The sedimentary record of mud areas is an important carrier of information on the Holocene evolution of marine environments. Based on fine interpretations of the shallow stratigraphic section data, a small mud deposit...The sedimentary record of mud areas is an important carrier of information on the Holocene evolution of marine environments. Based on fine interpretations of the shallow stratigraphic section data, a small mud deposit area has been found in the southern coastal waters off Shandong Peninsula. This mud area is mainly distributed in coastal waters north of Laoshantou to the vicinity of Rushan Estuary. Overall, it is parallel to the coastline and spreads in a banded pattern, gradually thinning from offshore to the sea. The isopach map of depth distribution is parallel with the shoreline, and the depocenter lies in coastal waters of the Aoshan Bay where the maximum thickness is up to 22.5 m. Accelerator mass spectrometry(AMS) ^(14)C dating shows that the mud area was formed in the Holocene. The test data of surface sediments from the mud area, including particle size, mineral characteristics, and rare earth element contents, are used in comparisons with the composition of materials from the major surrounding medium and small rivers flowing into the sea and the Huanghe(Yellow) River. In this paper, the sedimentary characteristics and provenance of the mud deposit area are discussed. The results show that the formation of this mud area resulted from the joint action of the Huanghe River and surrounding rivers flowing into the sea.展开更多
This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-re...This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 210 Pb dating and was sampled at 1–2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size(14.32–96.39 μm) contribution>30%, Zr/Rb ratio>1.5, and magnetic susceptibility>16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods.展开更多
Paleoclimate record was revealed in Core MZ01 covering the mid-Holocene in age,located in the mud area of the inner continental shelf of the East China Sea. The ancient environment featured low-energy shallow sea shel...Paleoclimate record was revealed in Core MZ01 covering the mid-Holocene in age,located in the mud area of the inner continental shelf of the East China Sea. The ancient environment featured low-energy shallow sea shelf deposition formed mainly by coastal currents. The results show that temporal variation in geochemistry corresponds with the climate changes inferred from historical record. Relatively low MgO/Al 2 O 3,CaO/K 2 O and high Al 2 O 3 /Na 2 O,K 2 O/Na 2 O,MnO/CaO values reflected a warm and humid climate in general,and vice versa. Therefore,these chemical indices could be applied to identify the variation of palaeoclimate in eastern China. The authors reconstructed the history of mid-Holocene climatic variation of the inner continental shelf of the East China Sea. From 8 300 a BP to 4 200 a BP,the climate was moderately warm and humid. From 4 200 a BP to 2 000 a BP,the climate turned cool and dry,and the regional climate frequently fluctuated in alternation of cool-dry periods(3 700 a BP,2 850 a BP and 2 400 a BP) and warm-wet periods(3 250 a BP and 2 650 a BP) . After 2 000 a BP,the climate of the study area gradually turned warm again,while the Little Ice Age,a cold event centered at around 250 a BP was indicated by those geochemical indices as mentioned above.展开更多
Long-term changes of composition,sources and burial fluxes of TOC(total organic carbon) in sediments of the central Yellow Sea mud area and their possible affecting factors are discussed in this paper.Firstly,similari...Long-term changes of composition,sources and burial fluxes of TOC(total organic carbon) in sediments of the central Yellow Sea mud area and their possible affecting factors are discussed in this paper.Firstly,similarity analysis is employed to confirm that the carbon burial features resulted from two collected cores are typical in the central Yellow Sea mud area where YSWC(Yellow Sea Warm Current) is prevalent.On this basis,the burial flux of TOC here was considered to be 235.5–488.4 μmol/(cm2?a) since the first industrial revolution,accounting for about 70%–90% among burial fluxes of TC(total carbon) in the sediments.Compared TOC/TC ratio in the two cores with that in other marine sediments worldwide,we suggest that the growth of calcareous/non-calcareous organisms and dissolution of IC(inorganic carbon) are important factors controlling the TOC/TC ratio in sediment.Results of two-end mixed model based on δ13C data indicate that marine-derived organic carbon(OCa)is the main part among total burial organic carbon which accounts for a ratio over 85%.Due to the high TOC/TC ratio in the two cores,TC in the sediments also mainly exists as OCa,and the proportion of OCa is about 60%–80%.Away from the shore and relatively high primary production in upper waters are the main reasons that OCa is predominant among