The sedimentary record of climate change in the Arctic region is useful for understanding global warming.Kongsfjord is located in the subpolar region of the Arctic and is a suitable site for studying climate change.Gl...The sedimentary record of climate change in the Arctic region is useful for understanding global warming.Kongsfjord is located in the subpolar region of the Arctic and is a suitable site for studying climate change.Glacier retreat is occurring in this region due to climate change,leading to an increase in meltwater outflow with a high debris content.In August 2017,we collected a sediment Core Z3 from the central fjord near the Yellow River Station.Then,we used the widely used chronology method of 210Pb,^(137)Cs,and other parameters to reflect the climate change record in the sedimentary environment of Kongsfjord.The results showed that after the mid-late 1990s,the mass accumulation rate of this core increased from 0.10 g/(cm^(2)·a)to 0.34 g/(cm^(2)·a),while the flux of^(210)Pb_(ex)increased from 125 Bq/(m^(2)·a)to 316 Bq/(m^(2)·a).The higher sedimentary inventory of^(210)Pb_(ex)in Kongsfjord compared to global fallout might have been caused by sediment focusing,boundary scavenging,and riverine input.Similarities between the inventory of^(137)Cs and global fallout indicated that terrestrial particulate matter was the main source of^(137)Cs in fjord sediments.The sedimentation rate increased after 1997,possibly due to the increased influx of glacial meltwater containing debris.In addition,the^(137)Cs activity,percentage of organic carbon(OC),and OC/total nitrogen concentration ratio showed increasing trends toward the top of the core since 1997,corresponding to a decrease in the mass balance of glaciers in the region.The results ofδ^(13)C,δ^(15)N and OC/TN concentration ratio showed both terrestrial and marine sources contributed to the organic matter in Core Z3.The relative contribution of terrestrial organic matter which was calculated by a two-endmember model showed an increased trend since mid-1990s.All these data indicate that global climate change has a significant impact on Arctic glaciers.展开更多
The coastal cities are the most advanced regions in China.In the past few decades,the environment changed very significantly due to large scale human activities in the coastal regions.Polycyclic aromatic hydrocarbons ...The coastal cities are the most advanced regions in China.In the past few decades,the environment changed very significantly due to large scale human activities in the coastal regions.Polycyclic aromatic hydrocarbons (PAHs)in three dated sediment cores from the west coast of the Yellow Sea (core A01),the Yangtze River estuary (YRE;core A02)and the Oujiang River estuary (ORE;core A03)were analyzed to reconstruct the environmental evolutionary process of the east China coastal region over the past century. In the three cores,PAHs concentrations were increased rapidly.Lower concentrations of PAHs were measured in core A02 than in cores A01 and A03.The vertical variation of PAHs in the YRE Was dominated by the petrogenic sources.Historical records of PAHs in the ORE were controlled by pyrolytic sources.PAHs on the west coast of the Yellow Sea were contributed by the two sources.展开更多
On the basis of multi-proxy analysis on TOC, TN, C/N, organic δ^13C and grain size, sediment record from Qinghai Lake provides evidences of stepwise-pattemed climatic change since 16 ka BE Results show that Qinghai L...On the basis of multi-proxy analysis on TOC, TN, C/N, organic δ^13C and grain size, sediment record from Qinghai Lake provides evidences of stepwise-pattemed climatic change since 16 ka BE Results show that Qinghai Lake underwent six environmental stages. From 16.2 to 14.3 ka BP and from 4.0 to 2.1 ka BP, the organic δ^13C value was controlled by the concentration of atmospheric CO2. Relative higher organic δ^13C values occurred between 14.3 to 10.4 ka BP indicative of water hardness decrease resulted from melting ice water, corresponding to two intervals of C/N peak values to the Boling and AIlerod warm periods in Europe respectively. From 10.4 ka BP, Qinghai Lake entered the Holocene and the climate was warm and a little dry. The Megathermal appeared at about 6.7 ka BP when the vegetation around the lake transformed into a forest. Between 6.3 ka BP and 4.0 ka BP, the temperature decreased and δ^13C value was controlled by the expansion of C3 plants and the retreat of C4 plants in river catchment. Since 4.0 ka BP, the climate gradually became cold and dry. From 2.1 ka BP, the cold-dry climate and human activity resulted in an abrupt increase in C/N with deceased δ^13C value; meanwhile, many coarse grains appeared in sediments.展开更多
Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang,northwestern China.A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS...Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang,northwestern China.A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS^(14)C.Grain size,total organic matter(TOC),total nitrogen(TN),and TOC/TN(C/N)analyses were used to reconstruct climatic conditions from 13.0 to 5.6 cal ka BP.The results showed fi ve main climatic stages.Zone I(13.0–11.3 cal ka BP)was a wet–dry environment,whereas Zone II(11.3–8.9 cal ka BP)consisted of a primarily wet environment.Zone III(8.9–7.7 cal ka BP)was subdivided into Zone IIIa(8.9–8.2 cal ka BP)that indicated lake constriction and dry climate,and Zone IIIb(8.2–7.7 cal ka BP)in which the proxies indicated wet conditions.In Zone IV(7.7–6.6 cal ka BP),the climate presented a bit wet conditions.In Zone V(6.6–5.6 cal ka BP),abundant glauberite is present in the sediment and silt dominates the lithology;these results indicate the lake shrank and the overall climate was dry.Abrupt environmental events were also identifi ed,including six dry events at 11.0,10.5,9.3,8.6,8.2,and 7.6 cal ka BP and one fl ood event from 7.8 to 7.7 cal ka BP in the Early–Middle Holocene.展开更多
The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic prox...The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic proxy record, was used to analyze the Holocene climate changes in the local region. The proxy record was established in the Sanjiaocheng (SJC), Triangle Town in Chinese, Section (103°20′25″E, 39°00′38″N), which is located at the northwestern boundary of the present Asian summer monsoon in China, and is sensitive to global environmental and climate changes. Applying singular spectrum analysis (SSA) to the TOC series, principal climatic oscillations and periodical changes were studied. The results reveal 3 major patterns of climate change regulated by reconstructed components (RCs). The first pattern is natural long-term trend of climatic change in the local area (Minqin Basin), indicating a relatively wetter stage in early Holocene (starting at 9.5 kaBP), and a relatively dryer stage with a strong lake desiccation and a declined vegetation cover in mid-Holocene (during 7–6 kaBP). From 4.0 kaBP to the present, there has been a gradually decreasing trend in the third reconstructed component (RC3) showing that the local climate changed again into a dryer stage. The second pattern shows millennial-centennial scale oscillations containing cycles of 1 600 and 800 years that have been present throughout almost the entire Holocene period of the last 10 000 years. The third pattern is a millennial-centennial scale variation with a relatively smaller amplitude and unclear cycles showing a nonlinear interaction within the earth’s climate systems.展开更多
The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores,along...The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores,along with the hydrologic data and human activities in the catchment.The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea,which could be divided into three stages as 1958–1970,1971–1990 and 1991–2009.Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes.There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010,i.e.,1940–1950,1951–1980,1981–1990 and 1991–2010.The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980,whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990.Despite the further reduction of the water and sediment input into the sea from 1990 to 2009,this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly,the significantly increased silt contents of the sensitive component.展开更多
The mid-Pleistocene climate transition (MPT) has been widely reported in worldwide geological events. As a key issue of the Quaternary geology, it has attracted much attention from the paleoclimate community. MPT re...The mid-Pleistocene climate transition (MPT) has been widely reported in worldwide geological events. As a key issue of the Quaternary geology, it has attracted much attention from the paleoclimate community. MPT refers to a period lasting for several hundreds of thousand years, during which the dominant climate periodicity gradually extended from 41 kyr to 100 kyr (Ruddiman et al., 1989),展开更多
Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (Qp and Qs) of th...Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (Qp and Qs) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1-10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0-500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 Mw4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average vp and Vs of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high ve/vs ratio of 4.3. We also modeled surface refleeted wave with propagating matrix method to constrain Qs and the near surface velocity structure. Our modeling indicates that Qs is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q(-10), but consistent with Qs modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0-50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borebole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.展开更多
