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1.
Inter- and intra-annual tree-ring cellulose oxygen isotope variability in response to precipitation in Southeast China 总被引:1,自引:0,他引:1
Chenxi Xu Huaizhou Zheng Takeshi Nakatsuka Masaki Sano Zhen Li Junyi Ge 《Trees - Structure and Function》2016,30(3):785-794
Key message
Compared with annual tree-ring cellulose δ 18 O, intra-annual cellulose δ 18 O has potential to reconstruct precipitation with higher resolution and stronger signal intensity.Abstract
Annual tree-ring cellulose oxygen isotope values (δ18O) of Fokienia hodginsii provide a promising proxy of monsoon-season precipitation in Southeast China. Measuring intra-annual cellulose δ18O values may reveal the seasonal variability of precipitation and the associated climate influences. Here, we examine intra-annual variation of cellulose δ18O values in Fokienia hodginsii and Cryptomeria fortune from Fujian Province, Southeast China. Both species exhibited considerable intra-annual variations in cellulose δ18O (range ~6 ‰) with a consistent pattern of enriched values near the annual ring boundary and depleted values in the central portion of the ring. Seasonal patterns in the tree-ring δ18O values generally followed changes in precipitation δ18O values. Compared with annual tree-ring cellulose δ18O, intra-annual cellulose δ18O has potential to reconstruct precipitation with higher resolution and stronger signal intensity. July tree-ring cellulose δ18O is significantly correlated (r = ?0.58, p < 0.05) with July precipitation, and June–August tree-ring cellulose δ18O and annual tree-ring cellulose δ18O, respectively, explain 52 and 41 % of the actual variance of April–August precipitation. In addition, May–October cellulose δ18O values during El Niño years are higher than in La Niña years, and April to October rainfall is lower in El Niño years than in La Niña years. Combining the significant correlations between inter-annual cellulose δ18O values and sea surface temperatures in the central tropical Pacific, our results support the hypothesis that El Niño–Southern Oscillation affects tree-ring cellulose δ18O in Southeast China by modulating seasonal precipitation.2.
Olga Vladimirovna Sidorova Rolf T. W. Siegwolf Matthias Saurer Alexander V. Shashkin Anastasia A. Knorre Anatoliy S. Prokushkin Eugene A. Vaganov Alexander V. Kirdyanov 《Oecologia》2009,161(4):825-835
Tree-ring width of Larix gmelinii (Rupr.) Rupr., ratios of stable isotopes of C (δ13C) and O (δ18O) of whole wood and cellulose chronologies were obtained for the northern part of central Siberia (Tura, Russia) for the period 1864–2006. A strong decrease in the isotope ratios of O and C (after atmospheric δ13C corrections) and tree-ring width was observed for the period 1967–2005, while weather station data show a decrease in July precipitation, along with increasing July air temperature and vapor pressure deficit (VPD). Temperature at the end of May and the whole month of June mainly determines tree radial growth and marks the beginning of the vegetation period in this region. A positive correlation between tree-ring width and July precipitation was found for the calibration period 1929–2005. Positive significant correlations between C isotope chronologies and temperatures of June and July were found for whole wood and cellulose and negative relationships with July precipitation. These relationships are strengthened when the likely physiological response of trees to increased CO2 is taken into account (by applying a recently developed δ13C correction). For the O isotope ratios, positive relationships with annual temperature, VPD of July and a negative correlation with annual precipitation were observed. The δ18O in tree rings may reflect annual rather than summer temperatures, due to the late melting of the winter snow and its contribution to the tree water supply in summer. We observed a clear change in the isotope and climate trends after the 1960s, resulting in a drastic change in the relationship between C and O isotope ratios from a negative to a positive correlation. According to isotope fractionation models, this indicates reduced stomatal conductance at a relatively constant photosynthetic rate, as a response of trees to water deficit for the last half century in this permafrost region. 相似文献
3.
