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1.
The δ18O variations in an 80.36 m ice core retrieved in the accumulation zone of the East Rongbuk Glacier, Mount Qomolangma (Everest), is not consistent with changes of air temperature from both southern and northern slopes of Himalayas, as well as these of the temperature anomalies over the Northern Hemisphere. The negative relationship between the δ18O and the net accumulation records of the ice core suggests the "amount effect" of summer precipitation on the δ18O values in the region. Therefore, the δ18O records of the East Rongbuk ice core should be a proxy of Indian Summer Monsoon intensity, which shows lower δ18O values during strong monsoon phases and higher values during weak phases.  相似文献   

2.
Chen  Jie  Huang  Wei  Zhang  Qiong  Feng  Song 《中国科学:地球科学(英文版)》2020,63(8):1199-1208
The Mongolian Plateau(MP) is located in the eastern part of arid Central Asia(ACA). Climatically, much of the MP is dominated by the westerly circulation and has an arid and semi-arid climate; however, the eastern part of the MP is also influenced by the East Asian summer monsoon(EASM) and has a humid and semi-humid climate. Several studies have shown that precipitation variability in the MP differs from that in western ACA but is consistent with that in the EASM region. Here we use monthly precipitation data for 1979–2016 to characterize and determine the origin of the summer precipitation variability of the MP and the EASM region. The results show that the MP and the mid-latitude EASM region exhibit a consistent pattern of precipitation variability on interannual and decadal timescales; specifically, the consistent regions are the MP and North and Northeast China. We further investigated the physical mechanisms responsible for the consistent interdecadal precipitation variability between the MP and the mid-latitude EASM region, and found that the mid-latitude wave train over Eurasia, with positive(negative) geopotential height anomalies over the North Atlantic and ACA and negative(positive) geopotential height anomalies over Europe and the MP, is the key factor responsible for the consistency of precipitation variability in the MP and the mid-latitude EASM region. The positive anomalies over the North Atlantic and ACA and negative anomalies over Europe and the MP would enhance the transport of westerly and monsoon moisture to the MP and North and Northeast China. They could also strengthen the Northeast Asian low, enhance the EASM, and trigger the anomalous ascending motion over the MP which promotes precipitation in the MP and in the mid-latitude EASM region. Overall, our results help explain the spatial variations of paleo-precipitation/humidity reconstructions in East Asia and clarify the reasons for the consistency of the regional climate.  相似文献   

3.
Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnec- tion pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast China via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern China. All these changes of circulations and moisture conditions finally result in an anoma- lous Asian summer monsoon and monsoon rainfall over India and northern China. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly corre- lated with Asian summer monsoon variability. The spring APNPO might therefore provide valuable in- formation for the prediction of Asian summer monsoon.  相似文献   

4.
This study investigates water vapor isotopic patterns and controls over China using high-quality water vapor δD data retrieved from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography(SCIAMACHY) observations.The results show that water vapor δD values on both annual and seasonal time-scales broadly exhibit a continental effect,with values largely decreasing northwestward from coastal lowlands to high-elevation mountainous regions.However,region-specific analysis reveals spatially distinct patterns of water vapor δD between seasons.In the monsoon domain(e.g.,China south of 35°N),depletion in D in the summer and fall seasons is closely tied to monsoon moisture sources(the Indian and Pacific oceans) and subsequent amount effect,but higher δD values in winter and spring are a result of isotopically-enriched continental-sourced moisture proceeded by less rainout.In contrast,farther inland in China(non-monsoon domain),moisture is derived overwhelmingly from the dry continental air masses and local evaporation,and δD values are largely controlled by the temperature effect,exhibiting a seasonality with isotopically enriched summer and depleted winter/spring.The observation that the spatial pattern of water vapor δD is the opposite to that of precipitation δD in the summer season also suggests that partial evaporation of falling raindrops is a key driver of water vapor isotope in the non-monsoon domain.This study highlights the importance of non-Rayleigh factors in governing water vapor isotope,and provides constraints on precipitation isotope interpretation and modern isotope hydrological processes over China.  相似文献   

