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1.
To decipher the sedimentary evolution and environmental changes since the late Last Deglaciation, two gravity cores were analyzed from the western North Yellow Sea (NYS). The two cores (B-L44 and B-U35) were sampled for grain size, clay minerals, detrital minerals, and 14C dating. They are comparable in lithofaies, and the observed succession was divided into four depositional units based on lithology and mineral assemblages, which recorded the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized with enrichment in sand, and was interpreted as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5-9.6 ka) displayed a fining-upward succession composed of sediments from local rivers, such as the Huanghe (Yellow) River, and from coastal erosion, which clearly were related to the Early Holocene transgression. Stable muddy deposition (DU 2) in NYS began to form at about 9.6 ka, which received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of fine sediment deposition in DU 1 (after 6.4 ka) after the sea level maximum.  相似文献   

2.
Diversion of the Yellow River is a unique geological event in offshore China, causing changes of the sedimentary environment in eastern China Seas. The last diversion took place in AD 1855, with the estuary diverted from the Yellow Sea into the Bohai Sea. The identification of the river diversion events in the shelf sediments would not only provide the definite ages for the sediments, but also give a clue for better understanding of the sedimentation in that area. In this study, 210 Pb, grain size, geochemical element, and foraminiferal data in core H205 from the north Yellow Sea were systematically investigated. A high-resolution sedimentary record was established, which was coupled with the Yellow River diversion and runoff changes. The results show that the foraminiferal composition and foraminiferal abundance of the sediments from the north Yellow Sea had good response to the Yellow River diversion in 1855. Before the change, shallow water assemblages dominated the foraminifera, and the abundance of each foraminiferal species was very low. After the diversion event, the abundance of most foraminifera increased sharply, with a maximum increase of 16 times, and the assemblage was still dominated by shallow water species. Furthermore, the changes in foraminiferal abundance in the core sediments corresponded well with the discharge fluctuation of the Yellow River since 1855. When the Yellow River began entering the Bohai Sea, the Yellow River water, which is rich in nutrients, along with the coastal currents affected the north Yellow Sea, increased the primary productivity in the north Yellow Sea, which is the main reason for the abrupt increase and fluctuation of foraminiferal abundance in this area. At the meantime, the East Asian winter monsoon could also promote the development of nearshore foraminiferal species by enhancing the coastal currents.  相似文献   

3.
Long chain alkyl diols have shown important potential for the reconstruction of sea surface temperature, productivities and upwelling conditions in marine or lacustrine environments. However, little is known about the distribution and sources of the diols in eastern China marginal seas (CMS), which are areas of important organic carbon sink. Here the contents of C30 and C32 1,15-diols were analyzed in 181 surface sediments from eastern CMS. The similar distribution pattern and strong linear correlation between C30 and C32 diols indicated that they had similar biological source, with a dominance of C30 diol. Their contents ranged from 7–2726 ng g?1 for C30 diol and 5–669 ng g?1 for C32 diol, and both showed higher values mainly in the mud area of the Yellow Sea, while the TOC normalized contents showed a more obvious seaward increasing trend. The similar distribution pattern and significant positive correlation between diols and the other marine biomarkers (brassicasterol, dinosterol, C37 alkenones) indicated C30 and C32 diols in eastern CMS were mainly from marine algae. This conclusion was also supported by principal component analysis (PCA). Our results also showed that sediment diol contents were generally related to marine productivity, suggesting that diols could be applied for marine productivity reconstruction in eastern CMS.  相似文献   