Masaki Sano M.S. Sheshshayee S. Managave R. Ramesh R. Sukumar Tatsuo Sweda 《Dendrochronologia》2010,28(2):93-98
A 50-year tree-ring δ18O chronology of Abies spectabilis growing close to the tree line (3850 m asl) in the Nepal Himalaya is established to explore its dendroclimatic potential. Response function analysis with ambient climatic records revealed that tree-ring δ18O is primarily governed by rainfall during the monsoon season (June–September), and the regression model accounts for 35% of the variance in rainfall. Extreme dry years identified in instrumental weather data are detected in the δ18O chronology. Further, tree-ring δ18O is much more sensitive to rainfall fluctuations than other tree-ring parameters such as width and density typically used in dendroclimatology. Correlation analyses with Niño 3.4 SST reveal time-dependent behavior of ENSO–monsoon relationships. 相似文献
4.
Tree-ring width (TRW) chronologies have been widely and long-time used to reconstruct past climate variations in the Andes in South America. The use of tree-ring isotopic chronologies is still not widespread in this region although they have proved to be very efficient climate proxies. Araucaria araucana (Molina) K. Koch is a conifer tree species with some multi-century-old individuals that offers an excellent opportunity to measure stable carbon (δ13C) and oxygen (δ18O) isotopes in cellulose from long tree-ring records. Here, we explore whether current or stored carbohydrates are used for A. araucana radial growth and we assess the potential of a tree-ring isotopic record of to study past climate variability. Eleven A. araucana cores from a dry and high-elevation forest at the northern border of Patagonia, Argentina (38°55’S, 70°44’W) were selected for stable isotopes analyses. The strong correlation between the isotopic composition of the first and second parts of the same ring, but also the strong relationships between δ13C and δ18O records with climate parameters of the current growing season such as temperature, show that tree-rings are built mostly with carbohydrates produced during the current growing season with little or no supply from storage or reserves. This finding leads to reconsidering the interpretation of the legacy effect (i.e. ecological memory effects) based on the previously described strong negative correlation between A. araucana TRW chronologies and previous growing season temperature and suggests a dependence of radial tree growth on the level of development of organs. Regarding climate sensitivity, the A. araucana tree-ring δ13C chronology is strongly related to current summer temperature (r = 0.82, p < 0.001), vapour pressure deficit (VPD; r = 0.79, p < 0.001), precipitation (r = −0.53, p < 0.001) and SPEI2 (r = −0.73, p < 0.001). These strong relationships support the use of δ13C of A. araucana tree-ring cellulose to reconstruct past temperature variations at regional scale in relation with large-atmospheric drivers of climate variability such as the Southern Annular Mode. The A. araucana tree-ring δ18O chronology is also correlated with temperature (r = 0.42, p < 0.01) and VPD (r = 0.45, p < 0.01) of the winter preceding the growing season. This suggests that trees are using water from precipitation infiltrated in the soil during the previous recharge period (autumn-winter). The weak correlations of δ18O with current summer atmospheric conditions and the decoupling between δ18O and δ13C, may be due to a high rate of oxygen exchange between sugars and xylem water (Pex) during cellulose synthesis, which dampens evaporative isotopic fractionation. 相似文献
5.
Climate reconstructions using stable isotopes (δ18O and δ13C values) in tree rings are based on relationships between present climatic conditions and isotopic series. This widely used approach relies on the assumption that correlations between stable isotopes and climatic conditions are steady over time. In this paper, we evaluate the strength of the correlations between δ18O and δ13C series with several climatic parameters on fourteen black spruce trees coming from three different sites, in northeastern Canada. We applied a 21-year moving window on the r Pearson calculated between stable isotopes and March–May and June–August precipitation, June–August and April–June maximal temperatures. Our results indicate that despite the large distance and differences in stand conditions between the sites, the three sites responded in the same way over time. We show that because the climatic ambiance has changed during the 1980–1990 period due to a positive North Atlantic Oscillation index the δ13C values are not controlled anymore by spring precipitation or summer maximal temperature in the following two decades. As opposed to δ13C series, the relationship between summer maximal temperature and δ18O values was stable over time, and decreased only in the last decade. All these results attest of a “divergence problem” in the last decades which is most pronounced for δ13C series. We conclude that the spruce δ18O series appears to be the most appropriate indicator for reconstructing June–August maximal temperature in the studied area despite the divergence issue, given that the calibration–validation tests and reconstruction can exclude the divergent last decade. 相似文献
6.
