Tree-ring Isotope Research Articles

Oxygen isotopes in tree rings record variation in precipitation δ18O and amount effects in the south of Mexico.

[1] Natural archives of oxygen isotopes in precipitation may be used to study changes in the hydrological cycle in the tropics, but their interpretation is not straightforward. We studied to which degree tree rings of Mimosa acantholoba from southern Mexico record variation in isotopic composition of precipitation and which climatic processes influence oxygen isotopes in tree rings (δ18Otr). Interannual variation in δ18Otr was highly synchronized between trees and closely related to isotopic composition of rain measured at San Salvador, 710 km to the southwest. Correlations with δ13C, growth, or local climate variables (temperature, cloud cover, vapor pressure deficit (VPD)) were relatively low, indicating weak plant physiological influences. Interannual variation in δ18Otr correlated negatively with local rainfall amount and intensity. Correlations with the amount of precipitation extended along a 1000 km long stretch of the Pacific Central American coast, probably as a result of organized storm systems uniformly affecting rainfall in the region and its isotope signal; episodic heavy precipitation events, of which some are related to cyclones, deposit strongly 18O-depleted rain in the region and seem to have affected the δ18Otr signal. Large-scale controls on the isotope signature include variation in sea surface temperatures of tropical north Atlantic and Pacific Ocean. In conclusion, we show that δ18Otr of M. acantholoba can be used as a proxy for source water δ18O and that interannual variation in δ18Oprec is caused by a regional amount effect. This contrasts with δ18O signatures at continental sites where cumulative rainout processes dominate and thus provide a proxy for precipitation integrated over a much larger scale. Our results confirm that processes influencing climate-isotope relations differ between sites located, e.g., in the western Amazon versus coastal Mexico, and that tree ring isotope records can help in disentangling the processes influencing precipitation δ18O.

Oxygen and carbon stable isotopes in coast redwood tree rings respond to spring and summer climate signals

AbstractInterannual variability in the oxygen and carbon isotope composition of tree ring cellulose was investigated in coast redwood (Sequoia sempervirens) from three sites in coastal Northern California. Middle and late wood samples from annual tree rings were compared to regional climate indices and gridded ocean‐atmosphere fields for the years 1952–2003. The strongest climate‐isotope relationship (r = 0.72) was found with summer (June–September) daily maximum temperature and middle wood δ13, which also responds positively to coastal sea surface temperature and negatively to summer low cloud frequency. Late wood δ18O reflects a balance between 18O‐enriched summer fog drip and depleted summer rainwater, while a combined analysis of late wood δ18O and δ13C revealed sensitivity to the sign of summer precipitation anomalies. Empirical orthogonal function analysis of regional summer climate indices and coast redwood stable isotopes identified multivariate isotopic responses to summer fog and drought that correspond to atmospheric circulation anomalies over the NE Pacific and NW U.S. The presence of regional climate signals in coast redwood stable isotope composition, consistent with known mechanistic processes and prior studies, offers the potential for high‐resolution paleoclimate reconstructions of the California current system from this long‐lived tree species.

A 520 year record of summer sunshine for the eastern European Alps based on stable carbon isotopes in larch tree rings

A 520-year stable carbon isotope chronology from tree ring cellulose in high altitude larch trees (Larix decidua Mill.), from the eastern European Alps, correlates more strongly with summer temperature than with summer sunshine hours. However, when instrumental records of temperature and sunshine diverge after AD1980, the tree ring time series does not follow warming summer temperatures but more closely tracks summer sunshine trends. When the tree ring stable carbon isotope record is used to reconstruct summer temperature the reconstruction is not robust. Reconstructed temperatures prior to the twentieth century are higher than regional instrumental records, and the evolution of temperature conflicts with other regional temperature reconstructions. It is concluded that sunshine is the dominant control on carbon isotope fractionation in these trees, via the influence of photosynthetic rate on the internal partial pressure of CO2, and that high summer (July–August) sunshine hours is a suitable target for climate reconstruction. We thus present the first reconstruction of summer sunshine for the eastern Alps and compare it with the regional temperature evolution.