Ecosystem response to climate change in high-altitude regions is a focus on global change research. Picea/Abies forests are widely distributed at high altitudes of East and Central Asia, and their distribution changes...Ecosystem response to climate change in high-altitude regions is a focus on global change research. Picea/Abies forests are widely distributed at high altitudes of East and Central Asia, and their distribution changes are sensitive to climate change. Humidity is an important climatic factor that affects high-altitude ecosystems; however, the relationship between distribution changes of Picea/Abies forests and millennial-scale variability of humidity is still not dear. Palynological records can provide insights into millennial-scale paleovegetation changes, which have been successfully used to reconstruct past climate change in East and Central Asia. In this study, we synthesized 24 Picea/Abies pollen and humidity/moisture changes based upon Holocene lake records in East and Central Asia in order to explore the response of high-latitude ecosystem to millennial-scale climate change. The changing pattern of Holocene lacustrine Picea/Abies pollen in arid Central Asia differs from that of monsoonal East Asia, which can be due to different millennial-scale climate change patterns between monsoonal and arid Central Asia. Then, the relationship between changes in Picea/Abies pollen and humidity/moisture conditions was examined based on a comparison of pollen and humidity/moisture records. The results indicate that millennial-scale Picea/Abies distribution changes aremainly controlled by moisture variability at high altitudes, while the temperature effect plays a minor role in Picea/Abies distribution changes. Moreover, this research proves that lacustrine Picea/Abies pollen can be used as an indicator of millennial-scale humidity/moisture evolution at high altitudes in East and Central Asia.展开更多
The results of sedimentary characteristics, grain-size, clay mineral, C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tr...The results of sedimentary characteristics, grain-size, clay mineral, C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tropical areas. It is testified that the Maar sediment system was sensitive in recording the rapid climate changes in the Holocene. These multidisciplinary results demonstrate that the thermal maximum in the Holocene climate lasted from 7200 to 2700 aBP, with several abrupt ephemeral vibrations occurring between 7250-6120 aBP and at around 4460, 3850 and 2700 aBP. In the late Holocene, particularly at ~2700 aBP, a distinct environmental change indicating an important climate transition in the tropical eastern Asia was recorded, probably responding to the enhancement of ENSO phenomena in the Pacific Ocean. In addition, the high-resolution algae record clearly indicates periodical climate fluctuations at 500 a cyclicity during the last 2500 years.展开更多
Diatom taxa in samples collected from the uppermost 1-cm sediment of the South China Sea (SCS) during cruises in 2000, 2001, and 2007 were investigated. Among them, two genera, Rutilaria and Trigoniurn, and 11 marin...Diatom taxa in samples collected from the uppermost 1-cm sediment of the South China Sea (SCS) during cruises in 2000, 2001, and 2007 were investigated. Among them, two genera, Rutilaria and Trigoniurn, and 11 marine taxa (species and varieties) were described for the first time in China. The 11 taxa, Rutilaria radiata, Asterolampra grevillei, Biddulphia turrigera, Cocconeis cyclophora var. decora, Cocconeis ocellata, Dictyoneis rnarginata, Entogonia davyana, Tryblionella campechiana, Plagiogramma kinkeri, Plagiogramma nankoorense and Trigonium cf. contumax, were mainly extant species, although Rutilaria radiata and Entogonia davyana are fossils. Available data show that these species are mainly present in the eastern and western Pacific Ocean and the Indian Ocean. A large number of taxa newly recorded in this study were previously reported in the Philippines. The presence of these taxa in both locations is likely a result of seawater exchange in the SCS through the Bashi Channel Taxonomic descriptions, habitats, and distributions of each diatom taxon are provided herein.展开更多
Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate ...Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate during higher lake level. Through detailed study on sediment grain sizes in Lake Erhai and Lake Chenghai, this paper reveals the different indication signifi- cances of sediment grain sizes in different time scales, different resolution investigations. For long time-scale and low resolution (102a or 103a) studies, larger sediment grain size indicates lower lake level, smaller lake area and drier climate while smaller sediment grain size indicates higher lake level, larger lake area and wetter climate. For short time-scale and high resolution (a or 10a) studies, larger sediment grain size reflects more rainfall and wetter climate while smaller sediment grain size reflects less rainfall and drier climate. Environmental information revealed by lacustrine sediment records is often different in different time scales because of the variance of sedimentation resolution, sampling resolution and dating precision. Therefore, paleoclimate im- plications of environmental proxies in long time-scale and low resolution investigations could not be mechanically applied to short time-scale and high resolution studies. Only after synthetically analyzing the influence manner and extent of all factors on the sediment records in different time scales, can credible conclusions be obtained.展开更多