4.
The well-known Three Gorges Dam(TGD) within the Yangtze catchment launched its operation in 2003. The effect of the TGD operation on the sediment size on the East China Sea shelf is rarely known. High resolution(0.5 cm sampling) grain size analysis and 137 Cs and 210 Pb dating of the DH8-1 core were conducted with core collected from the distal part of a main sink for the modern Yangtze sediment entering the sea, the Min-Zhe Coastal Mud Deposits(MZCMD) on the inner East China Sea shelf. The 137 Cs dating results show that the core DH8-1 formed during 1946–2012 with a mean deposition rate of 0.65 cm yr~(-1), indicating that the 0.5 cm sampling for grain size analysis in this local area could reflect environmental changes generally on a one-year time scale. The mean grain size of DH8-1 core sediment that deposited after 2003 is significantly larger than that deposited during 1988–2002. After ruling out other possible factors, we infer that the sediment coarsening of DH8-1 core after 2003 is attributed to the TGD operation which causes the erosion of the Yangtze subaqueous delta. Specifically, the TGD operation significantly intensifies the declining trend of the Yangtze sediment loads to the sea despite no decreased water discharge, which results in extensive erosion of the Yangtze subaqueous delta. The relatively coarse sediment of the subaqueous delta is eroded and resuspended by ocean dynamics and then transported by coastal current, finally depositing on the MZCMD area. In addition, the general sediment fining of core DH8-1 that deposited during 1988–2002, comparing with 1946–1987, is mainly caused by dam construction and soil and water conservation within the Yangtze catchment. Our findings are helpful for better understanding the effects of such a huge dam as the TGD on a sediment sink like the MZCMD of such a large river as the Yangtze River.  相似文献   

5.
Current data from a moored Acoustic Doppler Current Profiler(ADCP) deployed at 69?30.155′N,169?00.654′W in the central Chukchi Sea during 2012 summertime is analyzed in the present paper.Characteristics of tidal and residual currents are ob-tained with Cosine-Lanczos filter and cross-spectral analyses.The main achievements are as follows:1) Along with the local inertial frequency of 12.8 h,two other peaks at ~12-h and ~10-d dominate the time series of raw velocity;2) The M_2 dominates the 6 resolved tide constituents with significant amplitude variations over depth and the ratios of current speed of this constituent to that of the total tidal current are 54% and 47% for u and v components,respectively.All the resolved tidal constituents rotate clockwise at depth with the exception of MM and O1.The constituents of M_2 and S_2 with the largest major semi-axes are similar in eccentricity and orientation at deeper levels;3) The maximum of residual currents varies in a range of 20–30 cms~(-1) over depth and the current with lower velocities flow more true north with smaller magnitudes compared to the current in surface layer.The ~10 d fluctuation of residual current is found throughout the water column and attributed to the response of current to the local wind forcing,with an approximate 1.4 d lag-time at the surface level and occurring several hours later in the lower layer;4) Mean residual currents flow toward the north with the magnitudes smaller than 7 cms~(-1) in a general agreement with previous studies,which suggests a relatively weaker but stable northward flow indeed exists in the central Chukchi Sea.  相似文献   

6.
Two depositional processes controlled the muddy sediments in the South China Sea Basin. Bathyal sediments depositional rate was 7.66 cm/la in the northern continental slope of the Basin where turbidity current was almost nonexistent. In the northern margin of the Basin, abyssal sediment depositional rate was 5.05cm/ka and turbidity current occurrence averaged 0.22 per 1000 years. Turbidite was found in the middle of the Basin. Over half of the muddy sediments in the deep sea basin were deposited by turbidity currents, and had typically graded bedding, and contents of organic matter, calcareous material and micropaleontologic species inconsistent with the environment.  相似文献   

7.
Long chain alkyl diols have shown important potential for the reconstruction of sea surface temperature,productivities and upwelling conditions in marine or lacustrine environments.However,little is known about the distribution and sources of the diols in eastern China marginal seas(CMS),which are areas of important organic carbon sink.Here the contents of C_(30) and C_(32)1,15-diols were analyzed in 181 surface sediments from eastern CMS.The similar distribution pattern and strong linear correlation between C_(30) and C_(32) diols indicated that they had similar biological source,with a dominance of C_(30) diol.Their contents ranged from 7-2726 ng g~(-1) for C_(30) diol and 5-669 ng g~(-1) for C_(32) diol,and both showed higher values mainly in the mud area of the Yellow Sea,while the TOC normalized contents showed a more obvious seaward increasing trend.The similar distribution pattern and significant positive correlation between diols and the other marine biomarkers(brassicasterol,dinosterol,C_(37) alkenones) indicated C_(30) and C_(32) diols in eastern CMS were mainly from marine algae.This conclusion was also supported by principal component analysis(PCA).Our results also showed that sediment diol contents were generally related to marine productivity,suggesting that diols could be applied for marine productivity reconstruction in eastern CMS.  相似文献   

