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1.
This study presents a continental paleoclimatic record in the south of France, based on δ18O, δ13C and the 234U/238U activity ratio, dated by the 230Th/234U disequilibrium method with thermal ionization mass spectrometry. A stalagmite (Cla4) from the Clamouse Cave offers a discontinuous stable isotopic record between 189 ka and 74 ka which covers marine isotope stages (MIS) 7, 6.4, 5.5, 5.3 and 5.1. The growth phases of the Cla4 stalagmite correspond to high sea level stages, except during MIS 6.4 (169-162 ka). All the growth phases of Cla4 correspond to humid periods, corresponding to the sapropel events observed in the eastern Mediterranean basin. Thus, the influence of a strong hydrological activity in the eastern Mediterranean basin during these periods prevailed as far west as the south of France. Because the karstic system studied strongly buffers the isotopic composition of water, isotopic variations of the calcite deposited in the cave represent mainly global and large-scale environmental variations when isotopic equilibrium conditions prevailed for calcite crystallization. Sub-stage 5.3, the end of 5.5 and MIS 7 were colder by about 4-6°C (calculated temperature) compared to present-day temperature while the growth phases of sub-stages 5.1 and the beginning of 5.5 reflect environmental conditions close to present ones. The δ18O and δ13C values of cave deposits of the sub-stage 6.4 are: (1) strongly marked by kinetic fractionation processes such as evaporation due to moisture deficit within the cave atmosphere during the first step of this growth phase and (2) related to higher humidity due to a second period of enhanced rainfall during the second step of growth. This study shows that even if calcite has not been deposited at isotopic equilibrium, its isotopic composition can give insights into the environmental conditions at the time of deposition.  相似文献   

2.
Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ18O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ18O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ18O and Δ14C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257-1266; 294 (2001) 2130-2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations.  相似文献   

3.
Increases in calcite deposition rates combined with decreases in δ13C and δ18O in three modern stalagmites from Brown's Folly Mine, Wiltshire, England, are correlative with a well-documented re-vegetation above the mine. Increased soil PCO2 resulted in greater amounts of dissolved CaCO3 in the drip waters, which consequently increased annual calcite deposition rates. The absence of deposition prior to 1916 (28 years after the mine was closed) indicates that vegetation had not yet sufficiently developed to allow higher PCO2 values to form in the soil. Lower δ13C values through time may reflect the increased input of isotopically light biogenic carbon to the total dissolved inorganic carbon (DIC). δ18O decreased synchronously with δ13C, reflecting the increased importance of isotopically light winter recharge due to greater biomass-induced summer evapotranspiration. This is the first empirical demonstration that vegetation density can control stalagmite growth rates, δ13C, and δ18O, contributing critical insights into the interpretation of these climate proxies in ancient stalagmites.  相似文献   

4.
A new oxygen isotope record is reported from a stalagmite collected in the Argentarola Cave located on the Tyrrhenian coast of Italy. As shown from observations and numerical modeling of δ18O in modern precipitation, the recorded δ18O variability for this zone is dominated by the amount of precipitation (so-called ‘amount effect’). The δ18O profile measured in the stalagmite is characterized by a prominent negative excursion (ca. 2-3‰) between 180 and 170 kyr BP. This paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period, more precisely, during Marine Isotope Stage 6.5. This pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 (S6). Although this particular sapropel event occurred during a cold phase, the δ18O excursion is similar to those corresponding to other sapropels (S4, S3 and S2). The evidence for humid conditions during S6 in the western Mediterranean basin agrees with previous studies based on deep-sea sediment cores. Taken collectively, the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river Nile but was rather widespread over the entire Mediterranean Sea due to increased rainfall.  相似文献   

5.
A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3-26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a.We have analyzed 190 samples for δ18O and δ13C, mostly in the 2.3-26 cm part. The δ18O and δ13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial interval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period.The XY2 δ18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high frequency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology.The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water,rather than having climatic significance.  相似文献   

