Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whethe...Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whether deposits of the Banxi Period should be classified as Nanhua System.Another is the onset time of Nanhua glacial period.展开更多
Objective Climate fluctuations over suborbital or millennial timescale display significant instability during the last glacial period,which are often superimposed upon the orbital periodicity.They triggered some abrup...Objective Climate fluctuations over suborbital or millennial timescale display significant instability during the last glacial period,which are often superimposed upon the orbital periodicity.They triggered some abrupt climate events,展开更多
Reconstruction of the desert paleoclimate is important to understand the mechanisms that triggered and/or enhanced climate change.Through optically stimulated luminescence(OSL)dating,grain size,magnetic susceptibility...Reconstruction of the desert paleoclimate is important to understand the mechanisms that triggered and/or enhanced climate change.Through optically stimulated luminescence(OSL)dating,grain size,magnetic susceptibility,X-ray powder diffraction(XRD)and geochemical indicators,we provide a welldated record of a sedimentary outcrop on the southeast margin of the Bardain Jaran Desert,Northwest China,during the last glacial period.Four Qz-OSL ages are obtained,41.0±3.4 ka,54.7±4.4 ka,59.5±5.0 ka and 66.8±5.8 ka,corresponding to the depths of 35 cm,70 cm,150 cm and 200 cm respectively.Indicators like grain size,clay content,magnetic susceptibility,XRD and geochemical index(e.g.Sr,Ba,Sr/Ca)jointly indicate abrupt climate changes at the depth of 35 cm(age,ca.41.0 ka)and200 cm(age,ca.67 ka).Namely,the 280 cm sedimentary outcrop perfectly records a warm wet climate stage,corresponding to the late Marine Isotope Stages(MIS)4 to the early MIS 3.Besides,there is a trend of grain size increase after around 40ka BP,which is most likely a signal of wind strength change.Our research supports that enhancing Siberian High pressure system during the late MIS 3played a key role in NW East Asia climate evolution.展开更多
Several buried paleo-channels are located on the continental shelf of the western Yellow Sea. Research on the paleochannels is significant for both theoretical studies and practical applications. In this paper, we ana...Several buried paleo-channels are located on the continental shelf of the western Yellow Sea. Research on the paleochannels is significant for both theoretical studies and practical applications. In this paper, we analyse and discuss the mineralogy of sediments in a core(SYS-0803) recovered from a buried paleo-channel on the continental shelf of the western Yellow Sea. The aim is to determine the provenance of sediments that fill the paleo-channel. The heavy mineral assemblage of sediments in the core consists of schistose minerals, common hornblende, epidote, and ilmenite. The light mineral assemblage consists of plagioclase, quartz, lithic fragments, and K-feldspar. Analysis of the compositional maturity of the sand fraction revealed a quartz/feldspar ratio of < 1. A relatively high percentage of smectite is recorded throughout the entire paleo-channel fill, with the greatest percentage in the middle to lower parts. The detrital mineral assemblage and clay mineral content indicate that the paleo-channel sediments were sourced mainly from the Huanghe River during the last glacial period.展开更多
In terms of Earth\|Sun geometry, the Milankovitch theory has successfully explained most of the cyclic palaeoclimatic variations during the history of the Earth, especially in the Quaternary. In this paper, the author...In terms of Earth\|Sun geometry, the Milankovitch theory has successfully explained most of the cyclic palaeoclimatic variations during the history of the Earth, especially in the Quaternary. In this paper, the authors suggest that the impact of extraterrestrial bodies on the Earth may be another mechanism to cause palaeoclimatic cycles, global environmental changes and new glacial periods. Based on geological and geochemical records in the boundary layers produced by six huge Cenozoic bolide\|impact events (65, 34, 15, 2.4, 1.1, 0.73 Ma B.P.), including those at 34, 15, 1.1 and 0.73 Ma B.P. which are represented by four famous tektite\|strewn fields, the process and mechanics of palaeoclimatic cycles and global environmental catastrophes induced by extraterrestrial impact are discussed in detail. Impact\|generated dust, soot and aerosol floating in