THE formation and uplift of the Himalayas and the Tibetan Plateau may have been responsible for the past150 Ma global environmental changes, resulting in the development of a three-tiered landform in southernChina. Th...THE formation and uplift of the Himalayas and the Tibetan Plateau may have been responsible for the past150 Ma global environmental changes, resulting in the development of a three-tiered landform in southernChina. The Yunnan-Guizhou Plateau, as the middle tier in eastern slope of the Himalayas, has beencomplex environmental unit with great altitude gradients and plateau landform characters. Both monsoonsfrom the Pacific and the Indian resulting in apparent environmental changes on variable time scales influence it. Environmental geochemical effect of low latitude-high altitude could be yielded, and well recorded in the geological bodies in this region. To build and verify a quantitative model of environmental evolution it is necessary to obtain high-resolution data of elemental cycles and mass equilibrium.展开更多
Based on modern pollen studies and reliable chronology of nine AMS 14C dates, a detailed history of vegetation and climate changes during the past 8660 cal. a BP was reconstructed by a high-resolution pollen record fr...Based on modern pollen studies and reliable chronology of nine AMS 14C dates, a detailed history of vegetation and climate changes during the past 8660 cal. a BP was reconstructed by a high-resolution pollen record from Ugii Nuur in central Mongolia. Poaceae-steppe dominated the study area and the climate was mild and semi-humid before 7800 cal. a BP with a noticeable cool and humid interval at 8350―8250 cal. a BP. Xerophytic plant increased and the climate became warm and dry gradually since 7800 cal. a BP. From 6860 to 3170 cal. a BP, semi-desert steppe expanded, suggesting a prolonged warm and dry climate. Between 3170 and 2340 cal. a BP, regional forest steppe expanded whereas semi-desert steppe retreated, indicating the climate became cool and wet gradually and the humidity reached the maximum at the end of this stage. From 2340 to 1600 cal. a BP, a general cool and wet climate prevailed. And the climatic instability increased after 1600 cal. a BP. Review of regional pub-lished palaeoclimatic records implies that the mid-Holocene dry climate might have prevailed in vast areas from central Mongolia to arid areas of northwest China. Pollen-based climate reconstruction for UG04 core was well correlated with the result of climate model on Central Asia by Bush. In addition, several abrupt climatic events (cool and wet) were found and some could be broadly compared with the cool events in Atlantic.展开更多
To determine the characteristics and potential indicators of modern typhoon deposition in a sandy lagoon off the coast of Guangdong Province(southern China),we analysed the ^(210)Pb,sedimentology,and microfossils of s...To determine the characteristics and potential indicators of modern typhoon deposition in a sandy lagoon off the coast of Guangdong Province(southern China),we analysed the ^(210)Pb,sedimentology,and microfossils of samples from ten cores obtained before and after the passage of Typhoon Rammasun in 2014.Typhoon deposition showed a thinning trend from internal areas of the lagoon to its mouth,with the maximum thickness inside the lagoon of~35 cm.These typhoon deposits are dominated by overwash and differ from sediments deposited under normal weather conditions.Under normal weather conditions,lagoon sediment has a210 Pb curve that follows a model of exponential decay,has a unimodal granularity frequency curve,and lacks organic matter and microfossils(diatoms and foraminifera).However,210 Pb is low in the typhoon deposits,the grain size is coarse,and the granularity frequency curve is obviously bimodal.There are also abundant foraminifera in the typhoon deposits.We found a clear double-layered structure in the typhoon deposits,which was caused by strong hydrodynamic disturbance that mixed sediments originally from the offshore area with those of the lagoon.The lower layer has coarse-grained particles with medium sorting,low organic matter content,and low diatom content.The upper layer has fine-grained particles with poor sorting,high organic matter content,and abundant diatoms.The rate of fragmentation of diatoms in the upper layer was very high(40%-60%).The diatom assemblage contained offshore and freshwater species carried by storm runoff.Therefore,we believe that the sediments of this typical sand bar-lagoon environment retain evidence of typhoon events along the southern China coast that is displayed in the marked sedimentological and microfossil characteristics.展开更多
基金The National Natural Science Foundation of China under contract Nos 42107251 and 41706089the Natural Science Foundation of Fujian Province under contract No.2020J05232.