5.
The compound-specific stable carbon isotope compositions(δ~(13)C) of leaf wax n-alkanes from two short sediment cores recovered off the Pearl River estuary(PRE) were analyzed to check for their capability of indicating decadal scale catchment environmental change. Sedimentary long-chain n-alkanes exhibited an odd-over-even predominance, with a maximum at n-C_(29) or n-C_(31), indicating their leaf wax origin was from vascular plants. The δ~(13)C values of C_(29) and C_(31) n-alkane in all the sediment samples were in the range of -28.8‰ to -31.2‰, consistent with the C_3 plant-dominated vegetation in the Pearl River catchments. The time series of δ~(13)C records from the two cores were comparable and displayed a decreasing trend from the early 20 th century to the end of the 1970s, followed by a reversal in that change leading to continued increase for ca. 15 years. After being corrected for the effect of atmospheric CO_2 rise and δ~(13)C_(atm) decline, the δ~(13)C_(29) records largely retained their raw changing pattern; the post-1980 increase being more conspicuous. The slightly decreasing trend in corrected δ~(13)C records before around 1980 may have been caused by an increase in precipitation, whereas the subsequent increase of δ~(13)C is likely associated with the observed dry climate and/or intensive anthropogenic deforestation. Our results thus demonstrate that leaf wax n-alkanes buried in the sediments off the PRE may well reflect change in the regional climate and/or human activity in the river catchments over the past century.  相似文献   

6.
The question of whether or not global warming has paused since more than ten years ago, namely "warming hiatus", has attracted the attention of climate science community including the IPCC. Some authors have attributed the "warming hiatus" to the internal changes in the climate system, i.e., the recombination of ocean-atmosphere circulations. Therefore, it is necessary to propose higher requirements on reconstructing circulation background of climate change for the past millennium. However, the analyses of changes in atmospheric circulation over the last millennium as well as the conclusions of related regional climate patterns are so widely different and contradictory, bringing uncertainties to our understanding of regional even global climate change to a great extent. On the other hand, in the last 10 years the high-precision U/Th-dated stalagmite oxygen isotope ratio(δ~(18)O) sequences provided an accurate chronological frame for the paleoclimate study of the middle and late Pleistocene, in which all authors from China took the Chinese stalagmite δ~(18)O as the summer monsoon index without exception. However, this point of view misleads the climate scientists into thinking that the stalagmite δ~(18)O can be as the proxy of precipitation amount. Nevertheless, it is well known that all of these records have a lot in common in the low frequency trend. However, most sequences cannot be calibrated by instrumental precipitation records, and thus the uncertainty of the climate research framework of China and even of the world has increased. Therefore, it is imperative for climatology to clarify the origin of contradiction and to reduce the uncertainty as early as possible. On the basis of analyzing the significance of stalagmite δ~(18)O in the monsoon regions of China, the author tries to propose a new circulation proxy in this paper: integrating the Chinese stalagmite oxygen isotope sequence to reconstruct the tropical Pacific sea surface temperature gradient, i.e., the large-scale ENSO-like state over the past millennium. Furthermore, the author speculates that it was warm in the modern times and the Medieval Period, but the circulation recombination was different in both periods. And this inference could be supported by the longer record since Last Glacial Maximum. In other words, the attribution analysis of the identical low-frequency trends of Chinese stalagmite δ~(18)O on a large scale shows that the ENSO-like state controls the climate change in the monsoon regions of China at different time scales(from interannual to century or even longer time scales). Wherein the important connection of circulations is the western Pacific subtropical high(WPSH), that is to say, besides the interannual and decadal time scales, the WPSH would possess the circulation mode on longer timescales. For example, we may discuss the change of the WPSH in the whole Holocene epoch, i.e., the half precession period. These discussions could make sense to the study of not only the paleoclimate but also the modern climate.  相似文献   