the stratosphere could result in short\|term (<1 year), rapid drop in temperature immediately after impact. Through self\|regulation of the Earth’s climate system, the temperature at the surface slowly went up within 100a and maintained stable for a long time at 250K. If there were no other factors leading to the break\|down of the newly\|established equilibrium, a new glacial period would be initiated. Estimating from the thickness of \{δ\{\}\+\{13\}C\} and \{δ\{\}\+\{18\}O\} anomalies in sediments across the impact boundary layer and deposition rate, the duration of two stages of the palaeoclimate cycle in the form of cold weather—greenhouse effect—normal weather was 10\+4-10\+5a, respectively. The conclusion deduced from the above model is supported by palaeotemperature change recorded by oxygen isotope in sediments across the impact boundary layer.展开更多
The rainfall changes in East Asian summer monsoon(EASM)regions on the orbital timescale remain controversial due to the lack of reliable rainfall records.Here,we present new multiproxy records(δ^(18)O,δ^(13)C,Sr/Ca ...The rainfall changes in East Asian summer monsoon(EASM)regions on the orbital timescale remain controversial due to the lack of reliable rainfall records.Here,we present new multiproxy records(δ^(18)O,δ^(13)C,Sr/Ca and Mg/Ca)of a230Thdated stalagmite from Hulu Cave in central eastern China.Multiproxy records reconstruct a regional hydroclimate history from 340 to 261 kyr BP(thousand years before present),approximately covering the antepenultimate glacial period.Theδ^(18)O record is dominated by the precessional cycles,suggesting that EASM responds to changes in Northern Hemisphere summer insolation(NHSI)on the orbital timescale.Significant correlations amongst theδ^(13)C,Sr/Ca and Mg/Ca suggest that a common factor,i.e.,the local hydrological cycle,controlled their variability,and their leading principal component can be used as a proxy linked to regional rainfall.This composite record bears a good similarity to those from the Chinese Loess Plateau,showing a gradually decreasing rainfall during the antepenultimate glacial period,consistent with changes in global ice volume.Superimposed on the long-term trend,three relative wetter intervals were responding to the higher NHSI periods,suggesting that EASM rainfall variability was induced by integrated effects of global ice volume and NHSI.The increased ice sheets and lower NHSI resulted in an increased meridional temperature gradient and southward shift of the westerlies,which shortened the duration of Meiyu and midsummer rainfall.The differences between the rainfall record and the stalagmiteδ^(18)O record indicate that the latter represents the overall EASM intensity linked to monsoon circulation,but does not directly reflect the rainfall changes at the cave sites.展开更多
Diatoms are one of the predominant contributors to global carbon fixation by accounting for over 40% of total oceanic primary production and dominate export production. They play a significant role in marine biogeoche...Diatoms are one of the predominant contributors to global carbon fixation by accounting for over 40% of total oceanic primary production and dominate export production. They play a significant role in marine biogeochemistry cycle. The diatom mat deposits are results of vast diatoms bloom. By analysis of diatom mats in 136°00′―140°00′E,15°00′―21°00′N, Eastern Philippines Sea, we identified the species of the diatoms as giant Ethmodiscus rex (Wallich) Hendey. AMS 14C dating shows that the sediments rich in diatom mats occurred during 16000―28600 a B.P., which means the bloom mainly occurred during the last glacial period, while there are no diatom mat deposits in other layers. Preliminary analysis indicates that Antarctic Intermediate Water (AAIW) expanded northward and brought silicate-rich water into the area, namely, silicon leakage processes caused the bloom of diatoms. In addition, the increase of iron input is one of the main reasons for the diatom bloom.展开更多