all burial OC in sediments of the central Yellow Sea mud area.Burial of OC in this mud area is probably mainly influenced by the human activities.Although the economic development during the late 19 th century caused by the first industrial revolution in China did not obviously increase the TOC burial fluxes in the sediments,the rise of industry and agriculture after the founding of new China has clearly increased the TOC burial flux since 1950 s.Otherwise,we also realize that among TC burial fluxes,TIC account for about 10%–30% in sediments of the central Yellow Sea mud area,so its burial could not be simply ignored here.Distinct from TOC burial,long-term TIC burial fluxes variations relate with climate changes more closely:the East Asian summer monsoon may influence the strength of the Huanghe River(Yellow River) flood,which could further affect the transport of terrestrial IC from land to the central Yellow Sea as well as the burial of these IC in the sediments.展开更多
Large amounts of sediments originating from the Changjiang(Yangtze)River are deposited in the subaqueous delta and in the adjacent muddy area off the mouth and on the inner shelf of the East China Sea.The terrestrial ...Large amounts of sediments originating from the Changjiang(Yangtze)River are deposited in the subaqueous delta and in the adjacent muddy area off the mouth and on the inner shelf of the East China Sea.The terrestrial sediments deposited in these areas not only contain information about the composition and environment of the source area,but they also record changes in anthropogenic activities.A sediment piston core(CJ0702)was extracted from the Changjiang subaqueous depocenter(31.00°N,122.67°E)in a water depth of 22.0 m.The core was subsampled at 1–2 cm intervals and analyzed for grain size,clay mineralogy,and major element geochemistry.Results indicate a relatively high sediment accumulation rate of approximately 3.11 cm yr−1.These parameters exhibited only minor cyclical fluctuations in the core,which resulted from many factors.During the past 120 years,the Changjiang River-derived sediment is the primary source of sediment in the offshore mud area without evidence for the Yellow River-derived sediment increasing.After the trunk stream shifted from the North Branch to South Branch,the variations of proxies are controlled by the periodic fluctuation possibly linked to El Niño-Southern Oscillation(ENSO)and the Pacific Decadal Oscillation(PDO).In addition,anthropogenic heavy metal concentrations can be divided into three stages,which coincide well with economic development and environmental protection policies.展开更多
Three cores(ZY-1,ZY-2 and ZY-3) retrieved from the Central Yellow Sea mud(CYSM) were analyzed in sensitive grain size and AMS 14 C dating to reconstruct the history of the East Asian Winter Monsoon(EAWM) since the Mid...Three cores(ZY-1,ZY-2 and ZY-3) retrieved from the Central Yellow Sea mud(CYSM) were analyzed in sensitive grain size and AMS 14 C dating to reconstruct the history of the East Asian Winter Monsoon(EAWM) since the Middle Holocene in the study area.The results show that these data provide a continuous history of the EAWM over the past 7.2 ka and that the EAWM can be divided into three periods:strong and highly fluctuating during 7.2-4.2 ka BP;moderate and relatively stable during 4.2-1.8 ka BP;and weakened during 1.8-0 ka BP.Compared with the East Asian Summer Monsoon(EASM) recorded in the previous studies,the evolutionary history of the EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the EASM.At the centennial scale,however,the EAWM intensified events correlate well with the EASM weakened events and the North Atlantic climatic variations(Bond events 0 to 5) within the dating error,most likely forced by the reduction of solar irradiance through changes in the oceanic-atmospheric circulation patterns.展开更多
Environmentally sensitive grain-size component (ESGSC) extracted from grain-size data of a sediment core B2, which were retrieved from mud area southwest off Cheju Island (MACI), East China Sea (ECS), can be used to i...Environmentally sensitive grain-size component (ESGSC) extracted from grain-size data of a sediment core B2, which were retrieved from mud area southwest off Cheju Island (MACI), East China Sea (ECS), can be used to indicate the variations of East Asia Winter Monsoon (EAWM), with high (low) content/mean-size of ESGCS denote to strong (weak) EAWM. Combined with AMS14C datings core B2 provides a continuous high-resolution record of EAWM changes over the past 2300 years, with an average resolution of 13 years. The results show that the variations of EAWM are con-sistent with temperature changes inferred from historical documents in eastern China over the past 2300 years, from which four climate stages may be identified. In stages before 1900 aBP (50 AD) and 1450―780 aBP (50―1170 AD) the EAWM were comparatively weak, corresponding to warm climate periods in eastern China, respectively. And in stages of 1900―1450 aBP (50―500 AD) and 780―219 aBP (1170―1731 AD) the EAWM were strongly developed, which correspond well to climate changes of two cold periods in eastern China. It is also shown from this study that the stage at 780―219 aBP (1170―1731 AD) was the coldest climate period during the last 2300 years and could be, therefore, related to the Little Ice Age (LIA). Climatic fluctuations appeared obviously in all the four stages, and two climate events of abrupt changes from warm to cold occurred at around 1900 aBP (50 AD) and 780 aBP (1170 AD), of which the latter is probably related to globe-scale changes of atmospheric circulation at that time.展开更多