The oxygen isotopic composition (δ18O) of tree-ring cellulose has been recognized as a powerful tool for dendroclimatological and dendrochronological investigations in Asia. Only a few studies of cellulose δ18O so far published, however, have been conducted in Indonesia, and the spatial coherence of cellulose δ18O has yet to be clarified. In this study we measured cellulose δ18O of teak (Tectona grandis) collected from four sites on Java Island to evaluate the similarity between the different teak δ18O values and the potential for using teak δ18O both as a climate proxy and as a tool for cross-dating. Cellulose δ18O time series of Javanese teaks were found to be significantly correlated in all of the comparisons between sites, even between sites separated by a distance as great as 400 km. While significant correlations did not appear in the ring width data between our samples (expressed population signal (EPS) = 0.64; Rbar = 0.23; sample depth = 10), they were found between the cellulose δ18O values (EPS = 0.89; Rbar = 0.58; sample depth = 10). These results suggest that teak δ18O variations have higher spatial coherence and might be a useful tool for cross-dating. A significant negative correlation was observed between cellulose δ18O and the relative humidity/precipitation during the rainy season, indicating that the cellulose δ18O of Javanese teak is an effective proxy for relative humidity/precipitation during the rainy season. Cellulose δ18O was found to be positively correlated with precipitation during the dry season preceding the growing season, whereas it showed no correlations with the temperature and Palmer Drought Severity Index (PDSI), the key constraints of δ18O on the Indochina Peninsula. 相似文献
7.
Roberto Tognetti Fabio Lombardi Bruno Lasserre Giovanna Battipaglia Matthias Saurer Paolo Cherubini Marco Marchetti 《Trees - Structure and Function》2012,26(6):1805-1819
Palaeoclimate proxies have demonstrated links between climate changes and volcanic activity. However, not much is known about the impact of volcanic eruptions on forest productivity. Here we used tree-ring width and annually resolved carbon and oxygen isotopic records from tree rings of Araucaria araucana (Molina) K. Koch, providing a centennial-scale reconstruction of tree ecophysiological processes in forest stands nearby the Lonquimay Volcano (Chile). We observed a mean decrease in tree-ring width following the major eruption of 1988–1990 (with aerosol emission), most probably caused by the modified ecological conditions due to acid rain and ash deposition, while a generally negative relationship between δ13C and δ18O would point to a decline in humidity and precipitation. More negative δ13C and lower δ18O values (positive correlation) following the major eruption of 1887–1890 (without aerosol emission) would suggest high stomatal conductance and moisture availability, though tree-ring width (and probably photosynthetic rate) was unaltered. At least for this sample of trees, in the case of eruption with large tephra emission, the beneficial effect of aerosol light scattering on tree productivity appears to be outweighed by the detrimental effect of eruption-induced toxic deposition. Signals of the two major eruptions of the past 200?years at Lonquimay were present in tree rings of nearby A. araucana. No unique response of tree functions to volcanic eruptions can be expected, but rather (1) the variable volcanic properties and (2) the complex interplay of diffuse light increase (aerosol scattering), air temperature decrease (cloud shading), and toxic deposition impact (volcanic ash), makes any prediction of tree growth and ecophysiological response very challenging. 相似文献
8.