文摘The sedimentary record of climate change in the Arctic region is useful for understanding global warming.Kongsfjord is located in the subpolar region of the Arctic and is a suitable site for studying climate change.Glacier retreat is occurring in this region due to climate change,leading to an increase in meltwater outflow with a high debris content.In August 2017,we collected a sediment Core Z3 from the central fjord near the Yellow River Station.Then,we used the widely used chronology method of 210Pb,^(137)Cs,and other parameters to reflect the climate change record in the sedimentary environment of Kongsfjord.The results showed that after the mid-late 1990s,the mass accumulation rate of this core increased from 0.10 g/(cm^(2)·a)to 0.34 g/(cm^(2)·a),while the flux of^(210)Pb_(ex)increased from 125 Bq/(m^(2)·a)to 316 Bq/(m^(2)·a).The higher sedimentary inventory of^(210)Pb_(ex)in Kongsfjord compared to global fallout might have been caused by sediment focusing,boundary scavenging,and riverine input.Similarities between the inventory of^(137)Cs and global fallout indicated that terrestrial particulate matter was the main source of^(137)Cs in fjord sediments.The sedimentation rate increased after 1997,possibly due to the increased influx of glacial meltwater containing debris.In addition,the^(137)Cs activity,percentage of organic carbon(OC),and OC/total nitrogen concentration ratio showed increasing trends toward the top of the core since 1997,corresponding to a decrease in the mass balance of glaciers in the region.The results ofδ^(13)C,δ^(15)N and OC/TN concentration ratio showed both terrestrial and marine sources contributed to the organic matter in Core Z3.The relative contribution of terrestrial organic matter which was calculated by a two-endmember model showed an increased trend since mid-1990s.All these data indicate that global climate change has a significant impact on Arctic glaciers.
文摘The coastal cities are the most advanced regions in China.In the past few decades,the environment changed very significantly due to large scale human activities in the coastal regions.Polycyclic aromatic hydrocarbons (PAHs)in three dated sediment cores from the west coast of the Yellow Sea (core A01),the Yangtze River estuary (YRE;core A02)and the Oujiang River estuary (ORE;core A03)were analyzed to reconstruct the environmental evolutionary process of the east China coastal region over the past century. In the three cores,PAHs concentrations were increased rapidly.Lower concentrations of PAHs were measured in core A02 than in cores A01 and A03.The vertical variation of PAHs in the YRE Was dominated by the petrogenic sources.Historical records of PAHs in the ORE were controlled by pyrolytic sources.PAHs on the west coast of the Yellow Sea were contributed by the two sources.
基金Supported by National Key Basic Research Fund (No. 2004CB720205) and National Nature and Science Foundation of China (No. 40331003).
文摘On the basis of multi-proxy analysis on TOC, TN, C/N, organic δ^13C and grain size, sediment record from Qinghai Lake provides evidences of stepwise-pattemed climatic change since 16 ka BE Results show that Qinghai Lake underwent six environmental stages. From 16.2 to 14.3 ka BP and from 4.0 to 2.1 ka BP, the organic δ^13C value was controlled by the concentration of atmospheric CO2. Relative higher organic δ^13C values occurred between 14.3 to 10.4 ka BP indicative of water hardness decrease resulted from melting ice water, corresponding to two intervals of C/N peak values to the Boling and AIlerod warm periods in Europe respectively. From 10.4 ka BP, Qinghai Lake entered the Holocene and the climate was warm and a little dry. The Megathermal appeared at about 6.7 ka BP when the vegetation around the lake transformed into a forest. Between 6.3 ka BP and 4.0 ka BP, the temperature decreased and δ^13C value was controlled by the expansion of C3 plants and the retreat of C4 plants in river catchment. Since 4.0 ka BP, the climate gradually became cold and dry. From 2.1 ka BP, the cold-dry climate and human activity resulted in an abrupt increase in C/N with deceased δ^13C value; meanwhile, many coarse grains appeared in sediments.
