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1.
Cellulose and silica phytoliths were extracted from the leaves and stems of Calamovilfa longifolia, a C4 grass, grown under varying climatic conditions across the North American prairies. The oxygen-isotope compositions of both cellulose and silica record a complex signal of the isotopic composition of the soil water that feeds the plants and the relative humidity conditions that influence transpiration rates, stomatal conductance, and ultimately the 18O-enrichment of leaf water. As the initial stages of cellulose formation occur in the leaves, cellulose in both the leaves and stems forms primarily from leaf water and does not differ greatly in its oxygen-isotope composition between these locations. In contrast, the δ18O values of leaf phytoliths are significantly enriched in 18O relative to stem phytoliths, reflecting the varying isotopic composition of the water in these tissues. The oxygen-isotope compositions of leaf cellulose may be used as a proxy for the isotopic composition of water involved in leaf phytolith formation, while the δ18O values of stem phytoliths can be used to determine the δ18O values of stem water involved in partial exchange reactions during the transport of carbohydrates through the plant. A comparison of the isotopic compositions of phytoliths with cellulose allows for the deduction of soil and leaf water δ18O values as well as temperature and relative humidity conditions during plant growth. This approach has application in paleoclimate studies that traditionally have required estimations of one or more of these variables because direct measurements were unavailable.  相似文献   

2.
A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ2H and δ18O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area.  相似文献   

3.
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4.
It is important to understand the history and dynamics of climate in a transitional region between areas with different atmospheric circulation patterns, where the vegetation and ecosystems are vulnerable to environmental change. We investigated variations in the long-term oxygen isotope composition (δ18O) in tree rings of Qinghai spruce (Picea crassifolia) and their relationships to climatic parameters in the arid Qilian Mountains of northwestern China from 1870 to 2006. We found that the mean temperature from the previous November to the current February was significantly and positively correlated with the tree-ring δ18O values. The temperature effect, (the positive relationship between the temperature and the precipitation δ18O value) can explain the connection between temperature and the tree-ring δ18O values. Due to pooling of the earlywood and latewood into yearly tree-ring samples, it appears that the cellulose δ18O may be influenced by isotopically nonhomogeneous water sources and climatic conditions during the previous and current growing seasons. Subtle shifts and amplitude deviations in cellulose δ18O, which abruptly became more positive around 1977–1978, may be attributed to the shifting climatic regime in China and to temperature variations, respectively. Our results illustrated the potential for investigating climatic or atmospheric circulation patterns based on oxygen isotope records in tree rings in regions near the interface between different large-scale synoptic circulations.  相似文献   

5.
In regions with seasonal temperate climatic regimes, tree growth is rarely controlled by any single environmental factor. As a consequence, the development of robust palaeoclimate reconstructions has proved challenging. Tree‐ring stable carbon isotope ratios (δ13C), however, are controlled primarily by photosynthetic rate, not by net growth. Therefore, at sites where climatic controls on tree‐ring growth are not strongly expressed, a robust (isotopic) palaeoclimate signal may still potentially be preserved. This hypothesis was tested using a 160‐year record of δ13C measured from the pooled latewood cellulose of six Quercus petraea L. (sessile oak) trees from Allt Lan‐las in West Wales, UK. Raw δ13C values were corrected for changes in the isotopic ratio of atmospheric carbon dioxide and for changes in the behaviour of trees due to the increasing availability of atmospheric CO2 since AD 1850. Strong correlations with local summer temperature and sunshine are reported, and also with the Central England Temperature record over the full length of the isotopic chronology (AD 1850–2010) (r = 0.69, P < 0.001). We conclude that tree‐ring stable isotopes can be used to extract strong palaeoclimate signals even from oak trees growing in a temperate maritime climate. This demonstrates the potential for extracting robust palaeoclimatic information from the very long and well‐replicated oak chronologies which have been developed in western and central Europe primarily for dating rather than palaeoclimatic research purposes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