6.
According to the precipitation and δ18O data obtained during the GEWEX Asian Monsoon Experiment–Tibet Intensive Observation Period, based on the knowledge that δ18O is lower in precipitation formed from ocean air mass vapour than that from local evaporation vapour, the water vapour sources can be identified from the δ18O values in precipitation. We attempt to give the identification criterion of δ18O values in precipitation. The threshold values chosen to distinguish between ocean and local sources are δ18O < ?20‰ and δ18O > ?13‰ respectively. According to this criterion, the proportion of local evaporation‐formed precipitation and ocean air‐mass‐formed precipitation in total precipitation was estimated. The average value of precipitation at three sites (NODA, Amdo and AQB) is 249·76 mm. Among this, precipitation formed directly by the ocean air mass vapour is 80·08 mm at most. Precipitation formed by water vapour evaporated from local places is 117·05 mm at least. That is to say that precipitation formed directly by the ocean air mass vapour accounts for 32·06% of the total precipitation at most. Precipitation formed by water vapour evaporated from local places accounts for 46·86% of the total precipitation at least. At least 21·8% of the total precipitation came from water vapour that was evaporated on the way and transported by the monsoon circulation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
A mass-spectrometric uranium-series dated stalagmite from the Central Alps of Austria provides unprecedented new insights into high-altitude climate change during the peak of isotope stage 3. The stalagmite formed continuously between 57 and 46 kyr before present. A series of ‘Hendy tests’ demonstrates that the outer parts of the sample show a progressive increase of both stable C and O isotope values. No such covariant increase was detected within the axial zone. This in conjunction with other observations suggests that the continuous stable oxygen isotope profile obtained from the axial zone of the stalagmite largely reflects the unaltered isotopic composition of the cave drip water. The δ18O record shows events of high δ18O values that correlate remarkably with Interstadials 15 (a and b), 14 and 12 identified in the Greenland ice cores. Interstadial 15b started rapidly at 55.6 kyr and lasted ∼300 yr only, Interstadial 15a peaked 54.9 kyr ago and was even of shorter duration (∼100 yr), and Interstadial 14 commenced 54.2 kyr ago and lasted ∼3000 yr. This stalagmite thus represents one of the first terrestrial archives outside the high latitudes which record precisely dated Dansgaard-Oeschger (D/O) events during isotope stage 3. Provided that rapid D/O warmings occurred synchronously in Greenland and the European Alps, the new data provide an independent tool to improve the GRIP and GISP2 chronologies.  相似文献   

8.
The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high-resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope-based palaeoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to −4‰) and δD (up to −40‰) values characterize summer air masses, and lighter isotope composition (−41‰ for δ18O and −322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, and no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p <.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p < 0.01; n = 55) for δD. Secondary fractionation processes (e.g., contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west, that is, the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the European Centre/Hamburg version 5 (ECHAM5)-wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p <.01; n = 55) and air temperature (r2 = 0.99; p <.01; n = 71). However, the ECHAM5-wiso model fails to capture observed variations in d excess (r2 = 0.14; p < 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer.  相似文献   

9.
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   

10.
The functional relation between theδ18O values in the shell of gastropod Gyraulus sibirica and the air temperature in the warm half-yearly period, and that between Sr/Ca ratio and the precipitation in the warm half-yearly period were established by calibrating the δ18O and δ13C values, Sr/Ca ratio and Mg/Ca ratio in the shell Gyraulus sibirica, as well as the total organic carbon (TOC) and its δ13C values in the Xingcuo Lake sediment in the eastern Tibetan Plateau. The sequences of air temperature and precipitation in the last 200 years in the region were quantitatively recuperated on this basis. The results showed the following: (i) There was a negative correlativity between Sr/Ca ratio and the precipitation in the warm half-yearly period, its correlation coefficient was 0.86. (ii) There was an obviously positive correlativity between indexδ18O and the running average temperature in the warm half-yearly period, its correlation coefficient was 0.89. (iii) Evolution of the air temperature and the precipitation in the last 200 years can be divided into three phases distinctly. The precipitation in the later mid-19th century was 220 mm higher than that today; the air temperature in the warm half-yearly period was 2℃ lower than that of the present. The precipitation in the minimum air temperature period of the early 20th century was below that today by 60 mm, and the air temperature in the warm half-yearly period was 3.4℃ lower than that today. (iv) An evidently warming and drying trend existed in the last five decades.  相似文献   