Isoscapes of tree‐ring carbon‐13 perform like meteorological networks in predicting regional precipitation patterns

AbstractStable isotopes in tree rings provide climatic information with annual resolution dating back for centuries or even millennia. However, deriving spatially explicit climate models from isotope networks remains challenging. Here we propose a methodology to model regional precipitation from carbon isotope discrimination (Δ13C) in tree rings by (1) building regional spatial models of Δ13C (isoscapes) and (2) deriving precipitation maps from Δ13C‐isoscapes, taking advantage of the response of Δ13C to precipitation in seasonally dry climates. As a case study, we modeled the spatial distribution of mean annual precipitation (MAP) in the northeastern Iberian Peninsula, a region with complex topography and climate (MAP = 303–1086 mm). We compiled wood Δ13C data for two Mediterranean species that exhibit complementary responses to seasonal precipitation (Pinus halepensis Mill., N = 38; Quercus ilex L.; N = 44; pooling period: 1975–2008). By combining multiple regression and geostatistical interpolation, we generated one Δ13 C‐isoscape for each species. A spatial model of MAP was then built as the sum of two complementary maps of seasonal precipitation, each one derived from the corresponding Δ13C‐isoscape (September–November from Q. ilex; December–August from P. halepensis). Our approach showed a predictive power for MAP (RMSE = 84 mm) nearly identical to that obtained by interpolating data directly from a similarly dense network of meteorological stations (RMSE = 80–83 mm, N = 65), being only outperformed when using a much denser meteorological network (RMSE = 56–57 mm, N = 340). This method offers new avenues for modeling spatial variability of past precipitation, exploiting the large amount of information currently available from tree‐ring networks.

A simple and rapid preparation of pure cellulose confirmed by monosaccharide compositions, δ13C, yields and C%

A two-step method to extract pure cellulose from tree rings is presented in this study. The method employs the reagents diglyme (diethylene glycol dimethyl ether), hydrochloric acid and sodium chlorite in a 6-h reaction using ordinary equipment. Through separation of the chemical compositions (monosaccharides) using liquid chromatography, the product of this method is shown to contain only glucose from pure cellulose. In contrast, the chemical composition of the “α-cellulose” extract obtained by the traditional Jayme–Wise method is primarily glucose and mannose, which may come from hemicelluloses. These results are also verified by comparing the stable carbon isotope ratio (δ13C), yields and percentage of carbon (C%) of the product extracted by this method and “α-cellulose” for different tree species. The results suggest that this method is simple, rapid and appropriate for processing large numbers of small wood samples to develop tree-ring isotope series for high-resolution paleoclimatic research with softwood trees.

400-year May–August precipitation reconstruction for Southern England using oxygen isotopes in tree rings

Few long and well-dated summer precipitation reconstructions that extend beyond the longest records of instrumental measurements exist in Europe. Further understanding of the past trends in summer precipitation and the mechanisms driving that variability are necessary to improve the predictions of climate models. Tree rings are unique in their ability to provide high-resolution, absolutely dated climate signals for the study of palaeoclimatology. The physiological processes controlling oxygen isotope composition (δ18O) in wood are reasonably well understood highlighting its potential as a climate proxy in a variety of environments. Significant correlation between wood δ18O and precipitation has been demonstrated worldwide reflecting both direct rainout processes and indirectly evaporative enrichment. We present an annually resolved reconstruction of precipitation based upon oxygen isotope variations in tree ring cellulose covering the most recent ∼400 years for England. The May–August precipitation series, which was formed by combining reconstructed values based on oxygen isotope composition (δ18O) in tree ring cellulose of pedunculate oak (Quercus robur) (1613–1893) and instrumental data (1894–2003), indicates significant decadal and centennial precipitation variability culminating in dry conditions in the early-middle 17th century and the late 20th century. The analysis demonstrated statistically robust May–August precipitation signal in the δ18O values of oak cellulose back to 1697, the first year of the oldest instrumental precipitation series in England.

