We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last -21,000 years, with multiproxy data for pedogenesis, including magnetic susceptib...We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last -21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ^13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ^13C of organic matter and summer monsoon variations. The change in δ^13C values of organic matter （in accordance with the ratios of C3 to C4 plants） results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ^13C values of organic matter and the local climate system.展开更多
Numerous studies dated glacial deposits within the Himalayan-Tibetan orogen.While most focus on young deposits,i.e.,younger than the Last Glacial Maximum(LGM or Marine oxygen Isotope Stage(MIS)-2,~20 ka),older moraine...Numerous studies dated glacial deposits within the Himalayan-Tibetan orogen.While most focus on young deposits,i.e.,younger than the Last Glacial Maximum(LGM or Marine oxygen Isotope Stage(MIS)-2,~20 ka),older moraines such as those from MIS-6(~130–191 ka)are much harder to date and interpret due to the less well-preserved nature of their surfaces and boulders,as well as their scattered and continuous age distribution due to long-lived erosion since deposition.Here,we dated with~(10)Be,two imbricated moraines near Yadong in southern Tibet,as MIS-2 and 6,showing that the most extensive,smooth surfaces were abandoned during MIS-6.Compiling published data from 54 MIS-6 moraines on the Tibetan Plateau reveals that they exist in most regions,dry or humid.They are particularly well-preserved(sharp crests)in eastern and northern Tibet,while in southern and central Tibet,their crests are rounded to sub-rounded.Because both MIS-2 and 6 were equally cold,and because MIS-6 moraines are much more extensive than those from the LGM,we conclude that MIS-6 glacial advances were controlled by more abundant precipitation than during MIS-2.This would be consistent with the peak in Asian monsoon during MIS-6,revealed by sediments from the South China Sea.展开更多
The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon is...The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.展开更多
It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountai...It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.展开更多
Ahigh resolution study of sediments,microfaunas(ostracods and foraminifers),and stable isotopes of ostracod shells from core PRD05,sampled from the Da’ao plain of the Pearl River Delta,provides new data about palaeoe...Ahigh resolution study of sediments,microfaunas(ostracods and foraminifers),and stable isotopes of ostracod shells from core PRD05,sampled from the Da’ao plain of the Pearl River Delta,provides new data about palaeoenvironmental changes during the Late Quaternary.The basal fluvial gravelly sediments of the core,representing the lowest deposits of the Quaternary at the core site,were possibly formed prior to the transgression associated with the last interglacial stage.This fluvial setting changed into a marginal marine setting during the last interglacial stage,any record of calcareous fossils were destroyed by subsequent dissolution during the last glacial phase,when the upper part of the deltaic sediments experienced subaerial oxidation,indicated by a mottled clay layer in the core.The postglacial sealevel rise in the South China Sea began at16,700 cal yr B.P.During the first phase of sea-level rise(from ~16,700 to 10,100 cal yr B.P.),a swamp environment developed at the core site.At ~10,100 cal yr B.P.,marine waters intruded onto the Da’ao plain and reached the core site through the Modaomen channel.This timing was earlier than in other parts of the Pearl River Delta.Since then,a semi-enclosed estuarine environment developed and was maintained until ~5560 cal yr B.P.During this transgressive interval,short-term environmental fluctuations can be recognized based on microfauna and shell geochemical data.From ~10,100 to 8630 cal yr B.P.,the sea-level rose,which was followed by a fall from ~8630 to 8520 cal yr B.P.An expanded transgression occurred between ~8520 and 7900 cal yr B.P.The time intervals from ~8520 to 8200 cal yr B.P.and from ~8080 to 7900 cal yr B.P.were marked by peak transgression.From ~7900 to 5560 cal yr B.P.,the core site generally showed a reduced marine influence and enhanced freshwater input.A fluvial environment developed from ~5560 to 3100 cal yr B.P.,and was succeeded by an alluvial plain setting.展开更多
Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau （CLP）. This study presents analyses ...Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau （CLP）. This study presents analyses of total organic carbon isotopic composition （TOC） and n-alkane ratios （C31/C27） from the Lingtai loess-palaeosol sequence on the central CLP over the last 450 kyr. The results demonstrate that the vegetation in this region comprised a mix of C3 and C4 plants of herb and woody growth-form. C3 plants dominated for most of the last 450 kyr, but this did not lead to extensive forest. C3 woody plants were more abundant in MIS9 （S3 period） and MIS5 （S 1 period） during warm and humid climate conditions. Herbs increased in the region since 130 kyr, possibly as a result of increased aridity. On the orbital timescales, there was a reduction of C3 herbal plants in MIS 11 （$4） than in M1S 12 （L5）, and in Holocene than in the last glacial period. Our isotope and n-alkane proxy records are in agreement with Artemisia pollen changes in the region, which is/was the dominant species in this area and varying due to different heat and water conditions between glacial and interglacial periods. Though the climate in MIS1 （SO） was similar to that in MIS11 （S4）, a significant increase in woody plants during the Holocene suggests the impact of human activities and ecological effects of changes in fire activity.展开更多
A stacked ocean carbon isotope (δ 13C) record of 200 ka is established on the basis of planktonic foraminifer (Globigerinoides ruber) δ 13C data from 8 sites in the South China Sea (SCS). The δ 13C record from the ...A stacked ocean carbon isotope (δ 13C) record of 200 ka is established on the basis of planktonic foraminifer (Globigerinoides ruber) δ 13C data from 8 sites in the South China Sea (SCS). The δ 13C record from the SCS displays a trend similar to that from the Pacific and Atlantic oceans mainly re-sponding to long eccentricity and precession cycles, with all the three δ 13C minima occurring at glacial terminations. Thus, the changes of the oceanic car-bon reservoir in glacial cycles should not be consid-ered as a response only to ice-sheet variations, but could have been driven also by low latitude proc-esses, such as the monsoon.展开更多
文摘We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last -21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ^13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ^13C of organic matter and summer monsoon variations. The change in δ^13C values of organic matter （in accordance with the ratios of C3 to C4 plants） results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ^13C values of organic matter and the local climate system.
基金financially supported by the Second Tibetan Plateau Scientific Expedition of the Ministry of Science and Technology of China(Grant No.2019QZKK0901)the National Natural Science Foundation of China(Grant Nos.42020104007,41941016)the China Geological Survey(Grant No.DD20221630)。
文摘Numerous studies dated glacial deposits within the Himalayan-Tibetan orogen.While most focus on young deposits,i.e.,younger than the Last Glacial Maximum(LGM or Marine oxygen Isotope Stage(MIS)-2,~20 ka),older moraines such as those from MIS-6(~130–191 ka)are much harder to date and interpret due to the less well-preserved nature of their surfaces and boulders,as well as their scattered and continuous age distribution due to long-lived erosion since deposition.Here,we dated with~(10)Be,two imbricated moraines near Yadong in southern Tibet,as MIS-2 and 6,showing that the most extensive,smooth surfaces were abandoned during MIS-6.Compiling published data from 54 MIS-6 moraines on the Tibetan Plateau reveals that they exist in most regions,dry or humid.They are particularly well-preserved(sharp crests)in eastern and northern Tibet,while in southern and central Tibet,their crests are rounded to sub-rounded.Because both MIS-2 and 6 were equally cold,and because MIS-6 moraines are much more extensive than those from the LGM,we conclude that MIS-6 glacial advances were controlled by more abundant precipitation than during MIS-2.This would be consistent with the peak in Asian monsoon during MIS-6,revealed by sediments from the South China Sea.
基金Supported by the CAS Pilot Project of the National Knowledge Innovation Program (Project No. KZCFX3-SW-233)the National Natural Science Foundation of China (Grant Nos. 90411014 and 40506015)+1 种基金International Cooperation Projects of Ministry of Science and Technology of China (Project No. 2002DFG00034)Sino-French Joint Research Project (Project No. 40421150011)
文摘The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.
基金This study was supported by the National Key Basic Research Development Planning Project(Grant No.2003CB415201)the National Natural Science Foundation of China(Grant No.40572097)the Foundation for the Excellent Young Teachers from the National Education Administration(Grant No.2001BC12).
文摘It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.