The desert and sandy land are the products of arid climate. The spatial distribution of modern deserts and sandy land in China and their relation to climate show following characteristics: arid and hyper-arid desert z...The desert and sandy land are the products of arid climate. The spatial distribution of modern deserts and sandy land in China and their relation to climate show following characteristics: arid and hyper-arid desert zones, at isohyet of less than 200 mm, are dominated by mobile dunes; semi-arid steppe and arid desert steppe with the precipitation between 200?00 mm, are dominated by semi-fixed and fixed sand dunes; the precipitation of sub-humid forest grassland and humid forest zones with scattered fixed sand land is higher than 400 mm. With this as reference, in combination with considerable amount of paleoclimatic data in desert regions and adjacent regions, the distributions of desert and sandy land in China during the last intergla-cial period, the last glacial maximum (LGM), and the Holocene megathermal, were preliminarily reconstructed. The results compared with that of today show that the distribution of desert and sandy land in China was greatly dwindled during last interglacial period, and the mobile dune area was about two-thirds of that of today's, but greatly expanded during LGM. However, the dwindling area of desert and sandy land in the Holocene megathermal was smaller than that in the last interglacial period. The forcing mechanism was mainly related to the changes of East Asian winter and summer monsoon, south-northward swing of the westerlies and the variations of the Qinghai-Tibet Plateau monsoon intensity caused by global climate changes during the cold and warm intervals since the last interglacial period.展开更多
THE consequence of "nuclear winter" induced by nuclear war and climatic catastrophe induced by extraterrestrial impact were widely studied for fear of the potential danger of the basic nuclear war (the total...THE consequence of "nuclear winter" induced by nuclear war and climatic catastrophe induced by extraterrestrial impact were widely studied for fear of the potential danger of the basic nuclear war (the totalexplosive equivalent 5 000Mt TNT). Using zero-dimensional energy balance model authors reportedthe short-term climatic effect induced by six huge Cenozoic bolide-impact events (65, 34, 15, 2.4,1.1, 0.73 MaBP). However, only the direct climatic effect of dusts yielded by the impact was considered in the previous study. In this note, based on the previous simulation results the effect of variance ofglobal reflectance with temperature on the long-term climatic change was further taken into consideration.Combined with the strata records of palaeoclimatic change the relationship of impact energy with its in-展开更多
A 350-cm-long sediment core sequence from Dahu Swamp situated in the eastern Nanling Mountains was selected for high-resolution paleoclimatic reconstruction since the Late Glacial period. The multi-proxy records of th...A 350-cm-long sediment core sequence from Dahu Swamp situated in the eastern Nanling Mountains was selected for high-resolution paleoclimatic reconstruction since the Late Glacial period. The multi-proxy records of this paper reveal several evidently dry and cold events that may coincide with the Oldest Dryas, the Older Dryas, the Younger Dryas in the late deglacial period. Two relatively wetter and warmer phases occurred in ca. 15,000-14,400 cal yr B.P. and 13,500-12,800 cal yr B.P. respectively may correspond to the Boiling and Allerod warming events. The Younger Dryas event (ca. 12,800-11,500 cal yr B.P.) revealed by multi-proxies was characterized by relatively colder and drier climate. A warmer and wetter climate, occurred in ca. 10,000~5000 cal yr B.P., was consistent with the Holoeene Optimum, which coincided with the maximum Northern Hemisphere insolation. The "8.2kyr cool event" and even the "8.8kyr cool event" were indicated as well from our sediment core. A dry mid-Holocene period (ca. 60000 3000 cal yr B.P.) indicated by multi-proxies does not follow the traditional concept of the wet mid-Holocene conditions observed in other regions in China.展开更多
For the reconstruction of past climate variations,investigations on the history of glaciers are necessary.In the Himalaya,investigations like these have a rather short tradition in comparison with other mountains on e...For the reconstruction of past climate variations,investigations on the history of glaciers are necessary.In the Himalaya,investigations like these have a rather short tradition in comparison with other mountains on earth.At the same time,this area on the southern margin of Tibet is of special interest because of the question as to the monsoon-influence that is connected with the climate-development.Anyhow,the climate of High Asia is of global importance.Here for the further and regionally intensifying answer to this question,a glacial glacier reconstruction is submitted from the CentralHimalaya,more exactly from the Manaslu-massif.Going