On the reconstruction of precipitation in temperature-limited environments by the use of stable isotopes in tree-rings

On the reconstruction of precipitation in temperature-limited environments by the use of stable isotopes in tree-rings

U.S. Southwest monsoon precipitation inferred from tree-ring stable-carbon isotopes

U.S. Southwest monsoon precipitation inferred from tree-ring stable-carbon isotopes

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Nino-Southern Oscillation variability.

We present a unique proxy for the reconstruction of variation in precipitation over the Amazon: oxygen isotope ratios in annual rings in tropical cedar (Cedrela odorata). A century-long record from northern Bolivia shows that tree rings preserve the signal of oxygen isotopes in precipitation during the wet season, with weaker influences of temperature and vapor pressure. Tree ring δ(18)O correlates strongly with δ(18)O in precipitation from distant stations in the center and west of the basin, and with Andean ice core δ(18)O showing that the signal is coherent over large areas. The signal correlates most strongly with basin-wide precipitation and Amazon river discharge. We attribute the strength of this (negative) correlation mainly to the cumulative rainout processes of oxygen isotopes (Rayleigh distillation) in air parcels during westward transport across the basin. We further find a clear signature of the El Niño-Southern Oscillation (ENSO) in the record, with strong ENSO influences over recent decades, but weaker influence from 1925 to 1975 indicating decadal scale variation in the controls on the hydrological cycle. The record exhibits a significant increase in δ(18)O over the 20th century consistent with increases in Andean δ(18)O ice core and lake records, which we tentatively attribute to increased water vapor transport into the basin. Taking these data together, our record reveals a fresh path to diagnose and improve our understanding of variation and trends of the hydrological cycle of the world's largest river catchment.

Is the dual-isotope conceptual model fully operational?

The stable carbon isotopic composition (δ13C) of organic matter is a valuable measure of plant physiological processes. Unfortunately, the impacts of carbon assimilation (A, demand for CO2) and stomatal conductance (gs, supply of CO2) on Rubisco discrimination (through Ci/Ca) are difficult to separate. Thus, a conceptual model (Scheidegger et al. 2000) was developed to constrain the interpretation of δ13C variation by measuring oxygen isotopic composition (δ18O) on the same material (the ‘dual-isotope’ approach). The idea is that δ18O, as a proxy for evaporative flux, will be modified by gs but not A. Therefore, if changes in environmental conditions cause a long-term change in A and/or gs, this should be reflected in the carbon and oxygen isotope ratios of organic matter, respectively. This model is conceptually sound and a number of papers (Sidorova et al. 2009, Brooks and Mitchell 2011) have used this model for interpreting δ13C variation in tree rings. In the current issue of Tree Physiology, Barnard et al. have utilized the dual-isotope model to infer physiological responses of mature Pseudotsuga menziesii (Mirb) Franco trees to environmental variation associated with site differences and canopy position. They developed a novel approach to eliminate confounding factors by plotting relative changes (from the grand mean) in tree ring δ13C and δ18O values. They used the conceptual model to infer temporal changes in gs, spatial variation in A associated with leaf nitrogen content and different levels of physiological responsiveness to environmental forcing for trees from different canopy positions. This was an ambitious use of the dual-isotope model due to complex environmental variation associated with sites (slope and aspect differences), canopy position (three crown classes), seasonal separation (earlywood and latewood) and inter-annual climate (8 years). The dual-isotope model has not been tested under such complex conditions, and the highly variable results of Barnard et al. (2012) make model interpretation challenging. Our ability to take advantage of this conceptual model is limited by a number of model assumptions and constraints that are often overlooked. Barnard et al. (2012) recognized many of these assumptions and tried to quantify or limit confounding variation; however, they did not test whether model predictions regarding A and gs were realized in their system, which would have been a valuable confirmation of model applicability. They assumed that this conceptual model was operational for interpreting tree ring isotope variation in complex forest ecosystems. The purpose of this commentary is to highlight areas of caution that must be recognized before the dual-isotope model can be routinely utilized and encourage research that could help reduce model uncertainties. 1. The dual-isotope model interprets changes in δ18O as primarily influenced by gs. This requires that environmental influences on evaporative enrichment (Craig and Gordon 1965) including source water δ18O, atmospheric vapor δ18O, ambient humidity and leaf temperature must either be constant over time (for tree rings) or between treatments (common garden) or that all relevant fractionation events also influence gs (e.g., vapor pressure deficit [D] differences modify gs through a welldescribed relationship; thus, increasing D leads to enhanced evaporative enrichment in 18O, but it can also reduce gs leading to a concomitant increase in leaf water δ18O, amplifying the effect of D on organic matter δ18O). Documented inter-annual variation in the δ18O of precipitation, soil evaporative enrichment profiles and the fact that trees can tap different sources of water may reduce one’s confidence that constant source water δ18O is an appropriate assumption (Sarris et al. 2013). The paucity of data on δ18O variation in atmospheric vapor Commentary