8.
It is known that the organic matter in the upper layer of sediments gets lost fast, but not in the South Huanghai Sea (Yellow sea). Some of the major characteristics of organic geochemistry of sediments in the South Huanghai Sea can be summarized as follows:1. The contents of organic carbon and bitumen increase with the decrease in grain size.2.Loss of organic matter is closely related to grain size but less so in clay sediments.3.The contents of bitumen and hydrocarbon are low, about n ×102 ppm for bitumen and n ×10 ppm for hydrocarbon.A scattered show of organic matter does not necessarily indicate the presence of petroleum in recent marine sediments.In research into the genesis of petroleum, people pay more attention to the study of the organic geochemistry of recent marine sediments. How much organic materials was lost during the deposition up to the diagenesis ? The problem is as important as the study on the transformation of organic matter. This study on the organic geochemistry of the sediment  相似文献   

9.
Observations made on the northern Portugal mid-shelf between May 13 and June 15,2002 were used to characterise the near-surface velocity during one upwelling season. It was found that in the surface mixed layer,the 'tidal current' was diurnal,but the tidal elevation was semi-diurnal. Both the residual current and the major axes of all tidal constituents were nearly perpendicular to the isobaths and the tidal current ellipses rotated clockwise;the major axis of the major tidal ellipse was about 3 cm s-1. The extremely strong diurnal current in the surface layer was probably due to diurnal heating,cooling,and wind mixing that induced diurnal oscillations,including the diurnal oscillation of wind stress. This is a case different from the results measured in the other layers in this area. The near-inertial spectral peaks occurred with periods ranging from 1 047 min to 1 170 min,the longest periods being observed in deeper layers,and the shortest in the surface layer. Weak inertial events appeared during strong upwelling events,while strong inertial events appeared during downwelling or weak subinertial events. The near-inertial currents were out of phase between 5 m and 35 m layers for almost the entire measurement period,but such relationship was very weak during periods of irregular weak wind. Strong persistent southerly wind blew from May 12 to 17 and forced a significant water transport onshore and established a strong barotropic poleward jet with a surface speed exceeding 20 cm s-1. The subinertial current was related to wind variation,especially in the middle layers of 15 m and 35 m,the maximum correlation between alongshore current and alongshore wind was about 0.5 at the 5 m layer and 0.8 at the 35 m layer. The alongshore current reacted more rapidly than the cross-shore current. The strongest correlation was found at a time lag of 20 h in the upper layer and of 30 h in the deeper layer. The wind-driven surface velocity obtained from the PWP model had maximum amplitude of about 7 cm s-1,corresponding to a wind stress at 0.1 Pa,and the horizontal velocity shear due to thermal wind balance had the order of 3 cm s-1. So the local wind and thermal wind would only explain a part of the strong surface velocity variations.  相似文献   

10.
Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.  相似文献   

11.
We use the particle size of sediments in core YS01 A to study the sedimentary environment of the mud deposit in the central South Yellow Sea of China during late Marine Isotope Stages 3(MIS3;40.5 kyr–31.3 kyr).In addition,the East Asian Monsoon and its relationship with the North Atlantic Ocean climate change are discussed based on the sensitive grain-size calculation and the spectrum analysis.The results show that during late MIS3,the muddy area in the central South Yellow Sea experienced the evolution of coastal facies,shallow marine facies,coastal facies,and continental facies,with weak hydrodynamic conditions.Compared with other climate indicators,we found that there were many century to millennium-scale climate signals documented in the muddy area sediments in the central South Yellow Sea.According to our particle size results,three strong winter monsoon events occurred at 37.6 kyr,35.6 kyr and 32.2 kyr.The East Asian Winter Monsoon records in core YS01 A are consistent with the Greenland ice core and the Hulu cave stalagmite δ~(18)O.The millennial and centennial scale cycles,which are 55 yr,72 yr,115 yr,262 yr respectively,correspond to solar activity cycles,while the 1049 yr and 2941 yr cycles correspond to the Dansgaard-Oeschger cycles.These cycles indicate that the paleoclimate evolution of the area was controlled by the solar activities,with the high-latitude driving thermohaline circulation as the main energy conveyor belt,followed by the sea-air-land amplification of the winter monsoon variation in the central Yellow Sea in the late MIS3.  相似文献   