on down-valley from the glacial-historical investigations of 1977 in the upper Marsyandi Khola(Nadi) and the partly already published results of field campaigns in the middle Marsyandi Khola and the Damodar- and Manaslu Himal in the years 1995,2000,2004 and 2007,new geomorphological and geological field- and laboratory data are introduced here from the Ngadi(Nadi) Khola and the lower Marsyandi Nadi from the inflow of the Ngadi(Nadi) Khola down to the southern mountain foreland.There has existed a connected ice-stream-network drained down to the south by a 2,100-2,200 m thick and 120 km long Marsyandi Nadi main valley glacier.At a height of the valley bottom of c.1,000 m a.s.l.the Ngadi Khola glacier joined the still c.1,300 m thick Marsyandi parent glacier from the Himalchuli-massif(Nadi(Ngadi) Chuli) – the south spur of the Manaslu Himal.From here the united glacier tongue flowed down about a further 44 km to the south up to c.400 m a.s.l.(27°57'38 "N/84°24'56" E) into the Himalaya fore-chains and thus reached one of or the lowest past ice margin position of the Himalayas.The glacial(LGP(Last glacial period),LGM(Last glacial maximum) Würm,Stage 0,MIS 3-2) climatic snowline(ELA = equilibrium line altitude) has run at 3,900 to 4,000 m a.s.l.and thus c.1,500 altitude meters below the current ELA(Stage XII) at 5,400-5,500 m a.s.l.The reconstructed,maximum lowering of the climatic snowline(ΔELA = depression of the equilibrium line altitude) about 1,500 m corresponds at a gradient of 0.6°C per 100 altitude meters to a High Glacial decrease in temperature of 9°C(0.6 × 15 = 9).At that time the Tibetan inland ice has caused a stable cold high,so that no summer monsoon can have existed there.Accordingly,during the LGP the precipitation was reduced,so that the cooling must have come to more than only 9°C.展开更多
通过深沪湾高分辨率浅地层剖面声学地层和地质钻孔沉积地层的对比,并结合沉积物的粒度、微体古生物以及AMS14C测年的综合分析,揭示了研究区晚更新世末次冰期以来的地层层序,探讨了深沪湾的古环境演变。深沪湾高分辨率浅地层剖面自上而...通过深沪湾高分辨率浅地层剖面声学地层和地质钻孔沉积地层的对比,并结合沉积物的粒度、微体古生物以及AMS14C测年的综合分析,揭示了研究区晚更新世末次冰期以来的地层层序,探讨了深沪湾的古环境演变。深沪湾高分辨率浅地层剖面自上而下划分的5个声学地层单元与钻孔岩芯划分的5个沉积地层单元具有较好的对应关系。8.2 ka BP左右,全新世海侵使得海水进入深沪湾海域,海平面低于现今海平面10~12 m,气候凉爽;7 ka BP左右海水到达现今海平面位置,并于6 ka BP左右到达最高,约比现今海平面高2~3 m,气候温暖湿润,这一时期,近岸大量裸子植物被海水淹没并被沉积物快速掩埋;5 850~5 642 a BP研究区温度降低,该降温活动持续到2 ka BP左右,气候凉爽干燥;2 ka BP以来温度逐渐上升,600 a BP左右有一个相对冷期,之后温度又逐渐上升至现今水平。展开更多
Geochemical and grain size analysis on the DQ (Dongqi) profile from Gonghe Basin, northeastern Qinghai-Tibetan Plateau, indi- cates that regional climate has experienced several cold-dry and warm-wet cycles since th...Geochemical and grain size analysis on the DQ (Dongqi) profile from Gonghe Basin, northeastern Qinghai-Tibetan Plateau, indi- cates that regional climate has experienced several cold-dry and warm-wet cycles since the last glacial maximum (LGM). The cold and dry climate dominated the region before 15.82 cal. ka B.E due to stronger winter monsoon and weaker summer monsoon, but the climate was relatively cold and wetter prior to 21 cal. ka B.E. In 15.824.5 cal. ka B.E, summer monsoon strength in- creased and winter monsoon tended to be weaker, implying an obvious warm climate. Specifically, the relatively cold and dry condition appeared in 14.7-13.7 cal. ka B.E and 12.14.5 cal. ka B.R, respectively, while relatively warm and wet in 13.~12.1 cal. ka B.E. The winter and summer monsoonal strength presents frequent fluctuations in the Holocene and relatively warm and wet conditions emerged in 9.5~.0 cal. ka B.E due to stronger summer monsoon. From 7.0 to 5.1 cal. ka B.E, the cycle of cold-dry and warm-wet climate corresponds to frequent fluctuations of winter and summer monsoons. The climate becomes warm and wet in 5.1 2.7 cal. ka B.E, accompanying increased summer monsoon, but it tends to be cold and dry since 2.7 cal. ka B.R due to en- hanced winter monsoonal strength. In addition, the evolution of regional winter and summer monsoons is coincident with warm and cold records from the polar ice core. In other words, climatic change in the Gonghe Basin can be considered as a regional re- sponse to global climate change.展开更多
基金supported by the National Natural Science Foundation of China(grants No.41372124,41402103 and 41302091)
文摘Objective There has been considerable debate about the definition of the lower boundary of Nanhua System by far.One definition is based on sedimentary sequence of different stages of basin evolution,focusing on whether deposits of the Banxi Period should be classified as Nanhua System.Another is the onset time of Nanhua glacial period.