Resin tapping could affect water and nutrient transport processes in Chinese pine trees, rendering them more vulnerable to extreme climatic events, such as drought, and affecting the ecological function of forests in semi-arid regions. This study evaluated how resin tapping affects the tree-ring growth and climate sensitivity of Chinese pine in the Loess Plateau. We compared tree-ring growth patterns between the tapped and untapped faces of tapped trees, and investigated tree-ring growth and its response to climate between tapped and untapped trees in a forest stand during the 1967–2017 period. Tapped trees showed asymmetrical growth patterns after resin tapping, with narrower rings near the tapped face and wider ones near the untapped face. Furthermore, tapped trees had inter-annual variations consistent with those of untapped trees except for the years 2000 and 2001, with significantly lower values following resin tapping, and tree-ring growth then returning to normal. The climate response analysis indicated that the tree-ring growth of both tapped and untapped trees was negatively affected by monthly mean temperatures during the early growing season (May to July) in the post-resin-tapping period. Furthermore, tree-ring growth in tapped trees also revealed significant correlation with water vapour deficit and the Palmer drought index, which indicates that tapped trees are more vulnerable to drought. Further studies based on stable isotopes (i.e. δ13C, δ18O, and δ15N) could improve our understanding of the physiological mechanisms that regulate the effects of resin tapping on tree-ring growth. 相似文献
9.
Silver carp, Hypophthalmichthys molitrix, is one of the four major fishes in China for fishing and aquaculture. The Yangtze River and associated waterbodies are important home to silver carp. In this study, we collected 135 otoliths of juvenile silver carp from the two rivers and the Poyang Lake, and analyzed for stable oxygen and carbon isotope ratios (δ18O and δ13C). The isotopic data and correlation of δ18O versus δ13C showed a clear separation and significant differences (p?<?0.001 for both δ13C and δ18O) between otoliths from the Ganjiang River and the Yangtze River at δ18O values around ?10‰. The Poyang Lake samples were overlapped with those of the Ganjiang River, but distinctly different from the Yangtze River samples. These isotopic signatures agree well with the previous genetic investigation results that there are marked distinctions between one population in the Ganjiang River and the other in the Yangtze River, and the Poyang Lake population belongs to the Ganjiang River rather than to the Yangtze River. Thus we concluded that stable isotope analyses of otoliths can be effectively used to study natal sources and stock differences of silver carp. 相似文献
10.
Koichi Takahashi Isao Okuhara Yohei Tokumitsu Koh Yasue 《Trees - Structure and Function》2011,25(4):745-753
This study examined the effects of climate on tree-ring widths and maximum latewood densities of Abies
veitchii and Abies mariesii at the upper and lower distribution limits in central Japan. A. veitchii and A. mariesii dominated at the lower and upper parts of the subalpine zone, respectively. Residual chronologies of tree-ring width and
maximum latewood density were developed for the two Abies species at the upper and lower distribution limits, and were compared with monthly mean temperatures and monthly sums of
precipitation. Tree-ring widths of the two Abies species at the upper and lower distribution limits positively correlated with temperatures during the beginning of the dormant
season and during the growing season of the current year, except for A. veitchii at the lower distribution limit, which showed no positive correlation with temperature. Maximum latewood densities of the
two Abies species at the upper and lower distribution limits positively and negatively correlated with temperatures and precipitation,
respectively, during the growing season of the current year. Therefore, tree-ring widths and maximum latewood densities of
the two Abies species were sensitive to low temperature, except for the tree-ring width of A. veitchii at the lower distribution limit with the warmest thermal conditions along the altitude. Global warming is suggested to affect
maximum latewood densities and tree-ring widths of the two Abies species along the altitude. 相似文献
11.