AMS14C dating and analysis of grain size,major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea.Based on the environmentally sensitive grain size,clay min...AMS14C dating and analysis of grain size,major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea.Based on the environmentally sensitive grain size,clay mineral and major element assemblages,the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed.These three proxies,mean grain size(>9.71μm),chemical index of alteration(CIA)and ratio of smectite to kaolinite in particular,show similar fluctuation patterns. Furthermore,10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene;these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon.The cooling events correlated well with the results of theδ18O curves of the Dunde ice core and GISP2,which therefore revealed a regional response to global climate change.Four stages of the East Asia winter monsoon were identified,i.e.8300-6300 a BP,strong and unstable;6300-3800 a BP,strong but stable;3800-1400 a BP,weak and unstable;after 1400 a BP,weak but stable.展开更多
Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate chan...Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores(#34: 28.5°N, 122.272°E; CJ12-1269: 28.861 9°N, 122.515 3°E) from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970 s and increased rapidly after the late 1990 s at Site #34; and it started to increase gradually from the middle 1960 s and increased rapidly after the late 1980 s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B(dinosterol/brassicasterol) ratio of Core #34 since the 1960 s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950 s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios.展开更多
This paper presents a brief review of the results on the interaction between waves and muddy bottom obtained during the last decade including the results obtained by the author at the Coastal Engineering Laboratory of...This paper presents a brief review of the results on the interaction between waves and muddy bottom obtained during the last decade including the results obtained by the author at the Coastal Engineering Laboratory of Tianjin University.展开更多
基金The National Natural Science Foundation of China(NSFC)under contract Nos 41376079 and 41276060the Marine Geology Survey Project under contract Nos GZH200900501 and GZH201400204the Foundation of the Shandong Provincial Key Laboratory of Marine Ecology and Environment&Disaster Prevention under contract No.201304
文摘The sedimentary record of mud areas is an important carrier of information on the Holocene evolution of marine environments. Based on fine interpretations of the shallow stratigraphic section data, a small mud deposit area has been found in the southern coastal waters off Shandong Peninsula. This mud area is mainly distributed in coastal waters north of Laoshantou to the vicinity of Rushan Estuary. Overall, it is parallel to the coastline and spreads in a banded pattern, gradually thinning from offshore to the sea. The isopach map of depth distribution is parallel with the shoreline, and the depocenter lies in coastal waters of the Aoshan Bay where the maximum thickness is up to 22.5 m. Accelerator mass spectrometry(AMS) ^(14)C dating shows that the mud area was formed in the Holocene. The test data of surface sediments from the mud area, including particle size, mineral characteristics, and rare earth element contents, are used in comparisons with the composition of materials from the major surrounding medium and small rivers flowing into the sea and the Huanghe(Yellow) River. In this paper, the sedimentary characteristics and provenance of the mud deposit area are discussed. The results show that the formation of this mud area resulted from the joint action of the Huanghe River and surrounding rivers flowing into the sea.
基金Supported by the National Natural Science Foundation of China(Nos.41206073,41376079,41206051,41206052)the China Geological Survey(Nos.1212010611401,200900501)
文摘This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 210 Pb dating and was sampled at 1–2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size(14.32–96.39 μm) contribution>30%, Zr/Rb ratio>1.5, and magnetic susceptibility>16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods.