Cosmic Rays in the Heliosphere: Requirements for Future Observations

Since the publication of Cosmic Rays in the Heliosphere in 1998 there has been great progress in understanding how and why cosmic rays vary in space and time. This paper discusses measurements that are needed to continue advances in relating cosmic ray variations to changes in solar and interplanetary activity and variations in the local interstellar environment. Cosmic ray acceleration and transport is an important discipline in space physics and astrophysics, but it also plays a critical role in defining the radiation environment for humans and hardware in space, and is critical to efforts to unravel the history of solar activity. Cosmic rays are measured directly by balloon-borne and space instruments, and indirectly by ground-based neutron, muon and neutrino detectors, and by measurements of cosmogenic isotopes in ice cores, tree-rings, sediments, and meteorites. The topics covered here include: what we can learn from the deep 2008–2009 solar minimum, when cosmic rays reached the highest intensities of the space era; the implications of ^(10)Be and ^(14)C isotope archives for past and future solar activity; the effects of variations in the size of the heliosphere; opportunities provided by the Voyagers for discovering the origin of anomalous cosmic rays and measuring cosmic-ray spectra in interstellar space; and future space missions that can continue the exciting exploration of the heliosphere that has occurred over the past 50 years.

Comparison of stable carbon and oxygen isotopes in Picea glauca tree rings and Sphagnum fuscum moss remains from subarctic Canada

Stable isotope ratios from tree rings and peatland mosses have become important proxies of past climate variations. We here compare recent stable carbon and oxygen isotope ratios in cellulose of tree rings from white spruce (Picea glauca), growing near the arctic tree line; and cellulose of Sphagnum fuscum stems, growing in a hummock of a subarctic peatland, in west-central Canada. Results show that carbon isotopes in S. fuscum correlate significantly with July temperatures over the past ~20yr. The oxygen isotopes correlate with both summer temperature and precipitation. Analyses of the tree-ring isotopes revealed summer temperatures to be the main controlling factor for carbon isotope variations, whereas tree-ring oxygen isotope ratios are controlled by a combination of spring temperatures and precipitation totals. We also explore the potential of combining high-frequency (annual) climate signals derived from long tree-ring series with low-frequency (decadal to centennial) climate signals derived from the moss remains in peat deposits. This cross-archive comparison revealed no association between the oxygen isotopes, which likely results from the varying sensitivity of the archives to different seasons. For the carbon isotopes, common variance could be achieved through adjustments of the Sphagnum age model within dating error.