11.
Little is known about the spatial and temporal variability of the stable isotopic composition of precipitation in the North Atlantic and its relationship to the North Atlantic Oscillation (NAO) and anthropogenic climate change. The islands of the Azores archipelago are uniquely positioned in the middle of the North Atlantic Ocean to address this knowledge gap. A survey of spatial and temporal variability of the stable isotope composition of precipitation in Azores is discussed using newly presented analyses along with Global Network of Isotopes in Precipitation data. The collected precipitation samples yield a new local meteoric water line (δ2H = 7.1 * δ18O + 8.46) for the Azores region and the North Atlantic Ocean. The annual isotopic mean of precipitation shows a small range for the unweighted and precipitation mass‐weighted δ18O‐H2O values. Results show an inverse relation between the monthly δ18O‐H2O and the amount of precipitation, which increases in elevation and into the interior of the island. Higher amounts of precipitation (from convective storm systems) do not correspond to the most depleted values of stable isotopes in precipitation. Precipitation shows an orographic effect with depleted δ18O‐H2O values related to the Rayleigh effect. Monthly δ18O‐H2O values for individual precipitation sampling stations show little relationship to air temperature. Results show a local source of moisture during the summer with the characteristics of the first vapour condensate. The stable isotope composition of precipitation is strongly correlated to the NAO index, and δ18O‐H2O values show a statistically significantly trend towards enrichment since 1962 coincident with the increased air temperature and relative humidity due to climate change. Results are in line with observations of increasing sea surface temperature and relative humidity.  相似文献   

12.
The Asian monsoon is one of the largest climatic systems in the world, but age of its onset has been estimated differently ranging from the late Eocene to the Quaternary. We investigated the sedimentology and stable isotopic compositions of the upper Eocene Jiuziyan Formation, a terrestrial limestone unit in the Jianchuan basin, Yunnan Province in China. This limestone formation is restricted in several localities in the central part of the basin. Previously, this has been characterized as palustrine carbonate and the transition to the sublacustrine deposit of the overlying Shuanghe Formation was interpreted as the appearance of wetter climate during the late Eocene. Our observations of macro- and microfacies revealed sedimentary fabrics indicating rapid CaCO3 precipitation, such as dendritic calcite and calcified reed stems, which are unlikely to develop in a simple lacustrine setting. High carbonate content (mostly >90 %) and restricted distribution of the Jiuziyan limestone indicate a depositional setting spatially limited and isolated from clastic influx. These findings, together with clearly higher δ13C values (−0.7 ‰ to +6.9 ‰) and lower δ18O values (−14.6 ‰ to −10.5 ‰) than those of the Shuanghe Formation, indicate that the limestone was mainly travertine, carbonate formed from endogenic spring water. The elevated δ13C resulted from a large amount of CO2 degassing from spring water with high pCO2. In addition, the occurrence of centimeter-scale lamination coupled with cyclic changes in δ13C and δ18O is almost identical with the modern annually-laminated travertine reported from Baishuitai in northern Yunnan Province, implying comparable amplitude of seasonal temperature and precipitation changes to the record of the modern travertine at Baishuitai. Our results do not contradict the previous interpretation of late Eocene wetting and additionally suggest the existence of the late Eocene monsoon climate in the Jianchuan basin.  相似文献   

13.
Deciduous forest covers vast areas of permafrost under severe dry climate in eastern Siberia. Understanding the water cycle in this forest ecosystem is quite important for climate projection. In this study, diurnal variations in isotopic compositions of atmospheric water vapour were observed in eastern Siberia with isotope analyses of precipitation, sap water of larch trees, soil water, and water in surface organic layer during the late summer periods of 2006, 2007, and 2008. In these years, the soil moisture content was considerably high due to unusually large amounts of summer rainfall and winter snowfall. The observed sap water δ18O ranged from ?17.9‰ to ?13.3‰, which was close to that of summer precipitation and soil water in the shallow layer, and represents that of transpired water vapour. On sunny days, as the air temperature and mixing ratio rose from predawn to morning, the atmospheric water vapour δ18O increased by 1‰ to 5‰ and then decreased by about 2‰ from morning to afternoon with the mixing ratio. On cloudy days, by contrast, the afternoon decrease in δ18O and the mixing ratio was not observed. These results show that water vapour that transpired from plants, with higher δ18O than the atmospheric water vapour, contributes to the increase in δ18O in the morning, whereas water vapour in the free atmosphere, with lower δ18O, contributes to the decrease in the afternoon on sunny days. The observed results reveal the significance of transpired water vapour, with relatively high δ18O, in the water cycle on a short diurnal time scale and confirm the importance of the recycling of precipitation through transpiration in continental forest environments such as the eastern Siberian taiga. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3–26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ 18O and δ 13C, mostly in the 2.3–26 cm part. The δ 18O and δ 13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial interval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ 18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ 18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ 18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ 18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ 18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high frequency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology. The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having climatic significance. Supported by the National Natural Science Foundation of China (Grant Nos. 40672165, 90511004, 40672202) and the Academician Special Project of Chongqing Science Committee (Grant No. 2003-7835)  相似文献   