6.
We describe a strategy for development of chronological control in tropical trees lacking demonstrably annual ring formation, using high resolution δ18O measurements in tropical wood. The approach applies existing models of the oxygen isotopic composition of alpha-cellulose (Roden et al., 2000), a rapid method for cellulose extraction from raw wood (Brendel et al., 2000), and continuous flow isotope ratio mass spectrometry (Brenna et al., 1998) to develop proxy chronological, rainfall and growth rate estimates from tropical trees lacking visible annual ring structure. Consistent with model predictions, pilot datasets from the temperate US and Costa Rica having independent chronological control suggest that observed cyclic isotopic signatures of several permil (SMOW) represent the annual cycle of local rainfall and relative humidity. Additional data from a plantation tree of known age from ENSO-sensitive northwestern coastal Peru suggests that the 1997-8 ENSO warm phase event was recorded as an 8‰ anomaly in the δ18O of α-cellulose. The results demonstrate reproducibility of the stable isotopic chronometer over decades, two different climatic zones, and three tropical tree genera, and point to future applications in paleoclimatology.  相似文献   

7.
δ13C was determined in lignin extracted from present-day cladodes of Phyllocladus alpinus (a small coniferous tree) from seven well-lit sites across New Zealand. The δ13C values ranged from −30.9‰ to −23.6‰ and were compared with monthly means of temperature, precipitation, relative humidity and vapour pressure deficit from the nearest recording stations. Of these parameters, the leaf-to-air vapour pressure deficit of the first month of cladode growth and expansion proved to be the most significantly correlated with lignin δ13C, over a range of 0.3 to 0.8 kPa, confirming the importance of atmospheric moisture content on stomatal conductance. The carbon isotopic signature of lignin from fossilised cladodes preserved under the Kawakawa Tephra (22.6 k 14C yr BP) on the North Island is identical to that of the whole tissue, suggesting that for this species at least, fossil material can be used to approximate the lignin δ13C. The δ13C of species- and organ-specific fossil terrestrial plant material therefore provides an excellent method to quantify past changes in leaf-to-air vapour pressure deficit. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

8.
Samples from two lignite seams (Lower Seam, Upper Seam) of the Lavanttal basin (Austria) and additional xylite were investigated for variations in maceral composition, petrography-based facies indicators, bulk geochemical parameters, and molecular composition of hydrocarbons. Both seams originated in a topogenous mire and evolved within a transgressive setting. The final drowning of the mire is indicated by sapropelic shales. Whereas the sapropelic shale overlying the Lower Seam was deposited in a freshwater lake, the sapropelic shale above the Upper Seam represents a brackish lake.Numerous relationships are found between petrography-based facies indicators and the geochemical composition of organic matter. The contents of macerals of the liptinite group are positively correlated with soluble organic matter (SOM) yields and hydrogen index (HI). Consistent with maceral composition and high HI values, enhanced proportions of short-chain n-alkanes, which are predominantly found in algae and microorganisms, are obtained from samples of the sapropelic shales. The final drowning of the mire is reflected by decreasing pristane/phytane ratios, due to the rise in (ground)water table and the establishment of anaerobic conditions, as well as by decreasing ratios of diasterenes/sterenes, indicating increasing pH values in the mire. The degree of gelification of plant tissue (gelification index) is governed by the microbial activity in the mire, as indicated by the hopanes concentration. The differences in floral assemblage during the formation of the Lavanttal lignite seams are reflected by major differences in tissue preservation. Preservation of plant tissue (TPI) in the Lavanttal lignite is obviously controlled by the presence/absence of decay-resistant gymnosperms in the peat-forming vegetation, and additionally influenced by the relative contribution of wood to coal formation. The results provide evidence that valuable information for coal facies characterization could be obtained by petrography-based and geochemical facies indicators. An influence of the floral assemblage (gymnosperms/angiosperms ratio) and of the contribution of algal biomass on carbon isotopic composition of the organic matter (δ13C = − 24.2 to − 28.6‰) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is suggested to affect the δ13C values of the coal. The chemotaxonomical classification of the xylites as gymnosperm remnants, based on the molecular composition of terpenoid biomarkers, is corroborated by the carbon isotopic composition of the xylites (mean δ13C = − 24.1‰) and the extracted cellulose (mean δ13C = − 20.2‰). The higher isotopic difference of about 3.9‰ between cellulose and total organic carbon of the xylites, compared to the difference between cellulose and wood found in modern trees, is explained by the smaller effect of decomposition on δ13C of cellulose.  相似文献   