Pinus thunbergii trees growing on Pacific coastal sand dunes in Japan were immersed by the tsunami that followed the Great East Japan Earthquake on 11 March 2011. Even trees that survived direct physical damage began to die during the following summer, probably because of the physiological stress of salt water immersion. The objectives of this study were to analyze the relationship between the carbon and oxygen isotope values (δ13C and δ18O, respectively) of P. thunbergii tree-ring cellulose and the effects of salt water immersion caused by the tsunami. Pinus thunbergii trees were sampled in Yamamoto, Miyagi Prefecture, and in Misawa, Aomori Prefecture. Each tree-ring that formed between 2008 and 2012 was sliced into four to eight equal subdivisions, and the isotope values were analyzed at a high time-scale resolution. Tree rings that were immersed in seawater from the tsunami had higher δ13C values in the earlywood that formed in the spring following the tsunami than those formed prior to the disaster. This increase in δ13C values was likely caused by osmotic stress from root immersion in salt water. We did not observe a clear change in tree-ring δ18O values after the tsunami. This lack of variance might have resulted from the post-photosynthetic exchange of carbonyl oxygens with non-18O-enriched xylem water. 相似文献
12.
《Palaeoworld》2020,29(3):636-647
Planktonic foraminifera collected from a sediment trap deployed off Hainan in the northwestern South China Sea (SCS-NW) between July 2012 and April 2013 were studied to evaluate their seasonal variability and ecology as well as to infer the factors controlling their shell fluxes. The total planktonic foraminifera flux, as well as the fluxes of the dominant species (Globigerinoides ruber, Globigerinoides sacculifer and Neogloboquadrina dutertrei), showed three distinct maxima during SW-monsoon in August 2012, the SW-NE intermonsoon in October 2012 and the NE-monsoon in December 2012–February 2013. These periods were characterized by upwelling, aerosol fallout, and intense wind mixing, respectively, from which the foraminiferal assemblages benefitted, as indicated by the close correlation between wind speed, sea surface temperature (SST), chlorophyll a concentration (Chl-a), δ18O of G. ruber and the shell fluxes. The correlation also suggests that temperature and food availability might have been the primary drivers of the observed changes in foraminiferal abundance. The offset between the SST deduced from flux-weighted of G. ruber δ18O and annual mean SST is only ∼0.3 °C, much lower than ∼5.2 °C between the summer and winter temperature, indicating a balanced seasonality bias in the shell flux. The linear regression between the satellite-derived sea surface temperature and G. ruber δ18O reveals the strong potential of this species, at least in the studied region, as an ecological indicator for past oceanic environments. 相似文献
13.
R. Feranec N. García J.C. DÍez 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,297(2):263-272
Stable carbon and oxygen isotope analyses of mammalian carnivoran and herbivore species from the late Pleistocene Valdegoba cave site in northern Spain imply competition and partitioning in resource use. In general, the data support the previously recognized ecology for the analyzed species. δ13C values show that the ecosystem around the cave was dominated by C3 plants. The observed δ18O values are similar to what is found in modern environments. The analyzed bovids, Bos primigenius, Capra pyrenaica, and Rupicapra rupicapra, showed the most positive δ13C values. Bos primigenius had the most positive mean carbon isotope value and is suggested to feed on grasses in open environments. Values for Capra pyrenaica primarily indicate grass feeding, while Rupicapra rupicapra had the widest diet for the analyzed species, likely including grass and browse. Cervus elaphus, Equus ferus, Equus hydruntinus, and Stephanorhinus hemitoechus displayed more negative δ13C values indicating the use of similar resources. The smallest species analyzed, Castor fiber, displayed the most negative δ13C and δ18O values, implying a preference for eating C3 plants and being semi-aquatic. The canids, Canis lupus and Vulpes vulpes, displayed the most positive δ13C and δ18O values, and overlap many of the sampled ungulate species. Positive δ18O values in canids implies that this group obtains much of its water from its prey, uses a different water source, or has physiological differences from the other carnivorans that influence oxygen isotope values. Lynx pardinus had values similar to the canids. Crocuta crocuta had δ13C values more negative than expected for a generalist predator. These values are likely due to concentration of diet on taxa from more forested environments. The most negative δ13C values are observed in the bears, Ursus arctos and Ursus spelaeus. These values are the likely result of hibernation and the inclusion of significant vegetation in bear diets. 相似文献
14.