15.
Utilising datasets from the Global Network of Isotopes in Precipitation of the International Atomic Energy Agency, and previous isotopic studies, we investigated δ18O spatial and temporal patterns in Chinese precipitation. Significantly positive relationships existed between precipitation δ18O and air temperature above the north of 35°N and in high altitude regions above 32°N. Significantly negative relationships between precipitation δ18O and the precipitation amount existed below south of 35°N. These temperature and precipitation effects became stronger with increasing altitude except in high altitude regions between 32°N and 35°N. The NCEP/NCAR reanalysis data from 1980 to 2004 showed that variations in spatial and seasonal wind fields at 700 hpa and total precipitable water from the ground to the top of the atmosphere were correlated with the monthly spatial distribution of precipitation δ18O. Basing on this relationship, we established quantitative correlations between the mean monthly precipitation δ18O and both latitude and temperature in different seasons. We found that spatial variations in precipitation δ18O could be described well using the Bowen–Wilkinson model and second‐order equations developed during the present study only in winter (from December to February). During the rest of the year, patterns were too complex to predict using simple models. The results suggest that it is difficult to demonstrate variations of precipitation δ18O throughout the year and for all regions of China using a single model. Moreover, the new models for the relationships among precipitation, latitude, and temperature were better able to depict the variations in precipitation δ18O than the Bowen–Wilkinson model. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ18O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship between seawater δ18O and salinity is known). Such work assumes that temperature is the only, or at least the dominant, environmental controller of foraminiferal Mg/Ca. The semi-enclosed Mediterranean Sea, where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 °C to 8 °C, provides a relevant setting to test this assumption outside the laboratory. In this study, planktonic foraminifera (O. universa, G. siphonifera, G. bulloides and G. ruber (white) and (pink)) were picked from 11 box core tops spanning the Mediterranean salinity gradient and analysed for their trace-element concentrations. Mg/Ca ratios are higher, for the associated calcification temperatures, than in other regions where calibrations have been conducted and correlate poorly with calcification temperature. Mg/Ca ratios are particularly high for samples from the Eastern Mediterranean where salinity is unusually high. Correlations of Mg/Ca with the calcification salinity are statistically significant with Mg/Ca changing by 15–59% per psu, suggesting that salinity may act as a control on Mg/Ca ratios in addition to the dominant temperature control. We show that contamination by non-carbonate material and diagenetic high-Mg carbonate overgrowths cannot account for the observed trend of increasing Mg/Ca with salinity. A relationship between Mg/Ca and salinity is also suggested by re-analysis of calibrations from open-ocean settings. These new Mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the Mg/Ca palaeothermometer should be considered even in open-ocean settings, particularly where large salinity changes occurred in the past.  相似文献   

17.
13C/12C- and 18O/16O-signatures of Calcite Precipitations in Drainage Systems Measurements of drainage waters show two distinct processes of calcite precipitation: 1. reprecipitation of calcium carbonate previously dissolved in groundwaters and 2. absorption of atmospheric CO2 by alkaline solutions. Both processes may be distinguished by the stable isotopes of oxygen and carbon. Calcite precipitated from carbonate groundwater yields δ13C ≈ ?13%0 (PDB) and δ18O ≈ 24%0 (SMOW), whereas calcite produced by CO2-absorption shows δ13C ≈ ?25%0 (PDB) and δ18O ≈ 10%0 (SMOW).  相似文献   