7.
Chen  Chaojun  Yuan  Daoxian  Cheng  Hai  Yu  Tsailuen  Shen  Chuanchou  Edwards  R. Lawrence  Wu  Yao  Xiao  Siya  Zhang  Jian  Wang  Tao  Huang  Ran  Liu  Ziqi  Li  Tingyong  Li  Junyun 《中国科学:地球科学(英文版)》2021,64(10):1761-1773
It is conducive to the sustainable development of human beings in karst regions to research the mechanism of karst rocky desertification(KRD) expansion. Whether the large-scale KRD in southwestern China is caused by climate change or human activities is still controversial. In this study, the evolution of the KRD in southwestern China over the past 2000 years was reconstructed through the high-precision δ~(13) C record of stalagmites from Shijiangjun(SJJ) Cave, Guizhou Province, China. Theδ~(13) C of the stalagmites from SJJ Cave exhibited heavy values from the Medieval Warm Period(MWP) to the Little Ice Age(LIA). Furthermore, the δ~(13) C records of other stalagmites and tufa from southwestern China also showed the same significant heavy trend. Because the stalagmite δ~(13) C could record the change of ecological environment, it indicated that the consistent change of the stalagmites δ~(13) C may record the process of KRD expansion in the karst regions of southwestern China. During the MWP, the stronger Asian summer monsoon and the northward movement of the rain belt led to a dry period in southwestern China and a wet period in northern China. In contrast, it was wet in southwestern China and dry in northern China during the LIA.In addition, after the Jing-Kang event(JK event, AD1127) occurred at the end of the Northern Song dynasty, the political and economic center of China migrated to southern China for the first time, which changed the population distribution pattern of larger population in the north and smaller population in the south. Therefore, the expansion of KRD in southwestern China was exacerbated in the MWP due to the change of climate in southwestern China, the migration of a large number of people, wars, the large-scale reclamation of arable land, and the cultivation of large areas of crops.  相似文献   

8.
Using annual precipitation and discharge data measured in the past five decades,this paper analyzed the regional differences over west China in terms of climate and discharge variations,and investigated the relationship between the regional characteristics and the activities of South and East Asian sum-mer monsoon. Results revealed that the precipitation and discharge in the upper reaches of the Yellow River (Central West China) have a negative correlation with those in Xinjiang (northwest China) and the Yarlung Zangbo River (the upper reaches of the Brahmaputra Rive,southwest China) regions. The geographical patterns of precipitation and discharge variations are different over west China,i.e. the regional climate displays the alteration of dry-wet-dry or wet-dry-wet from north to south in west China. The negative correlation of annual discharges between Xinjiang and the upper reaches of the Yellow River is found statistically significant in the decadal scale,and that between the Yarlung Zangbo River and the upper reaches of the Yellow River is found active in the interannual scale. The regional char-acteristics indicate that the discharge/precipitation variations in the upper reaches of the Yellow River are dominated by the East Asian summer monsoon while their variations in Xinjiang are affected by both the west wind and East Asian summer monsoon.  相似文献   

9.
High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 450 ka during late Quaternary from Core MD05-2901 off Middle Vietnam in the western South China Sea are re-ported to reconstruct a history of East Asian monsoon evolution. Variations in Illite, chlorite, and kaolinite contents indicate a strong glacial-interglacial cyclicity, while changes in smectite content present a higher frequency cyclicity. The provenance analysis indicates a mixture of individual clay minerals from various sources surrounding the South China Sea. Smectite derived mainly from the Sunda shelf and its major source area of the Indonesian islands. Illite and chlorite originated mainly from the Mekong and Red rivers. Kaolinite was provided mainly by the Pearl River. Spectral analysis of the kaolin-ite/(illite chlorite) ratio displays a strong eccentricity period of 100 ka, implying the ice sheet-forced win-ter monsoon evolution; whereas higher frequency changes in the smectite content show an ice sheet-forced obliquity period of 41 ka, and precession periods of 23 and 19 ka and a semi-precession period of 13 ka as well, implying the tropical-forced summer monsoon evolution. The winter monsoon evolution is generally in coherence with the glacial-interglacial cyclicity, with intensified winter monsoon winds during glacials and weakened winter monsoon winds during interglacials; whereas the summer monsoon evolution provides an almost linear response to the summer insolation of low latitude in the Northern Hemisphere, with strengthened summer monsoon during higher insolation and weakened summer monsoon during lower insolation. The result suggests that the high-latitude ice sheet and low-latitude tropical factor could drive the late Quaternary evolution of East Asian winter and summer monsoons, respectively, implying their diplex and self-contained forcing mechanism.  相似文献   