Studies in dendroisotope chemistry suggested that latewood cellulose contains better climatic records than whole-ring cellulose. However, this approach has never been tested on northeastern Canadian spruce trees. This study compares dendroisotopic series of cellulose from late and whole ring, and analyses their statistical relationships with hydro-climatic variables with the aim of selecting the best suited protocol for future hydro-climatic reconstruction in the downstream sector of Churchill River basin of Labrador, Canada. To this end, δ13C and δ18O series from latewood (LW) and whole ring (WR) α-cellulose of black spruce trees (Picea mariana [Mill.] B.S.P.) were produced for the 1940–2010 period. The results show strong correlations between LW and WR isotopic series suggesting that there are no important variation in the isotopic ratios during the growing year and that black spruce trees use photosynthates of the current growing season to form their earlywood. Moreover, LW and WR δ13C and δ18O show similar relationships with both maximum temperature (Tmax) and Churchill River discharge. Correlations are higher when combining δ13C and δ18O for LW and WR. Overall, those correlations support the indirect relationship between tree-ring isotopic series and river discharge, as they are integrators of several climatic variables and derived parameters (Tmax, relative humidity, evapotranspiration, etc.). The LW and WR isotopic series give similar statistical relationships with hydro-climatic variables, and the WR treatment is faster (separation easier compared to LW). Thus, for black spruce the use of combined isotopic series in WR can be favored over LW for hydro-climatic reconstruction in the study region. 相似文献
15.
Variations of the nitrate isotopic composition in the St. Lawrence River caused by seasonal changes in atmospheric nitrogen inputs 总被引:1,自引:0,他引:1
We present 42 dual-isotope nitrate analyses of fresh water samples collected in the St. Lawrence River between June 2006 and July 2008. Measured δ15N–NO3 ? and δ18O–NO3 ? values correlate negatively, while δ18O–NO3 ? displays no negative correlation with nitrate concentration. This suggests that nitrate uptake and/or elimination by denitrification is not the main driver of observed variations in nitrate concentration and isotopic signature in the St. Lawrence River. In addition, δ18O–NO3 ? is negatively correlated with the seasonally variable δ18O of ambient water, indicating that the variation in the isotopic signature of nitrate is barely modulated by in-stream nitrate regeneration (nitrification). It rather is constrained by along-river changes in the external sources of nitrate. Given the distinct nitrogen (N) and oxygen (O) isotopic signature of atmospheric nitrate, we argue that observed seasonal variations of δ15N–NO3 ? and δ18O–NO3 ? in the St. Lawrence River are due to variable contributions of snowmelt-derived water. Based on a N and O isotope mass balance, we show that total nitrate loading in the St. Lawrence River is dominated by a N input from the Great Lakes (47 ± 28 %) and from nitrate regeneration of both internal and external N (48 ± 22 %). While temporal nitrate N and O isotope dynamics in the St. Lawrence River are mainly influenced by the atmospheric N input fluctuations, with an increase in atmospheric loading during spring, atmospheric N plays overall a rather insignificant role with regards to the N budget (5 ± 4 %). 相似文献
16.
