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 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 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
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 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.
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.