Are pooled tree ring δ13C and δ18O series reliable climate archives? — A case study of Pinus nigra spp. laricio (Corsica/France)

Stable carbon and oxygen isotopes in tree rings are considered as reliable climate archives as they provide past environmental information with high resolution. However, recent studies have shown that isotope chronologies may reveal a long-term age trend and be influenced by non-climatic factors as other tree-ring parameters as well. These trends can only be identified in chronologies measured on individual trees but not on pooled sample chronologies consisting of several trees. In order to test whether pooled chronologies from pine trees from the Island of Corsica (Mediterranean/France) can be used for climatic reconstructions, we compared calculated mean values from 5 individual trees with pooled chronologies from the same 5 individuals. Carbon and oxygen isotope chronologies for a 50-year interval with annual resolution and 400years with decadal resolution were analysed in order to document secular changes in inter-tree variability and to test for age related trends in the isotope ratios. Pooled carbon and oxygen isotope series correspond well to chronologies based on mean values calculated from analyses of individual trees. Inter-tree variability in oxygen isotope ratios is higher than in carbon isotope ratios but remains relatively constant over time. Similarities between the isotope series of individual trees are stronger over the 400-year time scale documenting a common long-term signal in the isotope values. No long-term age related trends are observed. Oxygen isotope values of the juvenile phase are characterised by a remarkable decrease over 40–50years, interpreted to be related to the less developed root system of the young trees. This age effect can be avoided by not considering the first 50years from the chronologies. Our results confirm that pooled carbon and oxygen isotope chronologies from Pinus nigra can be used for environmental reconstructions without statistical detrending.

Influence of atmospheric circulation patterns on the oxygen isotope ratio of tree rings in the Alpine region

The oxygen isotope ratio of precipitation and tree rings is a complex function of climate variables and atmospheric dynamics, which often makes the interpretation of δ18O for palaeoclimate research challenging. Here we analyzed monthly precipitation δ18O series for 1973–2004 and annually resolved tree ring δ18O chronologies for 1945–2004 for three sites in Switzerland: one north of the Alps, one at high‐elevation within the Alps, and one south of the Alps. The goal of the study was to improve the understanding of the tree ring archive by a systematic analysis of nonlocal parameters related to atmospheric circulation, in particular, geopotential height field anomalies and the frequency of synoptic weather situations, in addition to the usual local climate parameters like temperature, sunshine duration, and relative humidity. We observed that on average high‐pressure situations during summer were associated with relatively high δ18O and low‐pressure situations were associated with relatively low δ18O, for both the isotope ratio in precipitation and tree rings. However, correlations to the frequency of weather types were not higher than simple correlations to local temperature. Accordingly, we constructed a combined index from temperature and air pressure that proved to be a good predictor of δ18O in precipitation and used this as the source water term in a tree ring isotope fractionation model. This enabled us to use the model beyond the period where isotope values for precipitation are available, opening new perspectives in the interpretation of long tree ring δ18O chronologies.

Combining tree-ring metal concentrations and lead, carbon and oxygen isotopes to reconstruct peri-urban atmospheric pollution

ABSTRACTIn this study, we analysed the tree-ring metal concentrations and isotope ratios of five stands located in three contrasted settings to infer the diffuse air pollution history of the northern part of the Windsor–Québec City Corridor in eastern Canada. Tree-ring series show that the Cd and Zn accumulation rates were higher between 1960 and 1986 and that the long-term acidification of the soil (Ca/Al series) was likely induced by NOx and SOx deposition (δ15N and δ13C trends as proxy). The Pb concentrations and 206Pb/207Pb ratios indicate that the dominant source of lead from 1880 to the 1920s was the combustion of north-eastern American coal, which was succeeded by the combustion of leaded gasoline from the 1920s to the end of the 1980s. Our modelling approach allows separating the climatic and anthropogenic effects on the tree-ring δ13C and δ18O responses. Diffuse air pollution caused an enrichment in 13C in all stands and a decrease of the δ18O values only in three of the stands. This study indicates that dendrogeochemistry can show contrasted responses to environmental changes and that the combination of several independent indicators constitutes a powerful tool to reconstruct the air pollution history in the complex context of peri-urban regions.