12.
Vertical profiles of chl-a and primary productivity in the middle continental shelf area and eddy area of the East China Sea were studied using data from a cruise in the East China Sea in February to March, 1997 and a cruise in July, 1998. The results showed that chl-a vertical distribution closely related to in situ hydrological and nutrient conditions. Chla-a concentration ranged from 0.22 to 0.35 mg/m3 and 0.93–1.09 mg/m3 in the eddy area and in the middle continental shelf area, respectively. In both areas, chl-a concentrations in deep layers were slightly higher than those in shallow layers, but was of the same order of magnitude. In summer, when a thermocline existed in the water column, highest chl-a concentrations appeared at the base of the thermocline layers in both areas. In the eddy area, chl-a concentration maximized at 31.743 mg/m3, and averaged 1.143 mg/m3 below 30 m depth. In the middle continental shelf area, the highest chl-a concentration was 2.120 mg/m3, the average was 1.168 mg/m3. The primary productivity reached 1418.76 mgC/(m2·d) in summer and 1360.69 mgC/(m2·d) in winter. In the eddy area, the primary productivity was 787.50 mgC/(m2·d) in summer and 159.04 mgC/(m2·d) in winter. Vertical carbon sinking rate from the deep layer to the bottom in both areas is also discussed in this paper. Contribution NO. 4183 from the Institute of Oceanology, Chinese Academy of Sciences. Project No. 49636210 supported by NSFC.  相似文献   

13.
Coastal lagoons with small catchment basins are highly sensitive to natural processes and anthropogenic activities. To figure out the environmental changes of a coastal lagoon and its contribution to carbon burial, two sediment cores were collected in Xincun Lagoon, southeastern Hainan Island and (210) ~Pb activities, grain size parameters, total organic carbon(TOC), total nitrogen(TN), total inorganic carbon(TIC) and stable carbon isotopes(δ~(13)C) were measured. The results show that in 1770–1815, the decreasing water exchange capacity with outer open water, probably caused by the shifting and narrowing of the tidal inlet, not only diminished the currents and fined the sediments in the lagoon, but also reduced the organic matter of marine sources. From 1815 to 1950, the sedimentary environment of Xincun Lagoon was frequently influenced by storm events. These extreme events resulted in the high fluctuation of sediment grain size and sorting, as well as the great variation in contributions of terrestrial(higher plants, soils) and marine sources(phytoplankton, algae, seagrass). The extremely high content of TIC, compared to TOC before 1950 could be attributed to the large-scale coverage of coral reefs. However, with the boost of seawater aquaculture activities after 1970, the health growth of coral species was severely threatened, and corresponding production and inorganic carbon burial flux reduced. The apparent enhanced inorganic carbon burial rate after 1990 might result from the concomitant carbonate debris produced by seawater aquaculture. This result is important for local government long-term coastal management and environmental planning.  相似文献   

14.
Mangroves accumulate sedimentary sequences, where cores can provide historical records of mangrove evolution with past climate change and human activity. The study traced the history of mangrove evolution during the past one hundred years in a mangrove swamp of Maowei Sea, SW China. The sedimentation rates(0.38-0.95 cm yr~(-1)) were calculated on the basis of ln(~(210)Pb_(xs)/Al) and mass depth in the core sediments. Chemical tracers, such as δ~(13)C_(org) and C:N values, were utilized to trace the contribution of mangrove-derived organic matter using a ternary mixing model. Because of potential diagenetic alteration and / or overlap in the isotopic signatures of different components, simultaneous use of mangrove pollen diagrams can help to supplement some of these limitations. Combined with mangrove pollen, mangrove evolution was reconstructed and could be divided into three stages: flourishment(1886-1905 AD), slight degradation(1905-1949 AD) and rapid degradation period(1949-2007 AD), which was consistent with previous reports. The reclamation of mangrove swamps to shrimp ponds was the major reason for rapid degradation of mangrove ecosystems in recent years, rather than climate change in the region.  相似文献   