基金co-supported by the National Natural Science Foundation of China(Grants Nos:41572162.41290253)International Partnership Program of the Chinese Academy of Sciences(No:132B61KYS20160002)
文摘Objective Climate fluctuations over suborbital or millennial timescale display significant instability during the last glacial period,which are often superimposed upon the orbital periodicity.They triggered some abrupt climate events,
基金financial support from China University of Geosciences, Beijingsupported by the Project of National Nature Science Foundation of China (Grant No. 41572094)+2 种基金the Ph. D Research Start-up Fund of Fuyang Normal University (Grant No. 2016kyqd0004)the Scientific Research Project of Fuyang Normal University (Grant No. 2018FSKJ08ZD)the Key Project of Youth Science Funds of Fuyang Normal University (Gran No. rcxm201907)
文摘Reconstruction of the desert paleoclimate is important to understand the mechanisms that triggered and/or enhanced climate change.Through optically stimulated luminescence(OSL)dating,grain size,magnetic susceptibility,X-ray powder diffraction(XRD)and geochemical indicators,we provide a welldated record of a sedimentary outcrop on the southeast margin of the Bardain Jaran Desert,Northwest China,during the last glacial period.Four Qz-OSL ages are obtained,41.0±3.4 ka,54.7±4.4 ka,59.5±5.0 ka and 66.8±5.8 ka,corresponding to the depths of 35 cm,70 cm,150 cm and 200 cm respectively.Indicators like grain size,clay content,magnetic susceptibility,XRD and geochemical index(e.g.Sr,Ba,Sr/Ca)jointly indicate abrupt climate changes at the depth of 35 cm(age,ca.41.0 ka)and200 cm(age,ca.67 ka).Namely,the 280 cm sedimentary outcrop perfectly records a warm wet climate stage,corresponding to the late Marine Isotope Stages(MIS)4 to the early MIS 3.Besides,there is a trend of grain size increase after around 40ka BP,which is most likely a signal of wind strength change.Our research supports that enhancing Siberian High pressure system during the late MIS 3played a key role in NW East Asia climate evolution.
基金supported by the National Natural Science Foundation of China(No.41476051)China-ASEAN maritime cooperation fund(Comparative Study of Holocene Sedimentary Evolution of the Yangtze River Delta and the Red River Delta)+2 种基金the National Natural Science Foundation Project(No.41606059)Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology Foundation Project(No.MRE201309)the Shandong Provincial Natural Science Foundation,China(No.ZR2016DL04)
文摘Several buried paleo-channels are located on the continental shelf of the western Yellow Sea. Research on the paleochannels is significant for both theoretical studies and practical applications. In this paper, we analyse and discuss the mineralogy of sediments in a core(SYS-0803) recovered from a buried paleo-channel on the continental shelf of the western Yellow Sea. The aim is to determine the provenance of sediments that fill the paleo-channel. The heavy mineral assemblage of sediments in the core consists of schistose minerals, common hornblende, epidote, and ilmenite. The light mineral assemblage consists of plagioclase, quartz, lithic fragments, and K-feldspar. Analysis of the compositional maturity of the sand fraction revealed a quartz/feldspar ratio of < 1. A relatively high percentage of smectite is recorded throughout the entire paleo-channel fill, with the greatest percentage in the middle to lower parts. The detrital mineral assemblage and clay mineral content indicate that the paleo-channel sediments were sourced mainly from the Huanghe River during the last glacial period.