基金Supported by the National Natural Science Foundation of China(No.41271205)the PhD Research Startup Foundation of Heibei GEO Univerity(No.BQ201604)
文摘Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang,northwestern China.A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS^(14)C.Grain size,total organic matter(TOC),total nitrogen(TN),and TOC/TN(C/N)analyses were used to reconstruct climatic conditions from 13.0 to 5.6 cal ka BP.The results showed fi ve main climatic stages.Zone I(13.0–11.3 cal ka BP)was a wet–dry environment,whereas Zone II(11.3–8.9 cal ka BP)consisted of a primarily wet environment.Zone III(8.9–7.7 cal ka BP)was subdivided into Zone IIIa(8.9–8.2 cal ka BP)that indicated lake constriction and dry climate,and Zone IIIb(8.2–7.7 cal ka BP)in which the proxies indicated wet conditions.In Zone IV(7.7–6.6 cal ka BP),the climate presented a bit wet conditions.In Zone V(6.6–5.6 cal ka BP),abundant glauberite is present in the sediment and silt dominates the lithology;these results indicate the lake shrank and the overall climate was dry.Abrupt environmental events were also identifi ed,including six dry events at 11.0,10.5,9.3,8.6,8.2,and 7.6 cal ka BP and one fl ood event from 7.8 to 7.7 cal ka BP in the Early–Middle Holocene.
基金the National Natural Science Foundation of China (NSFC) (No. 40571169)the NSFC’s Innovation Team Project (No. 40421101), and the NSFC’s Key Program Project (No. 90502008)
文摘The total organic carbon (TOC) content series from the lake sediment of Minqin Basin (100°57′–104°57′E, 37°48′–39°17′N) in northwestern China, which has a 10 000-year-long paleo-climatic proxy record, was used to analyze the Holocene climate changes in the local region. The proxy record was established in the Sanjiaocheng (SJC), Triangle Town in Chinese, Section (103°20′25″E, 39°00′38″N), which is located at the northwestern boundary of the present Asian summer monsoon in China, and is sensitive to global environmental and climate changes. Applying singular spectrum analysis (SSA) to the TOC series, principal climatic oscillations and periodical changes were studied. The results reveal 3 major patterns of climate change regulated by reconstructed components (RCs). The first pattern is natural long-term trend of climatic change in the local area (Minqin Basin), indicating a relatively wetter stage in early Holocene (starting at 9.5 kaBP), and a relatively dryer stage with a strong lake desiccation and a declined vegetation cover in mid-Holocene (during 7–6 kaBP). From 4.0 kaBP to the present, there has been a gradually decreasing trend in the third reconstructed component (RC3) showing that the local climate changed again into a dryer stage. The second pattern shows millennial-centennial scale oscillations containing cycles of 1 600 and 800 years that have been present throughout almost the entire Holocene period of the last 10 000 years. The third pattern is a millennial-centennial scale variation with a relatively smaller amplitude and unclear cycles showing a nonlinear interaction within the earth’s climate systems.
基金The National Natural Science Foundation of China under contract Nos 41576043 and 40976051
文摘The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores,along with the hydrologic data and human activities in the catchment.The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea,which could be divided into three stages as 1958–1970,1971–1990 and 1991–2009.Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes.There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010,i.e.,1940–1950,1951–1980,1981–1990 and 1991–2010.The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980,whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990.Despite the further reduction of the water and sediment input into the sea from 1990 to 2009,this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly,the significantly increased silt contents of the sensitive component.
基金financially supported by the Geological Investigation Project of China Geological Survey(No.12120113006200)
文摘The mid-Pleistocene climate transition (MPT) has been widely reported in worldwide geological events. As a key issue of the Quaternary geology, it has attracted much attention from the paleoclimate community. MPT refers to a period lasting for several hundreds of thousand years, during which the dominant climate periodicity gradually extended from 41 kyr to 100 kyr (Ruddiman et al., 1989),
基金supported by National Natural Science Foundation of China (No.40676067)Knowledge Innovation Program of Chinese Academy of Sciences (No.kzcx2-yw-116-1)
文摘Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (Qp and Qs) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1-10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0-500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 Mw4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average vp and Vs of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high ve/vs ratio of 4.3. We also modeled surface refleeted wave with propagating matrix method to constrain Qs and the near surface velocity structure. Our modeling indicates that Qs is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q(-10), but consistent with Qs modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0-50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borebole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.