10.
The nature and dynamics of climate change in central Asia since the late Pleistocene are controversial. Moreover,most of the published studies focus mainly on the evolution of moisture conditions, and there have been few attempts to address changes in seasonality. In this study, records of δ13Corg, TOC, TN, C/N and grain size were obtained from lacustrine sediments at Yili Basin, Xinjiang, NW China. Our aim was to reconstruct the trend in seasonality of precipitation from the last glaciation to the Holocene. The organic matter content of the sediments is derived predominantly from terrestrial plants. The δ13Corgvalues vary from-19.4‰ to-24.8‰, indicating that the vegetation was dominated by C_3 plants. Winter-spring precipitation is identified as the factor determining the relative proportions of C_3 and C_4 plants in the region. A negative trend in δ13Corgcorresponding to an increase in the relative abundance of C_3 plants indicate a trend of increasing winter-spring precipitation from the last glaciation to the Holocene. The increased incidence of wintertime storms in the interior of Asia is suggested to result in the increase of winterspring precipitation in the Holocene.  相似文献   

11.
The planetary boundary layer(PBL)scheme in the regional climate model(RCM)has a significant impact on the interactions and exchanges of moisture,momentum,and energy between land,ocean,and atmosphere;however,its uncertainty will cause large systematic biases of RCM.Based on the four different PBL schemes(YSU,ACM2,Boulac,and MYJ)in Weather Research and Forecasting(WRF)model,the impacts of these schemes on the simulation of circulation and precipitation during the East Asian summer monsoon(EASM)are investigated.The simulated results of the two local turbulent kinetic energy(TKE)schemes,Boulac and MYJ,are more consistent with the observations than those in the two nonlocal closure schemes,YSU and ACM2.The former simulate more reasonable low-level southwesterly flow over East China and west pacific subtropical high(WPSH)than the latter.As to the modeling of summer monsoon precipitation,both the spatial distributions and temporal evolutions from Boulac and MYJ are also better than those in YSU and ACM2 schemes.In addition,through the comparison between YSU and Boulac experiments,the differences from the results of EASM simulation are more obvious over the oceanic area.In the experiments with the nonlocal schemes YSU and ACM2,the boundary layer mixing processes are much stronger,which lead to produce more sea surface latent heat flux and enhanced convection,and finally induce the overestimated precipitation and corresponding deviation of monsoon circulation.With the further study,it is found that the absence of air-sea interaction in WRF may amplify the biases caused by PBL scheme over the ocean.Consequently,there is a reduced latent heat flux over the sea surface and even more reasonable EASM simulation,if an ocean model coupled into WRF.  相似文献   

12.
The empirical mode decomposition(EMD) method is used to re-analyse the high-resolution and precisely-dated stalagmite record from Chinese caves over the past 640 ka. Results show that(1) the variation in the Asian Monsoon can be completely decomposed into ten quasiperiod oscillations, among which the precession and semiprecession band oscillations are the most prominent periodicities, with contribution rates of 31.1% and 30.7%, respectively;(2) the cross-spectrum analysis of the semiprecession component and bi-hemisphere insolation(BHI) are strongly correlated, indicating an amplified response of precipitation and temperature variability to the interhemispheric insolation in the low-latitude regions, thus further affecting the intensity of the Asian Monsoon;(3) on millennial timescales, obvious oscillations at the 5 ka and 1–2 ka bands roughly correspond to the classical Bond and Dansgaard-Oeschger(DO) cycles. Additionally, a strong correlation is found between the detrended stalagmite δ18 O records and Ca/Sr sequence from the North Atlantic(especially at the 5 ka band). This result means that the 5 ka cycle is characteristic of the glacial-interglacial cycle since the middle and late Pleistocene and may imply that climate change on the millennial timescale is the result of an interaction between global ice volume and insolation.  相似文献   