15.
Since the last rising of sea level, two branches of the Kuroshio, the Huanghai (Yellow Sea) coastal current (HCC; mainly cold water mass) and the Changjiang River outflow have controlled the modern dynamic deposition in the East China Sea. There are three depositing areas on the sea-bed under the above currents: a relict sand area un der the Taiwan Warm Current and the Huanghai Warm Current at the south-eastern area, the about 60 km2 round mud bank under the Huanghai Coastal Current at the northern area and the large subaqueous delta of mainly fine sand and silt under the Changjiang discharge flow in its estuary and the large narrow mud bank under the Zhejiang-Fujian Coastal Current, another round mud bank under the Changjiang discharge flow off Hangzhou Bay. The relict sand area has a coarsesand block under the Taiwan Warm Current bypassing Taiwan at the northern part of the island. The two round mud banks were formed in relatively static states by an anticlockwise converging cyclonic eddy. The coarsesand block was formed by a clockwise diverging cyclonic eddy. This new dynamic deposition theory can be used to explain not only the dynamic deposition process of clay, but also the patchy distribution of sediments on the shelves of the world ocean s.  相似文献   

16.
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17.
Biogenic silicate accumulation in sediments, Jiaozhou Bay   总被引：1，自引：0，他引：1  
1 INTRODUCTION Silicate, or silicic acid (H4SiO4), is a very im- portant nutrient in the ocean. Unlike other major nu- trients such as phosphate and nitrate or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical req…  相似文献   

18.
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19.
Direct current observations in the Yellow Sea interior are very scarce due to intense fishing and trawling activities. Most previous studies on tides in the area were based on coastal measurements or satellite altimeter sea levels and have not been rigorously compared with direct measurements. In this paper, tidal currents are studied with current profiles from three bottom-moored Sontek Acoustic Doppler Profilers （ADPs） deployed in the southern Yellow Sea in summer of 2001 and 2003. The measured current series were dominated by tidal currents. Maximum velocities are between 40-80 cm/s at the mooring stations. M2 current is the most dominant primary tidal constituent, while MS4 and M4 are the most significant shallow water tides with much smaller amplitudes than the primary tides.  相似文献   

20.
According to palaeoclimatic and modern instrumental data, numerous studies have indicated that the Arctic climate has undergone a significant warming during the past 100 years, and this may lead to significant impact on the fragile lake ecosystem. In this study, we collected a lake sediment core from the Ny-(A)lesund of Svalbard and determined the concentrations of four pigments including chlorophyll derivatives, total carotenoids, oscillaxanthin and myxoxanthophyll in the sediments. Combined with other physical and chemical proxies such as calcium carbonate, total organic carbon, biogenic silicon etc., we have reconstructed the historical changes of lacustrine primary productivity in Ny-(A)lesund, especially for the past 100 years. The results showed that during the period of Little Ice Age (LIA), the climate was unfavorable for the growth of the lake algae, and thus the lacustrine productivity declined. This result was supported by the relatively low contents of pigment and biogenic silica in the sediments. In contrast, the contents of total organic carbon (TOC) and sediment pigments increased significantly in the upper 5 cm (~1890AD), reflecting the rapid growth of the lake algae, thus the great increase of lacustrine primary productivity, corresponding to the warming climate after LIA. However, the biogenic silica in the upper sediments still had a relatively low level, and this might be related to the growth competition with other algae species. Over the past 100 years, the ratio of Osc/Myx in the sediments decreased continuously, indicative of durative increase of myxoxanthophyll in blue-green algal pigments, and this might imply that the human activity had enhanced the nutrition level of the lake in the Arctic region.  相似文献   

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