基金supported by the National Natural Science Foundation of China (Grant No. 41371009)the Fundamental Research Fund for the Central Universities of China (Grant No. lzujbky2013-127)
文摘Ecosystem response to climate change in high-altitude regions is a focus on global change research. Picea/Abies forests are widely distributed at high altitudes of East and Central Asia, and their distribution changes are sensitive to climate change. Humidity is an important climatic factor that affects high-altitude ecosystems; however, the relationship between distribution changes of Picea/Abies forests and millennial-scale variability of humidity is still not dear. Palynological records can provide insights into millennial-scale paleovegetation changes, which have been successfully used to reconstruct past climate change in East and Central Asia. In this study, we synthesized 24 Picea/Abies pollen and humidity/moisture changes based upon Holocene lake records in East and Central Asia in order to explore the response of high-latitude ecosystem to millennial-scale climate change. The changing pattern of Holocene lacustrine Picea/Abies pollen in arid Central Asia differs from that of monsoonal East Asia, which can be due to different millennial-scale climate change patterns between monsoonal and arid Central Asia. Then, the relationship between changes in Picea/Abies pollen and humidity/moisture conditions was examined based on a comparison of pollen and humidity/moisture records. The results indicate that millennial-scale Picea/Abies distribution changes aremainly controlled by moisture variability at high altitudes, while the temperature effect plays a minor role in Picea/Abies distribution changes. Moreover, this research proves that lacustrine Picea/Abies pollen can be used as an indicator of millennial-scale humidity/moisture evolution at high altitudes in East and Central Asia.
基金the National Natural Science Foundation of China (Grant No. 40071084)
文摘The results of sedimentary characteristics, grain-size, clay mineral, C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tropical areas. It is testified that the Maar sediment system was sensitive in recording the rapid climate changes in the Holocene. These multidisciplinary results demonstrate that the thermal maximum in the Holocene climate lasted from 7200 to 2700 aBP, with several abrupt ephemeral vibrations occurring between 7250-6120 aBP and at around 4460, 3850 and 2700 aBP. In the late Holocene, particularly at ~2700 aBP, a distinct environmental change indicating an important climate transition in the tropical eastern Asia was recorded, probably responding to the enhancement of ENSO phenomena in the Pacific Ocean. In addition, the high-resolution algae record clearly indicates periodical climate fluctuations at 500 a cyclicity during the last 2500 years.
基金Supported by the National Natural Science Foundation of China (Nos.40676026,41076079,40876079,40831160519,40906058)the National Basic Research Program of China(973 Program)(No. 2010CB428704)
文摘Diatom taxa in samples collected from the uppermost 1-cm sediment of the South China Sea (SCS) during cruises in 2000, 2001, and 2007 were investigated. Among them, two genera, Rutilaria and Trigoniurn, and 11 marine taxa (species and varieties) were described for the first time in China. The 11 taxa, Rutilaria radiata, Asterolampra grevillei, Biddulphia turrigera, Cocconeis cyclophora var. decora, Cocconeis ocellata, Dictyoneis rnarginata, Entogonia davyana, Tryblionella campechiana, Plagiogramma kinkeri, Plagiogramma nankoorense and Trigonium cf. contumax, were mainly extant species, although Rutilaria radiata and Entogonia davyana are fossils. Available data show that these species are mainly present in the eastern and western Pacific Ocean and the Indian Ocean. A large number of taxa newly recorded in this study were previously reported in the Philippines. The presence of these taxa in both locations is likely a result of seawater exchange in the SCS through the Bashi Channel Taxonomic descriptions, habitats, and distributions of each diatom taxon are provided herein.
基金supported by the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.KZCX2-105)the National Natural Science Foundation of China(Grant Nos.403030140 and 49894170).
文摘Sediment grain size is a conventional proxy of climatic changes. Larger sediment grain size is often interpreted to indicate dry climate during lower lake level while smaller sedi- ment grain size implies wet climate during higher lake level. Through detailed study on sediment grain sizes in Lake Erhai and Lake Chenghai, this paper reveals the different indication signifi- cances of sediment grain sizes in different time scales, different resolution investigations. For long time-scale and low resolution (102a or 103a) studies, larger sediment grain size indicates lower lake level, smaller lake area and drier climate while smaller sediment grain size indicates higher lake level, larger lake area and wetter climate. For short time-scale and high resolution (a or 10a) studies, larger sediment grain size reflects more rainfall and wetter climate while smaller sediment grain size reflects less rainfall and drier climate. Environmental information revealed by lacustrine sediment records is often different in different time scales because of the variance of sedimentation resolution, sampling resolution and dating precision. Therefore, paleoclimate im- plications of environmental proxies in long time-scale and low resolution investigations could not be mechanically applied to short time-scale and high resolution studies. Only after synthetically analyzing the influence manner and extent of all factors on the sediment records in different time scales, can credible conclusions be obtained.