13.
Land use effects on climate in China as simulated by a regional climate model   总被引：17，自引：0，他引：17  
A regional climate model (RegCM3) nested within ERA40 re-analyzed data is used to investigate the climate effects of land use change over China. Two 15-year simulations (1987―2001), one with current land use and the other with potential vegetation cover without human intervention, are conducted for a domain encompassing China. The climate impacts of land use change are assessed from the difference between the two simulations. Results show that the current land use (modified by anthropogenic ac- tivities) influences local climate as simulated by the model through the reinforcement of the monsoon circulation in both the winter and summer seasons and through changes of the surface energy budget. In winter, land use change leads to reduced precipitation and decreased surface air temperature south of the Yangtze River, and increased precipitation north of the Yangtze River. Land use change signifi- cantly affects summer climate in southern China, yielding increased precipitation over the region, de- creased temperature along the Yangtze River and increased temperature in the South China area (south-end of China). In summer, a reduction of precipitation over northern China and a temperature rise over Northwest China are also simulated. Both daily maximum and minimum temperatures are affected in the simulations. In general, the current land use in China leads to enhanced mean annual precipitation and decreased annual temperature over south China along with decreased precipitation over North China.  相似文献   

14.
Wu  Haibin  Li  Qin  Yu  Yanyan  Sun  Aizhi  Lin  Yating  Jiang  Wenqi  Luo  Yunli 《中国科学:地球科学(英文版)》2019,62(8):1269-1278
Quantitative paleoclimatic reconstruction is crucial for understanding the operation and evolution of the global climate system.For example,a quantitative paleoclimatic reconstruction for the Last Glacial Maximum(18±2 ka~(14)C,LGM)is fundamental to understanding the evolution of Earth’s climate during the last glacial-interglacial cycle.Previous quantitative palaeoclimate reconstructions in China are generally based on statistical comparison of modern pollen assemblages and modern climate data.These methods are based on the premise that vegetation-climate interactions remain the same through time,and implicitly assume that the interactions are independent of changes in seasonality and atmospheric CO_2concentration.However,these assumptions may not always be valid,which may affect the reconstructions.Here,we present the results of a quantitative study of the LGM climate of China based on an improved inverse vegetation model which incorporates physiological processes combined with a new China Quaternary Pollen Database.The results indicate that during the LGM,mean annual temperature(ANNT),mean temperature of the coldest month(MTCO)and mean temperature of the warmest month in China were lower by～5.6±0.8,～11.0±1.6 and～2.6±0.9°C,respectively,compared to today,and that the changes in ANNT were mainly due to the decrease of MTCO.The ANNT decrease in southern China was～5.5±0.5°C.Mean annual precipitation was lower by～46.3±17.8 mm compared to today and was especially low in northern China(～51.2±21.4 mm)due to the decrease in summer rainfall.Comparison of our results with recent outputs from paleoclimatic modelling reveals that while the latter are broadly consistent with our estimated changes in mean annual climatic parameters,there are substantial differences in the seasonal climatic parameters.Our results highlight the crucial importance of developing seasonal simulation on paleoclimatic models,as well as the need to improve the quality of paleoclimatic reconstructions based on proxy records from geological archives.  相似文献   