9.
树轮作为自然档案中的一种, 其同位素研究是较为新颖的领域文章比较系统地从树轮纤维素的提取、氧的来源、植物体内氧的分馏、与温度变化的关系等４ 个方面评述了树轮纤维素氧同位素组成的气候学意义已有的研究结果表明, 树轮纤维素氧同位素组成的变化是温度变化的良好载体, 但在定量恢复古温度变化时遇到了不少限制, 有待于进一步完善分馏模型  相似文献   

10.
This is a summary of new oxygen isotope record of diatoms from Lake Kotokel sediments, with implications for responses of the lake system and its environment to global change over the past 46 kyr. Fossil diatoms in all samples are free from visible contamination signatures and contain no more than 2.5% Al2O3, which ensures reliable reconstructions. The 518O values in diatoms vary between + 23.7 and + 31.2%c over the record. The results present mainly diatom assemblages of summer blooming periods, except for the time span between 36 and 32 kyr, when the isotopic signal records mainly a shift from summer to spring blooming conditions. Possible water temperature changes only partly explain the changes in the isotopic record. The observed isotopic patterns are produced mainly by isotope changes in lake water in response to variations in air temperature, hydrology, and atmospheric circulation in the region. During Marine Isotope Stage (MIS) 2 (Last Glacial maximum), high 518Odiatom resulted from rapid evaporation and low fluvial inputs. The high 518Odiatom values of about + 29 to + 30%c during the first half of MIS 1 (Holocene interglacial) suggest an increased share of summer rainfalls associated with southern/southeastern air transport. The 518Odiatom decrease to + 24%c during the second half of MIS 1 is due to the overall hemispheric cooling and increased moisture supply to the area by the Atlantic air masses. The record of Lake Kotokel sediments provides an example of complex interplay among several climatic/environmental controls of 518Odiatom during the Late Pleistocene and the Holocene.  相似文献   

11.
This paper investigates the stable isotopic composition from late Pleistocene–Holocene (~ 13 to ~ 10.5 cal ka BP) shells of the land snail Helix figulina, from Franchthi Cave (Greece). It explores the palaeoclimatic and palaeoenvironmental implications of the isotope palaeoecology of archaeological shells at the time of human occupation of the cave. Modern shells from around the cave were also analysed and their isotopic signatures compared with those of the archaeological shells. The carbon isotope composition of modern shells depicts the consumption of C3 vegetation. Shell oxygen isotopic values are consistent with other Mediterranean snail shells from coastal areas. Combining empirical linear regression and an evaporative model, the δ18Os suggest that modern snails in the study area are active during periods of higher relative humidity and lower rainfall δ18O, probably at night. Late glacial and early Holocene δ18Os show lower values compared to modern ones. Early Holocene δ18Os values likely track enhanced moisture and isotopic changes in the precipitation source. By contrast, lower late glacial δ18O could reflect lower temperatures and δ18Op, compared to the present day. Shell carbon isotope values indicate the presence of C3 vegetation as main source of carbon to late glacial and early Holocene snails.  相似文献   

12.
《Applied Geochemistry》1997,12(2):163-174
Oxygen isotopic compositions of weathering goethite pseudomorphs after pyrite in the lateritic profile of Yaou, French Guiana, were measured by laser fluorination. The laterite at Yaou is composed of a 25 m thick saprolite overlain by a 3 m thick latosol. Petrographic observations indicate that the pseudomorphic replacement of pyrite by goethite occurs at or near the weathering front and is complete. The goethite pseudomorphs are essentially devoid of Al and are progressively dissolved and partially replaced by a microcrystalline plasma of kaolinite and goethite in the upper horizons (latosol) of the profile.The laser technique used in this study permitted the determination of the δ18O value of individual grains of goethite and the investigation of grain-to-grain variation within a single sample (horizon) as well as vertical variation with depth. In the latosol, the goethite δ18O values range from 0.8 to 3.2%‰ and exhibit significant grain-to-grain and vertical variation. This most likely reflects undetected intragrain contamination with microcrystalline kaolinite. In the saprolite, the goethite δ18O values are consistent, ranging from 1.0 to 1.8%‰ between 3 and 18 m depth, and from 2.5 to 3.3‰ between 23 m depth and the weathering front at 28 m. Oxygen isotope compositions of present groundwater, “soil water” and rainfall at Yaou were also measured, and compared with calculated isotopic compositions for goethite-forming waters. Goethite pseudomorphs in the lower part of the saprolite are in isotopic equilibrium with present groundwater, indicating that they may be forming today or that they formed in the recent past under climatic conditions similar to present conditions. In contrast, goethite pseudomorphs found higher in the profile are not in isotopic equilibrium with present water but with a water depleted in18O by ≈ 1.50% relative to present groundwater. It is suggested that these low-δ18O pseudomorphs are probably older and formed under different paleoclimatic conditions, at a time when climatic regimes were possibly more monsoonal than today. This is in agreement with models of climatic evolution derived from pedological considerations.The results of this study suggest that goethite pseudomorphs in ancient saprolites may preserve their original O isotopic composition acquired at the weathering front, and may, therefore, be used as indicators of changes in weathering-climatic conditions during the evolution of a profile.  相似文献   