文摘In terms of Earth\|Sun geometry, the Milankovitch theory has successfully explained most of the cyclic palaeoclimatic variations during the history of the Earth, especially in the Quaternary. In this paper, the authors suggest that the impact of extraterrestrial bodies on the Earth may be another mechanism to cause palaeoclimatic cycles, global environmental changes and new glacial periods. Based on geological and geochemical records in the boundary layers produced by six huge Cenozoic bolide\|impact events (65, 34, 15, 2.4, 1.1, 0.73 Ma B.P.), including those at 34, 15, 1.1 and 0.73 Ma B.P. which are represented by four famous tektite\|strewn fields, the process and mechanics of palaeoclimatic cycles and global environmental catastrophes induced by extraterrestrial impact are discussed in detail. Impact\|generated dust, soot and aerosol floating in the stratosphere could result in short\|term (<1 year), rapid drop in temperature immediately after impact. Through self\|regulation of the Earth’s climate system, the temperature at the surface slowly went up within 100a and maintained stable for a long time at 250K. If there were no other factors leading to the break\|down of the newly\|established equilibrium, a new glacial period would be initiated. Estimating from the thickness of \{δ\{\}\+\{13\}C\} and \{δ\{\}\+\{18\}O\} anomalies in sediments across the impact boundary layer and deposition rate, the duration of two stages of the palaeoclimate cycle in the form of cold weather—greenhouse effect—normal weather was 10\+4-10\+5a, respectively. The conclusion deduced from the above model is supported by palaeotemperature change recorded by oxygen isotope in sediments across the impact boundary layer.
基金supported by the National Nature Science Fundation of China(Grant Nos.42002200&42071105)the Open Fund for the State Key Laboratory of Loess and Quaternary Geology(Grant No.SKLLQG1922)+1 种基金the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN201900536)the Chongqing Nature Science Fund(Grant No.cstc2020jcyj-msxm X0598)。
文摘The rainfall changes in East Asian summer monsoon(EASM)regions on the orbital timescale remain controversial due to the lack of reliable rainfall records.Here,we present new multiproxy records(δ^(18)O,δ^(13)C,Sr/Ca and Mg/Ca)of a230Thdated stalagmite from Hulu Cave in central eastern China.Multiproxy records reconstruct a regional hydroclimate history from 340 to 261 kyr BP(thousand years before present),approximately covering the antepenultimate glacial period.Theδ^(18)O record is dominated by the precessional cycles,suggesting that EASM responds to changes in Northern Hemisphere summer insolation(NHSI)on the orbital timescale.Significant correlations amongst theδ^(13)C,Sr/Ca and Mg/Ca suggest that a common factor,i.e.,the local hydrological cycle,controlled their variability,and their leading principal component can be used as a proxy linked to regional rainfall.This composite record bears a good similarity to those from the Chinese Loess Plateau,showing a gradually decreasing rainfall during the antepenultimate glacial period,consistent with changes in global ice volume.Superimposed on the long-term trend,three relative wetter intervals were responding to the higher NHSI periods,suggesting that EASM rainfall variability was induced by integrated effects of global ice volume and NHSI.The increased ice sheets and lower NHSI resulted in an increased meridional temperature gradient and southward shift of the westerlies,which shortened the duration of Meiyu and midsummer rainfall.The differences between the rainfall record and the stalagmiteδ^(18)O record indicate that the latter represents the overall EASM intensity linked to monsoon circulation,but does not directly reflect the rainfall changes at the cave sites.
基金Supported by the National Basic Research Program (Grant No. 2007CB815903)National Natural Science Foundation of China (Grant No. 40776031)Pilot Project of the National Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-221)
文摘Diatoms are one of the predominant contributors to global carbon fixation by accounting for over 40% of total oceanic primary production and dominate export production. They play a significant role in marine biogeochemistry cycle. The diatom mat deposits are results of vast diatoms bloom. By analysis of diatom mats in 136°00′―140°00′E,15°00′―21°00′N, Eastern Philippines Sea, we identified the species of the diatoms as giant Ethmodiscus rex (Wallich) Hendey. AMS 14C dating shows that the sediments rich in diatom mats occurred during 16000―28600 a B.P., which means the bloom mainly occurred during the last glacial period, while there are no diatom mat deposits in other layers. Preliminary analysis indicates that Antarctic Intermediate Water (AAIW) expanded northward and brought silicate-rich water into the area, namely, silicon leakage processes caused the bloom of diatoms. In addition, the increase of iron input is one of the main reasons for the diatom bloom.