15.
The studies of the oxgen and carbon isotopes of the rainwater in Guilin area, the drip water and the present carbonate deposit in Panlong cave of Guilin show that: (i) as to the general characteristics of the oxygen isotopes of the rainwater within a year and between years, the δ18O values decrease with an increase of air temperature and the rainfall, and the correlation between δ18O values and the mean monthly air temperature is much better than that between δ18O values and the rainfall, and the δ18O values of the rainwater during the summer monsoon are much smaller than those during winter monsoon; (ii) δ18O values of the drip water have a quite good correlation with the δ18O values of the rainwater in the same period; (iii) when the conditions are appropriate, δ13C can be used as an environmental proxy, that is, the smaller δ13C of speleothems is, the larger the proportion of C3 plants is and the more plentiful the rainfall is. On the contrary, C4 plants may be prevailing or the environment may be a stony desert caused by climate changes or human activity.  相似文献   

16.
Zhang  Yueting  Wu  Naiqin  Li  Fengjiang  Hao  Qingzhen  Dong  Yajie  Zhang  Dan  Lu  Houyuan 《中国科学:地球科学(英文版)》2020,63(9):1408-1421
Eco-environmental changes during interglacials with an astronomical background similar to that of the Holocene are potentially helpful for understanding the future climatic evolution. Marine oxygen isotope stage(MIS) 19 is similar to the Holocene in astronomical background, both being characterized by a low eccentricity of the Earth's orbit. However, MIS 19 has attracted research attention only recently and therefore less is known about eco-environmental changes during this interval,especially based on terrestrial records. In the Chinese Loess Plateau(CLP), the S7 paleosol can provide valuable terrestrial paleoclimatic and paleoenvironmental record for MIS 19. Here, high-resolution terrestrial snail records from the L8–L7 strata of the Huining, Xifeng and Luochuan sequences in the CLP were analyzed in order to characterize spatio-temporal changes in climate and eco-environment during MIS 20–18. The results show that in all three sections the late part of MIS 20 was dominated by abundant cold-aridiphilous mollusc species, indicating that cold and dry climatic conditions prevailed across the entire CLP,under the strong influence of the winter monsoon. The mollusc fauna of MIS 19 were dominated by warmth-loving and thermohumidiphilous species that enable the definition of two climatic stages. The early part of MIS 19(～790–778 ka) was marked by warm and humid conditions, as evidenced by high abundances of warmth-loving and thermo-humidiphilous species. This interval was slightly warmer than today and it lasted for ～12 kyr. The climate of the later part of MIS 19(～778–761 ka) was more moderate, and increased proportions of cold-aridiphilous and warmth-loving species were recorded. The warmth of this period was similar to that of today, but the climatic fluctuations were stronger. During the early part of MIS 18(～761–745 ka), the Xifeng and Luochuan sections in the eastern CLP still maintained high abundances of warmth-loving and thermo-humidiphilous species, indicating that the moderate climatic conditions during late MIS 19 continued during early MIS 18, lasting for another～15 kyr, and that the influence of the summer monsoon remained strong in the eastern CLP during early MIS 18. However, in the western CLP, cold-aridiphilous species in the Huining section became dominant during early MIS 18, reflecting the prevalence of a cold and dry glacial climate, with the strong influence of the winter monsoon. These findings indicate that a steeper climatic gradient and a pronounced regional environmental difference existed between the eastern and western CLP during the early part of MIS 18. Comparison of our mollusc results with the variation of Earth orbital parameters suggested that climate changes in the CLP during MIS 20–18 were likely controlled mainly by insolation changes forced by the configuration of Earth orbital parameters. The unique orbital configuration during the low eccentricity interglacial-to-glacial transition could have strengthened the East Asian summer monsoon which favored the amelioration of the eco-environment in the CLP, especially in the eastern CLP where the summer monsoon exerted a strong influence. Thus we speculate that, under natural climatic conditions,the climate of the CLP may remain in a warm, humid state for another 30 kyr, although climatic instability and the seasonal differences between winter and summer could strengthen.  相似文献   