13.
Determinations of δ18O values from 100 outcrops of Belt Supergroup (Wallace Fm.) metasedimentary rocks in the Idaho panhandle reveal a regular regional pattern that was produced by pervasive fluid infiltration and isotopic exchange. Low grade argillites at large distances (60 km) from the Idaho batholith have high δ18O values +15, compatible with their probable primary values. Pelitic rocks with anomalously low δ18O values of + 8.7 to + 12.7‰ occur in the following zones: (1) in a 5000 km2 zone of schist and gneiss peripheral to the Idaho batholith, generally coincident with high-grade (sillimanite-bearing) assemblages; (2) in high-grade metasedimentary roof pendants within the Idaho batholith; (3) peripheral to small Cretaceous stocks; and (4) within and near the scapolite-bearing zone south-west of St. Regis. On δ18O−δ18O plots, data from coexisting minerals define trends with unit slopes, indicating that the reductions in 18O occurred under high-grade metamorphic conditions. This metamorphism culminated in the emplacement of the Idaho batholith, probably as a consequence of profound crustal thickening associated with the Cretaceous accretion of the Wallowa-Seven Devils arc terranes with North America. The huge low-18O region is bounded by a “steep” δ18O gradient (0.1–0.5‰/km) that occurs in low-grade rocks along and near the Lewis and Clark Line, well below the biotite isograd. This boundary zone may be analogous to, but is not nearly as sharp as, those of meteoric-hydrothermal systems in many regions. The important ore deposits of the Coeur d'Alene district are located in this peripheral zone, suggesting that the metamorphic-hydrothermal system may have been intimately involved in their formation. In addition, the metamorphic-hydrotermal system in Idaho is larger, deeper and higher in temperature than typical meteoric-hydrothermal systems, and it involved fluids with much higher δ18O values that were probably dominantly derived from formation waters. Accordingly, this system produced rocks with δ18O values similar to those of the Idaho batholith, and mineral assemblages that approach isotopic equilibrium under high temperature conditions.  相似文献   

14.
Lake-water oxygen-isotope histories for three lakes in northern Russia, derived from the cellulose oxygen-isotope stratigraphies of sediment cores, provide the basis for preliminary reconstruction of Holocene paleohydrology in two regions along the boreal treeline. Deconvolution of shifting precipitation δ18O from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation, the isotopic composition of paleo-waters preserved in frozen peat deposits, as well as other supporting paleoclimatic information. These data indicate that during the early Holocene, when the boreal treeline advanced to the current arctic coastline, conditions in the lower Yenisey River region were moist compared to the present, whereas greater aridity prevailed to the east near the lower Lena River. This longitudinal moisture gradient is consistent with the suggestion that oceanic forcing (increased sea-surface temperatures in the Nordic Seas and reduced sea-ice cover) was a major contributor to the development of a more maritime climate in western Eurasia, in addition to increased summer insolation. East of the Taimyr Peninsula, large tracts of the continental shelf exposed by glacial sea-level drawdown may have suppressed maritime climatic influence in what are now coastal areas. In contrast, during the late Holocene the two regions have apparently experienced coherent shifts in effective moisture. The similarity of the records may primarily reflect reduced North Atlantic influence in the Nordic Seas and southward retreat of coastline in eastern Siberia, coupled with declining summer insolation.  相似文献   