文摘THE formation and uplift of the Himalayas and the Tibetan Plateau may have been responsible for the past150 Ma global environmental changes, resulting in the development of a three-tiered landform in southernChina. The Yunnan-Guizhou Plateau, as the middle tier in eastern slope of the Himalayas, has beencomplex environmental unit with great altitude gradients and plateau landform characters. Both monsoonsfrom the Pacific and the Indian resulting in apparent environmental changes on variable time scales influence it. Environmental geochemical effect of low latitude-high altitude could be yielded, and well recorded in the geological bodies in this region. To build and verify a quantitative model of environmental evolution it is necessary to obtain high-resolution data of elemental cycles and mass equilibrium.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40331012, 40671190, 40421101)U.S. National Science Foundation (Grant Nos. NSF-ESH-04-02509, NSF-BCS-06-23478, NSF-BCS00-78557)
文摘Based on modern pollen studies and reliable chronology of nine AMS 14C dates, a detailed history of vegetation and climate changes during the past 8660 cal. a BP was reconstructed by a high-resolution pollen record from Ugii Nuur in central Mongolia. Poaceae-steppe dominated the study area and the climate was mild and semi-humid before 7800 cal. a BP with a noticeable cool and humid interval at 8350―8250 cal. a BP. Xerophytic plant increased and the climate became warm and dry gradually since 7800 cal. a BP. From 6860 to 3170 cal. a BP, semi-desert steppe expanded, suggesting a prolonged warm and dry climate. Between 3170 and 2340 cal. a BP, regional forest steppe expanded whereas semi-desert steppe retreated, indicating the climate became cool and wet gradually and the humidity reached the maximum at the end of this stage. From 2340 to 1600 cal. a BP, a general cool and wet climate prevailed. And the climatic instability increased after 1600 cal. a BP. Review of regional pub-lished palaeoclimatic records implies that the mid-Holocene dry climate might have prevailed in vast areas from central Mongolia to arid areas of northwest China. Pollen-based climate reconstruction for UG04 core was well correlated with the result of climate model on Central Asia by Bush. In addition, several abrupt climatic events (cool and wet) were found and some could be broadly compared with the cool events in Atlantic.
基金the Key Program of National Natural Science Foundation of China(Grant No.41930538)the National Science Foundation of China(Grant No.41306083)+1 种基金the National Key Research and Development Program of China(Grant No.2019YFE0124700)the Scientific Research Foundation of Third Institute of Oceanography,Ministry of Natural Resources of China(Grant Nos.2019018,2019026,and 2020017)。
文摘To determine the characteristics and potential indicators of modern typhoon deposition in a sandy lagoon off the coast of Guangdong Province(southern China),we analysed the ^(210)Pb,sedimentology,and microfossils of samples from ten cores obtained before and after the passage of Typhoon Rammasun in 2014.Typhoon deposition showed a thinning trend from internal areas of the lagoon to its mouth,with the maximum thickness inside the lagoon of~35 cm.These typhoon deposits are dominated by overwash and differ from sediments deposited under normal weather conditions.Under normal weather conditions,lagoon sediment has a210 Pb curve that follows a model of exponential decay,has a unimodal granularity frequency curve,and lacks organic matter and microfossils(diatoms and foraminifera).However,210 Pb is low in the typhoon deposits,the grain size is coarse,and the granularity frequency curve is obviously bimodal.There are also abundant foraminifera in the typhoon deposits.We found a clear double-layered structure in the typhoon deposits,which was caused by strong hydrodynamic disturbance that mixed sediments originally from the offshore area with those of the lagoon.The lower layer has coarse-grained particles with medium sorting,low organic matter content,and low diatom content.The upper layer has fine-grained particles with poor sorting,high organic matter content,and abundant diatoms.The rate of fragmentation of diatoms in the upper layer was very high(40%-60%).The diatom assemblage contained offshore and freshwater species carried by storm runoff.Therefore,we believe that the sediments of this typical sand bar-lagoon environment retain evidence of typhoon events along the southern China coast that is displayed in the marked sedimentological and microfossil characteristics.