17.
Tan  Liangcheng  Liu  Wen  Wang  Tianli  Cheng  Peng  Zang  Jingjie  Wang  Xiqian  Ma  Le  Li  Dong  Lan  Jianghu  Edwards  R. Lawrence  Cheng  Hai  Xu  Hai  Ai  Li  Gao  Yongli  Cai  Yanjun 《中国科学:地球科学(英文版)》2020,63(10):1622-1632
Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models. In this study, we analyzed stable isotopes(δ~(18)O, δ~(13)C) and trace elements(Mg/Ca, Sr/Ca) of a stalagmite from Huangchao Cave in central Shandong, northern China.~(230)Th and AMS~(14)C dating results indicate the stalagmite deposited during 174BC and AD1810, with a hiatus between AD638 and 1102. Broad similarities of the δ~(18)O and trace elements in the stalagmite suggest they are reliable precipitation indexes. The δ~(13)C of the stalagmite, a proxy of vegetation change, was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century. It typically varied from –9.6‰ to –6.3‰, indicating climate controlled C3 type vegetation during this period. However, a persistent and marked increasing trend in the δ~(13)C record was observed since the 15th century, resulting in δ~(13)C values from –7.7‰ to –1.6‰ in the next four centuries. This unprecedented δ~(13)C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong. We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.  相似文献   

18.
It is a consensus that marine carbonate archives the isotopic composition of seawater dissolved inorganic carbon(DIC,δ~(13)C_(sw)),the largest active C reservoir in the hydrosphere.Carbonate carbon isotope(δ~(13)C_(carb)) excursions have been used to reflect perturbations of the global carbon cycle and related environmental change.However,the deep time δ~(13)C_(carb) records indicate faster and more pronounced perturbations of the carbon cycle compared to the present day.Here,we report δ~(13)C_(carb) and elemental compositions of Late Paleozoic carbonate sections from South China,showing negative correlations between δ~(13-)C_(carb) and Fe~(2+) content of carbonate(Fe_(carb)).We suggest that,because Late Paleozoic carbonate was mainly produced by benthic carbonate-secreting organisms,δ~(13)C_(carb)recorded the isotopic composition near the seafloor,where benthic flux derived from anaerobic organic matter degradation delivers both Fe~(2+) and ~(13)C-depleted DIC from porewater.The binary mixing between seawater and benthic flux would result in the deviation of δ~(13)C_(carb) fromδ~(13)C_(sw).The negative correlation implies that δ~(13)C_(carb) is influenced by benthic flux and is affected by the seafloor redox and sedimentation rate.The deep time spatially heterogeneous and temporally oscillatory δ~(13)C_(carb) records in the basin-scale could be alternatively attributed to the variations of local environmental factors rather than aδ~(13)C_(sw) depth-gradient.Thus,the seafloor carbonate precipitation is continuously affected by diagenetic reactions in sediments,suggesting that δ~(13)C_(carb) recording the seawater DIC composition is conditional.Our study urges that the interpretation of δ~(13)C_(carb) should also consider the sedimentary process and depositional environment of marine carbonate.  相似文献   

19.
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20.
The correlations of isotopic ratios in precipitation with temperature, air pressure and humidity at dif- ferent altitudes, in southwest China, are analyzed. There appear marked negative correlations for the δ 18O in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water (PW) at Mengzi, Simao and Tengchong stations on synoptic timescale; the marked negative correlations between the δ 18O in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850 hPa are different from the temperature effect in middle-high-latitude inland. Moreover, the notable positive correlation between the δ 18O in precipitation and the dew-point deficit △Td at different altitudes is found at the three stations. On annual timescale, the annual precipitation amount weighted mean δ 18O display the negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in southwest China and generates abnormally strong rainfall on the way. Meanwhile, the ab- normally strong condensation process will release more condensed latent heat into atmosphere, and lead to the rise of atmospheric temperature during rainfall, but decline of the δ 18O in precipitation. On the contrary, in the years with abnormally weak summer monsoon, the abnormally weak condensation process will release less condensed latent heat into atmosphere, and lead to the decline of atmos- pheric temperature during rainfall, but increase of the δ 18O in precipitation.  相似文献   

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