15.
Marine Isotope Stage (MIS) 11 palaeoclimate has so far been documented in marine and ice sheet isotopic records. However, excepting some lacustrine pollen records, very little is known about palaeoclimatic conditions in continental areas. This study uses geochemical records in calcareous tufa deposits from rivers as a basis for reconstructing temperate palaeoclimatic conditions. Tufa deposits are now proven to record high‐quality palaeoclimatic information in recent to Holocene deposits. Work on older interglacial tufas is just starting and in this paper we present the first comprehensive results from a MIS 11 tufa. The tufa comes from the Seine Valley (La Celle, northern France). Geochemical data in the tufa calcite are interpreted to record primarily air temperature (δ18O) and humidity (δ13C and Mg/Ca and Sr/Ca). The combined data identify a warm and wet climatic optimum followed by two temperature decreases associated with oscillations in humidity. These marked climatic variations recorded through the La Celle profile are strongly coherent with the palaeoenvironmental reconstructions from malacological data. The abrupt climatic and environmental events recorded could be related to short‐term degradation of vegetation cover in Europe, which is itself controlled by global palaeoclimatic events. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
Humidity is one of the fundamental variables controlling the energy balance of the climate, and thus its reconstruction represents a significant aspect of paleoclimate studies. We here report a study of oxygen and hydrogen isotopic compositions of tree-ring cellulose along a precipitation gradient in the Olympic Mountains of Washington, USA, to examine whether and how the relative humidity is recorded in the cellulose. According to the physically-based model described in this paper, the relationship between δD and δ18O of cellulose should have the same slope as that in the relationship between δD and δ18O in the source water (∼8.8 for the local meteoric water) if there is no systematic variation in the mean relative humidity among study sites and no physiologic differences among trees. However, our isotopic analyses of cellulose yielded a slope of 17.4, significantly greater than the slope of the Local Meteoric Water Line. We show that to produce such a slope, a positive covariation between the relative humidity and the δD and δ18O in the source water is required across the precipitation gradient. This work suggests that the δD vs. δ18O relationship in tree rings can be a useful tool for paleohumidity reconstruction.  相似文献   

17.
Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (δ18O and δ13C), and chemical composition (Sr/Ca and Mg/Ca) of authigenic carbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. Between 11,700 and 950014C yr B.P., the climate was cool and moist. A gradual decrease in effective moisture occurred between 9500 and 710014C yr B.P. A change at about 710014C yr B.P. inaugurated the most arid period during the Holocene. Between 7100 and 400014C yr B.P., three arid phases occurred at 6600–620014C yr B.P., 5400–520014C yr B.P., and 4800–460014C yr B.P. Effective moisture generally increased after 400014C yr B.P., but periods of low effective moisture occurred between 2900–280014C yr B.P. and 1200–80014C yr B.P. The data also suggest high climatic variability during the last few centuries. Despite the overall congruence, the biological (diatom), sedimentological, isotopic, and chemical proxies were occassionally out of phase. At these times the evaporative process was not the only control of lake-water chemical and isotopic composition.  相似文献   

18.
The stable isotopic ratios of oxygen, carbon and the non-exchangeable carbon-bound hydrogen of cellulose from marine plants (algae and higher vascular forms) and animals (tunicates) collected in their natural habitats and from freshwater vascular plants grown in the laboratory under controlled conditions were determined.The δ18Ovalues of cellulose from all the plants and animals were 27 ±3% more positive than the δ18O values of the waters in which the organisms grew. Temperature had little or no influence on this relationship for three species of freshwater vascular plants that were analyzed. The relationship between the δ18O values of cellulose and the water used in its synthesis is probably established by the isotopic fractionation that occurs during the hydration of carbonyl groups of the intermediates involved in cellulose synthesis.The δD values of the non-exchangeable hydrogen of cellulose (determined by analyzing cellulose nitrate) from different organisms that grew in the same environment differed by large amounts. This difference ranged up to 200‰ for different species of algae collected at a single site: the corresponding difference for different species of tunicates and vascular plants was 60 and 20‰ respectively. The δD values of cellulose nitrate from different species of freshwater vascular plants grown in water of constant temperature and isotopic composition differed by as much as 60‰ The relationship between the δD values of the carbon-bound hydrogen of cellulose and the water used in its synthesis displayed a significant temperature dependence for four species of freshwater vascular plants that were analyzed. The δD values of cellulose nitrate prepared from different parts of one of the plants grown under constant conditions differed by 40‰ Hydrogen isotopic fractionation during cellulose synthesis appears to be more variable among different species and displays a larger temperature dependence than was suggested by previous studies.  相似文献   