Werner Härdtle Thomas Niemeyer Thorsten Assmann Saskia Baiboks Andreas Fichtner Uta Friedrich Anne C. Lang Burkhard Neuwirth Laurent Pfister Christian Ries Andreas Schuldt Natalie Simon Goddert von Oheimb 《Ecosystems》2013,16(8):1413-1428
We investigated long-term responses (since 1850) of Fagus sylvatica (Luxembourg; central Europe) to shifts in temperature, precipitation, and nitrogen deposition by analyzing diameter at breast height (DBH) increment, basal area increment (BAI), and tree-ring stable isotopes (δ13C, δ15N). We compared stands on soils with contrasting water supply (Regosols and Cambisols with an available water capacity of ca. 40 and 170 mm, respectively) and of two different age classes (ca. 60 vs. 200 years). All stands showed a peak in DBH increment in the decade 1978–1987, but a decline in increment growth in subsequent decades. In addition, BAI declined in mature stands in the last two decades. Decreasing increment rates were attributable to an increasing drought limitation of stands, mainly induced by increasing temperatures in the last two decades. Contrary to our expectations, stands on Cambisols showed a similar susceptibility to shifts in temperature and precipitation as stands on Regosols, suggesting a strong adaptation of the respective ecotypes grown at dryer sites. This result was in line with long-term trends for tree-ring δ13C signatures, which did not differ significantly between stands on Cambisols and Regosols. Climate impacts on tree-ring δ15N signatures were low. High spring precipitation and temperatures caused increasing and decreasing δ15N values, respectively, but only in mature stands on Cambisols. Stands on Regosols tended to have lower δ15N values than stands on Cambisols. Decreasing δ15N values in recent decades suggest an increasing impact of allochthonous N loads with isotopically lighter N. 相似文献
17.
JIN KYUNG KIM BOO‐KEUN KHIM KYUNG SIK WOO SEOK HOON YOON 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2010,43(2):170-181
Kim, J.K., Khim, B.‐K., Woo, K.S., & Yoon, S.H. 2009: Records of palaeo‐seawater condition from oxygen‐isotope profiles of early Pleistocene fossil molluscs from the Seoguipo Formation (Korea). Lethaia, Vol. 43, pp. 170–181. High‐resolution δ18O profiles of early Pleistocene fossil molluscs (Mizuhopecten tokyoensis hokurikuensis) from the shallow‐marine sedimentary Seoguipo Formation (Korea) were found to exhibit distinct annual cycles identified by their unique seasonality (δ18O amplitude). A direct comparison of fossil δ18O profiles with that of living shells (Amusium japonicum japonicumi) indicated that the palaeoseawater conditions differed from present‐day seawater. Specifically, the positive δ18O shift in the isotope profile of the fossil specimens relative to that of the living mollusc shell reflected that palaeotemperature was lower than that today. However, a comparison of the coldest palaeotemperatures (determined from the heaviest δ18O values of fossil shells), with the present‐day winter temperatures indicates that temperature variation alone cannot account for the entire positive δ18O offset. These findings indicate that variation in the seawater δ18Ow values plays a dominant role in the biogenic carbonate precipitation of fossils. Thus, the fossil shells obtained from stratigraphic units suggest different palaeoenvironmental conditions, including lower temperatures and 18O‐enriched glacial seawater, when compared with the present‐day conditions. The Seoguipo Formation records at least five cycles of relative sea‐level fluctuations, with changes in fossil δ18O amplitudes separated by sequence boundaries likely to reflect variations of unique palaeoseawater condition, although the oxygen‐isotope profile of fossil molluscs appears to provide a snap‐shot of the palaeoclimatic signature. □Early Pleistocene, mollusc fossils, oxygen isotope, palaeoenvironment, seawater temperature. 相似文献
18.