基金supported by the Natural Science Foundation of China(Grant No.40872024 and No.40331007)by travel grants within the framework of the Project-based Personnel Exchange Programme of the DAAD(Deutscher Akademischer Austauschdienst) and CSC(China Scholarship Council)
文摘Ahigh resolution study of sediments,microfaunas(ostracods and foraminifers),and stable isotopes of ostracod shells from core PRD05,sampled from the Da’ao plain of the Pearl River Delta,provides new data about palaeoenvironmental changes during the Late Quaternary.The basal fluvial gravelly sediments of the core,representing the lowest deposits of the Quaternary at the core site,were possibly formed prior to the transgression associated with the last interglacial stage.This fluvial setting changed into a marginal marine setting during the last interglacial stage,any record of calcareous fossils were destroyed by subsequent dissolution during the last glacial phase,when the upper part of the deltaic sediments experienced subaerial oxidation,indicated by a mottled clay layer in the core.The postglacial sealevel rise in the South China Sea began at16,700 cal yr B.P.During the first phase of sea-level rise(from ~16,700 to 10,100 cal yr B.P.),a swamp environment developed at the core site.At ~10,100 cal yr B.P.,marine waters intruded onto the Da’ao plain and reached the core site through the Modaomen channel.This timing was earlier than in other parts of the Pearl River Delta.Since then,a semi-enclosed estuarine environment developed and was maintained until ~5560 cal yr B.P.During this transgressive interval,short-term environmental fluctuations can be recognized based on microfauna and shell geochemical data.From ~10,100 to 8630 cal yr B.P.,the sea-level rose,which was followed by a fall from ~8630 to 8520 cal yr B.P.An expanded transgression occurred between ~8520 and 7900 cal yr B.P.The time intervals from ~8520 to 8200 cal yr B.P.and from ~8080 to 7900 cal yr B.P.were marked by peak transgression.From ~7900 to 5560 cal yr B.P.,the core site generally showed a reduced marine influence and enhanced freshwater input.A fluvial environment developed from ~5560 to 3100 cal yr B.P.,and was succeeded by an alluvial plain setting.
基金supported by the National Natural Science Foundation of China(Grant No.41172149)the Science Fund for Creative Research Groups of NSFC(Grant No.41321062)the National Key Basic Research Program of China(Grant No.2015CB953804)
文摘Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau （CLP）. This study presents analyses of total organic carbon isotopic composition （TOC） and n-alkane ratios （C31/C27） from the Lingtai loess-palaeosol sequence on the central CLP over the last 450 kyr. The results demonstrate that the vegetation in this region comprised a mix of C3 and C4 plants of herb and woody growth-form. C3 plants dominated for most of the last 450 kyr, but this did not lead to extensive forest. C3 woody plants were more abundant in MIS9 （S3 period） and MIS5 （S 1 period） during warm and humid climate conditions. Herbs increased in the region since 130 kyr, possibly as a result of increased aridity. On the orbital timescales, there was a reduction of C3 herbal plants in MIS 11 （$4） than in M1S 12 （L5）, and in Holocene than in the last glacial period. Our isotope and n-alkane proxy records are in agreement with Artemisia pollen changes in the region, which is/was the dominant species in this area and varying due to different heat and water conditions between glacial and interglacial periods. Though the climate in MIS1 （SO） was similar to that in MIS11 （S4）, a significant increase in woody plants during the Holocene suggests the impact of human activities and ecological effects of changes in fire activity.
基金financially supported by Natural National Science Foundation of China (Nos.41272236 and 41202156)China Geological Survey (Nos.1212011121267, 1212020918036 and 12120114022901)+1 种基金Central Public-interest Scientific Institution Basal Research Fund (Nos.J1334 and J1126)European Marie Sklodowska-Curie Outgoing International Fellowship FP6 (No.040070)~~
文摘A stacked ocean carbon isotope (δ 13C) record of 200 ka is established on the basis of planktonic foraminifer (Globigerinoides ruber) δ 13C data from 8 sites in the South China Sea (SCS). The δ 13C record from the SCS displays a trend similar to that from the Pacific and Atlantic oceans mainly re-sponding to long eccentricity and precession cycles, with all the three δ 13C minima occurring at glacial terminations. Thus, the changes of the oceanic car-bon reservoir in glacial cycles should not be consid-ered as a response only to ice-sheet variations, but could have been driven also by low latitude proc-esses, such as the monsoon.