19.
The Southern Alps are an ideal locality for studying patterns of isotopic fractionation associated with orographic precipitation. We have evaluated whether altitudinal change is reflected in the stable hydrogen isotopic composition (δ2H) of stream water, plant stem water and leaf wax lipids (n-alkanes) from living plants and soils, as well as in soil temperature. Samples were collected along an altitudinal transect from the windward side of the Southern Alps to Lake Hawea in the rain shadow. The results indicate that δ2H values of stem water overlap with stream water, demonstrating a gradual decrease with elevation that complied with modeled Rayleigh distillation, reflecting an isotopic lapse rate of −18.0 (± 1.1, 1σ)‰/km. Leaf and soil n-alkanes shared similar δ2H values and were 2H depleted relative to stem/stream waters. The values for soil n-alkanes indicated an isotopic lapse rate of −21.8 (± 2.0, 1σ)‰/km, consistent with precipitation data and long term observations. MBT/CBT derived soil temperature values based on the relative distribution of microbial tetraether lipids were similar to midsummer temperature observations, displaying an elevational decrease rate of −5.6 (± 1.5, 1σ) °C/km, consistent with regional and global observations.The results indicate that sedimentary lipid δ2H and microbial tetraether temperature estimates captured altitudinal trends in the isotopic composition of precipitation and mean temperature and further support their application in the reconstruction of past climate and surface uplift histories. However, notable differences in isotopic composition and temperature estimates between in situ soils and those with downslope transport of material emphasize the importance of facies analysis when interpreting past systems.  相似文献   

20.
Palaeotemperatures for the Cretaceous of India and Madagascar have been determined on the basis of oxygen isotopic analysis of well-preserved Albian belemnite rostra and Maastrichtian bivalve shells of from the Trichinopoly district, southern India, and Albian nautiloid and ammonoid cephalopods from the Mahajang Province, Madagascar. The Albian (possibly late Albian) palaeotemperatures for Trichinopoly district are inferred to range from 14.9 °C to 18.5 °C for the epipelagic zone, and from 14.3 °C to 15.9 °C for the mesopelagic zone, based on analyses of 65 samples; isotopic palaeotemperatures interpreted as summer and winter values for near-bottom shelf waters in this area fluctuate from 16.3 to 18.5 °C and from 14.9 to 16.1 °C, respectively. The mentioned palaeotemperatures are very similar to those calculated from isotopic composition of middle Albian belemnites of the middle latitude area of Pas-de-Calais in Northern hemisphere but significantly higher than those calculated from isotopic composition of Albian belemnites from southern Argentina and the Antarctic and middle Albian belemnites of Australia located within the warm-temperate climatic zone. Isotopic analysis of early Albian cephalopods from Madagascar shows somewhat higher palaeotemperatures for summer near-bottom shelf waters in this area (20.2-21.6 °C) in comparison with late Albian palaeotemperatures calculated from southern India fossils, but similar winter values (13.3-16.4 °C); however, the latter values are somewhat higher than those calculated from early Albian ammonoids of the tropical-subtropical climatic zone of the high latitude area of southern Alaska and the Koryak Upland. The new isotopic palaeotemperature data suggest that southern India and Madagascar were located apparently in middle latitudes (within the tropical-subtropical climatic zone) during Albian time. In contrast to the Albian fossils, isotope results of well-preserved early Maastrichtian bivalve shells from the Ariyalur Group, Trichinopoly district, are characterised by lower δ18O values (up to −5.8‰) but normal δ13C values, which might be a result local freshwater input into the marine environment. Our data suggest that the early Maastrichtian palaeotemperature of the southern Indian near-bottom shelf waters was probably about 21.2 °C, and that this middle latitude region continued to be a part of tropical-subtropical climatic zone, but with tendency of increasing of humidity at the end of Cretaceous time.  相似文献   

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