Environmental and climatic signals from stable isotopes in Anatolian tree rings, Turkey

Dendrochronological and oxygen–carbon isotopic analysis was conducted on tree rings collected at two different elevations from three different regions in western Anatolia, Turkey. Tree rings were sampled from Anatolian black pines (Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe) of at least 200 years old through an N–S transect covering Bolu-Mengen (north), Kutahya–Simav, and Antalya–Alanya (south) forests. Cellulose was extracted from 5-year blocks of tree rings from lower to upper altitudes in each region. Dendrochronological site chronologies were built for each of the 6 sites, and response to climate was evaluated. The long-term δ13C chronologies comprising the period 1800–2008 strongly decline by an average of 2.5‰ from the mid-twentieth century, which corresponds with the commencement of industrialization in Turkey. Oxygen isotope (δ18O) time series show dominantly low undulations, although some high-frequency variations of up to 6‰ are also observed. As a result of latitude and continent effects, oxygen isotope values of tree rings show an average of 3‰ increase from south (Antalya) to the north (Bolu). Correlations between carbon isotope ratios yield high positive values indicating that industrial pollution exerts a major control on the δ13C systematics of the studied trees. Corrected δ13C ratios are mostly represented by strong positive responses to variations in temperature and precipitation, whereas δ18O and summer temperature/precipitation are negatively correlated. Tree-ring widths and δ18O display similar responses to the temperature and sensitivity to the climatic impact of historic volcanic eruptions, and changes in the solar irradiance record are also detected in other high-resolution paleoclimate archives for the region.

Methods to merge overlapping tree-ring isotope series to generate multi-centennial chronologies

Stable isotopes ratios in tree-rings are increasingly used to assess long-term environmental variation. As with conventional tree-ring investigations, crossdating overlapping sequences of wood material allows chronologies longer than the lifespans of individual trees to be developed. We measured data from four overlapping cohorts of recent (AD 1650–2004) and historic (AD 1100–1198, AD 1150–1325, AD 1256–1700) wood to yield millennial-length δ13C, δ​D and δ18O chronologies. However, we found that offsets in absolute isotopic values between overlapping segments challenge the preservation of low frequency climate signals. In this paper, we describe the development of these records, signal strength assessments, and present the problems associated with overcoming these offsets and preserving low-frequency variance. We then propose and evaluate four different solutions to link the cohorts. These methods include various types of transformations of mean and variance; all present potential advantages and drawbacks. Inflated variance, loss of absolute isotope values, and the loss of low-frequency signals are major problems. Only one method is capable of fully preserving low-frequency trends, but this method may also risk inducing long-term artifacts. While the various solutions we propose may be useful to help overcome such biases, the challenges described here, if typical for other isotopic series, will best be solved by additionally modifying sampling and measurement procedures. We recommend avoiding pooling of tree rings in the overlap period and to increase the replication in order to extract the original signal and to maintain low-frequency signals.

The long way down--are carbon and oxygen isotope signals in the tree ring uncoupled from canopy physiological processes?

The carbon (δ(13)C) and oxygen (δ(18)O) stable isotope composition is widely used to obtain information on the linkages between environmental drivers and tree physiology over various time scales. The tree-ring archive can especially be exploited to reconstruct inter- and intra-annual variation of both climate and physiology. There is, however, a lack of information on the processes potentially affecting δ(13)C and δ(18)O on their way from assimilation in the leaf to the tree ring. As a consequence, the aim of this study was to trace the isotope signals in European beech (Fagus sylvatica L.) from leaf water (δ(18)O) and leaf assimilates (δ(13)C and δ(18)O) to tree-ring wood via phloem-transported compounds over a whole growing season. Phloem and leaf samples for δ(13)C and δ(18)O analyses as well as soil water, xylem water, leaf water and atmospheric water vapour samples for δ(18)O analysis were taken approximately every 2 weeks during the growing season of 2007. The δ(13)C and δ(18)O samples from the tree rings were dated intra-annually by monitoring the tree growth with dendrometers. δ(18)O in the phloem organic matter and tree-ring whole wood was not positively related to leaf water evaporative enrichment and δ(18)O of canopy organic matter pools. This finding implies a partial uncoupling of the tree-ring oxygen isotopic signal from canopy physiology. At the same time, internal carbon storage and remobilization physiology most likely prevented δ(13)C in tree-ring whole wood from being closely related to intra-annual variation in environmental drivers. Taking into account the post-photosynthetic isotope fractionation processes resulting in alterations of δ(13)C and δ(18)O not only in the tree ring but also in phloem carbohydrates, as well as the intra-annual timing of changes in the tree internal physiology, might help to better understand the meaning of the tree-ring isotope signal not only intra- but also inter-annually.