《Dendrochronologia》2014,32(1):78-89
A main concern of dendroclimatic reconstruction is to distinguish in the tree ring proxy the influence of the climate variables of interest from other controlling factors. In order to investigate age, site and climate controls on tree ring width and cellulose δ18O, measurements have been performed in nearby groups of young (145 years old) and older (310–405 years old) oak trees in south-western France, covering the period 1860–2010.Within a given site, inter-tree deviations are small, pointing to a common climatic signal. Despite a similar inter-annual variability, the average level of cellulose δ18O in the young tree group is ∼0.8‰ higher than in the old trees. Such offsets might be caused by different soil properties and differences in the fraction of the source water used by trees from different depths. The δ18O of water in the top soil layer is directly related to the current growing season precipitation, while deeper water can have a lower and more constant δ18O. Local cave drip waters at 10 m depth indeed show a constant isotopic composition, which corresponds to pluri-annual mean precipitation.A 2‰ increasing trend is observed in cellulose δ18O of young trees in the first 30 years of growth, during a period when no trend is visible in older trees. This increase can be quantitatively explained by humidity gradients under the forest canopy, and a changing microclimate around the crown as trees grow higher.While relationships between tree ring width and climate appear complex, the isotopic composition of cellulose is strongly correlated with summer maximum temperature, relative humidity and evapotranspiration (r ≈ 0.70). Weaker correlations (r ≈ 0.40) are identified with precipitation δ18O from a 15-year long local record and from the REMOiso model output. These results imply that leaf water enrichment has a stronger control on the inter-annual variability of cellulose δ18O than the δ18O of precipitation.This study demonstrates the suitability of oak tree ring cellulose δ18O for reconstructing past summer climate variability in south-western France, provided that the sampling and pooling strategy accounts for the fact that trees from different sites and of different age can introduce non-climatic signals. 相似文献
19.
Sediment trap samples collected over a seven-year period (February 1991–October 1997) from Guaymas Basin in the Gulf of California were used to study the oxygen isotope composition of five species of planktonic foraminifera, Globigerinoides ruber (white), Globigerina bulloides, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii. The δ18O data were analyzed for temporal and interspecies variability and were compared to local hydrography to evaluate the use of each species in reconstructing past oceanographic applications. The two surface dwelling species, G. ruber and G. bulloides displayed the lowest δ18O values (~ 0.0 to ? 5.0‰), while δ18O values for the thermocline dwelling N. dutertrei, P. obliquiloculata, and G. menardii were higher (~ 0.0 to ? 2.0‰). The δ18O of G. ruber most accurately records measured sea surface temperatures (SSTs) throughout the year. G. bulloides δ18O tracks SSTs during the winter–spring upwelling period but for the remainder of the year records slightly colder, subsurface temperatures. The difference between the δ18O of the surface dwelling species, G. ruber and G. bulloides, and that of the thermocline dwelling species, N. dutertrei, P. obliquiloculata, and G. menardii, was used to estimate the surface to thermocline temperature gradient. During the winter these δ18O differences are small (~ 0.50‰) reflecting a well-mixed water column. These interspecies δ18O differences increase during the summer (~ 1.90‰) in response to the strong thermal stratification that exists at this time of year. 相似文献
20.
The 10-year juvenile records of three hybrid poplar and two aspen cultivars (Populus spp.) from a short rotation coppice (SRC) were assessed by measuring tree-ring width (annual radial increment, ir) and stable isotope ratios of carbon and oxygen (δ13C and δ18O) of α-cellulose. All cultivars showed common ‘juvenile trends’ that were modeled with nonlinear fit (NLF) functions. The ir of all cultivars culminated in the middle of the juvenile phase. Within the first ten years, δ13C showed a gradual decrease of approximately 2.5 ‰ in all cultivars and δ18O showed an asymptotic increase which was variable among the poplar cultivars and which was more pronounced in two hybrid poplars. Potential causes of the juvenile inter-annual variability of δ13C and δ18O were discussed. Likely, the maturation related changes in hydraulic architecture, the canopy closure and the resulting increase of the proportion of shaded crown segments which have lower photosynthetic capacities had an effect on δ13C. An additional effect of changes in N nutrition on δ13C is assumed at the present SRC trial because the NO3− concentration had significantly decreased after ten years. Interpretation of δ18O data remained difficult given the lack of soil water δ18O records.The maturation effect and the respective interaction have resulted in large temporal variability in the present three investigated tree ring traits. However, the impact of two drought vegetation periods (2003 and 2006) was still reflected by the juvenile tree ring records of all traits. Different juvenile trends in the records of the stable isotope ratios δ13C and δ18O, and the trend slopes, which may vary between genetically different cultivars, must be considered in tree ring investigations of SRC poplars. 相似文献