基金Coastal Investigation and Research Project of China under contract Nos 908-01-CJ12 and 908-ZC-I-05Marine Public Welfare Research Project under contract No. 200805063China Postdoctoral Science Foundation under contract No. 20100481304
文摘Paleoclimate record was revealed in Core MZ01 covering the mid-Holocene in age,located in the mud area of the inner continental shelf of the East China Sea. The ancient environment featured low-energy shallow sea shelf deposition formed mainly by coastal currents. The results show that temporal variation in geochemistry corresponds with the climate changes inferred from historical record. Relatively low MgO/Al 2 O 3,CaO/K 2 O and high Al 2 O 3 /Na 2 O,K 2 O/Na 2 O,MnO/CaO values reflected a warm and humid climate in general,and vice versa. Therefore,these chemical indices could be applied to identify the variation of palaeoclimate in eastern China. The authors reconstructed the history of mid-Holocene climatic variation of the inner continental shelf of the East China Sea. From 8 300 a BP to 4 200 a BP,the climate was moderately warm and humid. From 4 200 a BP to 2 000 a BP,the climate turned cool and dry,and the regional climate frequently fluctuated in alternation of cool-dry periods(3 700 a BP,2 850 a BP and 2 400 a BP) and warm-wet periods(3 250 a BP and 2 650 a BP) . After 2 000 a BP,the climate of the study area gradually turned warm again,while the Little Ice Age,a cold event centered at around 250 a BP was indicated by those geochemical indices as mentioned above.
基金The National Key Basic Research Program of China under contract No.2010CB428902the United Program of National Natural Science Foundation of China and Shandong Province under contract No.U1406403the Special Fund for Basic Scientific Research Business of Central Public Research Institutes under contrast No.20603022013003
文摘Long-term changes of composition,sources and burial fluxes of TOC(total organic carbon) in sediments of the central Yellow Sea mud area and their possible affecting factors are discussed in this paper.Firstly,similarity analysis is employed to confirm that the carbon burial features resulted from two collected cores are typical in the central Yellow Sea mud area where YSWC(Yellow Sea Warm Current) is prevalent.On this basis,the burial flux of TOC here was considered to be 235.5–488.4 μmol/(cm2?a) since the first industrial revolution,accounting for about 70%–90% among burial fluxes of TC(total carbon) in the sediments.Compared TOC/TC ratio in the two cores with that in other marine sediments worldwide,we suggest that the growth of calcareous/non-calcareous organisms and dissolution of IC(inorganic carbon) are important factors controlling the TOC/TC ratio in sediment.Results of two-end mixed model based on δ13C data indicate that marine-derived organic carbon(OCa)is the main part among total burial organic carbon which accounts for a ratio over 85%.Due to the high TOC/TC ratio in the two cores,TC in the sediments also mainly exists as OCa,and the proportion of OCa is about 60%–80%.Away from the shore and relatively high primary production in upper waters are the main reasons that OCa is predominant among all burial OC in sediments of the central Yellow Sea mud area.Burial of OC in this mud area is probably mainly influenced by the human activities.Although the economic development during the late 19 th century caused by the first industrial revolution in China did not obviously increase the TOC burial fluxes in the sediments,the rise of industry and agriculture after the founding of new China has clearly increased the TOC burial flux since 1950 s.Otherwise,we also realize that among TC burial fluxes,TIC account for about 10%–30% in sediments of the central Yellow Sea mud area,so its burial could not be simply ignored here.Distinct from TOC burial,long-term TIC burial fluxes variations relate with climate changes more closely:the East Asian summer monsoon may influence the strength of the Huanghe River(Yellow River) flood,which could further affect the transport of terrestrial IC from land to the central Yellow Sea as well as the burial of these IC in the sediments.
基金the National Natural Science Foundation of China(Nos.41676052 and 41206073)the State Scholarship Fund sponsored by China Scholarship Council(No.201609370007)the China Geological Survey(Nos.DD20190236,DD20160137,and DD20190205).
文摘Large amounts of sediments originating from the Changjiang(Yangtze)River are deposited in the subaqueous delta and in the adjacent muddy area off the mouth and on the inner shelf of the East China Sea.The terrestrial sediments deposited in these areas not only contain information about the composition and environment of the source area,but they also record changes in anthropogenic activities.A sediment piston core(CJ0702)was extracted from the Changjiang subaqueous depocenter(31.00°N,122.67°E)in a water depth of 22.0 m.The core was subsampled at 1–2 cm intervals and analyzed for grain size,clay mineralogy,and major element geochemistry.Results indicate a relatively high sediment accumulation rate of approximately 3.11 cm yr−1.These parameters exhibited only minor cyclical fluctuations in the core,which resulted from many factors.During the past 120 years,the Changjiang River-derived sediment is the primary source of sediment in the offshore mud area without evidence for the Yellow River-derived sediment increasing.After the trunk stream shifted from the North Branch to South Branch,the variations of proxies are controlled by the periodic fluctuation possibly linked to El Niño-Southern Oscillation(ENSO)and the Pacific Decadal Oscillation(PDO).In addition,anthropogenic heavy metal concentrations can be divided into three stages,which coincide well with economic development and environmental protection policies.