Regional And Watershed-Scale Coherence In the Stable-Oxygen and Carbon Isotope Ratio Time Series In Tree Rings Of Coast Redwood (Sequoia sempervirens)

Abstract Coast redwood (Sequoia sempervirens) ecosystems are strongly influenced by the presence of summer marine fog, and variation in fog frequency is closely linked to climate variation in the NE Pacific region. Because oxygen isotope composition (δ18O) of organic matter records distinct water sources (e.g. summertime fog vs. winter precipitation) and carbon isotopes (δ13C) are typically sensitive to humidity and water status, it then follows that inter-annual variation in tree-ring isotope ratios, which are coherent across multiple sites, should preserve a potentially powerful proxy for climate reconstruction. Here we present an analysis of a 50-year time series for both δ18O and δ13C values from subdivided tree rings obtained from multiple redwood trees at multiple sites. Within-site and between-site correlations were highly significant (p < 0.01) for the δ18O time series indicating a regionally coherent common forcing of δ18O fractionation. Within-site and between-site correlation coefficients were ...

The influence of climate on 13C/ 12C and 18O/ 16O ratios in tree ring cellulose of Pinus sylvestris L. growing in the central Scandinavian Mountains

The stable isotope composition of tree rings is known to contain valuable information of past climatic and environmental changes, which may be used as a complement to tree ring width and maximum latewood density in climate reconstructions. In this study we examine the character and strength of the climate signal captured in the δ 18O and δ 13C values of Scots pine ( Pinus sylvestris L.) trees growing at the tree-line in the central Scandinavian Mountains. Between 4 and 14 trees were pooled to produce annual records of carbon and oxygen isotope ratios from tree ring cellulose, spanning the period AD 1736–2006. Weather conditions of the current growing season most strongly influenced the carbon and oxygen isotope ratios in a given tree ring. Both records showed positive correlations with temperature, sunshine and air pressure, and negative associations with precipitation. The overall climate signal in δ 13C appeared to be slightly stronger than that of δ 18O. Spatial correlation analysis with gridded instrumental data demonstrated that the carbon series captured the summer temperature signal in a broad region of mid-west Sweden and the eastern part of Norway, greatly exceeding the spatial coverage of the signal derived from pine ring widths growing in the central Scandinavian mountains. A weak relationship between δ 13C and precipitation and a much stronger temperature and sunshine dependence may imply that photosynthetic rate rather than stomatal conductance is more important in controlling the inter-annual tree ring δ 13C variability in the area. Moreover, it was shown that, the climate– δ 18O and δ 13C relationship was temporally unstable throughout the twentieth century, which was linked to large-scale shifts in climate that may have altered the isotope-climate dependence. Our results thus demonstrate that, stable isotopes in tree rings from maritime high-altitude Scandinavia can provide high-resolution regional climate information, especially regarding parameters associated with temperature. The non-stationary nature of the isotope–precipitation relationship may provide important information on past changes in the large-scale atmospheric circulation during summer. However, these issues needs to be further investigated before pine tree ring isotopes from this region can be confidently used in palaeoclimate reconstructions.