18.
Deuterium and oxygen‐18 are common environmental tracers in water used to investigate hydrological processes such as evaporation and groundwater recharge, and to trace moisture source. In this study, we collected event precipitation from 01 January 2010 to 28 February 2011 at a site in Changsha, Yangtze River Basin to estimate the influence of moisture source and atmospheric conditions on stable isotope compositions. The local meteoric water line, established as δD = (8.45 ± 0.13) δ18O + (17.7 ± 0.9) (r2 = 0.97, n = 189), had a higher slope and intercept than global meteoric water line. Temperature–δ18O exhibited complex correlations, with positive correlations during Nov.–Apr. superior to during Jun.–Sep., which was attributed to distinctive moisture sources, but vague the overall period; amount effect examined throughout the year. Linear regressions between δ18O and δD value in different precipitation event size classes revealed progressively decreasing slope and intercept values with decreasing precipitation amount and increasing vapour pressure deficit, indicating that small rainfall events (0–5 mm) were subject to secondary evaporation effects during rainwater descent. In contrast, snowfall and heavy precipitation events exhibited high slope and intercepts for the regression equation between δ18O and δD. High concentrations of heavy isotopes were associated with precipitation events sourced from remote westerly air masses, degenerated tropical marine air masses from the Bay of Bengal (BoB), and inland moisture in the pre‐monsoon period, as determined from backward trajectories assessed in the HYSPLIT model. Meanwhile, low concentrations of heavy isotopes were found to correspond with remote maritime moisture from BoB, the South China Sea, and the west Pacific at three different air pressures in summer monsoon and post‐monsoon using HYSPLIT and records of typhoon paths. These findings suggest that stable isotope compositions in precipitation events are closely associated with the meteorological conditions and respond sensitively to moisture source in subtropical monsoon climates. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
Stable isotopes in precipitation are useful tracers to strengthen understanding of climate change and hydrological processes. In this study, the moisture sources of 190 precipitation events in Beijing were analysed using the Hybrid Single‐particle Lagrangian Integrated Trajectory model, based on which we studied the relation between variations in precipitation δ18O and dynamics in moisture sources and atmospheric circulation in seasonal and interannual timescales. Categorization of 7 groups of moisture sources was performed, among which oceanic moisture sources presented lower δ18O in precipitation than continental moisture sources. The results show that seasonal variations of precipitation δ18O were caused by changes of moisture sources. In summer, moisture from proximal oceans dominated vapour transport to Beijing due to increasing monsoon strength and resulted in a relatively small variation of precipitation δ18O. At the interannual timescale, the variations of δ18O in summer precipitation were related to dynamics in oceanic moistures, showing depleted values when the contribution of oceanic moistures, especially the proportion of long‐distance oceanic moisture, was high. Further analysis indicated that changes of oceanic moisture sources were controlled by the strength of summer monsoons. These findings address the complexity of moisture sources in midlatitude monsoon areas and suggest that isotopic signals in precipitation have the potential to deduce changes in moisture sources and atmospheric circulation and can therefore serve for palaeoclimate reconstruction.  相似文献   

20.
Dissolved organic carbon (DOC) originating in peatlands can be mineralized to carbon dioxide (CO2) and methane (CH4), two potent greenhouse gases. Knowledge of the dynamics of DOC export via run‐off is needed for a more robust quantification of C cycling in peatland ecosystems, a prerequisite for realistic predictions of future climate change. We studied dispersion pathways of DOC in a mountain‐top peat bog in the Czech Republic (Central Europe), using a dual isotope approach. Although δ13CDOC values made it possible to link exported DOC with its within‐bog source, δ18OH2O values of precipitation and run‐off helped to understand run‐off generation. Our 2‐year DOC–H2O isotope monitoring was complemented by a laboratory peat incubation study generating an experimental time series of δ13CDOC values. DOC concentrations in run‐off during high‐flow periods were 20–30 mg L?1. The top 2 cm of the peat profile, composed of decaying green moss, contained isotopically lighter C than deeper peat, and this isotopically light C was present in run‐off in high‐flow periods. In contrast, baseflow contained only 2–10 mg DOC L?1, and its more variable C isotope composition intermittently fingerprinted deeper peat. DOC in run‐off occasionally contained isotopically extremely light C whose source in solid peat substrate was not identified. Pre‐event water made up on average 60% of the water run‐off flux, whereas direct precipitation contributed 40%. Run‐off response to precipitation was relatively fast. A highly leached horizon was identified in shallow catotelm. This peat layer was likely affected by a lateral influx of precipitation. Within 36 days of laboratory incubation, isotopically heavy DOC that had been initially released from the peat was replaced by isotopically lighter DOC, whose δ13C values converged to the solid substrate and natural run‐off. We suggest that δ13C systematics can be useful in identification of vertically stratified within‐bog DOC sources for peatland run‐off.  相似文献   

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