文摘The desert and sandy land are the products of arid climate. The spatial distribution of modern deserts and sandy land in China and their relation to climate show following characteristics: arid and hyper-arid desert zones, at isohyet of less than 200 mm, are dominated by mobile dunes; semi-arid steppe and arid desert steppe with the precipitation between 200?00 mm, are dominated by semi-fixed and fixed sand dunes; the precipitation of sub-humid forest grassland and humid forest zones with scattered fixed sand land is higher than 400 mm. With this as reference, in combination with considerable amount of paleoclimatic data in desert regions and adjacent regions, the distributions of desert and sandy land in China during the last intergla-cial period, the last glacial maximum (LGM), and the Holocene megathermal, were preliminarily reconstructed. The results compared with that of today show that the distribution of desert and sandy land in China was greatly dwindled during last interglacial period, and the mobile dune area was about two-thirds of that of today's, but greatly expanded during LGM. However, the dwindling area of desert and sandy land in the Holocene megathermal was smaller than that in the last interglacial period. The forcing mechanism was mainly related to the changes of East Asian winter and summer monsoon, south-northward swing of the westerlies and the variations of the Qinghai-Tibet Plateau monsoon intensity caused by global climate changes during the cold and warm intervals since the last interglacial period.
文摘THE consequence of "nuclear winter" induced by nuclear war and climatic catastrophe induced by extraterrestrial impact were widely studied for fear of the potential danger of the basic nuclear war (the totalexplosive equivalent 5 000Mt TNT). Using zero-dimensional energy balance model authors reportedthe short-term climatic effect induced by six huge Cenozoic bolide-impact events (65, 34, 15, 2.4,1.1, 0.73 MaBP). However, only the direct climatic effect of dusts yielded by the impact was considered in the previous study. In this note, based on the previous simulation results the effect of variance ofglobal reflectance with temperature on the long-term climatic change was further taken into consideration.Combined with the strata records of palaeoclimatic change the relationship of impact energy with its in-
基金Under the auspices of National Natural Science Foundation of China (No. 40671189)Natural Science Foundation of Guangdong Province (No. 8151063101000044, 06025042)the Fok Ying Tung Education Foundation (No. 91021)
文摘A 350-cm-long sediment core sequence from Dahu Swamp situated in the eastern Nanling Mountains was selected for high-resolution paleoclimatic reconstruction since the Late Glacial period. The multi-proxy records of this paper reveal several evidently dry and cold events that may coincide with the Oldest Dryas, the Older Dryas, the Younger Dryas in the late deglacial period. Two relatively wetter and warmer phases occurred in ca. 15,000-14,400 cal yr B.P. and 13,500-12,800 cal yr B.P. respectively may correspond to the Boiling and Allerod warming events. The Younger Dryas event (ca. 12,800-11,500 cal yr B.P.) revealed by multi-proxies was characterized by relatively colder and drier climate. A warmer and wetter climate, occurred in ca. 10,000~5000 cal yr B.P., was consistent with the Holoeene Optimum, which coincided with the maximum Northern Hemisphere insolation. The "8.2kyr cool event" and even the "8.8kyr cool event" were indicated as well from our sediment core. A dry mid-Holocene period (ca. 60000 3000 cal yr B.P.) indicated by multi-proxies does not follow the traditional concept of the wet mid-Holocene conditions observed in other regions in China.
