the Yangtze River mouth

Sedimentary characteristics and processes on an estuarine marsh island in the Yangtze Estuary (East China Sea) show that (1) the mean grain size of the surficial sediments varies between 0.003 and 0.16 mm, the finest sediment being more enriched in the marsh center particularly under calm weather conditions during the flood season, and the coarsest sediment being more enriched on the low seaward tidal flats particularly after storms; (2) the sediment organic carbon content is generally less than 1.4 wt%; (3) the annual vertical marsh accretion is in the range of 20 cm, with a maximum value of 40 cm in the middle of the marsh; and (4) the seasonal cycle in plant growth strongly influences sediment grain size and erosion-accretion events.

Sedimentation on a Growing Intertidal Island in the Yangtze River Mouth

Based on surficial sediment samples, experiments of the trapping effect by vegetation on suspended particles, as well as measurements of changes in the sediment surface, this article deals mainly with general grain-size characteristics, the organic content of the sediments, the accretion rate in tidal marshes and the influence of the plant community along with the effect of benthic fauna on sedimentation. Conclusions that were reached included (a) mean grain-size Mz (Φ) is between 3·0 and 8·5 under fair-weather conditions and can be as low as 2·5 in storm events, the grain-size composition is similar to the composition of the Yangtze River sediment; (b) a trend that the finer half of the sediment samples covers a wider grain-size range than the coarse half is shown by the fact that Mz (Φ)>Φ50for 96% of the samples and SKI>0 for 97% of the samples; (c) positive correlation between Mz and σ1supports the observation that sediment sorting is functionally related to grain-size with the best sorting occurring at a median grain-size of 2·5Φ–3·0Φ. This fact corresponds to the theory that less energy is needed for the transport of fine sands (compared with both coarser and finer grains); (d) the organic content in surficial sediments is less than 1·5%. This low content of organic matter largely results from a high accretion rate of mineral grains from the river; (e) the grain-size of surficial sediment varies both temporally and spatially. The finest sediments occur in the centre of the marsh, becoming coarser peripherally. Around the island, the coarsest grain-size occurs on the seaside because of a higher water energy there. Grain-size in the main marsh is also influenced by seasonal changes in the plant community while the water energy especially during the storms has a large effect on the grain-size of the bare flats as well as on the outer area of the marsh; (f) accretion rates in marsh areas can be up to several decimeters. In this type of environment, the trapping effects of plants, as well as the biodeposition by benthic fauna, contribute very little to the total sedimentation.

Stoichiometry of carbon, hydrogen, nitrogen, sulfur and oxygen in the particulate matter of the western North Pacific marginal seas

Abstract The suspended particulate matter (SPM) in surface seawater was collected from 19 stations in the Sea of Japan, 42 stations in the East China Sea, 7 stations North of Taiwan and 6 stations in the Philippine Sea and the Bashi Channel. The particulate organic carbon (POC), particulate organic hydrogen (POH), particulate organic nitrogen (PON), particulate organic sulfur (POS), particulate organic oxygen (POO), particulate phosphorus (PP) and total organic matter (TOM) concentrations were determined. In the Sea of Japan these concentrations were generally lower in the region affected by the Kuroshio branch. In the East China Sea high concentrations of SPM and other organic components were found at stations nearest the Yangtze River mouth, reflecting the terrestrial input. On the other hand, the values were lower in regions influenced by the Kuroshio. In the Philippine Sea and the Bashi Channel, the effect of terrestrial input was not obvious, resulting in lower concentrations of organic matter. The average molar ratios for all samples were C:H:N:S:O = 7.69(± 0.33): 8.73(± 1.62): 1.0: 0.16(± 0.014): 4.12(± 0.64).

The Year Climates by the Climatic Types of Köppen and Thornthwaite on the Nansei Islands in Japan

In order to clarify the climate by year fluctuation of climatic condition on the Nansei Islands, the year climates were studied in comparison with the climates by the normal values. Formosa, the region around the Yangtze river mouth, and southern Kyushu are also included in the study for making clear the local differences of the Nansei Islands.The year climates based on the Köppen's climatic types reveal the differences clearer than the climates by normal values. Namely, Cwa appears to the north and south of the Cfa area, all over the Nansei Islands. The difference between humid and dry areas by the year climates based on the Thornthwaite's climatic types range widely as compared with the climates by normal values. The Nansei Islands are relatively humid in contrast to the surrounding areas. This can be explained by the Pacific Polar Frontal Zone which locats over the Nansei Islands in winter. In spring and autumn, on the other hand, there occurs frequent cyclogenesis on East China Sea and the cyclones move along the Nansei Islands. The different dry conditions by years has stronger effect on the Thornthwaite's year climates than the annual evapotranspiration. The water deficiency based on the year climates appears at the all stations. The amounts of the water deficiency are larger south of Okinoerabu Island than north. Especially, the areas at the northern part of Formosa, on the coast of the continents, at the southern part of Formosa and around the Minamidaito Island are the driest. When the middle latitude high pressure prevails strongly in summer, the dry conditions occur over southern part of the Nansei Islands.

330. Structural state and mechanical properties of polycrystalline Ni 3Fe alloys : Y Calvayrac and M Fayard, Phys Stat Sol (a), 17 (2), 1973, 407–421 ( in French)

AMS14C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core’s mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called “grain size vs. standard deviation”, we can divide the Core PC-6’s grain-size distribution into two populations at about 28 μm. The fine population (< 28 μm) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon.Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 76-78, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance.

STUDY OF THE SEASHORES OF THE CHINESE PEOPLE'S REPUBLIC,

The coastline of the Chinese People's Republic, more than 12, 000 kilometers long, is becoming increasingly important as an industrial site and as a potential source of raw materials. The author participated in the organization of research on coastal dynamics and morphology in several areas. During investigation of silt deposition in the port of Hsin-kang a collection of data on movement of saturated turbid suspensions under natural conditions, has been obtained for the first time. Other areas under investigation include: Liaotung and Shantung peninsulas, Hang-chou Bay and the Yangtze river mouth, Lei-chou-wan Tao peninsula (Kwangtung province), and Hainan Island. A sea-coast studies laboratory was organized recently in the Oceanographic Institute at Tsingtao; research programs are developing at Peiping University, Shanghai Teacher's Institute, and at Sun Yat-sen University in Canton. Perhaps the most difficult problem encountered was lack of data from previous studies or from hydrological observations. Present studies indicate that the seacoasts composed of silt develop uniquely; evidently their stability is determined by changing equilibrium between deposition of silty material into the ocean from river mouth9 and the amount of material stirred up and removed from the coastal zone by wave action. A low gradient (1:2, 000) is characteristic of the great Chinese plain, the drainage belt, and the shoals. Mountainous coastal areas are of the ria type; fringed by an archipelago of small islands. Along embayed, or incurved, areas of the coastline, sandy material tends to accumulate; heavy-mineral accumulations are to be found in these areas. Additional joint Soviet-Chinese coastal-zone studies are proposed under sponsorship of the Chinese People's Republic Academy of Sciences; a planned study on latitudinal zonality in coastal processes will involve comparison of data for the Pacific Ocean coastline from the Bering Strait to the tropics. D. D. Fisher