基金supported by National Basic Research Program of China (Grant No. 2010CB428901)National Natural Science Foundation of China (Grant Nos. 40976036 and40676032)Open Foundation of the State Key Laboratory of Loess and Quaternary Geology (Grant No. SKLLQG1107)
文摘Three cores(ZY-1,ZY-2 and ZY-3) retrieved from the Central Yellow Sea mud(CYSM) were analyzed in sensitive grain size and AMS 14 C dating to reconstruct the history of the East Asian Winter Monsoon(EAWM) since the Middle Holocene in the study area.The results show that these data provide a continuous history of the EAWM over the past 7.2 ka and that the EAWM can be divided into three periods:strong and highly fluctuating during 7.2-4.2 ka BP;moderate and relatively stable during 4.2-1.8 ka BP;and weakened during 1.8-0 ka BP.Compared with the East Asian Summer Monsoon(EASM) recorded in the previous studies,the evolutionary history of the EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the EASM.At the centennial scale,however,the EAWM intensified events correlate well with the EASM weakened events and the North Atlantic climatic variations(Bond events 0 to 5) within the dating error,most likely forced by the reduction of solar irradiance through changes in the oceanic-atmospheric circulation patterns.
基金supported by the National Natural Science Foundation of China(Grant Nos.90211022 and 40206007)the Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX3-SW-220).
文摘Environmentally sensitive grain-size component (ESGSC) extracted from grain-size data of a sediment core B2, which were retrieved from mud area southwest off Cheju Island (MACI), East China Sea (ECS), can be used to indicate the variations of East Asia Winter Monsoon (EAWM), with high (low) content/mean-size of ESGCS denote to strong (weak) EAWM. Combined with AMS14C datings core B2 provides a continuous high-resolution record of EAWM changes over the past 2300 years, with an average resolution of 13 years. The results show that the variations of EAWM are con-sistent with temperature changes inferred from historical documents in eastern China over the past 2300 years, from which four climate stages may be identified. In stages before 1900 aBP (50 AD) and 1450―780 aBP (50―1170 AD) the EAWM were comparatively weak, corresponding to warm climate periods in eastern China, respectively. And in stages of 1900―1450 aBP (50―500 AD) and 780―219 aBP (1170―1731 AD) the EAWM were strongly developed, which correspond well to climate changes of two cold periods in eastern China. It is also shown from this study that the stage at 780―219 aBP (1170―1731 AD) was the coldest climate period during the last 2300 years and could be, therefore, related to the Little Ice Age (LIA). Climatic fluctuations appeared obviously in all the four stages, and two climate events of abrupt changes from warm to cold occurred at around 1900 aBP (50 AD) and 780 aBP (1170 AD), of which the latter is probably related to globe-scale changes of atmospheric circulation at that time.
基金supported by the Coastal Investigation and Research Project of China(908-ZC-I-05 and 908-02-02-05)the Marine Public Welfare Research Project(200805063)the Key Program of the National Natural Science Foundation of China(40431002)
文摘AMS14C dating and analysis of grain size,major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea.Based on the environmentally sensitive grain size,clay mineral and major element assemblages,the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed.These three proxies,mean grain size(>9.71μm),chemical index of alteration(CIA)and ratio of smectite to kaolinite in particular,show similar fluctuation patterns. Furthermore,10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene;these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon.The cooling events correlated well with the results of theδ18O curves of the Dunde ice core and GISP2,which therefore revealed a regional response to global climate change.Four stages of the East Asia winter monsoon were identified,i.e.8300-6300 a BP,strong and unstable;6300-3800 a BP,strong but stable;3800-1400 a BP,weak and unstable;after 1400 a BP,weak but stable.
基金The National Basic Research Program of China(973 Program)under contract No.2010CB428901the National Natural Science Foundation of China under contract Nos 41020164005,40976042 and 41076036
文摘Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores(#34: 28.5°N, 122.272°E; CJ12-1269: 28.861 9°N, 122.515 3°E) from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970 s and increased rapidly after the late 1990 s at Site #34; and it started to increase gradually from the middle 1960 s and increased rapidly after the late 1980 s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B(dinosterol/brassicasterol) ratio of Core #34 since the 1960 s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950 s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios.
基金This project was financially supported by the China National Foundation of Natural Science
文摘This paper presents a brief review of the results on the interaction between waves and muddy bottom obtained during the last decade including the results obtained by the author at the Coastal Engineering Laboratory of Tianjin University.