文摘For the reconstruction of past climate variations,investigations on the history of glaciers are necessary.In the Himalaya,investigations like these have a rather short tradition in comparison with other mountains on earth.At the same time,this area on the southern margin of Tibet is of special interest because of the question as to the monsoon-influence that is connected with the climate-development.Anyhow,the climate of High Asia is of global importance.Here for the further and regionally intensifying answer to this question,a glacial glacier reconstruction is submitted from the CentralHimalaya,more exactly from the Manaslu-massif.Going on down-valley from the glacial-historical investigations of 1977 in the upper Marsyandi Khola(Nadi) and the partly already published results of field campaigns in the middle Marsyandi Khola and the Damodar- and Manaslu Himal in the years 1995,2000,2004 and 2007,new geomorphological and geological field- and laboratory data are introduced here from the Ngadi(Nadi) Khola and the lower Marsyandi Nadi from the inflow of the Ngadi(Nadi) Khola down to the southern mountain foreland.There has existed a connected ice-stream-network drained down to the south by a 2,100-2,200 m thick and 120 km long Marsyandi Nadi main valley glacier.At a height of the valley bottom of c.1,000 m a.s.l.the Ngadi Khola glacier joined the still c.1,300 m thick Marsyandi parent glacier from the Himalchuli-massif(Nadi(Ngadi) Chuli) – the south spur of the Manaslu Himal.From here the united glacier tongue flowed down about a further 44 km to the south up to c.400 m a.s.l.(27°57'38 "N/84°24'56" E) into the Himalaya fore-chains and thus reached one of or the lowest past ice margin position of the Himalayas.The glacial(LGP(Last glacial period),LGM(Last glacial maximum) Würm,Stage 0,MIS 3-2) climatic snowline(ELA = equilibrium line altitude) has run at 3,900 to 4,000 m a.s.l.and thus c.1,500 altitude meters below the current ELA(Stage XII) at 5,400-5,500 m a.s.l.The reconstructed,maximum lowering of the climatic snowline(ΔELA = depression of the equilibrium line altitude) about 1,500 m corresponds at a gradient of 0.6°C per 100 altitude meters to a High Glacial decrease in temperature of 9°C(0.6 × 15 = 9).At that time the Tibetan inland ice has caused a stable cold high,so that no summer monsoon can have existed there.Accordingly,during the LGP the precipitation was reduced,so that the cooling must have come to more than only 9°C.
文摘通过深沪湾高分辨率浅地层剖面声学地层和地质钻孔沉积地层的对比,并结合沉积物的粒度、微体古生物以及AMS14C测年的综合分析,揭示了研究区晚更新世末次冰期以来的地层层序,探讨了深沪湾的古环境演变。深沪湾高分辨率浅地层剖面自上而下划分的5个声学地层单元与钻孔岩芯划分的5个沉积地层单元具有较好的对应关系。8.2 ka BP左右,全新世海侵使得海水进入深沪湾海域,海平面低于现今海平面10~12 m,气候凉爽;7 ka BP左右海水到达现今海平面位置,并于6 ka BP左右到达最高,约比现今海平面高2~3 m,气候温暖湿润,这一时期,近岸大量裸子植物被海水淹没并被沉积物快速掩埋;5 850~5 642 a BP研究区温度降低,该降温活动持续到2 ka BP左右,气候凉爽干燥;2 ka BP以来温度逐渐上升,600 a BP左右有一个相对冷期,之后温度又逐渐上升至现今水平。
基金funded by National Natural Science Foundation of China (Nos. 40971005 and 41271215)
文摘Geochemical and grain size analysis on the DQ (Dongqi) profile from Gonghe Basin, northeastern Qinghai-Tibetan Plateau, indi- cates that regional climate has experienced several cold-dry and warm-wet cycles since the last glacial maximum (LGM). The cold and dry climate dominated the region before 15.82 cal. ka B.E due to stronger winter monsoon and weaker summer monsoon, but the climate was relatively cold and wetter prior to 21 cal. ka B.E. In 15.824.5 cal. ka B.E, summer monsoon strength in- creased and winter monsoon tended to be weaker, implying an obvious warm climate. Specifically, the relatively cold and dry condition appeared in 14.7-13.7 cal. ka B.E and 12.14.5 cal. ka B.R, respectively, while relatively warm and wet in 13.~12.1 cal. ka B.E. The winter and summer monsoonal strength presents frequent fluctuations in the Holocene and relatively warm and wet conditions emerged in 9.5~.0 cal. ka B.E due to stronger summer monsoon. From 7.0 to 5.1 cal. ka B.E, the cycle of cold-dry and warm-wet climate corresponds to frequent fluctuations of winter and summer monsoons. The climate becomes warm and wet in 5.1 2.7 cal. ka B.E, accompanying increased summer monsoon, but it tends to be cold and dry since 2.7 cal. ka B.R due to en- hanced winter monsoonal strength. In addition, the evolution of regional winter and summer monsoons is coincident with warm and cold records from the polar ice core. In other words, climatic change in the Gonghe Basin can be considered as a regional re- sponse to global climate change.